| Recently, a series of binary semiconducting oxide nanobelts (or nanoribbons), such as ZnO, In2O3, Ga2O3, CdO and PbO2 and SnO2, have been successfully synthesized in Dr. Zhong C. Wang’s laboratory at the Georgia Institute of Technology by simply evaporating the source compound (Science, 209 (2001) 1947). The as-synthesized oxide nanobelts are pure, structurally uniform, single crystalline and most of them are free from defects and dislocations; they have a rectangular-like cross-section with typical widths of 30~300 nm, width-to-thickness ratios of 5~10 and lengths of up to a few millimeters. The belt-like morphology appears to be a unique and common structural characteristic for the family of semiconducting oxides with cations of different valence states and materials of distinct crystallographic structures. Using Nanobelts to Understand Transport Phenomena in Functional Oxides, and Industry Applications of Nanobelts The nanobelts are an ideal system for fully understanding dimensionally confined transport phenomena in functional oxides and building functional devices along individual nanobelts. This discovery has been reported by over 20 media and professional society journals. Dr. Wang’s Nanotechnology and Nanoscience Group in the School of Materials Science and Engineering of the Georgia Institute of Technology has recently applied the nanobelt materials to make the world’s first field effect transistor and single wire sensors. Industry Applications for Piezoelectric Nanobelts The latest breakthrough is the success of the first piezoelectric nanobelts and nanorings for applications as sensors, transducers and actuators in micro- and nano-electromechanical systems (Science, 303 (2004) 1348). Owing to the positive and negative ionic charges on the zinc- and oxygen-terminated ZnO basal planes, respectively, a spontaneous polarization normal to the nanobelt surface is induced. Helical Nanosprings and Nanocoils, Piezoelectricity, and Ferrolectricity at the Nanoscale As a result, helical nanosprings/nanocoils are formed by rolling up single crystalline nanobelts. The mechanism for the helical growth is suggested for the first time to be a consequence of minimizing the total energy contributed by spontaneous polarization and elasticity. The nanobelts have widths of 10-60 nanometers and a thickness of 5-20 nanometers, and they are free of dislocations. The polar surface dominated ZnO nanobelts and helical nanosprings are likely to be an ideal system for understanding piezoelectricity and polarization-induced ferroelectricity at nanoscale. |
