X. Ma

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 ...

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.

Lubricant replenishment on carbon coated discs

The replenishment of a lubricant on a carbon coated disc was characterized through theoretical modeling employing experimentally acquired diffusion coefficient data. To quantify the reflow behaviour of a lubricant film, a parameter, the critical reflow time, was defined as the time to replenish a depleted hole of 1 /spl mu/m diameter in a 2 nm thick lubricant film. The results based on solving 2D diffusion equations showed that the critical reflow time is a strong function of the endgroup polarity and molecular weight of a lubricant, as well as the H and N content in the carbon film. Based on these results, design criteria have been provided for enhanced wear durability of magnetic media.

Simulation of ultrathin lubricant films spreading over various carbon surfaces

The mathematical modeling of the dynamics of ultrathin perfluoropolyalkylether (PFPE) films, taking into consideration both the disk carbon surface composition and lubricant endgroup functionality, is described. Theoretical development based on the Monte Carlo method was employed to emulate experimental spreading data. In this model, we construct a system Hamiltonian based on a lattice-gas model by explicitly incorporating four classes of interactions: molecule/molecule, molecule/surface, endgroup/endgroup, and endgroup/surface, where a molecule is denoted as a backbone in the absence of endgroups. Spreading properties are investigated by tuning the lubricant interactions to model PFPE Z (without polar endgroups) and PFPE Zdol (with polar endgroups) on several surfaces. The simulations qualitatively describe the spreading profiles for molecules with and without polar endgroups. Acquired from N-frame animations, L-t plots are constructed and provide a qualitative comparison with the experimental data obtai...

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.

MICROSCOPIC SPREADING CHARACTERISTICS OF NONPOLAR PERFLUOROPOLYETHER FILMS

The surface diffusion characteristics of nonpolar perfluoropolyether (PFPE) Z on carbon surfaces are investigated in two regimes, submonolayer and multilayer, for nano-thin films. For the submonolayer regime, the two-dimensional, cubic van der Waals equation of state is applied to determine the dependence of the surface diffusion coefficient on the film thickness, as experimental surface diffusion coefficients increase with increasing film thickness. For the multilayer regime, a conventional fluid mechanics analysis with position dependent viscosity and a van der Waals disjoining pressure gradient is applied to investigate the surface diffusion characteristics. The present theoretical analysis qualitatively agrees with the experimental results.

Observations regarding the tribological properties of SiC and AlTiC sliders

To accommodate pseudo-contact and contact recording, new slider materials for high-performance heads must be developed. A new candidate for an advanced slider material is SiC. To compare the tribological properties of SiC with Al/sub 2/O/sub 3/-TiC (AlTiC), todays standard thin film head slider/wafer material, heads with SiC dummy sliders have been manufactured and compared to an AlTiC slider. All test heads were subjected to both dynamic friction testing as well as an AFM mapping. Comparing surface topography and nano-friction, the friction for SiC heads was observed to be highly dependent on its surface roughness and may start out even higher than AlTiC. However, the increase in friction over contact time of SiC is much shallower than for AlTiC, therefore the long term friction and wear performance of SiC sliders is superior.

Monte Carlo simulation of lubricant spreading on nitrogenated and hydrogenated carbon surfaces

fb&Lct The investigation o f the spontaneous spreading ofpolymeric liquid films on solid iurfaces at l l ie (microscopic level has gained considerable interest in recent years due to increased scientific iiinporlance [ I ] and tribological applicatjons 121 The spreading ~iroperties of pertluoropolyalkylether (PFPF,) films, with and without reaGt:tlve end groups (Fornblin-%dol and Z, iespectwelyj,on various nitrogenated and hydrogenated carbon surfaccs were examined for application to high-performance diak drives To understand the spreading profiles obscrvd fi mil micro-ellipsometry measurements for the above systems, we performed a Monte Carlo (MrI siiiiulation The remarkable obsewation by Ma, et al. [Z] shows that the complex iniolec.iiliu Liyerin: structure foi PFPE films with reactive 2nd groups %as obsewed. wlicrcas for IflF 91 oups and the interaction hetween end goups and the substrate, respectively Therefore, lhy betting K=V=O, we recover the Harmltonian for non-reactive inolecule systems Even though l i ts treatment oversimplifies physical reality, the original formulation presented by Ma [?] qualitatively explains the obtained experimental results from scanning micro-cllrpsometry In this paper, we will present two novel modifications in addition to the predescribed model Eq ( l J uiifoltunately results in seve~e evaporation depending on the choice of the interaction parameter, 1. To investigate this issue, we systematically luncd interaction parameters and adopted several complex (non-cubic) lattice structures. Our results show that thc unexpected cvaporation is reduced as the lattice stnictiire becomes more compact. The second iniodificat~oii in~orpoiated the coinplex surface effects of hydrogentied and nitrogenated surfaces In Eq (I). IK(k) (wheie K varies with distance from the substrate k) is the coupling parameter between 2nd Sroupy where KzO implies favorable end group interadmn However, to describe complex siirface effects, we introduced the concept of screening lenglh, given by K(k) = K, exp(k/d), ishere d is the screening length Figure 1 illustrares spreading profiles for two ilifferent screening Icn:ehs, with (a) d=2 and @) d=4 When compared with expenmental data for nitrogenated carbon surfaces. it appears that results from d=2 and d 4 resemble spreading profiles obtained horn carbon surfaces with carbon to nitrogen ratios of 50% and 10%. respectively L3J It is interesting to note that d=rr; carresponds to carbon wthout nitrogen By vaqmy the K values, one may obtain similar profiles illustrating the effect of hydrosen content

Tribological properties of barium ferrite films

Acoustic emission and friction coefficients have been measured during start-stop and continuous sliding for pure and doped barium ferrite films, without lubrication, and compared with concomitant surface topography and magnetic properties. Barium ferrite films averaging about 100 nm in thickness, were produced on thermally oxidized Si substrates by sputter deposition and then furnace or rapid thermal annealed in order to develop optimum microstructure and magnetic characteristics. Four varieties of (hexagonal) barium ferrite were produced and investigated: pure barium ferrite with longitudinal and perpendicular c-axis orientation, pure barium ferrite with perpendicular orientation with Pt underlayer and doped barium ferrite. Results are compared with data obtained from commercial disks with a carbon overcoat.