Can anybody explain how to load zinc powder (dust) to the Mo boat for depositing ZnO thin film by thermal evaporation technique? I loaded the Mo boat with fine powder of Zinc dust. I found that, as I increased the current, the sample was bumping (dancing) in the boat without melting. Deposition was non-uniform, discontinuous. Should I use pellets of Zinc dust? Can anyone suggest modifications? I am using Indian made HINDHIVAC-12A4D vacuum coating unit.
Well, we had done the vapour deposition of ZnO thin film starting from the powder mixed with carbon black in order to reduce the melting temperature. Your ZnO, no matter powder or pellet needs similar thing, propably.
you can use 1- pellets of Zinc and make the evaporation current gradually and slowly
increased.
2- you can you a rotating sample holder to overcame the non uniform
deposition. (rotating sample holder you can get by hand made it is
easy.
It is not really possible to coat ZnO thermally from either a boat or from an e-gun. The material does not melt and sublimes poorly. A special mixture with a few percent Al2O3 is available that will melt, allowing evaporation. Full Oxidation is however only achieved with the aid of IAD. Sputtering is however the method of choice to Coat ZnO.
If possible use pulse laser deposition technique (PLD) that be best for ZnO thin film for structural property and Uniformity.
Please look at the suggestion by Adel. It is better use Zn pellets as the vapour pressure is very high . If you you use ZnO the vapour pressure becomes lower and the melting must be controlled with low flow rates of oxygen. If you use Zn evaporate with higher amount of oxygen gas at room temperature and then anneal 200-300oC. If you use ZnO, then you can directly deposit at 200oC.
Pl post me your result to comment further.
You can use the pallets. Better to use tungsten boat instead of moly.
Maybe the use of a Knudsen Cell is more reliable. We just loaded Zn-powder into a homebuilt molybdenum Knudsen Cell and used high purity Zn shot from GOODFELLOW ( lump size max. 2 mm; purity 99.98%). The Cell design is rather massive, therefore it takes a while until 300°C are reached. When the temperature is too high the Zn evaporation gets very fast and intense which makes it rather unstable. Therefore, it is better to choose lower rates at lower temperatures. It might also be that initially a little higher temperature is needed to get sufficient flux. This is most likely due to ZnO formed on the Zn grain surface.
Its hard to make ZnO thin films directly you can use Mo boat with Mo cap with small hole so that sample was not bumping and keep the evaporation rate 5 - 10 A. U. per second
DEpositing the oxide powder of ZnO may project many problems.
Alternately take a small chunk of Zinc (rather than poweder), deposit a thin films, and try to post deposition annealing (300 to 400 deg C.) You will be able to grow a polycrystalline ZnO films.
K. Sreenivas
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