(Invited) Synthesis, Characterization, and Applications of Single- and Double-Layer Graphene Grown on Epitaxial Metal Films

To develop graphene’s excellent and unique properties for future electronic devices, the synthesis of large area, high-quality graphene sheets with a controlled number of layers and well-defined structure is important.  Here, we present our work to grow high-quality graphene with controlled orientation.  Our method is based on heteroepitaxial CVD using highly crystalline metal catalyst deposited on single crystalline substrates, such as sapphire and MgO [1-6].  We investigated the CVD growth of single-layer graphene on Cu(111) and Cu(100) and found that the orientation of the graphene is strongly influenced by the underlying Cu lattice [2-4].  Large hexagonal graphene domains with a lateral size of 50-100 μm are aligned on the Cu(111) surface [5].  On the other hand, the orientation of graphene on Cu(100) has two main domain orientations, reflecting the symmetry mismatch between graphene and Cu(100) lattice.  The carrier transport across the neighboring domains merged with the same orientation was investigated.  We found a higher carrier mobility for devices inside one domain (mean value is 7,200 cm²/Vs at 280 K) than those with a domain interface in the channel (2,000 cm²/Vs), suggesting that the domain interface acts as a scattering site even when they merged with the same orientation [6]. 
Moreover, we have realized the selective growth of double-layer graphene on the heteroepitaxial metal films, which is expected to be applicable to semiconductor devices.  The growth mechanism and the stacking order of the double-layer graphene will be discussed.  Finally, our recent progress on the synthesis of two-dimensional heterostructures, such as graphene-MoS₂ and graphene-NbS₂hybrid structures, will be also presented [7,8].

[1] H. Ago et al., ACS Nano, 4, 7407 (2010). [2] B. Hu et al., Carbon 50, 57 (2012). [3] C. M. Orofeo et al., Carbon, 50, 2189 (2012). [4] Y. Ogawa et al., J. Phys. Chem. Lett., 3, 219 (2012). [5] H. Ago et al., Appl. Phys. Exp., 6, 75101 (2013). [6] Y. Ogawa et al., Nanoscale, 6, 7288 (2014). [7] W. Ge et al., Nanoscale, 5, 5773 (2013). [8] H. Ago et al., submitted.