We are using a high purity alumina crucible in a standard e-beam doser (we have Focus and home-made ones). We use Fe powder. The problem is that we are getting aluminum and oxygen on the surface, in addition to iron at the settings we need to get Fe (about 44W). We have used previously a self-supported iron rod, and it works fine, but for this particular experiments we need to use a crucible with Fe powder (we have some Fe57 powder). We have already bought new crucibles from another company, and the problem persists. Should we run it longer before assuming that we will always get Al and O contamination and thus need to get rid of the crucible?
Fe is always difficult to evaporate. I think you will have better luck with e-beam evaporation of Fe rod. This is the cleanest way to evaporate Fe.
If you must work with Fe powder you would have to try treating the alumina crucible
in hydrogen atmosphere at high temperature (above 900°C) for some hours before
introducing the Fe powder - if this procedure is possible anyway.
No, you never control the evaporation
e-beam evaporatpr with an iron rod if you want a slow deposition rate
e-beam evaporator from a crucible if you want an high rate
You would probably have better luck with a boron nitride crucible - although I'm surprised that alumina crucibles start decomposing before the Fe evaporates.
Boron nitride is costly and Alumni is causing problem. Try preparing a Silica crucible in a mold. We have seen that it is open to some fine machining in order to put it as ion source generator in an ion accelerator!
I am not sure what is the final quality or compositon of Fe that you are depsoiting. In order to get rid of other elements in the deposition, Iron rod is could be the answer, Yet, due to some reason given by you that you need to use crucible with iron powder, may I suggest you use a Fe Crucible instead.
Do you had care about atmosphere? I mean reducing atmosphere? It's possible that a not enough reducing atmosphere can favour oxidation of Al2O3 into Al and oxigen
Use 1-2 mm in diameter of Fe rod for a clean and low flux evaporation. That is ideal for very clean sub-monolayer regimes and evaporation with surfaces at low temperatures. You can keep pressure in the 10-11 mbar regime during evaporation in conventional UHV systems . Mo crucibles works pretty well if you need high flux, but it should be very well degased.
Maybe you can think a new way to do the evaporation: try to understand if it's possible to focalise in a different way or geometry, because I was wondering about the energy density; with a beam of 44 W and enough energy density you will ever evaporate a great amount of aluminium an d oxygen
So far, we have switched to using direct e-beam heating without a crucible. It is ok with a small plate of Fe57 held in place with Ta wire. But I still have some Fe57 powder, and clearly I cannot do it in that way. I do not want to use a Fe or Mo crucible, because the Fe57 powder will alloy.
if you are interested in growing films in monolayer thickness, you can build a classical e-beam evaporator with Fe rod separated by a filament. With this you have much better control of the rate of evaporation and even submonolayer growth can also be achieved.
If you use a crucible with powder you must carefully degas and melt the powder, as it may spit out of the crucible.
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