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.

It is shown that the electrochemical resistance of mixed conducting solid oxide fuel cell ͑SOFC͒ 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−␦ 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 ⍀ 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.High-temperature solid oxide fuel cells ͑SOFCs͒ receive considerable attention because they enable a highly efficient conversion of chemical into electric energy. A major goal in SOFC research is the development of cathodes with a sufficiently low electrochemical resistance ͑ϳ0.15 ⍀ cm 2 ͒ at operating temperatures substantially below 800°C. 1-3 It is generally accepted that this is hardly achievable with lanthanum strontium manganite ͑LSM͒-based oxygen electrodes, which are the most thoroughly studied and technically developed SOFC cathodes at the moment. Focus has been shifted toward other materials that offer a sufficient electrochemical performance already in the intermediate-temperature range, and particularly the mixed conducting perovskites of the ͑La,Sr͒͑Co,Fe͒O 3−␦ family are considered as promising candidates.In the literature, activation effects upon dc polarization have been reported for porous LSM and LSM/YSZ ͑yttria-stabilized zirconia͒ composite electrodes, 4-11 as well as for Pt electrodes. 11-13 However, a general agreement on the causes of these activation effects has not been achieved yet, and the reported magnitudes of the effect and the suggested mechanisms strongly vary in the literature. Measurements on morphologically and crystallographically well-defined electrodes are not available but are highly desirable in this context. 11 Moreover, to the best of the authors' knowledge, a significant performance improvement by electrochemical polarization has not been observed for the technologically important class of mixed conducting electrode materials.In this work, a strong electrochemical activation effect is reported for mixed conducting La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3−␦ ͑LSCF͒ electrodes. The performance improvement is achieved...

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.

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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 (ICP) process. Importantly, no traces of plasma-induced damages to the etched surface could be detected by X-ray photoelectron spectroscopy (XPS) 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 12 C isotopically purified diamond revealed a threefold increase in T2 times for NV centers with < 4 nm of depth (measured by NMR signal from protons at the diamond surface) in comparison to the initial oxygen-terminated surface.Keywords: diamond plasma etching, shallow NV centers, surface damage, spin coherence timesThe negatively-charged nitrogen-vacancy (NV) center in diamond has attracted increasing attention due to its outstanding properties. It is an atomic-sized, bright and stable single photon source[1] with relatively long coherence times, ranging milliseconds in isotopically purified single crystal diamond layers [2,3]. Additionally, its electron spin can be coherently manipulated by microwave and readout optically at room temperature. In the recent years the use of near-surface (shallow) NV centers as sensors to detect external nuclear [4][5][6] and electronic [7,8] spins have been successfully demonstrated. However, since the signal detection relies on the relatively weak dipolar coupling to the targeted external spins, decaying proportional to r −3 (with r being the distance between the targeted and sensor spins), NV centers must be located close to the diamond surface (< 5 nm) [4,5].Up to now, the engineering of near-surface NV centers has relied mostly on low-energy nitrogen implantation [9] or epitaxial growth of high quality nitrogen-doped CVD diamond followed by electron[10] or ion irradiation [11]. Furthermore, NV centers can be brought closer to the diamond surface by post-treatments such as thermal oxidation [12,13] and etching in plasma [13][14][15].A major drawback for thermal oxidation is the uncertainty in the resulting etching rate and infeasibility of selective etching. Overcoming these issues, plasma processes are widely employed, providing a smooth and uniform method to selectively etch diamond. In particular for reactive ion etching (RIE) processes, the pres- * Corresponding author: a.denisenko@physik.uni-stuttgart.de ence of a bias between the plasma source and the sample leads to ion bombardment on the diamond surface. This resu...

The x-ray standing wave (XSW) technique is used to measure the isotopic mass dependence of the lattice constants of Si and Ge. Backreflection allows substrates of moderate crystallinity to be used while high order reflection yields high accuracy. The XSW, generated by the substrate, serves as a reference for the lattice planes of an epilayer of different isotopic composition. Employing XSW and photoemission, the position of the surface planes is determined from which the lattice constant difference Deltaa is calculated. Scaled to DeltaM = 1 amu we find (Deltaa/a) of -0.36x10(-5) and -0.88x10(-5) for Ge and -1.8x10(-5) and -3.0x10(-5) for Si at 300 and 30 K, respectively.

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