An electron holographic study of electric charging and electric charge distributions

Some electron optical parts of a transmission electron microscope modify the object wave-function of an electron wave. As experimentally found by low-magnification holography, both the size of the condenser aperture and the excitation of the lenses between the electron gun and the biprism strongly modify the phase of the image wave. It appears that changing these parameters changes the charging-discharging equilibrium between sample, supporting foil, parts of the microscope, and the electron beam. By using a special procedure to process holograms which were acquired under different conditions of charge equilibrium it is possible to reveal the phase shifts caused by the charging effects only. These phase shifts observed for uniformly charged polymer particles are in excellent agreement with the phase shifts simulated using a simple model of charged spheres. A comparison of experimental and modeled phase images suggests that the charge is uniformly distributed inside the particles rather than on their surface. In addition, this comparison enables us to quantitatively correlate an increase in the positive charge to an increase in the mean inner potential. (C) 1998 Published by Elsevier Science B.V. All rights reserved.