Highlight Publications 2017

Lateral Fusion of Chemical Vapor Deposited N = 5 Armchair Graphene Nanoribbons
Zongping Chen, Hai I. Wang, Nerea Bilbao, Joan Teyssandier, Thorsten Prechtl, Nicola Cavani, Alexander Tries, Roberto Biagi, Valentina De Renzi, Xinliang Feng, Mathias Kläui, Steven De Feyter, Mischa Bonn, Akimitsu Narita, and Klaus Müllen
Lateral Fusion of Chemical Vapor Deposited N = 5 Armchair Graphene Nanoribbons
Bottom-up synthesis of low-bandgap graphene nanoribbons with various widths is of great importance for their applications in electronic and optoelectronic devices. Here we demonstrate a synthesis of N = 5 armchair graphene nanoribbons (5-AGNRs) and their lateral fusion into wider AGNRs, by a chemical vapor deposition method. The efficient formation of 10- and 15-AGNRs is revealed by a combination of different spectroscopic methods, including Raman and UV-Vis-near infrared spectroscopy as well as by scanning tunneling microscopy. The degree of fusion and thus the optical and electronic properties of the resulting GNRs can be controlled by the annealing temperature, providing GNR films with optical absorptions up to ~2250 nm.
© ACS (2017)
Left: CVD growth of N = 5 armchair GNRs (5-AGNRs) and their lateral fusion to wider GNRs. Right: Raman spectra of AGNRs annealed at different temperature. The numbers 5, 10, etc. indicate the position of the RBLM peaks of respective AGNRs (excitation wavelength: 785 nm).
Electrochemical TERS Elucidates Potential-Induced Molecular Reorientation of Adenine/Au(111)
Natalia Martín Sabanés, Tatsuhiko Ohto, Denis Andrienko, Yuki Nagata, Katrin F. Domke
Electrochemical TERS Elucidates Potential-Induced Molecular Reorientation of Adenine/Au(111)
Electrochemical surface activity arises from the interaction and geometric arrangement of molecules at electrified interfaces. We present a novel electrochemical tip-enhanced Raman spectroscope that can access the vibrational fingerprint of less than 100 small, non-resonant molecules adsorbed at atomically flat Au electrodes to study their adsorption geometry and chemical reactivity as a function of applied potential. Combining experimental and simulation data for showcase adenine/Au(111), we conclude that protonated physisorbed adenine adapts a tilted orientation at low potentials while it is vertically adsorbed around the potential of zero charge. Further potential increase induces adenine deprotonation and reorientation to a planar configuration. The extension of EC-TERS to the study of adsorbate reorientation significantly broadens the applicability of this advanced spectroelectrochemical tool for the nanoscale characterization of a full range of electrochemical interfaces.
© Wiley VCH (2017)
The potential-induced reorientation and chemical conversion of < 100 molecules at a solid/liquid electrode interface is monitored in situ with help of newly developed electrochemical tip-enhanced Raman spectroscopy.
Main-chain poly(phosphoester)s: History, syntheses, degradation, bio-and flame-retardant applications
Kristin N. Bauer, Hisaschi T. Tee, Maria M. Velencoso, Frederik R. Wurm
Main-chain poly(phosphoester)s: History, syntheses, degradation, bio-and flame-retardant applications
Nature on planet earth needs poly(phosphoester)s (PPEs). They determine life in the form of DNA & RNA, and, as pyrophosphates, they store chemical energy in organisms. Polymer chemistry, however, is dominated by polyolefins and polycarboxylic esters produced on a large scale today. Recent work has illustrated the potential of PPEs for future applications beyond flame-retardancy, the main application of PPEs today, and provided a coherent vision to implement PPEs in modern applications that demand biocompatibility and degradability as well as the possibility to adjust the properties to individual needs. This comprehensive review summarizes synthetic protocols to PPEs, their applications in biomedicine and their flame retardant properties. We highlight recent developments that may make phosphorus-based polymers attractive materials for various future applications.
© MPIP (2017)
A comprehensive review about poly(phosphoester)s
Role of Edge Engineering in Photoconductivity of Graphene Nanoribbons
Ivan Ivanov, Yunbin Hu, Silvio Osella, Uliana Beser, Hai I. Wang, David Beljonne, Akimitsu Narita, Klaus Müllen, Dmitry Turchinovich, and Mischa Bonn
Role of Edge Engineering in Photoconductivity of Graphene Nanoribbons
This collaborative synthetic-spectroscopic-theoretical study of the effect of edge engineering in graphene nanoribbons (GNRs) on their photoconductivity reveals that the variation of the side chains does not alter the photoconductive properties of GNRs, but the edge structure has a strong impact on the carrier mobility in GNRs by affecting the carrier momentum scattering rates. Calculations of the ribbon electronic structure and theoretical transport studies show that phonon scattering plays a significant role in microscopic conduction in GNRs with different edge structures.
© ACS (2017)
The mobility of electrons through nanoribbons depends on the shape of the edges, but not the chemical termination of the edges.
