二氧化釩(VO2)在340 K附近會發生一階的金屬-絕緣相變，同時伴隨熱滯現象，因為此相變溫度僅略高於室溫，所以受到相當多的關注。此外，也會發生結構的相變，由低溫的單斜晶結構(monoclinic, M1)轉變成高溫的金紅石結構(rutile, R)。在先前的研究中，有許多人提出許多不同的方法來調控這個相變溫度，像是利用薄膜與基板之間晶格常數的差異使薄膜受到應力、或是將雷射光照在整片薄膜上、也能以外加電場或是壓力調控。

　　在本研究中，我們先以電阻四點量測與拉曼光譜量測來觀察VO2的金屬-絕緣相變與結構相變。接著本研究的重點是以雷射光來調控VO2的導電特性，而與先前不同的是，我們是將雷射光聚焦在薄膜的一個直徑約只有1~2 μm的點上，透過改變雷射功率或照光時間或照光方式等，再利用導電原子力顯微鏡(Conductive Atomic Force Microscopy, CAFM)觀察照光區域VO2薄膜的導電特性變化，同時也利用表面電位顯微鏡(Kelvin probe Force Microscopy, KFM)觀察照光區域表面電位的變化。此外，為了對金屬-絕緣相變進行宏觀的量測，我們也透過電阻四點量測觀察照光前後電阻隨溫度的變化。

In this study, we investigate the conductive characteristics of vanadium dioxide (VO2) after various illumination conditions. After illumination, we use Conductive Atomic Force Microscopy (CAFM) as well as Kelvin probe Force Microscopy (KFM) to probe the changes of the conductive characteristics and surface potential. We also use four-probe resistance measurement and Raman spectroscopy to investigate the insulator-to-metal transition and structural transition. For macroscope measurement, we use four-probe resistance measurement to examine the difference of the temperature dependent electrical resistance before and after illumination.

The CAFM and KFM results indicate that negative charges accumulate in the peripheries of the illuminated regions rather than the center due to flexoelectric effect, and charge-accumulated region becomes more conductive which indicates electric field induced lower insulator-to metal transition temperature. For four-probe resistance measurement before and after illumination, the resistance-temperature curve becomes two sections after illumination due to two different conductive conditions induced by illumination.

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