Compact low-energy electron microscope for surface imaging

A compact electrostatic low-energy electron microscope is described. The electron optical system of the microscope was optimized in order to reduce the number of correcting elements and thus to simplify construction and operation of the instrument. The lenses are biased so that the specimen can be kept close to ground potential. The electrostatic tetrode objective lens allows to achieve a resolution below 10 nm at 10 eV. For beam separation, a magnetic sector with small deflection angle was used. The separator requires only one coil winding for excitation and does not introduce significant aberrations. A three-lens projector system enables magnifications from 600 to 60 000 times. The microscope was built and tested. The weight of the whole mumetal shielded instrument is less than 20 kg so that it can be attached to almost any specimen chamber via a 6 in. Con-flat flange. The microscope was operated in the mirror, low-energy electron microscopy, and low-energy electron diffraction modes. In the experimental system without vibration damping, 30 nm resolution was demonstrated.