Semiconductors Via Combustion

Combustion synthesis is a low-cost, low-tech, and energy-efficient preparation method that can be used to synthesize nanocrystalline tungsten trioxide, an important inorganic oxide semiconductor, according to Krishnan Rajeshwar, Norma R. de Tacconi, and coworkers at the University of Texas, Arlington (J. Am. Chem. Soc., DOI: 10.1021/ja8012402). Inorganic oxides such as WO₃ and TiO₂ are widely used in photovoltaic devices, in photocatalytic generation of hydrogen from water, and in related applications. Tungsten trioxide typically is synthesized in a variety of forms via chemical vapor deposition, electron-beam evaporation, and other high-tech procedures. Rather than using those methods, the UT Arlington team prepared the oxide by combusting a peroxopolytungstic acid derivative with compounds such as glycine, urea, and thiourea, which function as fuels. The researchers report that the particles of the combustion products tend to be three to four times smaller (10- to 20-nm diameter) and exhibit a lower band gap than commercial samples of WO₃. The band gap, an optoelectronic property that depends on "dopant" atoms originating in the fuel, can be tailored to broaden the spectrum of sunlight that can be absorbed by WO3, the team says.