Über die Natur der niederenergetischen Anregungen in amorphem Arsensulfid

Änderungen der Schallgeschwindigkeit und Dämpfung von akustischen Oberflächenwellen in aufgedampften As2S3-Filmen wurden bei tiefen Temperaturen unter dem Einfluss von Licht verschiendener Wellenlängen gemessen. Während der Belichtung bei Heliumtemperatur verringert sich die Schallgeschwindigkeit unabhängig von der Intensität des Lichts um etwa 4 Nach dem Belichten ist die Temperaturabhängigkeit der Schallgeschwindigkeit und Dämpfung steiler. Die Veränderungen sind im Bereich 325 nm 488 nm wellenlängenunabhängig und lassen sich durch thermisches Ausheilen an der Glasübergangstemperatur vollständig zurücksetzen. Ein Einfluss von Licht niedrigerer Energie (890 nm), was etwa der Hälfte der Bandlücke des amorphen Halbleiters entspricht, wurde nicht beobachtet. Die gemessenen Daten werden im Rahmen des sogenannten Modells der weichen Potentiale diskutiert. Aufgrund der Ergebnisse kann ein Zusammenhang der niederenergetischen Anregungen mit sogenannten valenzalternierenden Paaren weitestgehend ausgeschlossen werden. Stattdessen ist eine enge Verwandtschaft ersterer mit der in a-As2S3 beobachteten licht-induzierten Verringerung der Bandlücke (Photodarkening) wahrscheinlich. Als mikroskopisches Modell für die licht-induzierten Veränderungen im Tieftemperaturverhalten wird die Verkippung und Verdrillung von AsS3-Einheiten vorgeschlagen. Messungen an As2S3/Cu-Filmen mit Kupferkonzentrationen im Bereich 1 - 2,5 haben gezeigt, dass die Beigabe von Kupfer keinen Einfluss auf die akustischen Tieftemperatureigenschaften von a-As2S3 hat. Ein Effekt des Kupfers konnte jedoch in optischen Transmissionsmessungen nachgewiesen werden, wonach das Photodarkening unter dem Einfluss des Kupfers um 30 reduziert ist

Magnetic anisotropy of deposited transition metal clusters

We present results of magnetic torque calculations using the fully relativistic spin-polarized Korringa-Kohn-Rostoker approach applied to small Co and Fe clusters deposited on the Pt(111) surface. From the magnetic torque one can derive amongst others the magnetic anisotropy energy (MAE). It was found that this approach is numerically much more stable and also computationally less demanding than using the magnetic force theorem that allows to calculate the MAE directly. Although structural relaxation effects were not included our results correspond reasonably well to recent experimental data

A highly durable graphene monolayer electrode under long-term hydrogen evolution cycling

Achieving long term stability of single graphene sheets towards repeated electrochemical hydrogen evolution reaction (HER) cycling has been challenging. Here, we show through appropriate electrode preparation that it is possible to obtain highly durable isolated graphene electrodes, which can survive several hundreds of HER cycles with virtually no damage to the sp2-carbon framework and persistently good electron transfer characteristics.Peer Reviewe

Complex domain wall dynamics in compressively strained GaMnAs epilayers

The domain wall induced reversal dynamics in compressively strained GaMnAs was studied employing the magneto-optical Kerr effect and Kerr microscopy. Due to the influence of an uniaxial part in the in-plane magnetic anisotropy (90+/-Delta) domain walls with considerably different dynamic behavior are observed. While the (90+Delta) reversal is identified to be propagation dominated with a small number of domain walls, the case of (90-Delta) reversal includes the nucleation of many domain walls. The domain wall nucleation/propagation energy for both transitions are estimated using model calculations from which we conclude that single domain devices can be achievable using the (90+Delta) mode.Comment: 4 figure

Self-Assembled Nanometer-Scale Magnetic Networks on Surfaces: Fundamental Interactions and Functional Properties

Nanomagnets of controlled size, organized into regular patterns open new perspectives in the fields of nanoelectronics, spintronics, and quantum computation. Self-assembling processes on various types of substrates allow designing fine-structured architectures and tuning of their magnetic properties. Here, starting from a description of fundamental magnetic interactions at the nanoscale, we review recent experimental approaches to fabricate zero-, one-, and two-dimensional magnetic particle arrays with dimensions reduced to the atomic limit and unprecedented areal density. We describe systems composed of individual magnetic atoms, metal-organic networks, metal wires, and bimetallic particles, as well as strategies to control their magnetic moment, anisotropy, and temperature-dependent magnetic behavior. The investigation of self-assembled subnanometer magnetic particles leads to significant progress in the design of fundamental and functional aspects, mutual interactions among the magnetic units, and their coupling with the environment

Magnetic surface nanostructures

Recent trends in the emerging field of surface-supported magnetic nanostructures are reviewed. Current strategies for nanostructure synthesis are summarized, followed by a predominantly theoretical description of magnetic phenomena in surface magnetic structures and a review of experimental research in this field. Emphasis is on Fe- or Co-based nanostructures in various low-dimensional geometries, which are studied as model systems to explore the effects of dimensionality, atomic coordination, chemical bonds, alloying and, most importantly, interactions with the supporting substrate on the magnetism. This review also includes a discussion of closely related systems, such as 3d element impurities integrated into organic networks, surface-supported Fe-based molecular magnets, Kondo systems or 4d element nanostructures that exhibit emergent magnetism, thereby bridging the traditional areas of surface science, molecular physics and nanomagnetism