Final Phase of Alkanethiol Self-Assembled Monolayers on Au(111)

Abstract

Time-dependent phase transitions of closely packed alkanethiol self-assembled monolayers (SAMs) on Au(111) were investigated by scanning tunneling microscopy (STM). We report a new phase, the 6 × √3 superlattice, that exhibits deviations from the hexagonal packing arrangement formed through long-term rearrangement of the usual c(4 × 2) superlattice of alkanethiol SAMs. Our STM images show clearly systematic phase transitions with molecular-scale images from the c(4 × 2) phase to the 6 × √3 phase. This result implies that the monolayers in the c(4 × 2) phase are still in the nonequilibrium state, although it has been regarded to be in the equilibrium state in a number of previous studies. The striking implication in this study is to provide new features for closely packed alkanethiol SAMs for the first time.

Comparative Study of Tetrahydrothiophene and Thiophene Self Assembled Monolayers on Au(111): Structure and Molecular Orientation

“…Adsorption states, molecular structures, growth processes, and electronic structures of alkanethiol (AT) SAMs on gold have been extensively investigated using various surface characterization techniques. [4][5][6][7][8][9] The introduction of functional groups to the tail of the sulfur headgroup may be useful in future applications to organic electronic devices. For example, the use of a π-conjugated tail group is very simple and convenient method for obtaining functionality in organic electronics.…”

Effects of Solvent on the Structure of Octanethiol Self-Assembled Monolayers on Au(111) at a High Solution Temperature

“…[1][2][3][4][5] In particular, the formation and structure of alkanethiol SAMs on gold surfaces have been extensively studied using various surface characterization techniques. [6][7][8][9] Experimental conditions, such as solvent, temperature, concentration, immersion time, and substrate cleanliness significantly affect the formation and structure of alkanethiol SAMs. 1,[6][7][8][9] Among them, solvent choice is a very important factor for determining the structural quality and formation kinetics of SAMs.…”

“…[6][7][8][9] Experimental conditions, such as solvent, temperature, concentration, immersion time, and substrate cleanliness significantly affect the formation and structure of alkanethiol SAMs. 1,[6][7][8][9] Among them, solvent choice is a very important factor for determining the structural quality and formation kinetics of SAMs. [10][11][12][13][14][15][16][17][18] Ellipsometry measurements have shown that the solvent, including ethanol, N,N'-dimethylformamide (DMF), toluene, hexadecane, and cyclooctane, had no effect on the thickness of hexadecanethiol SAMs.…”

“…The packing structures of OT SAMs in ethanol are assigned as the c(4 × 2) superlattice observed at saturation coverage with an "upright adsorption orientation" on the gold surface (Figure 2a). 2,6,8,16,17 The unit cell contains four alkanethiolate, and the area occupied by a single molecule was calculated to be 21.6 Å 2 . Unlike this closely packed structure, OT SAMs in toluene yielded the formation of a low coverage striped phase with a "lying down adsorption orientation" on the gold surface (Figure 2b).…”

Surface Structures and Thermal Desorption Behaviors of Cyclopentanethiol Self-Assembled Monolayers on Au(111)

“…3,6,7,10 Several different two-dimensional (2D) phases were observed depending on the surface coverage and preparation conditions. 3,5 2D SAMs were formed by a delicate balance between sulfur atom-gold substrate interaction and molecule-molecule interaction. 1 In particular, the backbone structures of organic thiols strongly affect the structural order and 2D packing structures of SAMs.…”