Studies of surface diffusion by second harmonic fluctuation spectroscopy

Second harmonic generation response by gold nanoparticles at the polarized water/2-octanone interface: from dispersed to aggregated particles

“…In these regions, the remaining non-coalesced smaller particles again yield a strong signal. It is difficult at present to perform a statistical analysis of these fluctuations, but work along the lines reported by Zhao et al could well be envisaged [22]. Such an analysis would be desirable for disentangling any other possible effects such as instabilities [23].…”

Sum-frequency vibrational spectroscopic studies of Langmuir monolayers

“…Using SHG from stearic acid molecules as a probe, Xiao et al found that the surface pH of water subphase underneath a stearic acid Langmuir monolayer was significantly lower than that of the bulk solution [109]. Eisenthal and coworkers studied the water/silica interface with SHG from surface-field-induced polar orientation of water molecules and discovered that there existed two surface pKa values for the deprotonation reaction of the silanol terminal groups at the interface [110]. They also found the surface pKa value for the deprotonation reaction of aniline headgroups in a Langmuir monolayer [111,112].…”

Analysis of the second harmonic generation signal from a liquid/air and liquid/liquid interface

“…Like Sum Frequency Generation (SFG), [6][7][8][9][10][11] Second Harmonic Generation (SHG) with nonzero intensity for a non-centrosymmetric molecular environment, is a very suitable technique to probe buried interfaces. [12][13][14][15][16] A strong advantage of this technique is that it allows in principle, non-exhaustively, (i) to quantify the number of molecules (or a) Electronic mail: olivier.diat@cea.fr nonlinear dipoles) at the interface (contributing to the SHG signal) and even at more buried positions, 17 (ii) to determine the orientational order of these molecules, 18 (iii) to analyze the spectral response induced by chemical complexation (when the optical setup allows us to vary the wavelength of analysis), (iv) to monitor the kinetics of an interfacial adsorption equilibrium or of the ion transfer itself, 19,20 (v) to track and determine the characteristic time of the dynamics at the interface by analyzing the correlation of the collected intensity, 20 and (vi) to follow the kinetics of very fast surface reactivity using the time structure of the pulsed laser beam. However, for systems that do not contain chromophore sites, the interpretation of SHG results is generally based on physical ad hoc models, without providing a microscopic picture of the interface at the molecular level, though.…”