Estimating electron probe diameter in the scanning electron microscope

The research aims to produce the theoretical study on the objective magnetic lens to estimate the electron probe diameter through the study of the parameters that effect on the efficiency of the scanning electron microscope, the optical performance of the objective lens depends used in the scanning electron microscope by ability to form precise electron probe and it focus on the specimen surface to be examined. The affective final electron probe diameter represented dp of the most important parameters that determine the resolving power in the scanning electron microscope, which in it role depends on several parameters related by focal properties of the objective lens as focal length f, Spherical Cs, chromatic Cc and diffraction dd aberration coefficients ,As it has been calculating the affective total diameter dp to the incident electron beam on the specimen surface , and the accompanying from broadening due contributions the Spherical , chromatic and diffraction aberrations which suffers from it the objective lens as a function of the angle of aperture αp to get on the smaller size of the electron probe at optimal aperture angle Keywords: electron probe diameter, magnetic objective lens, magnetic lens focal properties