Trapping of argon in ion beam deposited thin films of CN x H y
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Trapping of argon in ion beam deposited thin films of CNxHy Asghar N. Kayani and David C. Ingram Condensed Matter and Surface Science Program Department of Physics and Astronomy, Edwards Accelerator laboratory, Ohio University, Athens OH 45701 ABSTRACT Unbalanced magnetron sputtering deposition of CNxHy films has been performed with various levels of negative substrate bias and with different flow rates of nitrogen and hydrogen. Argon was used as a sputtering gas and formed the majority of the gas in the plasma. The elemental concentrations of the films were measured in samples deposited on glassy carbon with a 2.2 MeV of He beam used to perform simultaneous RBS and ERS. Argon was found to be trapped in the non-hydrogenated films to a level of up to ~ 4.6 %. The concentration of argon increased for the films deposited under higher negative bias. With the introduction of hydrogen, argon trapping was first minimized and later completely eliminated, even at higher bias conditions, suggesting that the softness of the films brought on by hydrogenation also caused the films to be unable to trap argon during growth and thus showing that argon stability is dependent on burial below a surface of particular structural properties. INTRODUCTION Diamond-like carbon (DLC) films have attracted a great deal of attention because of properties closely related to that of diamond. The material is characterized by its high hardness, low friction, chemical inertness, low electron affinity and can be made optically transparent. Diamond-like carbon films are currently used as solid lubricants in computer hard disks. The properties of diamond-like carbon films depend upon the growth conditions i.e. ion energy and substrate temperature. Ion beam deposition of diamond-like carbon was first carried out by Aisenberg and Chabot [1]. In their experiment a carbon ion beams source was used and carbon ions were accelerated towards the substrate by means of negative bias. They were able to produce films exhibiting many of the properties of diamond and called them diamond-like. The development of carbon nitride (CN) has been a subject of intense investigation for the last ten years, because of the prediction of hypothetical super hard phase β-C3N4 by Liu and Cohen [2-4]. Cohen proposed that carbon nitride should have diamond-like properties with a relatively isotropic arrangement of short (~1.47 Ǻ in length) and predominantly covalent bonding [2-4]. This material, if it can be synthesized, will have a wide range of applications in high performance devices that use high hardness, high temperature, high power and high frequency for their operation [9, 10]. The experimental studies to synthesize carbon nitride materials through deposition at low pressure, are connected by analogy to the preparation of diamond-like carbon films [5-8]. However no credible report has yet been reported for the successful synthesis of continuous β-C3N4. The total hydrogen content critically determines the structure of DLC and CN films at the atomic level (the ratio b
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