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Title: Second harmonic generation study of liquid surface and amphilphile monolayer

Abstract

This thesis contains the following topics. In Chapter 2, we use temperature dependent SHC to study the surface structure of some neat liquids. It was found all the hydrogen bonding liquids have a stronger SHG dependence of temperature while for the non-hydrogen bonding liquids SH response is insensitive to temperature change. In Chapter 3, we discussed the general feature of the electric field induced second harmonic generation (EFISHG). We experimentally established the importance of the {chi}{sup (3)} mechanism at the air/water charged interface. In Chapter 4, we used SHG to study the p-nitrophenol (PNP) penetration into the insoluble monolayer of hexadecyl and pentadecyl acid. It was found that PNP preferentially adsorbs at the fatty acid monolayer. The population and orientation of PNP is strongly dependent on the fatty acid monolayer packing. In Chapter 5, SH signal fluctuation spectroscopy was used to study the surface self-diffusion within the monolayer gas-liquid co-existence region. Assuming the uniform distribution of the liquid phase cluster size, a diffusion model was developed to fit the experimental measured autocorrelation function. In Chapter 6, SH fluctuation spectroscopy was used to study the monolayer orientation spontaneous fluctuation. It was found that only the electron rich aromatic head groups exhibitmore » the orientational fluctuation while the electron poor aromatic molecules do not have a fluctuation anomalies. Fluctuation time scale is strongly influenced by the hydrophobic chain length. A quantitative theory was presented based on Landau-Ginzburg theory to fit the time dependent orientation fluctuation. In Chapter 7, we focused on the acid-base equilibrium constant measurement at the air/water interface using both {chi}{sup (2)} and {chi}{sup (2)} method. We have measured pKa of aniline, phenol, amine, and acid at the interface. It turned out that for all these species, the neutral form is more stable at the interface.« less

Authors:
Publication Date:
Research Org.:
Columbia Univ., New York, NY (United States)
OSTI Identifier:
111309
Resource Type:
Miscellaneous
Resource Relation:
Other Information: TH: Thesis (Ph.D.); PBD: 1992
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; 66 PHYSICS; LIQUIDS; HARMONIC GENERATION; INTERFACES; TEMPERATURE DEPENDENCE; SURFACES; AIR-WATER INTERACTIONS; NITROPHENOL; LAYERS; SPECTROSCOPY

Citation Formats

Zhao, X. Second harmonic generation study of liquid surface and amphilphile monolayer. United States: N. p., 1992. Web.
Zhao, X. Second harmonic generation study of liquid surface and amphilphile monolayer. United States.
Zhao, X. 1992. "Second harmonic generation study of liquid surface and amphilphile monolayer". United States. doi:.
@article{osti_111309,
title = {Second harmonic generation study of liquid surface and amphilphile monolayer},
author = {Zhao, X.},
abstractNote = {This thesis contains the following topics. In Chapter 2, we use temperature dependent SHC to study the surface structure of some neat liquids. It was found all the hydrogen bonding liquids have a stronger SHG dependence of temperature while for the non-hydrogen bonding liquids SH response is insensitive to temperature change. In Chapter 3, we discussed the general feature of the electric field induced second harmonic generation (EFISHG). We experimentally established the importance of the {chi}{sup (3)} mechanism at the air/water charged interface. In Chapter 4, we used SHG to study the p-nitrophenol (PNP) penetration into the insoluble monolayer of hexadecyl and pentadecyl acid. It was found that PNP preferentially adsorbs at the fatty acid monolayer. The population and orientation of PNP is strongly dependent on the fatty acid monolayer packing. In Chapter 5, SH signal fluctuation spectroscopy was used to study the surface self-diffusion within the monolayer gas-liquid co-existence region. Assuming the uniform distribution of the liquid phase cluster size, a diffusion model was developed to fit the experimental measured autocorrelation function. In Chapter 6, SH fluctuation spectroscopy was used to study the monolayer orientation spontaneous fluctuation. It was found that only the electron rich aromatic head groups exhibit the orientational fluctuation while the electron poor aromatic molecules do not have a fluctuation anomalies. Fluctuation time scale is strongly influenced by the hydrophobic chain length. A quantitative theory was presented based on Landau-Ginzburg theory to fit the time dependent orientation fluctuation. In Chapter 7, we focused on the acid-base equilibrium constant measurement at the air/water interface using both {chi}{sup (2)} and {chi}{sup (2)} method. We have measured pKa of aniline, phenol, amine, and acid at the interface. It turned out that for all these species, the neutral form is more stable at the interface.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1992,
month =
}

