Temporal evolution of benzenethiolate SAMs on Cu(100)

Area of Science:

• Surface Science
• Materials Chemistry
• Nanotechnology

Background:

• Self-assembled monolayers (SAMs) are crucial for modifying surface properties.
• Understanding the stability of benzenethiolate (BT) SAMs on copper is vital for electronic applications.

Purpose of the Study:

• To investigate the structure and thermal stability of benzenethiolate (BT) on Cu(100).
• To elucidate the decomposition pathways and phase transitions of BT SAMs at room temperature and elevated temperatures.

Main Methods:

• Utilized a suite of surface science techniques: thermal desorption spectroscopy (TDS), scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), UV photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray adsorption fine structure (NEXAFS).
• Investigated structural evolution and thermal decomposition under controlled conditions.

Main Results:

• A well-ordered, densely packed c(6 × 2) BT structure forms at room temperature but is metastable.
• The film undergoes partial decomposition via S-C bond cleavage, forming a less dense p(2 × 2) phase over days, reducing work function change from -0.9 eV to -0.5 eV.
• TDS revealed distinct intact and dissociative desorption channels, indicating varied Cu-S interaction strengths. Heating above 500 K leads to sulfide overlayer formation and substrate reconstruction, with BT maintaining an upright orientation.

Conclusions:

• Benzenethiolate SAMs on Cu(100) exhibit complex metastability and decomposition pathways.
• The thermal stability is influenced by adsorption site coordination and heating temperature.
• The upright molecular orientation is robust even during thermal degradation.