Reactive and nonreactive ion mixing of Ni films on carbon substrates

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Abstract
The effects of nonreactive and reactive ion mixing on the interfacial chemistry, morphology, and adhesion of Ni films on carbon substrates (glassy carbon, a-face pyrolytic graphite, and c-face pyrolytic graphite) were examined and compared to the effects of thermal processing. Nonreactive ion mixing was performed with 180-keV 84Kr+ at doses of 1 and 5×1016 Kr/cm2. Reactive ion mixing was performed with 150-keV 28Si+ at doses of 1 and 5×1017 Si/cm2. The as-deposited specimens were also vacuum annealed at 1000 °C for 3600 s. The chemistry and morphology induced by the 1000 °C anneal varied substantially with substrate structure. Adhesion enhancements resulting from the anneal were small (1–40×) and varied greatly with substrate structure. Krypton implantation induced collisional mixing at each of the different Ni/C interfaces, but did not influence specimen chemistry. Large adhesion increases (1–3 orders of magnitude) were observed in all of the 84Kr+ implanted specimens, regardless of substrate structure. Silicon implantation induced extensive Ni diffusion into the glassy carbon, a-face pyrolytic graphite, and c-face pyrolytic graphite substrates. Nickel segregation to the 28Si+ implant profiles resulted in the formation of buried Ni2Si layers. Substantial adhesion increases (1–3 orders of magnitude) were observed in all of the 28Si+ implanted specimens. These adhesion increases were attributed to the mechanical interlocking of films and substrates. The Ni2Si produced by 28Si+ implantation was formed too deep in the carbon substrates to influence interfacial bonding. Topographical changes induced by ion implantation included void and bubble formation, pitting, erosion, and carbon aggregation. These topographical changes varied with substrate structure, ion species, ion dose, and substrate temperature. Film characterization was performed using secondary ion mass spectrometry, Auger electron spectroscopy, scanning electron microscopy with energy dispersive x-ray analysis, and x-ray diffraction. Adhesion was examined using a scratch test.

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