• Dalmiglio, Matteo
• Soria, Rosa Georgina Ruiz
• Pichler, Thomas
• Sauer, Markus
• Rubio, Angel
• Yanagi, Kazuhiro
• Lacovig, Paolo
• Goldoni, Andrea
• Paz, Alejandro Perez
• Mowbray, Duncan J.
• Ayala, Paola
• Lizzit, Silvano

Abstract

<p>Pristine single-walled carbon nanotubes (SWCNTs) are rather inert to O₂ and N₂, which for low doses chemisorb only on defect sites or vacancies of the SWCNTs at the ppm level. However, very low doping has a major effect on the electronic properties and conductivity of the SWCNTs. Already at low O₂ doses (80 L), the X-ray photoelectron spectroscopy (XPS) O 1s signal becomes saturated, indicating nearly all of the SWCNT's vacancies have been oxidized. As a result, probing vacancy oxidation on SWCNTs via XPS yields spectra with rather low signal-to-noise ratios, even for metallicity-sorted SWCNTs. We show that, even under these conditions, the first-principles density functional theory calculated Kohn-Sham O 1s binding energies may be used to assign the XPS O 1s spectra for oxidized vacancies on SWCNTs into its individual components. This allows one to determine the specific functional groups or bonding environments measured. We find the XPS O 1s signal is mostly due to three O-containing functional groups on SWCNT vacancies: epoxy (C₂&gt;O), carbonyl (C₂&gt;C=O), and ketene (C=C=O), as ordered by abundance. Upon oxidation of nearly all of the SWCNT's vacancies, the central peak's intensity for the metallic SWCNT sample is 60% greater than that for the semiconducting SWCNT sample. This suggests a greater abundance of O-containing defect structures on the metallic SWCNT sample. For both metallic and semiconducting SWCNTs, we find O₂ does not contribute to the measured XPS O 1s spectra.</p>

Topics

• density
• impedance spectroscopy
• Carbon
• theory
• nanotube
• x-ray photoelectron spectroscopy
• density functional theory
• defect structure
• vacancy