engleski

Electron-phonon coupling in monolayer silver films ; interface effects

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 measures 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. Investigation of s-p derived quantum well states (QWS) in ultra thin silver films showed significant enhancement of e-ph coupling parameter at small thicknesses , which is followed by its oscillatory behavior with increasing number of layers . There is, however, a very limited information on the e-ph coupling in QW systems of the states of d-character . We have studied e-ph coupling in 4d quantum well states (QWS) formed in one monolayer (ML) silver films grown on different low index surfaces: Cu(100), Mo(110), Ni(111), Pd(111). Structural analysis performed by LEED and STM shows that 1ML silver films on all surfaces are very similar having 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 e-ph coupling constant across different substrate surfaces was correlated with the position of QW states with respect to the energy- and hybridization-band gaps of the substrates projected on the corresponding surfaces. This analysis provides the insight into the influence of the film-substrate interface on the strength of e-ph coupling parameter.

electron-phonon coupling; ultra thin films; silver; photoemission

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