Planar Defects in Formation of Novel Oxide Nanostructures.
Quasi-one-dimensional (1D) nanostructures (nanowires, nanobelts and nanorods) are the forefront nanomateirals for nanotechnology. Oxide nanostructures have been synthesized for a wide range of semiconducting oxides  that are potential building blocks for constructing numerous nanodevices. Using the technique demonstrated for measuring the mechanical properties of nanotubes [2,3], the mechanical and field emission properties of the oxide nanobelts have been characterized. Field effect transistors , ultra-sensitive nano-size gas sensors , nanoresonators and nanocantilevers  have been fabricated using nanobelts. Among all of the oxide nanostructures we have investigated, ZnO is very unusual. The two important characteristics of the wurtzite structured ZnO are the non-central symmetry and the polar surfaces. The structure of ZnO can be described as a number of alternating planes composed of tetrahedrally coordinated O2- and Zn2+ ions, stacked alternatively along the c-axis. The oppositely charged ions produce positively charged (0001)-Zn and negatively charged (000-1)-O polar surfaces, resulting in a normal dipole moment and spontaneous polarization along the c-axis. The polar surfaces give raise a few interesting growth features, such as the formations of nanosprings , nanorings , nanobows  and nanohelices . These nanostructure are semiconductive and piezoelectric and have potential applications as nano-scale sensors, traducers, and actuators. This presentation will be about the synthesis, characterization and potential applications of these novel nanostructures .  Z.W. Pan, Z.R. Dai and Z.L. Wang, Science, 209 (2001) 1947. P. Poncharal, Z.L. Wang, D. Ugarte and W.A. de Heer, Science, 283 (1999) 1513. R.P. Gao, Z.L. Wang, Z.G. Bai, W. de Heer, L. Dai and M. Gao, Phys. Rev. Letts., 85 (2000) 622. M. Arnold, P. Avouris, Z.L. Wang,. Phys. Chem. B, 107 (2002) 659.  E. Comini, G. Faglia, G. Sberveglieri, Zhengwei Pan, Z. L. Wang Applied Physics Letters, 81 (2002) 1869. W. Hughes and Z.L. Wang, Appl. Phys. Letts., 82 (2003) 2886. X.Y. Kong and Z.L. Wang, Nano Letters, 2 (2003) 1625 + cover. X.Y. Kong, Y. Ding, R.S. Yang, Z.L. Wang, Science, 303 (2004) 1348. W.L. Hughes and Z.L. Wang, J. Am. Chem. Soc., 126 (2004) 670 P.X. Gao, Y. Ding, W.J. Mai, W.L. Hughes, C.S. Lao and Z.L. Wang, Science, 309 (2005) 1700. Thanks the support from NSF, DARPA, NASA and Airforce. for details see: http://www.nanoscience.gatech.edu/zlwang/