Bright field electron microscopy of biological specimens. II preparation of ultra-thin carbon support films

Abstract

A routine method is described for preparing ultra-thin carbon films with an estimated thickness of less than 1nm. This is achieved using a carbon evaporator modified so as to vaporize a predetermined volume of carbon indirectly onto a circular mica substrate using a glass cylinder as a reflector. In order to provide additional strength to the fragile outer part of the film and at the same time facilitate handling, some carbon is allowed to be deposited directly on the periphery of the substrate by means of a circular screen or stop of appropriate diameter located directly beneath the evaporation source; this also prevents carbon from being directly deposited on the main central part of the substrate. In order to assist mounting of the ultra-thin carbon film and achieve a high level of mechanical and thermal stability, a plastic (Triafol) micro grid is mounted on a standard 3mm copper grid and coated with carbon, gold and silicon monoxide. The ultra-thin carbon film is then floated off the mica in water and mounted onto the coated grids after dissolving the plastic part of the micro grid with ethyl acetate. The image obtained with the ultra-thin film is less granular than seen with carbon films of conventional thickness; films of the former type, therefore, are particularly suitable for high resolution studies of biological specimens.