Specific Process Knowledge/Thin film deposition/Deposition of Zinc: Difference between revisions

Zinc is tricky to deposit in a multiuser vacuum system because it has a relatively high vapor pressure at low temperatures, which means that once Zn is inside it easily re-evaporates and contaminates films of other materials. Additionally, Zn cannot be deposited in systems with a cryo pump, as it will completely clog the cryo pumping system. A final consideration is that the ZnO that forms on the surface of Zn needs a higher temperature to evaporate than the Zn itself, so once the ZnO is gone, the Zn within may evaporate rapidly, making it hard to control the deposition rate. For this reason it is better to use sputtering than evaporation to deposit Zn.  

Unfortunately, in the lab at Nanolab the only physical vapor deposition system with no cryo pump is the Lesker Thermal Evaporator, so this is the only system that is an option for Zn evaporation. We tested it and found that Zn coats every surface in the chamber and re-evaporates during subsequent evaporation of other materials, contaminating the growing film. After a thorough chamber cleaning, we no longer detect Zn in Al or Ag films made in the evaporator. However, this kind of cleaning takes a full working day and while the chamber is used for Zn no other materials can be deposited without contamination. '''We are therefore hesitant to use the evaporator for Zn again. If you wish to deposit Zn, please first explore other options than Nanolab's systems.'''  

It is important not to use too high power as this will give a very fast increase in the deposition rate once the evaporation is started. For new Zn pellets, an oxide removal run is recommended before the actual deposition. The max power needs to bel slightly adjusted for this run (slightly higher than for already-melted pellets).