Highlight Publications 2017

Short-channel field-effect transistors with 9-atom and 13-atom wide graphene nanoribbons
Juan Pablo Llinas, Andrew Fairbrother, Gabriela Borin Barin, Wu Shi, Kyunghoon Lee, Shuang Wu, Byung Yong Choi, Rohit Braganza, Jordan Lear, Nicholas Kau, Wonwoo Choi, Chen Chen, Zahra Pedramrazi, Tim Dumslaff, Akimitsu Narita, Xinliang Feng, Klaus Müllen, Felix Fischer, Alex Zettl, Pascal Ruffieux, Eli Yablonovitch1, Michael Crommie, Roman Fasel & Jeffrey Bokor
Short-channel field-effect transistors with 9-atom and 13-atom wide graphene nanoribbons
Bottom-up synthesized graphene nanoribbons (GNRs) and GNR heterostructures have promising electronic properties for high-performance field-effect transistors (FETs) and ultra-low power devices such as tunneling FETs. However, the short length and wide band gap of GNRs have prevented the fabrication of devices with the desired performance and switching behavior. Here, by fabricating short channel devices with a thin, high-κ gate dielectric and a 9-atom wide armchair GNR as the channel material, we demonstrate field-effect transistors with high on-current and high I on /I off  at room temperature. We find that the performance of these devices is limited by tunneling through the Schottky barrier at the contacts and we observe an increase in the transparency of the barrier by increasing the gate field near the contacts. Our results thus demonstrate successful fabrication of high-performance short-channel FETs with bottom-up synthesized armchair GNRs.
© Nature Publishing Group (2017)
Schematic of the short channel GNRFET with a 9AGNR channel and Pd source-drain electrodes (top) and Scanning electron micrograph of the fabricated Pd source-drain electrodes with a scale bar of 100 nm (bottom)
A maximum in interfacial hydrogen bonding occurs at 200 K at the single crystalline ice – air interface.
Wilbert J. Smit, Fujie Tang, M. Alejandra Sánchez, Ellen H. G. Backus, Limei Xu, Taisuke Hasegawa, Mischa Bonn, Huib J. Bakker, and Yuki Nagata
A maximum in interfacial hydrogen bonding occurs at 200 K at the single crystalline ice – air interface.
Combining theory and experiment, we have studied the temperature dependent structure of water molecules at the surface of ice. Remarkably, a maximum in interfacial hydrogen bonding occurs at 200 K. This maximum results from two competing effects: above 200 K, thermal fluctuations cause the breaking of hydrogen bonds; below 200 K, the ordered crystalline bulk structure causes breaking of hydrogen bonds at the interface. These insights are particularly important for understanding (photo-) chemistry occurring on ice particles in the atmosphere.
© Yuki Nagata / MPI-P (2017)
Ice forms crystal structure even at topmost ice surface at 170 K, while ice structure becomes disordered at 230 K. At 200 K, ice forms maximum hydrogen bond by making five-ring structure rather than hexagonal structure.
Reversible Self-Assembly of Degradable Polymersomes with Upper Critical Solution Temperature in Water
Thomas Wolf, Timo Rheinberger, Johanna Simon, Frederik R. Wurm
Reversible Self-Assembly of Degradable Polymersomes with Upper Critical Solution Temperature in Water
Temperature-induced self-assembly of block copolymers allows the formation of smart nanodimensional structures. Mostly, non-degradable LCST segments are used to prepare such dynamic aggregates. However, degradable UCST block copolymers that would allow the swelling or disassembly at elevated temperatures with eventual backbone hydrolysis have not been reported to date. We present the first well-defined degradable poly(phosphonate)s with adjustable UCST in water between 43 °C and 71 °C. Block copolymers with PEG self-assemble into well-defined polymersomes. Depending on the responsive block, these structures either swell or disassemble completely upon an increased temperature.
© ACS (2017)
Upper critical solution temperature in degradable poly(phosphoester)s was installed to prepare block copolymer vesicles that self-assemble at room temperature and reversibly disassemble at elevated temperatures.
A Conjugated Microporous Polymer for Palladium-Free, Visible Light-Promoted Photocatalytic Stille-Type Coupling Reactions
Saman Ghasimi, Simon A. Bretschneider, Wei Huang, Katharina Landfester, and Kai A. I. Zhang
A Conjugated Microporous Polymer for Palladium-Free, Visible Light-Promoted Photocatalytic Stille-Type Coupling Reactions
The Stille coupling reaction is a versatile method to mainly form aromatic C-C bonds. However, up to now, the use of palladium catalysts is necessary. Researchers from the MPI-P reported a palladium-free and photocatalytic Stille-type coupling route between aryl iodides and aryl stannanes. The new coupling reaction pathway is catalyzed by a conjugated microporous polymer under visible light irradiation at room temperature. The novel coupling reaction mechanism occurs between the photogenerated aryl radical under oxidative destannylation of the aryl stannane, and the electron-activated aryl iodide, resulting into the aromatic C-C bond formation reaction.
