Selenium, Tellurium And Their Compound Nanowires --------liquid-phase Chemical Synthesis And Their Application In Nano-electronic Device

Group VI elements selenium (Se) and tellurium (Te) comprise a class of narrow bandgap semiconductors which exhibit excellent photoconductivity, piezoelectric effect and nonlinear optical property; and they show promise in boosting computing speed when doped into silicon. Ease in converting into other functional materials such as CdSe,Ag2Se,HgCdTe or CdTe further widened the application in thermoelectronics and piezoelectronic devices, photoconductors, and photovoltaic modules. In the booming era of nanotechnology, the science and technology of an easy, inexpensive, mass productive synthesis route for Se and Te as well as the control on their nanostructure are of essential significance.Since the first introduction by Xia's group, the liquid reducing route for synthesizing Se and Te nanowires has attracted great interest due to its low reaction temperature, mild reaction, and high purity and crystallinity of product without expensive and delicate equipments.In this work, nanowire were growth by the liquid reducing route, including the controlled synthesis of Te nanowires, the first successful synthesis of Se/Te heterojunction nanowires, the green chemical synthesis of Te nanowires, and templated conversion of Cu3Se2, Ag2Te nanowires and Te/Ag2Te heterojunction nanowires were investigated in details. The performance of the Se, Te, Ag2Te single nanowire field effect transistors (FETs), as well as the Cu3Se2,Te/Ag2Te nanowire electronic devices were characterized. The following acheievements were obtained:1,Ultrathin Te nanowires were successfully synthesized by reducing orthotelluric acid using hydrazine assisted with a variety of surfactants including SDBS, SDS, and NPE. Using different surfactants distinctly affects the product morphology. Monodispersed Te nanowires can be synthesized by using SDBS surfactants. With increasing SDBS concentration, the diameter of the nanowires decreases and the length increases. Increase of precursor concentration also leads to decrease in diameter and increase in length of the nanowires. These results indicate that nanowire diameter and length can be controlled by changing surfactant and precursor initial concentration.2,Se/Te heterojunction nanowires were fabricated for the first time by using Te nanorods as seeds. Short Te nanorods seeds lead to V-shaped heterojunction nanowires, the angles varing with the Se-Te ratio. Long Te seeds lead to straight heterojunction nanowires. A preliminary growth mechanism of the heterojunction nanowires was proposed based on the experiment results. 3,The green chemistry route to Se nanowires developed by Li, et al. was extended to Te synthesis. Te nanowires were prepared by hydrothermal method using a harmless reductant, ascorbic acid, andβ-cyclodextrin is used as template. The reaction temperature and the templating effect ofβ-cyclodextrin was investigated, and a growth mechanism which explains the role ofβ-cyclodextrin was discussed.4,The transport properties of the aforementioned"green"Se and Te nanowires were investigated. Se nanowire FET was fabricated for the first time which exhibits a carrier mobility of 30cm2V-1s-1. Te nanowire FET fabricated in this work exhibits a mobility of 299cm2V-1s-1 with reproducibility and stability, doubling that reported recently by Liang, et al. The effect of purity, crystallinity, the surface species of Te NWs, and the electrode contacts on the FET performance were discussed.5,Cu3Se2,Ag2Te nanowires and Te/Ag2Te heterojunction nanowires has been obtained from"green"Se and Te templates by simple reaction in aqueous solution with metal salts, and the electronic properties of their devices were characterized. It shows that Cu3Se2 exist in two phases at different temperature. The difference of resistance between the two phases reaches as high as 8 orders of magnitude, which might be used for volatile memory device. Ag2Te nanowire was found to be an n type semiconductor which showed a mobility of 31.8cm2V-1S-1; Te/Ag2Te heterojunction nanowire shows a current rectification property, and the rectification ratio is about 95.