Browsing by Author "Harper, JB"

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    Central atom size effect on the structure of group 14 tetratolyls
    (Wiley-VCH Verlag Berlin, 2009-07-06) Ng, MCC; Craig, DJ; Harper, JB; van Eijck, L; Stride, JA
    Size matters! The structure and dynamics of the tetratolyl Group 14 elements, which were probed by using high-resolution inelastic neutron scattering spectra, show a remarkable dependence on the size of the central atom. The para-methyl groups at the periphery of the molecules constitute the frontier intermolecular interactions of increasingly larger tetrahedra, which becomes critical at the molecular radius of the Si and Ge analogues. © 2009, Wiley-VCH Verlag Berlin
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    Central-atom size effects on the methyl torsions of group XIV tetratolyls
    (Wiley-V C H Verlag GMBH, 2012-10-01) Ng, MCC; Harper, JB; Stampfl, APJ; Kearley, GJ; Rols, S; Stride, JA
    The Group XIV tetratolyl series X(C6H4-CH3)4 (X=C, Si, Ge, Sn, Pb) were studied by using inelastic neutron scattering to measure the low-energy phonon spectra to directly access the methyl-group torsional modes. The effect of increased molecular radius as a function of the size of the central atom was shown to have direct influence on the methyl dynamics, reinforced with the findings of molecular dynamics and contact surface calculations, based upon the solid-state structures. The torsional modes in the lightest analogue were found to be predominantly intramolecular: the Si and Ge analogues have a high degree of intermolecular methylmethyl group interactions, whilst the heaviest analogues (Sn and Pb) showed pronounced intermolecular methyl interactions with the whole phonon bath of the lattice modes. © 2012, Wiley-VCH Verlag GmbH & Co. KGaA
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    Comparing the reactivity of alkynes and alkenes on silicon (100) surfaces
    (American Chemical Society, 2009-12-15) Ng, A; Ciampi, S; James, M; Harper, JB; Gooding, JJ
    The relative reactivities of alkynes to alkenes on hydrogen-terminated silicon (100) surfaces, under conditions where a monolayer will be produced via hydrosilylation, were measured using two different approaches. The first approach was to form monolayers from a series of solutions containing different mole fractions of an alkyne, with a trifluorothioacetate distal moiety and an alkene with a terminal carboxylic acid functional. X-ray photoelectron spectroscopic analysis of the resultant surfaces showed that the mole fraction of alkyne on the surface was larger than that in the respective alkyne/alkene mixture. By filling the XPS data, we estimated that the reactivity ratio of alkynec to alkene was approximately 1.7 +/- 0.2 when monolayers were formed at 120 degrees C. The second approach was using a molecule containing both an alkyne at one end and an alkene at the other, non-1-yne-8-ene, as the hydrosilylation reagent such that either end Could attach to the silicon surface. The relative orientation of this molecule, once reacted with it hydrogen-terminated Si(100) surface, was determined by coupling ail additional reagent to the distal end of the monolayer. The reagent used was azidoferrocene, which could attach onto free alkyne moieties on the surface only via the 1,3-Huisgen cycloaddition "click" reaction. Electrochemical analysis was then used to determine how many ferrocene moieties were attached to the SAM surface. In this way, it was shown that the alkyne end reacted preferentially with the silicon surface compared with the alkene end. The reactivity ratio of the alkyne end to the alkene end was increased front 2.0 +/- 0.2 to 9 +/- 1 when the temperature was decreased from 120 to 65 degrees C. © 2009, American Chemical Society
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    Functionalization of acetylene-terminated monolayers on Si(100) surfaces: a click chemistry approach
    (American Chemical Society, 2007-08-28) Ciampi, S; Bocking, T; Kilian, KA; James, M; Harper, JB; Gooding, JJ
    In this article, we report the functionalization of alkyne-terminated alkyl monolayers on Si(100) using "click" chemistry, specifically, the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction of azides with surface-bound alkynes. Covalently immobilized, structurally well-defined acetylene-terminated organic monolayers were prepared from a commercially available terminal diyne species using a one-step hydrosilylation procedure. Subsequent derivatization of the alkyne-terminated monolayers in aqueous environments with representative azide species via a selective, reliable, robust cycloaddition process afforded disubstituted surface-bound [1,2,3]-triazole species. Neither activation procedures nor protection/deprotection steps were required, as is the case with more established grafting approaches for silicon surfaces. Detailed characterization using X-ray photoelectron spectroscopy and X-ray reflectometry demonstrated that the surface acetylenes had reacted in moderate to high yield to give surfaces exposing alkyl chains, oligoether anti-fouling moieties, and functionalized aromatic structures. These results demonstrate that click immobilization offers a versatile, experimentally simple, chemically unambiguous modular approach to producing modified silicon surfaces with organic functionality for applications as diverse as biosensors and molecular electronics. © 2007, American Chemical Society
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    Oxidative acetylenic coupling reactions as a surface chemistry tool
    (2011-09-14) Ciampi, S; James, M; Darwish, N; Luais, E; Guan, B; Harper, JB; Gooding, JJ
    A novel method to prepare redox monolayers on silicon electrodes has been developed that employs CuI-catalyzed oxidative acetylenic coupling reactions for molecular electronic type applications. As the first case study, ethynylferrocene was covalently immobilized onto an acetylene-terminated monolayer on a Si(100) surface to give a 1,3-diyne (C[triple bond, length as m-dash]C-C[triple bond, length as m-dash]C-) linked redox assembly. The derivatization process requires no protection/de-protection steps, nor activation procedures. The effect of the conjugated diyne linkage on the rate of electron transfer between tethered ferrocenyl units and the silicon electrode is benchmarked against well-established "click" products (i.e. 1,2,3-triazole linkage). The surfaces, after each step, are characterized thoroughly using X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The coupling chemistry provides a useful strategy for functionalizing silicon surfaces and contributes to an expanding repertoire of wet chemistry routes for the functionalization of solid substrates.© 2011, Royal Society of Chemistry
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    Silicon (100) electrodes resistant to oxidation in aqueous solutions: an unexpected benefit of surface acetylene moieties
    (American Chemical Society, 2009-02-17) Ciampi, S; Eggers, PK; Le Saux, G; James, M; Harper, JB; Gooding, JJ
    Here we report on the functionalization of alkyne-terminated alkyl monolayers on highly doped Si(100) using click" reactions to immobilize ferrocene derivatives. The reaction of hydrogen-terminated silicon surfaces with a diyne species was shown to afford very robust functional surfaces where the oxidation of the underlying substrate was negligible. Detailed characterization using X-ray photoelectron spectroscopy, X-ray reflectometry, and cyclic voltammetry demonstrated that the surface acetylenes had reacted in moderate yield to give surfaces exposing ferrocene moieties. Upon extensive exposure of the redox-active architecture to oxidative environments during preparative and characterization steps, no evidence of SiOx contaminants was shown for derivatized SAMs prepared from single-component 1,8-nonadiyne, fully acetylenylated, monolayers. An analysis of the redox behavior of the prepared Si(100) electrodes based on relevant parameters such as peak splitting and position and shape of the reduction/oxidation waves depicted a well-behaved redox architecture whose spectroscopic and electrochemical properties were not significantly altered even after prolonged cycling in aqueous media between -100 and 800 mV versus AglAgCl. The reported strategy represents an experimentally simple approach for the preparation of silicon-based electrodes where, in addition to close-to-ideal redox behavior, remarkable electrode stability can be achieved. Both the presence of a distal alkyne moiety and temperatures of formation above 100 degrees C were required to achieve this surface stabilization. © 2009, American Chemical Society