Z.Q.12 Field Emission Electron Microscope

This classic device images the individual atoms of the crystalline structure of a tungsten needle tip. The needle tip with radius 10-4 cm is in the center of an evacuated spherical tube. With 10,000 volts applied the electric field is so strong at the needle tip that electrons are spontaneously emitted to travel along the radial field lines and impact on a zinc sulfide screen of radius 5 cm. Thus, a magnification of 500,000 is obtained, and individual atoms in the crystal structure of the needle tip can be seen. An auxiliary system will deposit a few barium ions on the needle tip, and they can be seen evaporating away. You can have the students come down to view the 10 cm screen, or project it up on the big TV screen. Instructions and description available.