Keywords: scanning electron microscopy, very low energy electrons, cathode lens, grain contrast, strain contrast, participates imaging, dopant contrast, very low energy STEM, graphene, nanotechnology
Very low energy scanning electron microscopy in nanotechnology
The group of low energy electron microscopy at ISI AS CR in Brno has developed a methodology for very low energy scanning electron microscopy at high image resolution by means of an immersion electrostatic lens (the cathode lens) inserted between the illumination column of a conventional scanning electron microscope and the sample. In this way the microscope resolution can be preserved down to a landing energy of the electrons one or even fractions of an electronvolt. In the range of less than several tens of electronvolts the image signal generation processes include contrast mechanisms not met at higher energies, which respond to important features of the 3D inner potential of the target and visualise its local crystallinity as well as the electronic structure. The electron wavelength comparable with interatomic distances allows observation of various wave–optical phenomena in imaging. In addition, the cathode lens assembly secures acquisition of electrons backscattered from the sample at large angles with respect to the surface normal, which are abandoned in standard microscopes although they provide enhanced crystallinity information and surface sensitivity even at medium electron energies. The imaging method is described and illustrated with selected application examples.