Plasma thermal stability

Uses. The chemical inertness, thermal stability, low toxicity, and nonflammability of PFCs coupled with their unusual physical properties suggest many useflil applications. However, the high cost of raw materials and manufacture has limited commercial production to a few, small-volume products. Carbon tetrafluoride and hexafluoroethane are used for plasma, ion-beam, or sputter etching of semiconductor devices (17) (see loN implantation). Hexafluoroethane and octafluoropropane have some applications as dielectric gases, and perfluorocyclobutane is used in minor amounts as a dielectric fluid. Perfluoro-1,3-dimethyl cyclohexane is used as an inert, immersion coolant for electronic equipment, and perfluoro-2-methyldecatin is used for... 

Plasma processing technologies ate used for surface treatments and coatings for plastics, elastomers, glasses, metals, ceramics, etc. Such treatments provide better wear characteristics, thermal stability, color, controlled electrical properties, lubricity, abrasion resistance, barrier properties, adhesion promotion, wettability, blood compatibility, and controlled light transmissivity. 

The exposure of n-type LPE GaAs layers to a hydrogen plasma for three hours at 300°C induces a neutralization of five deep electron traps at c - 0.13 eV, c - 0.36 eV, c - 0.38 eV, c - 0.54 eVand c - 0.73 eV (Pearton and Tavendale, 1982). The thermal stability of these neutralized centers is lower than for EL2 neutralization and can be compared with the shallow donors one. 

In MBE grown GaAs three dominant electron traps are usually observed Ml at c - 0.17 eV, M3 at c - 0.28 eV and M4 at c - 0.45 eV. Exposure of MBE grown material to a hydrogen plasma for 30 minutes at 250°C completely passivates these three deep levels as shown in Fig. 10 (Dautremont-Smith et al., 1986). After five minute anneals at 400°C or 500°C, the passivation remains complete while the shallow donors are fully reactivated. A five minute annealing at 600°C partially restores the electrical activity of M3. Therefore the thermal stability of the neutralization of deep levels in MBE material is much higher than in other materials and is compatible with most technological treatments. 

Before fluorination, the dielectric constant ofpoly(bisbenzocyclobutene) was 2.8, and this value was reduced to 2.1 after plasma treatment. No data were reported in the paper on characterization of structure or properties, except for the dielectric constant of the modified poly(bisbenzocyclobutene). The authors did report that the thermal stability offluorinatedpoly(vinylidenefluoride) was inferior to the original poly(vinylidenefluoride) when treated in a similar way. One of the probable reasons for the low thermal stability is that the NF3 plasma degraded the polymer. According to their results, the thickness of fluorinated poly(bisbenzo-cyclobutene) was reduced by 30%. The same phenomenon was observed for other hydrocarbon polymers subjected to the NF3 plasma process. A remaining question is whether plasma treatment can modify more than a thin surface layer of the cured polymer Additionally, one of the side products generated was hydrogen fluoride, which is a serious drawback to this approach. 

Like other salt melts ionic liquids are characterized by a specific combination of physicochemical properties high ionic conductivity, low viscosity, high thermal stability compared to conventional liquid solvents, wide electrochemical windows of up to 7 V and - in most cases - extremely low vapor pressures. Due to their low vapor pressure ionic liquids are not only well suited for the application of UHV-based analytical techniques (e.g. photoelectron spectroscopy [3]), but also for use in plasma reactors with typical pressures of the order of 1 Pa up to 10 kPa. Moreover, due to their high electrical conductivity, ionic liquids may even be used as electrodes for plasmas. To date there are just a few reports on the combination of low-temperature plasmas and ionic liquids available in the literature [4—6]. Therefore, the essential aspects of experiments with ionic liquids in typical plasma reactors are discussed in this section. 

C H layers have a limited thermal stability in the sense that they decompose at elevated temperature even in vacuum. The released product spectrum and the onset temperature for decomposition depend sensitively on the layer structure, in particular, the initial hydrogen content [29,30]. Hard a-C H layers with a typical H content of about 30% (see Table 11.1) start to decompose around 700 K with two distinct effusion maxima at about 800 and HOOK [29,30]. The product spectrum is dominated by H2 with minor contributions of CH4 and some higher hydrocarbons (C.. H y). These results are in good agreement with published data on ion-beam deposited C H layers [31,32], ion-bombarded pyrolytic graphite [33], and other plasma-... 

In DC discharge plasmas, the sudden decrease of contact angle after 15 min treatment has been assigned by S. Okasaki et al. to a structural change of the material surface from crystallised graphite to an amorphous state [93]. It has been shown that the fluorination of PAN-based carbon fibers is more effective in the case of CF4-He plasmas than in 5% F2—He plasmas [94]. The study of the thermal stability of these F-treated fibers has shown however that a 70% loss of fluorine occurred when the samples were heated at 293°C for 10 min. 

Electrothermal vaporization. With ETV/ICP-MS, a small amount of solid sample ( lmg) is introduced into a graphite furnace and subjected to a multi-step temperature program for atomization. Additionally, a modifier can be used for thermal stabilization of the analytes or to improve the matrix mineralization. The vapours produced during the vaporization step are transferred into the plasma by argon carrier gas. 

A glow discharge plasma is not in local thermodynamic equilibrium (LTE), as the number of collisions is too low to thermally stabilize the plasma. Thus the electron temperatures are high (5000 K for the electrons involved in recombination and >10000 K for the high-energy electrons responsible for excitation through electron impact) but the gas temperatures (below 1000 K) are low. 

Differential scanning calorimetry and thermal gravimetric analysis have been used by several authors (27,53) to show that plasma-derived polymers have no phase transitions until decomposition occurs. The remarkable thermal stability of these materials is evidenced by data which show that 80 wt.% of a film prepared from methyl chloride remains at 800 C and that 40 wt.% of a styrene derived film remains at 700°C. 

The desired thickness of the film for the solar sail application was 2.5 ym, but the thinnest commercially available film of this type was Du Font s Kapton O) with a thickness of <7.5 ym. Hence, a need existed to thin the latter film and to assess the photo-and thermal stability of the resulting, thinned film. This paper describes the use of a radiofrequency (RF) oxygen plasma for etching (thinning) of poly[, N-oxydiphenylene) pyromellitimide] (POP) film, and presents data on the photo/thermal degradation of etched and unetched film in vacuum. Although plasma etching has been applied to many polymers, it has scarcely been used on... 

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