Electron microscope and method for measuring the defocus scattering or the limit

摘要

The invention relates to an electron microscope and a method for measuring the defocus variation or the limit resolution of an electron microscope. It makes use of the fact that in the case of tilted illumination, an aberration possibly present and the defocus variation of the electron microscope change the intensity distribution in the diffractogram in a direction-dependent manner. In particular, the envelope of the diffractogram is narrowed in a direction-dependent manner. If both the tilting of the electron beam and an aberration possibly present are known, then, with a Gaussian focus distribution being assumed, the defocus variation of the electron microscope is the sole parameter not yet known which influences the direction-dependent changes in the intensity distribution. Quantitative conclusions about the defocus variation can thus be drawn from the changes. However, from the direction-dependent narrowing it is also possible to determine the focus distribution without any models and without a priori assumptions about the form thereof. The limit resolution of the electron microscope can thus be determined.