利用單根三硒化二銻奈米線製作而成的奈米溫度計

Abstract

一維奈米結構Sb2Se3奈米線為層狀結構的V-VI族化合物，在晶格構造屬於斜方晶晶體。半導體Sb2Se3屬於直接能隙，能帶範圍約為1.2eV，其特殊狹窄能帶提供了良好的熱電性質，近年來引起了大家廣泛的研究。我利用介電泳動奈米操控術結合電子束微影和聚焦離子顯微鏡技術，在矽基板上製作出適合量測單根Sb2Se3奈米線電性的電極。 在電性傳輸量測上，溫度從室溫加熱至523K。在所有溫度範圍內，所量測出電流-電壓特性曲線圖呈現線性和對稱，推測Sb2Se3奈米線和電極之間是形成歐姆接觸。隨著溫度的上升從300K至398K，Sb2Se3奈米線電阻隨之下降，符合thermally activated transport model。 然而，當溫度高於420K時，活化能(ΔEA)增加至約為1.0eV。從變溫拉曼圖譜和變溫XRD量測結果顯示，我們傾向排除高溫發生相變化的可能性；同時由拉曼圖譜顯示，在高溫約300K，看到Sb2Se3奈米線被氧化的訊號。在高溫時，Sb2Se3奈米線導電性遽增，我們推測和晶界能障機制有關。

Antimony triselenide (Sb2Se3) is a direct band gap semiconductor with band gap energy of ~1.2 eV. In recent years, one-dimensional (1D) nanostructure Sb2Se3 nanowire, which is a layer-structured of an orthorhombic crystal structure, has received a great deal of attention due to its excellent thermoelectric properties. In the thesis, suitable electrodes were fabricated to make electrical contact with a single Sb2Se3 nanowire on Si substrates by using the combination of dielectrophoresis, electron beam lithography and Focus ion Beam techniques. The electrical transport measurements were carried out from room temperature up to 523K.The current-voltage (I-V) characteristics showed linear and symmetric behavior in the entire temperature range, which indicated that the contacts between the Sb2Se3 nanowire and electrodes were ohmic. The resistance of the Sb2Se3 nanowires decreases with increasing temperature from 300 K to 398 K, which fits well the thermally activated transport model. However, a larger thermal activation energy of ~ 1.0 eV was found at temperature above 420 K. Results from temperature dependent Raman and XRD measurements have ruled out the possibility of phase transition due to oxidation of the nanowires at temperature below 500 K. We speculate that the reduction of resistance at high temperature is due to the breakdown of grain boundary barrier.