Surface vibrational spectroscopy of the vapor/solid and liquid/solid interface of acetonitrile on ZrO2

Hatch, S. R.; Polizzotti, R. S.; Dougal, S. M.; Rabinowitz, P.

doi:10.1016/0009-2614(92)85935-4

Cited by 54 publications

(62 citation statements)

References 23 publications

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“…[22][23][24][25] There are two advantages when one uses the TIR condition. First, both incident light to the interface and reflected light or generated light from the interface travel in only one of the two phases adjacent to the interface, which circumvents bulk absorption by the other phase.…”

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Total-internal-reflection Broad-bandwidth Sum Frequency Generation Spectroscopy of Hexadecanethiol Adsorbed on Thin Gold Film Deposited on CaF, 2

et al. 2003

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IntroductionFor the study of surface phenomena at various interfaces, the total internal reflection (TIR) condition has been used in a number of spectroscopic measurements, 1 such as fluorometry, 2-9 surface enhanced infrared spectroscopy (SEIRA), [10][11][12] second harmonic generation, [13][14][15][16][17][18][19][20][21] and sum frequency generation (SFG). [22][23][24][25] There are two advantages when one uses the TIR condition. First, both incident light to the interface and reflected light or generated light from the interface travel in only one of the two phases adjacent to the interface, which circumvents bulk absorption by the other phase. One corollary is the freedom of changing the composition of the adjacent phase that has a lower refractive index. Second, high sensitivity to the interfaces can be achieved owing to the enhancement of the electric field at the interfaces. 1 The TIR arrangement can be employed at metal interfaces if a very thin metal film is used to avoid the absorption of light. It has been successfully employed to detect adsorbed species on metal in the SEIRA, where the thickness of the metal film is about 10 nm on a transparent substrate. [10][11][12] Recently, Williams et al. showed that the TIR arrangement can also be employed to detect SFG signals from alkanethiols adsorbed on a thin gold film. 24 However, detailed analysis of the sum frequency vibrational spectra has not been reported. SFG in the TIR arrangement has some potential as a powerful tool to study molecular orientations at metal/liquid interfaces, such as electrochemical interfaces, because it is free from bulk absorption and has interfacial sensitivity in the order of nanometers. Unlike surface plasmon resonance and capacitance measurements that have been used as sensitive means of detecting adsorption and molecular interaction at the interfaces, TIR-SFG will enable us to obtain molecular information on the solution side of the interfaces. One drawback of the TIR arrangement is the roughness of the metal surfaces. The roughness is prerequisite for high sensitivity and can complicate the interpretation of the experimental data because of the orientational distribution of molecules in comparison with those adsorbed on a single crystal surface. It is therefore of crucial importance to assess the degree of the variation in orientation of molecules.By using broad-bandwidth sum frequency generation (BBSFG) [26][27][28] we recently analyzed the orientation of alkanethiols adsorbed on Au(111). 29It is worthwhile to examine the applicability of BBSFG in the TIR condition at metal interfaces to obtain SFG spectra with higher resolution. In the present paper, we report the results of TIR-BBSFG measurements for hexadecanethiol (HDT) adsorbed on a thin gold film on CaF2. We will show that BBSFG can be successfully employed in the orientation analysis of the HDT molecules and that the methyl groups of HDT are much more randomly orientated than those on Au(111) on mica. Experimental SubstrateA hemicylindrical CaF2 prism (Pier Optic...

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Total-internal-reflection Broad-bandwidth Sum Frequency Generation Spectroscopy of Hexadecanethiol Adsorbed on Thin Gold Film Deposited on CaF, 2

et al. 2003

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“…It has already been used in several cases to identify molecular species appearing and disappearing at the electrode surface in an electrochemical process (14)(15)(16). SFG spectra for other neat liquid interfaces have also been measured (48)(49)(50)(51). They all provide useful information about the liquid interfacial structures.…”

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A few selected applications of surface nonlinear optical spectroscopy.

Shen

1996

Proc. Natl. Acad. Sci. U.S.A.

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As a second-order nonlinear optical process, sum-frequency generation is highly surface-specific and accordingly has been developed into a very powerful and versatile surface spectroscopic tool. It has found many unique applications in different disciplines and thus provided many exciting new research opportunities in surface and surfacerelated science. Selected examples are discussed here to illustrate the power of the technique.In recent years, we have been developing and applying modern optical techniques to surface and interface studies. The one that has attracted much attention is surface optical second harmonic generation (SHG) and sum-frequency generation (SFG) (1). This is because the technique has very high surface specificity and wide applicability. SFG is a nonlinear optical process in which two laser beams at frequencies wi and w2 impinging on a medium mix and generate a sum-frequency output at ws = Wl + W2. SHG is a special case of SFG with wi = w2. It is well known that a second-order nonlinear optical process like SHG and SFG is forbidden in a medium with inversion symmetry (2). At a surface or interface, however, the inversion symmetry is necessarily broken. This then leads to the surface specificity of SHG and SFG. More formally, SFG (or SHG) originates from a nonlinear polarization P(2)(ws) induced in a medium by laser wave mixing (2): p(2)(W) = X(2):E()E(W2) [1] where E(wi) is the laser field at wi and X(2) is a tensor describing the nonlinear response of the medium to the fields. Inversion symmetry of the medium yields72) = _.i2), and therefore x (2) must vanish. The SFG Lor SHG) measurement on a surface allows the deduction of X(2)(Ws = Wl + W2), which is a tensor characteristic of the surface (3). For example, the symmetry of 2) provides information about the surface structural symmetry. The spatial variation of x42) over the surface directly reflects the spatial variation of the surface structure. The time variation of 92) indicates how the surface structure changes with time. Of particular importance is that 2) also carries spectroscopic information that enables us to learn microscopic details about the surface. As shown in Fig. 1

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“…In the frequency domain measurement, increasing the pulse energy cannot be done without sacrificing spectral resolution, for our type of experimental set-up. The measurements were done in a co-propagating total internal reflection geometry (after [10,19]) in which the reflected SFG field is detected (see Fig. 2).…”

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confidence: 99%