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Subject: Re: How To Control The Parameters In Al Vacuum Evaporation

Date: 04/29/02 at 11:10 AM
Posted by: Donald Mattox
E-mail: donmattox@svc.org
Message Posted:

In Reply to: How To Control The Parameters In Al Vacuum Evaporation posted by rshong on 04/29/02 at 3:43 AM:

If you are re-using the filaments - Tungsten filaments crystalize and crack on repeatded heating to high temperatures. On subsequent heating the cracks can open up a give high resistances.

Check your clamping arrangement - On heating the ohmic contact can become bad leading to high resistance.

When melting aluminum - When the aluminum melts and wets the filament the resistance goes down and current goes up essentially shorting the other filaments. Uneven melting between filaments can be a problem. The solution may be to pre-melt the aluminum on the tungsten fialment. Aluminum does nt evaporate very much at its melting point.

Rate of heating - Aluminum has to be heated several hundred 0C above its melting point before it begins to evaporate rapidly. If you heat slowly the non-wetted filaments are shorted out longer.

Try - Heating the filaments without anf aluminum and see if the urrent remains equal in all the legs. Don Mattox

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