We present experimental Raman scattering results on single-crystal silicon monoarsenide (SiAs). Based on a comparison between Raman measurements and first-principles density functional theory calculations, we found evidence that SiAs will occur in a monoclinic crystal structure rather than an orthorhombic one as has been discussed in the literature. Further, we provide a detailed discussion of the vibrational properties of the monoclinic structure

The scattering behavior of neutral ammonia clusters off a LiF(100) surface is studied. Ammonia clusters are produced by a coexpansion of NH and Kr with an average kinetic energy of 48 meV per monomer molecule. Using single photon VUV laser ionization at "118 nm (h "10.49 eV) the mass distribution of scattered particles is obtained in a reflecting time-of-flight mass spectrometer. Compared with the incoming cluster beam the average cluster size of the scattered particles is drastically decreased. The angular distribution of NH> and NH> after scattering reveals a strong inelastic interaction between the clusters and the LiF(100) surface which is described in the context of a thermokinetic model and a phonon excitation along the (001) azimuth of the LiF(100) surface.

Cathodic arc evaporation / Unbalanced magnetron sputtering / High power impulse magnetron sputtering / X-ray diffraction / Transmission electron microscopy / Ab initio calculations Abstract. A combination of microstructure analysis and ab initio calculations helped us to describe the interplay between the microstructure of Cr--Al--Si--N thin film nanocomposites and the ordering of the magnetic moments in the chromium-rich phase of (Cr,Al)N. The microstructure of the Cr--Al--Si--N nanocomposites was modified through the degree of ionisation of the deposited species in three physical vapour deposition processes -cathodic arc evaporation, unbalanced magnetron sputtering and high power impulse magnetron sputtering. According to the results of the ab initio calculations, the magnetic ordering was concluded from the expansion of the elementary cell and from the change of the crystal anisotropy of the elastic constants of (Cr,Al)N; these microstructure features were obtained from X-ray diffraction experiments. The microstructure of the Cr--Al--Si--N nanocomposites was furthermore characterised using the combination of X-ray diffraction and transmission electron microscopy with high resolution in order to obtain information about the phase composition of the thin films, distribution of individual elements and the crystallite size.

We present a general method to calculate thermodynamical properties of crystalline materials from first principles based on density functional theory (DFT). In order to introduce temperature effects we calculate the phonon dispersion for different volumes which allows to include their entropic effects in the Helmholtz free energy. As an example we focus on the calculation of the thermal volume expansion coefficient of tetragonal ZrO2.

It has recently been shown using high-resolution transmission electron microscopy that there may exist an hetero-epitaxial interface between austenitic steel and cubic ZrO2 for a certain crystallographic orientation between these two materials. Here we discuss possible bonding at that interface by means of density-functional-theory calculations. In particular, we use the electron localization function as a measure for bonding across the interface. We find that there should be no strong interface in the case of pure Fe and ZrO2. However, Si or C atoms at the interface layer appear to be able to bridge the interface providing possible covalent bonds. In contrast, metal atoms seem not to be able to provide sufficient changes to connect across the interface. The findings are rationalized in terms of ionic radius and electro-negativity of the atom.