Thermal Effect on Positive Patterned Self‐Assembled Monolayer Grown from a Droplet of Alkanethiol

Abstract

Atomic force microscope technique is widely used for the spatial narrow deposition of molecules inside the bare space of preexisting self‐assembled monolayer (SAM) matrix. Using molecular dynamics simulation, we studied the formation of positively patterned SAM from a globule of 1‐octadecanethiol (ODT) on predesigned SAM matrix of 1‐dodecanethiol (DDT) and effect of temperature on it. The alkyl chains of ODT SAM were densely packed and ordered by means of chemisorption through sulfur atoms. The circular SAM of ODT contained defects due to the molecules those were standing upside down or trapped inside ODT SAM. We found that with the increase of temperature, these defects moved out by flipping of inverted ODT molecules or building spaces to be adsorbed on Au surface. The ODT molecules on the top of the pile of stable circular SAM or those are upside down and trapped disperse in a unique fashion namely serial pushing through which molecules firstly make a free space to enter inside the adsorbed thiol molecules and then push neighboring molecules to get enough space to be adsorbed on the gold surface. The stability of ODT SAM was confirmed by analyzing different structural properties such as tilt angle, tilt orientation. and backbone orientation. We also calculated the diffusion coefficient of the ODT molecules which were on the top of SAM island. © 2019 Wiley Periodicals, Inc.

Effect of Concentration, Chain Length, Hydrophobicity, and an External Electric Field on the Growth of Mixed Alkanethiol Self-Assembled Monolayers: A Molecular Dynamics Study

“…They reported that while the structural parameters such as the lattice constant and the tilt angle are almost independent of the type of anchoring molecule, the alkyl-chain orientation in the matrix is critically controlled by the composition and the chemical nature of the molecule. An interesting study of SAM formation was recently reported by Sannyal et al 35 They predesigned a SAM matrix of 1-dodecanethiol (DDT) and simulated the formation of a SAM island from a droplet of 245 1octadecanethiol (ODT) molecules. With the use of an united atom force field and a Morse potential to model the chemisorption interaction, they successfully simulated the formation of SAM within a short simulation time of 40 ns.…”