# Binary Monolayers Formed from the Sequential Adsorption of Terphenylthiol and Dodecanethiol on Gold

## TL;DR

This paper explores how binary self-assembled monolayers on gold surfaces behave differently based on deposition order and temperature.

## Contribution

The study experimentally characterizes four distinct binary monolayer systems formed from terphenylthiol and dodecanethiol.

## Key findings

- Binary monolayers showed varied structures depending on deposition sequence and temperature.
- XPS analysis revealed oxygen in dodecanethiol monolayers but not in terphenylthiol ones.
- Electron transfer inhibition was observed, aligning with prior studies.

## Abstract

Binary self-assembled monolayers (SAMs) of 1-dodecanethiol
(DDT)
and 1,1′,4′,1″-terphenyl-4-thiol (TPT) were prepared
via sequential deposition on the surface of Au(111) on mica. The SAMs
were studied using scanning tunneling microscopy (STM), X-ray photoelectron
spectroscopy (XPS), cyclic voltammetry (CV), and reductive desorption
(RD). Varying the sequence of deposition and the deposition temperature
of DDT resulted in four distinct binary monolayer systems. Characterization
of DDT SAMs with STM exhibited a combination of ordered and disordered
domains, whereas the TPT monolayers were well-ordered into various
phases and aligned with extensive characterization in the literature.
Binary SAMs displayed varied behaviors, including retention of the
initial SAM structure, adsorption of the secondary compound at domain
boundaries, or temperature-dependent replacement of the initial SAM.
Elemental analysis via XPS revealed the presence of oxygen in single-component
DDT monolayers, which was absent in TPT monolayers, and the binary
SAMs exhibited nearly identical elemental compositions. RD results
indicate well-ordered domains for DDT, less ordered and less strongly
bound TPT regions, and distinct domains for binary SAMs that were
consistent with the binary STM results. CVs for single-component and
binary SAMs of DDT and TPT indicate an absence of significant defects
in the molecular layers. The inhibited electron transfer observed
aligns with prior studies for DDT and is more moderate for TPT and
mixed SAMs. This study addresses the need for an experimental understanding
of the phase behavior of binary SAMs.