Heteroepitaxial growth of metal thin films on chiral and achiral ceramic substrates.

摘要

This thesis describes the growth and characterization of heteroepitaxial metal thin films grown on single crystal ceramic substrates. Metals are deposited by pulsed laser deposition (PLD) and analyzed by X-ray diffraction, atomic force microscopy, low-energy electron diffraction (LEED), and transmission electron microscopy. The films are grown on low-index substrates as well as on high-index chiral substrates, with the goals of depositing films having both (1) flat surface morphologies and (2) epitaxial orientations.; Heteroepitaxial (111)-oriented Pt and Cu thin films were first successfully deposited on SrTiO3(111) substrates. Multiple in-plane rotational domains were observed by XRD for these thin films and are shown by density functional theory calculations to result from a stacking fault in the second metal monolayer. High-quality epitaxial thin films of (100)-oriented fcc metals (Pt, Cu, Ag, Au) can also be grown by PLD on single crystal (100)-oriented cubic ceramic substrates (SrTiO3, LaAlO3, and MgO). For both orientations, a substrate chemical and thermal treatment before film growth produces flat, well-crystallized surfaces having a step-terrace structure.; A three-step deposition procedure that consists of (1) depositing epitaxial seeds at high temperature, (2) growing a smooth film at low temperature, and (3) post-annealing to promote templated grain growth, was effective for attaining flat, epitaxial metal thin films. The structural characteristics of Pt, Cu, Ag, and Au thin films depend on both kinetic and thermodynamic factors, including oxygen affinity, surface energy anisotropy, surface diffusion, and supersaturation.; This work demonstrates that thin metal films having chiral surfaces can be achieved by using naturally chiral ceramic substrates as growth templates. Chirally-oriented SrTiO3(621) single crystals were shown by LEED to have a net surface chirality. These naturally chiral substrates promote the heteroepitaxial growth of (621)-oriented Pt and Cu thin films. Samples grown by three-step processing were again shown to have epitaxial (chiral) bulk orientations and relatively flat surfaces. The surfaces of flat, epitaxial Pt(621) films were evidenced to be homochiral by LEED patterns. This result demonstrates that materials having surfaces with a net chirality can be produced by heteroepitaxial growth of metals on chirally-oriented ceramic substrates and offers promise for the development of large-area enantioselective catalysts.