Substrate and material transfer effects on the surface chemistry and texture of diamond-like carbon deposited by plasma enhanced CVD
Diamond-like carbon (DLC), a thin amorphous carbon film, has many uses in tribological systems. Exploiting alternative substrates and interlayers can enable control of the hardness and modulus of the multi-layer system and improve wear or friction properties. We utilise XPS and AFM to examine DLC concurrently coated on an epoxy interlayer and a steel substrate by plasma enhanced chemical vapour deposition (PECVD). sp 2 /sp 3 ratios were calculated both by deconvolution of the XPS C1s line and analysis of the C KLL Auger spectrum. Altering the substrate causes changes in the carbon bonding configuration, evident with the same trend through both analysis methods, though with differing absolute values, related to hydrogen and oxygen content. There is significant variation in the microscale surface texture, exhibited both by average roughness values and size and uniformity of surface asperities. This suggests that alteration to the film surface structure is a factor to be considered in addition to interface adhesion, hardness and elastic modulus, in investigating substrates and interlayers for tribological coatings. Examination of a DLC film separately produced on a steel substrate, in comparison with that produced concurrently with DLC coating of epoxy, shows the possibility of effects on the chemistry of the film through transfer of material from adjacent samples within the plasma deposition, related to heating, out-gassing or sputtering processes. The possibility of such contamination has implications in coating parameter design and coating of multiple samples with PECVD.
Evaluation of a variety of a-C:H coatings on PEEK for biomedical implants
Abstract Four different hydrogenated amorphous carbon (a-C:H) coatings were deposited on poly-ether-ether-ketone (PEEK). Their properties in terms of surface roughness, wettability, nanoindentation, residual internal stress, adhesion, scratch resistance, friction and wear resistance were assessed. The two polymer-like carbon coatings were obtained without applying any bias voltage to the substrate. They exhibited very low hardness, Young's modulus and residual internal stress compared with what is generally achieved for diamond-like carbon films. Nonetheless, they enabled to significantly reduce wear when rubbed against an alumina ball. They also showed a very good adhesion to the PEEK substrate and a reduction of the coefficient of friction compared with that of the PEEK substrate. When the titanium layer deposited on the PEEK substrate was biased at either − 50 V or − 100 V during the deposition of the a-C:H coatings, the a-C:H coatings were harder, stiffer and more internally stressed than the two polymer-like carbon coatings. However, the a-C:H films obtained with bias voltages of − 50 V and − 100 V suffered from adhesive fracture in pull-off testing and early delamination in tribological testing. These results were assumed to be due to a titanium oxide layer which was not properly removed prior to the deposition of the hydrogenated amorphous carbon films and to the higher residual internal stress of the a-C:H films obtained with bias voltages of − 50 V and − 100 V compared with the two polymer-like films.
Influence of surface oxygen on chemoresistance of tin oxide film
The oxygen controlled chemoresistance of tin oxide based gas sensors was investigated in the temperature range from 20 to 320 °C. Polycrystalline thin film gas sensors were fabricated by the reactive dc‐magnetron sputtering. The parameters of the sensors were also modified by additional Pt or Sb doping. The effect of surface oxygen species on the chemoresistance was studied by x‐ray photoelectron spectroscopic (XPS) analysis of the surface chemical composition before and after different sample treatments. The oxygen peak at a binding energy 531.8 eV in the XPS core level spectrum was found to be related to the chemisorbed molecular oxygen O−2. The variation of an amount of the O−2 species is found to be the main cause of gas sensitivity of tin oxide films at temperatures from 20 to 230 °C.