Electrons In Single-wall Carbon Nanotubes Research Articles

Computational Study on Characteristic Radiation Originated from Channeled Relativistic Electrons in Single-Wall Carbon Nanotubes

I calculated the number of bound states n for channeled electrons through single wall carbon nanotubes (n,m) at different values of electrons energy by using (Wetzel, Kramer's, Brillouin approximation)(WKB) method. The calculations executed according to the continuum model approximation given by Lindhard for the case of an axial channeling in single crystals. The estimated results of the maximum number of bound states of the channeled electrons in a zigzag (n, 0), armchair (n,n) and chiral(n,m) nanotubes have been performed using the Moliere potential. In this work we determined the emitted photon energy due to n, (n-1) transitions between higher -quantum states as a function of the electron energy up to 500 MeV. Also the energy levels of electrons channeled in different types of single wall carbon nanotubes by using Moliere potential were defined. It has been showed that the emitted photon energy in the forward direction is the energy difference between the successive initial and final states of the channeled electron. The energy of the emitted channeling radiation has been calculated for incident electron at 50 MeV. We calculated the emitted channeling radiation for incident electrons at 10, 50 and500 MeV with frequency in X-ray range.

Mechanism of the Field Emission of Electrons in Single-Walled Carbon Nanotubes

A new interpretation of the emission properties of carbon nanotubes is presented using the theory of electron conjugation. The presence of emission molecular states in the energy spectrum of carbon nanotubes, characterized by specific localization of electron density on the end surfaces of carbon nanotubes, is explained from the viewpoint of the concepts of in-plane and ρ-electron conjugation. Based on an analysis of the behavior of emission molecular orbitals in a constant electric field, it is concluded that such localization of electron density is the physical basis for electron emission. It is established that this approach describes known experimental and theoretical results well and can be used to predict the emission properties of a wide range of objects.

Effect of increased crystallinity of single-walled carbon nanotubes used as field emitters on their electrical properties

Single-walled carbon nanotubes (SWCNTs) synthesized by arc discharge are expected to exhibit good field emission (FE) properties at a low driving voltage. We used a coating containing homogeneously dispersed highly crystalline SWCNTs produced by a high-temperature annealing process to fabricate an FE device by a wet-coating process at a low cost. Using the coating, we succeeded in reducing the power consumption of field emitters for planar lighting devices. SWCNTs synthesized by arc discharge have crystal defects in the carbon network, which are considered to induce inelastic electron tunneling that deteriorates the electrical conductivity of the SWCNTs. In this study, the blocking of the transport of electrons in SWCNTs with crystal defects is simulated using an inelastic electron tunneling model. We succeeded in clarifying the mechanism underlying the electrical conductivity of SWCNTs by controlling their crystallinity. In addition, it was confirmed that field emitters using highly crystalline SWCNTs can lead to new applications operating with low power consumption and new devices that may change our daily lives in the future.

Biological construction of single-walled carbon nanotube electron transfer pathways in dye-sensitized solar cells.

We designed and mass-produced a versatile protein supramolecule that can be used to manufacture a highly efficient dye-sensitized solar cell (DSSC). Twelve single-walled carbon-nanotube (SWNT)-binding and titanium-mineralizing peptides were genetically integrated on a cage-shaped dodecamer protein (CDT1). A process involving simple mixing of highly conductive SWNTs with CDT1 followed by TiO2 biomineralization produces a high surface-area/weight TiO2 -(anatase)-coated intact SWNT nanocomposite under environmentally friendly conditions. A DSSC with a TiO2 photoelectrode containing 0.2 wt % of the SWNT-TiO2 nanocomposite shows a current density improvement by 80% and a doubling of the photoelectric conversion efficiency. The SWNT-TiO2 nanocomposite transfers photon-generated electrons from dye molecules adsorbed on the TiO2 to the anode electrode swiftly.

Dispersion of single walled carbon nanotubes in amidine solvents

The excellent electronic and material properties of single walled carbon nanotubes (SWNTs) makes this nanomaterial very attractive for incorporation into flexible and stretchable electronics. However, the widespread application of SWNTs in electronic devices is still limited. To purify, process and place SWNTs, appropriate solvents for dispersion are needed. However, a fundamental understanding of the reasons why certain solvents are capable of dispersing SWNTs is still missing. Here we report on two new potential solvents containing amidine moieties, 1,8-diazabicycloundec-7-ene (DBU) and 1,5-diazabicyclo(4.3.0)non-5-ene (DBN). Even though these solvents’ molecular structures differ by only two –CH2– groups, we found that DBU is capable of dispersing SWNTs, while DBN is not. We carried out density functional theory (DFT) calculations to investigate the interaction between DBU and DBN, and we elucidated the reasons for the different performances of the two solvents. DBU has a preferential edge-on interaction with the SWNT, thus allowing for a higher solvent coverage than DBN. In addition, the CH2–SWNT interaction present for DBU substantially increases the adsorption energy compared to DBN. Our results point to the important interplay between the interaction of pi electrons, nitrogen lone pairs and the –CH2– groups present in aprotic solvent molecules and the delocalized pi electrons in SWNTs.

