Vibrational sum-frequency generation (VSFG) spectra of n-alkyltrichlorosilanes chemisorbed on quartz plate

Watanabe, Nobuyuki; Yamamoto, Hiroyoshi; Wada, Akira; Domen, Kazunari; Hirose, Chiaki; Ohtake, Tadashi; Mino, Norihisa

doi:10.1016/0584-8539(94)e0064-h

Cited by 67 publications

(94 citation statements)

References 13 publications

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“…41 This model can be applied to the C 3V symmetry for the methyl groups under the assumption that the zzz and xxz susceptibility elements dominate the SFG signal (for gold/silicon interfaces). 42 F zzz , F xxz > >F xzx , F zxx (4) Therefore, the tilt angle determination using eq 3 is not applicable to the silicon substrate; it is only valid after deposition of gold that significantly enhances the electric field of the z component.…”

Section: Effect Of Metal Deposition Methodmentioning

confidence: 99%

Probing the Molecular Conformation of Self-Assembled Monolayers at Metal/Semiconductor Interfaces by Vibrational Sum Frequency Generation Spectroscopy

et al. 2009

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The conformation of self-assembled monolayers (SAMs) buried at metal-semiconductor interfaces plays a crucial role in the functioning of the molecular junctions thus formed. We have studied by vibrational sum frequency generation (SFG) spectroscopy the influence of deposited gold films on the molecular orientation of a series of n-alkyl monolayers that are covalently bonded to silicon(111) via Si-C linkages (≡Si-C n H 2n+1 , n ) 10, 12, 14, and 18). The SFG spectra indicate that the gold contacts (overlayers) introduce significant gauche defects within the initially highly oriented alkyl chains. The methyl tilt angles of the buried n-alkyl monolayers depend on the gold deposition method (vacuum evaporation vs sputtering) and the alkyl chain length. These observations are supported by solid-state electrical measurements.

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Section: Effect Of Metal Deposition Methodmentioning

confidence: 99%

Probing the Molecular Conformation of Self-Assembled Monolayers at Metal/Semiconductor Interfaces by Vibrational Sum Frequency Generation Spectroscopy

et al. 2009

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“…β lmn,q = A lm,q M n,q , where A lm,q is the lm component of the Raman polarizability tensor and M n,q is the n component of the IR dipole moment vector. 43 (A lm,q should not be confused the amplitude A ijk,q in eq 2.) Therefore, only those vibration modes that are both Raman-and IR-active contribute to the hyperpolarizability tensor.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Molecular Structure of Poly(methyl methacrylate) Surface. I. Combination of Interface-Sensitive Infrared–Visible Sum Frequency Generation, Molecular Dynamics Simulations, and ab Initio Calculations

