單根氧化釩奈米線之電性與光學性質研究

Abstract

在本篇論文中，我利用「介電泳動法」成功的將單根的五氧化二釩奈米線跨接在各種不同的電極上，並且結合電子束微影技術及聚焦離子束顯微鏡技術製作出單根的電性量測元件，接著針對單根V2O5奈米線的電性量測結果進行分析和討論。 首先是兩點式的電性量測結果，我發現不同的金屬電極材料以及不同的懸浮溶劑種類都會造成不同的電性量測結果，並探討造成影響的原因。接下來，在為了更精確地量測出單根V2O5奈米線的電阻率，儘可能避除掉接觸電阻的影響，於是製作出四點式的電性量測元件，利用三種不同的電性量測方式計算出單根V2O5奈米線的電阻率，並且討論、比較量測的結果和差異。接著，為了想要知道溫度對單根V2O5奈米線電性的影響而進行了變溫的電性量測，藉由分析活化能以及電阻隨溫度的變化情形，發現在升溫通電流的情形下，奈米線的本質發生了改變。我們認為是因為加偏壓造成電流注入奈米線，使得V2O5奈米線提前在200℃左右就發生相轉變，而部份還原成為了V2O3，導致電阻的下降。最後，我們利用在氮氣下的升溫電性量測結果以及升溫後的高解析微拉曼光譜分析比對，證實了我們的推論。

In this thesis, by using e-beam lithography, dielectrophoresis and focused ion beam techniques, we demonstrate methods to manipulate, align and make electrical contacts with a single V2O5 nanowire(NW) on metal pads with different design shapes. Systematic investigations on optical and electrical properties of these vanadium pentoxide single nanowires were carried out. First, we present results of two-point-contact resistance measurements to discuss the effects of different electrode materials and different types of suspension solvent on the NW electrical properties. Then, in order to eliminate the influence of contact resistance and to accurately determine the resistivity of a single V2O5 NW, we devised a four-point-probe contact on a single V2O5 NW device. Finally, we analyzed results from three different electrical measuring methods and compared them with earlier reports on V2O5 NW resistance measurements. The activation energy of a single V2O5 NW was also determined by measuring the temperature dependence of NW resistance from RT to above 600 K. The variations of activation energy and dramatic reduction in resistance with increasing temperature indicated that there was a phase transition took place in the NW at about 500K. Similar results were observed when samples were placed in a N2 purged environment. From results of HR-Micro Raman spectrum analysis, we concluded that the phase of the single V2O5 NW was partially reduced to V2O3 during the heating processes and the phase transition took place at a temperature as low as 500 K due to the electrical injection of electrons into the NW while the sample was heated.