Optical and electrochemical properties of nanoscale materials.

摘要

Properties of porous silicon carbide (PSC), relaxor ferroelectric lead zinc niobate-lead titanate (PZN-PT), and nanoparticle oxides barium titanate and cerium oxide are examined. Electrochemical impedance spectroscopy during PSC formation indicates that for the conditions studied the charge transfer is Tafel-like. A combination of the space charge layer, surface states and the formation of a passivating film are involved during the formation of the porous film, and the evolving porous layer does not significantly impede charge transfer. Visible blue photoluminescence (PL) is observed at room temperature from PSC and a brief thermal oxidation is observed to increase the PL intensity. Infrared reflectance in the reststrahl band is shown to be sensitive to different stages of the brief oxidation and is modeled using effective medium theory. An effective medium model of PSC derived from a linear combination of the spectral distribution functions of phenomenological models gives the best agreement with observed IR spectra and is attributed to a wide spectrum of surface optical phonons. The use of PSC as a substrate for the regrowth of high quality SiC is demonstrated using polarized Raman scattering and electron microscopy, opening up a new process route for preparing isolated and micromachined structures in 6H-SiC and related materials.; Temperature-dependent polarized Raman scattering of the relaxor ferroelectric PZN-PT permits unambiguous noncontact measurement of structural and ferroelectric phase transitions, hysteresis and identification of long-range ferroelectric ordering, as well as a means of studying ferroelectric nanodomains in this material.; Raman studies of barium titanate and cerium oxide nanoparticles enable the study of size-induced effects on the Raman peak position and lineshape, providing information about the structural composition, structural and ferroelectric phases, phonon confinement, strain, and presence and contribution of defects. Optical absorption spectra of cerium oxide nanoparticle solutions at different stages of synthesis show evidence of quantum confinement, and can provide information about the kinetics of the synthesis process. The cerium oxide nanoparticles and micron-sized particles exhibit a novel, light-induced, temperature-dependent and reversible light emission.