et al. 2014

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The chemical composition and molecular structure of polymeric surfaces are important in understanding wetting, adhesion, and friction. Here, we combine interfacesensitive sum frequency generation spectroscopy (SFG), allatom molecular dynamics (MD) simulations, and ab initio calculations to understand the composition and the orientation of chemical groups on poly(methyl methacrylate) (PMMA) surface as a function of tacticity and temperature. The SFG spectral features for isotactic and syndiotactic PMMA surfaces are similar, and the dominant peak in the spectra corresponds to the ester-methyl groups. The SFG spectra for solid and melt states are very similar for both syndiotactic and isotactic PMMA. In comparison, the MD simulation results show that both the ester-methyl and the α-methyl groups of syndiotactic-PMMA are ordered and tilted toward the surface normal. For the isotactic-PMMA, the α-methyl groups are less ordered compared to their ester-methyl groups. The backbone methylene groups have a broad angular distribution and are disordered, independent of tacticity and temperature. We have compared the SFG results with theoretical spectra calculated using MD simulations and ab initio calculations. Our analysis shows that the weaker intensity of α-methyl groups in SFG spectra is due to a combination of smaller molecular hyperpolarizability, lower ordering, and lower surface number density. This work highlights the importance of combining SFG spectroscopy with MD simulations and ab initio calculations in understanding polymer surfaces. ■ INTRODUCTIONOne of the simplest and still commonly used technique to characterize surfaces of polymers is the measurement of water contact angle. Although this is a very simple technique to judge the wettability of surfaces, it lacks molecular level sensitivity to identify the chemical composition and molecular structure of surfaces. In addition, the rearrangement of molecules at the surface after exposure to water complicates the interpretation of contact angle results. 1 X-ray photoelectron spectroscopy (XPS), a vacuum-based technique, provides excellent information regarding the elemental composition present at the surfaces. However, to identify different hydrocarbon groups (or bondings) is not trivial and relies on subtle shifts of carbon binding energies in the high-resolution XPS analysis. 2 Attenuated-total-reflectance infrared can be used to pick up molecular fingerprints, but this technique samples a much thicker layer than the surface region that affects wetting, surface energy, and friction. 3 In the past two decades, surface-sensitive infrared−visible sum frequency generation spectroscopy (SFG) has been used to study polymer surfaces, 4−7 polymer/liquid interfaces, 7−11 polymer/metal or metal oxide interfaces, 5,12−15 and polymer/polymer interfaces. 12,16−19 SFG is a second-order nonlinear optical technique, and under electric dipole approximation, the SFG signal is only generated by the ordered molecules at surfaces or interfaces and the contribution from ...

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“…The nonlinear susceptibility equations for the asymmetric methyl stretching mode (r -) are similar in form to those of the symmetric mode and can be deduced directly from symmetry considerations but have also been published previously. 20,24,25 The ijk where ∆ is the phase variation in radians, l is the propagation distance, n is the refractive index of the propagation medium, and λ is the wavelength of the light in Vacuo. ∆ for each of the propagating beams depicted in Figure 1 can be calculated from the geometry of the system and are given in Appendix A.…”

Section: Calculation Details (A) Sum Frequency Intensities-ppp Polarimentioning

confidence: 99%

Interference Effects in Sum Frequency Spectra from Monolayers on Composite Dielectric/Metal Substrates

et al. 2002

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A theoretical model has been developed to describe the generation of Sum Frequency (SF) light from a monolayer film adsorbed to the surface of a dielectric and metal composite substrate. This type of substrate provides enhanced SF signals from the monolayer without modifying the intrinsic (hydrophilic) properties of the dielectric surface. The fundamental equations of both resonant and nonresonant SF generation have been extended from a single interface to encompass the two displaced sources, the air/dielectric interface at which the monolayer film is located, and the dielectric/metal interface. The model describes the coherent addition of three separate SF signals which coherently interfere with each other, thereby affecting the line-shape observed in the net SF spectrum. Representative calculations have been made for a highly ordered monolayer of an aliphatic hydrocarbon molecule, adsorbed on a dielectric with the optical properties of mica, which is itself in contact with a metal modeled to resemble gold. The SF spectral line-shapes are predicted as a function of the thickness of the dielectric material for the methyl terminal groups of the hydrocarbon chain. The model can be applied to any dielectric/metal composite by modifying the optical properties appropriately.

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Vibrational sum-frequency generation (VSFG) spectra of n-alkyltrichlorosilanes chemisorbed on quartz plate

Cited by 67 publications

References 13 publications

Probing the Molecular Conformation of Self-Assembled Monolayers at Metal/Semiconductor Interfaces by Vibrational Sum Frequency Generation Spectroscopy

Probing the Molecular Conformation of Self-Assembled Monolayers at Metal/Semiconductor Interfaces by Vibrational Sum Frequency Generation Spectroscopy

Molecular Structure of Poly(methyl methacrylate) Surface. I. Combination of Interface-Sensitive Infrared–Visible Sum Frequency Generation, Molecular Dynamics Simulations, and ab Initio Calculations

Interference Effects in Sum Frequency Spectra from Monolayers on Composite Dielectric/Metal Substrates

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