High-temperature Synthesis And Application Of Heterostructures Composites

With the development of modern society, a variety of toxic, hazardous, flammablegases have influenced seriously human living environment. The development of gassensors can detect a variety of target gas quickly and accurately, which was one of theimportant tasks of scientific research. The requirements of gas sensor included highsensitivity, good selectivity and stability, and mild operating temperature. ZnO, a wideband-gap semiconductor, has applied in light-sensitive material for long research.However, its UV excitation with wavelengths shorter than380nm was required toinduce effective charge separation for gas sensing process, which greatly hindered itspractical application. Therefore, narrow band-gap semiconductors (eg, CdS, Bi2S3,CdSe, PbS, LnP) as sensing materials in the visible light excitation gas sensing wererising today. This thesis included the following three aspects:(1) A visible light enhancement gas sensor based on cadmium selenide (CdSe)nanoribbons has been successfully developed. These nanoribbons were synthesized witha gold-catalyzed vapor-liquid-solid method and employed as visible-light-activatedgas-sensing for50to1000ppm ethanol at200℃. Visible light illumination on thesurface of CdSe nanoribbons could produce more electrons and increase theconductance of the sensor, which significantly enhanced the gas response.(2) CdSe/ZnO heterostructure was obtained via high temperature method andemployed as gas-sensors to improve the gas-sensing activity of ZnO-based device.Scanning electron microscopy, X-ray diffraction, transmission electron microscopy andenergy dispersive X-ray were employed to confirm the CdSe/ZnO heterostructure. Theheterostructure composite was applied in gas-sensing detection of low concentrations ofethanol. Moreover, the CdSe/ZnO materials exhibited a dramatic improvement in dark and visible-light-irradiation gas sensing activity, which was larger than that of ZnOnanorods in response to ethanol at160℃. The enhancement of sensing properties wasattributed to their advanced heterostructure and visible light illumination.(3) Highly ordered setaria-like Si/SiOx-Sn hierarchical heterostructures weresuccessfully fabricated via thermal evaporation process. The peculiar structures werecharacterized by scanning electron microscopy, X-ray diffraction, transmission electronmicroscopy and energy dispersive X-ray. A preliminary study on the formationmechanism was carried out. In addition, when Si/SiOx-Sn was annealed for half an hourin the furnace, an emission peak at560nm appeared in the luminescence spectra, whichwas attributed to the SnO2that came from the oxidation of Sn. They might havepotential applications in fiber optic fluorescence gas sensor due to thephotoluminescence of Si/SiOx-SnO2.