我們使用原子力顯微鏡(atomic force microscopy, AFM)及其衍伸技術研究了二氧化矽基板上的單層石墨烯表面的接觸摩擦起電效應。我們藉由使用施加了偏壓的原子力顯微鏡探針摩擦單層石墨烯表面，並觀察摩擦之後的石墨烯表面電位會如何隨著所加偏壓的大小、極性、環境溼度與石墨烯的結構缺陷而變化。我們發現在摩擦的過程中，探針上的電荷可以經由石墨烯的結構缺陷穿隧進入並累積在石墨烯與下層二氧化矽基板之間。我們使用克氏探針表面電位顯微鏡(Kelvin Probe Force Microscopy, KPFM)量測表面電位以監測累積電荷隨時間的改變。當我們使用+5V偏壓施加在探針上摩擦石墨烯後，摩擦與未摩擦區域表面電位差可以高達500mV，並表面電位會隨著時間逐漸降低，於3500分鐘後約穩定在150mV。然而，當我們在摩擦時使用負偏壓時，摩擦後的表面電位差會快速在500分鐘後消散到接近零，然後漸漸轉為正電位。這是因為當我們使用加了偏壓的原子力顯微鏡探針在環境條件下摩擦單層石墨烯時，其表面會產生摩擦化學反應，在石墨烯表面產生化學官能基，進而影響到摩擦後的表面電位。此外，我們也使用了氬氣電漿來處理石墨烯，以產生不同結構缺陷程度的單層石墨烯樣品。我們並發現結構缺陷愈多的石墨烯，其表面電位在摩擦後消散的愈快。我們的研究可以將石墨烯應用到新穎的奈米摩擦發電機(triboelectric nano-generators, TENG)之中。

We investigated the effect of contact electrification on the surface of single-layer graphene (SLG) deposited on silica employing atomic force microscopy (AFM)-based techniques. By rubbing a conductive AFM tip on the SLG surface with an applied electric bias, the triboelectric charges can tunnel through the structural defects of SLG, and trapped at the interface of SLG and the underlying silica substrate. Kelvin Probe Force Microscopy (KPFM) was used to monitor the evolution of surface potential due to the charge accumulation in this system as a function of time. We found that when a positive bias with +5V was applied during rubbing, the surface potential different between rubbed and unrubbed area can be as high as 500 mV. The observed surface potential different were found to gradually decrease with time, and became nearly a constant at 150 mV after 3500 minutes. On the contrary, when the applied bias was negative, the surface potential difference decreased to almost zero quickly after 500 minutes. Tribochemical reactions on SLG can occur when the surface was rubbed by the AFM probe with an applied electric bias in ambient conditions. Surface oxidation and hydrogenation, which are known to occur respectively when a negative or positive bias was applied to the tip during rubbing, may attribute to the observed differences in tunneling triboelectric behaviors. In addition, we treated the SLG with the argon plasma to generate different amount of structural defects in SLG and found that the degrees of structural defects have substantial influence on the observed tunneling triboelectric effect. Our results may find applications of graphene in the novel triboelectric nano-generators (TENG).

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