Thermally evaporating nickel is very difficult. Like titanium, it has a strong tendency to alloy with refractory metals. Attempting to thermally evaporate nickel out of a tungsten boat has proven futile. As the boat heats up and the nickel melts, it alloys with the boat, causing it to become brittle and crack shortly after exposure to the liquid nickel. Therefore, deposition is very limited.
Instead, we recommend an alumina coated, tungsten dimpled boat such as our EVS9AAOW if using a KJLC® system. The alumina acts as a barrier between the nickel and the tungsten, thus prolonging the life of the boat and increasing the amount of nickel deposition. Instead of wetting the boat, the nickel will form a ball on top of the alumina coating once it melts. Only four ⅛” diameter x ⅛” long pellets can be loaded safely into this boat at one time. These boats will fail often, lasting approximately 1-3 runs. Due to alumina’s limited heat conduction abilities, more power will be required to achieve evaporation.
Using the EVS9AAOW, we are able to deposit relatively thick films (approximately 1 micron per evaporation run) at rates from 0-5 angstroms per second using two Kepco© power supplies linked in parallel. The nickel only takes about 230A of current to melt and to start evaporating, but requires voltages greater than 4V to run at this current. Using only one Kepco© power supply, the nickel will still evaporate at about 100% power output but the rates will be closer to 1 Å/sec, and the film thickness will be limited to around 2,000 Å total before the rate begins to decrease.
The alternative option would be to use an Al2O3 crucible with a crucible heater. The problem is that it is very difficult to get to high enough temperatures to deposit the nickel. Crucibles rely on external heating and there is only so much power that can be applied in order to raise the temperature to achieve deposition
Category: Deposition Materials
Sub-Category: Evaporation Pellets, Pieces and Wire