Biogenic formation of photoactive arsenic-sulfide nanotubes by Shewanella sp. strain HN-41.

Microorganisms facilitate the formation of a wide range of minerals that have unique physical and chemical properties as well as morphologies that are not produced by abiotic processes. Here, we report the production of an extensive extracellular network of filamentous, arsenic-sulfide (As-S) nanotubes (20-100 nm in diameter by approximately 30 mum in length) by the dissimilatory metal-reducing bacterium Shewanella sp. HN-41. The As-S nanotubes, formed via the reduction of As(V) and S(2)O(3)(2-), were initially amorphous As(2)S(3) but evolved with increasing incubation time toward polycrystalline phases of the chalcogenide minerals realgar (AsS) and duranusite (As(4)S). Upon maturation, the As-S nanotubes behaved as metals and semiconductors in terms of their electrical and photoconductive properties, respectively. The As-S nanotubes produced by Shewanella may provide useful materials for novel nano- and opto-electronic devices.

The effect of excimer laser annealing on ZnO nanowires and their field effect transistors.

We have investigated the effect of excimer laser annealing on the chemical bonding, electrical, and optical properties of ZnO nanowires. We demonstrate that after laser annealing on the ZnO nanowire field effect transistors, the on-current increases and the threshold voltage shifts in the negative gate bias direction. These electrical results are attributed to the increase of oxygen vacancies as n-type dopants after laser annealing, consistent with the shifts towards higher binding energies of Zn 2p and O 1s in the x-ray photoelectron spectroscopy analysis of as-grown nanowires and laser-annealed ZnO nanowires.

Tuning of operation mode of ZnO nanowire field effect transistors by solvent-driven surface treatment.

We report on the adjustment of the operation voltage in ZnO nanowire field effect transistors (FETs) by a simple solvent treatment. We have observed that by submerging ZnO nanowires in isopropyl alcohol (IPA), the surface of the ZnO nanowires is etched, generating surface roughness, and their defect emission peak becomes stronger. In particular, ZnO nanowire FETs before IPA treatment operate in the depletion-mode, but are converted to the enhancement-mode with a positive shift of threshold voltage after submersion in IPA. This solvent treatment can be a useful method for controlling the operation mode of ZnO nanowire FETs for wide applications of nanowire-based electronic devices and circuits.

Comparison of Si doping effect on GaN nanowires and films synthesized by metal-organic chemical vapor deposition.

We investigated Si doping effect on GaN nanowires and GaN films grown by metal-organic chemical vapor deposition (MOCVD). Si as n-type dopant is incorporated to GaN nanowires and GaN films controlled by SiH4 flow rate (0, 1, 5, 8, and 10 sccm). The charge concentration and mobility of GaN films increased and decreased, respectively, as increasing the SiH4 flow rate, whereas those for GaN nanowires were not influenced by the SiH4 flow rate. Significant vacancies and impurities resulted in the intense yellow band in GaN nanowires as compared with GaN films, which leads to the large device-to-device variation and negligible dependence of Si doping and the SiH4 flux rate on the electrical properties of GaN nanowires.