氧電漿表面處理對少層數二硫化鉬表面特性的影響

Abstract

二硫化鉬由於其優異的光學、電性、以及磨潤性質，在未來的微米或奈米機電系統中，有著極大的應用潛力。在製作奈米元件的過程中，氧電漿表面處理是一種常用的表面處理方法。因此，了解氧電漿表面處理對二硫化鉬表面性質的影響是很重要的。在我們的研究中，我們使用了原子力顯微鏡研究化學氣相沉積法所製備出的少層數二硫化鉬經過不同氧電漿表面處理時間後，其表面形貌、表面摩擦力和表面吸附力隨電漿處理時間的變化。我們並藉由拉曼光譜和X射線光電子能譜來觀察二硫化鉬在經過氧電漿表面處理後，其晶格結構的變化與表面氧化的程度。我們發現原子力顯微鏡的探針與二硫化鉬表面間的表面摩擦力和表面吸附力會先隨著氧電漿表面處理時間增加而增加，原因是因為二硫化鉬表面經過氧電漿表面處理後，會產生硫缺陷，因此可能將環境中的水分吸引到二硫化鉬的表面上，使得針尖與樣品表面間形成奈米級水橋，導致表面吸附力量值增加。然而，在經過較長的氧電漿表面處理後，我們所量測到的二硫化鉬表面摩擦力和表面吸附力突然降低。這歸因於二硫化鉬表面上開始形成三氧化鉬，並且會出現多個明顯的裂縫和奈米捲，導致二硫化鉬表面變的十分粗糙。這種粗糙的表面將導致針尖與樣品表面間的有效接觸面積減小，因此造成我們量測到的表面摩擦力和表面吸附力較小。藉由我們的實驗結果可以知道，在元件製造過程中使用的氧電漿表面處理技術，在不同氧電漿處理的時間下，二硫化鉬的表面形貌及奈米磨潤特性都會發生變化。我們的實驗結果將可能應用在製做微奈米機電系統的過程中。Molybdenum disulfide (MoS2) has attracted broad attentions in the science community due to its excellent optical, electrical, nanotribological properties They have applications in surface protective or lubricative coatings for miniature moving components in future nano-electro-mechanical system (NEMS). For the fabrication of nano-devices, the oxygen plasma treatment is a commonly used surface processing method. Therefore, it is important to understand the how the oxygen plasma treatment may influence the surface properties of MoS2. In this work, we used atomic force microscopy (AFM) to study the morphological, frictional, and adhesive properties of CVD grown few-layer MoS2 with various oxygen plasma treating times. The variation of lattice structure and degree of surface oxidation in MoS2 were respectively examined by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). We found that after the oxygen plasma treatment, the frictional and adhesive forces between the silicon AFM probe and MoS2 firstly increased with oxygen plasma treating time due to the plasma-induced sulfur vacancies that could attract ambient moistures onto its surface. The absorbed water molecules will lead to the formation of nanoscale water meniscus between the AFM probe and MoS2 surface, resulting in the increase of adhesive force. However, after a longer period of oxygen treatment, both the friction and adhesion abruptly decreases. This was attributed to the formation of MoO3 and a number of obvious cracks and nanoscrolls on the MoS2 surface that leads to a much coarser topography. This rougher surface will result in a reduced effective contact area between the AFM tip and sample surface, and give rise to the observed smaller frictional and adhesive forces. Our findings show that oxygen plasma processing used in device fabrication may substantially alter the morphological and nanotribological properties of MoS2. These results may find applications in future NEMS.