Publications of

Rüdiger Berger

RID: A-5210-2009

Publications in 2021

Clathrate Adhesion Induced by Quasi-Liquid Layer,

Ngoc N. Nguyen, Rüdiger Berger, Michael Kappl, Hans-Jürgen Butt,
Journal of Physical Chemistry C (2021).

The adhesive force of clathrates to surfaces is a century-old problem of pipeline blockage for the energy industry. Here, we provide new physical insight into the origin of this force by accounting for the existence of a quasi-liquid layer (QLL) on clathrate surfaces. To gain this insight, we measure the adhesive force between a tetrahydrofuran clathrate and a solid sphere. We detect a strong adhesion, which originates from a capillary bridge that is formed from a nanometer-thick QLL on the clathrate surface. The curvature of this capillary bridge is nanoscaled, causes a large negative Laplace pressure, and leads to a strong capillary attraction.

"Liquid-like" Water in Clathrates Induced by Host-Guest Hydrogen,

Ngoc N. Nguyen, Rüdiger Berger, Manfred Wagner, Jürgen Thiel, Hans-Jürgen Butt, Rober Graf,
Journal of Physical Chemistry C 125, 15751-15757 (2021). https://DOI: 10.1021/acs.jpcc.1c05531

In this contribution we discuss the stability of clathrate structures. Clathrates are water molecules which form a host lattice structure and encapsulates guest molecules. Up to now, all water molecules in the host lattice are considered ice-like crystallized. Here, we discovered the occurrence of "liquid-like" water molecules and the resulting defects in (polar) tetrahydrofuran clathrates by liquid-state 1H-NMR experiments.

Revisiting Solvent Additives for the Fabrication of Polymer: Fullerene Solar Cells: Exploring a Series of Benzaldehydes,

C. Sprau, J. Kattenbusch, Y. Li, E. Müller, D. Gerthsen, R. Berger, J. J. Michels, A. Colsmann,
Solar Rapid Research Letters 5, 2100238 (2021).

The power conversion effciencies of organic solar cells delicately depend on the morphology of the light-harvesting bulk heterojunctions. Upon deposition from solution, the formation of tailored bicontinuous networks of polymers and fullerenes is often achieved using combinations of solvents and solvent additives. In order to differentiate material phases by molecular fingerprints, we used a novel combination of infrared (IR) absorption spectroscopy (nano-IR).

Adaptation of a styrene-acrylic acid copolymer surface to water,

Xiaomei Li, Simon Silge, Alexander Saal, Gunnar Kircher, Kaloian Koynov, Rüdiger Berger, Hans-Jürgen Butt,
Langmuir 37, 1571-1577 (2021).

Solid surfaces, in particular polymer surfaces, are able to adapt upon contact with a liquid. Adaptation results in an increase in contact angle hysteresis and influences the mobility of sliding drops on surfaces. To study adaptation and its kinetics, we investigated a random copolymer composed of styrene and acrylic acid (PS/PAA). By applying the latest adaptation theory (Butt et al. Langmuir 2018, 34, 11292), we estimated the time constant of this adaptation process to be significant smaller than 1 s.

Treffen sich drei Phasen...

Hans-Jürgen Butt und Rüdiger Berger,
Physik Journal 20 Nr. 4, 29-34 (2021). Physik Journal Ausgabe April 2021

In diesem Beitrag wenden wir uns an Physikinteressierte aus allen Bereichen der akademischen Forschung, Wirtschaft und Lehre. In den letzten 200 Jahren ist es gelungen, wesentliche Aspekte von Benetzungsphänomenen im Gleichgewicht zu verstehen und damit die Benetzung in vielen Fällen zu kontrollieren. Aber es liegt in weiter Ferne, dynamische Benetzung qualitativ zu verstehen oder sogar quantitativ vorherzusagen. Um beispielsweise die Bewegung eines Tropfens auf einer schiefen Ebene zu beschreiben, sind immer noch mehrere ad-hoc-Parameter notwendig. Es ist nicht geklärt, wie es zur Kontaktwinkelhysterese kommt und wie sich diese kontrollieren und vorhersagen lässt. Wir beschreiben den Stand der Forschung der dynamischen Benetzung. Um diese besser zu verstehen ist es notwendig, die Physik nahe der Kontaktlinie, an der Flüssigkeit, Festkörper und Gas aufeinandertreffen, zu betrachten.

