Synthesis and characterization of In₂O₃ micro- and nano-structures at low temperatures by the CSVT technique

Indium oxide microstructures were synthesized by close-spaced chemical vapor transport (CSVT) technique at low temperatures and without the use of catalysts. Morphological characterization by scanning electron microscopy (SEM) showed that the CSVT technique provides high mass-transport efficiency at temperatures as low as 650°C, considering that indium oxide powders were used as a source for the synthesis. It is observed that the microstructures are formed mainly of cubes with semi-spheroids attached to their faces. Additional measurements of X-ray (XRD), Raman, and Energy-dispersive X-ray spectroscopy (EDS) showed that the cubes tend to have the stoichiometry of cubic indium oxide while the semi-spheroids have a metallic nature. The microstructures were converted to indium oxide nanobelts by a simple post thermal annealing during 16 hours in a nitrogen environment, according to the morphological and structural characterizations. The results revealed that the indium oxide nanobelts have several micrometers in length with rectangular cross sections in the range from 50 to 250 nanometers and correspond to indium oxide in the cubic and face-centered phases. The growth mechanisms of the micostructures and nanobelts are discussed in detail.