4th internal biannual science meeting of the MLZ

24 Jun 2019, 08:00 → 27 Jun 2019, 18:00 Europe/Berlin

Seminarhaus Grainau

Henrich Frielinghaus (JCNS), Robert Georgii (FRM II)

The directorate of MLZ would like to continue the scientific exchange among the employees. The main subject is neutron scattering at the MLZ. We also want to come up with constructive consideration for our future success and have foreseen enough time for fruitful discussions. We kindly ask everybody working tightly with the Maier-Leibnitz Zentrum for own suggestions of presentations within the parallel sessions of the science groups and institute meetings. Poster presentations are possible and will be presented in parallel. An after dinner scientific talk will open up for broader perspectives. The venue will be again Grainau next to the Zugspitze. The seminar will take place in the Seminarhaus-Grainau (www.seminarhaus-grainau.de) with high level standard rooms (and WLAN). Students will be asked to share rooms (please give a suggestion of preferred room mates) . The seminar will take place between June 24 and 27. Organized busses will depart from FRM-2 and serve for the return. Independent travelers can also use public transportation to Grainau (DB-Stop Untergrainau+ Taxi or Stop Zugspitzbahn Grainau + 10 minutes to walk). We think that scientific exchange must also take place within a relaxed atmosphere, therefore there will be room for discussions after dinner while having a drink. An excursion and a conference dinner will also take place.

Programm_Grainau_2019_29_5_19.pdf

Monday, 24 June

13:00 Lunch

Plenary Session 1

Convener: Dr Robert Georgii (FRM II)

1 Welcome and Overview by the directors

Speaker: Stephan Förster (Forschungszentrum Jülich)

2 Deep learning for neutron and x-ray scattering

Nowadays, there is a lot of hype around big data, machine learning, deep learning. It is used by autonomously driven cars, in marketing for product recommendation or by search engines. The technique is very powerful. Could we apply it to neutron scattering data? Are the event-mode data from the PSD detector “big”? Can the neural network learn from it? What does the neural network learn and how?

In this talk I will explain the main terms, show the possible applications of deep learning for neutron/x-ray scattering and give an overview of the activities of the scientific computing group in this field.

Speaker: Marina Ganeva (JCNS at MLZ, Forschungszentrum Jülich GmbH)

Introduction of newly arrived personnel

3 R. Dutta

Introduction of my work

Speaker: Rajesh Dutta (Institut für Kristallographie, RWTH Aachen University)

4 A. Neslihan

Introduction in my work

Speaker: Neslihan Aslan (TUM)

5 A. Sarkar

Introduction in my work

Speaker: Anirban Sarkar (Forschungszentrum Jülich GmbH)

Grainau_introduction_sarkar240619.pptx

6 R. Tang

Introduction in my work

Speaker: Ran Tang (Technical Univertsity Munich)

7 A. Vagias

Introduction to my work

Speaker: Apostolos Vagias (MLZ-TUM)

8 M. Heere

Introduction in my work

Speaker: Michael Heere

16:00 Coffee

E13 Internal meeting 1

9 In-situ study of printed active layers of conjugated polymers and small acceptor molecules for application in high-efficiency organic solar cells

Resent research in organic photovoltaics focuses on identifying new high-efficiency polymers and acceptor molecules to reach high power conversion efficiencies (PCEs). To date, a PCE of 13% could be obtained with a PBDB-T-SF: IT-4F based organic solar cell device. However, towards commercialization, the solar cell performance must be optimized and an up-scale of the thin layer deposition is necessary. Printing of the active layer of organic solar cells can overcome the up-scale challenge. In-situ grazing incidence small angle X-ray scattering (GISAXS) during printing provides fundamental knowledge to better understand the drying kinetics and structure formation mechanism during printing. Characterization techniques such as UV/Vis spectroscopy, photoluminescence, optical microscopy and scanning electron microscopy (SEM) are applied after printing to get to get a deeper insight into the composition and morphology of the active layer of the printed films with the aim to further improve the solar cell efficiencies.

Speaker: Mrs Kerstin Wienhold (Lehrstuhl für Funktionelle Materialien E 13)

10 Thermal Behavior and Cononsolvency of the Thermoresponsive Diblock Copolymers PMMA-b-PNIPAM and PMMA-b-PNIPMAM in Aqueous Solution

Amphiphilic diblock copolymers having a hydrophobic poly(methyl methacrylate) (PMMA) block and a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) or poly(N-isopropylmethacrylamide) (PNIPMAM) block form core-shell micelles in aqueous solution. The transition temperature of the PNIPMAM block is 43 oC, thus significantly higher than the one of PNIPAM (32 oC), which has been attributed to steric hindrance by the additional methyl group which weakens the intermolecular interactions [1]. Both, the PNIPAM and PNIPMAM blocks are not only sensitive to temperature, but also to the solvent composition. Adding methanol as a cosolvent causes these blocks to collapse, which reduces the transition temperature, i.e. cononsolvency is observed [2]. In contrast, PMMA features the cosolvency effect in water-methanol mixtures, i.e. the solubility of PMMA block is increased by adding the cosolvent methanol [3]. In the present work, we investigate (i) the structure of the self-assembled micelles and the changes upon collapse and aggregation with increasing temperature, and (ii) the effect of methanol using turbidimetry, differential scanning calorimetry (DSC), dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The results reveal the role of the nature of the thermoresponsive block on the thermal behavior and the morphology changes upon temperature and solvent composition.
[1] E. I. Tiktopoulo et al., Macromolecules 28, 7519 (1995).
[2] F.M. Winnik, H. Ringsdorf, J. Venzmer, Macromolecules 23, 2415–2416 (1990).
[3] R. Hoogenboom et al, Aust. J. Chem. 63, 1173-1178 (2010)

Speaker: Chia-Hsin Ko (E13, Physik-Department, Technische Universität München.)

11 Investigating vapor-induced co-nonsolvency in thin films by TOF-NR

The diblock copolymer PMMA-b-PNIPAM in aqueous solution undergoes a reversible coil collapse transition at the lower critical solution temperature (LCST). This characteristic transition temperature can be tuned by the addition of organic co-nonsolvents such as ethanol or acetone. In order to investigate co-nonsolvency behavior in thin film geometry, we perform swelling experiments with a custom-made temperature-controlled vapor chamber. Complementary time-of-flight neutron reflectometry data and UV/Vis spectroscopic reflectometry data are used to access information about thickness and refractive index development, morphological changes, diffusion speeds and concentration gradients.

Speaker: Christina Geiger (Frau)

12 Morphological investigation on PTX-loaded poly(2-oxazoline) molecular brushes

Poly(2-alkyl-2-oxazoline)s (POx) are well known for their tunable thermoresponsive properties and good biocompatibility, which make them promising materials for biomedical applications, e.g. as drug carriers. Depending on the type of alkyl substituent, they can be hydrophilic, e.g. poly(2-methyl-2-oxazoline) (PMeOx), thermoresponsive, e.g. poly(2-ethyl-2-oxazoline) (PEtOx) and poly(2-propyl-2-oxazoline) (PPrOx), or hydrophobic, e.g. poly(2-butyl-2-oxazoline) (PBuOx). In the present work, molecular brushes, featuring PMeOx-b-PBuOx block copolymer side arms densely-grafted on a poly(methacrylic acid) backbone, are investigated in aqueous solution. As the PBuOx block is attached to the backbone, the PMeOx block is located near the periphery of the molecular brush. In this architecture, the PBuOx core may store the hydrophobic anticancer drug, Paclitaxel (PTX), whereas the PMeOx shell may facilitate transportation in human body. With small-angle neutron scattering, the morphology of the aqueous solutions of PTX-loaded molecular brushes was investigated for various degrees of polymerization of the backbone and the side arms, disclosing the effect of the molecular architecture on the drug-loading ability, providing hints on the optimum design of the drug delivery molecules.

Speaker: Jia-Jhen Kang (Technical University of Munich)

Science driven instrumentation: Material science

Science driven instrumentation: Quantum Phenomena

Science driven instrumentation: Softmatter

13 In situ Dynamic Light Scattering at Small Angle Neutron Scattering and Spin-Echo Instruments

Dynamic light scattering (DLS) is based on the temporal analysis of the intensity fluctuations of the scattered light caused by the Brownian motion of particles (protein molecules, aggregates, polymer particles etc.) in solution. It provides information on the translational diffusion coefficient, allowing the characterization of particles with average radii in a broad range from a few nanometers up to several microns. If several particles are present in the solution, they can be distinguished if they are at least one order of magnitude different in size. Monitoring the sample composition on the minute-time scale in situ during the neutron scattering experiment is crucial in case of biological samples, which are sensitive to slight changes of temperature, pH of the solvent, radiation damage etc. In case aggregates are found by DLS, the user can decide whether to prepare a fresh sample or disregard the data at some point, thus improving the neutron beam time usage.

Polymer and protein systems were investigated using small-angle neutron scattering and neutron spin echo spectroscopy with the in-situ DLS option. Technical aspects behind the adjustments of the standard sample holders at KWS-2 and the development of the two new sample holders for J-NSE Phoenix are presented, complemented by preliminary results. As this project is about to enter the standard user routine, the authors are grateful for any comments.

Speaker: Livia Balacescu (RWTH Aachen)

14 Polymer dynamics and the new J-NSE Phoenix at MLZ

In 2017 the Neutron Spin Echo (NSE) Spectrometer went through a refurbishment of the secondary spectrometer. A set of superconducting precession coils was realized following the results obtained for the design of ESSENSE, the proposed high-resolution NSE spectrometer at the ESS. One of the most innovative characteristics of the coils is their optimized geometry that maximises the intrinsic field-integral homogeneity along the flight-path of the neutrons. The installation of the new magnets was finalized in September 2017 and since 2018 the J-NSE has been back in user program. The new configuration yields an improved resolution that may be exploited to reach larger Fourier-times (t) and/or to benefit from significant intensity gains if shorter neutron wavelengths are used at a given t. Thus the refurbished J-NSE meets the needs to look into the microscopic dynamics of soft- or biological-matter with enhanced and new quality. The results of the first experiments have confirmed this and here we present some selected examples from the realm of polymer dynamics that largely rely on the enhanced properties of the new J-NSE.

Speaker: Stefano Pasini (Forschungszentrum Juelich GmbH)

Science driven instrumentation: Structure

18:30 Dinner

Tuesday, 25 June

08:00 Breakfast

Plenary Session 2

Convener: Wiebke Lohstroh

15 Magnetic fluctuations

Speaker: Christian Franz

16 A new GISANS instrument at the MLZ

The new twist in GISANS experiments aims at - for neutrons - relatively fast kinetics and processes in the time domain of 1h and below. Examples range from spray deposition over vapor exposure to tempering processes being all important for industrial applications. The considerably different contrast for neutrons adds valuable complementary information to the much faster GISAXS experiments. Due to the diversity of instruments at the MLZ there are quite a few options for performing GISANS experiments. All of the instruments are optimized for specific purposes and do - in general - perform well within their scope. When aiming at processes and kinetics at surfaces that shall be inspected by GISANS experiments, optimizations of all aforementioned instruments would leave room for faster measurements at the high intensity neutron source FRM-II. A dedicated view on a limited but well tunable Q-range with adaptable resolution for highest intensities would outperform with respect to existing options. A few experimental examples as motivation and technical details for a new instrument are discussed.

Speaker: Henrich Frielinghaus

Introduction of newly arrived personnel

17 A. Eich

Introduktion in my work

Speaker: Andreas Eich (Forschungszentrum Jülich GmbH)

18 N. Zec

Introduction in my work

Speaker: Nebojša Zec (Helmholtz-Zentrum Geesthacht, GEMS at MLZ)

19 V. Burwitz

Introduction in my work

Speaker: Vassily Burwitz

20 H. Thoma

Introduction in my work

Speaker: Henrik Thoma

10:30 Coffee

Plenary Session 3

Conveners: Juergen Neuhaus, Peter Link

21 Larmor diffraction and the relocation of the cold triple axis spectrometer FLEXX to MLZ

The cold triple-axis spectrometer (TAS) FLEXX at HZB is a well-designed and recently upgraded instrument [1-4]. There is a strong wish that this excellent instrument should be preserved for the community after shutdown of the HZB neutron source. One attractive gap in the present instrumentation suite, which could be filled by FLEXX, is the Larmor-diffraction technique [5-6] (LD) and, as a natural extension, cold neutron NRSE. LD permits the exact measurement of lattice constants and their distribution: the latter arising, for example, from internal strain, from a small splitting of Bragg peaks due to structural distortions or magnetostriction. In addition, spin correlation lengths in antiferromagnets and antiferromagnetic domain sizes of up to 1 μm can be determined with high accuracy. For looking at time-dependent processes one needs to switch to the NRSE mode.
The instrument will be placed on a cold neutron source. This will allow for a four-fold increase in Q resolution, as well as most importantly access to the low Q region, as compared to the existing TRISP@MLZ. Further, new developments are under way to allow for application of magnetic fields at the sample, hitherto not possible [7-9]. This opens up new vistas in the exploration of materials, magnetic or not. A last attractive gap to be filled within MLZ, is the possibility to combine high magnetic fields together with cold TAS.

[1] M. Skoulatos, K. Habicht, Nucl. Instr. and Meth. A 647, 100 (2011). 

[2] M.D. Le, D.L. Quintero-Castro, R. Toft-Petersen, F. Groitl, M. Skoulatos, K.C. Rule, K. Habicht, Nucl. Instrum. Methods Phys. Res. A 729, 220 (2013).
[3] F. Groitl, T. Keller, D. Quintero-Castro, K. Habicht, Rev. Sci. Instrum. 86 025110 (2015).
[4] K. Habicht, D.L. Quintero-Castro, R. Toft-Petersen, M. Kure, Lucas Mäde, F. Groitl, M.D. Le, EPJ Web of Conferences 83, 03007 (2015).
[5] M.T. Rekveldt, Journal of Applied Physics 84, 31 (1998). 

[6] M.T. Rekveldt, T. Keller, R. Golub, Europhysics Letters 54, 342 (2001). 

[7] Neutron Spin Echo - Proceedings of a Laue-Langevin Institut Workshop, Grenoble, Springer- Verlag, Ed: F. Mezei (1980). 

[8] M.T Rekveldt, J. Plomp, A.A. van Well, Jour. Appl. Cryst. 47, 436 (2014).
[9] K. Habicht, “Neutron-Resonance Spin-Echo Spectroscopy:
A High Resolution Look at Dispersive Excitations”, Habilitation, University of Potsdam (2016).

Speaker: Markos Skoulatos (TUM)

22 Discussion of new instrumentation based on input by the science groups

Discussion of new instrumentation based on input by the science groups

Speaker: Dr Robert Georgii (FRM II)

13:00 Lunch

E13 internal meeting 2

23 Nanostructured SnO2 Templated by Amphiphilic Block Copolymer for Lithium-Ion Battery Anodes

With the rapid development of wireless information communication products, electric vehicles, power tools and other fields, higher requirements are placed on the energy density, power density and lifetime of lithium-ion batteries. Compared with conventional graphite anodes, SnO2 offers a much higher theoretical specific capacity (1494 mAhg-1). However, the big volume change and the continuously generated SEI film during the cycling leads to a serious capacity recession, which therefore limits its practical application. In the present work, a novel mesoporous SnO2 anode has been was successfully synthesized by an amphiphilic block copolymer assisted sol-gel process, which is expected to facilitate the infiltration of the electrolyte and accommodate the volume expansion of the material during cycling, thereby improving the electrochemical performance of the electrode. The pore arrangement of the obtained SnO2 nanostructure is studied via scanning electron microscopy (SEM) and grazing-incidence small-angle X-ray scattering (GISAXS).

Speaker: Shanshan yin

24 Biopolymer templated hierarchical titania films for hybrid solar cells

Hybrid solar cells combine the advantages of inorganic and organic materials. This means long term stability and high charge carrier mobility, as well as flexibility and fabrication on a large industrial scale, respectively. However, the film morphology has crucial influence on the device performance, since a high surface-to-volume ratio is needed for efficient charge separation. So far, inorganic mesoporous matrices are successfully achieved by sol-gel chemistry in combination with block copolymer directed templating. As a novel approach, we use environmentally friendly biopolymers as tailoring agents. The whey protein ß-lactoglobulin was found to form different structures within denaturation, from fibrils to spheres. By combining heat denaturation at different acidic conditions and sol-gel chemistry, various nanosized structures are introduced into titanium dioxide. The resulting sol-gels are used as inks for film deposition via spray coating. In order to investigate the structural properties of these films, grazing incidence small-angle X-ray scattering (GISAXS) is performed. GISAXS measurements are supplemented by scanning electron microscopy.

Speaker: Julian Heger

25 Influence of nano-confinement on the crystallization of conjugated polymers P3HT and PffBT4T-2OD

Control of n-type inorganic morphology, chain orientation and crystallization of the donor polymers is of significance in hybrid solar cells. Here, we use slot-die printing combined with wet chemistry to fabricate controllable mesoporous TiO2 nanostructures in large scale. Subsequently, the mesoporous TiO2 films with different pore size are backfilled with P3HT and PffBT4T-2OD, respectively, using two different ways of infiltration. TiO2 film morphology is investigated by scanning electron microscopy (SEM) and grazing incidence small-angle X-ray scattering (GISAXS). Particularly, GISAXS reveals the sizes of the nanostructures and pores of the printed TiO2 films. In order to investigate the effect of TiO2 pore size on the crystalline properties of the conjugated polymers P3HT and PffBT4T-2OD, e.g. lattice distance, crystal size or orientation, grazing incidence wide-angle X-ray scattering (GIWAXS) is applied to probe the hybrid films. Both, P3HT and PffBT4T-2OD crystals with a denser packing of polymer chains exist in the large pore size of TiO2 films. For backfilling with PffBT4T-2OD, a high face-on to edge-on ratio preferentially appears in the large TiO2 pores.