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  • Second harmonics have been generated in GaAs/AlGaAs heterostructures with the free-electron laser and a molecular gas laser operating in the far infrared. The heterostructures were a multiple quantum well consisting of ten half-parabolic wells and a heterojunction. The intensity dependence of the generated second harmonic was measured and revealed a less than quadratic dependence on the fundamental intensity. The new measurements are analyzed allowing for a calculation of the second order nonlinear susceptibility and the fundamental field amplitudes in the heterostructures. It is observed that the two samples differ in how their second order nonlinear susceptibilities depend on the magnitudemore » of the fundamental field in the heterostructure.« less
  • This thesis reports on experimental studies of kinetics and equilibria at liquid interfaces using the technique of Second Harmonic Generation (SHG). In the first part, SHG was used to study the kinetics of adsorption of p-nitrophenol at the air/water interface of a flowing liquid jet. Measurements of the SH signal strength and the polarization of the SH light at various distances (times) along the jet axis yield information about the development of the density and orientation of p-nitrophenol at the air/water interface. The kinetics of adsorption was interpreted in terms of the Langmuir theory and was found to be consistentmore » with this model. The free energy of adsorption obtained from the jet experiments was found to be the same as that obtained from static (equilibrium) experiments. The orientation of p-nitrophenol at the jet air/solution interface was the same as for the static (equilibrium) interface,which indicates that orientational equilibrium was rapidly achieved. It was also found that adsorption of nitrophenol to the air/water interface is not diffusion controlled, but rather is kinetically controlled by a barrier. SHG was then used to probe the silica/water interface.« less
  • Surface diffusion of Sb on Ge(111) has been measured with the newly-developed technique of second harmonic microscopy. In this method, concentration profiles at submonolayer coverage are imaged directly by second harmonic generation with 5 [mu]m spatial resolution. A Boltzmann-Matano analysis of the concentration profiles yields the coverage dependence of the diffusivity D without parameterization. Experiments were performed at roughly 70% of the bulk melting temperature T[sub m]. In the coverage range of 0 < [theta] < 0.6, the activation energy E[sub diff] remains constant at 47.5 [+-] 1.5 kcal/mol. The corresponding pre-exponential factor decreases from 8.7 [times] 10[sup 3[+-]0.4] tomore » 1.6 [times] 10[sup 2[+-]0.4] cm[sup 2]/sec. The results are explained in terms of a new vacancy model for surface diffusion at high-temperatures. The model accounts semiquantitatively for the large values of E[sub diff] and D[sub o], and suggest that these quantities may be manipulated by bulk doping levels and photon illumination of the surface.« less
  • Presented in this dissertation is a series of second harmonic generation (SHG) experiments on the single crystal Ag(111), Cu(111) and Au(111) surfaces. These studies exploit the inherent surface sensitivity of this nonlinear optical technique to study surface electronic structure, surface oxidation, and surface reconstructions. Another advantage of the SH technique is the ability to make comparative measurements in ultra high vacuum (UHV) and in an electrolyte solution. Reported are measurements of the second harmonic response from these surfaces in the electrochemical environment and in UHV. The comparative wavelength dependent SH studies of the Ag(111) surface show that if the electrodemore » is biased at the potential of zero charge (PZC), all of the surface properties correlate well with the properties of the Ag(111) surface measured in UHV. A resonance feature is observed in the wavelength dependence (2[omega] = 300-350 nm) of the SH response. This resonance feature is assigned to known surface electronic structure of Ag(111) in UHV and exhibits sensitivity to the applied potential. A simple model is presented incorporating the change in applied potential to account for the observed potential dependence of the resonance feature. The Au(111) surface is known to reconstruct in UHV and in the electrochemical environment. The SH results presented exploit the azimuthal dependence of the response to probe symmetry changes effected by this reconstruction. In UHV the SH response from the Au(111) surface also exhibits the symmetry of the unreconstructed surface. The comparative measurements of the SH response from Cu(111) reveal that the electrode surface, at all bias potential, is very different than in UHV. In contrast to the rotational anisotropy observed under 1064 nm excitation when the electrode is biased at the PZC, with 532 nm excitation the SH response is isotropic. Exposing the surface in UHV to oxygen changes the SH response at both wavelengths dramatically.« less
  • Diffraction of optical second-harmonic generation from a monolayer grating created by laser desorption of adsorbates can be used to study surface diffusion of molecules on substrates. Application of this novel technique to CO on Ni(111) yields a diffusion activation energy of 6.9 kcal/mol and a preexponential factor of approx. =1.2 x 10/sup -5/ cm/sup 2/s/sup -1/.