Nanostructures by gas-phase reactions: Growth and applications

Gas-phase reactions between H2 and SnO2 surfaces led to novel nanostructures. Nanosheets of SnO2 were produced by a gas-phase reaction of solid SnO2 sintered disks in a reducing atmosphere between 700 and 800 degrees Celsius. The surface morphology was controlled by varying the reaction time and partial pressure of oxygen. It was found that SnO2 was etched by a reaction between H2 and lattice oxygen and a loss of SnO to the vapor phase. Single-crystalline nanofibers of SnO2 were synthesized by a gas-phase reaction of solid SnO 2 sintered disks in a reducing atmosphere between 650 and 750 degrees Celsius. The resulting nanostructures grew on regions of the sample that were coated with gold, which acted as a collector of SnO vapor. The nanofiber length was controlled by varying the reaction time and by the sintering agent used to densify the SnO2. SnO2 thin films were manufactured using DC reactive magnetron sputtering from a tin target in an Ar/O2 atmosphere. After exposure to H2 gas at temperatures between 600 and 680 degrees Celsius, nanofibers were grown on the surface with the aid of gold particles. The nanofiber growth was controlled by varying the reaction time and the orientation of the SnO2 films. The gold was shown to be necessary for both initiation and continuation of growth. Sensing tests were conducted with pure TiO2 and mixed oxide samples of TiO2 and SnO2 sintered samples having different surface areas. Nanostructures of solid solutions and spinodally decomposed samples of mixed oxides of SnO2 and TiO2 were compared to the oriented nanofibers formed in pure TiO2 created by the same heat treatment. Thin films with SnO2 nanofibers were also tested for their sensing response to H2. Comparisons between the sensing characteristics of the samples were made to determine that those samples with high surface areas and those with a gold coating were more sensitive to H2 in the presence of O2.