ELECTRON-EMISSION FROM ION-BOMBARDMENT OF HIGH-TC SUPERCONDUCTORS

We have performed first studies of secondary electron energy- and angular distributions (O eV less-than-or-equal-to E less-than-or-equal-to 40 eV, 25-degrees less-than-or-equal-to theta less-than-or-equal-to 90-degrees) from H+ and C+ (2 MeV) bombardment of single crystals of YBa2Cu3O7-x high T(c) superconductors. The angular distributions N(theta) have been measured at sample temperatures above (T = 300 K) and below (T = 35 K) the superconducting transition temperature (T(c) almost-equal-to 90 K) as a function of the angle of incidence (delta = 55-degrees, 65-degrees, 70-degrees, 75-degrees) of the projectiles. The ratio R = N(C+)/N(H+) of electron intensities from heavy C+ ion impact to the electron intensities from proton impact shows broad peaks (DELTA-theta almost-equal-to 25-degrees) at low electron energies E < 20 eV. The mean emission angle theta-em of the excess electrons belonging to this peak shifts to higher angles theta with increasing delta. Within the framework of a model for the refraction of low energy electrons at surfaces this can be explained by the directed emission of shock electrons perpendicular to the conical charge density fluctuations caused by the ion induced wake shock front. Furthermore, the influence of the superconducting phase transition at T = T(c) on the emission of electrons is discussed.