Polyphenylsilole multilayers--an insight from X-ray electron spectroscopy and density functional theory

Area of Science:

• Materials Science
• Surface Science
• Computational Chemistry

Background:

• Polyphenylsiloles are organic semiconductors with potential applications.
• Understanding their electronic structure and surface interactions is crucial for device development.

Purpose of the Study:

• To investigate the electronic structure and bonding of hexaphenylsilole (HPS) and tetraphenylsilole (TPS) multilayers.
• To elucidate the charge distribution within the silole core and its interaction with a copper substrate.
• To analyze the influence of growth conditions on film morphology and spectroscopic properties.

Main Methods:

• Combined X-ray photoelectron spectroscopy (XPS) and Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectroscopy.
• Density Functional Theory (DFT) calculations for electronic structure analysis.
• Angle-dependent measurements to probe molecular orientation.
• Variable temperature deposition to study growth modes.

Main Results:

• XPS and DFT calculations indicate a positively charged silicon and negatively charged adjacent carbons in the silole core of HPS and TPS.
• These charges are maintained upon deposition onto a Cu(111) substrate.
• NEXAFS spectra show distinct features assigned to different carbon species, with limited molecular orientation observed.
• Lowering deposition temperature leads to less ordered growth, evidenced by broadened spectra and shifted binding energies.

Conclusions:

• The electronic structure of HPS and TPS features a polarized silole core, with charges conserved at the molecule-substrate interface.
• Molecular orientation is not uniform, and growth conditions significantly impact film order and electronic properties.