Off-axis electron holography by field emission electron microscope

Abstract

Although the feasibility of electron holography has been verified by several authors, it has not yet been put to practical use. This is because of the lack of a coherent electron source, such as optical laser. In practice, the number of interference fringes produced with a biprism is 200 at most, the exception being one dimensional cases. Off-axis holography requires 5,000∼100,000 interference fringes. Therefore, the useful application of electron holography in higher resolution and phase contrast electron microscopy hinges on development of a coherent electron source capable of producing 5,000 fringes or more.To realize a coherent electron source, a 100 kV field emission electron gun was developed and attached to an electron microscope. In designing the microscope,special care was taken in the column and electric supply. This was done to minimize movement of the small beam spot, which is easily disturbed from outside, so as to maintain the field emission electron beam.