Dielectric-barrier discharge plasma source and its application to synthesis of diamond like carbon films
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Dielectric-barrier discharge plasma source and its application to synthesis of diamond like carbon films Xinpeng Wang1,2, Xiaoliang Tang3, and Peter Xianping Feng1,2 1 Department of Physics, University of Puerto Rico, San Juan, 00931, Puerto Rico 2 Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, 00931, Puerto Rico 3 Physics Department, Donghua University, Shanghai, 201620, China, People's Republic of ABSTRACT Dielectric barrier discharge plasma sources have been studied and used for syntheses of diamond like carbon thin films. The plasma electrical properties under different gas concentrations and pressures were analyzed. Based on the results of the characterizations, dielectric barrier discharge plasma at different methane-hydrogen-argon gas ratios was used to synthesize large areas of diamond-like carbon films. Experimental data indicate that only at argon concentrations equal to or less than 75% diamond like carbon film fabrication could be accomplished. This has been confirmed based on the Raman spectra and hardness measurements. On the other hand, high argon contents during deposition would result in graphite type of thin films. INTRODUCTION Developments in dielectric barrier discharge (DBD), commonly known as atmospheric pressure glow discharge [1], and in the filamentary or disperse DBD [2], proved its applicability for the growth of soft thin film materials and surface treatment techniques. For example, Klages et al [3] used glycidy methacrylate as a prototype precursor to investigate DBD-based plasma deposition for evaluating the applicability of dielectric barrier discharges to obtain plasma polymers with a high degree of structural retention of the starting precursor. Using pulsed excitation of the discharge, about 90% of the epoxy groups of GMA were retained in plasma polymers obtained at deposition rates in the order of 3-5 nm/s. Preliminary investigations of the mechanism of film formation under pulsed plasma conditions indicated that intact monomer molecules’ reaction with surface radicals generated during the pulses played a prominent role. Various studies based on DBD have been performed, such as the polymer surface modification [4], biomedical material surface modification [5], water treatment by the bipolar-pulsed dielectric barrier discharge [6], and pulsed-plasma deposition from ally alcohol and methacrylic acid derivatives [7]. Furthermore, measurements of electron energy by emission spectroscopy in pulsed corona and DBD [8], and gas temperature in a N2/Ar DBD [9] have also been reported. Systematic and comprehensive reviews of these surface modifications of polymers have been given by Y. Uyama et al [10]. Currently, a primary challenge for the DBD technique is to synthesize super hard nanocomposite carbon and nanostructured diamond. According to Liu’s report on the hardness of carbon films, it was up to 10GPa under CH4-to-H2 ratio of 1:2 based on DBD at atmospheric pressure [11]. Its hydrocarbon group ratio [CH3/ (CH2+CH)] and C-C bond type ratio (sp3C
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