單晶 Zn2GeO4 奈米線之合成與光電性質研究

Abstract

本研究採用碳熱還原法結合氣-液-固（Vapor-Liquid-Solid）機制，利用鍺粉、氧化鋅粉末、碳粉混合，藉由控制水平三區加熱式爐管中基板溫度、腔體壓力及載流氣體流量，成功合成出單晶鋅鍺氧化合物奈米線。成長出的奈米線利用掃描式電子顯微鏡作樣貌的觀察，再利用X光繞射(XRD)分析波峰位置藉以鑑定奈米線，可發現Zn2GeO4為菱方晶(rhombohedral)晶體結構。在高解析穿透式電子顯微鏡所拍攝的原子影像及其對應的繞射點，可以得知此奈米線為一單晶結構，晶體成長方向為[110]。藉由球面校正穿透式電子顯微鏡，在高角度環狀暗場像及明視野像可以看出原子分佈位置。在室溫螢光光譜量測下，可以發現奈米線發光來自兩個波長,分別是376 nm及504 nm，前者為鋅間隙放光造成，後者為氧空缺貢獻。在變溫瑩光光譜儀量測下，可以發現鋅間隙放光強度隨溫度上升放光強度逐漸減弱，也發現有放光能隙波長紅移的現象。為了探究單根奈米線之光電物理特性，製備出單根奈米線元件，在奈米線的兩端利用聚焦電子束顯微鏡鍍附鉑金屬當電極。以可攜式紫外燈具，在254 nm波長紫外光照射下顯示出快速切換開關的特性，顯示Zn2GeO4奈米線可應用於紫外光感測元件。除此之外，將成長於矽基板上的奈米線置放在甲基橙溶液中，在短波長紫外光的照射下，可以發現甲基橙被降解的現象發生，因此Zn2GeO4奈米線也擁有良好的光降解有機物的特性。

In this work, Zn2GeO4 nanowires (NWs) have been successfully synthesized on Si (100) substrate through carbon thermal reduction and vapor-liquid-solid method. The diameters of the NWs are in the range of 80-150 nm with high aspect ratio (AR>100). The X-ray diffraction (XRD) peaks revealed that the phase is rhombohedral Zn2GeO4. High resolution transmission electron microscopy (HRTEM) indicated that the NWs are perfect single-crystalline with [110] growth direction. Moreover, the atomic resolution high-angle annular dark-field (HAADF) and bright field images of scanning transmission electron microscopy (STEM) can distinguish the different elements of atoms. They further clarified the structure of Zn2GeO4 and the position of elements located. The room temperature photoluminescence spectra of Zn2GeO4 NWs revealed high UV emission and broad blue emission. The UV emission was attributed to the Zinc interstitial, of which the intensity decreased as temperature increasing. Furthermore, we have fabricated the device to measure electrical properties of the single NW. The platinum electrodes of the device were deposited by focus ion beam (FIB). It is remarkable that individual Zn2GeO4 NW device exhibited excellent optoelectronic property with fast switching speed under 254 nm UV illuminations. The result showed that Zn2GeO4 NWs can be served as the building blocks for UV photodetectors. In addition, while exposing Zn2GeO4 NWs, which soaking in methyl orange solution. With short wavelength UV illumination, the methyl orange were degraded. This result showed that Zn2GeO4 NWs can be used in degrading organic pollutants. In conclusion, Zn2GeO4 NWs show highly potential applications in UV photodetectors and degradation of organic pollutants.