Reflectance difference spectroscopy is used to probe the optical transitions between surface states on the Cu(110) surface. Upon deposition of smallest amounts of carbon monoxide (CO) the signal is strongly quenched, which translates into a huge cross section of the order of 1000 A(2) for a single adsorbed CO molecule. This strongly enhanced surface sensitivity is interpreted as the loss in anisotropy (depolarization) of the surface states due to scattering from the adsorbed CO molecules. This feature renders RDS an extremely sensitive tool to probe the adsorption kinetics on anisotropic metal surfaces.
We show that reflectance difference spectroscopy (RDS) is sensitive to the inhomogeneous surface and thin film strain which builds up during hetero- and homoepitaxial growth. The RDS signal is affected by the local, mean square atomic displacements in the substrate resulting from the stress relaxation of strained adlayer islands. For layer-by-layer growth an oscillatory variation of the RDS intensity is observed. These results demonstrate the potentiality of RDS to probe the growth kinetics on structurally anisotropic surfaces.
Reflectance
anisotropy spectroscopy (RAS) is a powerful optical
probe that works on a polarization contrast basis. It can be operated
in any environment, ranging from ultrahigh vacuum to vapor phases
and liquids. The measured optical anisotropies are caused by several
symmetry breaking effects and are exclusively assigned to the surface
for otherwise bulk isotropic materials. In this work, we present a
systematic study comprising in situ RAS-transient to assess the surface
thermodynamics of the chloride adsorption on Cu(110) upon systematic
variations of the applied electrode potentials in comparison to cyclic
voltammetry (CV). Numerical time-derivatives of the measured RAS-transients
are shown to be exclusively associated with electrical currents of
those electrochemical reactions, which change the properties of the
electrode surface. The recorded transient line-shapes track the Frumkin
type isotherm properties related to chloride coverage. Both connections
are theoretically discussed. Owing to the surface and interface specificity,
RAS is shown to exhibit a high surface sensitivity. In particular,
processes taking place in parallel, namely, the hydrogen evolution
reaction (HER) as well as the copper dissolution as Cu+ and Cu2+, do not contribute to the RAS response.
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