Highly pure, ultralong, and uniform-sized semiconductor nanowires in bulk quantity were synthesized by thermal evaporation or laser ablation of semiconductor powders mixed with oxides. Transmission electron microscopy study shows that decomposition of semiconductor suboxides and defect structures play important roles in enhancing the formation and growth of high-quality nanowires. A new growth mechanism is proposed on the basis of microstructure and different morphologies of the nanowires observed.
We obtained germanium dioxide (GeO2) whiskers in bulk quantity by ablating a germanium target at 820 °C with a pulsed KrF excimer laser in an argon atmosphere. Most of the GeO2 whiskers were smooth and straight with hexagonal or triangular, or quadrilateral cross sections while some of them had a bamboo-shoot-shaped form. Results of scanning electron microscopy, transmission electron microscopy, and x-ray diffraction showed that the whiskers are hexagonal crystalline GeO2.
Bulk-quantity Si nanosphere chains have been fabricated. This is accomplished via the spheroidization of Si nanowires of semi-infinite lengths. The process has been extensively investigated by transmission electron microscopy. The nanosphere chains consisted of equally spaced Si crystalline nanospheres connected by Si-oxide bars. The transition from Si nanowires to Si nanosphere chains was determined by the annealing temperature, ambient pressure, initial Si nanowire diameters, and the oxide state of the outer layers of Si nanowires. The relationships between the geometry (size and spacing) of Si nanospheres, the initial state (diameter and oxide state) of Si nanowires, and the experimental conditions are discussed.
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