Molecular Beam Epitaxal Growth of Graphene and Nanofin Networks


Fumihiko Maeda and Hiroki Hibino
Materials Science Laboratory

 For graphene, which is a material of great interest for the future electronics, establishing a method for its wafer-scale fabrication remains a challenge for its application to largescale integration. We have proposed a new approach to fabricate graphene based on gassource molecular beam epitaxy (MBE) and have shown its feasibility [1]. Then, we observed an interesting nanostructure, which forms a network. Here, we report an investigation of its structural details [2].
 As a substrate, we used graphene, from one to two layers, formed on n-type SiC(0001) by annealing at 1800ºC in Ar ambient at about 100 Torr. For the MBE growth, the substrate was heated under the flow of ethanol cracked by a W filament set at 2000ºC. By atomic force microscopy (AFM), the topographic image of a sample grown at 915ºC was obtained [Fig. 1(a)]. In this image, the network structure can be seen on the substrate surface. Crosssectional transmission electron microscopy (TEM) images of this sample in Fig. 2 reveal that these networks consist of one or two layers of graphene, which stick out from the surface like a fin whose height is about 5 nm. (Here, we call this ridge-structure a “graphene nanofin”.) We speculate that the nanofins would be formed by collisions between incommensurate domains of the laterally growing graphene at their boundary, which means that a single domain of graphene islands is surrounded by the nanofins. Thus, the domain size of the laterally grown graphene is estimated to be less than 100 nm using the average distance between the nanofins from the section analysis of Fig. 1(b). This fin structure of atomic layer thickness with an open end has not been reported previously and is observed here for the first time. We expect that the graphene nanofin could be applied for interconnection and devices as the thinnest material of one atomic layer.
 This work was supported by KAKENHI.

[1] F. Maeda and H. Hibino, Phys. Status Solidi B 247 (2010) 916.
[2] F. Maeda and H. Hibino, J. Phys. D: Appl. Phys. 44 (2011) 435305.

Fig. 1. (a) Topographic AFM image and (b) AFM section
analysis along the dotted line in the image.
Fig. 2. Cross-sectional TEM images after MBE growth.

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