Molecular and electronic structure of electroactive self-assembled monolayers

Area of Science:

• Molecular electronics
• Surface science
• Nanotechnology

Background:

• Self-assembled monolayers (SAMs) with electroactive groups are key for molecular electronics.
• Ferrocene-terminated alkanethiol SAMs are well-studied but their electronic structure and influence on work function changes remain unclear.

Purpose of the Study:

• To experimentally and theoretically investigate the molecular and electronic structure of ferrocene-terminated alkanethiol SAMs on gold.
• To clarify the role of the ferrocene group in SAM-induced work function modulation.

Main Methods:

• Experimental investigation of SAMs on Au surfaces.
• Theoretical calculations of molecular and electronic structure.
• Analysis of surface coverage and molecular geometry.

Main Results:

• Ferrocene-terminated alkanethiols form a compact monolayer on Au, with molecules tilted at 30° and bonded via a thiolate linkage.
• The ferrocene group, located 14 Å above the surface, has minimal influence on the work function decrease, which is dominated by the alkanethiol.
• The ferrocene moiety's Highest Occupied Molecular Orbital (HOMO) is at -1.6 eV relative to the Fermi level.

Conclusions:

• The study provides detailed molecular and electronic structure insights into electroactive SAMs.
• Findings are crucial for understanding and designing molecular electronic devices.
• Work function modulation in these SAMs is primarily dictated by the alkanethiol backbone, not the terminal ferrocene group.