Speaker: Nian Li

26 Quantum dot solids for photo-devices

Quantum dots (QDs) with near infrared emission are promising for use in photodetectors (PDs) for sensing and in photovoltaics (PVs) for solar energy conversion. High quality QDs are normally synthesized in solution and capped with organic ligands. To efficiently functionalize the QDs’ array for PD or PV devices, the ligand exchange treatments, in solution or on solids, to colloidal QDs are necessary by exchanging or removing the long chain organic ligands. These treatments will not only decrease the inter-dot spacing between neighboring QDs to improve their electro-coupling behavior, which is beneficial for the energy transfer, but also change the stacking behavior of QD particles in solid from colloidal state to close packed state. Herein, we used a halide ions solution to pretreat the surface of QDs in solution before ligand exchange process on solids. The inner structures of ligand exchanged solids are investigated by grazing incidence X-ray scattering (GIXS). The results indicate that, comparing with non-pretreated QD based solids, pretreated QD solids reveal optimized inner structures as a result of the optimized stacking behavior. Thus, the optimized solar cell devices demonstrate better device performances.

Speaker: Wei Chen (Technische Universität München)

Method driven instrumentation: Diffraction

27 Overview of the existing powder diffraction capabilities at MLZ and future prospects

Powder diffraction is the experimental technique, which stands on the forefront of the material characterisation, delivering the key information about the crystal structure. Being perfectly parametrized and standardized technique, the powder diffraction is in broad use and X-ray powder diffractometer is a part of equipment in nearly every lab specializing on materials research.
Neutron powder diffraction as a result of combining its strengths with the well-known advantages of neutrons provide unique structural information, whose use can be mostly explored in complementarity to X-ray or electron diffraction. The powder diffractometers serve as working horse of every research reactor facility. In the current contribution the Overview of the available powder diffraction capabilities at MLZ will be made along with the future prospects.

Speaker: Anatoliy Senyshyn

28 Single crystal diffraction

Speaker: Martin Meven

29 Polarised neutron diffraction at MLZ and beyond

Under the general name of “polarised neutron diffraction” indeed a variety of different experimental techniques are usually meant. Those are: classical polarised neutron diffraction (PND) called also Flipping-Ratio method or also in the recent years: Half-polarised neutron diffraction, this technique uses strong magnetic fields (> 1 T) on the sample position. Another method is Linear or Uniaxial, or simply, Polarisation Analysis, generalised version of it been called: XYZ Polarisation Analysis, this technique usually uses week magnetic fields (< 1 T) from dedicated coil arrangements or tuneable vector field magnet. Third method is Spherical Neutron Polarimetry (SNP), former times called also 3D Polarisation analysis, uses samples situated in the special zero- magnetic fields chambers, to screen stray field from surrounding and even Earth magnetic field (Cryopad, Mupad). In the last time also development of the polarised neutrons powder diffraction is promoted, so called Flipping - Difference method. A number of these measuring techniques are implemented at MLZ on instruments like e.g. POLI, DNS or soon Kompass and others. We will present an overview of the “polarised neutron diffraction” methods at MLZ, current situation in this field at other facilities and try to sketch out the trends for the next future.

Speaker: Dr Vladimir Hutanu (Institut für Kristallographie RWTH Aachen)

30 Aspects of Neutron Guides for Short Wavelength Neutrons

In view of state of the art supermirror coatings reaching m-values as high as 8 the topic of hot (short wavelength) neutron transport via neutron guides has entered into the discussion of future instrumentation projects as for example a future guide hall south at FRM II. Here basic properties of neutron guides and the performance of hot neutron transport is discussed. Some likely scenarios for a neutron guide delivering neutron beams to a future guide hall south have been simulated and will be discussed.

Speaker: Dr Peter Link

Method driven instrumentation: Engineering and imaging

31 Imaging

Imaging

Speaker: Michael Schulz

32 Stress scanner

Stress scanner

Speaker: Michael Hofmann

33 Positrons

Positrons

Speaker: Christoph Hugenschmidt

Method driven instrumentation: Large scale structure

34 Large Scale I

Large Scale I

35 Large Scale II

Large Scale II

Speaker: Aurel Radulescu (Forschungszentrum Jülich GmbH, Jülich Centre for Neutron Science at MLZ)

36 Sample changes with the reflectometer MARIA

Very frequently in soft matter studies at the solid liquid interface and in an effort to reduce the ambiguity of the model that is used for fitting neutron reflectivity experimental data, arises the need for the manipulation of the scattering length density of the solvent (usually water). Manual exchange of solvent is laborious while the control of the rate of solvent exchange is difficult. For these reasons we have developed and automatic system for such investigations, capable of automating the exchange of up to 5 solvent contrasts of 4 different solid/liquid cells at the MARIA reflectometer. We give examples of operation and representative data sets acquired by users.

Speaker: Alexandros Koutsioumpas (JCNS)

Method driven instrumentation: Spectroscopy

37 ToF Spectroscopy

Update and discussion of the current status of the time-of-flight spectrometer TOFTOF and the potential transfer of NEAT to MLZ.

Speaker: Wiebke Lohstroh

38 TAS Spectroscopy

Speaker: Thomas Keller

39 High resolution spectroscopy

Recent developments and perspectives at the MLZ of neutron spin echo spectroscopy instruments are presented.

Poster session

40 Bambus: a new inelastic neutron multiplexed analyzer for Panda at MLZ

A new multianalyzer Bambus is being constructed at Panda, MLZ. The objective is to construct broad reciprocal space maps at multiple energy transfers, in order to get insights of broad features at low energy or study complex dispersion laws. Because this spectrometer is designed as a complementary option to the normal TAS mode, a fast switch between the two setups is foreseen. The general concept will be presented together with the final design, and the results obtained with two prototypes.

Speaker: Dr Alexandre Bertin (TU Dresden)

41 Bulk heterojunction blends using a fullerene-free acceptor for photovoltaic applications

Over the last decades organic electronics (OE) have attracted the focus of research due to their advantageous properties. Advantages, such as the flexibility of OE, the ease of processablility and the applicability of industrial up-scalable and low-cost processing methods, open up a wide range of possible application fields. Especially organic photovoltaics (OPV) have drawn much attention, due to much lower energy payback times compared to their conventional inorganic counterparts and power conversion efficiencies (PCE) surpassing 10 %, which makes them a promising candidate to tackle the increasing energy demand. The most widely studied bulk heterojunction system used for photovoltaic applications is P3HT:PCBM, which is already well understood, offers PCEs of about 4 to 5 %. In the last decades optimized low-bandgap polymers, such as PTB7, PTB7-Th and PBDB-T, emerged with optimized properties for usage as donor materials. Also their counterparts, the acceptors were investigated to replace the fullerene derivate by non-fullerene acceptor molecules, like ITIC, optimizing the photoactive properties of the active layers in photovoltaic devices. Another important step is the morphology present in the photoactive layer. Since it is known that the exciton diffusion length within the active layer of bulk-heterojunction devices is about 10 nm the inner morphology and extraction pathways are key to an efficient photovoltaic device. Within this study we investigate the morphological changes upon variation of the active layer composition of photoactive thin films based on the bulk heterojunction system of PBDB-T:ITIC. This is done by utilizing grazing incidence small angle X-ray scattering (GISAXS) [1]. This technique gives insight into the applied photoactive layer and offers the possibility to optimize the inner morphology of OPV devices in order to increase their power conversion efficiencies.

Speaker: Sebastian Grott (TU München, Physik-Department, Lehrstuhl für Funktionelle Materialien)

42 Capillary breakup extensional rheology and SANS

Capillary breakup extensional rheomerty (CaBER) as a method for investigating short-time relaxation mechanisms and extensional properties of soft matter has immensely gained in importance since its invention almost 40 years ago. Despite its widespread use, this method has never been combined with high resolution in-situ structural investigations such as small angle scattering.
We demonstrate the general possibility of combining CaBER with small angle neutron scattering (SANS) at the KWS-2 diffractometer for high time-resolution structural investigations of soft matter with a focus on the liquid and gel state.
With a typical flux of 2.5 x 107 cm-2 s-1 for a collimation at 8 m with a 50 x 50 mm² aperture and a thermal neutron wavelength of 5 Å, we can investigate suspensions with suspension viscosities in the range of 0.1 – 1000 Pas under uniaxial elongational flow at high extension rates. Due to the limited scattering volume, we need on the order of 100 measurement cycles with an approximate duration of 1 h to obtain structural data with a minimum possible time resolution of 50 μs using the event mode for neutron detection. Reproducibility is ensured by our newly developed bottom plate geometry for the HAAKE CaBER 1 setup, preventing the liquid droplet from escaping the field of view over the relatively large number of cycles. Combining the setup with a highspeed camera, we can monitor the filament thinning and rupture with a frame rate of up to 15000 s-1. In this way, we can extract the extensional viscosity and even ultra-short time relaxation modes, e. g., on the order of 100 μs for dilute PEO suspensions.
Our CaBER-SANS setup is unique and has a large potential interest for investigating the structural changes of biopolymer suspensions such as cellulose, and DNA, but also for numerous other colloidal and polymer suspensions.

Speaker: Christian Lang (Forschungszentrum Jülich GmbH)

43 Combination of dilatometer with neutron scattering

A Quenching & Deformation Dilatometer is now operational at the Heinz Maier-Leibnitz Zentrum (MLZ). It is customized for running neutron scattering measurements during temperature/deformation treatment of the sample, in particular neutron diffraction (phase, texture, stress/strain) at STRESS-SPEC and neutron small-angle scattering (nanostructure) at SANS-1. The dilatometer offers a simultaneous high-precision measurement of the length changes of bulk samples at all times, also when heating/cooling or deforming the sample, adding an additional measurement quantity that is sensitive to the phase transformations in the sample. The combination of the neutron and dilatometry measurements yields a unique view on the microstructural evolution under thermomechanical treatment. The sample can be inductively heated and gas cooled according to a user-defined linear or exponential cooling rate. The temperature range is currently from room temperature up to 1500°C. The heating rate can be up to 4000°C/s, while specimens can be deformed with deformation rates between 0.01 and 200 mm/s. Depending on user demand, the temperature range can be extended down to -160°C with an additional furnace configuration. In addition to the dilatometer, we will present also first in-situ neutron scattering experiments.

Speaker: Dr Xiaohu Li

44 From microstructure to planetesimal evolution: An experimental approach to stony-iron meteorite formation with SAPHiR

Nicolas P. Walte 1, Giulio F.D. Solferino 2, Gregor J. Golabek 3

1 Heinz Meier-Leibnitz Zentrum (MLZ), FRM II, TU München.
2 Department of Earth Sciences, Royal Holloway University of London, UK.
3 Bayerisches Geoinstitut (BGI), Universität Bayreuth.

Pallasites, stony-iron meteorites composed of olivine crystals and Fe-Ni metal, are samples of the interior of early solar system bodies. However, the interpretation of pallasites is controversial with suggested origins either at the core-mantle boundary of planetesimals or from the shallower mantle that was disrupted by an impact. We present deformation experiments with the instrument SAPHiR to simulate pallasite formation. Our experiments show that pallasites preserve the two-stage evolution of their parent body including core-mantle differentiation and an impact event causing metal melt injection. Olivine clusters, important constituents of pallasites, are recognized as samples of a planetesimal mantle containing up to 15 vol% of primordial metallic melt not stemming from the impactor. This indicates high percolation thresholds and inefficient metal-silicate differentiation in asteroids not experiencing a magma ocean stage.

Speaker: Nicolas Walte

45 Germanium-based nanostructure synthesis guided by amphiphilic diblock copolymer templating

Latest research in the field of hybrid photovoltaics focuses on the benefits of inorganic and organic materials. Flexibility, low cost and large scale production are the most valuable properties of organic components whereas the inorganic components add chemical and physical stability. So far thin films based on titanium dioxide are well investigated, whereas less is known about germanium-based compounds. In this work, we analyze thin films with optical, electrical and morphological measurement techniques to understand and control the corresponding properties. An amphiphilic diblock copolymer templating with polystrene-b-polyethylene oxide (PS-b-PEO) and a metal precursor are used to prepare thin films via sol-gel synthesis. The copolymer templating results in nanoporous foam-like germanium-based thin films. In the present study different molar concentrations of germanium-based compounds are prepared and analyzed. The focus is to find the best compound ratio and set new benchmarks for photovoltaic applications.

Speaker: Christian Weindl (TUM Physik)

46 Growth and characterization of magnetite based artificial multiferroic heterostructure

We study the morphology, electric, magnetic, magneto-electric coupling
and magneto-transport properties of Fe$_3$O$_4$/Nb:SrTiO3(001) and
Fe$_3$O$_4$/PMN-PT(011) heterostructures. Studies like, interfacial capacitance,
magnetic depth profile, ferroelectric ordering, stress and charge
screening-control of the Verwey transition are of special interest. The
Fe$_3$O$_4$ films are grown in an oxide molecular beam epitaxy system.
We use x-ray diffraction and reflectometry for the structural characterizations,
and atomic force microscopy (AFM) for the morphology
of thin film. Magnetic and transport properties of the heterostructure
are studied using superconducting quantum interference device
(SQUID) magnetometer and physical property measurement system,
respectively. We propose that probing the depth profile of magnetization
using polarized neutron reflectrometry (PNR) can reveal more
information about the magnetic properties near the interface of such
ferromagnetic/semiconductor heterostructures.

Speaker: Dr Anirban Sarkar (Forschungszentrum Jülich GmbH, Jülich Centre for Neutron Science JCNS and Peter Grünberg Institute PGI, JARA-FIT)

Poster_Grainau_2019.pdf

47 Highly-Regular Porous Antimony Oxide Thin Film Electrode for Rechargeable Batteries

Due to limited supply of traditional fossil fuels, increasing carbon emission, and deteriorated environmental pollution, it is urgent for humankind to ensure alternative renewable energy sources. Because of high energy density, competitive working voltage, minimum self-discharge, and limited maintenance requirements, rechargeable lithium-ion batteries (LIBs) have been applied in various fields and regarded as the most promising power devices in the future. In recent years, the shortage of lithium source gradually became a noteworthy problem, which could limit the development of LIBs in next years. Since that sodium is an earth abundant material and sodium-ion batteries (SIBs) can meet these requirements better than LIBs, SIBs have come up as a more suitable alternative to LIBs for these applications[1]. Due to high theoretical capacity (Sb2O4 for 1220 mAh g-1, Sb2O3 for 1102 mAh g-1), appropriate reaction potential and abundant reserves in the earth crust, antimony oxides are regarded as a promising alternative anode materials which could be applied in both LIBs and SIBs[2]. However, antimony oxides suffer from volume expansion during charge and discharge, leading to a rapid capacity fading. Creating hollow or porous structure is an effective strategy to improve cycling stability of antimony oxides anodes, because it can provide enough void space to accommodate volume changes of antimony oxides[3].
Herein, we propose a novel method to synthesize highly-regular porous antimony oxide tin film anode materials assisted with block copolymer. Amphiphilic block copolymers (ABC) have been widely utilized as surface modification agents by constructing nanoscale architectures on various substrates through evaporation induced self-assembly processes[4]. Polymer/inorganic nanocomposites can be obtained via a microphase separation process in mixture solution of mixing block copolymer and precursor of metal oxide. Moreover, the morphology of nanocomposites could be controlled accurately by altering synthesis conditions[5]. After calcination, nanostructured metal oxide materials are gained. The morphology of as-prepared porous antimony oxide tin film anodes could be characterized by scanning electron microscopy (SEM) partially and grazing incidence small angle X-ray scattering (GISAXS) integrally[6]. Furthermore, in operando SAXS or Small-angle neutron scattering (SANS) measurements can be applied to investigated the evolving nanoscale morphology of electrode during charge and discharge processes[7, 8].
References
[1] S.P. Ong, V.L. Chevrier, G. Hautier, A. Jain, C. Moore, S. Kim, X. Ma, G. Ceder, Energy & Environmental Science, 4 (2011) 3680-3688.
[2] N. Li, S. Liao, Y. Sun, H.W. Song, C.X. Wang, Journal of Materials Chemistry A, 3 (2015) 5820-5828.
[3] J. Pan, N. Wang, Y. Zhou, X. Yang, W. Zhou, Y. Qian, J. Yang, Nano Research, 10 (2017) 1794-1803.
[4] Y. Deng, J. Wei, Z. Sun, D. Zhao, Chemical Society Reviews, 42 (2013) 4054-4070.
[5] Y.J. Cheng, J.S. Gutmann, Journal of the American Chemical Society, 128 (2006) 4658-4674.
[6] P. Müller-Buschbaum, Advanced Materials, 26 (2014) 7692-7709.
[7] G.E. Mohl, E. Metwalli, P. Muller-Buschbaum, Acs Energy Letters, 3 (2018) 1525-1530.
[8] G.E. Möhl, E. Metwalli, R. Bouchet, T.N.T. Phan, R. Cubitt, P. Müller-Buschbaum, ACS Energy Letters, 3 (2017) 1-6.

