Structural and optical study of SnO 2 nanobelts and nanowires

Abstract

1D semiconducting SnO 2 nanowires and nanobelts are successfully grown by low cost Chemical Vapour Deposition directly on large area (100 mm 2) Al 2O 3, SiO 2 and Si substrates. The nanocrystals are distributed in a very uniform entanglement in the growth plane over a deposited thickness of about 0.3 mm. Their lateral size ranges from 50 to 700 nm and their length can achieve several hundreds of micrometers. Transmission Electron Microscopy reveals either the nanowires and the nanobelts grow in the tetragonal Rutile structure parallel to a <101> direction. Diffraction contrast analyses and selected area diffraction investigations show the nanowires are single crystals without defects while the nanobelts often present twins inside. An almost cylindrical shape and an average diameter of about 30–50 nm for the smallest nanowire is reported. X-ray diffraction investigations exclude the presence of spurious phases. A broad band structured in two emissions peaked at about 460 nm and 570 nm is revealed by large area Photoluminescence and Cathodoluminescence. No evidence of near band edge transition is found. Single nanobelt spectroscopy carried out by Cathodoluminescence inside the Scanning Electron Microscope shows that reducing the lateral dimension of the nanobelts from 500 to 50 nm, a blue shift of the main emission band of about 20 nm is found at room temperature. The possible role of Oxygen vacancies and surface / volume ratio on the absence of the near band edge emission and on the blue shift of Cathodoluminescence spectra from single nanocrystals is discussed.