Carbon overcoating

Molecularly thin lubricant film is an important application of nanoscale confined polymeric fluids, and is the focus of this chapter. Ultrathin lubricant films are necessary in high-density data storage to increase the reliability and performance of hard-disk drive (HDD) systems [2-4]. Spinoff and intermittent contact between the slider (or head) and the lubricated disk [ultrathin perfluoropolyether (PFPE) films are applied to the disk s carbon-overcoated surface, as shown in Fig. 1.1] cause loss and reflow of the lubricant film. The relevant HDD technology is summarized briefly in the end-of-chapter Appendix Section A.I, which provides an overview of how certain information technology devices are controlled by nanoscale chemistry. 

Fig. 4 The components of the surface energy measured on hydrogenated carbon overcoated thin film magnetic recording media (A) The dispersive component of the surface energy for PFPE Z and Zdol (B) the polar component of the surface energy for PFPE Zdol with molecular weight (M-w) of 1100 (A) 1600 (O), and 3100 ( ) g/mol and (C) the disjoining pressure as a function of film thickness for PFPE Zdol (Mw is 3100 g/mol).

The atomic% substrate in the spectrum is then the sum of the substrate portions of the Cl and Ols integrated areas (plus the integrated area of the Si2p spectrum in the case of a non-carbon-overcoated silicon substrate). The ratio of the PFOM film... 

PFOM Thickness as Measured by Ellipsometry on Carbon-Overcoated Slider Rows Showing the Effect of Multiple Dip Coatings... 

Since the air bearing surface of the slider is carbon-overcoated, the same carbon overcoat was placed on some of the silicon strips to evaluate the PFOM film thickness and ellipsometric measurement procedure on carbon- and non-carbon-overcoated substrates. A nominally 12.5-nm-thick layer of sputtered carbon was deposited on silicon strips, and the strips were dip coated with PFOM. The ellipsometric angles A and T were measured. The two-layer model (two films on an absorbing substrate) was used with the optical constants for the materials listed in table 4.6 in calculating the PFOM thickness from A and T on carbon-overcoated silicon. The apparent... 

Optical Constants from Ellipsometry and Ellipsometric Angles A and P for the Carbon-Overcoated Silicon Strips... 

PFOM Thickness on Carbon-Overcoated Silicon Strips as Measured by Ellipsometry and as Estimated from XPS d/X... 

Since an additional ellipsometric measurement would be needed to determine the carbon-overcoat thickness, the ellipsometric measurement of PFOM thickness directly on non-carbon-overcoated silicon is more straightforward. Silicon strips and wafers were dip coated with PFOM. The PFOM thickness measnred by ellipsometry and the dIX from XPS are listed in table 4.8. The thickness measured by ellipsometry was divided by the dIX from XPS for each sample (last two columns in table 4.8). The experimentally determined average electron mean free path for PFOM film is X = 2.66 nm. Sliders were dip coated with PFOM at the same conditions as the silicon wafers and strips, and dIX was measured on the air bearing surface of each slider by XPS. These dIX were multiplied by A, = 2.66 nm, as determined above, to estimate the PFOM thickness on the air bearing surface. These results are listed in table 4.9. The concentration of the PFOM solution was 650 ppm, and the withdrawal rate was 1.6 mm/s. 

A test was done to evaluate the use of non-carbon-overcoated silicon wafers and strips as PFOM thickness monitors. The PFOM thickness on the silicon wafers and strips is shown in table 4.8 along with the dfX from XPS measured on the same samples. The data in table 4.8 were employed to derive the experimental mean free path relating PFOM thickness from eUipsometry with dJX from eq. (4.1) as... 

The electron mean free path of A, = 2.66 nm is within the range of mean free paths reported for polymer thin films on surfaces [8]. Equation (4.4) was used to estimate the PFOM thickness on air bearing surfaces from dIX. The values of dIX and PFOM film thicknesses are given in table 4.9. The PFOM film was 0.5-0.7 nm thicker on the carbon-overcoated air bearing surfaces (table 4.9, column 3) and on the carbon-overcoated rows (table 4.7, columns 3 and 7) than on the silicon wafers (table 4.8, column 3). This is attributed to the difference between the surface chemistry of the SiOj surface of the uncoated silicon and that of the carbon overcoat. 

Three approaches have been identified that reduce susceptibility of CA resists to airborne contamination. In the first, process engineering changes such as the addition of special activated carbon filters to the environmental chambers surrounding the exposure tools (76,79), overcoating the resist with a soluble protective film to isolate the resist from the environment (77,80,81), or modifications of the process flow to minimize the time interval between exposure and post-exposure bake have been shown to improve CA resist processibibty. 

The fuel for the Peach Bottom reactor consisted of a uranium-thorium dicarbide kernel, overcoated with pyrolytic carbon and silicon carbide which were dispersed in carbon compacts (see Section 5), and encased in graphite sleeves [37]. There were 804 fuel elements oriented vertically in the reactor core. Helium coolant flowed upward through the tricusp-shaped coolant channels between the fuel elements. A small helium purge stream was diverted through the top of each element and flowed downward through the element to purge any fission products leaking from the fuel compacts to the helium purification system. The Peach... 

Pierson, H. O., Sheek, J., and Tuffias, R., Overcoating of Carbon-Carbon Composites, WRDC-TR-4045, Wright-Patterson AFB, OH 45433 (Aug. 1989)... 

Although such acceleration factors were applied by Fisher et al. [129] in their discussion of the corrosion of Co alloys, there are only a few papers trying to establish the experimental acceleration factors for disk materials. One of these is the work of Novotny et al. [154], These authors observed that carbon-coated CoCr, CoPt, or CoP disks, when exposed to elevated humidity and temperature, show an accumulation of a corrosion product, similar to those seen on uncoated alloys, on the top surface of the carbon. For both overcoated and uncoated disks, oxides and hydroxides of cobalt were detected on the surface, but there was no detectable Cr, Pt, or P. The amount of Co was on the average less on the C-covered disks. The surface Co resulted... 

P.R.170 is broad in scope. It is found in wood stains, including solvent-based stains it is blended with carbon black and yellows to produce a variety of interesting shades of brown. The colorations are fast to overcoating in these media and resist nitro and acid hardening varnishes and polyester coatings. Its lightfastness in these media equals step 7 on the Blue Scale. 

P.O.38 is broad in scope. The list of applications includes special media, such as wax crayons, artists colors, and wood stains, including those that are solvent based. The products are very lightfast (step 7 on the Blue Scale) and fast to overcoating. Blends of P.O.38 with yellow pigments, such as P.Y.83 or P.Y.120, or with carbon black produce useful shades of brown. 

Kissinger [130] carried out similar experiments following lactate changes observed in a rat subcutaneous microdialysate upon an intraperitoneal injection of lactate. The half-life of the sensor, assembled by coating the enzyme lactate oxidase (LOD) on a glassy carbon electrode with an Os-redox polymer and a Nafion overcoating, was about 24 h. 

The continuous measurement of histamine released from rat basophilic leukaemia cells has been recently reported by Niwa [190], who coupled a microdialysis probe with a histamine oxidase-based carbon electrode obtained by coating the enzyme on the top of an Os-gel-HPR layer. For the exclusion of electrochemically active compounds, they suggested an overcoating of Nafion. In addition, a sensor using micro-machining techniques has been fabricated by the authors and apphed to the monitoring of histamine release from a small mast cell colony. 

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