Electrospun nanocomposite fibers from lignin and iron oxide as supercapacitor material,

Pichitchai Butnoi, Autchara Pangon, Rüdiger Berger, Hans-Jürgen Butt, Varol Intasanta,
Journal of Materials Research and Technology 12, 2153-2167 (2021).

Control of Electronic Properties of Functional Organic and Inorganic Materials Through Nano-Confinement,

Jongkuk Ko, Rüdiger Berger, Hyemin Lee, Hyunsik Yoon, Jinhan Cho, and Kookheon Char,
Chem. Soc. Review 50, 3585-3628 (2021).
--- manuscripts --- 😨 in preparation --- 🍀 submitted --- 👀 under review

How Tuning of Liquid Crystals Controls the Lateral Adhesion Force of Drop,

Chia-Ming Chang, Alexander Saal, Rüdiger Berger, Hans-Jürgen Butt, Yi Hsin Lin , 😨.

Publications in 2020

When and how self-cleaning of superhydrophobic surfaces works,

Florian Geyer, Maria D'Acunzi, Azadeh Sharifi, Alexander Saal, Nan Gao, Anke Kaltbeitzel, Tim-Frederik Sloot, Rüdiger Berger, Hans-Jürgen Butt, Doris Vollmer, Science Advances 6, eaaw9727 (2020). doi: 10.1126/sciadv.aaw9727

We clarify how contamintations are removed from surfaces by sliding drops. We monitored the removal of individual contaminant particles on the micron scale by confocal microscopy. We correlate this space- and time-resolved information with measurements of the lateral friction force of the sliding drop. Hydrophilic and hydrophobic particles hardly influence superhydrophobicity provided that the particle size exceeds the pore size, or the thickness of the contamination falls below the height of the protrusions. These detailed insights into self-cleaning allow the rational design of superhydrophobic surfaces that resist contamination as demonstrated by outdoor environmental and industrial standardized contamination experiments.
⬅ The movie shows a friction force measurement of a sliding drop over a contaminated surface.

Enhanced Vertical Charge Transport of Homo- and Blended Semiconducting Polymers by Nanoconfinement,

Jongkuk Ko, Youngkeol Kim, Jin Soo Kang, Rüdiger Berger, Hyunsik Yoon, and Kookheon Char, Advanced Materials 1908087 (2020). doi: 10.1002/adma.201908087

Here we employed the self-assembly of homo- and blended conjugated polymers in confined in nanostructures. The resulting structures lead to high charge mobility along vertical direction for both homo- and blended conjugated polymers. Both semicrystalline and amorphous polymers show highly increased population of face-on crystallite despite intrinsic crystallinity of polymers. They result in more than two orders of magnitude enhanced charge mobility along vertical direction revealed by nanoscale conductive scanning force microscopy and macroscale IV characteristic measurements.

Shuffling gait motion of an aerodynamically driven wall-bound drop,

Alexander Saal, Patrick M. Seiler, Daniel Rettenmaier, Michael Ade, Ilia V. Roisman, Rüdiger Berger, Hans-Jürgen Butt, and Cameron Tropea,
Phys. Rev. Fluids 5, 094006 (2021).

