Band Gap Opening of Graphene after UV/Ozone and Oxygen Plasma Treatments
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Band Gap Opening of Graphene after UV/Ozone and Oxygen Plasma Treatments
Adrianus I. Aria1, Adi W. Gani2 and Morteza Gharib1 Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena, California 91125, USA 2 Electrical Engineering, California Institute of Technology, Pasadena, California 91125, USA
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ABSTRACT Graphene grown by Chemical Vapor Deposition (CVD) on nickel subsrate is oxidized by means of oxygen plasma and UV/Ozone treatments to introduce bandgap opening in graphene. The degree of band gap opening is proportional to the degree of oxidation on the graphene. This result is analyzed and confirmed by Scanning Tunnelling Microscopy/Spectroscopy and Raman spectroscopy measurements. Compared to conventional wet-oxidation methods, oxygen plasma and UV/Ozone treatments do not require harsh chemicals to perform, allow faster oxidation rates, and enable site-specific oxidation. These features make oxygen plasma and UV/Ozone treatments ideal candidates to be implemented in high-throughput fabrication of graphene-based microelectronics. INTRODUCTION Graphene is a lattice of honeycomb-arranged carbon atoms tightly joined by sp2 bonds [1]. Graphene draws a lot of research interests due mostly to its unique band structures and excellent electrical properties [2]. Graphene has a superior carrier mobility and lowest resistivity than any other materials. These features enable graphene to be a promising future candidate for component of integrated circuit. However, graphene is a semimetal and zero bandgap material. This puts limitation on controlling and switching off electrical conductivity of graphene by means of gate electrode [3]. In order to harvest the maximum potential of graphene as a promising future electronic material, a number of approaches are currently done to create a bandgap opening in graphene. When single layer graphene is cut into ribbons of nanometers wide, a bandgap appears as a result of quantum confinement [4-6]. Another approach to introduce bandgap in grapheen is to apply electric field normal to a graphene plane [3]. Another method is to break the lattice symmetry of pristine graphene by introducing “dopant” atoms or functional groups, such as bismuth, antimony, gold [7], NO2 [8], and oxygen [9]. Among many dopant species that have been demonstrated to introduce band opening in graphene, oxygen has its own virtue for further refinements, because its chemical interaction with organic molecules have been well-understood. Current method of preparing graphene oxide stems mainly from established wet-chemical methods of preparing graphite oxide, such as the Hummer’s method [10]. These methods generally use graphite flakes as the starting material, which is oxidized in the presence of strong acids and oxidizing agents. The resulting graphite oxide consists of layered structure of stronglyhydrophilic graphene oxide, that enables intercalation of water molecules between the graphene oxide layers. A sonication or stirring will exfoliate the graphene oxide, producing aqueous
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