Contribution to the contamination problem in transmission electron microscopy.

The contamination of different supporting films is measured by irradiating a circular area of a few micron diameter and by using an electron probe of a few ten nm diameter. Contamination rings are generated by this method. They can be explained by diffusion of the hydrocarbon molecules on the specimen surface and by adsorption from the vacuum. The influence of specimen heating and charging are discussed. Some specimen cleaning methods have been examined. The best results were obtained by immersion of the specimen and the cartridge in methanol.