利用外加電場與光催化效應操縱氧化鋅表面奈米尺度的接觸起電現象

Abstract

在本研究中，我們利用基於原子力顯微鏡的技術，探討脈衝雷射沉積法製成的氧化鋅薄膜的接觸起電效應。在原子力顯微鏡的探針接觸氧化鋅薄膜時，我們藉由施加偏壓在探針上以及利用氧化鋅的光催化反應來進一步調控接觸起電實驗。透過使用峰值力輕敲式掃描模式，電荷載子可以在探針接觸到氧化鋅表面時被注入樣品並保存於其中。隨後我們再利用克氏探針表面電位顯微鏡監控樣品帶電區域的表面電位變化。由實驗我們發現 在接觸起電期間施加一個+10伏特的偏壓時，可以在樣品表面儲存正電荷使其產生相對 接觸前的表面電位差達約500毫伏特。然而，當我們改施加一個10伏特的偏壓時，則樣品表面可以儲存負電荷使其相對表面電位達約5000毫伏特。此實驗結果可以歸因於氧化鋅本質上為n型的半導體，較利於傳輸電子的關係。另外，我們使用波長為365奈米的紫外光照射氧化鋅薄膜表面來誘導光催化作用的發生。在紫外光照射後，氧化鋅的表面濕潤性將從疏水性轉變為超級親水性。透過實驗我們發現氧化鋅表面上來自吸收環境中水氣所形成的水層會阻礙摩擦起電時電荷的注入，使電荷需要透過量值更大的偏壓才可儲存於樣品表面中。我們的發現將可能有助於基於氧化鋅製成的摩擦起電式奈米發電機的後續發展。In this study, we investigated the effect of contact electrification (CE) on pulsed-laser-deposited zinc oxide (ZnO) thin film by using atomic force microscopy (AFM)-based techniques. The CE was further modulated by applying an electric bias to AFM probe during contact and the photocatalytic effect of ZnO. By using PeakForce tapping mode, charge carriers can be injected and stored in ZnO when the AFM probe was in contact with its surface. The evolution of surface potential on the charged area on ZnO was subsequently monitored by the Kelvin probe force microscopy (KPFM). We found that when a positive 10 V of electric bias was applied during CE, a surface potential of ~+500 mV can be attained. However, when a negative 10 V was applied, a surface potential as large as -5000 mV was found. This observation may be ascribed to the fact that ZnO is an intrinsic n-type semiconductor that favors electrons transport. Furthermore, we irradiate the ZnO surface by using UV light at 365 nm to induce the photocatalytic effect. The surface wettability of ZnO will be transformed from being hydrophobic to superhydrophilic after the UV illumination. We found that the adsorbed water layers from the ambient environment on the ZnO surface will impede the injection of charges during CE, and that a higher electric bias was needed to store charges in ZnO. Our findings may assist the development of ZnO-based TENGs.