Hygroscopic Properties of NaCl Nanoparticles on the Surface: A Scanning Force Microscopy Study,

Xiaoxiang Wang, Haozhi Lei, Rüdiger Berger, Yi Zhang, Hang Su, Yafang Cheng, Phys. Chem. Chem. Phys., 22, 9967 - 9973 (2020). doi: 10.1039/D0CP00155D

Adaptive Wetting of Polydimethylsiloxane,

William S.Y. Wong, Lukas Hauer, Abhinav Naga, Anke Kaltbeitzel, Philipp Baumli, Rüdiger Berger, Maria D‘Acunzi, Doris Vollmer, and Hans-Jürgen Butt, Langmuir, 36, 7236 - 7245 (2020). doi: 10.1021/acs.langmuir.0c00538

Vitamin C loaded polyethylene - synthesis and properties of precise polyethylene with vitamin C defects via acyclic diene metathesis polycondensation,

Oksana Suraev, Carole Champanha, Frederik R. Wurm, Henning Weiss, Rüdiger Berger, Markus Mezger, Katharina Landfester, Ingo Lieberwirth, Macromolecules, 53, 2932 - 2941 (2020).

Entangled Azobenzene-Containing Polymers with Photoinduced Reversible Solid-to-Liquid Transitions for Healable and Reprocessable Photoactuators,

Mingsen Chen, Bingjian Yao, Michael Kappl, Senyang Liu, Jinying Yuan, Rüdiger Berger, Faai Zhang, Hans-Jürgen Butt, Yuanli Liu, Si Wu, Advanced Functional Materials, 30, 1906752 (2020). doi: 10.1002/adfm.201906752

Premelting-Induced Agglomeration of Hydrates: Theoretical Analysis and Modelling,

Ngoc Nguyen, Rüdiger Berger, Hans-Jürgen Butt, ACS Appl. Mater. Interfaces, 12, 14599 - 14606 (2020).

Publications in 2019

Book Review:

Berger, R. (2019). Kelvin Probe Force Microscopy: From Single Charge Detection to Device Characterization, Second Volume Sascha Sadewasser and Thilo Glatzel (Eds.), Springer Series in Surface Sciences, Book 65, 2018, 521 pp. ISBN: 9783319756868. Microscopy and Microanalysis, 25(6), 1509-1510. doi:10.1017/S1431927619015083, Microscopy and Microanalysis 25(6), 1509-1510 (2019). doi:10.1017/S1431927619015083

When you hold this 1 kg heavy book in your hand you may say: "It is so thick and heavy, is it worth the effort of carrying the book home and reading it? Why bother? After all, this is only a book describing Kelvin probe force microscopy. Yet another mode from the plethora of modes that are known for scanning force microscopy. No one should care!"
My daughter liked it and I like the book.

⬅ thanks to Katharina Maisenbacher (MPI-P) for the drawing. I like it!

Surface Pre-melting and Interfacial Interactions of Clathrate Hydrate,

Ngoc N. Nguyen, Rüdiger Berger, Hans-Jürgen Butt, J. Phys. Chem. C 123, 39, 24080 - 24086 (2019). doi: 10.1021/acs.jpcc.9b06376

We measured the forces between a semi-clathrate hydrate formed by tetrabutyl ammonium bromide and a silica microsphere in air and in undecane. Significantly, the analyses of jump-in (attractive) and pull-off (adhesive) forces in force-distance curves indicate the presence of a quasi-liquid layer (QLL) on the hydrate surface resulting from interfacial premelting. We have shown that interfacial forces between the sphere and the hydrate surface are dominated by the capillary formation between the QLL and the sphere. The thickness of the QLL on the hydrate surface is around 11 nm at -4 °C.

Two-Stage Collapse of PNIPAM Brushes: Viscoelastic Changes Revealed by an Interferometric Laser Technique,

David van Duinen, Hans-Jürgen Butt, and Rüdiger Berger, Langmuir 35, 15776 - 15783 (2019). doi: 10.1021/acs.langmuir.9b03205

We studied the viscoelastic changes of a poly(N-isopropylacryamide) (PNIPAM) brush layers (51 ± 3 nm thick) with an interferometric laser method at different temperatures. With this method we were able to investigate the two-stage collapse of beads coated with a polymer brush layer. The change of the Brownian motion spectrum with temperature indicates two transitions of the PNIPAM brush layer, one at 36 °C and one at 46 °C. We attribute the first transition to the LCST volume collapse of PNIPAM. The second transition is dominated by a stiffening of the brush layer.

