The Role of Intermolecular and Molecule−Substrate Interactions in the Stability of Alkanethiol Nonsaturated Phases on Au(111)

Abstract

The structure and stability of alkanethiols self-assembled on Au(111) have been studied as a function of the molecular chain length by means of atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXD). Below saturation, phases consisting of molecules with different tilt angles and periodicities are formed. Differences in the mechanical stability of these phases are revealed by AFM experiments and discussed in terms of the competition between intermolecular and molecule-substrate interactions as a function of chain length. For long molecules, intermolecular interactions play a dominant role which stabilizes the formation of closed packed 30 degrees tilted ( radical 3x radical 3)R30 degrees structures. For short molecules, the van der Waals interaction with the gold substrate favors the formation of a 50 degrees tilted phase in which the molecules are arranged in a rectangular configuration.

Inelastic electron tunneling process for alkanethiol self-assembled monolayers

“…The formation process of a SAM and its structure on an Au(111) surface have been investigated with scanning tunneling microscopy (STM) [10][11][12][13][14][15], atomic force microscopy (AFM) [16,17], and X-ray diffraction [18]. Spectroscopic methods such as X-ray photoelectron spectroscopy [19], infrared absorption spectroscopy (IRAS) [20][21][22], high-resolution electron energy loss spectroscopy (HR-EELS) [23][24], Raman spectroscopy (RS) [25] and metastable atom electron spectroscopy [26] have also been employed to investigate the structure and electronic properties of SAMs.…”

Thermodynamic Study of the Reactivity of the Two Topological Point Defects Present in Mixed Self‐Assembled Monolayers on Gold Nanoparticles

“…[3] The ligand shell of a NP resembles its flat-surface counterparts: [4][5][6][7] highly ordered two-dimensional crystals [8][9][10] in which the molecules arrange with a tilt angle relative to the surface normal that maximizes intermolecular interactions. [11,12] SAMs are straightforward to prepare and their composition can be varied by exposing them to solutions of different thiolated molecules through a reaction called place-exchange, [13][14][15][16] which has been shown experimentally to occur more rapidly at point defects in the SAM. [17,18] However, thermodynamic studies of the reactivity of the point defects are hindered by difficulties inherent to surface analysis.…”

Adsorption of short-chain alkanethiols on Ag(111) studied by direct recoiling spectroscopy

“…A key feature for the kinetics of alkanethiol adsorption is the film growth in two or more steps, with characteristic phase transitions driven mainly by coverage [1,11,19,20,44]. For film growth from the vapour phase, this behaviour has been followed on a number of systems, mainly on Au [4,19,20], Ag [22,45], and Cu [46,47].…”

“…The kinetics of adsorption depends on the length of the hydrocarbon chain [1,48]. The ordered structures for short-chain thiols (C3) can be full of defects [25,44] and may never fully attain the ideal coverage. Moreover, it has been shown [23,26,27] that at low temperatures short-chain molecules adsorb non-dissociatively on Au(1 1 1) and Ag(1 1 0) and desorb below 200 K, except at defects where dissociation may be taking place.…”