arXiv subjects

Tobias Unruh

Publications and source records attributed to Tobias Unruh.

8 recordsLinked to original sources

arXiv2026

3D Electron Diffraction -- The Missing Slice for a Complete Nanoscale Analysis of Organic Solar Cells in TEM

Optimizing the performance of organic solar cells (OSCs) hinges on a comprehensive understanding of their nanostructures, yet traditional characterization methods often fall short, delivering incomplete structural snapshots. We introduce elastically filtered 3D Electron Diffraction (3D ED) as a ground-breaking technique bridging full reciprocal- and real-space structural analysis within a single transmission electron microscope (TEM). Using solvent-vapor annealed DRCN5T:PC71BM, 3D ED reproduces key structural parameters from GIWAXS including lattice spacings, coherence lengths, and mosaicity, while uniquely delivering true in-plane access and direct registration with high-resolution imaging, diffraction imaging and nano-spectroscopy on the same sample. A low-dose, distributed tilt strategy plus energy filtering yields high signal-to-background below damage thresholds. Extension to a second archetypal blend (P3HT:PC71BM; annealing evolution) demonstrates generality. Our findings underscore the transformative potential of 3D ED, particularly in analysing beam-sensitive organic thin films. This paves the way for new avenues in advanced correlative structural characterization of OSCs and holds potential for application to a multitude of other nanostructured materials.

cond-mat.mtrl-sci↗

arXiv2025

Understanding the effect of drying time in process-structure-performance relationships for PM6-Y6 organic solar cells

Making solution-cast organic solar cells industrially available generally comes at the cost of significant performance losses compared to device prototypes manufactured under laboratory conditions. Adjusting solvent evaporation kinetics is postulated to recover efficiency. Yet, a comprehensive characterization of their effect, independently of other property-defining parameters, is lacking. Thus, the present objective is to isolate the influence of the solvent drying rate on solution-deposited organic active layer nanomorphologies and performances. To this end, a specially designed gas quenching technique is employed to fabricate PM6:Y6 donor-acceptor films under systematic variations of evaporation conditions. Using an extensive investigation protocol that combines insights from numerical simulations and experimental measurements, process-structure-performance relationships are unraveled. It is found that higher drying rates imply finer and more dispersed nanomorphologies with increased fractions of amorphous material. This enhances electric charge generation, thereby improving short-circuit current density and overall cell performance. The open-circuit voltage is also boosted under accelerated evaporation due to changes in the aggregation mode of the Y6 small molecule that induce higher effective bandgaps. The results demonstrate that the developed gas-quenching technique is a valuable tool for optimizing the performance of upscaled organic photovoltaics, as it is readily compatible with high-throughput equipment, such as roll-to-roll coating machines.

cond-mat.mtrl-sci↗

arXiv2025

Identification of Polytypism and Their Dislocations in Bilayer MoS2 Using Correlative Transmission Electron Microscopy and Raman Spectroscopy

Stacking orders and topological defects substantially influence the physical properties of 2D van der Waals (vdW) materials. However, the inherent features of 2D materials challenge the effectiveness of single characterization techniques in identifying stacking sequences, necessitating correlative approaches. Using bilayer MoS2 as a benchmark, we differentiate its polytypism and specific dislocations through transmission electron microscopy (TEM) and Raman spectroscopy. Perfect and partial dislocations were revealed in TEM, which are closely linked to the stacking sequences, thus indirectly indicating the 2H and 3R polytypes. 3D electron diffraction reconstruction on relrods and low-frequency Raman spectroscopy further validated these polytypes owing to their reliance on crystal symmetry. Surprisingly, we unexpectedly resolved both polytypes despite starting with 2H bulk crystal, pointing to a possible phase transition during mechanical exfoliation. The correlative TEM-Raman approach can be extended to other 2D materials, paving the way for property alteration via stacking and defect engineering.

cond-mat.mtrl-sci↗

arXiv2020

A Novel Experimental Approach for Nanostructure Analysis: Simultaneous Small Angle X-ray and Neutron Scattering (SAXS/SANS)

