Röntgenabsorptionsmessungen an Eisen-, Nickel- und Kupferlegierungen und an amorphem Germanium

1. In this work the X-ray absorption near the K edges of 3d-impurities (V, Cr, Mn, Fe, Co, Ni, Cu, Ga and Ge) in dilute iron, nickel and copper alloys have been measured. A comparison with calculated absorption coefficients based on a KKR band structure calculation has been made. The structure in the absorption edges in due to the structure in the projected, empty electronic density of states. Deviations from the one-electron picture are discussed. Furthermore, the K edge of Cu and the L edges of Pt in the disordered system Cu$_{1-x}$ Pt$_{x}$ have been measured. 2. This work reports on a detailed investigation of the structure of amorphous and partially crystallized germanium by means of X-ray absorption spectroscopy. In a-Ge the interatomic distance of the first neighboring shell agrees within 0.1% with that in c-Ge. The corresponding coordination number, N, is equal to the crystalline value, 4, within the error limit of 1%. On the one hand, this implies that the maximum concentration of vacancies and divacancies in a-Ge is 1% and 0,5%, respectively. The reduced density observed in a-Ge must be due to voids with a minimum diameter of 14 $\mathring{A}$. On the other hand, this result shows that coordination numbers can be determined by EXAFS with an accuracy of 1% provided systematic errors in the data and data analysis are kept small (small harmonic content in the X-ray beam, homogeneous samples and well matched models). The crystallization of amorphous Ge is strongly dependent on the way of production, on the substrate and on the substrate temperature. Films evaporated on Al and Al$_{2}O_{3}$ crystallize between 220 and 290 ° C substrate temperature. Films evaporated on 25 pm Kapton are already crystallized at 220 ° C. Films produced by plasma decomposition of GeH$_{4}$ are still amorphous at 350 ° C. The crystallized areas have a minimum diameter of 190 $\mathring{A}$ as soon as they are detected, as was shown by X-ray diffraction