electron biprism

An "electron biprism" is an electron-wave interferometer to obtain an electron hologram in the first step of electron holography. The electron biprism consists of a fine string electrode placed at the center of the incident electron beam (perpendicular to the electron beam) and parallel-plate ground electrodes placed at the both sides of the string electrode (parallel to the electron beam). The biprism is located below the objective lens in a TEM. A positive voltage is applied to the string electrode, so that the scattered wave transmitted through the object (object wave) passes through one side of the electrode whereas the wave directly coming from the electron source passes through the other side of the electrode. These two waves are attracted each other by the positive potential, and are superposed to form interference fringes (hologram). The interference fringes contain information on the change of the amplitude and phase of the object wave.

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