Adsorption on Carbon Nanotubes Studied Using Polarization-Modulated Infrared Reflection-Absorption Spectroscopy
NAVAL RESEARCH LAB WASHINGTON DC ELECTRONICS SCIENCE AND TECHNOLOGY DIV
Pagination or Media Count:
Single-wall carbon nanotubes SWNTs, deposited onto an Al substrate from a liquid suspension, have been cleaned by annealing in ultrahigh vacuum. The effects of exposing the sample in situ to atomic H or D andor to dimethyl methylphosphonate DMMP, CH3O2CH3PO were then studied using polarizationmodulated infrared reflection-absorption spectroscopy. Atomic H reacts preferentially near strained or defective regions in the nanotube wall to produce a spectrum consistent with alkane-like species CH2 and -CH3. Only a small fraction of the CC sites in the nanotube wall react with H, and there is no clear evidence for monohydride CH-CH species. For DMMP, data were obtained under steady-state conditions in reagent pressures in excess of half the room-temperature vapor pressure. Adsorption occurs via the PO group with a coverage that depends on the ambient pressure. Varying the DMMP coverage by changing the pressure causes changes in the spectrum that can be related to the strength of the DMMPSWNT interaction. Preadsorbed H is seen to have little or no effect on the subsequent adsorption of DMMP. For DMMP, the molecular features are superimposed on a broad, smoothly varying background that can be related to adsorptioninduced changes in the Drude parameters characterizing the SWNT free-carrier density and scattering lifetime.
- Refractory Fibers