Mitsuharu Konuma

Charge-transfer-induced structural rearrangements at both sides of organic/metal interfaces

Organic/metal interfaces control the performance of many optoelectronic organic devices, including organic light-emitting diodes or field-effect transistors. Using scanning tunnelling microscopy, low-energy electron diffraction, X-ray photoemission spectroscopy, near-edge X-ray absorption fine structure spectroscopy and density functional theory calculations, we show that electron transfer at the interface between a metal surface and the organic electron acceptor tetracyano-p-quinodimethane leads to substantial structural rearrangements on both the organic and metallic sides of the interface. These structural modifications mediate new intermolecular interactions through the creation of stress fields that could not have been predicted on the basis of gas-phase neutral tetracyano-p-quinodimethane conformation.

Strong Performance Improvement of La0.6Sr0.4Co0.8Fe0.2O3 − δ SOFC Cathodes by Electrochemical Activation

It is shown that the electrochemical resistance of mixed conducting solid oxide fuel cell (SOFC) model cathodes can be reduced drastically by a short but strong dc polarization of the cell. The samples investigated are dense thin-film microelectrodes of La 0 . 6 Sr 0 . 4 Co 0 . 8 Fe 0 . 2 O 3 - δ on a yttria-stabilized zirconia solid electrolyte. Relative performance improvements of more than two orders of magnitude can be achieved with a cathodic dc bias of the order of 1 V, applied for a few minutes at fuel cell operating temperature. The positive effect on the electrode performance corresponds to an acceleration of the oxygen surface exchange reaction, initially the resistance determining process. For this surface-related resistance, absolute values as low as 0.065 Ω cm 2 at 700°C have been obtained. After such an activation, the resistance slowly increases again on a much larger time scale, indicating the possibility of a steady performance enhancement by a periodic activation with short dc pulses. X-ray photoelectron spectra show that a strong cathodic polarization severely changes the cation concentrations within the outermost surface layer of the electrode, and these field-induced surface compositional changes are assumed to be the main cause of the performance improvement.

Long-Range Ordered Single-Crystal Graphene on High-Quality Heteroepitaxial Ni Thin Films Grown on MgO(111)

Large-area single crystal monolayer graphene is synthesized on Ni(111) thin films, which have flat terraces and no grain boundaries. The flat single-crystal Ni films are heteroepitaxially grown on MgO(111) substrates using a buffer layer technique. Low-energy electron diffraction and various spectroscopic methods reveal the long-range single crystallinity and uniform monolayer thickness of the graphene. When transferred onto an insulating wafer, continuous millimeter-scale single domain graphene is obtained.

Structure and Morphology of 4H-SiC Wafer Surfaces after H2-Etching

Commercial on-axis wafers of 4H-SiC(0001) were etched in a standard reactor for chemical vapor deposition (CVD) using molecular hydrogen flux in order to improve the structure and morphology of the surface. The substrate temperature during etching was varied from 1400 to 1600°C. Characterization of the surface morphology was performed using optical and atomic force microscopy (AFM). Low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS) were also used to examine the surface structure and chemical composition of the samples. The sample of best quality was obtained for an etching temperature of 1400°C. Its surface is ° × 30 ) 3 3 ( R reconstructed and covered by an ordered “silicate” layer. Increasing the substrate temperature during etching to 1500°C leads to enhanced step-bunching and the formation of macroterraces. At 1600°C distinct depressions appear on the surface, presumably from etching of structural defects such as screw dislocations. Subsequent annealing at 1000°C in ultra-high vacuum (UHV) removes the surface oxide and produces the ° × 30 ) 3 3 ( R surface phase of clean 4HSiC( 0001).

Effect of low-damage inductively coupled plasma on shallow nitrogen-vacancy centers in diamond

Near-surface nitrogen-vacancy (NV) centers in diamond have been successfully employed as atomic-sized magnetic field sensors for external spins over the last years. A key challenge is still to develop a method to bring NV centers at nanometer proximity to the diamond surface while preserving their optical and spin properties. To that aim we present a method of controlled diamond etching with nanometric precision using an oxygen inductively coupled plasma process. Importantly, no traces of plasma-induced damages to the etched surface could be detected by X-ray photoelectron spectroscopy and confocal photoluminescence microscopy techniques. In addition, by profiling the depth of NV centers created by 5.0 keV of nitrogen implantation energy, no plasma-induced quenching in their fluorescence could be observed. Moreover, the developed etching process allowed even the channeling tail in their depth distribution to be resolved. Furthermore, treating a 12C isotopically purified diamond revealed a threefold increa...

Liquid phase epitaxy centrifuge for 100 mm diameter Si substrates

In a novel centrifuge, we perform silicon liquid‐phase epitaxy (LPE) on 100 mm diameter Si wafers. The epitaxial Si layers grow from indium solutions. The thickness uniformity of the layers is better than ±4.9% within the central circular area of 90 mm in diameter. The layers show smooth surfaces. The bulk of the layers is free of extended defects and of solution inclusions. Hall effect measurements and transmission electron microscopic observations confirm the high quality of this epitaxial material.

Strong p‐Type Doping of Individual Carbon Nanotubes by Prussian Blue Functionalization

Keywords: carbon nanotubes ; doping ; electrodeposition ; Prussian blue ; Field-Effect Transistors ; Electrochemical Preparation Method ; Modified Electrodes ; Charge-Transfer ; Single ; Oxidation ; Devices ; Bundles ; Composites ; Deposition Reference EPFL-ARTICLE-160520doi:10.1002/smll.200800803View record in Web of Science Record created on 2010-11-30, modified on 2017-05-12

Carbonization of polyethylene on gold oxide

Carbon layers are formed when gold oxide reacts under mild thermal conditions with molten aliphatic polymers such as polyethylene. This formation of carbon at relatively low temperature from chemically resistant polymers by addition of gold oxide to the polymers was unforeseen.

Synthesis of MgB2 films in Mg vapour flow and their characterization

Surface morphology, element distribution and superconducting properties of MgB2 films prepared by ex situ annealing of multilayer B/Mg precursors in a flow of Mg vapour have been studied. The composition of the films and distribution of the elements have been analysed by both Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). The films were found to be composed of a metallic Mg and an Mg-deficient Mg1−xB2 phase. Al and O have also been detected across the whole film, suggesting a reaction of the substrate with the adjacent Mg layer of the precursor. The films are nano-crystalline or even amorphous, which is ascribed to precipitation of impurities at grain boundaries. The critical current density of the MgB2 films extracted from both magneto-optical and magnetization measurements is Jc~1 × 107 A cm−2 at 10 K and self-field, and Jc~3 × 104 A cm−2 at 2 T and 5 K. The upper critical field is Hc 2 = 6.5 T at 5 K. Additionally, an unknown phase is found in the Mg–Al2O3 system after annealing of Mg films on sapphire in conditions similar to the synthesis process.

An experimental proof for negative oxidation states of platinum: ESCA-measurements on barium platinides.

ESCA-measurements on barium platinides provide the first spectroscopic evidence for negative oxidation states of platinum and are in excellent agreement with theoretical predictions based on quantum-chemical calculations.