Hi Ross, why do you insist on e-beam evaporation? There are quite a few easier ways to produce high quality ZrO2 films. Sputtering, either non-reactive from an oxide target, or reactive with a metal target plus some few % of oxygen in the sputter plasma both give good results.

I remember that we once have prepared ZrO2 by e-beam evaporation, but again, we made use of a Zr metal target and added some oxygen to the vacuum system (in the order of 10^-6 mbar or less. But for this you will probably need an e-beam source which is not affected by the oxygen and the "poor" vacuum conditions.

Good luck anyway, Dirk

Hi Ross, I agree with Dirk. I would prefer sputtering as well. Good luck!

Hi, I agree with both appinion given above. The sputtering from Zr metal target and mixture of oxygen and argon in the plasma. You should play with the oxyge:argon mixture in order to have stoichiometric ZrO2. Good luck

Hi, I guess that you should sublime and avoid melting of your material. E-beam should well sublime material shaped in 2-4mm grains.

KJLC catalog tells that ZrO2 should sublime by e-beam "fair", P=10-4Torr at 2200C. Additionally it recommends W-boat evaporation or sputtering as mentioned above. Generally, oxides could decompose during evaporation, loose oxygen and produce amorphous film. In this case some additional oxygen in substrate area may help. Good luck.

Thanks everyone for the replies. Unfortunately I can only use e-beam evaporation for this project at the moment.

I guess I'll have to experiment with temperature and oxygen partial pressure, also need to use a tungsten crucible (for most of the materials I use, molybdenum, copper or graphite are suitable).

Thanks again for the advice, I'll let you know how it goes!

Hi Ross,

for sure you have to use a tungsten crucible. I’ve never evaporated ZrO2, but for all the other oxides (HfO2, SiO2, Ta2O5, Nb2O5, TiO2, etc..) I always use the tungsten crucible. Evaporation in oxygen partial pressure is also necessary to keep film stoichiometry and I suggest you also to heat the substrate to a temperature of about 100-200 °C. Moreover, ion assistance (with Ar or Xe gas) could be helpful to increase film density. But these tricks will only improve your film characteristics, while for what concerns your problem during the evaporation, you should work on the e-beam parameters, the current (to be increased step by step) and the rate until your thickness monitor detect a stable evaporation rate. Most of the times I evaporate the materials starting from small grains. Only if the material is in the form of a very fine powder I prefer to make a pellet to avoid all the powder to be spread when hit by the e-beam. Perhaps you can try to divide your pellet in some smaller pieces, taking care to cover all your crucible with the grains/pellet. Consider that during the evaporation not all the materials necessary melt completely.

Finally, powders used for optical coatings are usually very pure (99,999%); therefore you must be sure that the magnesium oxide addition does not affect the refractive index of your ZrO2 film.

Good luck!

Another way to deposit oxides by evaporation is to assist the metal evaporation by flow of atomic oxygen. You will need a cracker of the molecules (RF plasma, for example, but can be others), installed outside the chamber and then a tube (teflon works pretty well) delivering the gas to the sample surface. In this way you can keep low pressure in the chamber.

Have fun.

ZrO2 does not melt properly and predominantly sublimes causing an uneven material surface with craters etc. ZrO on the other hand, does melt well into a pool of molten material that evaporates stable. The material is usually coated directly from the water cooled copper crucible or from a Mo liner. Index and intrinsic stress can be controlled by optimizing the process parameters such as oxygen partial pressure, rate and substrate temperature. Spitting is normally not a problem given that pure material and proper control parameters are used. Granules are usually better to use as starting material, but if only tablets are available, it can be crushed into smaller pieces. The material is melted in small amounts, layer by layer until the crucible or liner is full. Durable layers can be manufactured at low substrate temperature. The material is however in-homogeneous and of limited value in multilayer AR coatings without using an IAD process to control this aspect.