Measuring spherical and chromatic aberrations in cathode lens electrode microscopes

An electron microscope system, comprising:

• an optical element for directing an electron beam of the electron microscope system;
• an aperture in a diffraction plane of the electron microscope for selecting a portion of a dispersed energy-momentum relation of the electron beam formed at the diffraction plane;
• and
• a processor configured to:
• measure a displacement of an image of the aperture in an image plane of the electron microscope for the selected portion of the dispersed energy-momentum relation;
• determine an aberration coefficient from the measured displacement and the selected portion of the dispersed energy-momentum relation;
• and
• alter a setting of the optical element to control the aberration of the electron microscope based at least in part on the determined aberration coefficient.

A method of operating an electron microscope, comprising:

• obtaining a dispersed energy distribution for electrons at a diffraction plane of the electron microscope;
• placing an aperture at a selected location of the dispersed energy distribution in the diffraction plane;
• measuring at a detector displacement of an image of the aperture in an image plane of the electron microscope for the selected location of the aperture;
• determining, using a processor, an aberration coefficient of the electron microscope from the measured displacement and the selected location of the aperture;
• altering a setting of an element of the electron microscope to control the aberration of the electron microscope based at least in part on the determined aberration coefficient;
• and
• obtaining an image of a sample using the electron microscope having the controlled aberration.