LIGHT-EMISSION FROM ROUGH TUNNEL-JUNCTIONS IN UHV

Light on both sides of Al-Al2O3-Ag junctions is emitted only by the fast surface plasmon polariton mode. The intensity integrated over the spectral distribution and normalized with respect to the tunnel current is about 30 times higher at positive bias (electrons tunneling into Ag). The explanation of this difference by Kirtley et al's model of excitation of the fast mode by hot electrons is corroborated by 'O quenching' of the emission only at positive bias without a change of the optical reflectivity. We postulate increased hot-electron-photon coupling within the inhomogeneous electron gas at sites of atomic-scale surface roughness.