Production of amorphous metallic surfaces by means of a pulsed glow discharge electron beam
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J. J. Rocca Department of Electrical Engineering, Colorado State University, andN.S.F. Optoelectronic Computing System Center, Fort Collins, Colorado 80523 (Received 23 September 1991; accepted 19 December 1991)
A pulsed glow discharge electron beam has been used for the production of metallic amorphous surfaces in MgZn alloys. Electron beam pulses of 20 /-is pulse width produced by a 40 A, 22.5 kV glow discharge were found to provide sufficient energy for melting the metallic surfaces; that due to the rapid cooling to the substrate yielded amorphous phases. The system allows control of the energy density, penetration, and pulse width of the heating pulse.
I. INTRODUCTION In this paper we present, for the first time to our knowledge, the production of amorphous metallic surfaces by means of a pulsed electron beam produced by a cold cathode glow discharge. The material selected to demonstrate this novel technique was the eutectic alloy Mg7OZn3o. Most of the previous work on electron beam surface processing has been restricted to surface recrystallization with hot cathode electron guns.1 Continuous wave electron beams from cold cathode electron guns have also been utilized for semiconductor recrystallization.2^ The technique here described offers several advantages over alternative pulsed laser surface amorphization5: increased energy per pulse, higher penetration, higher energy absorption coefficient, simpler construction, and more control over the processing parameters (energy density, penetration, and pulse width). In particular, the higher penetration is critical, because the energy used in our experiments would result in sample sublimation if a laser pulse of similar energy is used, not yielding the desired amorphous phase. As compared to hot cathode electron guns, the cold cathode system here described is simpler and works at higher pressures, requiring only the use of a mechanical pump. Also, it allows when necessary working in an inert gas atmosphere, typically He, to prevent oxidation of the substrate to be heated. II. THE EXPERIMENTAL SETUP The electron gun used is similar to the cold cathode glow discharge gun developed by Ranea-Sandoval et al. for the generation of intense pulsed electron beams, and it consists of an aluminum cathode 7.5 cm diameter surrounded by a closely spaced shield made out of polycarbonate and machinable ceramic.6 When this cathode 1096 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 5, May 1992 Downloaded: 18 Mar 2015
structure is introduced in a low pressure environment and connected to a negative high voltage source, a glow discharge develops. A high electric space charge region with a high electric field, known as the cathode sheath, is generated in front of the cathode. Most of the discharge voltage drops in this region and the rest of the glow is practically electric field free. Ions from the glow discharge plasma are accelerated in the cathode sheath and bombard the cathode, emitting secondary electrons. The emitted electrons are accelerated in the opposite dire
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