We report results for the electronic structures of extended silver single-wall nanotubes ͑AgSWNTs͒ within a first-principles, all-electron self-consistent local density functional approach adapted for helical symmetry. We carried out calculations on twenty-one different AgSWNTs ranging in radii from approximately 1.3 Å to 3.6 Å. AgSWNTs with radii greater than 2.2 Å were also calculated with a silver atomic chain inserted along the nanotube axis; we refer to these composite structures as silver nanowires ͑AgNWs͒. Energetic trends for the AgSWNTs are not as predictable as expected. For example, the total energy does not necessarily decrease monotonically as nanotube radius increases, as is the case for single-wall carbon nanotubes. The conductivity of these AgSWNTs and AgNWs is also addressed. Similar to the case for helical gold nanowires, the number of conduction channels in the AgSWNTs does not always correspond to the number of atom rows comprising the nanotube. However, for all AgNWs considered, the additional silver atomic chain placed along the tube's axis results in one additional conduction channel.
A series of PbSe thin films grown on a (111)-oriented Si substrate by molecular beam epitaxy were passivated by high-purity oxygen at different annealing temperatures. The photoluminescence intensity increased by more than two orders of magnitude at 4.5μm after annealing the samples in an O2 atmosphere at 350°C. X-ray photoelectron spectroscopy revealed that PbO and SeO2 were formed during the oxidation process of PbSe, thus confirming the formation of the surface passivation layer which resulted in the observed significant increase in PL intensity.
We report simulations of the electronic structures and optical properties of ZnO single-wall nanotubes (SWNTs) within a first-principles, local-density functional approach adapted for helical symmetry. Recent theoretical reports have addressed the possibility of ZnO existing in flat graphitic-like sheets as well as a single-wall nanotubular structures analogous to carbon nanotubes. We present results for a range of different ZnO SWNTs, both chiral and achiral, with radii ranging from approximately 2.10 to 5.02 Å. Optical cross-sections for these nanostructures were estimated on the basis of the first-principles electronic structure results. The optical absorption spectra exhibited a first optical absorption peak associated with a direct transition that remained relatively stationary as nanotube radius varied but with a second direct optical peak blue-shifting with decreasing nanotube radius.
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