What would cause sudden change in evaporation chamber behavior?

[warfreak131]

Hello all,

I use an evaporation chamber at my lab every day. Basically, put some substance in the chamber, close it, bring it down to vacuum, and pump enough current through it to vaporize it where it deposits on a substrate.

I've been using 175A to create a deposition rate of about 1 angstrom/sec. All of a sudden, a few days ago, 175A doesn't generate any deposition. Even if I bring it up to 200A, there is almost no deposition taking place. I've checked the electrodes both physically and with a DMM to the best of my abilities, and there doesn't appear to be any loose connections or damage. I've also ruled out the possibility of the rate monitor being faulty.

Does anyone have experience with evaporation chambers who could help me out?

 

[nsaspook]

Have you checked your vacuum? There might be a leak or a bad pump.

 

[Baluncore]

Did the evaporator once have a DC voltage bias applied to encourage the flow of positive ions away from the charge and towards the deposition surface?

 

[warfreak131]

I actually figured out the problem. The electrodes were too tight when securing the evaporator boat. I don't know why this happens, I'd figure better electrical contact would mean better performance, but no. I loosened them significantly to the point where I can still shimmy the boat around in the electrodes and I'm getting better performance than I ever have in the past.