CHARACTERISATION OF INSTRUMENTAL PARAMETERS IN THE HIGH RESOLUTION ELECTRON MICROSCOPE.

It is shown that the detailed matching of experimental high resolution electron micrographs of a well-known test object, namely Ti//2Nb//1//0O//2//9, with computed image simulations can be used to characterize a number of the electron-optical parameters relevant to the imaging process. These include the objective lens defocus and its spherical aberration coefficient as well as the root-mean-square focal spread. The effective resolution of a particular series of images recorded with the Cambridge University 600 kv high resolution electron microscope was determined to be about 0. 233 nm and was shown to be limited by chromatic aberration. This structural resolution is superior to that estimated for commercial 100 and 200 kv microscopes, although these latter machines appear to have better overall instrumental resolution. However, extensive image simulations would be required in order to utilize this latter numerical advantage.