ON THE SPATIAL-RESOLUTION IN ANALYTICAL ELECTRON-MICROSCOPY

The effect on spatial resolution of the spherical aberration of the ob jective prefield of a Philips CM30 (S)TEM has been investigated. For t his purpose, the lattice mismatch of a 20 nm thick Si-Ge film in a cro ss-sectioned Si/Si0.9Ge0.1/Si heterostructure has been determined by c onvergent beam electron diffraction (CBED), performed at 100 kV with a spot size of 20 nm. It has been found that, if the disk of minimum co nfusion is focused onto the specimen plane: the measurement is not aff ected by a change in the size of the condenser-2 aperture. Therefore, the mismatch information is contained within the Gaussian part of the electron probe. In strain profile determinations by CBED, this allows one to use higher beam intensities (larger C2-apertures) with improved signal/noise ratios and reduced sample drift due to shorter acquisiti on times.