Non-chemisorbed gold-sulfur binding prevails in self-assembled monolayers

Area of Science:

• Physical Chemistry
• Surface Science
• Nanotechnology

Background:

• Gold-thiol contacts are crucial for linking organic molecules to surfaces in various scientific fields.
• The bonding state of hydrogen in thiol-gold interactions within self-assembled monolayers (SAMs) is a long-standing debate.
• Understanding this interaction impacts knowledge of SAMs' physical properties, spectroscopy, and formation.

Purpose of the Study:

• To investigate the nature of the gold-sulfur bond in self-assembled monolayers (SAMs).
• To determine the fate of the hydrogen atom during the formation of gold-thiol contacts in SAMs.
• To clarify the implications for molecular junction properties and SAM formation mechanisms.

Main Methods:

• Utilizing single-molecule conductance measurements of molecular junctions.
• Comparing conductance data from SAMs with solution-based measurements of the same molecules.
• Performing control experiments, conductance noise analysis, and density functional theory (DFT) transport calculations.

Main Results:

• Single-molecule conductance measurements are highly sensitive to molecule-electrode contact properties.
• Dithiol-terminated molecular junctions in SAMs exhibit significantly lower conductance than solution measurements.
• Analysis indicates that the gold-sulfur bond in solution-deposited SAMs lacks chemisorbed character.

Conclusions:

• The widely used solution deposition method for preparing dithiols on gold likely results in retained hydrogen.
• The gold-sulfur bond in these SAMs is not chemisorbed, challenging previous assumptions.
• This finding has significant implications for the understanding and application of molecular junctions and SAMs.