Modeling of Plasma Expansion during Pulsed Electron Beam Ablation of Graphite
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Modeling of Plasma Expansion during Pulsed Electron Beam Ablation of Graphite Muddassir Ali and Redhouane Henda Bharti School of Engineering, Laurentian University, 935 Ramsey Lake Road, Sudbury, ON P3E 2C6, Canada. ABSTRACT Pulsed electron beam ablation (PEBA) has proven to be a promising and powerful technique for the growth of high quality thin films. Pulsed electron beam film deposition consists of many physical processes including target material heating, target ablation, plasma plume expansion, and film growth on a substrate. Plasma plume expansion into a vacuum or an ambient gas is a fundamental issue in PEBA as the quality of thin films deposited onto the substrate depends on the composition, energy and density of particles ejected from the target. In the present study, gas-dynamics equations are solved to investigate plasma expansion induced by interaction of a nanosecond electron beam pulse (~100 ns) with a graphite target in an argon atmosphere at reduced pressure. The spatio-temporal profiles of the temperature, pressure, velocity, and density of the plasma plume are numerically simulated for a beam efficiency of 0.6 and accelerating voltage of 15 kV. The preliminary results show a rich variety of behaviors. The model is validated by comparing some of the obtained simulation results with experimental data available in the literature. INTRODUCTION One of the key developments in pulsed energy processing techniques of materials is the emergence of pulsed electron beam ablation (PEBA) for thin film growth [1,2]. Pulsed electron beam ablation has been recognized as an effective, powerful and promising technique for the fabrication of thin films and structures of high quality. PEBA offers numerous advantages over other conventional techniques, e.g., versatile setup, congruent material transfer from bulk to film under optimum conditions, low cost, and small footprint. One of the most attractive features of PEBA is the possibility of fabricating films under non-thermal conditions [1-3]. During PEBA, an intense electron pulse (~100 ns) strikes the target surface, triggering a sequence of strongly coupled processes. Electron beam radiation is absorbed by the target surface inducing ablation (heating and vaporization of a target surface) and expansion of a plasma plume just above the impinged target surface. The plasma, consisting of ablated particles, expands with a supersonic velocity in the ambient atmosphere towards a properly placed substrate relatively to the target. Despite PEBA increasing technological significance, details of the complex processes responsible for its characteristic features are not well explored. The processes controlling PEBA are strongly coupled and nonlinear. For a better understanding of phenomena affecting the quality of thin film growth, it is expedient to develop a comprehensive model of the process. Material ablation, plasma expansion, and the interaction of plume particles with an ambient gas are critical in defining the morphology and structure of thin films. The properties of th
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