Effects of Solvent on the Formation of Octanethiol Self-Assembled Monolayers on Au(111) at High Temperatures in a Closed Vessel: A Scanning Tunneling Microscopy and X-ray Photoelectron Spectroscopy Study

Abstract

Self-assembled monolayers of 1-octanethiol (OT-SAMs) on Au(111) substrates prepared using ethanol, N,N′-dimethylformamide (DMF), toluene, or hexane were examined using scanning tunneling microscopy (STM) and Xray photoelectron spectroscopy (XPS) to investigate the effects of the solvent on the molecular packing at high solution temperatures (90°C) and high pressures (21 psi) in a closed vessel. STM imaging revealed the formation of ordered OTSAMs with a (3 × √7)R11°overlayer structure on Au(111) surfaces in ethanol, whereas OT-SAMs prepared in DMF revealed large ordered domains with a (√3 × √3)R30°phase and a c(4 × 2) superstructure. OT-SAMs prepared in toluene produced a mixture of ordered and striped phases, while no clear ordered structures were observed for OT-SAMs prepared in hexane. The disposition of OT bound to the Au(111) surfaces depended on the solvent, which also affected whether the OT-SAMs formed ordered or disordered phases. The intensities of XPS peaks at 161 and 162.3 eV increased with domain disorder, possibly due to changes in the adsorption configurations of the OT molecules.

Phase Segregation in the Mixed Alkyl Thiol Self‐assembled Monolayers on a Gold Surface at a High Incubation Temperature in a Sealed Container

“…The intensity ratio (S2/S1) is 0.15, 0.14, and 0.27 for OT SAM and DT SAM than for mixed SAM, respectively. The relative intensity of the peak S2 increased with increasing surface molecular randomness . It is highly possible that the increase of vacancy islands and defects and surface roughness in mixed SAM (revealed by STM imaging) are associated with the increase in surface disorders.…”

“…These results suggested that the mixed SAM surface was much rougher than the OT SAM and DT SAM surfaces. For monocomponent SAMs, the average surface heights were calculated to be 0.81 and 0.72 nm for OT SAM and DT SAM, respectively . Furthermore, the R rms values were calculated to be 0.13 nm for OT SAM and 0.11 nm for DT SAM.…”

“…In this study, we present the formation of well‐ordered and stable mixed SAMs with largely separated domains that form at high temperatures in a sealed bath. Previously we investigated the structure of 1‐octanethiol SAMs on Au(1 1 1) substrates formed at a higher temperature and pressure . To minimize the contribution of surface defects and increase the domain size to obtain highly packed SAMs, higher incubation temperature and pressure were necessary.…”

Effect of amino, hydroxyl, and carboxyl terminal groups of alkyl chains of self‐assembled monolayers on the adsorption pattern of gold nanoparticles

“…The samples were immersed in solution at 90°C in a sealed stainless steel (SUS 314) chamber with an oxygen‐free, high‐conductivity copper (OFHC) gasket seal at a pressure greater than 1 atm. The elevated temperature and pressure were used to produce a larger terrace area of the SAM . Higher incubation temperatures at elevated pressures in an ethanol solution can promote the structural transition of a SAM and wider domains with a low density of defects .…”

Influence of Thiol Molecular Backbone Structure on the Formation and Reductive Desorption of Self-Assembled Aromatic and Alicyclic Thiol Monolayers on Au(111) Surface

“…To understand these fundamental issues, STM has been used as one of the very powerful tools for visualizing the atomic-and molecular-scale surface structures of SAMs on metal surfaces, as demonstrated in many previous reports. [1][2][3][4][6][7][8][9][10][11][12][13][14][15][16][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Additionally, thermal desorption spectroscopy (TDS) 10,11,32,[34][35][36][37] and electrochemical measurements [38][39][40][41][42][43] are very useful techniques to investigate the adsorption conditions, thermal stability, and the electrochemical behavior and stability of SAMs. TDS measurements revealed that alkanethiol SAMs exist as a form of monomer (alkanethiolate), not dimers (dialkyl disulfides) derived from associa-tive reactions of the sulfur headgroups, 10,11,34,…”