Bertrand Busson

Non-Uniqueness of Parameters Extracted from Resonant Second-Order Nonlinear Optical Spectroscopies

Experimental data from second-order nonlinear optical spectroscopies (SFG, DFG, and SHG) provide parameters relevant to the physical chemistry of interfaces and thin films. We show that there are in general 2 N or 2 N-1 equivalent sets of parameters to fit an experimental curve comprising N resonant features, of vibrational or electronic origin for example. We provide the algorithm to calculate these sets, among which the most appropriate has to be selected. The main consequences deal with the existence of ghost resonances, the need of a critical analysis of fit results, and the procedure to search for better sets of parameters coherent with applied constraints.

Effect of a static electric field on the vibrational and electronic properties of a compressed CO adlayer on Pt(110) in nonaqueous electrolyte as probed by infrared reflection–absorption spectroscopy and infrared-visible sum-frequency generation spectroscopy

The CO–Pt(110) in nonaqueous electrolyte electrochemical interface was studied by infrared reflection–absorption spectroscopy (IRAS) and infrared (IR)-visible sum-frequency generation (SFG) nonlinear vibrational spectroscopy over a wide range of applied potentials (−1.7⩽Φ⩽1 V/NHE). The integrated intensities of the IRAS and SFG peaks associated with resonant excitation of the atop CO internal stretch vibration (AIR and ASFG) showed distinct variations with Φ. The influence of vibrational and electronic properties on the observed variations is discussed. Potential dependent dynamical charge transfer is not sufficient to explain the observed value of ∂AIR/∂Φ. It is shown that screening factors due to dipolar interactions between molecules within the compressed adsorbed layer must be taken into account in order to explain the variations of the IRAS and SFG data and that the observed behavior differences of AIR and ASFG with the potential are not necessarily related to changes in the Raman cross section of th...

In Situ Electrochemical SFG/DFG Study of CN − and Nitrile Adsorption at Au from 1-Butyl-1-methyl-pyrrolidinium Bis(trifluoromethylsulfonyl) Amide Ionic Liquid ((BMP)(TFSA)) Containing 4-{2-(1-(2-Cyanoethyl)-1,2,3,4- tetrahydroquinolin-6-yl)diazenyl} Benzonitrile (CTDB) and K(Au(CN)2)

In this paper we report an in situ electrochemical Sum-/Difference Frequency Generation (SFG/DFG) spectroscopy investigation of the adsorption of nitrile and CN− from the ionic liquid 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl) amide ([BMP][TFSA]) containing 4-{2-[1-(2-cyanoethyl)-1,2,3,4-tetrahydroquinolin-6-yl]- diazenyl}benzonitrile (CTDB) at Au electrodes in the absence and in the presence of the Au-electrodeposition process from K[Au(CN)2]. The adsorption of nitrile and its coadsorption with CN− resulting either from the cathodic decomposition of the dye or from ligand release from the Au(I) cyanocomplex yield potential-dependent single or double SFG bands in the range 2,125–2,140 cm−1, exhibiting Stark tuning values of ca. 3 and 1 cm−1 V−1 in the absence and presence of electrodeposition, respectively. The low Stark tuning found during electrodeposition correlates with the cathodic inhibiting effect of CTDB, giving rise to its levelling properties. The essential insensitivity of the other DFG parameters to the electrodeposition process is due to the growth of smooth Au.

Linear and nonlinear optical properties of functionalized CdSe quantum dots prepared by plasma sputtering and wet chemistry

We develop an innovative manufacturing process, based on radio-frequency magnetron sputtering (RFMS), to prepare neat CdSe quantum dots (QDs) on glass and silicon substrates and further chemically functionalize them. In order to validate the fabrication protocol, their optical properties are compared with those of QDs obtained from commercial solutions and deposited by wet chemistry on the substrates. Firstly, AFM measurements attest that nano-objects with a mean diameter around 13 nm are located on the substrate after RFMS treatment. Secondly, the UV-Vis absorption study of this deposited layer shows a specific optical absorption band, located at 550 nm, which is related to a discrete energy level of QDs. Thirdly, by using two-color sum-frequency generation (2C-SFG) nonlinear optical spectroscopy, we show experimentally the functionalization efficiency of the RFMS CdSe QDs layer with thiol derived molecules, which is not possible on the QDs layer prepared by wet chemistry due to the surfactant molecules from the native solution. Finally, 2C-SFG spectroscopy, performed at different visible wavelengths, highlights modifications of the vibration mode shape whatever the QDs deposition method, which is correlated to the discrete energy level of the QDs.

Localised detection of thiophenol with gold nanotriangles highly structured as honeycombs by nonlinear sum frequency generation spectroscopy

AbstractnGold nanotriangles structured as honeycombs and fabricated by nanosphere lithography on a gold film are functionalised by thiophenol molecules in order to be used as plasmonic sensors in nonlinear optical sum frequency generation (SFG) spectroscopy. The monitoring and the characterisation of the surface optical properties are performed by UV–visible differential reflectance spectroscopy showing an absorbance maximum located at 540xa0nm for p- and s-polarisation beams. SFG spectroscopy proves to be effective for thiophenol detection in ssp-polarisation scheme, while the molecular SFG signal disappears in ppp-configuration due to the strong s–d interband contribution of gold. However, in ssp-configuration, the vibration modes of thiophenol molecules at 3050 and 3071xa0

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

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Doubly Resonant Sum Frequency Generation Spectroscopy of Adsorbates at an Electrochemical Interface

cm-1 are yet observed thanks to the excitation of a transversal plasmon mode by the incident visible laser beam, whereas they are usually very difficult to distinguish by surface-enhanced Raman scattering and other vibrational optical probes.

Chiral Specificity of Doubly Resonant Sum-Frequency Generation in An Anisotropic Thin Film

We experimentally determine the effective nonlinear second-order susceptibility of gold over the visible spectral range. To reach that goal, we probe by vibrational two-color sum-frequency generation spectroscopy the methyl stretching region of a dodecanethiol self-assembled monolayer adsorbed on a gold film. The sum-frequency generation spectra show a remarkable shape reversal when the visible probe wavelength is tuned from 435 to 705 nm. After correcting from Fresnel effects, the methyl stretching vibrations serve as an internal reference, allowing to extract the dispersion of the absolute phase and relative amplitude of the effective nonlinear optical response of gold in the visible range.