CVD Growth of Graphene on Three Types of Epitaxial Metal Films on Sapphire Substrate
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CVD Growth of Graphene on Three Types of Epitaxial Metal Films on Sapphire Substrate Katsuya Nozawa, Nozomu Matsukawa, Kenji Toyoda and Shigeo Yoshii Advanced Technology Research Laboratories, Panasonic Corporation, 3-4 Hikaridai, Seika, Kyoto 619-0237, Japan ABSTRACT Graphene growth by chemical vapor deposition (CVD) was studied on three types of epitaxial metal films with different crystal structures on sapphire. Nickel (face-centered-cubic: fcc), Ru (hexagonal-closed-pack: hcp), and Co (fcc at temperature for graphene growth and hcp at R.T.) were deposited on c-face sapphire substrates and annealed in a furnace for solid phase epitaxial growth. Graphene layers were grown by CVD with methane gas on the epitaxial metal film. The graphene layer uniformity was consistent with the structural simplicity of the metal film. The Ru sample had a single domain in the metal film and the highest graphene uniformity. The Co sample had a very complex crystal structure in the metal film and the poorest uniformity in graphene. The Ni sample had two types of stacking domains in the metal film and the graphene layer was uniform on each domain, but inhomogeneity was observed at domain boundaries. INTRODUCTION Graphene has been attracting a lot of attention [1] because of its remarkable properties, including high mobility [2] and long spin coherent length [3]. To utilize such properties in practical devices, a technique must be developed to grow a single domain and layer number controlled graphene films for each device on large substrates. Graphene growth on a metal surface is one candidate. Some metals work as catalysts for graphene growth [4]. High quality graphene films are synthesized by this method, but it is quite difficult to make a single metal substrate large enough for practical use. Recently, experiments on chemical vapor deposition (CVD) growth of graphene on metal catalyst films have been reported [5, 6]. Some are sputtered metal films on amorphous layers such as SiO2 [5], and others are freestanding metal foils [6]. It is easy to obtain large substrates for this method; even substrates as large as 30-inch are possible [6]. However, the metal films are poly-crystals. Crystal orientation of metal domain determines graphene orientation on it as shown in figure 1 (a). Grain boundary formation is unavoidable between graphene films grown on different orientation metal domains. In addition, grain boundary causes graphene layer number inhomogeneity [7]. Epitaxial growth of a metal catalyst film on a single crystal semiconductor substrate may solve this problem [8]. Some semiconductor substrates have similar lattice constant with catalyst metals and can have metal films epitaxially grown on them [9, 10]. Large semiconductor substrates are much easier to obtain than metal substrates of the same size. By using this method,
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an orientation controlled single domain metal surface may possibly be obtained for high quality graphene growth. However, just using single crystal semiconductor substrates does not guarantee that a single
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