Michael-Anthony Ferrato

University of Windsor, Windsor, Ontario, Canada

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Publications (3)19.45 Total impact

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    ABSTRACT: We report the formation and characterization of self-assembled monolayers (SAMs) of dialkyldithiophosphinic acid adsorbates [CH3(CH2)n]2P(S)SH (R2DTPA) (n = 5, 9, 11, 13, 15) on ultrasmooth gold substrates prepared by the template stripping method. The SAMs were characterized using x-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, contact angle measurements, lateral force microscopy, and electrochemical impedance spectroscopy. The data show these SAMs exhibit an unusual trend in alkyl chain crystallinity: SAMs formed from adsorbates with short alkyl chains (n = 5) are ordered and crystalline, and the alkyl groups become increasingly disordered and liquid-like as the number of methylene units is increased. This trend is the opposite of the typical behavior exhibited by n-alkanethiolate SAMs, in which the alkyl layer becomes more crystalline and ordered as the alkyl chain length is increased. We discuss four factors that operate together to determine how R2DTPA self-organize within SAMs on TS gold: (i) adsorbate-substrate interactions; (ii) gold substrate morphology; (iii) lateral van der Waals interactions between alkyl groups; and (iv) steric demands of the alkyl groups. We also present a model for the structures of these SAMs based on a consideration of the data and the structural parameters of a model nBu2DTPA adsorbate. In this model, interdigitation of short alkyl chains stabilizes a trans-extended, crystalline arrangement and produces an ordered alkyl layer. As the alkyl chain length is increased, the increased steric demands of the alkyl groups lead to liquid-like, disorganized alkyl layers.
    Journal of the American Chemical Society 02/2014; · 10.68 Impact Factor
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    ABSTRACT: We report the formation and characterization of self-assembled monolayers (SAMs) based on dialkyldithiophosphinic acid adsorbates {[CH(3)(CH(2))(n)](2)P(S)SH (n = 5, 9, 11, 13, 15)} on gold substrates. SAMs were characterized using X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, contact angle measurements, and electrochemical impedance spectroscopy. Data show that there is a roughly 60:40 mixture of bidentate and monodentate adsorbates in each of these SAMs. The presence of monodentate adsorbates is due to the numerous and deep grain boundaries of the underlying gold substrate, which disrupt chelation. Comparing the characterization data of dialkyldithiophosphinic acid SAMs with those of analogous n-alkanethiolate SAMs shows that both SAMs follow a similar trend: The alkyl chains become increasingly organized and crystalline with increasing alkyl chain length. The alkyl groups of dialkyldithiophosphinic acid SAMs, however, are generally less densely packed than those of n-alkanethiolate SAMs. For short alkyl chains (hexyl, decyl, and dodecyl), the significantly lower packing densities cause the alkyl chains to be liquid-like and disorganized. Long-chain dialkyldithiophosphinic acid SAMs are only slightly less crystalline than analogous n-alkanethiolate SAMs.
    Langmuir 08/2012; 28(37):13253-60. · 4.38 Impact Factor
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    ABSTRACT: We report the fabrication and characterization of new self-assembled monolayers (SAMs) formed from dihexadecyldithiophosphinic acid [(C(16))(2)DTPA] molecules on gold substrates. In these SAMs, the ability of the (C(16))(2)DTPA headgroup to chelate to the gold surface depends on the morphology of the gold substrate. Gold substrates fabricated by electron-beam evaporation (As-Dep gold) consist of ∼50-nm grains separated by deep grain boundaries (∼10 nm). These grain boundaries inhibit the chelation of (C(16))(2)DTPA adsorbates to the surface, producing SAMs in which there is a mixture of monodentate and bidentate adsorbates. In contrast, gold substrates produced by template stripping (TS gold) consist of larger grains (∼200-500 nm) with shallower grain boundaries (<2 nm). On these substrates, the low density of shallow grain boundaries allows (C(16))(2)DTPA molecules to chelate to the surface, producing SAMs in which all molecules are bidentate. The content of bidentate adsorbates in (C(16))(2)DTPA SAMs formed on As-Dep and TS gold substrates strongly affects the SAM properties: Alkyl chain organization, wettability, frictional response, barrier properties, thickness, and thermal stability all depend on whether a SAM has been formed on As-Dep or TS gold. This study demonstrates that substrate morphology has an important influence on the structure of SAMs formed from these chelating adsorbates.
    Langmuir 07/2011; 27(16):10019-26. · 4.38 Impact Factor