The CM200 Feg-Twin Optimized for Cryo-Electron Microscopy

Abstract

The requirements for cryo-electron microscopy are: good vacuum, high resolution under low-dose conditions at low magnification, low drift with cooled cryo-transfer holders and, in some cases, fast spotscan imaging. For our cryo microscopes we have introduced special factory tests in which these specifications will be met.In order to obtain high spatial frequencies at low magnification an appropriate specimen with a statistical distribution of small spacings and a fine-grained recording film is needed. We used amorphous tungsten on carbon as specimen and overexposed and underdeveloped Agfa Scienta film (Fig. 1). The laser diffractogram in Fig. 2 presents Thon rings out to 0.19 nm in a one-second exposure flood-beam image. The result of a similar experiment done with a cooled cryo-transfer holder is shown in Fig. 3. Flood-beam images of gold islands and carbon black on a thin carbon film were taken at 66 OOOx at liquid-nitrogen temperature with one second exposure under low-dose conditions. The laser diffractogram clearly shows Thon rings out to 0. 2 nm.