Formation of n-Alkanethiolate Self-Assembled Monolayers onto Gold in Aqueous Micellar Solutions of n-Alkyltrimethylammonium Bromides

Abstract

We have investigated the kinetics of formation for n-alkanethiolate self-assembled monolayers (SAMs) onto gold in aqueous micellar solutions of n-alkyltrimethylammonium bromides (C m TAB; m = 12, 14, 16, and 18). The cationic micelles provide hydrophobic domains to solubilize the alkanethiols and facilitate their delivery to the gold surface. The kinetics results for SAM formation in aqueous micellar solutions of C m TAB are well described by a first-order Langmuir adsorption model. The measured rate constant decreases exponentially with increasing hydrophobicity (chain length) of the alkanethiol adsorbate and the C m TAB surfactant. The measured rate also decreases with increasingly positive potentials of the gold electrode. A mechanism to describe SAM formation in C m TAB(aq) that is consistent with reported results of solute exchange between ionic micelles in solution consists of (1) fragmentation of thiol-laden micelles to produce submicelles, (2) incorporation of thiol-laden submicelles into adsorbed micelles (admicelles) at the gold surface, (3) displacement of surfactants and counterions (rate-limiting step) by the alkanethiols, and (4) chemisorption of the alkanethiol.

Study of the solvent effect on the quality of dodecanethiol self-assembled monolayers on polycrystalline gold

“…Yan et al reported the preparation of alkanethiolate SAMs (n = 8-18) formed onto gold from aqueous solutions containing micelles of ionic or nonionic surfactants. Interestingly, compared to the equivalent SAMs prepared from an ethanolic solution, these SAMs showed an overall increased chain density, as deduced from infrared spectroscopy experiments, and a higher electrochemical blocking ability, this result can be explained by the hydrophobic interactions in aqueous environment [6][7][8][9]. These authors also reported that the n-alkanethiols SAMs obtained from liquid and super-critical carbon dioxide exhibit similar crystallinities but greater packing densities when compared to SAMs formed from ethanol [10][11].…”

Organic semiconductors for device applications: current trends and future prospects

“…In order to adjust the electrical conditions at different interfaces encountered in practice, various types of SAMs were developed in the past and used in different contexts such as patterning of nanoscale devices, corrosion prevention, and controlling surface properties [518,[552][553][554][562][563][564][565][566][567][568][569][570][571][572][573][574]. SAM modification of a metal surface offers a better possibility to improve the performance of OE devices as well [518,[562][563][564][565][566][567][568][569][570][571][572][573][574].…”

“…SAM modification of a metal surface offers a better possibility to improve the performance of OE devices as well [518,[562][563][564][565][566][567][568][569][570][571][572][573][574]. The formation of SAMs on a metal surface, in the present context of OFETs, is basically meant for improving the contact properties across a semiconductor-metal interface.…”

“…The formation of SAMs on a metal surface, in the present context of OFETs, is basically meant for improving the contact properties across a semiconductor-metal interface. In reality, it is not only the work function of a metal that is modified with SAMs on its surface [537,570,[574][575][576] but also the morphology of the pentacene layer subsequently grown on SAMs is influenced compared to the layer grown directly on a metal surface [577][578][579][580]. The formation of SAMs employs the chemical reaction between the functional groups of the molecule and the surface, such as in chemisorption of alkanethiols on Au, hydrolysis of alkyl-trichlorosilanes on hydrated surfaces, and adsorption of carboxylic acids on metal oxides [556].…”

“…Consequent upon using the above criteria of interface engineering in OS device fabrications, the influence of SAMs on oxides such as SiO 2 , Al 2 O 3 , and TiO 2 [563,[565][566][567][568][569], metals such as Au and Pt [562,570,572,573,579], and native oxides of metals such as Cu, Ag, Ti, Al, and Fe were investigated in detail [562,571]. For instance, in the case of Mo thin films, although it has a low resistivity of 5 μΩ cm, its work function is in the range of 4.6 to 4.9 eV [581], resulting in a larger barrier height to hole injection in pentacene than that with Au.…”