Speaker: Mr Suzhe Liang (E13)

48 How to Rationally Select an Interfacial Modifier for High Performance Organic Photovoltaics

Due to low cost, flexibility, solution processing and large-scale fabrication, enormous attention is focusing on the research and development for higher OPV performance over the last decades. To improve the overall performance of organic photovoltaics, interfacial modifiers are widely applied in the device architecture to facilitate charge collection, tune the distribution of materials, and avoid pitfalls presented by traditional blocking layers such as PEDOT:PSS. Typically, interfacial layer are screened through a very laborious and empirical process that is dependent upon fabricating and testing of a large complete of devices to obtain statistically relevant data. Here, based on the surface energies of polymers and interfacial modifiers, we describe a fast and straightforward approach to enable rational selection of an interfacial modifier on device performance, prior to device fabrication. Surface energies play an integral role in device performance due to the profound influence on phase segregation within the bulk heterojunction. By simply determining the surface energies of polymers and interfacial layers, the composition of the BHJ at the interfaces could be predicted, thus enabling the user to determine the effect, positive or negative, of the interfacial layer on the device performance. Predictions were confirmed by experimental characterization and device production and testing.

Speaker: Dan Yang (Lehrstuhl für Funktionelle Materialien E 13)

49 Humidity chamber for grazing incidence neutron scattering

The investigation of thin polymer films with neutrons allows a non-destructive probe on their structure and composition. In the framework of the FlexiProb project, which plans an interchangeable sample environment for different neutron experiments at the European spallation source (ESS), we designed a setup for grazing incidence small angle neutron scattering (GISANS). The new sample chamber offers a wide range of adjustable relative humidity with fast switching times. Moreover, a homogeneous heat distribution and reduced condensation of the humid air is realized by a spherical design with fluidic channels inside the chamber walls. A separate gas-mixing and air-flow setup, gives precise control over the air conditions inside the chamber. To demonstrate its options, thin microgel films constituted of thermos-responsive NIPAM with N,N'-methylenebisacrylamide as cross-linkers are placed inside and humidified. The film response is analyzed with time-of-flight GISANS in order to observe structural changes in the films over the course of the humidification.

Speaker: Tobias Widmann (TU München, Physik Department, LS Funktionelle Materialien)

50 In-situ GISAXS investigation of the sputter deposition of metal contacts on photoactive polymer films

Although based on organic materials, organic solar cells often include metal electrodes due to their unrivaled electronic conductivity. Thus, polymer-metal interfaces are inherently present in most OPV devices and have a major influence on their behavior. Understanding the growth mechanisms of metal contacts on polymer thin films plays a crucial role in identifying potential ways to enhance the device performance. We investigate the morphological changes at the metal-polymer interface during the sputter deposition of metal contacts onto photoactive polymer films via in-situ GISAXS. This technique allows insights into the structural evolution of the metal on the organic film. A model describing the process is developed based on earlier work on different material systems. Comparing the deposition behavior of typical electrode materials on thin films of photoactive organic materials helps to understand their influence on the respective device performance.

Speaker: Franziska Löhrer (Lehrstuhl für Funktionelle Materialien, Department für Physik E13, TU München)

51 In-situ neutron diffraction study of engineering materials under thermo-mechanical treatment at STRESS-SPEC

The understanding of structure-property relationships is essential for the development and improvement of engineering materials. In-situ characterization of materials under external thermo-mechanical treatment is usually required. The materials science diffractometer STRESS-SPEC is designed to be applied equally to structure, texture and residual stress analyses by virtue of its very flexible configuration. In order to meet the needs of in-situ characterisation STRESS-SPEC has been dedicated with mechanical loading and dilatometry equipment.
First a unique load rig was designed for in-situ structure and lattice strain analysis both at ambient and high temperatures (~ 1000 °C). This rig is also fully rotatable to emulate Eulerian cradle like sample positioning, which allows intensity and peak position pole figure measurements. Second is a quenching and deformation dilatometer has been recently adapted. It offers simultaneous high-precision measurements of length changes while heating/cooling or deforming the sample, and thus adding an additional measurement quantity that is sensitive to phase transformations. The combination of neutron and dilatometry measurements yields a unique view on the microstructural evolution during thermomechanical treatment. As examples the in-situ measurements of a high ductility Mg alloy, a shape memory Ni-Mn-Ga alloy, and newly selective laser beam manufactured Ti will be presented in this contribution.

Speaker: Weimin Gan (Helmholtz-Zentrum Geesthacht)

52 Influence of benzocaine and propranolol on phospholipid bilayers

Cell membranes play a fundamental role in protecting the cell from its surroundings, in addition to hosting many proteins with fundamental biological tasks. Drugs are able to perturb the structure of cell membranes, which can ultimately give rise to undesirable effects. Thus, a study of drug/lipid interactions is a necessary and important step in fully clarifying the role and action mechanism of active ingredients, and shedding light on possible complications caused by drug overdosage. Here we present the results obtained in our research focused on the understanding of the influence of benzocaine and propranolol active principles on the structure of L--phosphatidylcholine-based membranes. The investigation has been performed by means of neutron reflectivity, grazing incidence small angle neutron scattering, and small/ultra-small angle neutron scattering. Investigations allowed discovering a stiffening of the membranes and the formation of stalks, caused by the presence of benzocaine. On the other hand, disordered bilayers (lamellar powders) and highly curved structures were found in the presence of propranolol. The results obtained may be rationalized in terms of the molecular structures of drugs and may serve as a starting point for explaining the toxic behavior in long-term and overdosage scenarios.

Speaker: Gaetano Mangiapia (German Engineering Materials Science Centre (GEMS) am Heinz Maier-Leibnitz Zentrum (MLZ))

53 Influence of Pressure on Poly(N-isopropylacrylamide) Mesoglobules above Cloud Point

Bart-Jan Niebuur1, Geethu P. Meledam1, Vitaliy Pipich2, Marie-Sousai Appavou2,
Alfons Schulte3, and Christine M. Papadakis1

1 TU München, Physik-Department, Garching, Germany
2 FZ Jülich, JCNS at MLZ, Garching, Germany
3 University of Central Florida, Orlando, U.S.A.

The thermoresponsive polymer Poly(N-isopropylacrylamide) (PNIPAM) in aqueous solution forms dehydrated, smaller mesoglobules upon heating through their cloud point, at atmospheric pressure. On the other hand, at high pressures, larger clusters of PNIPAM mesoglobules are formed and are more hydrated [1]. Here, we explore the influence of pressure on the structural evolution and hydration of PNIPAM mesoglobules above the cloud point using very small-angle neutron scattering (VSANS). Strikingly, a critical pressure is observed at which a sharp transition between small mesoglobules and large clusters occurs and this transition pressure depends on temperature. Further, the formation of large clusters of mesoglobules from smaller ones is found to be not completely reversible. We conjecture that the pressure induced structural changes in PNIPAM mesoglobules could be due to the pressure dependent hydration and subsequent aggregation of mesoglobules.

Reference:
[1] B.-J. Niebuur et al., ACS Macro Lett. 6, 1180 (2017).

Speaker: Dr Geethu Pathirassery Meledam

54 KOMPASS – the polarized cold neutron triple-axis spectrometer at the FRM II

D. Gorkov a,b,c, G. Waldherr b, A. Grünwald a,b,c, J. Stein a, S. Giemsa c, P. Böni c, and M. Braden a
a II. Physikalisches Institut der Universität zu Köln, D-50937 Köln, Germany.
b Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München,
D-85747 Garching, Germany.
c Physik-Department E21, Technische Universität München,
D-85747 Garching, Germany

KOMPASS is a polarized cold-neutron three axes spectrometer (TAS) currently undergoing its final con¬struction phase at the MLZ in Garching. The instrument is designed to exclusively work with polarized neutrons and optimized for zero-field spherical neutron polarization analysis for measuring all elements of the polarization matrix.
In contrast to other TASs, KOMPASS is equipped with a unique polarizing guide system. The static part of the guide system hosts a series of three polarizing V-cavities providing a highly polarized beam with expected polarization above 98%. The exchangeable straight and parabolic front-end sections of the guide system allow adapting the instrument resolution for any particular experiment and provide superior energy- and Q-resolution values when compared with the existing conventional guide and instrument concepts [1, 2].
In combination with the end position of the cold neutron guide NL-1, the large doubly focusing monochromator and analyzer using highly oriented pyrolytic graphite, the cavity of trapezoidal geometry for analysis of polarization of scattering beam, the KOMPASS TAS will be very well suited to study various types of weak magnetic order and excitations in variety of complex magnetic structures. Special emphasis was put on a compact design of the instrument in order to maximize intensity.

[1] M. Janoschek et al., Nucl. Instr. and Meth. A 613 (2010) 119.
[2] A. C. Komarek et al., Nucl. Instr. and Meth. A 647 (2011) 63.

The construction of KOMPASS is funded by the BMBF through the Verbundforschungsprojekt 05PK16PK1.

Speaker: Dr Dmitry Gorkov (FRM2)

55 Magnetic spin structures in amorphous DyCo thin film systems

Alloys of rare-earth elements and 3d transition metals became recently again in the focus of attention due there rich variety of magnetic effects owed to the different anisotropies of both material classes [1-3].
In this work, various thin film systems containing the amorphous DyxCo100-x alloy will be discussed. Despite of their amorphous nature, the film system show non trivial magnetic ordering leading to extraordinary phenomena. Neutron scattering techniques, in particular polarized neutron reflectometry are essential to investigate such thin film systems providing the sensitivity to study the magnetic structures on a microscopic level that is essential to understand the underlying principles. In DyCo4 a very large Atomic Exchange Bias effect was observed in a single film owned to the competition between the atomic exchange and the Zeemann interaction [4]. In contact with a soft magnetic thin film of permalloy a chirality based exchange bias effect could be created[5]. Here, the direction of the exchange bias effect can be isothermal switched by a moderate perpendicular magnetic field. The presence of an interfacial Dyzaloshinskii-Moriya is one of the keys to explain the observation. In a very recent study, it could be demonstrated how skyrmionic objects could be created in DyCo3 single films. The utilization of ferrimagnetic skyrmions as well as the of novel concepts of exchange bias may be of crucial importance for the development of future applications in the field of magnetic sensors.

[1] S. Mangin et.al, Phys. Rev. B 80, 224424 (2009), S. Mangin et.al, Phys. Rev. Lett. 82, 4336 (1999)
[2] Chen, K., Lott, D. et al.. Phys. Rev. B 91, 024409 (2015)
[3] F. Radu, R. Abrudan, I. Radu, D. Schmitz H. Zabel, Nat. Communications 3, 715 (2012).
[4] Chen, K., Lott, D. et al., Sci. Rep. 5, 18377 (2015)
[5] Chen, K., Lott, D. et al., submitted

Speaker: Dieter Lott (Helmholtz-Zentrum Geesthacht)

56 Morphology Tuning of ZnO Nanostructures for Hybrid Solar Cells

Electronic skin (E-skin) as the medium between ambient environment and bionic robots is an advanced technology that provides an electronic readout or even produces a visualized response that can be easily captured for postprocessing. Since this concept birth, different electronic skins have been fabricated and utilized for various sensing applications, such as pressure, humidity, temperature et al. However, to mimic human skin better, combining more sensing capabilities into one E-skin system is highly in demand.
Here, we envisioned a new type of wearable E-skin system based on triboelectric and luminescent effect for both pressure and tensile sensing. This device consists of a triboelectric nanogenerator as a pressure sensor and a luminescent layer realized by CdSe/CdS quantum rods for tensile sensing.

Speaker: Ms Ting Tian (TUM Lehrstuhl für Funktionelle Materialien E 13)

57 Multiprobe Imaging using Neutrons in conjunction with Gammas at the NECTAR Beam-Line

NECTAR is a superior beam-line with access to fission neutrons for non-destructive inspection of large and dense objects, where thermal neutrons or X-rays face limitations due to their comparatively low penetration. With the production of fission neutrons at the instrument [1], as well as neutrons interacting with beamline geometry, such as the collimator, gamma rays are produced in the process. The production of these gamma rays is inevitable as they are inherent with the principles of collimating or stopping the neutrons. Furthermore, these gamma rays are highly directional due to their constraint to the same beam-line geometry and come with similar divergence as the neutrons. While difficult to shield, it is possible to utilize them by using gamma sensitive scintillator screens in place of the neutron scintillators, viewed by the same camera and swapped-out in-situ.

Here we present the advantages of combining the information gained from neutron imaging in conjunction with gamma imaging at the NECTAR beam-line, providing a unique probe with unparalleled isotope identification capabilities. Initial results were produced from data measured in the 2019 run-cycle, performed at and supported by the Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRMII). Furthermore, future improvements and advancements for the development of this technique will be discussed.

Speaker: Adrian Losko (MLZ)

58 Non-destructive in-situ slot-die coating x-ray and neutron scattering experiments on perovskite thin films for photovoltaic application

Organic-inorganic metal halide perovskite solar cells (PSCs) offer a potentially cheap source for clean and low cost electrical energy. Improving stability1, 2 and minimodule power conversion efficiencies over 17% in 20183 promise commercial devices possibly capable of competing with multi-crystalline silicon solar cells with current module efficiencies of around 22% in 20173. This calls for developing large scale production techniques which are not yet available. The lab-to-fab process is not easily done since experience in perovskite layer deposition has long been limited on spin-coating which is a flexible but small area coating method easily applicable in lab scale production.4 However, among other techniques, slot-die coating offers the possibility of cheap and high-throughput large area perovskite deposition compatible to roll-to-roll fabrication.5-7 A homogeneous perovskite film with low defect concentration and high crystallinity is paramount for supreme device performance and therefore optimized printing parameters are key to high quality films.8, 9 In order to understand the printing, crystallization and drying process during deposition non-destructive in-situ X-ray and neutron scattering experiments (GISAXS/GIWAXS, GISANS) are proposed. This allows for detailed crystallization analytics and printing parameter optimization for the next step towards large area PSC fabrication.

Speaker: Mr Manuel Scheel (Lehrstuhl für Funktionelle Materialien E 13)

59 Post-treatment methods of semiconducting polymer films and investigation of the influence on thermoelectric properties

The constantly increasing energy demand raises the need for renewable energies and the reduction of energy dissipation. Thermoelectric materials are of great interest in terms of waste heat recovery and the use of solar thermal energy, as they enable the direct conversion of a temperature gradient into electrical power. In particular, thermoelectric polymers are attractive, as they own some advantages over inorganic thermoelectric materials, such as low cost, high mechanical flexibility, low or no toxicity, lightweight and intrinsically low thermal conductivity. A typical way to evaluate thermoelectric properties is the power factor PF=S2𝜎. This parameter depends on the Seebeck coefficient S and the electrical conductivity 𝜎, which are affected by the electronic and morphological features of the polymer. In order to investigate ways to influence these features and improve the values S and 𝜎, we fabricate thin semi-conducting polymer films and post-treat them in different ways. With measurements of parameters such as S, 𝜎, absorbance, layer thickness and determination of the structure, we investigate the morphology-function relation.

Speaker: Anna-Lena Oechsle

60 Protein dynamics of a thermophile photosystem

Photosynthesis is the key mechanism in utilization of solar radiation for living organisms and thus provides the base for most food chains and all fossil fuels. The functionality of photosynthetic proteins is -in part- critically influenced by dynamics on a timescale of pico- to milliseconds and on sub-nanometer length scale. The neutron time of flight spectrometer TOFTOF at MLZ-Garching is well suited to study such dynamics, and we currently develop a laser pump setup for TOFTOF allowing us to trigger photoreactions and subsequently probe the dynamics of specific functional states with neutrons. In a first step towards time-resolved measurements, static quasielastic neutron scattering (QENS) experiments were performed on photosystemII (PSII) complexes of the thermophile bacterium thermococcus elongatus, whose protein dynamics is expected to play a pivotal role in thermal adaptation. Using QENS, we have directly investigated PS II protein dynamics on the picosecond timescale in a range from 200 K to 340 K. The results suggest a shift of the onset of protein dynamics towards higher temperatures in thermophile PSII.

Speaker: Dominik Schwaiger (TUM Physik E13)

61 Putative spin-nematic phase in BaCdVO(PO4)2

We report neutron scattering and AC magnetic susceptibility measurements of the 2D spin-1/2 frustrated magnet BaCdVO(PO4)2. At temperatures well below TN ≈ 1K, we show that only 34% of the spin moment orders in a up-up-down-down strip structure. Dominant magnetic diffuse scattering and comparison to published μsr measurements indicates that the remaining 66% is fluctuating. This demonstrates the presence of strong frustration, associated with competing ferromagnetic and antiferromagnetic interactions, and points to a subtle ordering mechanism driven by magnon interactions. On applying magnetic field, we find that at T = 0.1K the magnetic order vanishes at 3.78T, whereas magnetic saturation is reached only above 4.5T. We argue that the putative high-field phase is a realisation of the long-sought bond-spin-nematic state.

