Reflectance difference spectroscopy study of Ag growth on W(1 1 0)

We report a reflectance difference spectroscopy (RDS) investigation of the epitaxial growth of Ag on the W(1 1 0) surface. Monitoring the growth in real time, the RDS signal at 4.6 eV shows an oscillatory behavior corresponding to the layer-by-layer growth of the first three monolayers. The oscillations are attributed to the variation of the optical anisotropy contributed by the W(1 1 0) substrate and the Ag film. By analyzing the spectral evolution during growth, characteristic optical-electronic fingerprints can be deduced for each added atomic layer. In particular, the binding energy of d-like quantum well states has been used as an indicator for the number of Ag atomic layers and, hence, as a sensitive probe of the Ag thin film growth.