The carbon overcoat (COC) on heat-assisted magnetic recording (HAMR) media was deposited at increasing temperature. The optical extinction (k) of this media was measured with ellipsometry and found to increase with temperature from 0.2 to 0.9 over the temperature range from 220 degrees C to 360 degrees C. Raman spectroscopy of these COC surfaces had an increasing G-peak position and decreasing G-peak width along with an increasing I(D)/I(G). An increasing sp(2) ring/chain and aromatic cluster size and decreasing optical gap were inferred from these changing parameters. HAMR writing on this media was found to require incrementally less laser power (from 100% to 92%) with increasing optical extinction to attain a fixed track width. This was determined to be due to the increased imaginary component of the dielectric function in this film (2nk). The SNR of these written tracks was observed to improve by approximately 0.65 dB with deposition temperature. A finite-element method model of the head and media showed that the thermal gradient of the hot spot in the media increases with optical extinction and increases the SNR. A small decrease in the COC density with temperature was observed and was calculated to further decrease the COC thermal conductivity and thus enhance the increased thermal gradient.

An apparatus has been designed and built to measure the adsorption of contaminants on the surfaces of lubricated carbon overcoats such as those used on magnetic data storage media. The device is based on a quartz crystal microbalance housed in a high vacuum chamber and can be used to make rapid measurements of both the amounts and the rates of contaminant adsorption from the gas phase during exposure. Initial measurements of the adsorption of water during exposure to water vapor indicate that at room temperature and moderate humidity levels (∼50% RH) the amount of water on a surface is of the order of one adsorbed monolayer. Adsorption and desorption is remarkably rapid indicating that equilibrium with ambient humidity is reached on timescales of minutes. Finally, the comparison of H2O and D2O adsorption indicates that the adsorbed water either forms a hydrogen bonded network on the surface or is hydrogen bonded to some species exposed at the surface of the carbon overcoat.

Density functional theory- (DFT-) based ab initio calculations were used to investigate the surface-to-surface interaction and frictional behavior of two hydrogenated C(100) dimer surfaces. A monolayer of hydrogen atoms was applied to the fully relaxed C(100)2x1 surface having rows of C=C dimers with a bond length of 1.39 Å. The obtained C(100)2x1-H surfaces (C–H bond length 1.15 Å) were placed in a large vacuum space and translated toward each other. A cohesive state at a surface separation of 4.32 Å that is stabilized by approximately 0.42 eV was observed. An increase in the charge separation in the surface dimer was calculated at this separation having a 0.04 e transfer from the hydrogen atom to the carbon atom. The Mayer bond orders were calculated for the C–C and C–H bonds and were found to be 0.962 and 0.947, respectively. σ C–H bonds did not change substantially from the fully separated state. A significant decrease in the electron density difference between the hydrogen atoms on opposite surfaces was seen and assigned to the effects of Pauli repulsion. The surfaces were translated relative to each other in the (100) plane, and the friction force was obtained as a function of slab spacing, which yielded a 0.157 coefficient of friction.

The oxidation kinetics of a-CHx overcoats during exposure to oxygen and water vapor have been measured using X-ray photoemission spectroscopy (XPS) in an apparatus that allows oxidation and analysis of freshly deposited a-CHx overcoats without prior exposure of the overcoats to air. The uptake of oxygen on the surfaces of the a-CHx overcoats has been measured at O2 and H2O pressures in the range 10(-7)-10(-3) Torr at room temperature. The uptake of oxygen during O2 exposures on the order of 10(7) Langmuirs leads to saturation of the a-CHx overcoat surfaces at oxidation levels on the order of 20%. This indicates that the surfaces of a-CHx overcoats are relatively inert to oxidation in the sense that the dissociative sticking coefficient of O2 is approximately 10(-6). Oxygen uptake during exposure to H2O vapor is similar to the uptake during exposure to O2 gas. Although the surfaces of the a-CHx overcoats are quite inhomogeneous, it has been possible to model the uptake of oxygen on their surfaces using a fairly simple Langmuir-Hinshelwood mechanism. Interestingly, the saturation coverage of oxygen during exposure to air at atmospheric pressure is approximately 6%, significantly lower than that obtained during low-pressure exposure to O2 gas or H2O vapor.

Electron spectroscopy for chemical analysis (ESCA) has been commonly used as a metrology tool for lubricant film-thickness measurement on magnetic hard disks. The accuracy of the ESCA-thickness measurement rests solely with the calibration accuracy of the characteristic photoelectron attenuation length in the lubricant film. Several past studies on this subject yielded widely divergent results, due to the difficulty in obtaining an accurate, absolute lubricant film-thickness measurement. In this paper, we revisited the calibration issue and, instead of following the same paths pursued in the past, used a derivative method to yield an accurate calibration of the photoelectron attenuation length. We also compared the various methods for lubricant film-thickness calculation based on ESCA measurements and determined that the most accurate method is to use only the photoemission signal from the lubricant film. In addition, by studying the lubricant film-thickness effect on the electrical readback signal, we found that the lubricant film leads to an increase in the head-medium spacing by an amount greater than one times, but less than two times, its physical thickness.

High resolution electron energy loss spectroscopy has been used to obtain vibrational spectra of Fomblin Z-tetraol lubricant films on a commercial magnetic hard disk. The energy loss intensities of the ν(CF2) stretching mode are roughly independent of scattering angle up to angles of Δθ<14° indicating that they are excited by impact scattering. As a consequence there is little information that can be gleaned from the spectra about molecular orientation on the surface. A negative ion resonance enhances the energy loss cross section of the ν(CF2) stretching mode at the impact energy of EI=4eV. It is possible that this resonance is associated with the known sensitivity of fluorocarbons to electron induced dissociation. Annealing the disk sample to T=700K causes a dramatic decrease in the intensity of C–F stretching modes and an increase of the loss features due to C–H stretching. This indicates that the Fomblin Z-tetraol has decomposed and is exposing the a-CHx overcoat on the magnetic media surface.

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.

In this paper, we describe carbon film morphology under different deposition conditions using Monte Carlo simulation.

Humidity influences the tribological performance of the head-disk interface in magnetic data storage devices. In this work a quartz crystal microbalance was used to measure the uptake of water on amorphous hydrogenated carbon (a-CH x ) films at room temperature and pressures of water corresponding to relative humidities of ∼25%. These experiments have used a-CH x films of varying thickness with and without lubricant. The lubricants used included Fomblin Z-03, Z-disoc, and Z-tetraol deposited on the surfaces of a-CH x films of various thickness. The amount of water adsorbed on the unlubricated a-CH x films is roughly independent of a-CH x film thickness. The presence of the lubricant reduces the amount of adsorbed water; however, the amount of water adsorbed in the presence of a lubricant does not depend significantly on the type of lubricant. These observations imply that water is adsorbed on the surfaces of the lubricant or the a-CH x film rather than being absorbed in their bulk.