标题: 以帮浦油气作为碳源生长大面积石墨烯及其电性研究
Large-Area Graphene Growth Using Pump Oil as Carbon Source and Its Electrical Properties
作者: 詹博全
Chan, Po-Chuan
张振雄
Chang, Chen-Shiung
光电工程学系
关键字: 石墨烯;化学气相沉积;铜箔;大面积;Graphene;Chemical vapor deposition, (CVD);Copper foil;Large-area
公开日期: 2012
摘要: 石墨烯是一种单层原子厚度,以sp2键结成六角晶格结构的碳材料,具有许多优异的特性,如高电子迁移率、高透光性、导热性好、机械强度强、可挠性佳,是极有潜力的前瞻性材料。在各界的热烈研究之下,石墨烯已经有许多的制备方式,如微机械剥离法、碳化矽磊晶法、化学气相沉积法等等,其中以化学气相沉积法最有潜力。一般化学气相沉积法使用铜箔作为基板,通入氢气、甲烷(作为碳源)生长石墨烯,可以生长出均匀的单层石墨烯(占总面积的95%),有少部分区域为两层或三层石墨烯(占5%),但无法控制层数、也无法长出均匀之多层石墨烯。因此,为了研究少数层石墨烯(两层以上)的有趣特性,研发出控制不同层数的石墨烯成长方式,是需要突破的课题。
本研究发现了新式的化学气相沉积法,以回旋油垫帮浦的油气回流作为碳源,不通氢气与烷类气体,在真空度3mTorr的情况下在铜箔基板生长出不同层数的石墨烯。我们以清洗过全新的石英管、通高纯度氮气以及更换油垫帮浦为干式帮浦等三种方式,证明碳的来源就是帮浦油气的回流。经过拉曼光谱分析样品,得知当成长的温度为1050°C,时间为30分钟,基板是使用0.01mm厚度的铜箔时,可以稳定成长大面积的单层石墨烯,但使用0.1mm厚度的铜箔时会生长出不同层数石墨烯及石墨。
生长后的石墨烯可利用聚甲基丙烯酸甲酯(PMMA)转移至任意的目标基板。在霍尔量测中,石墨烯之电子迁移率可达440cm2/Vs,与普通化学气相沉积方式生长的石墨烯电子迁移率526 cm2/Vs相距不远。我们将石墨烯转移到二氧化矽基板上制作成石墨烯电晶体,在石墨烯电晶体的场效电性量测中,可知石墨烯为高的p型掺杂,主要由于大气中的水气、氧气吸附与残留的光阻。
虽然品质仍需改善,但以油气为碳源提供了一种新式简便的方式成长不同层数之大面积石墨烯,不需通氢气也使得制程更安全。不仅如此,此新方法可在铜箔基板上长出多层石墨烯,突破了已往在铜箔上只能成长单层石墨烯的情形,若是能稳定的控制石墨烯的层数,将会是石墨烯成长的一大进展。
Graphene, an atomically thin sheet of sp2-bonded carbon atoms arranged in a hexagonal lattice, possesses many exceptional properties, such as high mobility, high transparency, great thermal conductivity, strong mechanical property and high elasticity. Owing to the much study all over the world, there are already many ways to produce graphene, such as micromechanical exfoliation, epitaxial growth on silicon carbide, and chemical vapor deposition (CVD). Among them, CVD is the most promising method. In a typical CVD method, copper foil substrate is chosen to grow graphene in hydrogen and methane (as carbon source) flowing. It can grow uniform monolayer graphene (95% of total area) while some regions are 2 or 3 layers graphene (5% of total area). But the number of graphene layers cannot be controlled and uniform multi-layer graphene cannot be grown either. Therefore, in order to study the interesting properties of few-layer graphene, developing a graphene production method to control different numbers of graphene layers is an issue to overcome.
In this work, we found a new kind of CVD method, using oil backstreaming from the oil seal rotary vane pump as carbon source to grow different numbers of graphene layers in 3 mTorr on copper foil without hydrogen and hydrocarbon gas flow. We use three ways of cleaned new quartz tube, high purity nitrogen flow and replacing oil seal rotary vane pump with dry pump to prove that the carbon source is exactly the backstreaming of oil vapor. In Raman spectrum analysis, we discovered that graphene can grow on 0.01mm thick (99.9% purity) copper foil in 1050°C and 30 minutes growth condition while different numbers of graphene layers and graphite grow on 0.1mm thick (99.96% purity) ones randomly.
After growth, graphene can be transferred to arbitrary target substrate with Polymethylmethacrylate (PMMA). In Hall effect measurement, graphene mobility can reach 440cm2/Vs and it is comparable to normal CVD graphene’s mobility 526 cm2/Vs. We transferred graphene to SiO2 substrate to fabricate graphene field effect transistor (FET). In graphene FET electricity measurement, we found that graphene are highly p-doped mainly due to the absorption of water and oxygen in air or photoresist residue.
Although the quality still needs to be improved, using oil vapor as carbon source provided a new and easy way to grow different numbers of graphene layers. It also makes the production safer without hydrogen flow. Moreover, this new method enables multi-layer graphene to grow on copper foil, overcoming the situation of only monolayer graphene formation on copper foil in the past. If we can control the numbers of graphene layers stably, it will be a milestone in graphene growth.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT070050510
http://hdl.handle.net/11536/40165
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