Critical analysis of Micro-Thermogravimetry of CuSO4 · 5H2O crystals using heatable Microcantilevers,

Nikhilendu Tiwary, Marjan Zakerin, Filipe Natalio, Eugen Biegler, Fritzsche Marco, Hermann Kaubitzsch, Apurba Laha, Rüdiger Berger, V. Ramgopal Rao, Journal of Micromechanics and Microengineering 29, 105009 (2019). doi:10.1088/1361-6439/ab30a3

We have critically analysed Micro/nano thermogravimetry (TG) method. In cooperation with the Indian Institute of Technology we have designed and fabricated a microelectromechanical thermogravimetric device (MMTG) with integrated microheaters and temperature sensors. The final mass loss ratio corresponds to the theoretically expected value, although the obtained TG curve deviated from the standard TG curve of CuSO4 · 5H2O crystals obtained from commercial TG instruments. We attributed the deviation to the inherent temperature non-uniformity, non-isothermal conditions and temperature gradients of metallicwire based microheaters.
⬅ The image shows a red glowing microelectromechanical thermogravimetric device.

Removal of Surface Oxygen Vacancies increases Conductance through TiO2 Thin Films for Perovskite Solar Cells

Alexander Klasen, Phillip Baumli, Qu Sheng, Ewald Johannes, Simon A. Bretschneider, Ilka M. Hermes, Victor W. Bergmann, Christopher Gort, Amilie Axt, Stefan A.L. Weber, Heejae Kim, Hans-Jürgen Butt, Wolfgang Tremel, Rüdiger Berger,
Journal of Physical Chemistry 123, 22, 13458 - 13466 (2019). doi:10.1021/acs.jpcc.9b02371

We report that UV-ozone treatment of TiO2 anatase thin films is an efficient method to increase the conductance through the film by more than one order of magnitude. The increase in conductance is quantified via conductive scanning force microscopy on freshly annealed and UV-ozone treated TiO2 anatase thin films on fluorine-doped tin oxide substrates. The increased conductance of TiO2 anatase thin films results in a 2 % increase of the average power conversion efficiency (PCE) of methylammonium lead iodide based perovskite solar cells. PCE values up to 19.5 % for mesoporous solar cells are realized. The additional UV-ozone treatment results in a reduced number of oxygen vacancies at the surface, inferred from X-ray photoelectron spectroscopy (XPS). These oxygen vacancies at the surface act as charge carrier traps and hinder charge extraction from the adjacent material.

Wie sich Tropfen bewegen

Florian Geyer, Patrick M. Seiler, Doris Vollmer, Rüdiger Berger,
Physik in Unserer Zeit 2, 90-96 (2019).

In diesem Beitrag wenden wir uns an Physikinteressierte aus allen Bereichen der akademischen Forschung, Wirtschaft und Lehre. Wir beschreiben, wie Reibung zwischen einem Flüssigkeitstropfen und einer festen Oberfläche gemessen und berechnet werden kann. Im Rahmen des Sonderforschungsbereichs 1194 Wechselseitige Beeinflussung von Transport- und Benetzungsvorgängen erläutern wir, wie diese Grundlagenforschung mit angwandter Forschung der Automobilindustrie verzahnt ist.

Scanning probe microscopy for energy-related materials

Rüdiger Berger, Benjamin Grévin, Philippe Leclère and Yi Zhang,
Beilstein J. Nanotechnol. 10, 132-134 (2019). doi:10.3762/bjnano.10.12

The term "energy applications" refers to materials that are used for energy conversion, energy transport and energy storage. In particular, material properties on the nanometer scale play a major role. The understanding of these nanoscale phenomena occurring at material interfaces is therefore essential. Furthermore, these interface phenomena are strongly linked to material properties such as grain size, roughness, mechanical properties and work function. In an attempt to address the diversity of phenomena on the nanoscale, scanning probe microscopy (SPM) methods play an significant role for the in-operando characterization. SPM methods offer a plethora of operation modes beyond topography imaging, which is well reflected in the articles of this thematic issue.
Here is a link to the full thematic issue: Scanning probe microscopy for energy-related materials

