Raman and Photoluminescence Spectroscopy Investigations of ZnO Nanostructures
B. Chen, H.T. Ng and C. Chen
NASA Ames Research Center, US
ZnO, nanowire, metal oxides, Raman spectrum, photoluminescence spectra
One-dimensional inorganic nanowires are expected to play important roles in optoelectronic device applications. The unique properties such as grain boundary and high surface area of these nanostructures are clearly different from the corresponding bulk material.
Highly orientated ZnO nanowires are studied with Raman and photoluminescence spectroscopy. The high efficiency of the phonon and electron coupling enable us to observe up to 4th order of the Raman scattering. The nanowire orientation relative to the substrate correlated to optical characteristics will be discussed. The results are analyzed and compared with other forms of ZnO such as thin film, polycrystalline powder and solid. The Raman bandwidths and shifts were also studied to reveal the difference in the nanowire to investigate phonon confinement. This confinement is further demonstrated with In2O3 nanowires at 5, 10, 20, 30 nm in diameter. Photoluminescence results show the band gap shifts with the different nanowire sizes. Raman spectroscopy reveals the structural changes related to the strain with the unique properties of nanowire. We will discuss that how the sizes, as well as the defects and the strains possibly induced by the synthesis conditions, influence the band structure and optical phonon properties. We demonstrate the changes of the band gap in the concept of the strain associated with the nanometer structure of nanowires with the correlation between the increased band gap and decreased lattice constants of InN nanowire of 20 nm diameter. Preliminary results from the other Ga2O3, SnO2, CdO and GaN nanowires will also be discussed in the context.
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Nanotech 2006 Conference Program Abstract