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.