Low temperature synthesis of thin films of carbon nitride
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Thin films of carbon nitride have been prepared using triode ion plating. It has been observed that the compound formation occurs at ambient substrate temperature itself. Though the films are completely amorphous at temperatures below 900 °C, they are hard and transparent down to a wavelength of 200 nm. It has also been observed that the film transmission can be modulated using nitrogen ion flux and partial pressure. The IR transmission spectra clearly show the C-N stretch band around 2200 cm" 1 . Onset of crystallization, as evidenced from electron diffraction, occurs around 900 °C substrate temperature.
There has been considerable interest in the preparation and characterization of carbon nitride thin films, after the early reports of Liu and Cohen,1 Chen et al.,2 and Niu et al. ,3 due to their predicted and observed properties such as hardness, wear resistance, etc. The main difficulty has been the synthesis of crystalline carbon nitride thin films. Although characterization of carbon nitride thin films for potential applications is in progress, it has not yet reached a stage of reasonable understanding. Carbon nitride has evinced interest mainly due to its promise as an optical, optoelectronic, and tribological material.4"6 It is thus of great importance to synthesize this material in thin film form to realize its potential fully. Most of the processes used to synthesize this material as a thin film have been plasma-assisted ones, due to the extremely critical nature of the carbonnitrogen reaction for compound formation. In this paper we report on the synthesis of crystalline carbon nitride thin films by ion plating and the properties of the films so deposited. In ion plating, which has been described in detail elsewhere,7"9 briefly, the evaporant (graphite in the present case) is evaporated from an electron beam gun and the vapor traverses through a plasma (reactive or inert) created by biasing the substrates. Thus, both sputtering of the substrate surface and condensation of the vapor on the substrate take place simultaneously. At high substrate bias values, interdiffusion of the deposit into the substrate also occurs, resulting in an interface that is very important for tribological and metallurgical applications. Substrate bias can be direct current (dc) or radio frequency (RF), depending on the nature of the substrate. A third electrode, a thermionic filament, can also be added to enhance the ion flux; this configuration is called triode ion plating, as opposed to the diode ion plating, and has been used in the present study. J. Mater. Res., Vol. 10, No. 5, May 1995
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In the present investigation high purity graphite was evaporated from an electron beam gun (KA 6 of Leybolds, Germany). The plasma was generated by introducing nitrogen at a pressure of 20 mTorr and biasing the substrates to 200 V. The substrates were heated during deposition from ambient to 900 °C. In the absence of deliberate heating, the temperature rise during the process was only ab
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