Dear Baoshan,

For MoS2 or TMDs just carbon coated TEM grid is used, and most of people is using Quantifoil TEM grid. It is little bit expensive but supports MoS2 or TMDs atomically thin film a lot. The wet transfer, especially surface tension, easily destroy your sample and even carbon film during PMMA washing. (some of samples are washed away by Acetone).

There are some dry transfer process but these are not easy. For PMMA based process, all process is wet, so you have to be trained well.

As you said, < worrying about >....indeed: the Formvar film

(if formerly mounted to the grid to establish some support to the PMMA-[=polymethyl methacrylate] film with the MoS2 on it  )

in the solvent acetone for sure will be dissolved completely. If there is another solution of your problem perhaps depends on the possibility to use another transfer method for the MoS2. I regret not to be able to help with a solution. Best of luck!

Dear Baoshan,

you informed here about the wet transfer method (PMMA assisted) for preparing MoS2 to be visualized by TEM. Unfortunately you didn't include at least one or two references where the method you are following can be followed by the / a "novice" or interested -more sophisticated - colleague. I found an article commenting at least in brief on a method for demonstrating MoS2 particles using in the end also PMMA and would like to point you to (not knowing whether you already know that paper / that method or not):

Preparation of MoS2-Coated Three-Dimensional Graphene Networks for High-Performance Anode Material in Lithium-Ion Batteries

 by Xiehong Cao et al, 2013

small 2013, 9,No. 20, 3433–3438    

(www.small-journal.com;  ©2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)                                        DOI: 10.1002/smll.201202697         SMALL [Nano Micro] 

Another description for dissolving PMMA (and there might be more sources out in the wild...)  I found in:

Supporting Information

Fang et al. 10.1073/pnas.1405435111:

cf.: http://www.pnas.org/content/suppl/2014/04/10/1405435111.DCSupplemental/pnas.201405435SI.pdf

Best of luck!

 Dear Dr. Muss,

    Your answer is  very helpful to my research. Thanks a lot for your help. 

Dear Baoshan,

For MoS2 or TMDs just carbon coated TEM grid is used, and most of people is using Quantifoil TEM grid. It is little bit expensive but supports MoS2 or TMDs atomically thin film a lot. The wet transfer, especially surface tension, easily destroy your sample and even carbon film during PMMA washing. (some of samples are washed away by Acetone).

There are some dry transfer process but these are not easy. For PMMA based process, all process is wet, so you have to be trained well.

Dear Kazunori, 

Thanks a lot for your answer. The TEM grid type is critical for the transfer process. We considered the Quantifoil TEM grid, but finally bought some TEM grid without the formvar layer. Hope we  can success with the new TEM grid.