EXCITATION OF CU ATOMS BY AR IONS AND SUBSEQUENT RADIATIONLESS DEEXCITATION OF SCATTERED PARTICLES NEAR A CU SURFACE

The profile of a Cu I spectral line, excited by bombardment of a Cu crystal with 80 keV Ar ions is measured. The Doppler profile shows that the light-emitting particles have energies in the keV region. The wavelength shift of 0-0.5 Å depends on crystal and monochromator orientation. Measurements of the line shape as a function of the angle of the target with respect to the primary beam and also as a function of azimuthal rotation of the target, indicate that the emitting particles originate predominantly from collisions of Ar ions with surface Cu atoms. The fact that the emission is found in front of the target points in the same direction. Evidence is presented for the occurrence of a radiationless deexcitation process, which is supposed to be tunnelling of an electron from the excited atom into the metal. The probability for escape from the surface in an excited state depends therefore on the particle velocity. A calculation of the line profile based on this assumption is made. Comparison with the experiments yields a value 1014s-1 for the transition rate for the tunnelling process, when the distance of excited atom to the metal surface is a few Å. © 1969.