Polymer Adsorption on Graphite and CVD Graphene Surfaces Studied by Surface-Specific Vibrational Spectroscopy

Area of Science:

• Surface science
• Materials science
• Spectroscopy

Background:

• Chemical vapor deposition (CVD) graphene is prone to contamination during transfer processes.
• Understanding polymer adsorption is crucial for maintaining graphene quality.

Purpose of the Study:

• To identify polymer contaminants on CVD graphene.
• To investigate alkane and polyethylene (PE) adsorption on graphite surfaces.
• To determine the adsorption energy of PE on graphite.

Main Methods:

• Sum-frequency vibrational spectroscopy (SFVS) was used to analyze polymer contaminants.
• SFVS was employed to study alkane and PE adsorption on graphite.
• Adsorption free energy was calculated for PE on graphite.

Main Results:

• Contaminants on CVD graphene were identified as long-chain alkane or PE-like molecules.
• Polyethylene (PE) forms a self-assembled ordered monolayer on graphite with a high adsorption free energy (∼42 kJ/mol).
• The C-C skeleton plane of adsorbed PE is oriented perpendicular to the graphite surface.

Conclusions:

• The strong adsorption energy of PE-like impurities explains the facile contamination of CVD graphene.
• Minimizing contamination requires using purified polymers devoid of PE-like impurities.
• SFVS is effective for probing molecular contaminants and adsorption on graphene and graphite.