The Microstructure of Co Nanoparticles Directly Deposited on Si (001) Substrates Using DC Magnetron Sputtering
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The Microstructure of Co Nanoparticles Directly Deposited on Si (001) Substrates Using DC Magnetron Sputtering Bing-Xian Chung a, Chuan-Pu Liu a, Jiun-Nan Chen b a b
Department of Materials Science and Engineering, National Cheng-Kung University, Tainan, Taiwan Department of Electrical Engineering, Fortune Institute of Technology, Kaohsiung, Taiwan
Abstract Dispersive cobalt nanoparticles are fabricated directly on Si (001) substrates by DC magnetron sputtering at room temperature. During deposition, the parameters chosen for the investigation are substrate bias (from +525 To –100 Volts), target-to-substrate distance (from 6 to 12 cm) and deposition time (from 10 to 30m sec), while the other parameters are kept the same, including the power of 50 watts. Atomic force microscope (AFM) is employed to determine the density and morphology of cobalt nanoparticles whereas high-resolution electron microscope (HRTEM) is used to visualize the resulting microstructure in the nanoparticles. It is found that Co nanoparticle array can be formed by combining the optimum substrate bias and target-to-substrate distance. The size uniformity of the nanoparticle array can be enhanced by positive bias due to charging effects. The nanoparticle of as small as a few nanometers can be successfully fabricated by DC-sputtering and can be applied to nanotube growth as catalysts. Introduction Nanoparticles grown on substrate can act as a template with catalysts for controlled nanotube growth and would be the key technology for the integration process of nanotubes. Additionally, nanotube characteristics are determined by the nanoparticle parameters including size, shape and microstructure, which might be easily controlled by varying processing variables in a magnetron sputtering. Therefore, we investigate the feasibility of growing various cobalt nanoparticles by a simple DC magnetron sputtering in this study. Cobalt and cobalt alloy has been shown to be a useful catalyst for the carbon nanotube (CNT) growth [1,2] and we choose cobalt grown on Si (001) substrate as a model system for the simplicity. In sputtering, ad-atom clustering usually forms during transportation and lands on the substrate. The surface morphology of the nucleation stage can be varied effectively by effects imposed by the sputtering process, such as ion bombardment, electron charging and energy transfer. Therefore, cobalt nanoparticles with various morphology, microstructure might be fabricated by sputtering. Experimental A DC magnetron sputter is employed to deposit Co nanoparticles on p-type Si(001) substrates. The substrates were chemically cleaned before loading into the chamber. The Co target (99.95% purity) is pre-sputtered for 5 minutes after base pressure of 2.5×10-6 torr is
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reached. During deposition, working pressure is fixed at 8×10-3 torr, while total gas flow and applied power are maintained at 40 sccm and 50 W, respectively. The experiment was performed at room temperature. Substrate bias, target-to-substrate and growth time are varied to
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