| Summary: | 博士 === 國立清華大學 === 電子工程研究所 === 92 === In this dissertation, two topics are discussed. The first part is concerning the rotational anisotropy SHG studies of the group-III nitride compound films on Si(111) substrates. The symmetry behavior of AlN/Si(111) and GaN/AlN/Si(111) structures grown by molecular beam epitaxy (MBE) have been analyzed by measuring the rotational dependence of the polarized second harmonic generation intensity for different polarized fundamental beams. The crystalline structure has also been checked by reflection high-energy electron diffraction (RHEED), X-ray diffraction and photoluminescence (PL) spectroscopy. Considering various contributions of the nonlinear response from the bulk and interfaces, the interface strain implies an nonuniform inhomogeneous intensity variation of second harmonic generation as functions of the surface azimuthal rotation angle ψ.Therefore, the observation of nonlinear optical effect provides a valuable illustration of the epitaxy quality and growth parameter characterization by a nondestructive method.
The second part is about the rotational anisotropy SHG studies of Ag thin films and nanoparticles on Si(111) substrates. The asymmetric distributions of the surface optical second harmonic generation (SHG) through azimuthally angular scans for thin silver films deposited on Si(111) wafers have been detected with different polarizations of output beams. On account of the inversion symmetry of silicon crystals, the SHG for the Ag/Si system is mainly contributed from silver film and silicon surface. In this work, we found that the interface strain implies an asymmetric intensity variation of SHG with respect to the surface azimuthal angle as an ultra thin Ag film is deposited on silicon wafers. This asymmetric behavior is prominent as the deposited silver layer is heated to change from a continuous film to granular nanoparticles. Similar change of the surface asymmetric SHG is observed for a bare Si wafer imposed with an external force or adsorbed with a drop of epoxy glue.
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