1 Mev Stem: A Progress Report

Abstract

A high voltage scanning transmission electron microscope(HVSTEM) has a number of unique features: Compared with a high voltage conventional electron microscope, it can provide better resolution and contrast for thick specimens, because of the absence of the chromatic aberration contributed by energy-loss events; Compared with a low voltage STEM, it can collect inelastically scattered electrons more efficiently, since the the characteristic angle of single inelastic scattering varies inversely with energy; The size of the beam can be varied over a wide range for the purpose of selected-area-diffraction. The application of this promising technique in particular to the study of biological molecules which form crystals too thick to be studied with low voltage electron microscopies awaits exploration. In addition, in theory, the spot size of a HVSTEM is better than one Ångstrom – which undoubtly could not be achieved by a low voltage STEM unless the spherical aberration is corrected.