Synthesis of graphene nanoribbons from amyloid fibrils by solid-phase graphitization using liquid gallium catalyst
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Synthesis of graphene nanoribbons from amyloid fibrils by solid-phase graphitization using liquid gallium catalyst Katsuhisa Murakami1,2, Tianchen Dong1,2, Yuya Kajiwara1,2, Takaki Hiyama1, Ryuichi Ueki1,2, Gai Ohashi1, Kentaro Shiraki1, Yoichi Yamada1, and Jun-ichi Fujita1,2 1
Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
2
Tsukuba Research Center for Interdisciplinary Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan ABSTRACT Amyloid fibrils, which are linear proteins with widths of less than 10 nm and lengths of more than 1 m, were used as an amorphous carbon template for graphene nanoribbons (GNRs) synthesized by solid-phase graphitization using liquid Ga as the catalyst. The crystal quality of the GNRs improved with increasing synthesis temperature. However, the shape of the GNRs synthesized at temperatures higher than 900 °C became broader, losing the original amyloid shape, whereas the GNRs synthesized at 900 °C seemed to maintain the original amyloid shape in the SEM observation. The conducting paths of GNRs synthesized at 900 °C were found to be slightly diffused outside the topography of the GNRs in the conductive atomic force microscopy map. In addition, some of the sapphire terrace edges of the substrate showed conductivity, which indicates that the growth mechanism of graphene on a sapphire substrate might be a step-flow growth mode. INTRODUCTION Graphene has great potential as a material for next-generation field-effect transistors (FET) in terms of its high carrier mobility [1]. The band-gap opening in graphene is one of the most important issues for realizing graphene-based electronic devices because graphene naturally has no band gap. Graphene nanoribbons (GNRs) are a promising route towards opening a band gap in graphene because the reduction of the GNR width to a true nanometer scale induces a band gap of up to 100 meV due to the quantum confinement effect [2, 3]. Many challenges are, therefore, associated with the synthesis of GNRs using top-down or bottom-up techniques such as conventional electron beam lithography [4], chemical “scissoring” of graphene and/or carbon nanotubes [5], and the self-assembly of template molecules [6]. However, the reproducible synthesis of GNRs with widths of less than 10 nm has not yet been established. In our previous study, solid-phase graphitization induced at the interface between amorphous carbon and liquid gallium was reported [7-9]. Various starting materials of amorphous carbon such as photo- and electron-beam resist polymers [10, 11] and biomaterials can be used for graphitization in this technique. We focused on amyloid fibrils as a carbon template for GNRs because they are long (greater than a micrometer) and linear proteins with widths of less than 10 nm, which can be controlled by a combination of amino acids. In this study, we demonstrate a new approach to synthesizing GNRs from amorphous carbon templates made from amyloid fibrils using a solid-phase graphitization technique at the in
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