Nanoscale Work Function Contrast Induced by Decanethiol Self-Assembled Monolayers on Au(111).

Area of Science:

• Surface science
• Nanotechnology
• Materials science

Background:

• Self-assembled monolayers (SAMs) of organosulfurs on metal surfaces are crucial for nanotechnology.
• Understanding the relationship between molecular structure and surface properties is key to designing functional materials.

Purpose of the Study:

• To map spatial variations in tunnel barrier height and work function at the sub-nanometer scale.
• To investigate the influence of different decanethiol phases (β, φ, λ) on surface properties.
• To elucidate the mechanisms governing work function modulation and molecular binding to the Au(111) substrate.

Main Methods:

• Combining topographic scanning tunneling microscopy (STM) with dI/dz spectroscopy.
• Analyzing ratios of tunnel barriers to quantify work function contrast.
• Comparing work function variations across different decanethiol phases (lying-down, standing-up, oxidized).

Main Results:

• Spatial maps of tunnel barrier variations were obtained with sub-nanometer resolution.
• The pillow effect in low-density phases and the surface dipole effect in dense phases contribute similarly to work function lowering.
• Oxidation of decanethiol (λ phase) significantly reduces molecular binding to the Au(111) substrate compared to the nonoxidized β phase.

Conclusions:

• STM combined with dI/dz spectroscopy provides detailed insights into surface properties of SAMs.
• Both lying-down and standing-up molecular configurations induce comparable work function modulations.
• Molecular oxidation disrupts strong substrate binding, altering surface characteristics.