Photocurrent studies of individual and isolated VO 2 nanowires (NWs) with Pt metal contacts were conducted by using a focused laser beam. With localized probing, the photoresponse arising from the NW-Pt contact junctions and the main body of the NW can be separately examined. Rapid photoresponse (with and without bias) toward visible and infrared laser irradiation was observed to arise primarily from the NW-Pt contacts. Experiments at elevated temperature (above the semiconductor-metal transition temperature of VO 2 ) revealed a remarkable ∼500 fold enhancement in the photocurrent generated at the NW-Pt contact junctions at zero external bias. Photoinduced thermoelectric effect is proposed as the key carrier transport mechanism dictating the photocurrent generated at the NW-Pt interface.

Photoresponse of isolated Nb(2)O(5) nanowires (NW) padded with platinum (Pt) at both ends were studied with global irradiation by a laser beam and localized irradiation using a focused laser beam. Global laser irradiation on individual NW in ambient and vacuum conditions revealed photocurrent contributions with different time characteristics (rapid and slowly varying components) arising from defect level excitations, thermal heating effect, surface states and NW-Pt contacts. With a spot size of < 1 µm, localized irradiation highlighted the fact that the measured photocurrent in this single NW device (with and without applied bias) depended sensitively on the photoresponse at the NW-Pt contacts. At applied bias, unidirectional photocurrent was observed and higher photocurrent was achieved with localized laser irradiation at reverse-biased NW-Pt contacts. At zero bias, the opposite polarity of photocurrents was detected when the two NW-Pt contacts were subjected to focused laser beam irradiation. A reduced Schottky barrier/width resulting from an increase in charge carriers and thermoelectric effects arising from the localized thermal heating due to focused laser beam irradiation were proposed as the mechanisms dictating the photocurrent at the NW-Pt interface. Comparison of photocurrents generated upon global and localized laser irradiation showed that the main contribution to the photocurrent was largely due to the photoresponse of the NW-Pt contacts.

Single-crystalline MoO3 nanobelts were prepared on a wide variety of substrates by a simple evaporation and deposition process using a thermal hot plate. This cost-effective technique has the potential for large-scale production of MoO3 nanobelts with a unique layered structure. The MoO3 nanobelts dispersed on silicon substrates exhibited a wide variety of colors attributable to the difference in the thicknesses of the nanobelts. Due to the weak interlayer binding, partial and localized removal of the layered nanobelts was readily achieved via atomic force microscope micromachining, resulting in multicolored patterns on individual nanobelts.