Raman Studies of Semiconducting Oxide Nanobelts

Crystalline nanobelts of ZnO and SnO₂ were prepared from a thermal evaporation of oxide powders inside an alumina tube in the absence of catalysts. Typical dimensions of the nanobelt samples ranged from ∼ 10 to 100 μm in length, 30 to 300 nm in width, and 6 to 30 nm in thickness. Room temperature Raman spectra were obtained on pressed mats of nanobelt samples and compared with the corresponding spectra of the starting oxide powders and bulk materials. Collectively, our Raman data indicated that the as-prepared nanobelt samples used in this study were oxygen deficient. Upon annealing at 900 °C in flowing oxygen for 1 h, the nanobelt samples exhibited Raman features that corresponded to those expected in respective bulk semiconducting oxides. The dimensions of the nanobelts were a bit too large to expect significant quantum size effects on the phonon structure similar to those observed in carbon nanotubes and short-period semiconductor superlattices.