Practical Electron Microscopy and Database

Changing the fringe spacing in electron holography can be categorized by two ways:

         i) Enlarge the deflection angle in the electron biprism. However, the deflection angle is controlled by the applied voltage to the filament electrode, and the applied voltage is limited by the electric discharge, e.g. ≤ 300 V for some systems.

         ii) Adjust the optical system. In this way, the fringe spacing is changed by turning off the current of the objective lens [1,2] or by controlling the distance between the electron biprism and the crossover position in an interferometer [3]. This is more promising way.

The fringe spacing in off-axis electron holography can be given by the intensity (I) in a format of cosinoidal interference pattern,

          -------- [4202d]

where,
          q_c - Spatial frequency (=kβ)
          β -- The angle of the superposition

Here, the cosinoidal term produces the fringes.

[1] Hasegawa S, Matsuda T, Endo J, Osakabe N, Igarashi M, Kobayashi T, Naito M, and Tonomura A (1991) Magnetic-flux quanta in superconducting thin films observed by electron holography and digital phase analysis. Phys. Rev. B 43: 7631–7650.
[2] Bonevich J E, Harada K, Matsuda T, Kasai H, Yoshida T, Pozzi G, and Tonomura A (1993) Electron holography observation of vortex
lattices in a superconductor. Phys. Rev. Lett. 70: 2952–2955.
[3] Wang Y Y, Kawasaki M, Bruley J, Gribelyuk M, Domenicucci A, and Gaudiello J (2004) Off-axis electron holography with a dual-lens
imaging system and its usefulness in 2-D potential mapping of semiconductor devices. Ultramicroscopy 101: 63–72.