I want to evaporate Au in a customized evaporator, it will be small amounts (less than 20nm or so) and maybe Ge as adhesion layer. I have experience using Cr and Ti, but due to the fact the Ge has a lower melting point it will be probably easier to evaporate, but if it is easier why people use Cr and Ti instead? Does any one have experience to share about it? How controllable/easy is compare with Cr or Ti? What about degassing? Supposing that I can successfully evaporate Ge, how much should I put?
the adhesion layer selection is not related to the choice of selecting a low melting point. It has to do more with metallurgy.
Chromium a high melting point material is often very difficult to handle with simple thermal evaporation.
But there is a way to do it very conveniently.
Instead of putting chunks of chromium in a boat and trying to evaporate. Try the following, you will be successfull.
But a Chrome plated tungsten rod. Available in various lenths. For a typical laboratory thermal evaporation system, you need a Cr plated Tungsten rod which is about two inches long. Just pump up the current to about 40 to 60 Amps, and flash evaporate Chromium for a few seconds ( say (15 to 20 seconds to obtain a thin adhesive layer of chromium , and then in another boat evaporate your gold layer in another boat. You should have two separate electrode posts in your thermal evaporation system.
You can by Cr-plated Tungsten rods from R. D. Mathias companyin USA, for a very small price.
there are some excellent papers by D. M. Mattox, and also the "hand book of thin technology explains the Cr-Au layers very nicely.
Germanium can try, but I not sure.
K. Sreenivas
You can order these chromes rods as Sreenivas has already mentioned from R.D. Mathis. If needed you can also add O2, so that you have an oxide.
In case someone else is wondering about this topic, let me share my experience.
- Ge doesn't degas that much compare with Ti
- Ge is really hard to controlable evaporate using Ta, it is better to stick with W
- Using a boat is preferable, but higher current will be necessary. I used a home made W basket (0.25mm diameter wire). It is doable, but after a couple of time the basket breaks.
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