Dear Hien, I feel that more input from your side is required, such as the materials of the film and the substrate, as well as the structure of the substrate (polycrystalline / single crystal / glass?), desired film thickness, etc - otherwise answering the question is a bit arbitrary. Nevertheless, I think that your results are not too bad - assuming that you have a film thickness of e.g. 100 nm and a polycrystalline film, then a roughness of some few nm is quite o.k. - if you wanted to have an epitaxial film however, things are different. So, again, more input from your side is needed! Best regards, Dirk

Dear Prof. Dirk,

Thank you for your commend. The substrate here is DyScO3(110) and Strontium Cobaltite is thin film (I did try STO(100) substrate, it also shown the same issue). The thickness is around 30 nm. I would like to get the epitaxial film with the roughness is below 1nm.

I guess we are discussing laser molecular beam epitaxy here, therefore the issue of droplets is mostly related to defects in the ceramic target which is laser ablated. This is a typical issue with Pulsed laser deposition and the density of the target is a crucial parameter here.

Increasing target substrate distance could help. Some commercial systems introduce a droplet trap to avoid them. You can look into it.