Interplay between transmission background and Gundlach oscillation in scanning tunneling spectroscopy

It is known that when the electronic structure beyond the vacuum level of a metal film is probed by scanning tunneling spectroscopy, both transmission resonance and Gundlach oscillation may be revealed in the tunneling spectrum. The manifestation of transmission resonance implies that there exists a transmission background involving the information about the electron transmissivity in the spectrum, superposing with the Gundlach oscillation. In this paper, it is shown that the spectral intensity of the Gundlach oscillation can vary with observed location on a Ag Si (111) 7×7 surface and a reconstructed Au(111) surface. The variation can naturally be attributed to the local change of electron transmissivity. A general phenomenon is also observed that the total intensity in the range of the Gundlach oscillation is conserved, although its intensity distribution is location dependent. By inspecting the Gundlach oscillation on the Ag(100) surface, it is demonstrated that the transmission background can be correlated to the projected bulk band structure.