Conical Ionic Amphiphiles Endowed with Micellization Ability but Lacking Air– and Oil–Water Interfacial Activity
Hirohisa Nitta, Koji Harano, Mayuko Isomura, Ellen H.G. Backus, Mischa Bonn, and Eiichi Nakamura
Conical Ionic Amphiphiles Endowed with Micellization Ability but Lacking Air– and Oil–Water Interfacial Activity
In collaboration with the Nakamura group (Tokyo), a new type of amphiphiles is presented that serve as selective "surfactants": they are not surface active at the water-air interface, but they are very active at the solid-water interface. The amphiphiles possess a conical shape consisting of a hydrophobic apex and five ionic termini at its base of the cone. The conical shape and the high charge density cooperatively impede the monolayer formation at the interfaces, and hence prevent foaming and emulsification. On the other hand, the conical shape strongly assists micelle formation in water, and hemimicelle formation on a solid surface to promote dissolution of nanoparticles such as magnetic nanoparticles and nanocarbons in water.
© ACS (2017)
New surfactants are not surface active at the water/air interface, but very active at the water/solid interface.
Ultrafast Delamination of Graphite into High-Quality Graphene Using Alternating Currents
Sheng Yang, Antonio Gaetano Ricciardulli, Shaohua Liu, Renhao Dong, Martin R. Lohe, Alfons Becker, Marco A. Squillaci, Paolo Samorì, Klaus Müllen, Xinliang Feng
Ultrafast Delamination of Graphite into High-Quality Graphene Using Alternating Currents
To bridge the gap between laboratory-scale study and commercial applications, mass production of high quality graphene is essential. Researchers from MPIP, TU Dresden demonstrate a scalable exfoliation strategy towards the production of graphene sheets with excellent yield, great production rate and outstanding electronic property. The high-quality solution-processable exfoliated graphene holds great promise for a wide spectrum of applications, such as inkjet printing, solar cells and composites.
© WILEY-VCH (2017)
Delamination of graphite using alternating currents
Dipolar Molecular Capping in Quantum Dot-Sensitized Oxides: Fermi Level Pinning Precludes Tuning Donor-Acceptor Energetics
Hai I. Wang, Hao Lu, Yuki Nagata, Mischa Bonn, and Enrique Cánovas
Dipolar Molecular Capping in Quantum Dot-Sensitized Oxides: Fermi Level Pinning Precludes Tuning Donor-Acceptor Energetics
Exploiting quantum dot (QD) nanocrystals as sensitizers of mesoporous metal oxides represents a promising path towards low cost solutions for solar energy conversion (e.g. in sensitized solar cells or in photocatalytic H2 generation). After photon absorption in the QD, an exciton is created; this exciton can be dissociated at the QD-oxide interface by a cost of energy that is given primarily by the energy difference between donor-acceptor states (QD LUMO and oxide conduction band). In this respect, reducing the energy offset between donor and acceptor is a necessary requirement for improved photoconversion efficiencies in sensitized architectures. One proposed path for reducing energy losses at QD sensitized interfaces refers to the fine tuning of donor workfunction by exploiting QD dipolar molecular capping treatments. However, previous attempts revealed a very modest gain in device efficieny induced by these treatments. In this contribution we rationalize these observations by demonstrating that Fermi level pinning at the strongly coupled QD-oxide interfaces precludes tuning donor-acceptor energetics by dipolar molecular capping. These results highlight that reducing photoconversion losses at QD sensitized interfaces by dipolar treatments will requires decoupling between the donating and accepting states (e.g. by introducing an insulating layer in bettwen QD and oxide).
© Enrique Cánovas (2017)
Can we tune interfacial electron transfer in quantum dot sensitized oxides by dipolar capping?
Single-crystal Ih ice surface: Connecting macroscopic etch pits and molecular structure
Alexandra Brumberg, Kevin D. Hammonds, Ian Baker, Ellen H. G. Backus, Patrick J. Bisson, Mischa Bonn, Charles Daghlian, Markus Mezger, Mary Jane Shultz
Single-crystal Ih ice surface: Connecting macroscopic etch pits and molecular structure
Physics and chemistry of ice surfaces are not only of fundamental interest but also have important impacts on biological and environmental processes. It is well known that the microscopic structure of the ubiquitous hexagonal ice crystal consists of stacked layers of chair-form hexagonal rings, referred to as molecular hexagons. Crystallographic unit cells can be assembled into a regular right hexagonal prism. The bases are labeled crystallographic hexagons. The molecular and crystallographic hexagons are rotated 30° relative to each other. The connection between the familiar macroscopic shape of hexagonal snowflakes and either of the hexagons is not obvious per se. Direct comparison of etch pit images, reporting on the macroscopic shape, and the electron backscatter diffraction results, providing the microscopic structure, compellingly connects the macroscopic etch pit (or: snowflake) hexagon to the crystallographic, and not molecular, hexagon.
© MPI-P (2017)
From where does the snow flake get its form? Connecting macroscopic etch pits and molecular structure of single-crystal hexagonal ice.
 
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