Work Functions and Surface Functional Groups of Multiwall Carbon Nanotubes

Abstract

We have studied the work function and density of states (DOS) of multiwall carbon nanotubes (MWNTs) using ultraviolet photoelectron spectroscopy (UPS). Raw MWNTs were purified by successive sonication, centrifugation, sedimentation, and filtration processes with the aid of a nonionic surfactant. The purified MWNTs showed a slightly lower work function (4.3 eV) than that of highly oriented pyrolytic graphite (4.4 eV). Effects of three different oxidative treatments, air-, oxygen plasma-, and acid-oxidation, have also been studied. It was found that oxidative treatments affect the DOS of valence bands and increase the work function. X-ray photoelectron spectroscopy (XPS) measurements have suggested that gas-phase treatment preferentially forms hydroxyl and carbonyl groups, while liquid-phase treatment forms carboxylic acid groups on the surface of MWNTs. These surface chemical groups disrupt the π-conjugation and introduce surface dipole moments, leading to higher work functions up to 5.1 eV. We expect the information on the work function of the MWNTs to be of importance to the development of electronic or optoelectronic applications.

Characterizing Functionalized Carbon Nanotubes for Improved Fabrication in Aqueous Solution Environments

“…The XPS spectrum shows distinct carbon peaks, representing the major constituents of the oxidized MWNT surface. The dominant peak structure for the C 1s core level at a BE of 284.4 eV corresponds to the bare, untreated MWNT surface (Ago et al, 1999;Suzuki et al, 2002). C 1s core level shifts at 287.6 and 288.3 eV indicate that the moieties consist of CO-/C=O and COO-respectively, in agreement with literature values reported for these groups tethered onto the MWNTs (Langley et al, 2005).…”

“…The presence of these peaks verified that the MWNTs remained largely intact during sonochemical treatment and after deposition of the Pt nanoparticles. The XPS Pt 4f 7/2 core level of the Pt-CNT (not shown; prepared using a 2-hr sonochemical treatment), referencing the graphitic C 1s orbital at a BE equal to 284.4 eV (Ago et al, 1999; www.intechopen.com…”

Combined XPS and TPD study of oxygen-functionalized carbon nanofibers grown on sintered metal fibers

“…2 presents the superposition of the XP spectra in the C1s region for non-heated samples A1 (untreated), C2 (H 2 O 2 -treated), D4 (ozone-treated) and additionally for sample C2 heated to 1043 K. The difference spectra between oxidized and non-activated samples (D4 and A1) and oxidized C2 (RT) and heated samples C2 (840 K) are shown at the bottom. The observation of the changes in the C1s spectra allows us to elucidate the presence of defect sites in the CNF and thus the degree of graphitization [19,25,26]. In the case of the ozone-treated sample, D4, the intensity of the peak associated with graphitic carbon (284.5 eV) decreases slightly upon going from the untreated sample to the oxygen-functionalized sample.…”

Electroactive shape memory performance of polyurethane composite having homogeneously dispersed and covalently crosslinked carbon nanotubes

“…In the case of the pristine tubes, there are peaks at 285.5eV, 286.5eV, and 287.5eV corresponding to C-C, -C-O-, and -C=O bonds, respectively. However, a newly observed peak at 288.9eV in the acid-treated tubes indicates the introduction of -COO-groups [20]. TEM observations also support the effectiveness of acid treatment for the introduction of defects and chemical moieties ( figure 1(c)) since the relatively long straight fringes are easily transformed into short corrugated fringes by generating structural defects preferentially on the sidewall of the tubes.…”