Hello all-
Does anyone have any experiences regarding use of a carbon coater with a diffusion pump vs a turbopump? Is hydrocarbon contamination really cut down significantly? Is a turbopump justified when coating samples for field-emission work?
I'm just trying to get a feel for what people have experienced. I would *think* that a turbopump would reduce potential for hydrocarbon residue building up but I'm not sure if other factors are a major source of hydrocarbons.
-Dan
I don't know how a field emission gun matters to the carbon deposition unless you are running at *really* low beam energies which is possible with an FEG.
As for diffusion vs. turbo, as a former "vac tech", I agree that turbo pumping should provide less hydrocarbon contamination than a diffusion pump, but it depends on the primary pump too.
On our venerable Edwards 306A carbon coater we started seeing about 200 PPM of Cl in samples that should not have any chlorine in them so we started looking around and found that the primary backing pump on the Edwards carbon coater had been changed out from gum rubber to a PVC hose that was "non food grade". Apparently it was back streaming just enough PVC vapor to cause the 200 PPM contamination we observed.
Once that PVC hose was replaced and the system cleaned all was well again.
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