Improvements in the Characterization of the Crystalline Structure of Acid-Terminated Alkanethiol Self-Assembled Monolayers on Au(111)

Abstract

We report a study of acid-terminated self-assembled monolayers of alkanethiols of different length, 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHDA), on Au(111). Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and contact angle techniques were used for characterization, and the results were compared with those obtained from n-alkanethiols of similar chain length, providing a detailed description of the two-dimensional crystalline structure. Molecular resolution STM images show that 11-MUA forms a dense-packed monolayer arranged in a (√3 × √3)R30° structure with a c(2 × 4) superlattice, where the simple hexagonal phase, the c(2 × 4) superlattice, and nonordered areas coexist. 16-MHDA assembles in a uniform monolayer with similar morphology to that of 11-MUA, but molecular resolution could not be reached in STM due to both the hydrophilicity of the acid groups and the poor conductivity of the thick monolayer. Nevertheless, the monolayer thicknesses estimated by XPS and electrochemistry and the highly blocking character of the film observed by electrochemistry as well as the low water contact angle are consistent with 16-MHDA molecules forming a compact monolayer on the Au(111) substrate with fully extended alkyl chains and acid groups pointing away from the surface. The results obtained for 16-MHDA were reproducible under different preparation conditions such as the addition or omission of acetic acid to the ethanolic solution. Contrary to other reports, we demonstrate that ordered acid-terminated self-assembled monolayers are obtained with the same preparation conditions as those of the methyl-terminated ones, without any additional treatment.

AFM topography and friction studies of hydrogen-bonded bilayers of functionalized alkanethiols

“…2B). 13 It can be expected that the bottom layer SAM bound to the gold surface is closely packed, as has been described before, 6 and consequently the large increase in friction can be mainly attributed to the presence of the second layer of HSC n COOH-molecules. This layer is expected to be more dynamic and less well stabilized by van der Waals interactions than the first one, leading to an imperfect packing.…”

“…They are predominantly organized in a (O3 Â O3)R30 -based structure and a c(4 Â 2) superlattice in which the hydrocarbon chains are closely packed and tilted under an angle of $30 with respect to the surface normal. [1][2][3][4][5][6] However, many conflicting results have been reported for the characterization of highly ordered SAMs of carboxyl-terminated alkanethiols, in contrast to for example unfunctionalized thiols. In particular the proper experimental conditions for the construction of the functionalized SAMs continues to be a topic of debate.…”

A 3:1 Site-Differentiated [4Fe-4S] Cluster Immobilized on a Self-Assembled Monolayer

“…33 The ratio between these sulfur-bound and nonsulfur-bound carbon atoms was found to be somewhat too low. Possibly, the peak fitting underrepresented the sulfur-bound carbon signal, but the fact that the overall carbon signal intensity is also too high suggests that some carbon contamination has taken place.…”

Estudio de estructuras de cis- y trans-estilbeno mediante microscopiade fuerza atómica

“…Seguidamente, se depositaron 150 nm de Au al 99.99 % manteniendo la mica a 640 K. Finalmente, el sustrato se enfrió hasta llegar a temperatura ambiente en el transcurso de 8 horas. Mediante este método se obtuvieron terrazas atómicamente planas de Au(111), tal como se ha descrito en otras oportunidades [15]. La elección de dichos sustratos se debe a que sus propiedades son bien conocidas y resultan convenientes para ser analizados por AFM [16].…”