Adsorption of oriented carborane dipoles on a silver surface

Modification of surfaces with self-assembled mono-layers (SAMs) represents a powerful and innovative tool for adjusting physical and chemical properties of surfaces. The adsorption of isomeric molecules with relatively strong and oppositely oriented molecular dipoles, 1,2-(HS)(2)-1,2-C2B10H10 and 9,12-(HS)(2)-1,2-C2B10H10, on a flat silver surface is investigated in order to adjust its work function in a desired way. Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) are used to prove that both isomers (i) chemisorb on a silver surface as thiolates and (ii) exhibit comparable surface densities. Densely packed surfaces of both SAMs are additionally investigated by electrochemical impedance spectroscopy, and effective surface passivation is observed. Co-deposition of both derivatives is shown to enable effective and fine adjustment of the surface work function value within a range of similar to 1V, which is confirmed by Kelvin probe force microscopy (KPFM). Experimental data indicate faster SAM formation for the former isomer. Contribution of the interface Ag-S bonds to the work function changes is quantified. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim