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Gomez Addams
Has it been a while since you ran the system?
Perhaps the oil in the roughing pump needs to be warmed up and outgassed a bit through the interstage ballast valve, assuming yours has one, or the exhaust if not. How new is the oil in the roughing pump? I assume you haven't had any disasters in the chamber that could have outgassed anything. Wipe down all internal chamber surfaces with anhydrous alcohol perhaps? At that high a pressure, I think of things like water vapor or leaks. On Feb 12, 2013, at 7:55 PM, Guy Brandenburg wrote: Just tried and failed to aluminize a mirror because the pressure would not go below 1.7x10^-4 torr; as a result the coating was semi transparent. If it goes below 1.0e-4 all is good. This is unusual. Persisted even when i tightened stuff up. - Bill "Gomez" Lemieux, The Highland Tinker |
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Guy,
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Al coating performance strongly depends on vacuum and deposition rate. In general, it is recommended to evaporate Al on a cold substrate at pressures at least below 2x10-5 torr with deposition rate at least 10 A/s. Othervice the growing coating will trap air molecules, adhesion and mechanical properties will be not good, and you won't be able to obtain really high reflectance. The substrate pre-cleaning with an ion beam or glow discharge is also needed. Regards, Vladimir Chutko On 2/12/2013 6:55 PM, Guy Brandenburg wrote:
Just tried and failed to aluminize a mirror because the pressure would not go below 1.7x10^-4 torr; as a result the coating was semi transparent. If it goes below 1.0e-4 all is good. This is unusual. Persisted even when i tightened stuff up.------------------------------------ |
¿ªÔÆÌåÓýWe get normally get good results after plasma cleaning if we get anything below 1.0e-4 Torr. We coat a few mirrors a month. This time we could not get below 1.7e-4 torr. Guy On Feb 17, 2013, at 18:23, Vladimir Chutko <chutko@...> wrote:
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