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Novel applications of micro-reflectance difference spectroscopy in condensed matter physics

Authors Wang, Chunhua
Issue Date 2009
Summary Reflectance difference/anisotropy spectroscopy (RDS/RAS) has become a widely used technique to measure the anisotropy in materials since its development in the late 80‘s. It is often performed as a function of wavelength and the specific peaks can provide much information of the structure and electronic state in a material. In this thesis I demonstrate the new applications of spatially resolved microscopic-RDS (micro-RDS). In this study, anisotropic domains were observed in epitaxial AlN layers grown on Si and sapphire substrates. They were identified to be strain domains and the strain calculated from the RD signal corresponded well with most existing experimental values. Depending on the growth process the strain domains were in the sub-micrometer to several micrometers scale. Each domain consists of hundreds of AlN grains. Anisotropic domains were also observed in magnetic CrSe/Fe and La0.7Sr0.3MnO3 materials. They changed under external fields so we knew they were related to magnetization. By adjusting the aperture between the objective lens and the sample surface, the in-plane magnetization and off-plane magnetization can be discriminated. Geometrical optical approximation was found inapplicable to the experiments and we proposed an explanation based on nano-optical principle. The temperature-dependence MDs in CrSe/Fe, La0.7Sr0.3MnO3 and Ga0.95Mn0.05As were studied. The size of MDs was observed to increase when the temperature was lowered. For GaMnAs, the formation of MDs was observed when the temperature decreased from above the Curie temperature Tc to below Tc. We also used the micro-RDS to search the spin Hall Effect in several kinds of semiconductor materials including InGaAs/InAlAs, ZnSe, and HgTe. No spin accumulation was detected at the unit edges, meaning no spin Hall Effect existed. The reason may lie on the serious scattering caused by the defects. Finally the potential applications of micro-RDS in condensed matter physics were discussed.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2009
Language English
Format Thesis
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