Effects of Co-Sputtering

The incorporation of other elements or compounds during the production of sputtered coatings ( co-sputtering ) has been intensively studied in the last few years, mainly to overcome the defects in the performance of sputtered coatings in moist air. Some of the earliest studies were performed by Laboratoire Suisse de Recherches Horlogferes (LSRH) in Switzerland and Hohman Plating and Manufacturing (HPM) in the United States. 

Further work was carried out with 3% - 5% of co-sputtered nickel to evaluate the effects of film thickness and test speed and load. He found that the life of a co-sputtered film increased almost linearly with coating thickness, while that of a conventional film reached a maximum at a thickness of about 4000 nm (40,000A), These are far thicker than coatings described by other authors. A comparison of life 

In general the effect of co-sputtered metals seems to be to increase film density and hardness, as well as modifying molybdenum disulphide crystal size. The increase in density may have some beneficial effect by reducing penetration of oxygen or water vapour into the bulk of the coating, but otherwise there is no 

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Table 10.3 Effects of Co-Sputtered Nickel in Different Atmospheres (Ref.287)...

Fig. 13. Effects of CO level (ppm) in the hydrogen feed stream on the performance of a PEFC at 80 °C. Both electrodes were based on an ionomer-impregnated Pt/C catalyst and thin sputtered platinum film, of total loading 0.45 mg Pt/cm [17].

The Effect of Sputtered RuCte Overlayers on the Photoelectrochemical Behavior of CdS Electrodes Instead of RuCh co-catalyst islands, the use of overlayers examined to protect CdS against photocorrosion. See also Entry 29 in Table 2 and Ref. 498. 180... 

The basic Brophy and Ingraham technique was studied by several other authors. Bayer and Trivedi " found that the effectiveness of the technique depended more on the nature of the coating than on its thickness, and that retained moisture in the electroplate was essential for effective conversion. They recommended a current density of 21.5 A/m for 5 minutes to produce a coating thickness of 1.25 to 2.5 tjm. Nishimura and co-workers found that the presence of air or water or both in the conversion gas improved the wear life. Table 9.5 compares the properties of the in situ films with those of burnished and sputtered films, and shows superior wear life for the in situ films. Their friction results were curious, in that they found that the initial films which were formed gave low friction in air or nitrogen but not in vacuum. Low friction in vacuum was obtained when the initial product was heated in vacuum to 400°C. 

Coating life in moist atmospheres is also influenced by the effects of moisture on the substrate-coating interface, and marked improvements in life have been claimed by the use of moisture-protective pre-treatments of the substrate. Niederhauser et al ° studied a wide range of metals and titanium nitride, titanium carbide and chromium carbide as pre-treatments. The material was sputter-deposited on a steel substrate, and then sulphided by introducing hydrogen sulphide into the sputtering chamber in order to improve molybdenum disulphide adhesion. They found a marked improvement in life, particularly with a rhodium or palladium interlayer, but the actual degree of improvement is confused because they also used co-sputtered PTFE, and this is discussed further in Section 10.6. 

Stupp, B.C., Synergistic Effects of Metals Co-Sputtered with MoS , Thin Solid Films, 84, 257, (1981). 

Designing alloy electrocatalysts by the so-called ad-atom method, and by alloy sputtering for oxidation of CH3OH and CO, and for CO tolerance in H2 oxidation, respectively, as well as for O2 reduction are discussed. Many years of experience are summarized and collaborations with other groups are highlighted. The particle size effect in electrocatalysis by small particle electrodes, and the effect of corrosion of carbon-black supported nanoparticles on the electrocatalytic activity are also discussed. All these factors, as well as catalyst lifetimes, are very important in fuel cell performance and in the final cost estimates for the practical fuel cell applications. 

Fig. 32 Effect of chemical shift of Pt 4d5/2 binding energy in Pt skin layer, prepared on a bare PtsoFeso alloy surface by sputtering deposition, onto (top) the kinetically controlled H2 oxidation current (/ <) and (bottom) the steady-state CO coverage (6co) at room temperature in 0.1 M HCIO4 solution saturated with 100 ppm CO/H2 balance [96, 98]. (Reprinted with permission from Ref. 96, Copyright 2003 by John Wiley Sons Ltd).

Effect of reactive co-sputtering of RuOx has been studied and determined not to have any beneficial... 

The main focus of this year s effort has been on the deposition and characterization of platinum-ruthenium films of various compositions produced by co-sputtering of the individual elements. The effect of ruthenium deposited by reactive cosputtering has also been studied. The sputtering chamber was modified with a linear drive to be able to produce films on graphite foils, porous carbon structures, and on membranes. Thin films were deposited on graphite foil electrodes and characterized by XRD, XPS, SEM and polarization experiments. 

High catalyst activity and utilization of sputtered thin films was demonstrated in operating fuel cells. Optimal sputter-deposition conditions for platinum-ruthenium alloys have been determined. The effect of composition on the performance of Pt-Ru films was studied, and optimal composition has been determined. Novel methods of enhancing surface area and improving porosity have been identified. Co-sputtered ruthenium oxide has been demonstrated not to have any significant beneficial effect on the activity of the catalyst layers. While cost presents a major obstacle to commercialization of DMFCs for mobile applications, this project demonstrates novel means to reduce the catalyst costs in DFMC fuel cells. Efficiency enhancements that are also necessary for DMFCs to be viable will be addressed... 

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