ABSTRACT
We report the growth of ultrathin single-crystal ZnO nanobelts by using a Ag-catalyzed vapor transport method. Extensive transmission electron microscopy and atomic force microscopy measurements reveal that the thickness of the ultrathin ZnO nanobelts is approximately 2 nm. Scanning electron microscopy and post-growth annealing studies suggest a '1D branching and 2D filling' growth process. Our results demonstrate the critical role of catalyst in the deterministic synthesis of nanomaterials with the desired morphology. In addition, these ultrafine nanobelts exhibit stable field emission with unprecedented high emission current density of 40.17 mA cm(-2). These bottom-up building blocks of ultrathin ZnO nanobelts may facilitate the construction of advanced electronic and photonic nanodevices.
ABSTRACT
Controlled synthesis of one-dimensional materials, such as nanowires and nanobelts, is of vital importance for achieving the desired properties and fabricating functional devices. We report a systematic investigation of the vapor transport growth of one-dimensional SnO(2) nanostructures, aiming to achieve precise morphology control. SnO(2) nanowires are obtained when SnO(2) mixed with graphite is used as the source material; adding TiO(2) into the source reliably leads to the formation of nanobelts. Ti-induced modification of crystal surface energy is proposed to be the origin of the morphology change. In addition, control of the lateral dimensions of both SnO(2) nanowires (from approximately 15 to approximately 115 nm in diameter) and nanobelts (from approximately 30 nm to approximately 2 microm in width) is achieved by adjusting the growth conditions. The physical properties of SnO(2) nanowires and nanobelts are further characterized and compared using room temperature photoluminescence, resonant Raman scattering, and field emission measurements.
ABSTRACT
The origin of the magnetism in some oxide-based diluted magnetic semiconductors is still a puzzle. In this work, significantly ferromagnetic states of the oxygen-depleted In(2)O(3)(001) surfaces are investigated on the basis of first-principles density functional calculations. Our results show that the perfect oxygen-depleted surfaces are nonmagnetic; however, the surface states become ferromagnetic with the appearance of vacancies on the most outward In sites. The origin of the surface state magnetization can be explained using the Stoner model, and the exchange coupling between surfaces In s-p hybridization orbitals implies a ferromagnetic ground state. Our investigation gives a reasonable explanation for the source of the magnetism in oxygen-depleted In(2)O(3) nanostructures observed in previous experiments.
ABSTRACT
Single-crystalline Ni nanowires have been successfully fabricated with anodic aluminum oxide as template by electrodeposition. Structural characterization (X-ray diffraction, XRD, and high-resolution transmission electron microscopy, HRTEM) shows that the single-crystalline Ni nanowire has a preferred orientation along the [220] direction. The effects of electrochemical deposition conditions on the structure of Ni nanowires are systematically studied to investigate the growth mechanism. Possible reasons for the growth of the single-crystalline Ni nanowires were discussed on the basis of electrochemistry and thermodynamics. These single-crystalline Ni nanowires have exhibited excellent magnetic properties (large anisotropy, large coercivity, and high remanence). By a similar process, single-crystalline Co nanowires with hexagonal close-packed (hcp) structure were achieved, also having large anisotropy, large coercivity (1.8 kOe), and high remanence ratio (80.8%).