Speaker: Markos Skoulatos (TUM)

62 Reversible tuning of structural, magnetic and transport properties via oxygen desorption/absorption in epitaxial La0.7Sr0.3MnO3-δ thin films

An oxygen vacancy induced topotactic transition from perovskite to brownmillerite and vice versa in epitaxial La0.7Sr0.3MnO3-δ thin films is identified by real-time x-ray diffraction. A novel intermediate phase with a non-centered crystal structure is observed for the first time during the topotactic phase conversion which indicates a distinctive transition route. Polarized neutron reflectometry confirms an oxygen deficient interfacial layer with drastically reduced nuclear scattering length density, further enabling a quantitative determination of the oxygen stoichiometry (La0.7Sr0.3MnO2.65) for the intermediate state. Associated physical properties of distinct topotactic phases (i.e. ferromagnetic metal and anti-ferromagnetic insulator) can be switched reversibly by an oxygen desorption/absorption cycling process.

L. Cao, O. Petracic, P. Zakalek, A. Weber, U. Rücker, J. Schubert, A. Koutsioubas, S.Mattauch, and Th. Brückel, Reversible Control of Physical Properties via an Oxygen-Vacancy-Driven Topotactic Transition in Epitaxial La0.7Sr0.3MnO3−δ Thin Films,
Adv. Mater. 2018, 1806183 (2018)

Speaker: Oleg Petracic (Jülich Centre for Neutron Science (JCNS-2) and Peter Grünberg Institut (PGI-4), JARA-FIT Forschungszentrum Jülich GmbH, Jülich, Germany)

63 RHEED measurements on Sapphire Al2O3

Within the scope of this thesis, we modified and tested the new experimental set up for measuring Total Reflection High-Energy Positron Diffraction (TRHEPD [1]) and Reflection High-Energy Electron Diffraction (RHEED). The remoderated positron beam from NEPOMUC will be used for investigation of surface reconstructions with topmost atomic layer sensitivity.
In order to benchmark the RHEED system, various measurements of RHEED on sapphire (Al2O3) with orientation (0001) were performed [2]. These first test comprised: diffraction images for 360° rotation of sample in XY plane, identify high symmetry directions (0° and 30°), diffraction images with different incident angles on the same position of sample. Change in diffraction images after heating sample to 1000 °C was observed. Diffraction spots for high symmetry directions were compared with theory and labeled [3].
For measurements with different incident angles, magnetic deflection coils in Helmholtz-like geometry have been designed. In sample preparation several possibilities of connection between sample and sample carrier were tested and obtained respected diffraction images: ceramic glue, conductive silver paste, clamps connection, molten and solidified silver.
1) Fukaya Y., Kawasuso A., Ichimiya A., Hyodo T. 2018: Total-reflection high-energy positron diffraction (TRHEPD) for structure determination of the topmost and immediate sub-surface atomic layers, J. Appl. Phys. 52 013002.
2) V. Oderno and C. Dufour and K. Dumesnil and A. Mougin and Ph. Mangin and G. Marchal: Hexagonal surface structure during the first stages of niobium growth on sapphire (1120), Philosophical Magazine Letters, v. 58, 1998, pp 419-426.
3) Williams, David B., Carter, C. Barry 2009: Transmission electron microscopy a textbook for material science, pp 283-303.

Speaker: Artur Elovskii (Tum Master Student)

64 Self-assembly of large iron oxide nanoparticles in ultrahigh molecular weight linear diblock copolymer films

The preparation of block copolymer (DBC) nanocomposite films that consist of magnetic nanoparticles (NPs) with diameters (D) of more than 10 nm is a challenging task. In the present work, this limitation is addressed by using an ultrahigh molecular weight (UHMW) DBC polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) as templates for the self-assembly of periodic hybrid materials containing large iron oxide NPs (D = 27 ± 0.6 nm). Via hydrogen bonding between the carboxylic acid groups on the iron oxide NPs and the PMMA side chains of the DBC, the NPs are selectively incorporated inside the PMMA cylinders. Due to the rearrangement of the polymer chains for accommodating the NPs, a well-ordered cylindrical nanostructure is readily generated at low NP concentration (c = 0.5 wt%). Most interestingly, a chain-like network appears inside the hybrid films at a high NP loading (c ≥ 10.0 wt%). Additionally, the magnetic properties of the hybrid films are determined at various temperatures in one direction (with PMMA cylinders vertical to the applied magnetic field). All hybrid films show ferromagnetism, but the hysteresis loops narrow slightly with increasing temperatures.

Speaker: Wei Cao (TU München)

65 Spin structure of superparamagnetic iron oxide nanoparticles

We have studied superparamagnetic iron oxide nanoparticles by various experimental techniques in order to characterize the observed reduced saturation magnetization as compared to bulk. Magnetic nanoparticles of the size of 12 nm and 15 nm have been studied by means of small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), inductively coupled plasma with optical emission spectroscopy (ICP-OES) and magnetometry to obtain a detailed understanding of the internal magnetization distribution. The particles are spherical colloidal iron oxide particles with an oleic acid coating embedded in a paraffin matrix. The concentration of particles inside the matrix is chosen in such a way that the inter-particle interactions are negligible. SAXS data provides a precise measure of the particle radius and their polydispersity as well as volume fraction of the magnetic nanoparticles, which is in agreement with the amount of iron obtained by ICP-OES. The combination of XRD, HRTEM and magnetometry yields details on the specific iron oxide phase composition and the magnetic behavior. The shapes of both the hysteresis loops and the ZFC/FC curves confirm a superparamagnetic behavior of the particles. The presence of exchange bias indicates an antiferromagnetic, most probably, wüstite contribution to the particle composition. To obtain complementary information about the inner spin structure of the nanoparticles small-angle scattering of polarized neutrons (SANSPOL) will be utilized.

Speaker: Tobias Köhler (JCNS-2)

66 Sputter deposition of Al & Ag on nanostructured PMMA-b-P3HT and PS-b-PMMA copolymer thin films

Nanostructured polymer-metal-composite films demonstrate great perspectives
for optoelectronic applications, e.g. as sensors or photovoltaics. To enhance properties of such devices the self-assembly process needs to be understood. We studied the cluster morphology growth by grazing incidence small-angle X-ray scattering (GISAXS), as well as the crystallinity of the metal film formation with grazing incidence wide-angle X-ray scattering (GIWAXS) in situ during sputter deposition. The scattering experiments were combined with surface differential reflectance spectroscopy (SDRS). Our study reveals the selective wetting of aluminum and silver on the polymer blocks and the influence of the template on the percolation behavior of the metal layers.

Speaker: Marc Gensch (DESY Hamburg)

67 Structural characterization of high temperature VDM-780 Ni-based superalloy by means of Neutron scattering and transmission electron microscopy

Ni-based superalloys based on the /’ system are widely used for high temperature applications, as parts for jet engines, due to their good mechanical properties at high temperatures. In these materials, the austenitic matrix () is strengthened by intermetallic precipitates of Ni3Al (’) and Ni3Nb (’’) and it has been also observed the existence of co-precipitates of both phases with different morphologies (plate, needle, cube or disc shape). Other phases that can also be formed are Ni3Nb-based () and Ni3Ti- based (). The existence of the different phases and the quantity and shape of the different precipitates and co-precipitates depend on composition, heat treatment and processing conditions. Especially, it is crucial to control the evolution of the different phases at high temperature in order to tailor the mechanical properties at high temperatures.
In this work we present the structural studies on VDM-780 superalloy. By means of neutron diffraction (ND) we have determined the different phases present in this material after three different aging conditions performed for setting up different microstructures. Apart from the  matrix, the presence of the ’ and a high temperature phase have been observed and the amount depends on aging treatment, but no traces of ’’ phase has been found. The high temperature phase is compatible with both  and  phases but diffraction patterns do not allow to distinguish between the orthorhombic  phase and the hexagonal  phase. Both phases are usually present at the grain boundaries and the correct identification of them is crucial for the high temperature applications, as a small amount of  phase is essential for a good workability of the alloy.
In addition, high resolution transmission electron microscopy (HRTEM) study of the high temperature precipitates have allowed to identify both  and  phases in the high temperature precipitates and first results are shown in this work.

Speaker: Cecilia Solis

68 Sub-picosecond dynamics of water studied by neutron scattering and molecular dynamics simulations

Abstract:

The dynamics and the structure of materials on the atomic scale can be measured by x-ray and neutron scattering. The structure on the Ångström scale is by now well established, as is the diffusive dynamics on time scales above roughly one picosecond as measured for example by the neutron time-of-flight spectrometer TOFTOF at MLZ. However, recent measurements of the dynamics in the femtosecond to picosecond range on the resonant neutron spin-echo spectrometer RESEDA at MLZ showed some surprising features at these very short time scales. These two measurements will be compared in this contribution to see if their results are compatible with each other to exclude any instrumental effects. The dynamics will also be modeled by a molecular dynamics simulation and the calculated scattering function will be compared to the data. The results can be used to improve the water model used in the simulation and in turn to identify how different motions leave their mark in the data.

Speaker: Doaa Ali (TUM)

69 Surface residual stress profiles by neutrons-treatment of spatial resolution effects and spurious strains

A method for near surface strain scanning measurements using neutron diffraction with large gauge volumes is described and validated against x-ray diffraction (XRD) and neutron diffraction experiments with very high spatial resolution. The approach corrects for pseudo strains related to partially buried gauge volumes and enables to deconvolute the averaging effects associated with the use of a large gauge volume. The results show that neutron diffraction based strain measurements with standard sized gauge volumes are possible. Compared to measurements with smaller gauge volumes gains in counting time of up to a factor of fifteen can be achieved without appreciable loss in spatial resolution.

Speaker: Dr Joana Rebelo Kornmeier

70 Tailoring optoelectronic properties of mixed halide perovskites via the versatile 2-Step deposition method

Recently organic lead mixed-halide perovskite based solar cells surpassed a power conversion efficiency of 22 %. In particular the unique properties of perovskites, e.g. the highly tunable chemical composition, allow optimizing the hybrid crystal structure in a way to meet the desired demands. To take full advantage of this tunability of the perovskite materials, we apply a 2-step deposition technique to fabricate thin films. Those films of different chemical compositions and concentrations are probed with spectroscopic measurements. To get insights in their morphological and crystalline structure, these measurements are complemented by grazing incidence small- and especially wide-angle X-ray scattering. Especially the latter technique yields statistically relevant information about the crystalline features in the perovskite film, which enables us to relate optoelectronical to morphological characteristics. This offers the possibility to systematically tune the unique optoelectronic properties in order to achieve highly tailored high-quality perovskite thin films for a broad range of promising applications.

Speaker: Lennart Reb (TUM E13)

71 Temperature and Charge Rate dependant phase relaxation of graphite anodes

Poster (preferred) or short talk (15min).

In situ / operando Neutron Diffraction is a powerful tool to study phase inhomogeneity and relaxation phenomena in lithium-ion batteries.
Time-resolved operando neutron diffraction measurements of a commercial high power LiCoO2/Graphite pouch bag battery operated in the temperature range of −20 °C to 40 °C were done at STRESS-SPEC.
Analysis of the relaxation times allows to attribute the slow lithium transport due to limitations of grain boundaries between different phase domains or crystallites within the particles rather than in-plane transport.

Speaker: Stefan Seidlmayer

72 Temperature or Light Stress Induced Degradation of Perovskite Materials

The rapid development of metal halide perovskite solar cells (PSCs) makes such solar cells power conversion efficiency (PCE) comparable with silicon solar cells and the certified PCE has already reached 23.7%1. However, long-term device stability is one of the most critical issues in PSCs. To improve the stability of PSCs, interface passivation, inorganic materials and encapsulation strategies were introduced and the stability of PSCs had been enhanced to 11000 hours under the light (AM 1.5G conditions)2. Nevertheless, there are a few studies to investigate the metal halide perovskite crystal structure related degradation mechanisms. Therefore, we propose to observe perovskite materials degradation process under light or temperature stress using in-situ grazing incidence wide-angle X-ray scattering (GIWAXS) and grazing incidence small angle X-ray scattering (GISAXS), which will broaden our understanding of degradation mechanisms of metal halide perovskite materials. Moreover, after understanding degradation mechanisms of metal halide perovskite materials, potential solutions can be found to suppress the degradation process of these materials.

Speaker: Renjun Guo (Physics E13, Technical University in Munich)

73 The Neutron Depth Profiling Instrument N4DP at the PGAA facility

Neutron Depth Profiling (NDP) is a non-destructive method to probe concentration profiles of a few light nuclides (mainly Li-6, B-10, N-14) in different host materials. The energy loss of the charged particles produced upon neutron capture of the investigated nuclei is correlated to origin of depth and their signal intensity to concentration amount. Here, depth resolutions down to 5 nm can be achieved, depending on the host material. Applications for NDP are boron implantation profiles in wafers and solar cells, boron distributions in heat-treated superalloys and lithium distributions in OLED prototypes. A main demand for NDP have been coming up lately from lithium-based secondary batteries, where NDP reveals insights into the functionality and aging processes of these devices [1-4]. The here presented N4DP setup is situated at the PGAA facility of MLZ, which provides ideal conditions for NDP: a cold neutron flux up to 5E10 s-1cm-2, while maintaining a low background signal. Furthermore, both techniques complement each other, since NDP provides depth distributions of single nuclides within the material, whereas PGAA probes the bulk material composition.

[1] M. Trunk, et al., Mat. Char., doi: 10.1016/j.matchar.2018.09.030.
[2] L. Werner, et al., NIM A, doi: 10.1016/j.nima.2018.09.113.
[3] M. Wetjen, et al., Electrochem. Soc., doi: 10.1149/2.1341810jes.
[4] M. Wetjen, et al., Electrochem. Soc., submitted.
[5] Zs. Revay et al., Nucl. Instr. Meth. A 2015, 799, 114-123.

Speaker: Markus Trunk

74 The order/disorder transformation of β phase in binary and ternary γ TiAl based alloys studied by synchrotron and neutron diffraction

