Electron Spectroscopy Studies of Carbon Nanotubes

Abstract

Abstract. Electron spectroscopies play an essential role in the experimental characterization of the electronic structure of solids. After a short description of the techniques used, the paper reviews some of the most important results obtained on purified single-and multi-wall carbon nanotubes, and intercalated nanotubes as well. An analysis of the occupied and unoccupied electron states, and the plasmon structure of the nanotubes is provided. How this information can be used to characterize the samples is discussed. Whenever possible, a comparison between nanotube data and those from graphite and C60 fullerene is made, as to draw a coherent picture in the light of recent theories on the electronic properties of these C-sp 2 materials.Carbon-based π-electron system are becoming more and more important in solid state physics, chemistry and in material science. These systems comprise graphite, conjugated polymers and oligomers, fullerenes and carbon nanotubes. Many systems can be "doped" or intercalated. In this way new materials can be tailored having interesting properties. These new materials have often become model compounds in solid state physics since they show metallic and semiconducting behavior, superconductivity and magnetism. Correlation effects, which result from electron-electron interactions, and the electron-phonon interaction, are important in many of these systems. Dimensionality plays an important role, too. Thus many of the interesting questions of present solid state research are encountered again in the carbon-based π-electron systems. Moreover, some of these materials have high technical potential. They show remarkable mechanical properties, e.g., a record-high elastic modulus. In addition, electronic devices from conjugated carbon systems are coming close to realization and commercialization. Transistors and organic light-emitting diodes based on conjugated polymers or molecules are already on the market. Industry is strongly interested in the field emission from carbon nanotubes to fabricate bright light sources and flat-panel screens. Finally, future nanoscale electronics systems can possibly be realized using carbon materials such as nanotubes.

Hot Exciton Relaxation and Exciton Trapping in Single-Walled Carbon Nanotube Thin Films

“…The surface work function of the sample obtained from the SECO is 4.24 ± 0.10 eV, which is slightly lower than the work function (4.5–4.6 eV) of pristine graphene and graphite. , Figure b shows the valence band structure of the nanotubes. Two main peaks at ∼3 eV (π- band) and ∼8 eV (σ-band) below E f can be identified, which are the typical features found in the s-SWCNT spectrum …”

Diameter dependence of oxidative stability in multiwalled carbon nanotubes: Role of defects and effect of vacuum annealing

“…This is likely to be caused by higher ordering in graphitic stacking and diminishing defect density. 35 …”

Electronic and vibrational properties of chemically modified single-wall carbon nanotubes

“…The second dispersive feature, a high-energy peak located in the range of 21-25 eV, originates from s + p-plasmon excitation. The lower energy of the s + p-plasmon in SWCNTs -as compared to graphite -results from the anisotropy of the graphene layer in the nanotubes [242]. More recently, EELS studies on individual SWCNTs have demonstrated that both the p-and the s + p-plasmon have two components, namely a bulk and a surface mode, with the former appearing at slightly higher energies [198,199].…”

“…While in the initial UPS experiments, it has been impossible to observe a fine structure reflecting the vHs in the density of occupied states, even when the spectra were recorded with the highest energy solution [242], this task has recently been reached with more homogeneous SWCNT samples [250]. This achievement has significantly contributed to an understanding of many-electron effects in SWCNTs.…”