Microplasmas generated within cavities having the form of a truncated paraboloid, introduced by Kim et al (2009 Appl. Phys. Lett. 94 011503), have been simulated numerically with a two-dimensional, fluid computational model. Microcavities with parabolic sidewalls, fabricated in nanoporous alumina (Al2O3) and having upper (primary emitter) and lower apertures of 150 µm and 75 µm in diameter, respectively, are driven by a bipolar voltage waveform at a frequency of 200 kHz. For a Ne pressure of 500 Torr and 2 µs, 290 V pulses constituting each half-cycle of the driving voltage waveform, calculations predict that ∼10 nJ of energy is delivered to each parabolic cavity, of which 26–30% is consumed by the electrons. Once the cathode fall is formed, approximately 65% and 8% of the input energy is devoted to driving the atomic ion and dimer ion currents, respectively, and the peak electron density of ∼6 × 1012 cm−3 is attained ∼90 ns following the onset of the first half-cycle (positive) voltage pulse. Specific power loading of the microplasma reaches 150 kW cm−3 and the loss of power to the wall of the microcavity drops by as much as 24% when the excitation voltage is increased from 280 to 310 V. The diminished influence of diffusion with increasing pressure is responsible for wall losses at 600 Torr accounting for <20% of the total electron energy.
Nonreactive perfluoropolyether lubricants were processed by ultraviolet (UV) radiation to make them chemically bonded to thin film magnetic disks. The tribological performance of these disks was then investigated. Disks with a range of 30–50 Å thick perfluoropolyether lubricant, were treated by using the different sources of UV radiations in air, argon, and nitrogen atmospheres. By changing the power density from 40 mW/cm2 to 50 W/cm2 and UV wavelength 185 to 365 nm, in either dry nitrogen or argon gas, a maximum of 38 Å of lubricant was chemically bonded to the thin film disks. Stiction and friction forces during 1 rpm testing were dramatically decreased with the increase in UV exposure time. Contact-start-stop test performance of disks with ∼15%–30% of chemically bonded lubricant was also significantly enhanced. An optimum amount of chemically bonded lubricant provides excellent tribological performance for thin film disks.
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