Recently we reported noncovalent functionalization of nanotubes in an aqueous medium with ionic liquid-basedsurfactants, 1-dodecyl-3-methylimidazolium b
romide (
1) and 1-(12-mercaptododecyl)-3-methylimidazolium b
romide(
2), resulting in positively charged single-wall carbon nanotube (SWNT)-
1,
2 composites. Thiolation of SWNTs with
2 provides their self-assembly on gold as well as templating gold nanoparticles on SWNT sidewalls via a covalent-S-Au bond. In this investigation, we studied the electronic structure, intermolecular interactions, and packing withinnoncovalently thiolated SWNTs and also nanotube alignment in the bulk of SWNT-
2 dried droplets and self-assembled submonolayers (SAMs) on gold by high-resolution X-ray photoemission spectroscopy (HRXPS), C K-edgeX-ray absorption fine structure (NEXAFS) spectroscopy, and polarization-modulated infrared reflection-absorptionspectroscopy (PM-IRRAS). HRXPS data confirmed the noncovalent nature of interactions within the nanocompositeof thiolated nanotubes. In PM-IRRAS spectra of SWNT SAMs on gold, the IR-active vibrational SWNT modes havebeen observed and identified. According to PM-IRRAS data, the hydrocarbon chains of
2 are oriented with less tiltangle to the bare gold normal in a SAM deposited f
rom an SWNT-
2 dispersion than those of
1 deposited f
rom anSWNT-
1 dispersion on the mercaptoethanesulfonic acid-primed gold. For both the dried SWNT-
2 bulk and theSWNT-
2 SAM on gold, the C K-edge NEXAFS spectra revealed the presence of CH-
interactions betweenhydrocarbon chains of
2 and the
electronic nanotube structure due to the highly resolved vibronic fine structureof carbon 1s
R*/
*
C-H series of states in the alkyl chain of
2. For the SWNT-
2 bulk, the observed splitting andupshift of the SWNT
* orbitals in the NEXAFS spectrum indicated the presence of
-
interactions. In the NEXAFSspectrum of the SWNT-
2 SAM on gold, the upshifted values of the photon energy for R*/
*
C-H transitions indicatedclose contact of
2 with nanotubes and with a gold surface. The angle-dependent NEXAFS for the SWNT-
2 bulkshowed that most of the molecules of
2 are aligned along the nanotubes, which are self-organized with orientationparallel to the substrate plane, whereas the NEXAFS for the SWNT-
2 SAM revealed a more normal orientation offunctionality
2 on gold compared with that in the SWNT-
2 bulk.
