[Spectra and influences of Rayleigh and stimulated Brillouin scattering in fiber-optic distributed disturbance sensor].

Spectra and influences of Rayleigh backscattering (RB) and stimulated Brillouin scattering (SBS) in the fiber-optic distributed disturbance sensor (FDDS) were investigated. Models of RB, double RB (DRB) and SBS in long fibers were established. By numerical simulation, it was found that optical signal-to-noise ratio is extraordinarily reduced due to SBS and RB, which results in location errors. Numerical results were confirmed by experiments and helpful to improving the location precision for applications with long monitored length.

The growth of porous ZnO nanowires by thermal oxidation of ZnS nanowires.

The growth of porous ZnO nanowires (NWs) via phase transformation of ZnS NWs at 500-850 degrees C in air was studied. The ZnS NWs were first synthesized by thermal evaporation of ZnS powder at 1100 degrees C in Ar. On subsequent annealing at 500 degrees C in air, discrete ZnO epilayers formed on the surface of ZnS NWs. At 600 degrees C, polycrystalline ZnO and the crack along the (0001) interface between the ZnO epilayer and ZnS NW were observed. At 700-750 degrees C ZnS NWs transformed to ZnO NWs, meanwhile nanopores and interfacial cracks were observed in the ZnO NWs. Two factors, the evaporation of SO2 and SO3 and the stress induced by the incompatible structure at the interface of ZnO epilayer and ZnS NW, can be responsible for the formation of porous ZnO NWs from ZnS NW templates on annealing at 700-750 degrees C in air. Rapid growth of ZnO at 850 degrees C could heal the pores and cracks and thus resulted in the well-crystallized ZnO NWs.

Ag-catalyzed growth of Ge nanostructures via the thermal evaporation of Ge powder.

The Ag-catalyzed growth of straight Ge nanowires (GeNWs), serrated Ge nanobelts (GeNBs), and hexagonal Ge nanotowers (GeNTs) by thermal evaporation of Ge powder at 950 degrees C in Ar was studied. The growth of GeNWs and GeNBs at 550-600 degrees C followed the top-growth mode via the vapor-solid-solid process, while that of GeNTs at 700-750 degrees C followed the bottom-growth mode via the vapor-liquid-solid process. This result shows that the growth mode of Ge nanostructures catalyzed by Ag nanoparticles is temperature-dependent. The larger size of AgGe droplets assembled at high temperatures is beneficial to the growth of GeNTs with the bottom-growth mode. In addition, the growth mechanisms of Ge nanostructures are discussed.

Room temperature oxidation of Cu(3)Ge films grown on Si and Si(1-x)Ge(x) substrates.

Room temperature oxidation of Cu3Ge films grown on Si, Si(0.85)Ge(0.15) and Si(0.52)Ge(0.48) substrates, respectively, at a temperature of 200-300 degrees C was studied using transmission electron microscopy (TEM) in conjunction with energy dispersive spectrometry (EDS) and scanning electron microscopy (SEM). For Cu(3)Ge films grown at 200 degrees C and subsequently exposed in air for 1 week oxide protrusions and oxide networks appeared in the film surface and grain boundaries of Cu(3)Ge, respectively. At room temperature O from air and Si from the substrate, diffused along the grain boundaries of Cu(3)Ge to react with Cu(3)Ge grains, initiating the Cu(3)Si-catalyzed oxidation. Cu(3)Ge films are superior to Cu(3)(Si(1-x)Gex) films in retarding Cu(3)Si-catalyzed oxidation. Annealing at 300 degrees C allowed Si diffusion from the substrate into the Cu(3)Ge overlayer to form Cu(3)(Si(1-x)Gex), enhancing the Cu(3)Si-catalyzed oxidation rate. In the present study, Cu(3)Ge films grown on Si(0.52)Ge(0.48) at 200 degrees C show the best resistance to room temperature oxidation because higher Ge concentration in the substrate and lower temperature annealing can more effectively retard Si diffusion from the substrate into the Cu(3)Ge overlayer, and hence reduce the Cu(3)Si-catalyzed oxidation rate.