We are using a resistive evaporator to deposit tin on substrates. Tin that we are using is of 99.999 % pure and it is inside a Al2O3 crucible( 3mm inner diameter and 30mm length).We are using tungsten filament that has 0.25 diameter. Earlier, when we were increasing the filament current, then all the molten tin came out from the crucible. Now, when we are increasing the current slowly, we can see that the molten tin inside the crucible is coming to the top and then it is getting settled there. When we are increasing the current again, it is again going to the bottom of crucible. Before also we have used Tin evaporator, but this kind of problem was not happening then. Can anyone please explain why this is happening?
Dear Smruti,
I assume that your effect is connected with the surface tension of liquid tin.
If a liquid is heated, the surface tension decreases. At the vaporization point the surface tension is equal to zero. With increasing temperature the liquid wets increasingly the surface of the crucible. You can compare this behaviour with the using of a dish liquid. If the surface tension decreases, the wetting increases. In your case, you slowly approach to the wetting point and can optically observe this process. If you heat quickly the tin evaporates before it can wet the crucible.
With Regard
R. Mitdank
Dear Smruti,
Further Rüdiger Mitdank's explanations, this phenomenon also very often happens with Aluminium thermal evaporation. The way to overcome is to use Alumina coated baskets for such metal thermal evaporation, which works well. You can contact your local supplier to order it if you eant to try.
Best wishes
Xuhua
Dear Xuhua,
Here we are using the alumina crucible, so will the Alumina coated baskets be of any different?
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