New Dialkyldithiophosphinic Acid Self-Assembled Monolayers (SAMs): Influence of Gold Substrate Morphology on Adsorbate Binding and SAM Structure

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• 作者：Michael S. Miller ; Ronan R. San Juan ; Michael-Anthony Ferrato ; Tricia Breen Carmichael
• 刊名：Langmuir
• 出版年：2011
• 出版时间：August 16, 2011
• 年：2011
• 卷：27
• 期：16
• 页码：10019-10026
• 全文大小：895K
• 年卷期：v.27,no.16(August 16, 2011)
• ISSN：1520-5827

文摘

We report the fabrication and characterization of new self-assembled monolayers (SAMs) formed from dihexadecyldithiophosphinic acid [(C<sub>16sub>)<sub>2sub>DTPA] molecules on gold substrates. In these SAMs, the ability of the (C<sub>16sub>)<sub>2sub>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<sub>16sub>)<sub>2sub>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鈥?00 nm) with shallower grain boundaries (<2 nm). On these substrates, the low density of shallow grain boundaries allows (C<sub>16sub>)<sub>2sub>DTPA molecules to chelate to the surface, producing SAMs in which all molecules are bidentate. The content of bidentate adsorbates in (C<sub>16sub>)<sub>2sub>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.