Cherenkov and transition radiation from thin plate crystals detected in the transmission electron microscope

Cherenkov radiation and transition radiation generated by electrons of the energy of 80 to 200 kV are detected in a transmission electron microscope. Optical spectra of forward and backward emission from thin films of various materials, i.e. mica, silicon and silver, were studied with respect to the dependence on film thickness and accelerating voltage. The forward emission from mica mainly contains Cherenkov radiation at accelerating voltages higher than the threshold value, and backward emission shows an oscillating intensity against wavelength due to interference of radiations generated in the film and at the surfaces. The emission from a silicon thin film has the characteristics of transition radiation, showing oscillations in intensity due to interference and emission peaks corresponding to interband transitions. Transition radiation from a thin silver film involves characteristic emission due to the radiative surface plasmon mode (Ferrell mode) which gives a sharp peak in the spectra. The spectral shape is sensitive to the morphology of the film.