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In this work We report on the extensive characterization of amorphous silicon carbide (a-SiC) coatings prepared by physical deposition methods. We compare the results obtained on two different sputtering systems (a standard RF magnetron sputtering and a ion-beam assisted sputtering) to seize the impact of two different setups on the repeatably of the results. After a thorough characterization of structural, morphological, and compositional characteristics of the prepared samples, we focus on a detailed study of the optical and mechanical losses in those materials. Mechanical losses are further investigated from a microscopic point of view by comparing our experimental results with molecular dynamic simulations of the amorphous SiC structure: first we define a protocol to generate a numerical model of the amorphous film, capturing the main features of the real system; then we simulate its dynamical behaviour upon deformation in order to obtain its mechanical response. Our results are discussed within the perspective application of a-SiC as an optical material for high-precision optical experiments and in particular in gravitational wave interferometry., Comment: 30 pages, 11 figures

Despite its potential in the fields of optoelectronics and topological insulators, experimental electronic band structure studies of Bi-doped GaAs are scarce. The reason is the complexity of growth which tends to leave bulk and in particular surface properties in an undefined state. Here we present an in depth investigation of structural and electronic properties of GaAsBi epilayers grown by molecular beam epitaxy with high (001) crystalline order and well-defined surface structures evident from low-energy electron diffraction. X-ray and ultraviolet photoemission spectrocopy as well as angle-resolved photoemission data at variable photon energies allows to disentangle a Bi-rich surface layer with $(1\times3)$ symmetry from the effects of Bi atoms incorporated in the GaAs bulk matrix. The influence of Bi concentrations up to $\approx 1$\% integrated in the GaAs bulk are visible in angle-resolved photoemission spectra after mild ion bombardment and subsequent annealing steps. Interpretation of our results is obtained via density functional theory simulations of bulk and $\beta 2(2\times 4)$ reconstructed slab geometries with and without Bi. Bi-induced energy shifts in the dispersion of GaAs heavy and light hole bulk bands are evident both in experiment and theory, which are relevant for modulations in the optical band gap and thus optoelectronic applications., Comment: 13 pages, 15 figures

We present the manipulation of magnetic and electrical properties of (Ga,Mn)As by the adsorption of dye-molecules as a first step towards the realization of light-controlled magnetic-semiconductor/dye hybrid devices. A significant lowering of the Curie temperature with a corresponding increase in electrical resistance and a higher coercive field is found for the GaMnAs/fluorescein system with respect to (Ga,Mn)As. Upon exposure to visible light a shift in Curie temperature towards higher values and a reduction of the coercive field can be achieved in photo-sensitized (Ga,Mn)As. A mayor change in the XPS spectrum of (Ga,Mn)As indicates the appearance of occupied levels in the energy range corresponding to the (Ga,Mn)As valence band states upon adsorption of fluorescein. This points towards a hole quenching effect at the molecule-(Ga,Mn)As interface which is susceptible to light exposure., Comment: 4 pages, 4 figures

Extensive Kerr microscopy studies reveal a strongly temperature dependent domain wall dynamics in Hall-bars made from compressively strained GaMnAs. Depending on the temperature magnetic charging of domain walls is observed and nucleation rates depend on the Hall-geometry with respect to the crystal axes. Above a critical temperature where a biaxial-to-uniaxial anisotropy transition occurs a drastic increase of nucleation events is observed. Below this temperature, the nucleation of domains tends to be rather insensitive to temperature. This first spatially resolved study of domain wall dynamics in patterned GaMnAs at variable temperatures has important implications for potential single domain magneto-logic devices made from ferromagnetic semiconductors., Comment: Figures 2 and 6 not correctly TeXified

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 figures

Mulheran and Blackman have provided a simple and clear explanation of the scale invariance of the island size distribution at the early stage of film growth [Phil. Mag. Lett. 72, 55 (1995)]. Their theory is centered on the concept of capture zone properly identified by Voronoi cell. Here we substantiate experimentally their theory by studying the scale invariance of InAs quantum dots (QDs) forming on GaAs(001) substrate. In particular, we show that the volume distributions of QDs well overlap the corrisponding experimental distributions of the Voronoi-cell areas. The interplay between the experimental data and the numerical simulations allowed us to determine the spatial correlation length among QDs.

The two- to three-dimensional growth transition in the InAs/GaAs(001) heterostructure has been investigated by atomic force microscopy. The kinetics of the density of three dimensional quantum dots evidences two transition thresholds at 1.45 and 1.59 ML of InAs coverage, corresponding to two separate families, small and large. Based on the scaling analysis, such families are characterized by different mechanisms of aggregation, involving the change of the critical nucleus size. Remarkably, the small ones give rise to a wealth of "monomers" through the erosion of the step edges, favoring the explosive nucleation of the large ones., Comment: 10 pages, 3 figures. Submitted to Phys. Rev. Lett