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Ultrathin Graphene Structure, Fabrication and Characterization for Clinical Diagnosis Applications
Published in Suvardhan Kanchi, Rajasekhar Chokkareddy, Mashallah Rezakazemi, Smart Nanodevices for Point-of-Care Applications, 2022
Ganesh Gollavelli, Yong-Chien Ling
CVD is one of the sophisticated best methods to produce large-area (in cm) high-quality graphene with no or fewer defects with controllable sheet size and sheet number in large quantity. This method requires metal foil (Ex: Cu, Ni, Pt, Co, Fe, Ta, Ru, etc.), carbon source (e.g., methane, CO2, hexachlorobenzene, etc.), hydrogen gas and furnace [56–58]. The heavy atomic weight carbon from methane vapors deposit on the surface of Cu around 800–1,000° C and the light atomic weight hydrogen leaves the surface and the copper does not chemically interact much with it. The gaseous carbon atoms on the Cu surface form a stable atomic thick network by following C–C terravalency in a hexagonal framework. If the metals interact strongly with carbon it may form metal carbides and can disturb the hexagonal symmetry thereby sacrificing quality in terms of layers, size, defects, wrinkles, conductivity, etc. The carbon film growth on the metal surface can be explained by catalyst theory [59] and metal-induced crystallization [60]. Usually, transition metals are known to be good catalysts and help the gas molecules to adsorb on their surface and lower the reaction temperature and activation energies. Among all metals Cu can provide a low-energy pathway; as a result, it is the most widely adopted material for CVD-grown graphene above other metals [56,61]. Thirty-inch graphene films for transparent electrodes have been fabricated by roll-to-roll production using Cu foil and the Cu etched away to recover the graphene from it (Figure 21.8) [62]. Very recently, Li et al. [63] prepared super-clean graphene with > 99% clean regions by avoiding all impurities during the manufacturing process. Several authors have worked on this strategy by changing the carbon source, proton source, time, temperature and metals to produce different kinds of graphene for diversified applications [37,64,65]. Synthesis of graphene from CVD, the yellow base is a Cu foil and the hexagonal carbon network deposition on Cu at 1,000° C from methane vapors. The roll-to-roll production and description of fabrication have been provided on the right side of the image. Image reprinted from [34].
Solid-state amorphization of gold and silicon bilayer films by annealing
Published in Philosophical Magazine, 2022
The interfacial reactions of metal films on amorphous semiconductors are also interesting because they cause amorphous semiconductors to crystallize at low temperatures, which is referred to as metal-induced crystallization. Many studies have explored gold on amorphous silicon systems. Even at room temperature, the mixing of silicon in gold [28,29] and the formation of a-Au–Si [6] were observed. The crystallization of amorphous silicon and the appearance of crystalline gold silicides during annealing have also been reported [6,30,31]. However, in some cases, no silicide formation was observed during annealing or after crystallization of the silicon films [25,32]. These discrepancies are also thought to depend on the film preparation and substrate conditions.