Thermodynamic approach to tailor porosity in piezoelectric polymer fibers for application in nanogenerators,

Mohammad Mahdi Abolhasani, Minoo Naebe, Kamyar Shirvanimoghaddam, Hossein Fashandi, Hamid Khayyam, Matthew Joordens, Achilleas Pipertzis, Saleem Anwar, Rüdiger Berger, George Floudas, Jasper Michels, Kamal Asadi,
Nano Energy, 62, 594 - 600 (2019). doi: 10.1016/j.nanoen.2019.05.044

Publications in 2018

How the Formation of Interfacial Charge Causes Hysteresis in Perovskite Solar Cells,

S.A.L. Weber, I.M. Hermes, S.H. Turren Cruz, C. Gort, V.W. Bergmann, L. Gilson, A. Hagfeldt, M. Grätzel, W. Tress, W and R. Berger,
Energy Environmental Science, 11, 2404 - 2413 (2018). doi: 10.1039/C8EE01447G

The underlying mechanism of the current-voltage hysteresis in a hybrid lead-halide perovskite solar cell is still sketchy. We have developed a method based on Kelvin probe force microscopy that enables mapping charge redistribution in an operating device upon a voltage- or light pulse with sub-millisecond resolution. We observed the formation of a localized interfacial charge at the anode interface, which screened most of the electric field in the cell. Our observation of a time-dependent ion concentration in the perovskite layer suggests that iodide ions adsorbed and became neutralized at the hole-selective spiro-OMeTAD electrode. Thus the formation and the release of interfacial charges is the dominating factor for current-voltage hysteresis.

How drops start sliding over solid surfaces,

Nan Gao, Florian Geyer, Dominik W. Pilat, Sanghyuk Wooh, Doris Vollmer, Hans-Jürgen Butt, Rüdiger Berger,
Nature Physics, 14, 191 - 196 (2018). doi: 10.1038/NPHYS4305

It has been known for more than 200 years that the maximum static friction force between two solid surfaces is usually greater than the kinetic friction force. In contrast to solid-solid friction, there is a lack of understanding of liquid-solid friction, i.e. the forces that impede the lateral motion of a drop of liquid on a solid surface. Here, we report that the lateral adhesion force between a liquid drop and a solid can be divided into a static and a kinetic regime. This striking analogy with solid-solid friction is a generic phenomenon that holds for liquids of different polarities and surface tensions on smooth, rough and structured surfaces.
Response of public media: Süddeutsche Zeitung, Max Planck Society, Inside Science, Wissenschaft Aktuell

Adaptive Wetting - Adaptation in Wetting,

Hans-Jürgen Butt, Rüdiger Berger, Werner Steffen , Doris Vollmer, and Stefan A. L. Weber,
Langmuir, 34, 11292 - 11304 (2018). 10.1021/acs.langmuir.8b01783

Young's modulus of plasma-polymerized allylamine films using micromechanical cantilever sensor and laser-based surface acoustic wave techniques,

Masaya Toda, Koji Miyake, Liqiang Chu, Marjan Zakerin, Renate Förch, Rüdiger Berger, Akiko N. Itakura,
Plasma Process Polym., e1800083 (2018). doi: 10.1002/ppap.201800083

Genetically encoded lipid-polypeptide hybrid biomaterials that exhibit temperature-triggered hierarchical self-assembly,

Davoud Mozhdehi, Kelli M. Luginbuhl, Joseph R. Simon, Michael Dzuricky, Rüdiger Berger, H. Samet Varol, Fred C. Huang, Kristen L. Buehne, Nicholas R. Mayne, Isaac Weitzhandler, Mischa Bonn, Sapun H. Parekh and Ashutosh Chilkoti,
Nature Chemistry, 10, 496 - 505 (2018).

