Kevin J. Grannen

Spreading of perfluoropolyalkylether films on amorphous carbon surfaces

Spreading of perfluoropolyalkylether thin films on amorphous carbon surfaces has been studied by scanning microellipsometry. Two types of perfluoropolyalkylethers with the same main-chain structure and various molecular weights (between 1000 and 6000 g/mol) were used: Zdol, with OH functional end groups, and Z, with nonfunctional CF3 groups. For Zdol, the thickness of the molecular layers in the spreading profile increase as Mn0.6, where Mn is the mean molecular weight, with the second layer being nearly twice as thick as the first layer. This layered structure was not observed for Z in the molecular weight range under study. As expected, the thickness-dependent diffusion coefficient D(h) was found to decrease with increased molecular weight. Possible molecular conformations near the solid surface are discussed. The spreading of binary blends of Zdol–Zdol, Z–Z, and Zdol–Z were also studied. The results show that the spreading of the binary blend of the same kind of polymer with different molecular weight behaved like that of a lubricant with an intermediate molecular weight. The diffusion coefficient of a blend was found to obey the additivity of viscosity. For Zdol–Z blends, however, the faster moving Z molecules migrate through the network of the slower moving Zdol molecules, and form a monolayer ahead of Zdol.Spreading of perfluoropolyalkylether thin films on amorphous carbon surfaces has been studied by scanning microellipsometry. Two types of perfluoropolyalkylethers with the same main-chain structure and various molecular weights (between 1000 and 6000 g/mol) were used: Zdol, with OH functional end groups, and Z, with nonfunctional CF3 groups. For Zdol, the thickness of the molecular layers in the spreading profile increase as Mn0.6, where Mn is the mean molecular weight, with the second layer being nearly twice as thick as the first layer. This layered structure was not observed for Z in the molecular weight range under study. As expected, the thickness-dependent diffusion coefficient D(h) was found to decrease with increased molecular weight. Possible molecular conformations near the solid surface are discussed. The spreading of binary blends of Zdol–Zdol, Z–Z, and Zdol–Z were also studied. The results show that the spreading of the binary blend of the same kind of polymer with different molecular weight ...

Photoluminescence and Raman spectroscopy in hydrogenated carbon films

a-C:H films prepared by DC-magnetron sputtering in an H/sub 2/:Ar mixture exhibit strong photoluminescence (PL) peaks superimposed upon the Raman scattering spectrum. PL becomes observable at a hydrogen content of ca. 34%, and increases exponentially thereafter, driven by the progressive saturation of carbon dangling bonds. In this %H range, hardness and elastic modulus decrease and CSS durability reaches an optimum. The Raman G peak position is very sensitive to deposition temperature (shift of 0.1 cm/sup -1///spl deg/C) and was found to correlate with the sp/sup 3//sp/sup 2/ bonding ratio as measured by EELS, and therefore can also be used as a predictor of carbon tribological performance.

Spreading of PFPE lubricants on carbon surfaces: effect of hydrogen and nitrogen content

The spreading of OH-terminated perfluoropolyalkylether (PFPE), Zdol, on amorphous carbon surfaces was studied as a function of hydrogen or nitrogen content in the carbon film, using scanning micro-ellipsometry. A layered structure of the thickness profiles was observed, which remained qualitatively the same for all carbon types. The sharpness of the second layer was gradually eroded as either hydrogen or nitrogen content in the films was increased. The thickness-dependent diffusion coefficient was calculated using the Matano interface method. It was observed that the surface mobility of Zdol increased as hydrogen content increased, but decreased as nitrogen content increased. Implications of these results on the boundary lubrication properties of Zdol on carbon films are discussed.

Ion beam deposition of carbon overcoats for magnetic thin film media

Ion beam deposited carbon has been investigated for its use as an overcoat for magnetic thin film media. By using a gridless end-Hall ion source, carbon has been deposited that possesses hardnesses to 18 GPa, stress to 4.5 GPa, and densities up to 2.6 g/cc. Contact-start-stop testing of ion beam deposited carbon to fifty thousand cycles shows a marked improvement in failure rate compared to hydrogenated and nitrogenated carbon. Energetic deposition of carbon thin films can lead to implantation of energetic species into the magnetic layer. Simulations have been performed to assess the vulnerability of the magnetic layer to energetic implantation of carbon. In addition, the effect of the partial pressure on the magnetic performance is assessed and a critical impurity concentration defined.

Properties and durability of thin a-C:H overcoats produced by plasma enhanced chemical vapor deposition

Abstract Radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) technique was used to deposit thin amorphous hydrogenated carbon (a-C:H) overcoats on glass ceramic disc substrates. Raman spectroscopy results showed that higher sp3 carbon content films can be obtained by applying appropriate kinetic energy of ion bombardment (∼100 eV) during film growth. However, a higher content of hydrogen was also observed in such films. The results suggest that a certain fraction of sp3 carbon bonds is likely to be terminated by hydrogen and become dangling bonds. These dangling bonds may be important to the durability performance in the tribo-contact interface. The highly hydrogenated carbon overcoats (∼40 at.%) showed significant improvement in tribological performance compared with the less hydrogenated films. The contact-start-stop test at ambient environment of such overcoats showed good durability over 10 K cycles at the film thickness of 3.6 nm.