Secondary electron effect on electron beam induced charging of SiO2 particle analyzed by electron holography.

Charging of a SiO2 particle induced by electron illumination was investigated by changing the illuminated area of the particle and its support film through control of the position of the mask plate inserted in a transmission electron microscope illumination system. The electric fields around the charged SiO2 particle were analyzed using electron holography. The amount of charge was evaluated quantitatively by comparing the reconstructed phase images with the simulated phase images. When the support film was not covered against the incident electron beam, secondary electrons emitted from the conductive support film were attracted to the charged particle, resulting in particle discharge. In contrast, when the support film was completely covered, secondary electrons were not emitted from the film, so that the particle remained positively charged.