title: Influence of a dielectric layer on photon emission induced by a scanning tunneling microscope.
abstract: We investigate theoretically the influence of a dielectric layer on light emission induced by a scanning tunneling microscope through a combined approach of classical electrodynamics and first-principles calculations. The modification of the junction geometry upon the insertion of a dielectric layer is treated first by using the density functional theory to calculate the effective potential along the surface normal and then by solving a one-dimensional Schrodinger equation to obtain the exact distance between the tip and the substrate for a given current and bias voltage. The modified external field with the inclusion of a dielectric layer is evaluated by using the Fresnel formula. The local-field enhancement factor and radiated power are calculated by the boundary element method for two typical systems, W-tip/C(60)/Au(111) and W-tip/Al(2)O(3)/NiAl(110). The calculated results indicate that the insertion of a dielectric layer tends to reduce the light emission intensity considerably but hardly changes the spectral profile with no substantial peak shifts with respect to the layer-free situation, in agreement with experimental observations. The suppression of the radiated power is mainly due to the increase in the tip-metal separation and the resultant reduction in the electromagnetic coupling between the tip and metal substrate.
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: X
authors.initials: X
authors.lastname: Tao
authors.forename: Z C
authors.initials: ZC
authors.lastname: Dong
authors.forename: J L
authors.initials: JL
authors.lastname: Yang
authors.forename: Y
authors.initials: Y
authors.lastname: Luo
authors.forename: J G
authors.initials: JG
authors.lastname: Hou
authors.forename: J
authors.initials: J
authors.lastname: Aizpurua