engleski

Valence band structure of subnanometer thick Ag films on Ni(111)

We have studied electronic and structural properties of ultra thin Ag films deposited on Ni(111) by HRARPES and STM. The HRARPES experiments were focused mainly on the development of the Ag 4d bands. Of particular interest was the segment of the 4d band lying in the projected energy gap of the Ni substrate where Ag d states are quantized. To resolve between individual d-QWS due to their large number in the relatively narrow energy range, high energy resolution is required. In our experiments, the resolution < 25 meV was estimated for He I line. The interpretation of the spectra of multilayer Ag d-QWS is also complicated by the fact that already after the completion of first layer, the next two layers grow simultaneously, as shown by our STM study. For 3ML nominal coverage, the photoemission spectrum is dominated by the peak at 4.84 eV, corresponding to the energy of the direct transition peak from Ag(111) surface for the He I excitation energy. Spectrum for the 7ML nominal coverage, exhibits all the major properties of photoemission from Ag 4d bulk band. The electronic structure of all Ag films of up-to 1ML thickness is characterized by two intense 4d features that are explained in terms of spin orbit split d-quantum well states. The splitting of 0.25 eV in the Gamma point of the surface Brillouin zone was found to be constant in this coverage range. The experimentally determined band structure of the 1ML Ag film along the Gamma-M direction in the surface Brillouin zone is compared with DFT calculations. Starting from an unsupported Ag monolayer and taking into account the electronic structure of the Ni(111), the possible hybridization effects are discussed. Temperature dependence of the two d-QWS for 1ML Ag film, revealed their electron&#8211; phonon coupling constant. STM experiments showed that the outcome of Ag growth on Ni(111) are Moiré structured Ag fcc layers. Structural and electronic properties of Ag/Ni(111) were correlated to the Ag/Pd(111) and Ag/Cu(100) where Ag films are also of fcc structure.

Quantum well states; Quantum effects; Ultra-thin films; Electronic properties

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