Synthesis of ultrasmooth nanostructured diamond films by microwave plasma chemical vapor deposition using a He/H 2 /CH 4
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Ultrasmooth nanostructured diamond (USND) films were synthesized on Ti–6Al–4V medical grade substrates by adding helium in H2/CH4/N2 plasma and changing the N2/CH4 gas flow from 0 to 0.6. We were able to deposit diamond films as smooth as 6 nm (root-mean-square), as measured by an atomic force microscopy (AFM) scan area of 2 m2. Grain size was 4–5 nm at 71% He in (H2 + He) and N2/CH4 gas flow ratio of 0.4 without deteriorating the hardness (∼50–60 GPa). The characterization of the films was performed with AFM, scanning electron microscopy, x-ray diffraction (XRD), Raman spectroscopy, and nanoindentation techniques. XRD and Raman results showed the nanocrystalline nature of the diamond films. The plasma species during deposition were monitored by optical emission spectroscopy. With increasing N2/CH4 feedgas ratio (CH4 was fixed) in He/H2/CH4/N2 plasma, a substantial increase of CN radical (normalized by Balmer H␣ line) was observed along with a drop in surface roughness up to a critical N2/CH4 ratio of 0.4. The CN radical concentration in the plasma was thus correlated to the formation of ultrasmooth nanostructured diamond films.
I. INTRODUCTION
In the United States, the need for long service life medical implants such as artificial joints is increasing rapidly. Wear of articulating surfaces is a major concern in orthopedic and dental implant devices, including the temporo-mandibular joint (TMJ), which resides in very close proximity to the eye, the ear, various nerves, and the brain.1,2 The National Institute of Dental and Craniofacial Research (NIDCR) of the National Institutes of Health (NIH) states that over 10 million people in the United States suffer from TMJ problems at any given time.3 In some cases, TMJ implant devices are needed, and their success is greatly influenced by the degree of wear at articulating surfaces. Complications arising from wear include component loosening, deleterious biological responses, osteolysis, mechanical instability, decreased joint mobility, increased pain, and ultimately implant failure.4 A major goal is to develop smooth and wear-resistant films on the articulation surfaces to reduce the friction and wear in mating total joint replacement components. Hard, ultrasmooth, and wear resistance a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0334 J. Mater. Res., Vol. 21, No. 10, Oct 2006
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diamond films on metal surface can serve this purpose very well. Chemical vapor deposited (CVD) diamond films grown using gas mixtures such as hydrogen, nitrogen, and methane have been investigated primarily to obtain smooth nanocrystalline diamond film.5–8 The surface roughness value of 15–20 nm (root-mean square; rms) and grain size of 13–15 nm were achieved. The film grown without nitrogen addition shows large, welldefined crystalline facets indicative of high-phase-purity diamond.9 In contrast, the films grown with added nitrogen exhibit a nanocrystalline appearance with weak agglomeration
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