| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 99 === The present thesis has focused on the optical property, especially the polarization-dependent and size-dependent Raman spectroscopic studies on single aluminum nitride nanowire. For the growth of high quality aluminum nitride nanowires, thermal chemical vapor deposition (CVD) was employed. Scanning electron microscopy, x-ray diffraction, high resolution transmission electron microscope measurements and energy dispersive X-ray spectroscopy, revealed aluminum nitride nanowires to be single crystal of low defect.
After transferring the CVD-grown nanowires on another patterned substrate, a micro Raman system was used to investigate well-isolated nanowire. Polarization-dependent Raman scattering of single aluminum nitride nanowire has been clearly observed. In theoretical simulation, intensity of different Raman modes is related to Raman tensor. For wurtzite structure, the relationship between polarization of light (electric field vector) and crystal axis (Raman tensor) of nanowire is a function of two variations (θ & β). The angle θ is the angle between the polarization of light to the long axis of wire, whereas the angle β is the angle between the incident light to the short axis of wire. Our experimental polarized Raman spectra obtained from nanowires with different crystal orientations, m-, a-, c- axis are closed to the simulated results.
The nanowires, with inherently large length to width ratio (~30:1) make their optical property quite different to that of the bulk structure. We have performed a series of Raman studies, using different diameter of nanowires, ranging from 4000 to 30 nm. Strong size-dependent Raman scattering is observed. Enhancement of Raman scattering rapidly increases by orders of magnitude when the diameter of nanowires is reduced to below 158 nm.
|
|---|
