Why in SEM, a dielectric specimen coated with a metallic? and why the metallic coating should be a carbon or gold?
Dear Kasim, a metallic coating prevents charging of the non-conducting specimen, that otherwise occurs because of accumulation of static electric fields during the bombardment of electrons. This coating does not necessarely have to be gold, it's just commonly used.
I would just add that the metal coating, whichever the material chosen, must be thin enaugh to assure that the surface morphology is not altered or smeared out and that the most of your probed volume involves your original sample. Gold or Carbon are typical choices either because easy to be quickly deposited as thin films and because they do not affect surface stoichiometry of the sample
Thanks a lot to everyone for your precious time to give such helpful information
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