The Philips CM 200Cs was the first high-resolution transmission electron microscope with variable spherical aberration, ranging from the uncorrected value of 1.23 mm over zero to negative values. Perfect compensation of the spherical aberration and zero defocus yields delocalisation-free amplitude-contrast images. A small residual positive spherical aberration and a small underfocus extend the point resolution to the information limit, yielding black-atom images of a thin object with reduced delocalisation. In particular the latter imaging mode is well-suited for the imaging of weakly scattering atom columns, such as oxygen, in the vicinity of strongly scattering atom columns.
The field emission instrument is operated at 200 kV; the semi-automatic alignment routine of the aberration corrector uses an aberration measurement derived from a Zemlin tableau of diffractograms, calculated from images of amorphous material. Digital images are taken with a 2k charge coupled device camera system.
Availability of the instrument: Dismantled Instrument not available to users anymore.