Exploiting small angle X-ray and neutron scattering (SAXS/SANS) on the same sample volume at the same time provides complementary nanoscale structural information at two different contrast situations. Compared with an independent experimental approach, the truly combined SAXS/SANS experimental approach ensures the exactness of the probed samples particularly for in-situ studies. Here, we introduce an advanced portable SAXS system that is dimensionally suitable for installation at D22 zone of ILL. The SAXS apparatus is based on a RIGAKU copper/molybdenum switchable microfocus rotating anode X-ray generator and a DECTRIS detector with a changeable sample-to-detector distance of up to 1.6 m in a vacuum chamber. A science case has been presented to demonstrate the uniqueness of the newly established method at ILL. Temporal structural rearrangements of both, organic stabilizing agents and organically capped gold colloidal particles during gold nanoparticle growth are simultaneously probed, enabling immediate correlated structural information. The newly established nano-analytical method at ILL will open the way for real time investigations of a wide range of innovative nanomaterials and will enable comprehensive in-situ studies on biological systems. A potential development of a fully-automated SAXS/SANS system with a common control environment and additional sample environments, permitting a continual and efficient operation of the system at the hands of ILL users, has also been introduced.

physics.ins-det↗

arXiv2018

Kinky DNA in solution: Small angle scattering study of a nucleosome positioning sequence

DNA is a flexible molecule, but the degree of its flexibility is subject to debate. The commonly-accepted persistence length of $l_p \approx 500\,$Å is inconsistent with recent studies on short-chain DNA that show much greater flexibility but do not probe its origin. We have performed X-ray and neutron small-angle scattering on a short DNA sequence containing a strong nucleosome positioning element, and analyzed the results using a modified Kratky-Porod model to determine possible conformations. Our results support a hypothesis from Crick and Klug in 1975 that some DNA sequences in solution can have sharp kinks, potentially resolving the discrepancy. Our conclusions are supported by measurements on a radiation-damaged sample, where single-strand breaks lead to increased flexibility and by an analysis of data from another sequence, which does not have kinks, but where our method can detect a locally enhanced flexibility due to an $AT$-domain.

physics.bio-ph↗

arXiv2011

The slow short-time motions of phospholipid molecules with a focus on the influence of multiple scattering and fitting artifacts

Quasielastic neutron scattering is a powerful tool for the study of non-periodic motions in condensed matter as a detailed line shape analysis can give information about the geometry and rate of the scatterers' displacements. Unfortunately, there are also a number of artifacts which can masquerade as signatures of motions and can therefore lead to erroneous results. Their influence on the evaluation of the motions of the phospholipid dimyristoylphosphatidylcholine (DMPC) is discussed. On a 60 ps time scale, the long-range motion of the molecules has a flow-like character with similar velocities above and below the main phase transition. It is proposed that the concepts of dynamical heterogeneities and "floppy modes" developed in glass physics provide a framework to explain the observed behaviour.

cond-mat.soft↗

arXiv2002

Instrument Control at the FRM-II using TACO and NICOS

At the new neutron source FRM--II in Garching, Germany, the TACO control system, originally developed at the ESRF in Grenoble, France is used for instrument control purposes. TACO provides an object oriented, distributed control system including a clearly defined API. In order to equip TACO with a general user front end, a network based instrument control system named NICOS has been developed at the FRM-II. NICOS is divided into three parts: the NICOS Client, the NICOS Server and the NICOSMethods.

cond-mat↗

arXiv2002

Common data file definitions for neutron inelastic scattering instruments using NeXus

The NeXus format allows the storage of measured data next to a description of sample and instrument setup in a standardized manner. The NeXus standard itself gives only general rules how an instrument setup is described. A so called instrument definition contains a minimal set of information and the location of that information within a file. In this paper instrument definitions for neutron triple-axis and time-of-flight reactor machines are suggested. Furthermore a structure for the storage of instrument logbook information is presented.

cond-mat.mtrl-sci↗