Structural and Electrochemical Properties of 4‑Methyl-4′‑(n‑mercaptoalkyl) Biphenyls Self-Assembled on the Au(100)–​(1 × 1) Surface

TL;DR

This study explores how 4-methyl-4′-(n-mercaptoalkyl) biphenyls self-assemble on a gold surface and how their structure affects electrochemical properties.

Contribution

The paper reveals distinct surface chemistry of BPn on Au(100) compared to Au(111), including phase behavior and electrochemical stability.

Findings

Short alkane chain BPn on Au(100) does not induce gold surface vacancies unlike on Au(111).

BPn adlayers on Au(100) exhibit two coexisting phases (α and β) that evolve with chain length.

Electrochemical stability and capacitance of BPn adlayers correlate with the number of methylene units.

Abstract

Scanning Tunneling
Microscopy (STM) and electrochemical studies
were conducted on a series of 4-methyl-4′-(n-mercaptoalkyl) biphenyls CH3(C6H4)2(CH2)
n
SH (BPn, where n = 1–6) self-assembled
on the unreconstructed Au(100)–(1 × 1) surface. The study
investigated the role of substrate crystallography in the electrochemical
and surface properties of BPn adlayers. Notably,
unlike BPn on Au(111)–(1 × 1), short
alkane chain BPn (1 to 4) does not induce gold surface
vacancies when adsorbed on the Au(100)–(1 × 1) indicating
distinct surface chemistry. The adlayers exhibit two coexisting phases
(α and β), the presence of which evolves with the number
of methylene units. The electrochemical properties of the BPn adlayers are characterized by higher thermodynamic stability
during reductive desorption with charge values alternating with the
number of methylene units. The molecule adsorption modifies an important
parameter such as the work function of the underlying Au(100)–(1
× 1) metal substrate. The reciprocal capacitance exhibits a linear
dependence on the length of the alkane spacer. Its change per CH2 group agrees well with the values of n-alkanethiols
on Au(111).

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