Angle resolved photoemission spectroscopy has been proven as a reliable tool for the investigation of state specific electron phonon (e-ph) coupling parameter in quasi two-dimensional systems. The high energy- and k-resolved photoemission spectrometers directly measure the photo-hole spectral function. In this way the slight temperature induced changes of the peak width can be correlated to the electron-phonon coupling constant.
Investigations of s-p derived quantum well states (QWS) in ultra thin silver films showed significant enhancement of the e-ph coupling parameter at smallest thicknesses [1,2] which was followed by its oscillatory behavior with increasing number of layers [3]. There is, however, a very limited information on the e-ph coupling in QW states of d-character [4].
We have studied the e-ph coupling in 4d quantum well states formed in one monolayer (ML) thick silver films grown on several low index surfaces: Cu(100), Mo(110), Ni(111), and Pd(111). Structural analysis performed by LEED and STM shows that 1 ML silver films on all surfaces are very similar exhibiting perfect or slightly distorted hexagonal structure. Electron phonon coupling constants were extracted from the linear fit of the temperature dependence of the photoemission peak widths. The measured variation of the e-ph coupling constant across different substrate surfaces is correlated with the position of the QW states with respect to surface-projected energy- and hybridization-band gaps. This analysis provides an insight into the influence of the film-substrate interface on the strength of the e-ph coupling parameter.
[1] T. Valla, M. Kralj, A. Šiber, M. Milun, P.Pervan P.D. Johnson and D. P. Woodruff, J. Phys. Condens. Matter 12, L477 (2000)
[2] D. –A. Luh, T. Miller, J.J. Paggel and T.-C.Chiang, Phys. Rev. Lett. 88, 256802 (2002)
[3] S. Mathias, M. Wiesenmayer, M. Aeschlimann and M. Bauer, Phys. Rev. Lett. 97, 236809 (2006)
[4] J.J. Paggel D. –A. Luh, T. Miller, and T.-C.Chiang, Phys. Rev. Lett. 92, 186803 (2004)
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