ENHANCED INVERSE-PHOTOEMISSION BY HOT-ELECTRONS AT STRONGLY CHARGED SILVER SURFACES

Hot electrons, injected into silver films on top of tunneling junction s, excite surface plasmon polaritons (SPP), which are converted into l ight by macroscopic surface roughness [M. Hanisch and A. Otto, J. Phys . Condens. Matter 6 (1994) 9659]. The coupling between hot electron ga s at the silver vacuum surface [A. Liebsch, G.V. Benemanskaya and M.N. Lapushkin, Surf. Sci. 302 (1994) 303] is enhanced by atomic scale rou ghness. Gies and Gerhardts [J. Vac. Sci. Technol. A 5 (1987) 936] pred icted an enhancement by negatively charging a jellium surface (electro n density equal to silver). We have inserted aluminum-aluminum oxide-s ilver-tunneling contacts into a glycol/0.9M Na acetate electrolyte, ch anging the surface charge by variation of the electrochemical potentia l E (friscolyt reference) of the electrolyte with respect to the Fermi energy of silver. We observed an increase of the integrated photon yi eld per tunneling electron by a factor of about 150-200 by changing th e electrochemical potential from E = - 0.8 V (approximately neutral si lver surface) to E = - 1.2 V (negatively charged silver surface). The wavelength of maximum light emission shifts towards the red by chargin g negatively. This result will be discussed with respect to the theore tical models by Liebsch et al. and Gies and Gerhardts.