Growth and characterization of ZnO, SnO2 and ZnO/SnO2 nanostructures from the vapor phase

Zinc oxide (ZnO), tin dioxide (SnO2) and compounds ZnO/SnO2 (ZTO) nanostructures have been synthesized successfully from the vapor phase without a catalyst using three different approaches. XRD analyses showed that ZnO with a wurtzite crystal structure, SnO2 with a rutile crystal structure and zinc stannate (ZnSnO3) and/or dizinc stannate (Zn2SnO4) were condensed from the vapor phase when Zn and/or Sn metal powders or their oxides individually or mixed were used as the starting materials. The formation of either zinc or dizinc stannate was controlled by the Zn/Sn ratio and growth technique. SEM and TEM investigations showed that ZnO grew mainly in the form of wires, rods and belts. These are believed to be originated from the common tetrapod structure of ZnO. While SnO2 grew in the form of tetragonal rods with rectangle-like cross section and nanoparticles, ZTO grew in the form of nanobelts. The final length, width and thickness were as low as 40, 10 and 5 nm, respectively. The driving forces for growth of nanowires, nanorods, nanobelts, and nanoparticles were found to be vapor density or supersaturation, temperature, pressure and location of deposition from the source materials. The optical absorbance and photoluminescence spectra of all samples showed excitonic character at room temperature implying good crystal quality, and high photocurrent properties suggesting possible applications in nanoscaled functional devices such as optoelectronics and gas sensors.