Layer-dependent morphologies of silver on n-layer graphene
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NANO EXPRESS
Open Access
Layer-dependent morphologies of silver on n-layer graphene Cheng-wen Huang1, Hsing-Ying Lin2, Chen-Han Huang2, Ren-Jye Shiue3, Wei-Hua Wang3, Chih-Yi Liu1,4 and Hsiang-Chen Chui1,4*
Abstract The distributions of sizes of silver nanoparticles that were deposited on monolayer, bilayer, and trilayer graphene films were observed. Deposition was carried out by thermal evaporation and the graphene films, placed on SiO2/Si substrates, were obtained by the mechanical splitting of graphite. Before the deposition, optical microscopy and Raman spectroscopy were utilized to identify the number of the graphene layers. After the deposition, scanning electron microscopy was used to observe the morphologies of the particles. Systematic analysis revealed that the average sizes of the nanoparticles increased with the number of graphene layers. The density of nanoparticles decreased as the number of graphene layers increased, revealing a large variation in the surface diffusion strength of nanoparticles on the different substrates. The mechanisms of formation of these layer-dependent morphologies of silver on n-layer graphene are related to the surface free energy and surface diffusion of the n-layer graphene. The effect of the substrate such as SiO2/Si was investigated by fabricating suspended graphene, and the size and density were similar to those of supported graphene. Based on a comparison of the results, the different morphologies of the silver nanoparticles on different graphene layers were theorized to be caused only by the variation of the diffusion barriers with the number of layers of graphene. Keywords: Graphene, Nanoparticle growth mechanisms, Diffusion difference barriers PACS: 68.65.Pq (graphene films), 68.70.+w (whiskers and dendrites), 78.67.Wj (optical properties of graphene)
Background A single atomic layer of graphene is the thinnest sp2 allotrope of carbon. It, therefore, has various unique electrical and optical properties of interest to scientists and technologists [1-3]. Graphene samples are widely fabricated by the micromechanical cleavage of highly oriented pyrolytic graphite (HOPG) with scotch tape. Layers of oxides such as SiO2 and Al2O3 with special thickness between graphene and the substrate are typically used to make graphene optically visible [4-7]. The effect of the substrate on Raman measurements has been widely investigated [8]. Raman and surfaceenhanced Raman spectroscopy have been widely utilized to elucidate the vibration properties of materials [9-14]. * Correspondence: [email protected] 1 Department of Photonics, National Cheng Kung University, Tainan 70101, Taiwan 4 Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan Full list of author information is available at the end of the article
Recently, they have been used as powerful techniques for characterizing the phonons of graphene [15-20]. The profile and peak position of the Raman second-order (2D) band can be used to determine the number of graphene layers [21,2
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