X-ray diffraction and computation yield the structure of alkanethiols on gold(111)

Area of Science:

• Surface Science
• Materials Chemistry
• Computational Chemistry

Background:

• Self-assembled monolayers (SAMs) form ordered molecular layers on surfaces.
• Understanding SAM structure on gold is crucial for applications in electronics and nanotechnology.
• Alkyl sulfides on gold(111) present complex interfacial structures.

Purpose of the Study:

• To resolve the detailed atomic structure of long-chain alkyl sulfide SAMs on gold(111).
• To investigate the interplay between alkyl chain ordering and gold surface restructuring.
• To elucidate the binding sites of sulfur atoms and the behavior of gold atoms at the interface.

Main Methods:

• Density functional theory-based molecular dynamics (DFT-MD) simulations.
• Grazing incidence X-ray diffraction (GIXRD).
• Analysis of molecular dynamics trajectories and relative energies of SAM structures.

Main Results:

• Identified two distinct surface binding sites for sulfur atoms.
• Observed gold atom vacancies and adatoms in the first gold surface layer.
• Revealed a competition between van der Waals forces driving SAM ordering and sulfur-gold interactions driving gold surface disorder.

Conclusions:

• The structure of alkyl sulfide SAMs on gold(111) is a balance between ordering and disordering forces.
• Sulfur-gold interactions significantly impact the gold surface structure, creating vacancies and adatoms.
• DFT-MD and GIXRD provide complementary insights into complex interfacial phenomena.