Parallel Bias-Enhanced Sulfur-Assisted Chemical Vapor Deposition of Nanocrystalline Diamond Films
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P9.54.1
Parallel Bias-Enhanced Sulfur-Assisted Chemical Vapor Deposition of Nanocrystalline Diamond Films Joel De Jesús1, Juan A. González2, Oscar O. Ortiz3, Brad R. Weiner4, and Gerardo Morell5 1
University of Puerto Rico, Dept. of Physics, PO Box 23343, San Juan, PR 00931, U.S.A. University of Puerto Rico, Dept. of Physics Applied to Electronics, Humacao, PR, U.S.A. 3 Polytechnic University of Puerto Rico, Dept. of Chemical Engineering, San Juan, PR, U.S.A. 4 University of Puerto Rico, Dept. of Chemistry, PO Box 23346, San Juan, PR 00931, U.S.A. 5 University of Puerto Rico, Dept. of Physical Sciences, PO Box 23323, San Juan, PR 00931, U.S.A., [email protected] 2
ABSTRACT The transformations induced by the application of a continuous bias voltage parallel to the growing surface during the sulfur-assisted hot-filament chemical vapor deposition (HFCVD) of nanocrystalline diamond (n-D) films were investigated by Raman spectroscopy (RS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The films were deposited on molybdenum substrates using CH4, H2 and H2S. Bias voltages in the range of 0 - 800 VDC were applied parallel to the substrate surface continuously during deposition. The study revealed a significant improvement in the films’ density and a lowering in the defect density of the nanocrystalline diamond structure for parallel bias (PB) voltages above 400V. These high PB conditions cause the preferential removal of electrons from the gaseous environment, thus leading to the net accumulation of positive species in the volume above the growing film, which enhances the secondary nucleation. The nanoscale carbon nuclei self-assemble into carbon nano-clusters with diameters in the range of tens of nanometers, which contain diamond (sp3-bonded C) in their cores and graphitic (sp2-bonded C) enclosures. Hence, the observed improvement in film density and in atomic arrangement appears to be connected to the enhanced presence of positively charged ionic species, consistent with models which propose that positively charged carbon species are the crucial precursors for CVD diamond film growth. INTRODUCTION The synthesis of nanocrystalline diamond with narrow particle size distribution and high 3 sp -bonded carbon phase purity is currently being actively pursued [1], in order to achieve highly transparent smooth diamond films on a variety of substrates, while maintaining within reasonable parameters the many useful superlative properties of diamond, such as its mechanical strength, chemical inertness, and biological compatibility. Although the synthesis of nanocrystalline diamond (n-D) was pioneered decades ago [2,3], only recently there have been successful developments towards the control of the average crystallite size and size distribution, which are paving the way to accomplishing the nanotechnology of diamond [1,4]. Our group has previously shown [5,6] that fundamental changes in the film deposition process take place when th
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