Adsorption of oriented carborane dipoles on a silver surface

Abstract

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 ∼1 V, 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.

Light-Activated Intercluster Conversion of an Atomically Precise Silver Nanocluster

“…This is also supported by the previous results of desorption experiments and time-of-flight secondary ion mass spectrometry data of flat silver surfaces, both pointing at strong Ag−S bonds. 64,65 Along with the systematic loss of carborane fragments, other peaks in the lower mass range, shown in Figure S6, indicate the detachment of different silversulfide motifs during fragmentation. Spectral analysis reveals the formation of a few smaller carborane-thiolate silver clusters at m/z 1580.82, 1158.96, and 736.28 with the composition of…”

Influence of Terminal Carboxyl Groups on the Structure and Reactivity of Functionalized m-Carboranethiolate Self-Assembled Monolayers

“…5,[17][18][19][20] In this regard, special attention has been paid to the dipole moment orientation, which is mainly given by the positioning of the carbon atoms in the cage, and to its effect on work function changes. [21][22][23][24][25] Building on these advances, we prepared two isomeric bifunctional cage molecules based on the meta-carborane skeleton, juxtaposing them to their organic analogue, metamercaptobenzoic acid, as well as the previously studied para-isomer as building blocks for SAMs. Both new isomers show practically identical orientations of functional groups with respect to the centroid of the meta-carborane cage but differ in chemical and physical properties as determined by the electron-donating and withdrawing properties of the molecular cage scaffold.…”

Mixed Monomolecular Films with Embedded Dipolar Groups on Ag(111)

“…Alternative strategies, suggested recently by us and others, involve the use of a dipolar molecular backbone or embedding of a dipolar group into the backbone, untangling thus, completely or at least to a significant extent, dipole engineering and interfacial chemistry and protecting the dipolar group from possible modification or reorientation upon deposition of a buffer or organic semiconductor layer during the assembly of an organic solar cell or an organic transitor. − In particular, the concept of embedded dipoles was successfully demonstrated for both aliphatic and aromatic SAMs using the dipolar ester and pyrimidine groups, respectively. , These groups were introduced in two opposite orientations with respect to the backbone, with the dipole moment directed either from or to the substrate, resulting in a work function difference of 1–1.1 eV. , By combining the molecules with the oppositely oriented dipolar groups in a joint mixed SAM, flexible variation of the work function within the above energy window could be achieved, which is potentially useful for precise tuning of the energy level alignment in organic electronics and photovoltaics devices. , As an additional “bonus”, the electrostatic homogeneity of these mixed SAMs, down to the molecular level, could be precisely monitored by X-ray photoelectron spectroscopy (XPS), relying on the electrostatic effects in photoemission …”