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Paul B. Davies

Bio: Paul B. Davies is an academic researcher from University of Cambridge. The author has contributed to research in topics: Langmuir–Blodgett film & Tunable diode laser absorption spectroscopy. The author has an hindex of 5, co-authored 5 publications receiving 654 citations.

Papers
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Journal ArticleDOI
TL;DR: Sum frequency generation vibrational spectroscopy (SFS) as discussed by the authors is a nonlinear optical technique which provides vibrational spectrum of molecules solely at interfaces, which can be analyzed to provide the polar orientation, molecular conformation, and average tilt angle of the adsorbate to the surface normal.
Abstract: The interfacial regions between bulk media, although often comprising only a fraction of the material present, are frequently the site of reactions and phenomena that dominate the macroscopic properties of the entire system. Spectroscopic investigations of such interfaces are often hampered by the lack of surface specificity of most available techniques. Sum frequency generation vibrational spectroscopy (SFS) is a non‐linear optical technique which provides vibrational spectra of molecules solely at interfaces. The spectra may be analysed to provide the polar orientation, molecular conformation, and average tilt angle of the adsorbate to the surface normal. This article is aimed at newcomers to the field of SFS, and via a tutorial approach will present and develop the general sum frequency equations and then demonstrate how the fundamental theory elucidates the important experimental properties of SFS.

660 citations

Journal ArticleDOI
09 Aug 2003-Langmuir
TL;DR: The polar orientation and degree of conformational order of SDS adsorbed at the hydrophobic octadecane thiol/aqueous solution interface has been investigated as a function of the surfactant concentration in the presence and absence of a fixed concentration of poly(ethylene oxide) (PEO) as discussed by the authors.
Abstract: The polar orientation and degree of conformational order of sodium dodecyl sulfate (SDS) adsorbed at the hydrophobic octadecane thiol/aqueous solution interface has been investigated as a function of the surfactant concentration in the presence and absence of a fixed concentration of poly(ethylene oxide) (PEO). Sum frequency vibrational spectroscopy, based on the nonlinear optical phenomenon of sum frequency generation, was employed to obtain spectra of the interfacial surfactant; weak signals from PEO at the interface were also obtained. The phase of the spectra indicated that both the surfactant and the polymer had a net orientation of their CH2 and/or CH3 groups toward the hydrophobic surface. Spectra of SDS in the presence of mixed polymer/surfactant solutions showed increasing conformational order as the surfactant concentration was raised. At the lowest surfactant concentration, the spectra of SDS were weaker in the presence of the polymer than in its absence. Probing interfacial PEO specifically th...

30 citations

Journal ArticleDOI
TL;DR: In this article, the sum frequency vibrational spectroscopy (SFS) spectra of the uppermost and lowermost fatty acid layers of a multilayer C-H stretching region were derived from the summation of spectra from the upper and lower layers.
Abstract: Langmuir-Blodgett (LB) multilayer films of the cadmium salts of five long chain fatty acids (C n COOH, n = 14, 16, 18, 20, and 22) deposited onto hydrophobic gold have been investigated in the C-H stretching region by sum frequency vibrational spectroscopy (SFS). The highly ordered multilayer films were found to be strongly SF active, although the spectra were complicated by the presence of an interference effect dependent upon the number of layers deposited. This interference effect was evident in the phase of the measured asymmetric methyl stretching mode (r - ). Conversely, the phases of the symmetric stretching modes (r + and r + F R ) were largely unaffected. The measured SF spectra were shown to arise from the summation of spectra from the uppermost and lowermost fatty acid layers. The SF spectrum of the uppermost fatty acid layer has a characteristic interference behavior arising from interaction of its resonant signal with the nonresonant signal from the substrate. Quantification of the periodicity of this interference effect gives a value in satisfactory agreement with previous theoretical predictions. The SF spectrum of the lowermost fatty acid is, as expected, independent of the multilayer thickness. Summation of individual SF spectra of the uppermost and lowermost fatty acid layers of multilayer films (achieved via selective deuteration) has been shown to accurately reproduce experimental spectra of fully monoisotopic multilayers. These findings imply that interpretation of SF spectra of LB multilayer films deposited on metal substrates must be performed with care and that deconvolution of spectra in terms of contributing layers is imperative.

19 citations

Journal ArticleDOI
TL;DR: In this paper, the Pand R-branch lines of the fundamental bands of the 12C14N and 13C 14N radicals in their ground (2Σ+) electronic state have been measured at high resolution by diode laser absorption spectroscopy.
Abstract: Many Pand R-branch lines of the fundamental bands of the 12C14N and 13C14N radicals in their ground (2Σ+) electronic state have been measured at high resolution by diode laser absorption spectroscopy. The radicals were generated in a 2.45 GHz planar microwave plasma in methane with varying proportions of N2 and H2. From a fit to the spectra the origins of the fundamental bands of the two isotopomers were determined to be 2042.42104(84) cm−1 and 2000.084 70(30) cm−1. The main product detected in the plasma by diode laser spectroscopy is HCN, with concentrations about three orders of magnitude higher than CN.

