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During the last 20 years interest in high-resolution x-ray diffractometry and reflectivity has grown as a result of the development of the semiconductor industry and the increasing interest in material research of thin layers of magnetic, organic, and other materials. For example, optoelectronics requires a subsequent epitaxy of thin layers of different semiconductor materials. Here, the individuallayer thicknesses are scaled down to a few atomic layers in order to exploit quantum effects. For reasons of electronic and optical confinement, these thin layers are embedded within much thicker cladding layers or stacks of multilayers of slightly different chemical composition. It is evident that the interface quality of those quantum weHs is quite important for the function of devices. Thin metallic layers often show magnetic properties which do not ap pear for thick layers or in bulk material. The investigation of the mutual interaction of magnetic and non-magnetic layers leads to the discovery of colossal magnetoresistance, for example. This property is strongly related to the thickness and interface roughness of covered layers.
This book presents a physical approach to the diffraction phenomenon and its applications in materials science. An historical background to the discovery of X-ray diffraction is first outlined. Next, Part 1 gives a description of the physical phenomenon of X-ray diffraction on perfect and imperfect crystals. Part 2 then provides a detailed analysis of the instruments used for the characterization of powdered materials or thin films. The description of the processing of measured signals and their results is also covered, as are recent developments relating to quantitative microstructural analysis of powders or epitaxial thin films on the basis of X-ray diffraction. Given the comprehensive coverage offered by this title, anyone involved in the field of X-ray diffraction and its applications will find this of great use.
InAs/GaSb superlattices grown via molecular beam epitaxy, and containing InSb-like interfacial layers, were analyzed with a combination of x-ray diffraction (XRD) and structural refinement techniques. The superlattice refinement from x-rays (SUPREX) method determines with high accuracy the average thicknesses and d-spacings of the individual InAs and GaSb layers in addition to standard structural parameters usually obtained by XRD, such as the modulation length (periodicity), average out-of-plane interplanar spacings, and total thickness. The combined SUPREX/XRD experiments show that the absence of certain odd order satellite features in the x-ray data is due to asymmetric and inhomogeneous lattice strain. \textit{Ex situ}-annealed InAs/GaSb superlattices were studied using atomic force microscopy (AFM) and XRD methods. Results show that annealing at temperatures between 200 °C and 300 °C for 1 hour in HVAC improves the structural quality of these superlattices. Strain relaxation occurs during the annealing process indicating that there are chemical intermixing and anion segregation in the superlattices. The effect of the inner-molecular electron density on the x-ray diffraction profile of a layer-stacked thin film is studied. Important phase information contained in the x-ray diffraction profile of highly anisotropic molecular-based thin films is charaterized. The experimental and calculated results show that the intensity distribution of the diffraction peaks belonging to the same lattice orientation provides important structural information. For example, tilt angle and core electron density of a molecule can be determined from the intensity distribution. The out-of-plane tilt angle relaxation is studied numerically. The results show that the relaxation can only occur at the first phthalocyanine monolayer above the substrate. The lateral grain size effect and the polar angle anisotropy are studied using a three-dimensional model. The FWHM of the center peak in associated rocking curves gives lateral coherence length or lateral grain size, and the ratio of the intensities from the diffraction peaks in normal diffraction curves shows the uniaxial angular anisotropy of the phthalocyanine thin films.
Discusses the advances in methods of research into the structure of Langmuir-Blodgett multilayers and films with the predetermined alternation of molecular layers. Also included are the structural analysis of films on substrates, the diffraction effects associated with very thin films and news on the latest method of determining the packing of molecules in monomolecular layers.