Crystallographic Characterization of GaN Nanowires by Raman Spectral Image Mapping
Obtaining structural information of nano structured materials often requires electron microscopy for suficient spatial and crystallographic resolution. This study uses Raman spectral imaging to extract information regarding crystalline orientation and structure by non-invasive means. Seeking a correlation between crystallographic facet and favored Raman mode, Gallium Nitride (GaN) nanowires were imaged by confocal Raman microscopy with a 532nm laser, and scanning electron microscopy. Raman spectral maps containing pixel-by-pixel spectra were acquired. Comparison to scanning electron microscope (SEM) images revealed that for regularly-shaped wires at least 230nm in width, the E2 mode is observed more strongly in the [1 1 2] and [-1 -1 2] "smooth" facets of the wire, while the A1(TO) mode is only observed in the [0 0 1] "rough" facet, suggesting a strong surface-structure dependence of Raman signal that can be exploited for imaging. Further experimentation on irregular and small wires that exhibit only the E2 peak, on other favored modes in GaN, and with other group III/V nitrides is recommended.The Journal of Young Investigators is not affiliated with the US Department of Energy. This paper was written by a student intern with the Department of Energy and does not constitute a declarative position of either the Department of Energy or the Journal of Young Investigators.