Disentangling Vacancy Oxidation on Metallicity-Sorted Carbon Nanotubes

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• 作者：Duncan J. Mowbray ; Alejandro Pérez Paz ; Georgina Ruiz-Soria ; Markus Sauer ; Paolo Lacovig ; Matteo Dalmiglio ; Silvano Lizzit ; Kazuhiro Yanagi ; Andrea Goldoni ; Thomas Pichler ; Paola Ayala ; Angel Rubio
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：August 18, 2016
• 年：2016
• 卷：120
• 期：32
• 页码：18316-18322
• 全文大小：374K
• 年卷期：0
• ISSN：1932-7455

文摘

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>O), carbonyl (C₂>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.