Nonlinear optical response of a gold surface in the visible range: A study by two-color sum-frequency generation spectroscopy. III. Simulations of the experimental SFG intensities

Abstract

We model the amplitude line shape and absolute phase of the infrared-visible sum-frequency signals produced by a thiolated polycrystalline gold surface as a function of the visible wavelength. We follow two hypotheses: in the interband scenario, the resonant features are attributed to interband transitions, whereas in the effective surface state scenario, they stem mostly from the excitation of surface transitions. We find that both scenarios lead to a satisfactory account of the experimental data and that only free electrons may spill out of the gold bulk, as expected. For the interband scenario, the balance between free and bound electron contributions to sum-frequency generation has to be adjusted to fit the data. The surface transitions are shown to take their origin inside gold and we investigate the surface states involved in such transitions, with a comparison to the silver surfaces. We finally provide a work program dedicated to discriminate between the two scenarios.

An in situ IR-Vis Sum Frequency Generation Spectroscopy study of cyanide adsorption during zinc electrodeposition

“…In the case of raw spectra exhibiting a tilted background, we removed the slope and set the background level to its average. The non-resonant background originates indeed from the combination of the nonlinear responses of free and bound electrons in the metal [13][14][15] associated with plasmonic resonances, especially in the case of electrodeposition, that intrinsically generates nanocrystals [6]. This signal does not vary significantly with the IR frequency range of the measurements.…”

“…Indeed, for gold it is found to vary of a factor of three moving from 400 to 700 nm the visible excitation wavelength (i.e. spanning about 10 4 cm -1 ) [13][14][15], The deconvolution yielding the SFG data plots is reported in [10]…”

Determining nonlinear optical coefficients of metals by multiple angle of incidence heterodyne-detected sum-frequency generation spectroscopy

“…27,62 Surface and bulk effective susceptibilities, calculated separately, reconstruct the total SFG response from gold. 28 The second formulation for the bulk terms describes the bulk as an infinite stack of thin plates, just like the surface terms. Considering that the bulk polarization in Eq.…”

“…These five elements cannot be separated from surface contributions in our measurements (see Table I). Therefore, in order to estimate the most important terms among the nine remaining ones, we calculate the total effective contribution by summing free and bound electron terms (although their mutual weights may be debated 28 ) and weighting them by the appropriate Fresnel coefficients (Fig. 3).…”

“…thiolated) self-assembled molecular layers, its chemical stability in air and its intense SFG nonresonant response (due to contributions from its free and bound electrons. 27,28 ) We begin by introducing some formalism that relates the surface fields to the incidence and reflected SFG fields. We also describe the quadrupolar response from the bulk of the material.…”