| Summary: | 碩士 === 國立清華大學 === 生醫工程與環境科學系 === 97 === Thermal outgassing rates of aluminum and titanium chambers, which were vented to dry nitrogen atmospheres with different conditions, were measured. The vacuum surface states were compared with different venting conditions in order to obtain lower outgassing rates. Both hot and cold nitrogen gas purging dried water vapor, which was adsorbed on surface, were compared by FT-IR. The surface coverage model was also discussed.
The results showed that vented by dry nitrogen (1.3 ppb humidity) and protected the vacuum chamber from atmosphere environment by glove box, had the lowest outgassing rate. The outgassing rates of aluminum chamber at the 1st and 10th hour were showed as q1=1.1x10^(-11) mbar.L/s.cm2 and q10=1.6x10^(-12) mbar.L/s.cm2, which were 100 and 80 times relatively lower than general venting to air. In the same condition, outgassing rate and H2O residual gas signal of titanium chamber were 3.4 and 3.3 times relatively higher than aluminum chamber. It indicated that, aluminum chamber had a better result, when venting to dry nitrogen. In surface model calculating, the surface coverage was from 10^12 to 10^15 molecules/cm2, and the sticking coefficient was in the order of 10^(-5). The outgassing rate was inversed proportional to the square of time (t^(-2)) by venting with extremely dry nitrogen gas, the results showed that the surface state was much different from regular. In FT-IR experiment, both hot and cold nitrogen gases had the same ability of blowing the water vapor which was adsorbed on the surface.
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