High-temperature oxidation of CrN/AlN multilayer coatings §

Abstract Experiments are reported on sputter depth profiling of CrN/AlN multilayer abrasive coatings by secondary ion mass spectrometry (SIMS) coupled with sample current measurements (SCM). The coatings were deposited by a closed-field unbalanced magnetron sputtering. It is shown that after oxidation tests, performed in air at 900 8C for 2 h and at 1100 8C for 4 h, the layered structure begins to degrade but is not destroyed completely. Oxidation at 1100 8C for 20 h causes total destruction of the coatings that can be attributed to a fast diffusion of oxygen, nickel, manganese and other elements along defect paths (grain boundaries, dislocations, etc.) in the coating. There are practically no nitrides in the near-surface layer after such a treatment and all the metallic components are in the oxidized form as follows from the data obtained by X-ray photoelectron spectroscopy (XPS). According to XPS and mass-resolved ion scattering spectrometry (MARISS), the surface content of Al in the heat-treated coatings has decreased in comparison with the as-received sample and that of Cr increased. Both XPS and MARISS data exhibit real increase in superficial concentration of the substrate materials (Mn and Ni) that is controversial if using SIMS alone. SCM turned out to be an informative depth profiling method complementary to more expensive and complicated SIMS, being particularly useful for structures with different secondary electron emission properties of the layers. SCM with predetermined SIMS calibration allows a routine characterization of coatings and other multilayer structures, particularly, in situations where the expenses of analysis can be justified. www.elsevier.com/locate/apsus

Low temperature plasma-assisted chemical vapour deposition of amorphous carbon films for biomedical-polymeric substrates

Preliminary results have been obtained on the biocompatibility of amorphous carbon hydrogen (αC:H) coatings deposited on polystyrene. Deposition was carried out at low substrate temperatures using pulsed r.f. plasma-assisted chemical vapour deposition from a methane-hydrogen gas mixture. Cytotoxicity tests using a standard cell line indicate a high degree of biocompatibility. Specifically, αC:H is not toxic to cells, appears to increase cell attachment and affords normal cell growth rates. Wear and other tests have revealed no significant differences between these αC:H coatings and those deposited on a stainless steel at a higher substrate temperature, except for a more pronounced surface texture. However, position in the r.f. plasma was found to be critical for the deposition of good, adherent low temperature coatings