Measurement of the roughness of supersmooth surfaces using an electron mirror interference microscope

Abstract

In an electron mirror interference microscope for 25 keV electrons, i.e. with a wavelength of 0.008 nm, two band-shaped coherent partial waves, each about 5 mu m in width and with a transverse separation of about 10 mu m, are reflected at an electrostatic electron mirror. The small deviations from ideal smoothness of the mirror result in small deviations from homogeneity of the electrostatic field in front of its surface and hence in small phase variations in the reflected electron waves. The reflected partial waves are then superimposed by means of an electron optical biprism. They form an interference pattern consisting of a system of fringes. An analysis of the deviation of the fringes from parallel straight lines permits the determination of the deviation from ideal smoothness of the mirror surface.