High-Energy Resolution Electron Energy-Loss Spectroscopy Study of Interband Transitions Characteristic to Single-Walled Carbon Nanotubes

Abstract

An electron energy-loss spectroscopic (EELS) study using a monochromator transmission electron microscope was conducted for investigating the dielectric response of isolated single-walled carbon nanotubes (SWCNTs) owing to interband transitions characteristic to chiral structures. Individual chiral structures of the SWCNTs were determined by electron diffraction patterns. EELS spectra obtained from isolated SWCNTs showed sharp peaks below π plasmon energy of 5 eV, which were attributed to the characteristic interband transitions of SWCNTs. In addition, unexpected shoulder structures were observed at the higher energy side of each sharp peak. Simulations of EELS spectra by using the continuum dielectric theory showed that an origin of the shoulder structures was because of the surface dipole mode along the circumference direction of the SWCNT. It was noticed that the electron excitation energies obtained by EELS were slightly higher than those of optical studies, which might be because of the inelastic scattering process with the momentum transfers. To interpret the discrepancy between the EELS and optical experiments, it is necessary to conduct more accurate simulation including the first principle calculation for the band structure of SWCNTs.

Momentum- and space-resolved high-resolution electron energy loss spectroscopy of individual single-wall carbon nanotubes

“…3 to literature values obtained from Rayleigh scattering spectroscopy [9,10], fluorescence excitation spectroscopy [11], interpolation from experimental data [9], optical absorption spectroscopy [12], and a prediction based on fluorescence data [34]. In agreement with Sato and Terauchi [18] the π → π * VHS EELS peaks appear at up to ≈0.2 eV higher energy than those measured by optical techniques. While the EEL spectrum is proportional to the loss function, the optical absorption spectrum is given by the imaginary part of the dielectric function (see, e.g., Ref.…”

“…[18,19,37]. While, to the knowledge of the authors, experimental literature values confirming the energies of the (15,10) E 55 − E 77 and (15,1) E 33 − E 66 peaks are lacking, these peaks were tentatively assigned to transitions between higher energy VHSs, as this is their most likely origin.…”

“…While, to the knowledge of the authors, experimental literature values confirming the energies of the (15,10) E 55 − E 77 and (15,1) E 33 − E 66 peaks are lacking, these peaks were tentatively assigned to transitions between higher energy VHSs, as this is their most likely origin. Alternatively, assignment as "VHS peaks" might be done on the basis of theoretical modeling [18]; however this was beyond the scope of the present study.…”

“…Due to recent advancements in transmission electron microscope (TEM) electron source monochromation [15][16][17], an EEL spectrometer coupled to a TEM column now allows for detailed investigations of π → π * transitions between the SWCNT conduction and valence VHSs [18,19]. Moreover, TEM and scanning (S) TEM allow for the determination of the chiral indices of each investigated tube using either a Fourier transform (FFT) of a high-resolution image [19,20] or an electron diffraction pattern [18,21,22].…”

“…Moreover, TEM and scanning (S) TEM allow for the determination of the chiral indices of each investigated tube using either a Fourier transform (FFT) of a high-resolution image [19,20] or an electron diffraction pattern [18,21,22]. Note that the CNT valence loss spectrum (EEL < 50 eV) does not only contain peaks corresponding to chirality-dependent π → π transitions but also provides information about higher energy interband transitions involving σ states, as well as two collective modes of the system: the π and π + σ plasmons.…”