Introduction
Due to their high melting point, low density, and good oxidation resistance, γ-TiAl based alloys have recently started to replace Ni-based superalloys as a material for turbine blades in aircraft engines [1]. Conventional γ -TiAl alloys usually contain the ordered phases γ-TiAl and α2-Ti3Al at lower temperatures and disordered α-Ti(Al) phase above 1120°C. Additional alloying elements like Nb, Mo, Ta, Cr or Fe, can stabilize the disordered β-Ti(Al) phase (A2 structure), which could stay at lower temperatures in its ordered βo-TiAl (B2 structure) state or sometimes transforms to more complex phases [2].
The ductile body centered cubic (bcc) β phase is important for processing because it significantly improves the hot forming behaviour of the material. Otherwise the ordered low temperature βo phase is said to embrittle the material at service temperature. Unfortunately little is known about the exact order/disorder transformation temperatures of β/βo in ternary alloy systems and the influence of β stabilizing element content is still under research. Additionally, even for the binary TiAl phase diagram the existence of an ordered βo phase field at high temperatures has yet not been finally proofed or rebutted [3].
In situ HEXRD could be used for determination of the βo↔β phase transformation, if the superstructure reflex of the βo phase is not too weak. Neutron diffraction (ND) is best suited to study order/disorder transformations in titanium aluminides [4, 5]. The fundamental reflections in ordered and unordered beta phase are very weak because of the opposite sign of the scattering lengths of Al sites and Ti sites which sum up to the overall signal. Otherwise, the superstructure reflections of the ordered TiAl crystal structures including the ordered βo-phase become rather large, because they scale with the difference of the scattering lengths of each site. Thus, the application of in situ neutron diffraction in situ is expected to be a powerful tool to determine the temperature of βo↔β order-disorder transformation. Nevertheless, it is found that a combination of in situ neutron and synchrotron diffraction is even more powerfull as also the fundamental peaks can be monitored yielding additional information about the disordered phases. If the order-disorder transformation temperatures in thermodynamic equilibrium are the aim of the investigation it is obligatory to take the heating ramp into account. The heating velocity determines the measured phase transformation temperatures and could yield to different results of neutron and synchrotron measurements. Application of the same heating ramp, when possible, with the same furnace would give the best correspondence between results.
Materials and Methods
We studied three binary TiAl alloys (Ti-xAl with x = 39, 42 and 45), two semi-binary (with boron addition for finer grain size Ti-xAl-0.2B with x = 39 and 42) and fifteen alloys with additional alloying elements (Ti-42Al-ay with ay = 2; 8.5; 10 at.% of Nb, 2; 4; 6 at.% of Mo, 2; 8.5; 10 at.% of Ta, 2; 3;4 at.% of Cr and 1; 2; 3 at.% of Fe). All alloys except Ti-42Al-8,5Nb were produced by arc melting under Ar atmosphere. The melt buttons were remelted 5 times to ensure chemical homogeneity and subsequently heat-treated at 1100°C for 5 and 7 days in order to homogenize the microstructure. Samples have fine and medium grain size up to 200 µm with duplex microstructure. The sample of Ti-42Al-8,5Nb has been produced by Markus Rackel and production conditions are described in [6].
In situ ND measurements were performed in the materials science diffractometer STRESS-SPEC (FRM II in Garching near Munich, Germany) twice. Two different furnaces have been applied for heating. A standard high temperature furnace (HTF) and a dilatometer, which differ from each other by heating method and applied sample size. The gauge volume for the first experiment was 5 mm×5 mm×20 mm=500 mm3 and for the second 5 mm×5 mm×10 mm=250 mm3. We used a wavelength of 2.1 Å. By a 3He-PSD, 25 x 25 cm2 neutron detector an angular range of 15° has been covered. The detector covered the q-range of 1.7-2.3 2πÅ^(-1) which enables to monitor superstructure reflections of all three ordered phases simultaneously, namely α2 101, βo 100 and γ 110. Because of longer exposure time needed for better statistics the samples were stepwise heated between 1100°C and 1440°C with a minimum step of 10°C in ranges of special interest. The exposure time was varied from 20 minutes to 1 hour in order to have a better peak to background ratio. Some problems with the dilatometer cooling system appeared during the second neutron experiment. Therefore measurements have been performed between 1100 and 1250°C. Neutron measurements with HTF have been performed up to 1450°C.
Complementary in situ synchrotron XRD measurements were performed in the High Energy Material Science (HEMS) beamline at DESY in Hamburg, Germany. Because of very good detector time resolution, one picture has been recorded every 0.5 sec and continuous heating was applied. High-energy X-rays with a photon energy of 100 and 87.1 keV, corresponding to a wave length of 0.124 Å and 0.14235 Å were used. The gauge volume was 1 mm×1 mm×5 mm=5 mm3. The heat treatments were performed in a DIL805A/D dilatometer with a heating rate of 5 K/min from 1000-1250 °C and 20 K/min from 1250-1450 °C. The high intensity of the synchrotron beam and corresponding short measurement times allowed to cover also the RT – 1000°C temperature region. Complete Debye-Scherrer diffraction rings up to a q-value of 5.5 2πÅ-1 were continuously recorded on a PerkinElmer XRD 1621 flat panel detector with a frame rate of 0.15 Hz and an exposure time of 3 s.
Results and Discussion
Data analysis showed some differences between neutron and synchrotron results. When measuring samples of identical composition different temperatures of the βo↔β phase transformation were detected. Such differences could be explained by the application of different heating ramps. Based on our literature knowleges and experiment results during the in situ ND measurements the superstructure reflection βo-100 was never observed in the binary TiAl alloys [7]. However the in situ high-energy XRD experiments clearly show the formation of disordered β phase at about 1360 °C and 1400 °C for Ti-42Al and Ti-45Al respectively. These results proof the direct transformation of disordered α to disordered β in the binary Ti-Al system without the formation of a high temperature ordered βo-TiAl phase. The grain size of Ti-39Al is too big and therefore due to bad grain statistic no reliable measurements could be made.
In ternary alloys namely with 1; 2; 3 at. % of Fe; 2; 6 at. % of Mo; 2; 4 at. % of Cr; 8.5; 10 at. % of Nb; 8,5 at. % of Ta the superstructure βo reflection was observed by ND]. The synchrotron experiments show that after the βo 100 disapeared β is stable up to the highest measured temperatures. The ternary alloys with 2 at.% of Nb and Ta show no ordered βo phase. No superstructure βo reflection was observed by ND. Samples with 3 at. % of Cr; 10 at. % of Ta, as well as the semi-binary Ti-39/42Al-0.2B alloys were not measured by ND, but this is planned if the project will be continued.
References
[1] F. Appel, J.D.H. Paul, M. Oehring, Gamma Titanium Aluminide Alloys: Science and Technology, Wiley-VCH, Weinheim, 2011.
[2] A. Tokar, L. Levin, A. Katsman, A. Ginzburg, A. Berner, A. Fein, F. Simca b, A. Stern Materials Science and Engineering A351 (2003) 56_/69
[3] V.T. Witusiewicz, A.A. Bondar, U. Hecht, S. Rex, T.Y. Velikanova, Journal of Alloys and Compounds. 2008, 465, 64.
[4] I.J. Watson, K.-D. Liss, H. Clemens, W. Wallgram, T. Schmoelzer, T.C. Hansen, M. Reid, Advanced Engineering Materials. 2009, 11, 932.
[5] P. Erdely, T. Schmoelzer, E. Schwaighofer, H. Clemens, P. Staron, A. Stark, K.-D. Liss, S. Mayer, Metals. 2016, 6,10.
[6] Andreas Stark, Marcus Rackel, Aristide Tchouaha Tankoua, Michael Oehring, Norbert Schell, Lars Lottermoser, Andreas Schreyer, Florian Pyczak Metals 2015, 5(4), 2252-2265; doi:10.3390/met5042252
[7] V. Kononikhina, A. Stark, W. Gan, A. Schreyer, F. Pyczak, MRS Advances. 2017, 1-6.

Speaker: Victoria Kononikhina (Helmholtz-Zentrum Geesthacht)

75 Thiophene based Semiconductors and Graphene Oxide for Organic Solar Cells

The polymers poly(3-hexylthiophene), poly(3-thiopheneacetic acid), poly(3-thiopheneethanol) and the related copolymers are prepared starting from the respective monomer units by chemical oxidative polymerization. Graphene has also been oxidized to graphene oxide, which becomes due to the functionalization highly dispersible in organic solvents, forms far more homogeneous layers than pure graphene and is also liquid processable. The synthesized molecules and nanoparticles are used as electron donor or electron acceptor materials in an organic solar cell and are characterized via infrared, absorption and fluorescence spectroscopy. The organic materials are electrically conductive due to their extended conjugated π-electron system and therefore require neither heavy metals / heavy metal complexes nor dopants for charge transport and can be easily deposited via spin-coating from a solution.

Speaker: Roy Schaffrinna (Lehrstuhl für Funktionelle Materialien E 13)

76 Tracking the morphology formation of printed non-fullerene active layer for solar cells

Non-fullerene organic solar cells (OSCs) have attracted great interests due to the low cost materials, which make it easier to be commercialized in industries. Despite the power conversion efficiency (PCE) of related devices have been well developed with lab scaled fabrication processes, like spin-coating deposition, the situation for the devices fabricated by industry preferred depositions, like printing as one of the most promising methods, might be quite different. This is because the inner morphology of the active layer, namely the bulk heterojunction (BHJ) layer, is strongly influenced by the deposition method. Thus, to understand the inner structure as well as the structure forming process during the printing deposition is important for the device optimizations in the future. In this work, we employed a low band gap polymer, pffBT4T-2OD, as donor and a non-fullerene material, EH-IDTBR, as acceptor to form a BHJ film as active layer in our solar cell architecture. The solution containing donor and acceptor was deposited on the substrate by printing in ambient conditions. During the printing process, the film morphology was observed in situ by grazing incidence small-angle X-ray scattering (GISAXS). In addition, atomic force microscopy (AFM) and scanning electron microscope (SEM) techniques were used to get the surface morphology information of the printed active layers.

Speaker: Xinyu Jiang (Technische Universität München Fakultät für Physik)

77 Wearable Electronic Skin based on Triboelectric and Luminescent Effect for Pressure and Tensile Sensing

Electronic skin (E-skin) as the medium between ambient environment and bionic robots is an advanced technology that provides an electronic readout or even produces a visualized response that can be easily captured for postprocessing. Since this concept birth, different electronic skins have been fabricated and utilized for various sensing applications, such as pressure, humidity, temperature et al. However, to mimic human skin better, combining more sensing capabilities into one E-skin system is highly in demand.
Here, we envisioned a new type of wearable E-skin system based on triboelectric and luminescent effect for both pressure and tensile sensing. This device consists of a triboelectric nanogenerator as a pressure sensor and a luminescent layer realized by CdSe/CdS quantum rods for tensile sensing.

Speaker: Mr Tianxiao Xiao (Lehrstuhl für Funktionelle Materialien E 13)

17:30 Walk to the Hotel Badersee

18:30 Barbecue in the Hotel am See

Wednesday, 26 June

08:00 Breakfast

Plenary Session 4

Convener: Henrich Frielinghaus

78 No dark side to neutron decay

The question on the nature of dark matter is one of the major challenges of particle physics. So it is clear that the possibility of a dark decay channel as a solution to persisting discrepancies in measurements of the neutron lifetime using different techniques initiated massive research activity. In this presentation we will discuss recent results by PERKEO which largely rule out this interpretation.

Speaker: Bastian Märkisch (Physik Department, TU München)

79 Final Discussion: Road Map

Speaker: Henrich Frielinghaus

Science group meetings 1: Material Science

80 Neutron Activation Analysis (NAA) at FRM II - trace element analysis in samples from high purity silicon to meteorites

Neutron activation analysis is a nuclear analytical technique mainly used for the determination of trace elements. NAA is typically applicable to the chemical elements from the 4th period of the Periodic Table, and is highly sensitive for Na, Mn, Sc, Ta, Ir, In as well as the rare-earth elements. Its advantage is simple sample preparation, high sensitivity, non-destructiveness and multi-element analysis in a wide range of concentrations. Detection limits down to fg (femtogram) level can be reached. With its highly thermalized neutron flux, the reactor FRM II offers exceptional opportunities for the instrumental neutron activation analysis (INAA).

In my presentation, I will talk about some recent analytical studies, such as impurities in high-purity silicon, “finger-print” elements in archeological objects (bronze, ceramics) and meteorites incl. the meteorite “Cloppenburg” found in Germany in 2017.

Speakers: Dr Xiaosong Li (RCM / TU München), Christian Stieghorst (TUM / FRM II), Zsolt Revay (PGAA)

81 Molecular Dynamics and Hydrogen Diffusion in (NH2)- and (BH4)-based Hydrogen Storage Materials

There are several methods to store hydrogen, e.g. with physical technologies (compression), in metal hydrides or in complex hydrides. Within the complex hydrides, the metal amides Mg(NH2)2-LiH have recently gained in importance. They have good hydrogen storage properties with high capacity (ca. 4 wt%) and good reversibility. The drawback of these materials is the high kinetic barrier for hydrogenation, which results in a long loading time. This can be overcome with the addition of LiBH4, thus, the reaction is faster.
So far Mg(NH2)2-LiH-LiBH4 is an outstanding candidate to be used for hydrogen storage. Interestingly, some compositions can even reach operation temperatures below 100 °C and the desorbed products contain amongst others liquid phases. The hydrogen uptake and release properties of this system are well characterized in terms of capacity, kinetics and phase composition, but the basic mechanism how the reaction takes place and why it has these excellent storage facilities is still unknown. For these studies we have chosen the system 6Mg(NH2)/9LiH/LiBH4.
We will present first data of neutron scattering experiments using quasielastic scattering at TOFTOF to study hydrogen diffusion of the desorbed and absorbed state, as well as small angle neutron scattering to study particle sizes to gain further insight on the hydrogenation/dehydrogenation mechanisms.

Speaker: Mrs Neslihan Aslan (GEMS, HZG)

82 Contrast Matched SANS for Observing SEI and Pore Clogging in Silicon-Graphite Anodes

Silicon-graphite (SiG) electrodes are attractive candidates as anodes for Li-ion batteries due to their high theoretical specific capacity. However, repeated lithiation/delithiation during charge/discharge cycling causes significant morphological changes of the silicon particles. This results in the formation of highly porous silicon structures and severe side reactions at the silicon/electrolyte interface. To quantify these morphological changes, small-angle neutron scattering (SANS) was applied with selective contrast matching of Si nanoparticles (200 nm diameter) and the surrounding electrolyte decomposition products. Using electrolytes consisting of 1.5 M LiPF6 dissolved in either deuterated or protonated ethylene carbonate (EC) resulted in solid-electrolyte-interphase (SEI) compounds with scattering length densities either matching or mismatching that of the Si nanoparticles. SiG anodes with 35 wt% silicon nanoparticles were aged for 10 and 20 charge/discharge cycles against capacitively oversized LiFePO4 cathodes. Afterwards, the morphological changes and size distribution of the SEI compounds were evaluated by means of ex-situ SANS measurements of the SiG electrodes in their fully discharged state. Transmission electron microscopy (TEM) images of the pristine and cycled silicon nanoparticles complement the interpretation of the SANS analysis.

Speaker: Dr Neelima Paul

83 Engineering materials research with high-energy X-rays – GEMS at DESY

The possibilities of neutron scattering and imaging for materials science are perfectly complemented by those offered by high-energy X-rays from a synchrotron source. While neutrons stand out with their large penetration depths and contrast and magnetic properties, the synchrotron offers high enough intensities to achieve sufficient time resolution for studying fast processes. In addition, with focussing spatial resolutions in the 10 … 100 nm range can be achieved. With high-energy photons, even thick samples can be penetrated. The status of the GEMS beamlines at the photon source PETRA III at DESY in Hamburg and new developments will be reported. A few examples of the latest in-situ experiments at the high-energy materials science beamline (HEMS/P07) will be presented.

Speaker: Peter Staron (Helmholtz-Zentrum Geesthacht)

Science group meetings 1: Neutron Methods

84 Development of the high count-rate neutron detector SoNDe

Modern neutron sources deliver high fluxes of neutrons. Most current detector technologies therefore need to shield the primary beam, or cannot use the full dynamic range of the neutron flux. Therefore we created the Solid-State Neutron Detector (SoNDe).
SoNDe is a project for the development and construction of a high-flux capable neutron detector. The development focuses on the following specifications:
• high-flux capability, capable of handling the peak-flux of up-to-date spallation sources (>20 MHz/m2)
• high-resolution of 3 mm by single-pixel technique, below by interpolation
• high detection efficiency of 80 % or more
• strategic independence of 3He
• time-of-flight (TOF) capability, necessary to exploit maximum flux, with a time resolution in the µs regime
• modularity, improving maintenance characteristics of today’s neutron detectors
In order to achieve those goals, a pixelated scintillation detector with a multi-anode photomultiplier (MaPMT) readout was designed. This design allowed us to increase the achievable count-rate both per pixel and per area considerably. Additionally, in this fully modular setup it is possible to use each single 5 × 5 cm2 as an independent detector, therefore allowing a multitude of different detector geometries.
This project includes partners from France (Laboratoire Léon-Brillouin), Norway (IDEAS) and Sweden (ESS and Lund University) and Germany (Forschungszentrum Jülich).
Detectors such as this are required to be able to use high flux neutron sources as the FRMII or the upcoming European Spallation Source (ESS) to capacity. They will enable outstanding research on a range of neutron instruments allowing research in areas such as physics, chemistry and biology ranging over material science medical and pharmaceutical science.
In SoNDe this is reached by using a pixelized scintillation detector based on multi-anode photomultipliers.

References
[1] S. Jaksch, R. Engels, G. Kemmerling et al., arXiv:1707.08679, (2017).
[2] S. Jaksch, H. Frielinghaus et al., Proceedings of the International Conference on Neutron Optics (NOP2017), (2018) 011019.
[3] K. Kanaki, S. Jaksch et al., arXiv:1805.12334, (2018).

Speaker: Sebastian Jaksch (Physicist)

85 Development of a curved multiwire detector for the upcoming instrument ERWIN

In addition to providing day-to-day maintenance and service, the detector and electronics group of the MLZ is engaged in the development and construction of new detector systems. We will present results from our current major project, a 130-degree curved multi-wire proportional counter for the upcoming diffractometer instrument ERWIN, as well as details on other ongoing work.

Speaker: Dr Alan Howard (MLZ)

86 New primary optics for the ErwiN ‘Energy research with Neutrons’ option at MLZ

The further development of the ErwiN – Energy research with Neutrons – neutron powder diffraction (NPD) beamline is presented with three distinctive events: Firstly, during the second funding period the primary beam optics will be replaced to bring this diffractometer to the same level as the high flux and high resolution instrument D20 at the ILL. The ErwiN instrument will be used for the investigation of energy storage materials, also integrated in complete components and under real operating conditions. Thus, it is possible to scan a large parameter space (e.g. temperature, state of charge, charge rate, fatigue degree) for the investigation of modern functional materials in kinetic and time-resolved experiments. Diffraction data will be obtained from the entire sample volume or in a spatially resolved mode from individual parts of the sample. ErwiN is designed for different scenarios: for very fast measurements at medium resolution, for medium fast measurements at higher resolution and for very high resolutions still at reasonable velocity. The final commissioning and integration of ErwiN is the second important objective during the next funding period, while thirdly, the integration of newly developed and strongly needed sample environment, e.g. high pressure H2-gas system, will enhance the attractiveness for a wider community in energy research as well as materials science while furthermore developing novel methods for the neutron science community.

Speaker: Michael Heere

87 New deveopments on scintillation screens doped with boron, lithium and dysprosium

In collaboration with Idaho National Lab, several dozens of new scintillation screens for neutrons were tested at FRM II.
Existing mixtures with LiF were tested, but also new mixtures with boron, which were very promising on the way to higher spatial resolution in neutron imaging. A third class comprised dysprosium-doped screens which are not only more sensitive in the epithermal range for a Cd-filtered beam, but also produce an afterglow image that is so bright that a scintillation screen can be irradiated in a high gamma radiation environment (e.g. spent fuel) and then removed remote-controlled to be read out with a camera detector in a shielded containment.
By the time of the meeting, we hope to to have new measurements about the next batch of screens based on the first measurements.

Speaker: Burkhard Schillinger

Science group meetings 1: Quantum Phenomena

88 Vortex Lattice Domain Formation in the Type-II/1 Superconductor Niobium

Besides the well-known vortex lattice (VL), type-II/1 superconductors exhibit the intermediate mixed state (IMS), where VL domains and Meissner domains coexist, due to an attractive component of the VL interaction [1]. Despite some work in the 1970s, no detailed theoretical model for the IMS exists. Primary obstacles are the inapplicability of most standard models of superconductivity and the importance of demagnetization effects and vortex pinning.

