A glass plate covered with an evaporated silver film of about 200 å thickness is irradiated by a line-shaped electron-probe in a vacuum of 10-4 Torr. A hydrocarbon polymerisation film of very low electrical conductivity is formed at places subjected to high electron current density. An electrolytically deposited copper film leaves these places free from copper. When the copper film is stripped a grating with slits free of any material is obtained. 50 Μ long and 0·3 Μ wide slits with a grating constant of 1 Μ are obtained. The maximum number of slits is five. The electron diffraction pattern obtained using these slits in an arrangement analogous to Young's light optical interference experiment in the Fraunhofer plane and Fresnel region shows an effect corresponding to the well-known interference phenomena in light optics.