Properties of carbon films deposited by pulsed laser vaporization from pyrolytic graphite
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S.V. Rajarshi School of Energy Studies, University of Poona, Pune-411007, India
S.T. Kshirsagar National Chemical Laboratory, Pune-411007, India (Received 28 September 1988; accepted 21 April 1989) Amorphous carbon films have been deposited on silicon (111) and quartz substrates by pulsed ruby laser vaporization from pyrolytic graphite. Depositions have been carried out at different substrate temperatures, and the properties of the deposited carbon films have been studied using IR and UV-VIS transmission, ellipsometry, and laser-Raman spectroscopies. Chemical and electrical resistivity measurements have also been performed. It is shown that the film properties depend critically on the substrate temperature and that at the substrate temperature of 50 °C films with substantial proportion of sp 3 hybridized orbitals are obtained.
I. INTRODUCTION The structural states of carbon have been a subject of immense interest for quite some time in view of their implications for our understanding the connection between the nature of chemical bonding and the short-, medium-, and long-range order in the solid state. It is known that depending on the preparation method, carbon can exist in different structural forms such as amorphous carbon, glassy carbon, microcrystalline carbon, graphitic carbon, and diamond-like carbon; and these forms exhibit significantly different chemical, optical, and mechanical properties.1"5 It is generally believed that these variations in the properties are a consequence of the relative populations of sp3, sp2, and sp' hybridized orbital states of carbon atoms, the last one being least probable.6 It is of interest to examine whether these populations can be controlled and the structural state of carbon tailored by resorting to newer, especially far from equilibrium, thin film deposition methods. An interesting proposition in this context is the technique of pulsed laser vaporization, which has attracted significant attention recently.7"9 Sato et a/.10 have used this method (employing excimer laser) to deposit carbon films, and their preliminary characterization results indicate that diamond-like carbon films can be synthesized by this method. In this paper we report on the optical (laser Raman, IR, UV-VIS transmission, spectroscopic ellipsometry), electrical (resistivity), chemical (etching in strong acids), and structural (glancing angle x-ray diffraction) properties of carbon films deposited on quartz and silicon substrates by pulsed ruby laser vaporization from pyrolytic graphite.
694 nm, tp = 30 ns) and a vacuum chamber, where a target and the substrates can be mounted. Prior to the deposition the chamber was evacuated to a vacuum better than 5 X 10"7 Torr by a Varian diffstack pump. The laser beam
Lens
Ruby Loser (pulsed mode)
II. EXPERIMENTAL The experimental setup for the pulsed laser deposition (PLD) (Fig. 1) mainly consists of a pulsed ruby laser (A = 1238
http://journals.cambridge.org
J. Mater. Res., Vol. 4, No. 5, Sep/Oct 1989
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FIG. 1. Schematic of pulsed las
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