Vlad J. Novotny

Lubricant dynamics in sliding and flying

The dynamics of molecularly thin liquid lubricant films in sliding and flying experiments is studied principally by scanning microellipsometry and complemented with both scanning x‐ray photoelectron spectroscopy and infrared spectroscopy. Microellipsometric profiling of lubricant thickness is performed in situ, either dynamically or statically on films ranging from 1 to 10 nm. The removal of liquid polyperfluoroether lubricants from sliding and flying tracks, which includes the displacement and loss depends on film thickness, molecular weight, and chemical structure. In flying and sliding, the lubricant removal rate from monolayer films is significantly slower than from multilayer films. In flying, lubricant displacement and loss increase with a decrease in molecular weight.

Processing effects on the tribological characteristics of reactively sputtered chromium oxide (Cr2O3) overcoat films

The mechanical and tribological characteristics of thin chromium oxide films are investigated by controlling the process parameters in reactive deposition and subsequent annealing. From this, the correlation between the deposition process, film structure, and properties is established. Substrate heating and oxygen partial pressure are found to be the critical parameters that alter the oxygen concentration and crystallization of the films which, in turn, affect their stress, hardness, and wear resistance. The chromium oxide film deposited at 150 °C in pure argon and annealed at 300 °C shows a hardness of 25 GPa, which is near the bulk hardness of Cr2O3, and exhibits a good wear resistance with adhesive wear being the dominant wear mechanism. Reactive deposition at 25 °C or with excessive oxygen leads to films with nonstoichiometric composition, which hinders their crystallization upon low‐temperature annealing. As a result, the hardness is reduced, and the wear resistance deteriorates several orders of mag...

Pin-on-disk tribology of thin-film magnetic recording disks

Tribological studies of friction and wear were performed on carbon overcoated thin‐film magnetic recording media with pin‐on‐disk tests. Scanning microellipsometry was employed to measure the wear of carbon overcoats on rigid magnetic media. Severe wear produced after the carbon film wore through was measured by mechanical profilometry. The wear rate of the carbon is three orders of magnitude lower than that of the underlying metallic layers and is nearly proportional to slider load. Micrographs of the wear tracks and the magnitude of the wear coefficient from the Archard wear equation indicate three‐body abrasive wear.

Glow‐discharge optical spectroscopy as a diagnostic of sputtered permalloy film composition and saturation magnetostriction

We show that the composition and saturation magnetostriction of sputtered permalloy films can be correlated with the relative intensities of iron and nickel atomic emissions from a 13.56‐MHz rf glow discharge. Wavelength‐resolved emission spectra as a function of discharge pressure were recorded while sputtering iron and permalloy targets. Intensities of some emission lines were highly correlated, so that their ratios were nearly independent of argon pressure. This occurred in spite of a ∼50‐fold change in the brightness of the glow over the pressure range studied, and suggested that the stoichiometry of the sputtering target and the sputtered permalloy film can each be assessed during the sputtering process. The selection of appropriate emission lines is discussed, along with considerations of the type of equilibrium distribution prevalent in a sputtering discharge. We used five sputtering targets with different Ni/Fe ratios to grow films. The films were analyzed in terms of composition, stress, and satu...

Solid-State NMR Studies of the Bonding Structure of Diamondlike Amorphous Carbon Films

Amorphous carbon films are (a-C:H) of interest because of their useful physical properties. They are extremely hard and chemically inert, resisting degradation by both acids and alkalis. They are insoluble and can be conformably coated onto virtually any substrate. These properties make the films ideal protective coatings on magnetic disks and tools. We have studied several thin (one to two micron) films prepared by plasma enhanced chemical vapor deposition with varying radiofrequency fields strengths to determine structural differences at the atomic level. Several properties of the films, such as hardness and wear rate, are dependent on deposition power. We have found that the sp 2 /sp 3 ratio increases with increasing deposition power. Thus, films that are harder are more “graphitic” and less “diamondlike”. The films studied here contain 11–16 atomic percent hydrogen, most of which is associated with sp 3 carbon sites. At least two distinct phases of hydrogens exist. Variable temperature studies reveal that, in contrast to amorphous hydrogenated silicon, proton linewidths in carbon films are temperature dependent, suggesting some molecular motion is present at room temperature.