Part A. Depth-dependent lattice parameter variation and stress induced magnetic anisotropy of $Dy_2BiFe_4GaO_12$ garnet films by pyrolysis
$Dy_2BiFe_4GaO_12$ thin films were synthesized by pyrolysis on the glass substrate and rapid thermally annealed and/or furnace-annealed in the glass transition range. The lattice parameters were determined by grazing incidence x-ray in asymmetric Bragg diffraction(GIABD). X-ray diffraction results show that film stress is compressively greater near the glass/film interface and becomes smaller in magnitude toward the free film surface. This observation has been interpreted as a result of softening of the glass substrate during annealing in the glass transition range and the subsequent larger shrinkage of the glass substrate with respect to the deposited crystalline film upon cooling. The thermal expansion difference between the substrate and the deposited film can in turn cause the stress-induced magnetic anisotropy(SIMA). A few researchers so far have simply determined the stress based on the thermal expansion coefficients both of the deposited film and the glass substrate at room temperature and apply them even in high temperatures. Likewise, SIMA of garnet films has been also determined via typical material constants (e.g. thermal expansion coefficients of the film and the substrate, magnetostriction coefficient etc.) regardless of their thickness variation. However, especially for the glass substrate, its linear thermal expansion behavior near room temperature may not be extrapolated well into the glass transition range since glass exhibits sudden large jump in thermal expansion in the glass transition range. Therefore, the primary goal of this thesis is to investigate the lattice parameter variation as a function of depth from the free surface of ultra thin $Dy_2BiFe_4GaO_12$ garnet films for magneto-optic application and subsequently how it affect the SIMA of films with respect to the thickness variation. The induced magnetic anisotropy factor $K_u$ has the maximum value above a threshold film thickness, about 600Å. Down to this limit, $K_u$ increases with the decreasing film thickness. On the other hand, the coercive force is seen to increase with the increasing film thickness. This coercivity behavior seems to stem from the nonhomogeneous crystal structure of thin films which may tend to amplify with the volume fraction as the film thickness increases.
Part B. Analysis of the interface roughness of $CoSi_2/Si$ and $Al_xGa_{1-x}As/GaAs$ buried layer system by specular and diffuse x-ray scattering
There has recently been a veritable explosion of interest in x-ray reflectivity as a tool for studying surface and interface structure on microscopic length scales. X-ray reflectivity studies of the structure of the surface have been given a powerful boost with the advent of synchrotron radiation. In this thesis, the scatteringof x-rays from rough surfaces is calculated. It is split into specular reflection and diffuse scattering terms. Specular reflection term is calculated by Parratt's recursive formula with the Tanh type roughness model. Then, diffuse scattering term is calculated in the first Born approximation(BA), and explicit expressions are given for surfaces whose roughness can be described as self-affine over finite length scales by fractal concept. The distorted-wave Born approximation(DWBA) is next used to treat the case where scattering is large(i.e., near the critical angle for total external reflection). The computer simulation studies are carried out on the case that assumed that buried single crystalline layers of $CoSi_2$ in Si are produced by ion beam synthesis. Nonlinear differential equation(Kardar-Parisi-Zhang theory) is introduced as a relevant continuum model describing atomistic kinetic growth under ideal MBE conditions. Based on this theory, two different cases of the buried single crystalline $Al_xGa_{1-x}As$ layer in GaAs are presented to simulate the specular and diffuse scattering. Finally, diffuse scattering results of $GaAs/Al_xGa_{1-x}As$ are compared with experimental results on x-ray scattering by Y.H.Phang et al.
