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Photo-electrical Effect of Pristine and Functionalized Graphene Grown by Chemical Vapor Deposition Jian Lin1, Jiebin Zhong1, Jennifer Reiber Kyle2, Miroslav Penchev2, Mihrimah Ozkan2, Cengiz S. Ozkan1,3 1

Department of Mechanical engineering, 2 Department of Electrical engineering, 3 Department of Material science and engineering, University of California at Riverside, Riverside, CA 92521, U.S.A. ABSTRACT In this poster we will present the photo-electrical effect of pristine and nitric acid treated graphene field effect transistors made by chemical vapor deposition (CVD). The results of the decreased electrical conductance and shift of Dirac point arise from the molecular photodesorption from graphene. When post treated with nitric acid the photodesorption efficiency was decrease from 52% to 21%, which was proposed to be caused by the passivation of oxygen-bearing functionalities to CVD graphene structural defects. This result provides a new strategy of stabilizing the electrical performance of CVD graphene which is promising candidate as highly conductively photoelectrical material. INTRODUCTION A number of theoretical [1-3] and experimental [4-9] studies have investigated the molecular absorption and desorption behavior of mechanically exfoliated or chemically derived graphene and graphene oxide layers. However, only a few experimental studies so far have investigated the molecular photodesorption and absorption behavior of CVD grown graphene layers and their functionalized counterparts. In this paper, we describe recent research on molecular photoinduced desorption of pristine and nitric acid (HNO3) treated CVD grown graphene field effect devices under ultraviolet (UV) light illumination in the presence of oxygen and ammonia. Electrical characterization including time evolution of conductivity, transfer characteristics, and sheet resistance show the photodesorption of gas molecules from pristine graphene layers. The presence of HNO3 weakens the photodesorption induced current reduction behavior in functionalized CVD grown graphene layers. EXPERIMENT

2.1 Synthesis and HNO3 functionalization of CVD grown graphene layers In the CVD growth process, few-layer graphene films were synthesized on nickel thin films at 900°C using a highly diluted methane gas source under ambient pressure conditions in a hot wall furnace. 200nm thick Ni catalyst films were deposited by electron beam evaporation on Si/SiO2 substrates. Nickel deposited substrates were heated to 900°C in an Ar/H2 (300:300 standard cubic centimeter per minute- sccm) atmosphere and annealed for 30 minutes in order to increase

the nickel grain size. After flowing methane (30sccm) mixed with Ar/H2 at 900°C under ambient pressure for 1 minute, the furnace was cooled down to 25°C at a medium/fast cooling rate of 10°C/s. After that, the residual Ni layer underneath was etched in a mild 3% HCl aqueous solution. Next, each graphene film was transferred onto a Si/SiO2 substrate with highly doped Si backgate electrode and 300nm thermal oxide gate dielectric. The few