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New Dihexadecyldithiophosphate SAMs on Gold Provide Insight into the Unusual Dependence of Adsorbate Chelation on Substrate Morphology in SAMs of Dialkyldithiophosphinic Acids
journal contribution
posted on 2013-10-23, 00:00 authored by Ronan
R. San Juan, Christopher J. Allan, Muhammad Iqbal, S. Holger Eichhorn, Charles L. B. Macdonald, Tricia Breen CarmichaelWe
report the formation and characterization of new self-assembled
monolayers (SAMs) formed from dihexadecyldithiophosphate (C16)2DDP and compare their properties with those of SAMs
formed from the structurally similar adsorbate dihexadecyldithiophosphinic
acid (C16)2DTPA. The new (C16)2DDP SAMs were characterized using X-ray photoelectron spectroscopy,
reflection–absorption infrared spectroscopy, contact angle
measurements, and electrochemical impedance spectroscopy. The data
indicate that (C16)2DDP forms SAMs on gold films
formed by e-beam evaporation in which all adsorbates chelate to gold,
in contrast to (C16)2DTPA SAMs, in which 40%
of the adsorbates are monodentate. The alkyl chains of the (C16)2DDP SAM are also less densely packed and ordered
than those of the (C16)2DTPA SAM. To understand
these differences, we present density functional theory calculations
that show that there are only minimal differences between the geometric
and electronic structures of the two adsorbates and that the energetic
difference between monodentate and bidentate binding of a gold(I)
ion are surprisingly small for both adsorbates. This study leads to
the conclusion that differences in intermolecular interactions within
the SAM are the driving force for the difference in chelation between
the two adsorbates.
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gold filmsDialkyldithiophosphinic AcidsWe reportelectrochemical impedance spectroscopyAdsorbate ChelationSubstrate Morphologytheory calculationscontact angle measurementsNew Dihexadecyldithiophosphate SAMsbidentate bindingadsorbate dihexadecyldithiophosphinic acidUnusual Dependenceadsorbates chelatealkyl chains
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