Enhanced inverse photoemission by hot electrons at strongly charged silver surfaces

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