TEM OBSERVATIONS USING BRIGHT FIELD HOLLOW CONE ILLUMINATION.

As well as a substantial improvement in resolution, several previously unreported advantages of bright field hollow-cone illumination are outlined and then illustrated by application to the structure of thin amorphous carbon films. In particular it is demonstrated that there is an optimum focus position and that there are no contrast reversals in the experimental contrast transfer function for considerable focal changes from this position. The possible implications for the high resolution electron microscopy of amorphous materials are briefly discussed.