Dear sanjay,

I must say there are two possible way to deposit your nano particles on TEM grid, as I did it for my wear debris nano particles:

1) Take your sample in a pure ethanol and rise the temperature of the solution by putting beaker on a hot plate (45C-65C) for couple of minutes, then do the ultra sonication for few minutes.For fine segregation you can repeat the test, after this dip the TEM grid in the solution for a few seconds and take it out gently and wait for ethanol to evaporate.

2) You can make small concentrated ethanol solution by allowing the ethanol to evaporate then carefully put a small single ethanol drop on a TEM grid in such a way that drop can not disperse around, by doing this you will find a small concentrated drop containing suspended nano particles on TEM grid and then wait for ethanol to evaporate.

The advantage of 1 over 2 is that you will get single segregated nano particles for TEM analysis.

Hope this may help you.

Dear Son The Le, thanks for reply. I will try to dilute it. Should i change the solvent also?

What about the purity of your Ethanol ? 

First of all, you may to deposite CZTS NP's on NaCl substrate. After that the sample will be placed onto chemically active solution - the substrate would dissolved - voila, NP's array is given. 

You don't have to change the solvent. As I know Ethanol is very appropriate material for this purpose. You just can dilute it more and then put it in the ultrasonic at least  for five minutes and immediately after stopping the ultrasonic device, take very Small drop and put it on the Grid. It should work!!  

ethanol is quite o.k., but the concentration CZTS NPs should be low. Ultrasonication is very important, both the duration and the power of the ultrasonic bath play a role. Deposit a very small droplet on your grid and then remove the biggest part of the droplet by touching the droplet with the edge or tip of a piece of  blotting-paper. Do not dry the whole droplet on the grid, otherwise the particles will cluster on the grid.

I think that the problem is not from the sample preparation for TEM. Supposed that your nanoparticles are discrete. Even though you prepare TEM samples at a very high concentration, you should see the overlapped individual nanoparticles rather than large aggregates. I would believe that your nanoparticles have chemically formed aggregation, probably when they are being synthesised. In this case, the aggregates should look like a whole.

This is from my experience on synthesising silica nanoparticles. Hope this may help.

Dear Driss Hafedh,

Purity of ethanol is 99.9%.

Often agglomeration occurs during the evaporation of solvent since, during this process the droplets on the grid surface  becomes smaller and smaller and this increases the concentration of particles in the suspension. Try to reduce the amount of suspension you put on the grid. Instead of putting a small drop try to just immerse the grid into the suspension for a few seconds.

Dear sanjay,

I must say there are two possible way to deposit your nano particles on TEM grid, as I did it for my wear debris nano particles:

1) Take your sample in a pure ethanol and rise the temperature of the solution by putting beaker on a hot plate (45C-65C) for couple of minutes, then do the ultra sonication for few minutes.For fine segregation you can repeat the test, after this dip the TEM grid in the solution for a few seconds and take it out gently and wait for ethanol to evaporate.

2) You can make small concentrated ethanol solution by allowing the ethanol to evaporate then carefully put a small single ethanol drop on a TEM grid in such a way that drop can not disperse around, by doing this you will find a small concentrated drop containing suspended nano particles on TEM grid and then wait for ethanol to evaporate.

The advantage of 1 over 2 is that you will get single segregated nano particles for TEM analysis.

Hope this may help you.

I want to give my heartily thanks to every one for their good suggestions. I will try these things in next TEM characterization.

Hi Sanjay,

the mechanisms that lead to agglomeration of nanomaterials in suspension as well as a novel protocol to avoid drying artifacts are discribed in the following articles:

http://www.nature.com/srep/2015/150512/srep09793/full/srep09793.html

http://www.imaging-git.com/science/electron-and-ion-microscopy/tem-sample-preparation-nanoparticles-suspensions

Hi Benjamin Michen,

thanks for sending the interesting articles.