AVS 50th International Symposium
    Surface Science Wednesday Sessions
       Session SS+NS-WeA

Invited Paper SS+NS-WeA5
Stark-Effect and Two-Electron Photon Emission in Scanning Tunnelling Spectroscopy

Wednesday, November 5, 2003, 3:20 pm, Room 328

Session: Perspectives and New Opportunities
Presenter: J. Kroeger, University of Kiel, Germany
Authors: R. Berndt, University of Kiel, Germany
G. Hoffmann, University of Kiel, Germany
L. Limot, University of Kiel, Germany
T. Maroutian, University of Kiel, Germany
P. Johansson, University of Örebro, Sweden
J. Kroeger, University of Kiel, Germany
Correspondent: Click to Email
We report a quantitative low-temperature scanning tunnelling spectroscopy (STS) study on the Ag(111) surface state over an unprecedented range of currents (50 pA to 6uA) through which we can tune the electric field in the tunnel junction of the microscope. We show that in STS a sizeable Stark effect causes a shift of the surface state binding energy E@sub S@ , even at very low currents. Data taken are reproduced by a one-dimensional potential model calculation, and are found to yield a Stark-free energy E@sub S@ in agreement with recent state-of-the-art photoemission spectroscopy measurements. Next, unusual emission of visible light is observed in scanning tunnelling microscopy of the quantum well system Na on Cu(111). Photons are emitted at energies exceeding the energy of the tunneling electrons. Model calculations of two-electron processes which lead to quantum well transitions reproduce the experimental fluorescence spectra, the quantum yield, and the power-law variation of the intensity with the excitation current.