Influence of in-process copper incorporation on the quality of diamond-like carbon films deposited by pulsed laser depos
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Influence of in-process copper incorporation on the quality of diamond-like carbon films deposited by pulsed laser deposition technique S. J. Dikshit, Pramada Lele, and S. B. Ogale Center for Advanced Studies in Materials Science and Solid State Physics, Department of Physics, University of Poona, Pune-411 007, India
S. T. Kshirsagar National Chemical Laboratory, Pashan, Pune-411 008, India (Received 6 March 1995; accepted 3 May 1996)
Copper-incorporated carbon films have been prepared on Si(100) and Corning (7059) glass substrates by the pulsed excimer laser deposition technique using KrF radiation (l 248 nm). Cold-pressed composite pellets, having compositions from 2 at. % to 11 at. % copper in carbon, were used as targets for ablation. Good quality, scratch-proof films were obtained at a laser energy density of 2–3 Jycm2 and a substrate temperature of 50 ±C. The films were characterized by x-ray diffraction (XRD), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), UV-visible spectrometry, ellipsometry, and four-point probe resistivity measurements. Under similar deposition conditions, films obtained from composite targets of lower copper concentration are seen to have better diamond-like character as compared to those obtained from a pure graphite target. At such low concentrations, copper is seen to cluster in the form of nanoparticles. As the copper concentration increases in the films, they tend to acquire disordered graphitic network with degraded DLC characteristics, and the size of copper agglomerates increases from about 5 nm (for the 2 at. % case) to 85 nm (for the 11 at. % case). It is seen that an increase in the copper content leads to modifications in the carbon network, additional interband transitions, and reduction of the band gap.
I. INTRODUCTION
Diamond-like carbon films (DLC) have attracted significant attention from scientists as well as industrialists in recent years due to their wide applicability in diverse fields such as optics, electronics, tribology, and medicine. Such films are prepared by different methods such as rf glow discharge,1 sputtering,2 ion beam deposition,3 pulsed laser ablation,4 etc. These films have been shown to contain sp 2 -sp 3 bonds in different proportions.5 A higher percentage of sp 3 bonds is desirable for a higher level of performance in applications; hence, most efforts in this area are directed toward the optimization of growth conditions so as to enhance the sp 3ysp 2 ratio. An interesting possibility that has not been too widely examined in this context is the use of elemental promoters of sp 3 hybridization. Copper, for instance, bears a lattice-matching condition with diamond structure, and hence it can be considered as a potential sp 3 promoter. It is also interesting to examine the implications of such metal incorporations in DLC films in the context of its properties. The effect of incorporation of various transition elements including Cu in a-C : H films has been studied.6–11 However, the chang
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