Sensitivity-Enhanced Interference Electron Microscopy

Interference electron microscopy by holographic reconstruction has been applied to many fields: An interferogram of a specimen having nonunifom thickness can be interpreted as a thickness contour map. In case of a ferromagnetic thin film, contour lines in an interferogram follow the magnetic lines of force. The contour interval of a phase-shift ƛ (ƛ is an electron wave length) correspons to a thickness of 2 ϕ0 ƛ/V0 (V0 is the mean inner potential and ϕ0 is the accererlating voltage) and a magnetic flux of h/e (= 4.1X10—15 Wb) respectively. For detailed observation such as that of atomic scale thickness variation or weak magnetic fields from single domain fine particles, electron phase shifts recorded in a hologram has to be amplified. In recent experiment conducted by authors, interferograms phase amplified 10 times were obtained. The method employed a higher-order diffracted beam and its conjugate utilizing the film's nonlineality. However the phase amplification of factor 10 is not sufficient for the above purposes. In the present experiment, successful attempt to detect an electron phase shift of order ƛ /100 was made using another phase-amplification technique introduced by Bryngdahl and improved by Matsuda.