Spatially resolved solid-state reduction of graphene oxide thin films,

Maria Morant-Minana, Jonas Heidler, Gunnar Glasser, Hao Lu, Rüdiger Berger, Nerea Gil-Gonzalez, Klaus Müllen, Dago de Leeuw, Kamal Asadi,
Materials Horizons, 5, 1176-1184 (2018). doi: 10.1039/c8mh00895g

Calcium-Induced Molecular Rearrangement of Peptide Folds Enables Biomineralization of Vaterite Calcium Carbonate,

Hao Lu, Helmut Lutz, Steven J. Roeters, Matthew A. Hood, Arne Schäfer, Rafael Munoz-Espi, Rüdiger Berger, Mischa Bonn and Tobias Weidner,
Journal of the American Chemical Society, 140, 2793 - 2796 (2018). doi: 10.1021/jacs.8b00281

Pico-thermogravimetric material properties analysis using a diamond cantilever beam,

Ioana Voiculescu, Meiyong Liao, Marjan Zakerin, Rüdiger Berger, Takahito Ono, Masaya Toda,
Sensors and Actuators A, 271, 356-363 (2018). doi: 10.1016/j.sna.2018.01.004

Engineering Proteins at Interfaces: From Complementary Characterization to Material Surfaces with Designed Functions,

Svenja Morsbach, Grazia Gonella, Volker Mailänder, Seraphine Wegner, Si Wu, Tobias Weidner, Rüdiger Berger, Kaloian Koynov, Doris Vollmer, Noemi Encinas, Seah Ling Kuan, Tanja Weil, Mischa Bonn, Hans-Jürgen Butt and Katharina Landfester,
Angewandte Chemie, 57, 12626 - 12648 (2018).

Publications in 2017

Thiolated Lysine-Leucine Peptides Self-Assemble into Biosilica Nucleation Pits on Gold Surfaces,

Hao Lu, Yeneneh Yimer, Rüdiger Berger, Mischa Bonn, Jim Pfaendtner, Tobias Weidner
Advanced Materials Interfaces, 4, 1700399 (2017). doi: 10.1002/admi.201700399

Thermal Characterization of Dynamic Silicon Cantilever Array Sensors by Digital Holographic Microscopy,

Marjan Zakerin, Antonin Novak, Masaya Toda, Yves Emery, Filipe Natalio, Hans-Jürgen Butt, Rüdiger Berger
Sensors, 17, 1191 (2017). doi: 10.3390/s17061191

Photoswitching of glass transition temperatures of azobenzene-containing polymers induces reversible solid-to-liquid transitions,

Hongwei Zhou, Changguo Xue, Philipp Weis, Yasuhito Suzuki, Shilin Huang, Kaloian Koynov, Günter K. Auernhammer, Rüdiger Berger, Hans-Jürgen Butt and Si Wu,
Nature Chemistry 9, 145 - 151 (2017). doi: 10.1038/nchem.2625

Energy Dissipation of Moving Drops on Superhydrophobic and Superoleophobic Surfaces,

Hans-Jürgen Butt, Nan Gao, Periklis Papadopoulos, Werner Steffen, Michael Kappl, Rüdiger Berger,
Langmuir 33, 107 - 116 (2017). doi 10.1021/acs.langmuir.6b03792

Reliable Work Function Determination of Multicomponent Surfaces and Interfaces: The Role of Electrostatic Potentials in Ultraviolet Photoelectron Spectroscopy,

Thorsten Schultz, Thomas Lenz, Naresh Kotadiya, Georg Heimel, Gunnar Glasser, Rüdiger Berger, Paul Blom, Patrick Amsalem, Dago de Leeuw, Norbert Koch,
Advanced Materials Interfaces 4, 1700324 (2017). 10.1002/admi.201700324

