Formvar with "heavier" 15-25nm carbon coating
These grids have a layer of carbon on a thin Formvar film. The carbon layer is thicker than that applied to other support films, making this an extremely strong and resilient specimen support for most applications. Films are mounted on the darker side of the grid. They are extremely stable under the electron beam. For high resolution applications the Formvar may be removed. This results in less electron density, increased contrast and almost no granularity at high magnifications.
To remove the Formvar film: (use a fume hood)
Note, dipping grids in a solvent to remove Formvar causes the carbon film to float off. It is more effective to only partially remove the Formvar. This method leaves some Formvar under the grid support bars.
- Place two pieces of filter paper in a glass Petri dish and raise one side of the dish slightly.
- Saturate filter paper with chloroform; a little liquid should be visible in the lower end of the dish.
- Using tweezers hold a grid with the carbon side up and touch the grid several times against the filter paper.
- Briefly touch the grid to the free chloroform (do not immerse). Then blot on dry filter paper.
Thickness of support films
The thickness of our support films tends to be towards the lower end of each indicated range.
- Formvar Films: While floating on water during processing these have a colourless to pale grey appearance in reflected light. The films have been measured using a Tencor Alpha-Step 200 profilometer. The thickness across the film ranges from 35 - 70nm.
- Carbon layer (measured by a film thickness monitor during the carbon evaporation process): 20 to 30nm.
Handling and care of support films
Grids should be gripped by the outside rim to avoid rupturing the support film. When removing grids from the storage box it is advisable to do so under a dissecting microscope. If a grid must be laid on a flat surface, use a fibre-free tissue.
When specimen preparation involves dipping a grid into liquid, always immerse edge first.
When using double-sided adhesive tape to hold a grid during specimen preparation, allow only the extreme outer edge of grid to contact the adhesive and remove grid by pulling horizontally away from adhesive to avoid support film damage.