Adsorption on carbon nanotubes studied using polarization-modulated infrared reflection-absorption spectroscopy

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• Single-wall carbon nanotubes (SWNTs) are crucial nanomaterials with unique electronic properties.
• Understanding their surface interactions is key to controlling their behavior in devices.
• Previous studies have explored SWNT functionalization, but detailed in-situ analysis of specific chemical reactions is ongoing.

Purpose of the Study:

• To investigate the surface reactions of SWNTs with atomic hydrogen and dimethyl methylphosphonate (DMMP).
• To elucidate the reaction mechanisms and identify the resulting chemical species.
• To understand how these adsorbates affect the electronic properties of SWNTs.

Main Methods:

• SWNTs deposited on an aluminum substrate were cleaned via ultrahigh vacuum annealing.
• In-situ exposure to atomic hydrogen (H or D) and DMMP.
• Polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) was employed for analysis.

Main Results:

• Atomic hydrogen preferentially reacts with strained or defective sites on the SWNT wall, forming alkane-like species (>CH2 and -CH3).
• Only a small fraction of C=C sites react with H; no clear evidence for monohydride species was found.
• DMMP adsorbs via its P=O group, with coverage dependent on ambient pressure, influencing the SWNT/DMMP interaction strength.
• Preadsorbed hydrogen showed minimal effect on DMMP adsorption.
• DMMP adsorption induced changes in SWNT free-carrier density and scattering lifetime, observable as a broad background in the spectra.

Conclusions:

• Atomic hydrogen functionalization of SWNTs is selective towards defect sites.
• DMMP adsorption is governed by the P=O group and influences SWNT electronic properties.
• PM-IRRAS is effective in characterizing in-situ surface reactions and their impact on nanomaterials.