Resolution Theory for SEM and STEM
Abstract: In scanning transmission electron microscopy (STEM), the formula for optimum beam half angle and attainable resolution of STEM proposed by Crewe and Salzman in 1982 are well known. This optimum beam angle is derived from a condition where the statistical mean information content of an optical image is maximum. This paper describes processes that derives statistical mean information content of optical image from information theory of Shannon and that derives the optimum beam half angle of optical system suffering from spherical aberration. A calculation method for information passing capacity and spatial resolution of an optical system for SEM and/or STEM with consideration for spherical aberration, chromatic aberration, and brightness of electron source is also explained.
Key words: STEM, SEM, information content, resolution, optimum condition