We have readdressed the IMS in bulk niobium by combining several neutron based techniques [2],[3]. Using small angle scattering, we characterized the VL crystallography. For the larger IMS domains, we used ultra-small angle scattering to investigate the domain morphology. Additionally, neutron grating interferometry revealed information about the spatial distribution of IMS domains.

Following a field cooling protocol, we find that while the macroscopic magnetic properties remain homogeneous, vortices are gradually rearranged microscopically from a uniform VL to inhomogeneous domains. Surprisingly, this process takes place below the macroscopic freezing transition of the VL. The IMS domains form at a preferred length scale which remains nearly unchanged with temperature. These results shed new light on the detailed formation of the IMS in bulk superconductors.

[1] E. H. Brandt and M. P. Das, J. Supercond. Novel Magn. 24, 57 (2011)
[2] T. Reimann, et al, Nat. Com. 6, 8813 (2015)
[3] T. Reimann, et al, Phys. Rev. B 96(14), 144506 (2017)

Speaker: Alexander Backs (Heinz Maier-Leibnitz Zentrum)

89 Quests for fractionalized excitations in frustrated quantum magnets

Yixi Su$^1$, Xiao Wang$^1$, Fengfeng Zhu$^1$, Junda Song$^1$, Viviane Pecanha-Antonio$^1$, Erxi Feng$^1$, Thomas Müller$^1$, Thomas Brückel$^2$

1Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich, D-85747 Garching, Germany
2Jülich Centre for Neutron Science (JCNS) and Peter Grünberg Institute (PGI), Forschungszentrum Jülich, D-52425 Jülich, Germany

An unambiguous realization of quantum spin liquid (QSL), characterized by fractionalized excitations, non-local quantum entanglement and emergent Gauge symmetry in the ground state, has yet to be achieved in frustrated and topological quantum magnets, often due to preemptive long-range magnetic order or spin freezing at finite temperature. In this talk, I will present some examples from our recent polarized and inelastic neutron scattering studies of magnetic order and excitations in several QSL candidate materials with frustrated pyrochlore, honeycomb and triangular lattices. Our central aim is to search for possible experimental signatures of fractionalized excitations at finite temperature.

Speaker: Yixi Su (JCNS-MLZ, Garching)

90 Neutron Depolarization Measurements of Quantum Critical Ferromagnets

In ferromagnetic quantum critical systems it is possible to suppress the Curie temperature to 0 K by changing an external control parameter such as a magnetic field or hydrostatic pressure. Recent theories suggest a generic phase diagram for clean quantum critical ferromagnets featuring a tricritical point where the order of the phase transition changes from 2nd to 1st. This behavior has already been observed e.g. in ZrZn₂ and MnSi, and is also discussed for SrRuO₃. An exception to this behavior could be the ferromagnetic Kondo lattice CePt as no tricritical point was observed, yet. The neutron depolarization technique offers new insight into ferromagnetic quantum critical systems as it enables us to directly probe ferromagnetism in challenging sample environments, such as magnetic fields, low temperatures, and high pressures. We present two neutron depolarization studies of the compounds SrRuO₃ and CePt up to hydrostatic pressures of 17 GPa and 12 GPa, respectively.

Speaker: Marc Seifert (Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München)

91 Valence bond breaking and re-arrangement in YbMgGaO4

Rare-earth based triangular antiferromagnets provide a novel playground for frustrated magnetism and quantum spin liquid behavior of spin-orbit coupled moments. YbMgGaO4 features spin-orbit moments from a Kramers doublet, which remain fluctuating down to very low temperatures. We discuss recent inelastic neutron scattering experiments which point at valence bond excitations [1,2].

[1] Y. Li et al., Nat. Commun. 8, 15814 (2017).

[2] Y. Li et al., Phys. Rev. Lett. 122, 137201 (2019)

Speaker: Prof. Philipp Gegenwart (Uni Augsburg)

Science group meetings 1: Softmatter

92 Characterising self-assembly of magnetic nanoparticles

Self-assembly is the phenomenon of spontaneous organization of nanoparticles into a stable 1D, 2D or 3D assemblies on a substrate or in solution. Understanding the origin of self-assembly will allow us to harness unique properties of the material that are both multifunctional and adaptable with applications in various fields of biomedical engineering and material science. Self-assembly of magnetic nanoparticles (MNPs) in solutions depends on parameters like the particle size, external magnetic field, the thickness of surfactant, concentration and synthesis routines. Here, we aim to understand the mechanism that governs self-assembly by tuning the size, field, and concentration of NP's in solution.

Superparamagnetic iron oxide nanoparticles (NPs) of 20nm and 27nm were characterized using Transmission Electron microscopy (TEM) to determine the size and size distribution. The 2-D pattern obtained from Small Angle X-ray Scattering (SAXS) and Small Angle Neutron Scattering (SANS) of 20nm NPs is isotropic up to high concentrations (1%vol) and maximum fields (2.2 T) indicative of no self-assembly. On the other hand, the 27nm NPs revealed anisotropy in the 2-D pattern for even low concentrations (0.42%) and low fields (0.004T) indicative of an order in the system. A linear pearl model best describes the radially averaged SANS and SAXS data of 27nm NPs, indicating the presence of chains even at zero field. The weakly interacting 20nm NPs are further understood using half-polarized neutron scattering (SANSPol) which allowed us to separate the magnetic form factor from dominating nuclear one. The difference signal exhibits a $sin^{2}θ$ behavior which yields the nuclear and magnetic interference term for dispersed non-interacting 20nm NPs. SANSPol measurements on 27nm are similar to their SANS pattern, which is further analyzed using sector analysis to obtain the form and structural factors. Moreover, such analysis will allow us to estimate the role of dipolar interactions. Macroscopic magnetization measurements revealed a different magnetic behavior in dilute and concentrated samples indicating the influence of interactions in both NPs. We obtained a crystal structure of two NPs in order to gain more insights into the possible origin of this profound size effect on self-assembly. We used x-ray PDF (Pair distribution function) to determine composition and lattice constants, as well as to separate between various forms of iron oxides often present in NPs of our size.

Speaker: Nileena Nandakumaran

93 Measurement of Dynamic Coherent Excitations in Phospholipid Membranes

Phospholipid membranes are the basic construction material of cell membranes. Also, solutions of phospholipid vesicles find a wide array of applications in technical, medical and biological applications. Hence, the basic understanding of these membranes, both in terms of structure and dynamics is of paramount importance in order to better understand the mechanisms of cell membrane permeability, stability, and solubility in vesicle solutions.
In our previous publications, we showed both the structure and the dynamic behavior of phospholipid membranes made from L-α-phosphatidylcholine (SoyPC). [1,2] The investigations presented there were performed by means of grazing-incidence small-angle neutron scattering (GISANS) and grazing-incidence small-angle neutron spin echo spectroscopy (GINSES). We established a multi-lamellar structure with repeat distances of approximately 6 nm as well as a mode in the GINSES data, that we attributed to a coherent dynamic mode in the membranes, a kind of thermally excited eigenmode.
Following up on this experiment, we performed additional GISANS measurements in order to identify features in the coherent scattering that we could attribute to the coherent mode in the membrane.[3] For that, we specifically adapted the resolution settings during the GISANS experiment and were then able to find the coherent scattering contribution of the dynamic modes of the phospholipid membranes. Moreover, as we assumed the coherent mode was linked to a specific phase of the lipid membrane, we investigated the system at different temperatures and could show that the excitation mode indeed disappeared at temperatures below 25°C and reappeared when the system was reheated.
The experimental advantage of identifying modes such as these in a coherent scattering experiment, such as GISANS is the time required for an experiment. While the GINSES measurements take up to 5 days for a single curve at a single Q-value, GISANS experiments can be performed within hours. This gives an approximated gain of one order of magnitude. After the modes have been identified in GISANS, additional detailed scans using GINSES become feasible. This allows to access a wide range of the parameter space, that would be impossible to cover with GINSES.

References
[1] S. Jaksch, H. Frielinghaus et al., Phys. Rev. E 91(2), (2015) 022716.
[2] S. Jaksch, H. Frielinghaus et al., Scientific Reports 7(1), (2017) 4417.
[3] S. Jaksch, H. Frielinghaus et al., Colloids and Interfaces 2(3), (2018) 31.

Speaker: Sebastian Jaksch (Physicist)

94 Spray Deposition of Water-processed Active Layers for Hybrid Solar Cells Investigated with in situ Grazing Incidence X-ray Scattering Techniques

Hybrid solar cells with an active layer based on low temperature processed titanium dioxide and a water-soluble polymer have been developed [1]. In this all-embracing green technology approach TiO2 nanoparticles are produced with laser ablation in liquid in order to initiate a functionalization of TiO2 with the polymer for the active layer. Combining these TiO2 nanoparticles and water-soluble poly[3-(potassium-6-hexanoate)thiophene-2,5-diyl] (P3P6T) hybrid solar cells are realized. For the fabrication of hybrid photovoltaic devices we applied spray-coating as the deposition method for the active layer which could easily scale-up to industrial cost-effective fabrication. For the deposition of the active layer with laser-ablated particles spray deposition provides a good control of the film thickness. The morphology of the active layer is of major importance for the performance of hybrid solar cells. As we are especially interested in how the morphology changes with ongoing deposition process, we use the in situ GISAXS technique. This allows us to follow the development of the morphology of the active layer with high spatial and temporal resolution [2, 3]. Whereas the mesoscale of the active layer for hybrid solar cells was probed with in situ GISAXS, the crystallinity of the polymer and the inorganic component was investigated with in situ GIWAXS. The changes of the morphology and the influence on photovoltaic performance with the introduction of a compositional gradient are discussed. As the synchrotron-based investigation allowed for a high temporal resolution of 0.1 s, insights into the very first stages of the deposition process were obtained. From the overall situ study improvements for the spray deposition procedure are derived that allow for a better control of the morphology of the devices.

Speaker: Volker Körstgens (TU München)

95 Model-Independent Recovery of Interfacial Structure from Neutron Reflectivity Data

Neutron specular reflectivity at soft interfaces provides sub-nanometer information concerning the molecular distribution of thin films, while the application of contrast variation permits to highlight the scattering from different parts of the system and can lead to an overall reduction of fitting ambiguity. Traditional modelling approaches involve the construction of a trial scattering length density profile based on initial speculation and the subsequent refinement of its parameters through minimisation of the discrepancy between the calculated and measured reflectivity. In practice this might produce an artificial bias towards specific sets of solutions. Here we present an integrated Indirect Fourier Transform/Simulated annealing method that when applied to multiple solvent contrast reflectivity data, leads to reliable reconstructions of the interfacial structure without the need for any a priori assumptions. The generality of the method permits its straightforward application in common experimental contrast variation investigations.

Speaker: Alexandros Koutsioumpas (JCNS)

Science group meetings 1: Structure

96 Pr(BH4)3 - polymorphic transitions and a hint of stepwise negative thermal expansion

In this work, praseodymium(III) borohydride, Pr(BH4)3, and the isotopically enriched analogue, Pr(11BD4)3, are prepared by two routes. The first approach started by mechanochemical synthesis of PrCl3 and LiBH4, and extraction of LiCl [1], while the second approach, shows a new route and proceeded via a solvate complex, Pr(11BD4)3S(CH3)2 starting from the metal Pr itself. α-Pr(BH4)3 is isostructural with cubic unit cells (Pa-3) stable at room temperature (RT) and unit cell volume per formula unit (V/Z) of 180.1 and 175.8 Å3, respectively. Heating α-Pr(BH4)3 to T = 190 °C, p(Ar) = 1 bar, introduces a transition to a rhombohedral polymorph, r-Pr(BH4)3 (R3 ̅c) with smaller unit cell volume and denser structure, V/Z = 156.06 Å3. However, heat treatment of α-Pr(BH4)3, at T = 190 °C, p(H2) = 40 bar facilitates reversible formation of another three cubic polymorph, denoted β, β’-Pr(BH4)3 and β’’-Pr(BH4)3 (Fm3 ̅c). Moreover, the transition β- to β’- to β’’- is considered a rare example of stepwise negative thermal expansion, which we pursue to validate via PDF analysis. For Pr(BH4)3, 2/3 of the sample take this route of transformation whereas in argon only 5 wt%, and the remaining transforms directly from alpha- to r-Pr(BH4)3. The β-polymorphs are porous with V/Z = 172.4 and 172.7 Å3 for β’’-Pr(BH4)3, and are stabilized by the elevated hydrogen pressures. The polymorphic transitions occur due to rotation of RE(BH4)6 octahedra without breaking or forming chemical bonds. Structural DFT optimization reveals decreasing stability of α-Pr(BH4)3 > β-Pr(BH4)3 > r-Pr(BH4)3.

Speaker: Michael Heere

97 A New Measuring Cell for Operando Neutron Diffraction on Li-Ion Battery Cathode Materials

The use of operando diffraction has taken a major step forward, in no small part due to the increase in flux at large scale facilities such as synchrotrons and neutron spallation sources. While the X-rays are absorbed by the battery casing which necessitates special cells with windows, neutrons have a penetration depth large enough to probe the entirety of cell. This has allowed measurements directly on commercial batteries, giving unique insights into the evolution of cell parameters and composition of the cathode and anode phase, but also showing Li-consumption by decomposition of the electrolyte and plating of lithium metal.
When measuring on commercial cells, contributions from all parts of the cell are observed which complicates the analysis of the diffraction data. A desire also exists to measure on non-commercial electrode materials prepared in the lab. Thus, there exists an incentive to develop a measuring cell which allows easy measurement on a variety of different cathode materials, either commercial or synthesized.

In this work, we present a new operando neutron diffraction battery cell, especially designed for the new beamline ErwiN at the FRM-2 research reactor outside of Munich, Germany. The cell uses a Zr/Ti-alloy with negligible scattering strength to eliminate contributions from the casing. We present data on the commercial cathode materials LiFePO4 and LiNi1/3Mn1/3Co1/3O2 to demonstrate the capabilities of the cell, as well as on the non-commercial cathode material Li3V2(PO4)3. Li3V2(PO4)3 is interesting, as it has the highest gravimetric capacity among the known phosphates (197 mAh g-1). The material displays a complex series of phase transformations during charge and discharge, and interestingly, these transformations are very dependent on the number of Li-ions extracted during charging. The material has been investigated using operando synchrotron X-ray diffraction, but operando neutron diffraction is important to uncover the exact nature of the Li-ion dynamics.

Speaker: Dr Daniel Sørensen (MLZ)

98 Diffraction studies of prismatic Li-ion cell with neutrons

In the last decades Li-ion batteries, occupied an important role in energy market, are widely used in powering portable devices, off-grid energy storage and e-mobility applications. In a number of publications, it was shown that a neutron powder diffraction pattern taken on cylindrical cells like 18650-type can be successfully refined using a contribution from the cell constituencies: positive and negative electrodes, current collectors and cell housing. The cylinder-type Li-ion cells are rather difficult for lab manufacturing due to rollover design which leads to numerous issues regarding reproducibility, current and electrolyte distribution etc. On the other hand, prismatic cells are much easier to manufacture in the lab. Also, from the ergonomic point of view, the prismatic cells supply improved stacking/volumetric density, when compared to cylinder ones. This leads to the increased interest of cell manufacturers to the cells in prismatic shape for both low and high current applications and inspired us to start the thorough characterization of the cells of this type using high-resolution neutron powder diffraction. In the current contribution, we present an optimized approach for the neutron diffraction measurements of prismatic cells which allows to collect data set of similar quality to cylindrical cells. This approach also allows data collection not only for ex situ but also upon in situ/in operando conditions using a specially designed setup. In the contribution, the behavior of the prismatic cells is compared to those observed for the of 18650-type cells.

Speaker: Volodymyr Baran

99 Powder diffraction computed tomography: a combined synchrotron and neutron study

Diffraction and imaging using X-rays and neutrons are widely utilized in different fields of engineering, biology, chemistry and/or materials science. Combined information gained by X-ray diffraction computed tomography (XRD-CT) is a powerful approach with high potential due to enhanced sensitivity of the method. Its active development over the last decade revealed structural details in a non-destructive way with unprecedented sensitivity. In the current contribution a first attempt to adopt well-established XRD-CT technique for neutron diffraction computed tomography (ND-CT) is reported. A specially designed "phantom", an object displaying adaptable contrast sufficient for both XRD-CT and ND-CT was used for method validation. The feasibility of ND-CT was demonstrated and it was also shown that ND-CT technique is capable to provide a non-destructive view into the interrrior of the “phantom” delivering structural information consistent with a reference XRD-CT experiment.

Speaker: Anatoliy Senyshyn

11:45 Exkursion to the Osterfeldkopf and the Kreuzeck

18:30 Dinner

100 Evening Talk: Vulcans

Speaker: Prof. Donald Dingwell (LMU)

Thursday, 27 June

08:00 Breakfast

Science group meetings 2: Material Science

101 Total Reflection High-Energy Positron Diffractometer at NEPOMUC

Total Reflection High-Energy Positron Diffraction (TRHEPD) has been established as an ideal technique to determine the crystalline structure of topmost and immediate subsurface atomic layers. In contrast to Reflection High-Energy Electron Diffraction (RHEED), TRHEPD features an outstanding surface sensitivity, which stems from the repulsive crystal potential for positrons and the phenomenon of total reflection.

