How far the chemistry of self-assembled monolayers on gold surfaces affects their work function?

Area of Science:

• Surface science
• Materials science
• Physical chemistry

Background:

• Self-assembled monolayers (SAMs) are crucial for tuning surface properties.
• Understanding SAMs' electronic behavior is key for molecular electronics.
• Previous studies focused on tail group dipoles, but other factors may be significant.

Purpose of the Study:

• To investigate the influence of aliphatic chain length and tail group functionality on the work function of SAMs on Au(111).
• To explore the role of hydrogen bonding and humidity on SAM work function.
• To develop theoretical models for interpreting experimental SAM work function data.

Main Methods:

• Synthesis of SAMs with varying chain lengths (C6-C16) and functional groups (carboxy, amino, thio, methyl) on Au(111).
• Characterization using Kelvin probe force microscopy (KPFM) for work function measurements and ultraviolet photoelectron spectroscopy (UPS).
• Density functional theory (DFT) modeling with large supercells to simulate SAMs and hydrogen bonding.

Main Results:

• Work function is significantly modulated by aliphatic chain length and tail group interactions, particularly hydrogen bonding.
• Humidity changes (40% to 3% RH) induced work function shifts up to 0.3 eV.
• DFT calculations accurately reproduced experimental work function values, validating the models.

Conclusions:

• Aliphatic chain length and hydrogen bonding networks play a more dominant role in tuning SAM work function than tail group dipole moments.
• Experimental and theoretical findings provide a deeper understanding of SAM electronic properties.
• This research facilitates the rational design of SAMs for applications in molecular electronics and organic transistors.