Arc-Discharge Evaporation of Silver-Plated Graphite Rods
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Arc-Discharge Evaporation of Silver-Plated Graphite Rods M. Vaziri Department of Computer Science, Engineering Science and Physics University of Michigan-Flint Flint, MI 48502 ABSTRACT In this work, several silver-plated graphite rods have been evaporated using the dc-arc discharge technique in the presence of helium quenching gas. The evaporated materials deposited on the cathode and the chamber walls were characterized. It was found that the inner core of the deposited materials contains no encapsulated silver but unusually long bundles of carbon nanotubes. In addition, the soot removed from the walls presents evidence for encapsulated nanocrystalline silver as well as low-mass fullerene cages. INTRODUCTION Nanotubes and nanosized particles have attracted considerable interest because of their novel physical and chemical properties and their potential applications in nanotechnology Various methods and metals [1-15] have been used to synthesize these materials; to date, no study using metal-plated graphite rods for the arc-discharge production of these materials has been reported. It has been shown by many researchers that shape of the carbon structure that is formed in a carbon arc depends strongly on the growth conditions [9]. Although various metal impurities have been used to produce metallofullerenes, encapsulated nanocrystals, and carbon nanotubes, typically the anode electrode used has been a graphite rod drilled out and filled with a mixture of metal impurities and graphite powder. This approach tends to increase the current density in the central region of the graphite rod. In contrast, a metal-plated rod tends to have a greater current density at the outer surface of the rod. Thus, it is reasonable to suggest that evaporating a metal-plated rod generates a different arc profile and presents different growth condition than the usual approach mentioned above. Since the current density is higher on the surface layer of the electroplated rod, the metal layer will evaporate more readily than graphite. This time differential, one can speculate, influences the residency time for bonding rearrangement and annealing of various carbon rings and cages; therefore, it is expected to create a different growth environment. The motivation to consider silver as an electroplated metal was based on the following considerations. First, nanosized crystalline silver encapsulated in graphite or inside the nanotubes is expected to have interesting electrical and optical properties as well as significant applications in nanotechnology. Second, although various transition metals and rare earth metals have been encapsulated, it has been reported [16] that silver
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cannot be encapsulated into graphite sheets by the arc discharge method. Third, since pure silver possess the highest electrical conductivity among metals and is prone to oxidation, the protective nature of a graphite coating will provide a more stable system of nanocrystalline material. The study of electrical conduction mechanism in such host is quit
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