Hydrogen plasma cleaning

Hydrogen plasma cleaning (cleaning) Using a hydrogen plasma to promote reduction reactions or to hydrogenate hydrocarbons, thus making them more volatile. 

Blistering has been couched traditionally in the context of materials performance in a fusion environment, and, as such, has been considered a problem in the longterm sense. There exists, however, some indication that blistering-like phenomena may occur when hydrogen discharge cleaning techniques are used to condition the plasma containment chamber walls of existing devices. (See Sect. 5.6.2.)... 

Substrates used included fiber-reinforced epoxy base polymer [FRP], nylon 66, polytetrafluoroethylene [Teflon], poly(ethylene terephthalate) [PET], phenolic resin, and thermoplastic polyimide [ULTEM, GE]. FRPs were the primary substrates used. Initially, they were cleaned with detergent in an ultrasonic bath followed by rinsing with deionized water and alcohol. For further cleaning, they were treated with oxygen plasma (1.33 seem, 60 W, 5 min) followed by a hydrogen plasma treatment (3 seem, 60 W, 5 min). 

Gold substrates were dipped in a solution of 8.4 mmol/L hexadecanethiol in ethanol for 1 min, rinsed with ethanol, and cleaned by a hydrogen plasma. A 1 mM solution of each of 1-11 in absolute THF as well as absolute ethanol, was prepared under a stream of nitrogen. Substrates were stored in these solutions for 24 h in the absence of light, rinsed with ethanol, blown dry under a stream of nitrogen and stored in the dark until further use. 

The most common in situ cleaning procedure used in PVD processing is plasma cleaning with a reactive gas such as oxygen or hydrogen to produce volatile reaction products, e.g. hydrocarbons to CO, CO2, or CH4 (Sec. 13.11). 

Of course, oxygen is not the only impurity that will react with beryllium. Another material that is important in forming mixed-material layers with beryllium is carbon. The saturated value of retention that has been found in beryllium surfaces exposed to a large deuterium ion fluence could easily be overshadowed if a carbon rich layer forms on the beryllium surface due to impurity carbon ions in the incident plasma flux. The hydrogen retention properties of plasma deposited carbon films has been shown to dominate the total retention in beryllium samples exposed to the plasma at lower temperature. Once the sample temperature during exposure approaches 500°C there is little difference between the retention in Be/C mixed-material layers compared to clean beryllium samples [48]. The temperature dependence of the retention of carbon containing mixed material layers, as well as that of clean beryllium surfaces is shown in Fig. 14.10. There are two possible explanations for the reduced retention in the mixed-material layers formed at elevated temperature. The first is that beryllium carbide forms more readily at elevated temperature and less retention is expected in beryllium carbide [11]. The second is that carbon films deposited at elevated temperature also tend to retain less hydrogen isotopes [49]. 

Can be used in the flame or flameless mode. In the latter instance, a very low fuel (hydrogen) flow is used to form a plasma around a heated bead of potassium or rubidium salts. This results in a reduced response to hydrocarbons and subsequently less interference. Halogens as well as organolead compounds respond to the NPD detector in the flame mode. Phosphates (from cleaning detergents), chlorinated solvents and silanizing reagents can deplete the alkali beads and should thus be avoided ... 

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