15 citations

Journal ArticleDOI
TL;DR: In this article, the phase of the symmetric methyl stretching mode (r + ) was constant with film thickness, while that of the asymmetric stretching mode varied linearly with increasing film thickness.

15 citations


Cited by
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Journal ArticleDOI
TL;DR: A critical assessment of the results from this technique is made by comparing them with the information available from other techniques used to investigate adsorption at this interface, from neutral polymers with ionic surfactants to oppositely charged polyelectrolyte/ionic surfactant mixtures.

405 citations

Journal ArticleDOI
01 Mar 1966-Nature
TL;DR: Hellwege et al. as mentioned in this paper presented a series of articles about magnetische Eigenschaften freier Radikale. But they focused on the atom-and Molekularphysik.
Abstract: Zahlenwerte und Funktionen aus Naturwissenschaften und Technik Von Landolt-Bornstein. Neue Serie. Gesamtherausgabe: K. H. Hellwege. Gruppe II: Atom- und Molekularphysik. Band 1: Magnetische Eigenschaften freier Radikale. Von H. Fischer. Herausgeber: K. H. Hellwege und A. M. Hellwege. Pp. x + 154. (Berlin: Springer-Verlag, 1965.) 68 D.M.

358 citations

Journal ArticleDOI
TL;DR: A review of the experimental and theoretical advances made in the last several decades in understanding the structure, dynamics, and transport of the proton and hydroxide ions in different aqueous environments, ranging from water clusters to the bulk liquid and its interfaces with hydrophobic surfaces is provided.
Abstract: Understanding the structure and dynamics of water's constituent ions, proton and hydroxide, has been a subject of numerous experimental and theoretical studies over the last century. Besides their obvious importance in acid-base chemistry, these ions play an important role in numerous applications ranging from enzyme catalysis to environmental chemistry. Despite a long history of research, many fundamental issues regarding their properties continue to be an active area of research. Here, we provide a review of the experimental and theoretical advances made in the last several decades in understanding the structure, dynamics, and transport of the proton and hydroxide ions in different aqueous environments, ranging from water clusters to the bulk liquid and its interfaces with hydrophobic surfaces. The propensity of these ions to accumulate at hydrophobic surfaces has been a subject of intense debate, and we highlight the open issues and challenges in this area. Biological applications reviewed include proton transport along the hydration layer of various membranes and through channel proteins, problems that are at the core of cellular bioenergetics.

342 citations

Journal ArticleDOI
TL;DR: This review covers the compositional, structural and morphological aspects of SEI, both artificially and naturally formed, and metallic dendrites using in situ/in operando cells and various in situ analytical tools.
Abstract: Lithium-ion batteries, simply known as lithium batteries, are distinct among high energy density charge-storage devices. The power delivery of batteries depends upon the electrochemical performances and the stability of the electrode, electrolytes and their interface. Interfacial phenomena of the electrode/electrolyte involve lithium dendrite formation, electrolyte degradation and gas evolution, and a semi-solid protective layer formation at the electrode–electrolyte interface, also known as the solid–electrolyte interface (SEI). The SEI protects electrodes from further exfoliation or corrosion and suppresses lithium dendrite formation, which are crucial needs for enhancing the cell performance. This review covers the compositional, structural and morphological aspects of SEI, both artificially and naturally formed, and metallic dendrites using in situ/in operando cells and various in situ analytical tools. Critical challenges and the historical legacy in the development of in situ/in operando electrochemical cells with some reports on state-of-the-art progress are particularly highlighted. The present compilation pinpoints the emerging research opportunities in advancing this field and concludes on the future directions and strategies for in situ/in operando analysis.

328 citations

Journal ArticleDOI
TL;DR: Phase-sensitive vibrational sum frequency generation is employed to investigate the water structure at phospholipid/water interfaces and zwitterionic DPPC and DPPE reveal weaker water orienting capability relative to net negative DPPA, DPPG, and DPPS.
Abstract: Phase-sensitive vibrational sum frequency generation is employed to investigate the water structure at phospholipid/water interfaces. Interfacial water molecules are oriented preferentially by the electrostatic potential imposed by the phospholipids and have, on average, their dipole pointing toward the phospholipid tails for all phospholipids studied, dipalmitoyl phosphocholine (DPPC), dipalmitoyl phosphoethanolamine (DPPE), dipalmitoyl phosphate (DPPA), dipalmitoyl phosphoglycerol (DPPG), and dipalmitoyl phospho-l-serine (DPPS). Zwitterionic DPPC and DPPE reveal weaker water orienting capability relative to net negative DPPA, DPPG, and DPPS. Binding of calcium cations to the lipid phosphate group reduces ordering of the water molecules.

322 citations