The Role of Hydrogen in Laser Deposition of Diamond-Like Carbon
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THE ROLE OF HYDROGEN IN LASER DEPOSITION OF DIAMOND-LIKE CARBON
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2 2 D. THEBERT-PEELER', P.T. MURRAY , L. PETRY , AND T.W. HAAS 'Clare Boothe Luce Scholar, Graduate Materials Engineering, University of Dayton, Dayton, OH 45469 2 University of Dayton Research Institute, University of Dayton, Dayton, OH 45469-0167 3 Wright Laboratory, WL/MLBM, Wright -Patterson Air Force Base, OH 45433
ABSTRACT Thin films have been grown on Si (100) substrates by pulsed laser evaporation of graphite using both IR and UV radiation. The character of the resulting film is found to be independent of the presence of H'. Diamond-like films are found to be a result of low (RT) temperature deposition of the higher energy incident particles of the UV (versus IR) laser ablation process. INTRODUCTION Superior mechanical, electrical, optical, chemical, and thermal properties of diamond make it attractive for many applications ranging from mechanical and optical wear-resistant coatings to substrates for advanced semiconducting devices. When compared to the semiconducting properties of both Si and GaAs, diamond is clearly superior in several critical properties such as band gap, hole mobility, breakdown voltage, electron velocity, thermal coefficient, melting temperature, hardness, and optical transparency [1]. The various metastable deposition techniques which are being used to grow the diamond and diamondlike films include (a) carbon ion beam (b) carbon sputtering with or without substrate ion bombardment (c) rf, dc, or mw plasmas sustained in various hydrocarbon gases, (d) ion beam plating of benzene or other hydrocarbon , and (e) laser ablation of a graphite or other carbon bearing target. Laser ablation for growth of diamond thin film is the basis of this work. The technique has several attractive features, including the ability for easy, congruent target ablation of almost any material, the growth of high purity films, and the potential for low temperature depositions using this relatively simple process. Several types of lasers have been used in the deposition of diamond thin films, including ArF (193 nm), KrF (248 nm) [2-5] and XeCI (308 nm) excimers [6-10], Nd:YAG (1064 and 532 nm) lasers [11-15], Nd:glass lasers [16], and continuous CO2 lasers [17]. We have used both excimer (248 nm) and Nd:YAG (1064 nm) laser radiation in our experiments. Depending upon the deposition parameters, the films range in character from amorphous carbons, graphite, and diamond-like carbon to diamond,distinguishable by the form of the C-C bonds present. In this work, valence-level electron energy loss spectroscopy (EELS) will be used to distinguish among the various carbon allotropes. The most important forms to distinguish in the analysis of these films are graphite and diamond, characterized by 3 sp 2 and sp bonding, respectively. The low energy valence region of the EELS spectrum clearly shows that the plasmon peaks for different forms of carbon appear at different energies. There are two prominent peaks for graphite, near 6.5 and 26.5 eV. The lower ener
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