1998/09/17 by Peter Johansson
Engineering · Physics and Astronomy · #Force Microscopy Techniques and Applications #Molecular Junctions and Nanostructures #Surface and Thin Film Phenomena #cond-mat
paper · pdf · doi:10.1103/physrevb.58.10823
published as Phys. Rev. B 58, 10823 (1998) · 16 pages, 10 figures (1 ps, 9 tex, automatically included); To appear in Phys. Rev. B (15 October 1998)
arxiv created 1998/09/17 · openalex publication_date 1998/10/15 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
The light-emission rate from a scanning tunneling microscope (STM) scanning a noble-metal surface is calculated taking retardation effects into account. As in our previous, nonretarded theory [P. Johansson, R. Monreal, and P. Apell, Phys. Rev. B 42, 9210 (1990)], the STM tip is modeled by a sphere, and the dielectric properties of tip and sample are described by experimentally measured dielectric functions. The calculations are based on exact diffraction theory through the vector equivalent of the Kirchoff integral. The present results are qualitatively similar to those of the nonretarded calculations. The light-emission spectra have pronounced resonance peaks due to the formation of a tip-induced plasmon mode localized to the cavity between the tip and the sample. At a quantitative level, the effects of retardation are rather small as long as the sample material is Au or Cu, and the tip consists of W or Ir. However, for Ag samples, in which the resistive losses are smaller, the inclusion of retardation effects in the calculation leads to larger changes: the resonance energy decreases by 0.2--0.3 eV, and the resonance broadens. These changes improve the agreement with experiment. For a Ag sample and an Ir tip, the quantum efficiency is \ensuremath≈10^\ensuremath-4 emitted photons in the visible frequency range per tunneling electron. A study of the energy dissipation into the tip and sample shows that in total about 1% of the electrons undergo inelastic processes while tunneling.