© Wiley VCH (2017)
Bye-Bye Palladium: A photocatalytic, palladium-free Stille-type coupling reaction is described.
A triaxial supramolecular weave
Urszula Lewandowska, Wojciech Zajaczkowski, Stefano Corra, Junki Tanabe,Ruediger Borrmann, Edmondo M. Benetti, Sebastian Stappert, Kohei Watanabe, Nellie A. K. Ochs, Robin Schaeublin, Chen Li, Eiji Yashima, Wojciech Pisula, Klaus Müllen & Helma Wennemers
A triaxial supramolecular weave
Despite recent advances in the synthesis of increasingly complex topologies at the molecular level, nano- and microscopic weaves have remained difficult to achieve. Only a few diaxial molecular weaves exist these were achieved by templation with metals. Here, we present an extended triaxial supramolecular weave that consists of self-assembled organic threads. Each thread is formed by the self-assembly of a building block comprising a rigid oligoproline segment with two perylene-monoimide chromophores spaced at 18 Å. Upon π stacking of the chromophores, threads form that feature alternating up- and down-facing voids at regular distances. These voids accommodate incoming building blocks and establish crossing points through CH–π interactions on further assembly of the threads into a triaxial woven superstructure. The resulting micrometer-scale supramolecular weave proved to be more robust than non-woven self-assemblies of the same building block. The uniform hexagonal pores of the interwoven network were able to host iridium nanoparticles, which may be of interest for practical applications.
© Helma Wennemers/ETH und Klaus Müllen/MPI-P (2017)
Woven topologies endow macroscopic objects with mechanical stability, but their molecular counterparts have remained difficult to prepare. Now, an extended triaxial supramolecular weave has been formed by the self-assembly of a judiciously shaped organic building block - a rigid oligoproline segment featuring two perylene-monoimide moieties - through π-π stacking and CH-π interactions.
Diffusion and Permeation of Labeled IgG in Grafted Hydrogels
A. Vagias,K. Sergelen,K. Koynov,P. Košovan,J. Dostalek,U. Jonas,W. Knoll,and G. Fytas
Diffusion and Permeation of Labeled IgG in Grafted Hydrogels
The transport of antibodies through hydrogel materials is of fundamental relevance for many biological systems, but equally important in medical and technological applications. With this in mind we used fluorescence correlation spectroscopy (FCS) to study the permeation and diffusion of immunoglobulin G (IgG) in model hydrogel layers based on thermo-responsive poly(N-isopropylacrylamide) (pNiPAAm). Our findings demonstrated the outmost importance of the various interactions between proteins and the polymer network and suggest a model approach to explore the synergy between crowding and thermodynamics with respect to the controlled protein transport in pNiPAAm-based hydrogels.
© ACS (2017)
Schematic illustration of the variability of IgG and PNiPAAm interactions, depending on external stimulus employed: pH, ionic strength (I), temperature (T). IgG trajectory through the FCS focal spot is also depicted.
Solution-Processable High-Quality Graphene for Organic Solar Cells
Antonio Gaetano Ricciardulli, Sheng Yang, Xinliang Feng, Paul W. M. Blom
Solution-Processable High-Quality Graphene for Organic Solar Cells
Researchers from MPIP and TU Dresden report the first example of organic solar cells (OSCs) with a solution-processed transparent electrode based on electrochemical exfoliated graphene (EG). Thanks to the high-quality of EG, the fine control of the morphology and uniformity of the film, the OSCs fabricated in this study exhibit improved features compared to other solution-processable graphene-based organic photovoltaic devices up-to-date. Our work is a step forward toward the application of solution-processable high-quality graphene as transparent electrode in solar cells as well as other organic electronics.
© ACS (2017)
Spray coating of solution-processable graphene and the related solar cell performance
Photoswitchable Micro-Supercapacitor Based on a Diarylethene-Graphene Composite Film
Zhaoyang Liu, Hai I. Wang, Akimitsu Narita, Qiang Chen, Zoltan Mics, Dmitry Turchinovich, Mathias Kläui, Mischa Bonn, and Klaus Müllen
Photoswitchable Micro-Supercapacitor Based on a Diarylethene-Graphene Composite Film
Stimuli-responsive micro-supercapacitors (MSCs) controlled by external stimuli can enable a wide range of applications for future on-chip energy storage. Here, we report on a photoswitchable MSC based on a diarylethene-graphene composite film. The microdevice delivers an outstanding and reversible capacitance modulation of up to 20%, demonstrating a prototype photoswitchable MSC. Terahertz spectroscopy indicates that the photoswitching of the capacitance is enabled by the reversible tuning of interfacial charge injection into diarylethene molecular orbitals, as a consequence of charge transfer at the diarylethene–graphene interface upon light modulation.
© ACS (2017)
Schematic illustration of photoresponsive micro-supercapacitor (MSC) device with Diarylethene (DAE) on the top of graphene electrodes.
 
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