Dissertation > Industrial Technology > General industrial technology > Materials science and engineering > Special structural materials

Designment, Fabrication of Semiconductor/Metal Micro-Nano Structures and Transport Studies in Optical and Electronic Fields

Author ZhaoXingChen
Tutor ZhuJiaZuo;SunJiaLin
School Tsinghua University
Course Physics
Keywords nanowires heterojunctions Schottky nanojunctions photoelectric properties
CLC TB383.1
Type PhD thesis
Year 2010
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The main topics of this dissertation are about the fabrication of silver and nickel nanowires and the heterojunctions formed by metals and corresponding oxysulfides. The heterojunctions were undergone by exterior laser lighting as well as electric field to study their transport characteristics. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were employed to study the morphologies, components and crystal structures of the nanowires detailedly.Firstly, attempts to fabricate silver nanowires in AgNO3 solution show some interesting silver nanostructures, like nanoflakes and dendritic shapes, under different AgNO3 concentration as well as electronic field. Silver nanowires with diameter of 200 nm and length about 10μm were also made in alumina oxide template through electrochemical deposition. Macro-long Ni/Ag heterojunctions with excellent photo-response were got with the as-prepared silver nanowire bundles by state-ionic method.Secondly, nickel nanowire arrays were synthesized by the electrochemical deposition method using an anodic aluminum oxide template with a mean diameter of 200 nm and a length of 60μm. Oxidized in the atmosphere for about 12 h, the exposed surface of the Ni nanowire was oxidized and formed a Ni core/NiO shell architecture. SEM and TEM were introduced to characterize the sample and the band gap of NiO nanolayer could be calculated from the absorbance spectrum. With the help of Atomic Force Microscopy (AFM), single NiO-Ni Schottky nanojunction was studied and semiconductor-metal transition was observed. Furthermore, Au-NiO-Ni dual Schottky nanojunctions were formed, manifesting a replicable, fast-responded switch trait after certain treatments. Due to the face-to-face Schottky contact, forward current was restrained and high ratio of ON/OFF current was available.Finally, through sulfurization of the micro-long silver nanowire bundles, silver sulfide/silver nano-heterojunction was obtained. Unlike the negative photocon- ductivity of silver nanowires, its photoconductivity can change from negative to positive gradually with different silver sulfide thickness, which implies a new approach to manipulate the photoconductivity of nanomaterials.

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