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|Title: ||What types of defects are created on supported chemical vapor deposition grown graphene by scanning probe lithography in ambient?|
|Keywords: ||石墨烯;結構性缺陷;掃描式探針微影技術;拉曼光譜;光電子能譜;graphene;structural defects;Scanning probe lithography;Micro-Raman;XPS|
|Issue Date: ||2014-10-15 14:47:44 (UTC+8)|
天然的石墨烯在室溫下擁有高傳導速度的電子還有其近乎透明的光學特性。但是沒有能量間隙卻成為石墨烯被應用在電晶體上的一種障礙。石墨烯的能隙能透過添加奈米尺度的缺陷來修正。目前為止存在多種在石墨烯裡添加缺陷的方法。其中，原子力顯微鏡中的掃描式探針顯影技術被用來製造許多材料的奈米尺度結構，包括石墨烯。石墨烯被鋪在二氧化矽的基板上，使用探針微影製造缺陷時，我們發現在相同的負偏壓在探針上，產生的缺陷其形貌有時為突起有時為凹陷。 一般而言，探針微影會在探針與石墨烯表面之間形成水橋並產生氫氧根OH-離子。突起與凹陷形貌通常各別被解釋成碳原子的不完全的氧化與完全的氧化。碳原子的不完全氧化為sp3鍵所造成突起，完全氧化則影響碳原子與OH-汽化產生空缺的缺陷。近年來，拉曼光譜已被證實可以用來判斷石墨烯缺陷的種類，藉由D和 D’ 的強度的比例。 然而此實驗的發曼光譜顯示(ID/ID’)，不管突起或凹陷的形貌，都為空缺的缺陷。微米尺度的光電子顯微鏡，也證實了在形貌為突起的缺陷中，僅有微弱的C-O鍵訊號，並且還擁有很強C-C鍵扭曲的訊號。透過拉曼光譜與光電子能譜，我們推斷造成突起形貌的原因不是因為sp3的部分氧化。關鍵因素為碳原子在室溫下因為在掃描探針微影過程中遭受到離子衝撞與汽化，產生了重新鍵結並造就了最後的形貌。
Pristine graphene has demonstrated ballistic electron transport at room temperature and nearly transparency optical properties. Nevertheless, the absence of band gap in graphene sets an obstacle for its application in graphene based transistor. Band gap in graphene can be modified by introducing nano-scale defects in it. There exist several promising ways for defect introduction in graphene to date. Among them, scanning probe lithography (SPL) with atomic force microscope (AFM) is a mask-less method for fabricating nano-meter-scale structure in various materials, including graphene. With the same negative bias at the AFM probe tip, nano-meter-scale-defect protrusions or depression could be produced on graphene supported on a substrate. Conventionally, SPL process on graphene results in reaction of decomposed OH- ions and graphene in the water meniscus formed between the tip and sample surface. The protrusion and depression are usually explained in term of incomplete (non-volatile) or complete oxidation (volatile) of carbon atom in graphene, respectively. The scenario above implies that sp3 and vacancy type defects are expected to dominate in protrusion and depression structure, respectively. Recently, Raman spectroscopy has been proved to be an effective tool for probing different defect type in graphene by measuring the ratio of D and D’ intensities (ID/ID’). However, we found that both SPL structures are composed of vacancy defect from ID/ID’. Micro-Photoelectron microscopy (μ-PEM) further reveals weak presence of C-O bonding around the C 1s peak. Instead, strong distortion of C-C bonds and evidence of strain around the SPL patterns are found by both μ-RS and μ-PEM. We conclude that protrusion topography is not result of sp3 partial oxide. Rather, it is probable that room temperature recombination of distorted carbon bond after the ion impact or volatile oxidation by SPL process is the deterministic factor for resultant topography.
|Appears in Collections:||[物理研究所] 博碩士論文|
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