Propriedades vibracionais de nanotubos e nanobastões de óxido de molibidênio

Abstract

We have studied in this work the vibrational, structural and morphological properties of nanostructured Molybdenum oxide. The investigation is focused in MoO 3 nanorods and MoO 3 nanotubes. Raman spectroscopy measurements in MoO 3 nanorods revealed morphological changes in the 150 o C-350 o C temperature range. No structural phase transitions were observed thus showing the stability of the orthorhombic phase from room temperature (nanorods) up to 750 o C (bulk like phase) where large plates have been formed by the coalescence of the nanorods. This interpretation of temperature-dependent Raman data (frequency and linewidth) is supported by microscopy electronic images which clearly indicate the morphology changes. Single Walled MoO 3 nanotube were found to be very sensitive to laser power density used in the Raman spectroscopy experiments. We establish the experimental conditions for which MoO 3 nanotubes can be studied using Raman spectroscopy. By increasing the thermal treatment temperature we observed at about 220 o C that the Raman spectrum characteristic of single walled MoO 3 nanotubes changes and the new spectrum is identiØed as being originated from the MoO 3 bulk in the orthorhombic phase. Ex situ Raman measurements as a function of temperature conØrm the collapse of the nanotube structure at about 210 o C. Scanning electron microscopy images conØrm the morphology changes in the single walled molybdenum oxide (MoO 3 ) nanotubes for samples treated at diÆerent temperatures. We have showed that Raman spectroscopy is an important technique for investigative both structural and morphological changes in MoO 3 nanostructures