We have developed a new positron diffractometer that is coupled to the high-intensity positron source NEPOMUC at the FRM II. The setup features UHV down to 10-10 mbar, sample temperatures up to 1000°C and a RHEED system for complementary measurements. The positron beam is accelerated and focused by an electrostatic lens system. A transmission-type remoderator foil can be used to enhance the brightness of the beam optionally. We simulated the particle trajectories to optimize the beam properties in order to obtain a parallel, slightly converging beam with a small diameter of around 1mm (with remoderation). First experimental results are expected in spring 2019. Beside the identification of surface structures, the diffractometer will also enable us to investigate surface related phenomena such as phase transitions, reconstruction or surface melting. The project has been supported by the BMBF (funding number 05K16WO7).

Speaker: Matthias Dodenhoeft

102 Results of the SINE2020 Industry Consultancy and the role of neutron science in industrial innovation

How to develop an innovative process for efficient and high-quality development of advanced materials and components?

The EU-Horizon2020 project SINE2020 aims at strengthening the cooperation between industry and European neutron sources. Free of charge, the project offers training and education of industrial researchers and the possibility to perform test measurements at the participating neutron facilities.

In this presentation we introduce the results of the industry consultancy initiative in the H2020 project SINE2020 and share our success stories and obstacles in improving cooperation between industry and neutron facilities. We will introduce our strategy paper for the future in this field and show the results of different neutron based experiments we provided to industrial users via the SINE2020 free feasibility study offer:

• Residual stress measurement with neutron diffraction
• Neutron scattering of interpenetrating polymer networks (IPNs) as medical devices
• Behaviour of a surfactant by small angle neutron scattering (SANS)
• Insights in fuel cells with neutron radiography
• and more

Speaker: Marc Thiry (Helmholtz-Zentrum Geesthacht)

103 Optimization and characterization of the FaNGaS facility at MLZ

Prompt Gamma Neutron Activation Analysis (PGNAA) with cold/thermal neutrons is a well-established, nondestructive nuclear analytical technique to determine the elemental composition of different materials, especially small and thin samples. Thanks to their penetration depth, neutrons with a higher energy are a better choice for the analysis of large samples. For this purpose, an instrument called FaNGaS (Fast Neutron Gamma Spectrometry) was designed in the framework of a joint research project (FZJ/MLZ, financially supported by BMBF) and installed at the research neutron source Heinz Maier-Leibnitz (FRM II, Garching).
FaNGaS is a new instrument at the MEDAPP (MEDical APPlication) irradiation facility and uses the intense fission neutron beam delivered by the SR10 guide. The instrument is an electro-mechanically cooled, well-shielded HPGe detector connected to a digital spectrometer. In the first version of FaNGaS, the fast neutron beam was collimated using two collimators located at the outlet of the beam port and designed to filter thermal and epithermal neutrons.
A first characterization of FaNGaS was presented in 2015. Since then, certain changes have been made on the instrument. Further improvements and performance studies of FaNGaS are carried out jointly by JCNS/FZJ and the PGAA group of MLZ. The detector shielding will be modified supported by Monte Carlo simulations. The idea of a new collimator and filter arrangement will also be presented as well as the analytical method for large samples.
The aim of the FaNGaS project is to develop a nondestructive method for chemical analysis of large samples. The method is based on the analysis of prompt gamma radiation induced by fission neutrons. The main reaction for these fast neutrons is the inelastic neutron scattering or (n,n´γ) reaction. To perform chemical analysis of large samples with fission neutrons a comprehensive library on (n,n´γ) reaction needs to be improved. We are currently working on an update of the existing atlas. The outcome of the modifications and the characterization together with the first experimental results will be shown.

Speaker: Zeljko ILIC

104 Temperature and Strain induced Transformation in Austempered Ductile Iron (ADI)

Austempered ductile iron (ADI) has undergone a special heat treatment to enhance mechanical properties. This heat treatment process consists of austenitization, quenching to a temperature between 250°C and 450°C and isothermal austempering [1, 2], after which the microstructure consists of acicular ferrite and high carbon enriched retained austenite.

The high carbon enriched retained austenite can transform to martensite during plastic deformation. The treatment parameters (austenitization temperature, austempering temperature, austempering time and alloying composition) can influence the retained austenite fraction, grain size and its stabilization [2], which in turn will influence the following martensitic transformation.

The influence of different treatment and composition parameters on the martensitic transformation and texture formation during plastic deformation has been investigated using neutron diffraction. The combination of texture analysis and in-situ deformation tests allowed quantitative phase analysis and extraction of martensite phase fractions as a function of strain level.

In this presentation, we will give an overview of the current status of these experiments together with new results from recent atom probe tomography measurements.

References
[1] L. Meier, M. Hofmann, P. Saal, W. Volk, H. Hoffmann, Mater. Char. 85 (2013) 124-133
[2] P. Saal, L. Meier, X.J. Li, M. Hofmann, M. Hölzel, J. N. Wagner, W. Volk, Met. Mat. Trans. A47 (2016) 661-671
[3] Srinivasmurthy Daber et al, J.Mater.Sci 43 (2008) 4929-4937

Speaker: Michael Hofmann

Science group meetings 2: Neutron Method

105 High-resolution neutron depolarization microscopy of the ferromagnetic transitions in Ni3Al and HgCr2Se4 by using Wolter mirrors

Imaging with polarized neutrons has in recent years increasingly gathered interest due to its ability to visualize bulk magnetic properties and magnetic fields in 2D and 3D. Currently the spatial resolution of typical setups is limited to ~500µm by the space consumed by the polarization analyzer which needs to be placed between sample and detector. This increases the minimum sample to detector distance which is achievable and results in such mediocre spatial resolution.
To obtain higher spatial resolution, we employed a novel neutron microscope equipped with Wolter mirrors as a neutron image-forming lens and a focusing neutron guide as a neutron condenser lens at the instrument ANTARES at FRM II. The Wolter optic creates a magnified image of the sample at the detector position while at the same time removing the general requirement in neutron imaging to place the sample as close as possible to the detector. With the current prototype Wolter mirrors we could achieve a magnification factor of four and a spatial resolution of ~100µm was reached. The spatial resolution was in our case mainly limited by the surface quality of the employed neutron optical mirrors in the prototype optic and we see potential for the improvement by another order magnitude.
To demonstrate the potential of the technique we performed spatially resolved bulk imaging of ferromagnetic transitions in Ni$_3$Al and HgCr$_2$Se$_4$ crystals. These neutron depolarization measurements discovered magnetic inhomogeneities in the ferromagnetic transition temperature with spatial resolution of about 100 μm.
The images of Ni$_3$Al show that the sample does not homogeneously go through the ferromagnetic transition. The improved resolution allowed us to identify a distribution of small grains with slightly off-stoichiometric composition. Additionally, neutron depolarization imaging experiments on the chrome spinel, HgCr$_2$Se$_4$, under high pressures up to 15 kbar highlight the advantages of the new technique especially for small samples or sample environments with restricted sample space. The improved spatial resolution enables to observe domain formation in the sample while decreasing the acquisition time despite having a bulky pressure cell in the beam.

Speaker: Michael Schulz

106 Simultaneous determination of spin flip and non-spin flip neutrons using multi-analyzer setup at PUMA, FRM-II

The thermal triple-axis-spectrometer PUMA is one of the most robust and yet extremely flexible instruments worldwide of its kind. In addition to the 'normal triple axis' set up, PUMA delivers a good number of unique features to meet the ever growing demands of the scientific community worldwide. One of them is the multiplex system, which consists of eleven arbitrarily configurable analyzer-detector channels. This is particularly suited for single shot kinetic experiments since it allows the realization of an entire (Q,E)-scan within a time scale even less than a minute as a function of any external stimulant. Moreover, this set up can be used for polarization experiments very efficiently. By directing the spatially separated different spin-states of the scattered neutrons into the different analyzer channels, the spin flip (SF) and the non-spin flip (NSF) components can be determined simultaneously and to best of our knowledge none of the conventional existing neutron instruments collects both spin-states at the same time. Especially, in case of kinetic time-resolved experiments, where both spin states need to be registered synchronously at the same state of the sample, this set up is of absolute necessity. To allow an easy and efficient operation of this sophisticated polarization set up and provide support for subsequent data analysis, we have developed GUI based MAX-PA software. In this talk, I will report on the details of the current polarization analysis setup at PUMA and show few results from the pilot experiments.

References:
[1] S. Schwesig et al., Nuclear Instruments and Methods in Physics Research A 877 (2018) 124–130.
[2] O. Sobolev et al., Nuclear Instruments and Methods in Physics Research A 772 (2015) 63–71.
[3] G. Eckold et al., Nuclear Instruments and Methods in Physics Research A 752 (2014) 54–64.

Speaker: Dr Avishek Maity (Institute of physical chemistry, University of Goettingen)

107 The upgraded neutron grating interferometer at ANTARES – Design, Performance and Applications –

Neutron grating interferometry (nGI) is a relatively new neutron imaging technique which is the adaption of a Talbot-Lau Interferometer for neutrons [1]. It simultaneously delivers information about the transmission (TI), phase shift (DPC) and the scattering (DFI) inside a sample [1].
In particular the DFI has generated high interest, due to its ultra-small-angle neutron scattering (USANS) contrast mechanism, allowing to indirectly resolve structures which cannot be directly resolved by an imaging instrument [2],[3].
For instance, nGI is sensitive to magnetic domain walls and consequently allows to measure the effect of induced stress in a sample onto the mobility of its magnetic domains [4]. Moreover, the distribution of flux domains within type-I and type-II superconductors has recently been visualized [5],[6]. Also there have been strong efforts to use nGI and particularly the DFI as tools for quantitative measurements of microstructures in materials. A theory has been proposed, which directly links the DFI contrast within the material to a Fourier back transform of its scattering function evaluated at a correlation length ξGI~λ [7].
A prerequisite for such quantitative measurements is a high signal-to-noise-ratio (SNR). For DFI measurements it has been shown that the main reasons for statistical uncertainties are (i) low DFI signal and (ii) low visibility [8]. Here, the visibility is the quotient between the amplitude and the mean value of the oscillation during an nGI scan and is an indicator for the performance of an nGI setup.
While the DFI signal is, as mentioned above, connected to the correlation length which can be tuned during the experiment, the visibility is strongly dependent on the quality of the gratings. Especially the quality (absorptivity) of the analyzer grating (G2) is a great concern here, as it is generally the grating with the smallest period (several µm). Current fabrication techniques cause the grating to strongly deviate from an ideal binary absorption profile. As has been shown in [9] this strongly degenerates the visibility. Furthermore, tuning the correlation length either lowers the achievable real space resolution or results in a change in neutron wavelength which also causes a decrease in visibility.
Hence a high visibility is an essential basis for quantitative measurements. In our contribution we will present the upgraded nGI setup at the ANTARES beamline at FRM II. This nGI setup has been heavily redesigned, compared to its precursor [10]. The redesign allowed to optimize the distances between the gratings, as well as the grating periods. In particular, the source and analyzer gratings, which are both absorption gratings, have been improved towards binary absorption profiles. With these changes in the improved ANTARES nGI we have achieved a visibility of 75% over the whole detector area (76mm x 76mm) at the design wavelength of 4 Å. It is worth noting that this visibility is very close to the theoretical limit imposed by the spatial coherence generated by the used G0 grating.

[1] C. Grünzweig, PhD thesis (2009)
[2] C. Grünzweig et al., PRL 101, 025504 (2008)
[3] M. Strobl et al., 101, 123902 (2008)
[4] H. Weiss et al., pending (2018)
[5] T. Reimann et al., accepted at JLTP
[6] T. Reimann et al., Nat. Commun. 6:8813 (2015)
[7] M. Strobl, Sci. Rep. 4, 7243 (2014)
[8] R. Harti et al., Review of Scientific Instruments 88, 103704 (2017)
[9] R. Harti et al., Opt. Express 25, 1019-1029 (2017)
[10] T. Reimann et al., J. Appl. Cryst. 49, 1488-1500 (2016)

Speaker: Tobias Neuwirth

108 Instrument Development on HEiDi for Hot Topics and Extreme Conditions

Single crystal diffraction is one of the most versatile tools for detailed structure analysis. Due to their specific pecularities neutrons are a very useful probe for structural studies on various hot topics related to physics, chemistry and mineralogy. The single crystal diffractometer HEiDi uses the hot source of FRM II to offer high flux, high resolution and large Q range, low absorption and high sensitivity for light elements.
In order to adapt this instrument to the most recent scientific topics its hardware, sample environment and data collection software are continously extended and improved. For instance, temperature dependent multidimensional Q mapping at low temperatures down to 2.5 K in the multiferroic DyMnO3 reveals accurately the evolution and interplay between the incommensurate magnetic sublattice of Mn and the commensurate magnetic sublattice of Dy.
At very high temperatures studies on Nd2NiO4+δ and Pr2NiO4+δ brownmillerites concerning their oxygen diffusion pathways reveal anharmonic diplacements of the apical oxygens pointing towards the interstitial vacancy sites which create a quasicontinuous shallow energy diffusion pathway between apical and interstitial oxygen sites [1]. Recent studies use a special mirror furnace developped at MLZ which allows not only temperatures > 1300 K but also atmospheres with various oxygen content and pressure around the sample to study their influence to the evolution of the occupation of the interstitial sites.
Last but not least recently a BMBF funded project was launched in 2016 in order to develop new pressure cells for HEiDi which can be combined with its existing low temperature equipment in order to study structural properties down to temperatures below 10 K, e.g. on MgFe4Si3 compounds and their magnetic features [2]. For this reason new high pressure cells have been developed and different components of the neutron optics of HEiDi have been optimized.

[1] M. Ceretti et al.; Low temperature oxygen diffusion mechanisms in Nd2NiO4+δ and Pr2NiO4+δ via large anharmonic displacements, explored by single crystal neutron diffraction; J. Mater. Chem. A 3, 21140-21148 (2015).
[2] A. Grzechnik et al.; Single-Crystal Neutron Diffraction in Diamond Anvil Cells with Hot Neutrons; J. Appl. Cryst. 51, 351-356 (2018).

Speaker: Martin Meven

Science group meetings 2: Quantum Phenomena

109 Single crystal growth and neutron diffraction study of non-collinear antiferromagnets Mn3Sn

Following the recent observations of large anomalous Hall effect (AHE) and the possible realisation of magnetic Weyl fermions in the intermetallic non-collinear antiferromagnet (AFM) Mn3Sn, this compound has rapidly emerged as a promising quantum material that may find huge potentials for future information and quantum technologies [1-3]. Geometric frustration in the Kagome lattice of Mn atoms within the ab-plane leads to a non-collinear AFM order with an inverse triangular spin configuration below TN=420 K. However, it has been controversial concerning the low-temperature phase transition to a modulated triangular AFM i.e. a spiral magnetic order[4]. For instance, the transition at T1 is clearly shown in a flux method grown crystal, it has not been observed in any Czochralski method grown crystals. This strong sample dependence is largely due to small variations of the Mn content in various samples. We have grown Mn3Sn single crystals via flux method successfully. Magnetometry measurement showed an obvious transition at T1=275K, and it was also verified by neutron diffraction measurement at DNS. When temperature decreases below 275K, two spiral phases were observed as indicated by the satellite peaks around (-100) peak in neutron spin flip measurement at DNS. Besides, temperature dependence of the spiral phases was also disscussed.

[1] S. Nakatsuji, et al., Nature 527, 212 (2015).
[2] K. Kuroda, et al., Nat. Mat. 16, 1090 (2017).
[3] A.K. Nayak, et al., Sc. Adv. 2, e1501870 (2016).
[4] N.H. Sung, et al., Appl. Phys. Lett. 112, 132406 (2018).

Speaker: Mr Xiao Wang (1 Jülich Center for Neutron Science JCNS at Heinz Maier-Leibnitz Zentrum (MLZ))

110 Strain and electric-field control of magnetism in iron oxide nanoparticle - BaTiO3 composites

Ferrimagnetic iron oxide nanoparticle monolayers on top of ferroelectric BaTiO3 (BTO) substrates were prepared and a magnetoelectric coupling effect was observed. Grazing incidence small angle X-ray scattering and scanning electron microscopy confirm a hexagonal close-packed supercrystalline order of the nanoparticle monolayers. We employed a magnetoelectric AC susceptibility setup as modification of a commercial superconducting quantum interference device magnetometer. The magnetoelectric coefficient shows two jumps at the BTO phase transition temperatures. Moreover, the magnetic depth profile of the nanoparticle monolayer was probed by polarized neutron reflectivity. The data recorded at various electric field values show that the electric field is able to alter the magnetism of the nanoparticle monolayer by a strain mediated magnetoelectric coupling effect. Moreover, we prepared BTO films by pulsed laser deposition (PLD) where iron oxide nanoparticles were embedded in the BTO films. We observe also for this system a magnetoelectric coupling between the BTO film and the NPs via strain and interface charge co-mediation. This is demonstrated by measurements of the magnetization as function of DC and AC electric fields.

