I prefer carbon coated formvar film for negative staining. It reduces specimen drift under the beam. It is not self-evident - which factor is the main: thermal conductivity, electrical conductivity or just mechanical reinforcement of the film, but carbon coating really works. Nevertheless, formvar grids without carbon coating can be used too, it is not a big deal. Fresh prepared are better than old. It is possible to improve adhesion with glow discharge treatment, but usually it is not needed.

Good luck!

Formvar films are not electrically conductive and you are bombarding the film with electrons in the TEM. Applying a thin layer of carbon on top of the formvar film helps make the film a bit more conductive.

Second part of the answer (I had a minor TEM emergency);

With the formvar film carbon coated and therefore more electrically conductive, you will minimize specimen drift. Looking at virus like particle samples requires intermediate magnifications (30-50 K X's). If the film is not electrically conductive, you will probably see a lot of specimen drift, making imaging of the samples difficult.

A fresh carbon coat also makes the formvar films hydrophilic which helps your sample stick to the grids for negative staining. Bare formvar films are hybrophobic. Not many particles will stick to such a film.

Old carbon/formvar films become hydrophobic in a few days and so glow discharge will make them hydrophilic again for a day or two.

Charging is not really a problem for TEM, so you do not need a conductive specimen, no need to coat with carbon. Formvar film should be OK for your task.

Disclaimer: I prefer carbon film, not formvar, but it's just personal preference. A lot of people (should I say - most of researchers?) work with formvar film with no problems.

I prefer carbon coated formvar film for negative staining. It reduces specimen drift under the beam. It is not self-evident - which factor is the main: thermal conductivity, electrical conductivity or just mechanical reinforcement of the film, but carbon coating really works. Nevertheless, formvar grids without carbon coating can be used too, it is not a big deal. Fresh prepared are better than old. It is possible to improve adhesion with glow discharge treatment, but usually it is not needed.

Good luck!

Well these answers clear thing up; not !

I agree with Denis Kornneev when he says it is not self-evident which factor is the main one.

In my experience, without carbon coating drift is more evident. I have seen 300 mesh formvar grids with a fair amount of drift. If you take those same grids and put more carbon on them, the drift is removed. Is this due to the removal of potential charging, or thermal conductivity or ??? Either way; carbon coating of formvar films helps.

However, like Vladimir, I like to use pure carbon films off of freshly cleaved mica films on 600 mesh grids for some small protein samples; with moinimal drift resulting.

Dear Brent and Denis thank you for the suggestions. I got a clear answer for sure.

Best,

Mah