Structure and properties of carbon nitride films synthesized by low energy ion bombardment
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Structure and properties of carbon nitride films synthesized by low energy ion bombardment Xiao-Ming He, Li Shu, Wen-Zhi Li, and Heng-De Li Department of Materials Science and Engineering, Tsinghua University, Beijing, 100084, People’s Republic of China (Received 30 September 1996; accepted 3 February 1997)
Carbon nitride films have been synthesized at low substrate temperature by Ar1 sputtering a graphite target with concurrent N1 assisted bombardment. It was disclosed that N1 bombardment with low energies of 150–400 eV and beam densities of 0.16–0.23 mA cm22 was favorable to grow carbon nitride films with high NyC atomic composition ratios of 0.47–0.56. The spectra of x-ray photoelectron spectroscopy and infrared spectroscopy show that the low energy N1 bombardment activates nitrogen atoms to combine carbon atoms in unpolarized covalent bonds. Under the 150–300 eV and 0.16–0.23 mA cm22 N1 assisted bombardment, the formed films are identified by transmission electron microscopy to possess the b –C3 N4 microcrystalline structure. The films exhibit an extremely high hardness of 5260 kgfymm2 , a high resistivity of 4.8 3 1012 V 3 cm, and excellent optical transmittance. Friction and wear tests show that carbon nitride films on steel substrate can perform the even wear in low friction coefficients of 0.05–0.16 while raising wear loads up to 20 N.
I. INTRODUCTION 1–3
Based on the recent theoretical calculations predicting the superhardness, good thermal conductivity, and high chemical stability of the hypothetical b –C3 N4 , the preparation and characterization of this carbon nitride compound has been a new exciting focus in current materials research, referring to its structure, properties, and possible applications in future.4–17 So far, carbon nitride has evinced interest mainly due to its promise as an optical, optoelectronic, and tribological material.4–7 It is thus of great importance to synthesize this material in thin film form to realize its potential fully. Recently, considerable efforts with various film synthesis techniques have been directed to deposit this elusive phase, such as rf diode sputtering,8 ion implantation,9,10 magnetron sputtering,11 pulsed laser ablation of graphite targets with concurrent nitrogen ion assisted bombardment,12 and dual ion beam sputtering and ion beam assisted deposition (IBAD).13–15 It is believed that IBAD can provide the energy by bombarding ions to overcome the energy barrier encountered in the b –C3 N4 formation process and can be used to obtain different NyC ratios by adjusting the graphite deposition rates and beam densities of bombarding ions such as nitrogen. Results have indicated that IBAD can be employed to grow extremely hard carbon nitride films using ion and vapor deposition,15 wear-resistant carbon nitrogen films using nitrogen IBAD,7 and crystalline b –C3 N4 using NH3 IBAD.14,16 All the films deposited using nitrogen ion beam assisted deposition are amorphous,13,15,19 although tiny crystallites of b –C3 N4 have b
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