Synthesis of Graphene-ZnO Heterogeneous Nanostructures by Chemical Vapor Deposition
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Synthesis of Graphene-ZnO Heterogeneous Nanostructures by Chemical Vapor Deposition Jian Lin1, Miroslav Penchev2, Guoping Wang2, Rajat K Paul1, Jiebin Zhong1, Xiaoye Jing2, 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 work, we report the synthesis and characterization of three dimensional heterostructures graphene nanostructures (HGN) comprising continuous large area graphene layers and ZnO nanostructures, fabricated via chemical vapor deposition. Characterization of large area HGN demonstrates that it consists of 1-5 layers of graphene, and exhibits high optical transmittance and enhanced electrical conductivity. Electron microscopy investigation of the three dimensional heterostructures shows that the morphology of ZnO nanostructures is highly dependent on the growth temperature. It is observed that ordered crystalline ZnO nanostructures are preferably grown along the direction. Ultraviolet spectroscopy indicates that the CVD grown HGN layers has excellent optical properties. A combination of electrical and optical properties of graphene and ZnO building blocks in ZnO based HGN provides unique characteristics for opportunities in future optoelectronic devices.
INTRODUCTION Graphene based nanostructures have been employed for an increasing number of applications ranging from field effect transistors[1]and bio-molecule sensing[2, 3], to optoelectronic devices[4-6] and doping of graphene[7]. Recently, graphene based hybrid nanostructures with inorganic nanomaterials have been attracting more attention since the integrated inorganic nanomaterials provide additional functionality onto graphene layers in applications of electronics and optoelectronics [8-11]. With a direct band gap of 3.37eV and a large binding energy of 60 meV as well as the piezoelectric effect, Zinc Oxide nanostructures are important onedimensional architectures and building blocks for nano-electronics[12], optoelectronics[13], and nanogenerators[14, 15]. Accordingly, the growth of semiconductor ZnO nanostructures on large area graphene layers would allow the unique properties of the heterostructures to be exploited in optoelectronic device applications. Here we demonstrate the synthesis and the structural and optical properties of three dimensional heterostructures comprising large area graphene layers and Zinc oxide nanostructures by chemical vapor deposition. EXPERIMENTAL DETAILS In the CVD process, few-layer large area graphene layers were grown on thin Ni catalyst films using highly diluted methane gas source at 900°C under ambient pressure conditions in a
tube furnace. 250nm thick Ni catalyst films were deposited on Si/SiO2 substrates using electron beam evaporation. Ni deposited samples were heated to 900°C in a Ar/H2 (600:500 standard cubic centimeter per minute- sccm) atmosphere and annealed for 30 minutes in order to form a polycrystal
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