1. L.-M. Wang, O. Petracic, E. Kentzinger, U. Rücker, M. Schmitz, X.-K. Wei, M. Heggen, Th. Brückel, Strain and electric-field control of magnetism in supercrystalline iron oxide nanoparticle - BaTiO3 composites, Nanoscale 9, 12957 (2017)

2. L.-M. Wang, O. Petracic, S. Mattauch, A. Koutsioumbas, X.-K. Wei, M. Heggen, V.Leffler, S. Ehlert, and Th. Brückel, Magnetoelectric coupling in iron oxide nanoparticle - barium titanate composites, J. Phys. D: Appl. Phys. 52, 065301 (2019)

Speaker: Oleg Petracic (Jülich Centre for Neutron Science JCNS and Peter Grünberg Institut PGI, JARA-FIT, Forschungszentrum Jülich GmbH)

111 The spin structure of highly ordered arrangements of magnetic nanoparticles

Asmaa Qdemat1, Emmanuel Kentzinger1, Giuseppe Portale2, Marina Ganeva3, Stefan Mattauch3, Oleg Petracic1, Ulrich Rücker1, Thomas Brückel1

1Jülich Centre for Neutron Science (JCNS) and Peter Grünberg Institute (PGI), JARA-FIT, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
2 Zernike Institute for Advanced Materials, Nijenborgh 4, 9747 AG Groningen,
The Netherlands
3 Jülich Centre for Neutron Science, Forschungszentrum Jülich, at Heinz Maier Leibnitz Zentrum MLZ, 85748 Garching, Germany

Magnetic nanoparticles and their assembly in highly ordered structures are fundamentally interesting regarding the understanding of magnetic interactions and for a rational design towards potential applications in information technology as e.g. magnetic data storage media or as material for spintronics. With regard to these applications, the main aspects of fundamental interest include magnetic anisotropy, Van-der-Waals forces and interparticle interactions leading to aggregation or even ordered assemblies of nanoparticles.
This work focuses on the chemical and magnetic characterization of monolayers of CoFe2O4 nanoparticles on silicon substrates. The system was characterized laterally by Scanning Electron Microscopy (SEM) and Grazing Incidence Small Angle X-ray Scattering (GISAXS) at the laboratory high brilliance GALAXI instrument [1] with simulation using the BornAgain software [2]. We deduce both the height profile of the individual nanoparticles, and a hexagonal ordering between the nanoparticles. Macroscopic magnetization measurements and polarized neutron reflectometry on a MARIA reflectometer [3] were used to find that the nanoparticles are weakly magnetized with respect to bulk CoFe2O4 and that a random in plane relative orientation of the nanoparticle magnetizations is obtained at zero applied fields.
References
[1] Jülich Centre for Neutron Science. (2016). GALAXI: Gallium anode low-angle x-ray instrument. Journal of large-scale research facilities, 2, A61. http://dx.doi.org/10.17815/jlsrf-2-109

[2] J. Burle, C. Durniak, J. M. Fisher, M. Ganeva, G. Pospelov, W. Van Herck and J. Wuttke, BornAgain – Software for simulating and fitting X-ray and neutron small-angle scattering at grazing incidence, Version 1.11.0 (2013-2018), http://www.bornagainproject.org (2018)

[3] Jülich Centre for Neutron Science. (2015). MARIA: Magnetic reflectometer with high incident angle. Journal of large-scale research facilities, 1, A8. http://dx.doi.org/10.17815/jlsrf-1-29

Speaker: Mrs Asmaa Qdemat (1Jülich Centre for Neutron Science (JCNS) and Peter Grünberg Institute (PGI), JARA-FIT, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany)

112 The magnetic moment of polycrystalline and epitaxial Co thin films

The variation of the magnetic moment with dimensionality of magnetic materials, i. e. from atoms to bulk, is a longtime studied issue. For thin films, a constant magnetic moment is often assumed in modelling, however, intermixing and surface roughness may also have an impact.
With the help of polarised neutron reflectometry (PNR) we study the magnetic moment of polycrystalline Co/20 nm Pt/MgO(001) and epitaxial Co/W(110). The samples were grown by molecular beam epitaxy and subsequently measured with PNR at room temperature and in saturation in UHV.
Our results reveal the vertical depth profile of the magnetic moment of the Co films. In fact, the magnetisation is not constant but smeared out at the edges, due to roughness. Measurements at different film thicknesses reveal the evolution of the magnetic moment which may be separated in a bulk and a surface contribution and discussed with respect to published results.
This project has received funding from the EU’s H2020 research and innovation programme under grant agreement n. 654360.

Speaker: Sabine Pütter (Jülich Centre for Neutron Science JCNS, Outstation at MLZ, Forschungszentrum Jülich GmbH)

Science group meetings 2: Softmatter

113 Contacting functional polymer thin films for lithium-ion batteries via sputter deposited metal nanolayers revealing their growth with in-situ GISAXS

Understanding the interface between metals, commonly used as current collectors, and ion-conducting polymers used in polymer lithium-ion batteries (LIBs) is crucial to develop highly reproducible, low-cost and reliable devices. To address these issues, sputter deposition is the technique of choice to fabricate scalable, reproducible and controllable nanometer and sub-nanometer metal layers on polymer thin films. The sputter deposition process, being well understood and controlled, offers advantages over chemical methods to tailor metal thin-flim morphologies on the nanoscale and offers a superior adhesion of the deposited material. We use in-situ grazing incidence small angle X-ray scattering (GISAXS) to investigate the formation, growth and, self-assembled structuring on polymer thin films and composites used in LIBs. Different polymer films are compared with respect to the metal layer growth.

Speaker: Simon Schaper (TU München, Physik-Department, Lehrstruhl für Funktionelle Materialien)

114 Phase transition kinetics in a doubly thermo-responsive block copolymer thin film followed with in-situ neutron reflectometry

Thermo-responsive polymers can show a strong change in volume towards even slight changes of their surrounding temperature. This behavior makes them promising candidates for the implementation in a manifold application fields such as nano-sensors, artificial pumps and muscles, or optical switches. While the underlying mechanisms of such polymers in solution are well understood, less is known about thermo-responsive polymers in thin film morphology. In our recent work, we follow the phase transition kinetics upon increasing temperature in a doubly thermo-responsive block copolymer thin film via in-situ time of flight neutron reflectometry (TOF-NR). The block copolymer consists of a poly(N-isopropylmethacrylamide) (PNIPAM) block, which shows a lower critical solution temperature (LCST) and a zwitterionic poly(sulfobetaine) (PSB) block, which exhibits an upper critical solution temperature (UCST) that is lower than the corresponding LCST of the PNIPMAM block. A combination of spin-coating and solvent vapor annealing is used to prepare polymer thin films in the range of 30 nm to 150 nm with high homogeneity. At a temperature below the UCST, the polymer film is swollen in D2O atmosphere in order to increase the mobility of the polymer chains. Subsequent, temperature is increased to an intermediate regime (between UCST and LCST) and high regime (above LCST). The kinetic processes (swelling and temperature steps) are followed with high time resolution via TOF-NR. Static measurements and TOF grazing incidence small angle neutron scattering (GISANS) measurements are performed at the beginning and in between the kinetic dynamics in order to gain a complete picture of the swelling and temperature-dependent behavior of the polymer thin film.

Speaker: Lucas Kreuzer (TU München, Physik Department, E13)

115 In situ GISAXS Investigations of Multi-responsive Block Copolymer Thin Films during Solvent Vapor Annealing

Responsive block copolymer thin films are of interest for many applications, e.g. as fast sensors or switchable membranes. They may be based on physical hydrogels formed by telechelic copolymers featuring a stimuli-responsive midblock and hydrophobic end blocks. For temperature-responsive end blocks, a weak gel is formed below their collapse temperature, while a frozen network is formed above [1]. In thin films, a pH-responsive midblock, e.g. a weak polyelectrolyte, may be used to tune the self-assembly process, while a temperature change may be used to immobilize the end blocks and to freeze the so created nanostructure. The latter feature is especially interesting for solvent vapor annealing (SVA), which is a versatile technique to improve long-range order in polymer thin films and alter its morphology, but with the drawback that non-equilibrium morphologies are often difficult to preserve during solvent removal [2,3].
In the present work, thin films from the telechelic pentablock terpolymer P(n-BuMA8-co-TEGMA8)-b-PDMAEMA50-b-PEG46-b-PDMAEMA50-b-P(n-BuMA8-co-TEGMA8) were investigated in-situ during SVA with water using grazing-incidence small-angle X-ray scattering (GISAXS). The endblocks are statistical copolymers of the thermoresponsive TEGMA (triethylene glycol methyl ether methacrylate) and the hydrophobic n-BuMA (n-butyl methacrylate). Increasing the temperature increases its hydrophobicity and thus leads to a reduced mobility. The intermediate DMAEMA (2-(dimethylamino)ethyl methacrylate) block is a weak cationic polyelectrolyte, which becomes ionized at low pH values and assumes a stretched conformation. The permanently hydrophilic poly(ethylene glycol) (PEG) block enhances water solubility. The role of the solvents used for film preparation and for SVA on the structural evolution will be presented.

References

[1] C. Tsitsilianis, F. Jung, C. M. Papadakis, C. S. Patrickios et al., Macromolecules 51, 2169–2179 (2018).
[2] D. Posselt, J. Zhang, D.-M. Smilgies, A. V. Berezkin, I. I. Potemkin, C.M. Papadakis, Progr. Polym. Sci. 66, 80-115 (2017).
[3] A. V. Berezkin, F. Jung, D. Posselt, D.-M. Smilgies, C. M. Papadakis, Adv. Funct. Mater. 28, 17606226 (2018).

Speaker: Florian Jung (Technische Universität München)

Science group meetings 2: Structure

116 Role of interstitials oxygen ordering on the electronic correlation in hole-doped Pr2-xSrxNiO4+𝛿

Stripe ordered La2-xSrxM(M=Cu,Co,Ni)O4+𝛿 oxides have been investigated intensively, as one of its family member La2CuO4+𝛿, showing the similar electronic ordering, gets superconducting at low temperature. A very special excitation of the ordered/disordered spin-stripes, shaped like an ‘hour-glass’, is discussed to be an important signature for the appearance of superconductivity. So far to best of our knowledge, the modulation of the stripe order has been considered solely to be modified by the Sr-doping. Not much attention has been put towards the inevitable presence of excess interstitial oxygen in these as-grown compounds at the low doping level of Sr. These interstitial oxygen are not only changing the hole concentration (hence stripe modulation of charge and spin) of these compounds, which leads to electronic phase segregation at low temperature, but also the interstitial oxygen itself gets ordered in long-range in the parent lattice. We have chosen Pr2-xSrxNiO4+𝛿 as a model system as it holds a wide range of interstitial oxygen inside the lattice. From several synchrotron and neutron diffraction measurements on different compositions of Pr2-xSrxNiO4+𝛿, we have derived models for charge dis-commensuration, to determine the possible ordering of spin stripes which could give very important information on spin microstructure for spin-wave calculation. Most importantly, in the presence of interstitial oxygen, we have evidenced that the stripe modulation is always scaled with the interstitial oxygen ordering.

Speaker: Dr Rajesh Dutta (2nd Instrument Scientist at Heidi, FRM-II, IFK, RWTH University)

117 High Pressure Diffraction Experiments on Single Crystals with Hot Neutrons on HEiDi

The single crystaldiffractometer HEiDi at the research neutron source at the Heinz Maier-Leibnitz Zentrum (MLZ) offers high flux, high resolution and large q range, low absorption and high sensitivity for light elements.
In 2016 a BMBF funded project (05K16PA3) was launched in order to allow studys on tiny samples < 1 mm³ and with high pressure cells for isotropic pressure on single crystals, for instance in order to study structural properties down to low temperatures on MgFe4Si3 compounds and their magnetic features [A. Grzechnik et al.; J. Appl. Cryst. 51 (2018)].
Within this project the optimizations on the instrument focus on optimized optical components (new Cu220 monochromator, soller collimators and guides) as well as in the development of various high-pres¬sure diamond anvil cells (DAC) (panoramic and transmis-sion cells) for which first data collections could be performed. The panoramic DAC offer a large opening angle and can be placed in the modified cryostat with an optical window. Pressure changes with temperature are fol¬lowed with ruby luminescence. The new low-tempera¬ture set up allows temperatures down to 3 K. Transmission DAC are suitable for both neutron and X-ray diffraction. The membrane version can be operated remotely changing its pressure via a He gas filled membrane.

Speaker: Martin Meven

118 Temperature dependence of the crystal structure and magnetic properties of MnFe$_4$Si$_3$ at high pressures

Refrigeration based on the magnetocaloric effect is a potential alternative to conventional vapor compression refrigeration. One system of particular interest with regard to application is Mn$_{5-\textit{x}}$Fe$_\textit{x}$Si$_3$ [1-3]. Pressure affects the interatomic distances in the crystal structure and thus has an influence on the magnetic properties.

The aim of this work is to establish the influence of hydrostatic pressure on the crystal structure of MnFe$_4$Si$_3$ as well as the pressure dependence of the magnetic transition of MnFe$_4$Si$_3$, which at ambient pressure orders ferromagnetically at $\textit{T}_C$ ≈ 300 K. Synchrotron X-ray powder diffraction measurements were carried out up to 12.5 GPa between 100 K and 373 K. Isofield magnetization measurements and neutron single-crystal diffraction were used to determine the magnetic transition temperature up to pressures of 1 GPa.

MnFe$_4$Si$_3$ shows no clear indication of phase transitions at high temperatures (296 K–373 K) and high pressures. At low temperatures (200 K, 250 K), anomalies in the lattice parameters occur as a function of pressure. They might be related to a transition into a magnetically ordered phase. The trend of decreasing magnetic transition temperature with increasing pressure is also observed in magnetization data and in the intensities of selected magnetic reflections from neutron diffraction experiments at 1 GPa. The pressure-dependent unit cell volume data at 100 K and 150 K exhibit anomalies as two equations of state are necessary to fit each of the data sets, respectively.

[1] Bińczycka et al. Phys. Stat. Sol. 1973 19, K13-K17
[2] Hering et al. Chem. Mater. 2015 27, 7218-7136
[3] Song et al. J. Alloys Compd. 2002 334, 249-252

Speaker: Mr Andreas Eich ((1) Institute of Crystallography, RWTH Aachen University; (2) Jülich Centre for Neutron Science-2/Peter Grünberg Insitute-4, Forschungszentrum Jülich GmbH)

119 Reconstruction of Magentization Density Distributions in Antiferromagnets with the new Polarized Neutron Diffraction Setup on POLI

A dedicated polarized neutron diffraction (PND) setup, using a symmetric-field high Tc superconducting magnet with a maximal field of 2.2 T in combination with a ³He polarizer and Mezei-type flipper, has been developed at the instrument POLI. Each component is optimized by numerical simulations and the complete setup is successfully tested and calibrated.

This new PND setup was used to collected flipping-ratio (FR) data as function of the applied magnetic field and temperature for different antiferromagnetic compounds. A new advanced approach for the reconstruction of maximum entropy spin density maps from FR measurements is presented. Using this approach, 3D spin density maps can be built for the first time not only for the paramagnetic, but also for the antiferromagnetic phase. These 3D maps reveal new features compared to the results from conventional maximum entropy software and might be used to directly visualize magnetic multipoles.

Speaker: Mr Henrik Thoma (Jülich Centre for Neutron Science JCNS at MLZ, Lichtenbergstr. 1, 85748 Garching, Germany)

10:30 Coffee

Plenary Session 5

Convener: Dr Robert Georgii (FRM II)

120 Conversion strategy for the FRM II compact core

To support the global nonproliferation efforts, FRM II is actively working towards the conversion of its compact fuel element to a uranium enrichment, which is significantly lower than its current enrichment of 93%. Thereby, it is of utmost importance that the scientific performance does not suffer and that such new fuel element fits in the current core geometry to provide a continuous operation. This cannot be achieved with the currently available fuel systems, which therefore, requires a new high-density fuel to be developed and qualified to be used in high performance research reactors. Based on a preliminary parameter study, two promising core designs are presented: One using dispersed, high-density U3Si2 and a more promising one using a monolithic uranium-molybdenum alloy. Not only new fuel fabrications methods have to be developed, also, the changed material properties like thermal conductivity have to be measured.

Speaker: Dr Christian Reiter (FRM II)

121 Effect of nanoscopic confinement on the dynamics of ionic liquids

Ionic liquids (ILs) are molten salts without additional solvent composed by organic cations and organic or inorganic anions. ILs show very interesting physical-chemical properties, such as high thermal and chemical stability, negligible vapour pressure, low flammability, high ionic conductivity, remarkable solvation capability towards a large variety of compounds, and in some cases even biocompatibility. These peculiarities make ILs as very attractive for a broad and diverse range of applications, from energy conversion to extraction and separation, pharmaceutics, biocatalysis, biomass treatment etc. Structure and ionic transport processes are extremely important for several of such applications in modern industry.

We have investigated the influence of nanoscopic confinement on the structure and diffusion properties of the IL EmimAc (1-Ethyl-3-methylimidazolium acetate). Structural modifications induced by the confinement were observed by means of xray diffraction. Neutron backscattering measurements at SPHERES@MLZ were used to investigate the dynamics in the ps/ns range. We observed thermal activated diffusion dynamics, well described by a jump diffusion model, with diffusion coefficients of the order of 6-9 10-7 cm2/s at 80 C. The effect of confinement is here evidenced by different dynamic behaviour as a function of the temperature.

Speaker: Daria Noferini (Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz-Zentrum (MLZ), Forschungszentrum Jülich GmbH)

122 Wrap up & Road Map

Wrap up & Road Map

Speakers: Peter Müller-Buschbaum (TU München, Physik-Department, LS Funktionelle Materialien), Stephan Förster (Forschungszentrum Jülich)

13:00 Lunch