Publications in 2016

Local Time-Dependent Charging in a Perovskite Solar Cell,

Victor Bergmann, Yunlong Guo, Hideyuki Tanaka, Ilka Hermes, Dan Li, Alexander Klasen, Simon Bretschneider, Eiichi Nakamura, Rüdiger Berger, Stefan Weber, ACS Applied Materials & Interfaces, 8 (30), 19402 - 19409 (2016). doi: 10.1021/acsami.6b04104

Efficient charge extraction within solar cells explicitly depends on the optimization of the internal interfaces. In the case of perovskite solar cells, slow processes happening on timescales of seconds cause hysteresis in the current-voltage characteristics. Here, we localized and investigated these slow processes with frequency modulation Kelvin probe force microscopy (FM-KPFM) on cross sections of planar methylammonium lead iodide (MAPI) perovskite solar cells. FM-KPFM can map the charge density distribution and its dynamics at internal interfaces. Upon illumination, space charge layers were forming at the interfaces to the MAPI layer within several seconds. We observed distinct differences in the charging dynamics at interfaces of the MAPI to adjacent layers. Our results attest that more than one process is involved in hysteresis.

Stability of a Split-RNA-Aptamer, Capable of Streptomycin Binding,

Thomas A. Nick, Tiago E. de Oliveira, Dominik W. Pilat, Felix Spenkuch, Hans-Jürgen Butt, Mark Helm, Paulo A. Netz, and Rüdiger Berger, Journal of Physical Chemistry Part B, 120 (27), 6479 - 6489 (2016). doi: 10.1021/acs.jpcb.6b02440

In this paper we investigated the stability of an aptamer, which is formed by two RNA-strands and binds the antibiotic streptomycin. Molecular dynamics simulations in aqueous solution confirmed the geometry and the pattern of hydrogen bond interactions that was derived from the crystal-structure. The result of umbrella sampling simulations indicated a favored streptomycin-binding. Experimentally, the increase in oligonucleotide stability upon binding of streptomycin was probed by single-molecule force spectroscopy. Rate dependent force spectroscopy measurements revealed a decrease in the natural off-rate for the aptamer-streptomycin complex compared to the aptamer having an empty binding pocket. The simulated binding pattern and the experimental results led to the conclusion that hydrogen-bonds between both RNA strands mainly contribute to the decrease in natural-off rate.

Controlled Mutual Diffusion between Fullerene and Conjugated Polymer Nanopillars in Ordered Heterojunction Solar Cells,

Jongkuk Ko, Jiyun Song, Hyunsik Yoon, Taeyong Kim, Changhee Lee, Rüdiger Berger and Kookheon Char, Advanced Materials Interfaces, 1600264 (2016). doi: 10.1002/admi.201600264

This paper descibes a new approach to control the nanomorphology of organic solar cells in a predictable, controllable, and easily-scalable way. In particular, the nanomorphology was studied in nanostructural and electrical properties of the pillar samples using scanning probe microscopy. Conductive scanning force microscopy in quantitative imaging mode, applied to the pillar-based samples for the first time, allows us to establish a clear relationship between nanomorphology, nanoelectrical property, and macroscale device performance.

Surface forces between colloidal particles at high hydrostatic pressure,

D. W. Pilat, B. Pouligny, A. Best, T. A. Nick, R. Berger, and H.-J. Butt,
Physical Review E, 022608 (2016). doi: 10.1103/PhysRevE.93.022608

It was recently suggested that the electrostatic double-layer force between colloidal particles might weaken at high hydrostatic pressure encountered, for example, in deep seas or during oil recovery. We have addressed this issue by means of a specially designed optical trapping setup that allowed us to explore the interaction of a micrometer-sized glass bead and a solid glass wall in water at hydrostatic pressures of up to 1 kbar. The setup allowed us to measure the distance between bead and wall with a subnanometer resolution. We have determined the Debye lengths in water for salt concentrations of 0.1 and 1 mM. We found that in the pressure range from 1 bar to 1 kbar the maximum variation of the Debye lengths was smaller than 1 nm for both salt concentrations. Furthermore, the magnitude of the zeta potentials of the glass surfaces in water showed no dependency on pressure.

