Initial quantum well states in Ag thin films on the In/Si(111)-[formula omitted] surface

Abstract

Silver thin films have been formed by room temperature deposition of Ag on In/Si(111)-3×3. The Ag films have been investigated using both angle-resolved photoelectron spectroscopy (ARPES) and scanning tunneling microscopy and spectroscopy (STM/STS). This creates a powerful link between the electronic structures and the film morphology. The valence band spectra show a clear evidence of quantum well state (QWS) formation already for a 2 monolayer (ML) film. This QWS moves towards the Fermi level for the 3 ML film, which also reveals a second QWS. The QWSs’ dispersions have been plotted along the Γ¯M¯ and Γ¯K¯ symmetry lines of the 1×1 surface Brillouin zone (SBZ), where the Γ¯M¯ direction shows the umklapp-mediated QWSs. The valence band spectra for the 3 ML Ag film also show a strong Ag sp band close to the edge of the Ag(111) 1×1 SBZ. In the STS spectrum from 2 ML, two peaks are visible below the Shockley surface state. These peaks are compared with the ARPES data and attributed to different features of the QWS, namely the turning part where the QWS band intersects with the bulk Si valence band region and the local binding energy minimum close to the Γ¯ point.