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Composed of packed nanophase nodules in which the carbon atoms are linked with the tetrahedral bonding of diamond, laser plasma films are deposited in vacuum onto almost any substrate by condensing carbon ions carrying keV energies. These multiply charged ions are obtained from the laser ablation of graphite at intensities in excess of 10 n W cm" 2 . The high energy of condensation provides both for the chemical bonding of such films to a wide variety of substrates and for low values of residual compressive stress. Coatings of 2 - 5 yttm thicknesses have extended lifetimes of important optical materials against the erosive wear from high-speed particles and droplets by factors of tens to thousands. In this work, the optical properties of these films at infrared (IR) wavelengths were studied. Transmission spectra of several freestanding films on silicon frames were measured. Using a model considering rough surface scattering and free carrier absorption, satisfactory fits to these transmission spectra were obtained and from them the optical parameters were extracted. The characterization studies performed in this work indicated a great potential for the laser-deposited nanophase diamond films in optical applications.

I. INTRODUCTION The utilization of processes of energetic condensation could be expected to enlarge the scope of the search for a practical coating of carbon with many of the properties of diamond. Elevated process temperatures would provide a wider selection of precursive species and favor the possibilities for quenching to new metastable forms, while a duty cycle lowered by pulsed operation would make average temperatures manageable. Recently,1"3 three new carbon materials have been shown to condense from ions of carbon with kinetic energies in excess of 0.5 keV produced by the laser ablation of graphite at intensities above 10" W cm" 2 . Deposited without catalysts and without columnar habits of growth, they display a range of diamond-like properties that increases with the energies of condensation. The best of these new materials was originally called amorphic diamond. However, the recent improvements have succeeded in bringing the hardness of such films above 80 GPa, and the term nanophase diamond seems more appropriate.4 This material seems to be a unique product of energetic condensation from C 3 + and C 4 + ions produced in a laser plasma. No source of this material has been found at lower characteristic energies.5 Nanophase diamond films have been produced entirely without hydrogen, fluorine, or any other catalysts. These films are composed of hard dense nodules with grain sizes on the order of 20-100 nm.1"5 The diamond characteristics of these novel materials have been evalu2548

J. Mater. Res., Vol. 10, No. 10, Oct 1995

http://journals.cambridge.org

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ated by several analytical methods. Measurements agree in supporting sp3 contents of better than 75% for the nominally produced films.6"8 No other technique has been reported for the production of this material, and to d