Humidity-induced grain boundaries in MAPbI3 perovskite films,

Dan Li, Simon A. Bretschneider, Victor W. Bergmann, Ilka M. Hermes, Julian Mars, Alexander Klasen, Wolfgang Tremel, Markus Mezger, Hans-Jürgen Butt, Stefan A. L. Weber, Rüdiger Berger,
Journal of Physical Chemistry C, 120, 6363 - 6368 (2016). doi: 10.1021/acs.jpcc.6b00335

Methylammonium halide perovskites (MAPbI3) are sensitive to humidity environments. We performed in-situ scanning force microscope and in-situ X-ray diffraction measurements on MAPbI3 films to track changes in the film morphology and crystal structure upon repeated exposure to a high relative humidity of 80%. The appearance of mono-hydrate diffraction peaks (MAPbI3 H2O) coincided with the appearance of additional grain boundaries outlined as black lines in the left handed sketch. Prolonged exposure to humidity induced more steps in the MAPbI3 films and the peak intensities of the mono-hydrated phase increased. The mono hydrated phase was not stable under dry atmosphere and could be reversed to MAPbI3. However, the humidity induced grain boundaries persisted. The presence of these additional grain boundaries is most likely the reason for an increase in hysteresis in JV behavior.

Nanoscale heterogeniety and workfunction variations in ZnO thin films,

Anirudh Sharma, Maria Untch, Jamie S. Quinton, Rüdiger Berger, Gunther Andersson, David A. Lewis,
Applied Surface Science, 363, 516 - 521 (2016). doi: 10.1016/j.apsusc.2015.11.190

Nano-roughened, sol-gel derived polycrystalline ZnO thin films prepared by a thermal ramping procedure were found to exhibit different work function values on a sub-micrometer scale. By Kelvin probe force microscopy (KPFM) two distinct nanoscale regions with work function differing by over 0.1 eV were detected which did not coincide with the nano-roughened surface topography. Such heterogeneity in the electronic properties of materials in thin film devices can significantly influence the interfacial charge transport across materials.

Influence of the mixed organic cation ratio in lead iodide based perovskite on the performance of solar cells,

Manuel Salado, Laura Calio, Rüdiger Berger, Samrana Kazim and Shahzada Ahmad,
Physical Chemistry Chemical Physics 18, 27148 - 27157 (2016). doi: 10.1039/C6CP03851D

Ferroelastic Fingerprints in Methylammonium Lead Iodide Perovskite,

Ilka Hermes, Simon Bretschneider, Victor Bergmann, Dan Li, Alexander Klasen, Julian Mars, Wolfgang Tremel, Frederik Laquai, Hans-Jürgen Butt, Markus Mezger, Rüdiger Berger, Brian Rodriguez, Stefan Weber,
Journal of Physical Chemistry C 10, 5724 - 5731 (2016). doi 10.1021/acs.jpcc.5b11469

Bottom-up Fabrication of Nanopatterned Polymers on DNA Origami by In-situ Atom Transfer Radical Polymerization,

Yu Tokura, Yanyan Jiang, Alexander Welle, Martina H. Stenzel, Katarzyna Krzemien, Jens Michaelis, Rüdiger Berger, Christopher Barner-Kowollik, Yuzhou Wu and Tanja Weil,
Angewandte Chemie 128, 5786 - 5791 (2016). doi 10.1002/ange.201511761

Semifluorinated Alkanes at the Air-Water Interface: Tailoring Structure and Rheology at the Molecular Scale,

Antigoni Theodoratou, Ulrich Jonas, Benoit Loppinet, Thomas Geue, Rene Stangenberg, Rabea Keller, Dan Li, Rüdiger Berger, Jan Vermant, Dimitris Vlassopoulos,
Langmuir 32, 3139 - 3151 (2016). doi 10.1021/acs.langmuir.5b04744

Do you want a list of all my publications? Then please go to my Reseracher ID: RID: A-5210-2009