Dear Rui,

Effect of post-annealing the membranes depends on the membrane material. If your membrane material e.g. polymer is crystalline or with high Tg then annealing will make the membranes more stronger, however they might become too brittle.

If the material is soft or with low Tg then material might decompose and will not give desired properties.

Best is to check the decomposition temperature of the material and then giving post-treatment or annealing. 

Also, step by step annealing will be beneficial than immediate annealing.

I hope this answers your question.

DEAR PARIMAL, THANKS FOR YOUR ANSWER.

I got what you mean,  I am sorry that I forgot to limit my subject in ceramics and alloys, but  in some what you said are also suitable for . 

As to some high-temperature phase materials, the high temperature fabrication of thin films requires more strict condition of equipment .  Even though we know the preparation temperature of thin film material is much lower than  the corresponding bulk material.  

However during review some papers about crystalline material , I found the crystallinity of post-annealed material  is better the as -deposited materials ,even the temperature of annealing is almost equal to the temperature of  preparation. we all know that the bulk-diffusion in annealing is inferior to the surface-diffusion in thin film preparation.  For example  we could  deposit  films in ambient temperature at first  and then anneal in 500 ℃, under this  situation films we get  crystallizes better than we directly deposit at 500℃, why do we prefer to the latter preparation technology, while indeed we struggle  in directly deposition to lower temperature or pure the material. 

so in my opinion , the more than one process of  the post-treatment  which usually longer time,  the films may be changed like oxidation etc. all above limit the technology applications of the thin film materials .  

But I can't  convince myself. so I came here. Thank you all. 

When you deposit a film, 

i) It may be amorphous, or polycrystalline. Formation of a good single phase means, having the right crystallographic structure, and the correct stoichiometry.

ii) Many a times films with complex oxides, or complex compositions, the single pphase is formed properly.

iii) So you being to do post deposition annealing. Which then ensures, the raction of the deposited product, and sets in the single phase formation, provided the deposited stoichiometry is correct. In case of oxide thin films, the films when annealed in oxygen take up oxygen, and become a good oxide.

iv) Instead of post deposition annealing, so people deposit the film itself at very high temperature.  This is normally see in epitaxial growth, where the film is deposited on a matching single crystal substrate. If there is good matching, then at a certain temperature suitable for epitaxial growth, you begin to get the right single crystal phase, and also pick up the right stoichiometry.

 Obviously to do the above you need high temp. substrate heaters, to deposit film at high temperature.  Sometime this is a tricky attachment, but nowadays, you can fabricate, or purchase ready made heaters.

those who do not have such insistu substrate heating attachments, resort to deposit a film at a low substratte temperature, and then try to do the post deposition annealing.  But you will mostly end up with a polycrystalline films in this case. and it not possible to achieve epitaxial growth by post deposition annealing. Epitaxial growth means picking up the orientation of the substrate, which closely matches with one of the lattice parameters of the deposited film.

I hope I have given you a good idea, when people do post deposition annealing and when deposition is carried out insitu at high temperatures.

K. Sreenivas