First-principles study of quantum tunneling from nanostructures: Current in a single-walled carbon nanotube electron source

We present a first-principles calculation of the emission current in a single-walled carbon nanotube electron source. We have employed the nonequilibrium Green's function and Fisher-Lee's transmission formulation to describe electronic transport through the system. The simulation results reproduce the trends observed in experimental data closely and, in particular, the current saturation and deviation from the Fowler-Nordheim behavior. The proposed numerical approach is useful whenever a region of vacuum is present in the system Hamiltonian.

Electron Spin Resonance Signal of Luttinger Liquids and Single-Wall Carbon Nanotubes

A comprehensive theory of electron spin resonance (ESR) for a Luttinger liquid state of correlated metals is presented. The ESR measurables such as the signal intensity and the linewidth are calculated in the framework of Luttinger liquid theory with broken spin rotational symmetry as a function of magnetic field and temperature. We obtain a significant temperature dependent homogeneous line broadening which is related to the spin-symmetry breaking and the electron-electron interaction. The result crosses over smoothly to the ESR of itinerant electrons in the noninteracting limit. These findings explain the absence of the long-sought ESR signal of itinerant electrons in single-wall carbon nanotubes when considering realistic experimental conditions.

High-current-density field emission display fabricated from single-walled carbon nanotube electron sources

Single-walled carbon nanotubes can be used as electron sources in the process of field emission, and have great potential for practical application of the field emission display (FED) panels with large screen size. We fabricated a FED using the single-walled carbon nanotubes (SWNTs) as the cathode by the screen-printing process. Test showed that the SWNTs emitters exhibit excellent macroscopic emission properties. It has low turn-on voltage (2.7 V/μm) and high brightness, with a high current density of good uniformity and stability. It was observed that the field emission qualitatively follows the conventional Fowler–Nordheim (F–N) theory, and aging treatment played an important role in improving the image uniformity and stability. Compared to other complicated processes, the simple fabrication using screen-printing process seems to be advantageous for practical application.

Four-probe measurements of carbon nanotubes with narrow metal contacts

We find that electrons in single-wall carbon nanotubes may propagate substantial distances (tens of nanometers) under the metal contacts. We perform four-probe transport measurements of the nanotube conductance and observe significant deviations from the standard Kirchhoff's circuit rules. Most noticeably, injecting current between two neighboring contacts on one end of the nanotube, induces a non-zero voltage difference between two contacts on the other end.

Chirality effect on carbon nanotube electron resonators

AbstractThe quantum conductance oscillations of metallic single‐walled carbon nanotube (SWNT) electron resonators with different chirality have been studied numerically. It is found that the slow oscillation background as well as fast conductance oscillations are intrinsic properties of SWNT electron resonators. All metallic SWNT except zigzag type electron resonators can present slow conductance oscillations background, whose oscillation period is increase as the chiral angle decrease, and the zigzag type SWNT resonators don't show the slow oscillation background. For the armchair SWNT resonators the slow oscillation background have distinctly different transport behavior depending on whether the length of the tube is commensurate with a (3N + 1) rule, with N the number of basic carbon repeat units along the nanotube length. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Quantum interference in nanotube electron waveguides

We have calculated the quantum conductance of single-walled carbon nanotube (SWNT) waveguide by using a tight binding-based Green’s function approach. Our calculations show that the slow conductance oscillations as well as the fast conductance oscillations are manifestations of the intrinsic quantum interference properties of the conducting SWNTs, being independent of the defect and disorder of the SWNTs. And zigzag type tubes do not show the slow oscillations. The SWNT electron waveguide is also found to have distinctly different transport behavior depending on whether or not the length of the tube is commensurate with a (3N+1) rule, with N the number of basic carbon repeat units along the nanotube length.

Photoexcited electron relaxation processes in single-wall carbon nanotubes

The relaxation processes for photoexcited electrons in single-wall carbon nanotubes (SWNTs) are discussed in connection with recent photoluminescence excitation (PLE) spectroscopy experiments. The electron-phonon $(e\text{\ensuremath{-}}\mathrm{ph})$ interaction of SWNTs is calculated for each phonon mode as a function of photoexcited electron energy. Because of the cylindrical surface of a SWNT, the twisting and radial breathing phonon modes are responsible for the $e\text{\ensuremath{-}}\mathrm{ph}$ interaction in the lower phonon energy region. Optic phonon modes are also responsible for the relaxation of photoexcited electrons. Compared with graphite, the relaxation of electrons is much faster in SWNTs because of their cylindrical shape. We identify and explain some aspects of both photoluminescent and Raman processes appearing in PLE plots for SWNTs.

Tunneling energy barriers of emitted electrons in single-walled carbon nanotubes

By use of the first-principles calculations, we systematically investigate and demonstrate the localized characteristics of electronic wave functions, corresponding to quantized energy levels in the vicinity of the Fermi level, in one individual finite-length single-walled carbon nanotube. Within the framework of the energy levels emission model, quantized energy levels relevant to electron emission are considered, and the corresponding tunneling energy barriers and integrated emitting energy levels widths are calculated with respect to the spatial emission locations. The emission trend and contributions to the emission current from $\ensuremath{\pi}$ electrons at the tip are sensitively dependent on the locations of $\ensuremath{\pi}$ electrons and the orientations of corresponding localized electronic states under the external electric field. This would give rise to the nonhomogeneous electron emission energy distribution.