Hi

If suitable, a simple method is to grow you film on a NaCl substrate, then simply dissolve away the substrate  in water and 'scoop' up the film onto a TEM grid. Alternatively there are specialized TEM sample preparation procedures for preparing planar and cross sectional specimens of your thin film. We have obtained great results by mechanically thinning down the sample till is is approximately 50 micrometers thick followed by Ar ion beam milling.

What is the material and thickness of your "ultrathin film"?

There are two solutions 

1. use wet chemical methods to etch the substrate under the thin film. 

2. Use as grown specimen, there is procedure to prepare thin film based TEM sample. Plz consult TEM operator.

Hi

If suitable, a simple method is to grow you film on a NaCl substrate, then simply dissolve away the substrate  in water and 'scoop' up the film onto a TEM grid. Alternatively there are specialized TEM sample preparation procedures for preparing planar and cross sectional specimens of your thin film. We have obtained great results by mechanically thinning down the sample till is is approximately 50 micrometers thick followed by Ar ion beam milling.

There is a very simple method, but it works not always. Just stick an adhesive tape to the sample and detach it. Then put it in a dichloroethane  or acetone for dissolving a tape and catch the thin film to a TEM grid.  

Good luck!

Hi

If there isn't any thermal procedure after thin film deposition and no need to control the thin film growth (for example, amorphous thin film), you can use Kapton® Tape.

Kapton Tape is made for vacuum procedures, presents flexible electrical insulation with low outgassing characteristics.  Place it over silicon wafer, and after deposition, simply remove it from Silicon surface. Your thin film will detach into little pieces easily.

This procedure have been used for preparing amorphous thin films containing metallic nanoparticles for HR-TEM measurements.

Good luck!

Thanks to all for these valuable suggestions...... Frederico Lima, My sample is Bi Nanosheets with thickness ranging from 5 to 25 nm

Just scratch with a diamond pen then take the dust with a TEM grid covered with a holley carbon membrane by toutching the scratch with the side where is the membrane.

The main Pb with this method is that you have to search the good dust on the grid , and because Bi is very soft you'll have defects in the layer, induced by mechanical strain.

the best way to study thin film on silicon is to use the tripod method to obtain an edge very thin for all the TEM characterisation .

The safest method is to ion etch the substrate in a small area.

You can use a small bar of glass, then try peeling the surface carefully and put the glass bar on methanol. do this way many times, send the solution directly to TEM.

Naveed, a physical removal of 5 - 25 nm sheet does not seem to be a reasonable solution. According to what you said the adhesion is not so low.

Therefore, I would suggest to do it chemically. There are several solutions which can etch Si and SiO2. There is a list online: http://www.cleanroom.byu.edu/wet_etch.phtml

I would select one which does not etch Bi and according to your SiO2 thickness. It would be interesting if you post your solution here. Thanks!  

Use FIB for your sample....

One can prepare the TEM lamella using the Dual Beam microscope (combined FIB/SEM).

Hello,

you can try exfoliation with ultrasounds (don't know if it works for your samples) or just try to prepare the substrate first, make some etching or other technique to make some TEM friendly thin places and then deposit your thin film and put whole thing to the a microscope.

It is possible to release your sample from the silicon wafer by using the HF, but be careful.

Hello respected researchers.  Thanks for your suggestions. However, i wanted to post the method through which i got reasonable results.

Physical removal of nanosheets on nanometer scale wasn't proved to be a better technique. I was able to remove Bi Nanosheets by using PMMA transfer technique (a wet chemical method). Coat a small amount of PMMA on Si/SiO2 using spin-coater. Then etch the oxide layer underneath the PMMA layer using some base solution (e.g. 1M KOH at 100c-150c). The Pealed off layer of PMMA is then transferred to TEM grid and  dissolved by  acetone on mild heating. Though, the probability of getting the sample on TEM grid by this method is low (~1:4 in my case) but it works.

Attached below is some nice literature about some other transfer methods of Graphene and other 2D nanomaterials. This should be helpful for beginner like me.

Good luck to all

How about using water soluble tape to peel off and transfer to TEM grid?