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The control of light-matter interaction at the most elementary level has become an important resource for quantum technologies. Implementing such interfaces in the THz range remains an outstanding problem. Here, we couple a single electron trapped in a carbon nanotube quantum dot to a THz resonator. The resulting light-matter interaction reaches the deep strong coupling regime that induces a THz energy gap in the carbon nanotube solely by the vacuum fluctuations of the THz resonator. This is directly confirmed by transport measurements. Such a phenomenon which is the exact counterpart of inhibition of spontaneous emission in atomic physics opens the path to the readout of non-classical states of light using electrical current. This would be a particularly useful resource and perspective for THz quantum optics., Strong light-matter coupling has been realized at the level of single atoms and photons throughout most of the electromagnetic spectrum, except for the THz range. Here, the authors report a THz-scale transport gap, induced by vacuum fluctuations in carbon nanotube quantum dot through the deep strong coupling of a single electron to a THz resonator.

Spin polarized transport through a quantum dot coupled to ferromagnetic electrodes with noncollinear magnetizations is discussed in terms of nonequilibrium Green functions formalism in the finite-U slave boson mean field approximation. The difference of orientations of the magnetizations of electrodes opens off-diagonal spin-orbital transmission and apart from spin currents of longitudinal polarization also spin-flip currents appear. We also study equilibrium pure spin current at zero bias and discuss its dependence on magnetization orientation, spin-orbit coupling strength and gate voltage. Impact of these factors on tunneling magnetoresistance (TMR) is also undertaken. In general spin-orbit coupling weakens TMR, but it can change its sign., 5 pages, 4 figures

Group velocity and slow down factor are discussed by adjusting the transverse magnetic field in the presence or absence of spin-orbit interaction SOI. The transparency window of the probe light can be changed due to presence of SOI. Moreover, the transparency window of the probe light becomes large by enhancing the value of transverse magnetic field. Our proposed model is may be useful for construction of optical buffer based on carbon nano-tube (CNT) quantum dot nanostructure controlled by magnetic field.

arXiv:2006.10837v2, Generating and detecting radiation in the technologically relevant range of the so-called terahertz gap (0.1–10 THz) is challenging because of a lack of efficient sources and detectors. Quantum dots in carbon nanotubes have shown great potential to build sensitive terahertz detectors, usually based on photon-assisted tunneling. A recently reported mechanism combining resonant quantum dot transitions and tunneling barrier asymmetries results in a narrow linewidth photocurrent response with a large signal-to-noise ratio under weak THz radiation. That device was sensitive to one frequency, corresponding to transitions between equidistant quantized states. In this work we show, using numerical simulations together with scanning tunneling spectroscopy studies of a defect-induced metallic zigzag single-walled carbon nanotube quantum dot, that breaking simultaneously various symmetries in metallic nanotube quantum dots of arbitrary chirality strongly relaxes the selection rules in the electric dipole approximation and removes energy degeneracies. This leads to a richer set of allowed optical transitions spanning frequencies from 1 THz to several tens of THz, for a ∼10 nm quantum dot. Based on these findings, we propose a terahertz detector device based on a metallic single-walled carbon nanotube quantum dot defined by artificial defects. Depending on its length and contacts transparency, the operating regimes range from a high-resolution gate-tunable terahertz sensor to a broadband terahertz detector. Our calculations indicate that the device is largely unaffected by temperatures up to 100 K, making carbon nanotube quantum dots with broken symmetries a promising platform to design tunable terahertz detectors that could operate at liquid nitrogen temperatures., This work has been partially supported by the Spanish Ministry of Science and Innovation with PID2019-105488GB-I00 and PCI2019-103657 (A.A.) and FIS2017-82804-P (D.B.). The work of D.B. is partially supported by by the Transnational Common Laboratory QuantumChemPhys. The Basque Government supported this work through Project No. IT-1246-19 (A.A.). J.W.G. acknowledges financial support from FONDECYT: Iniciación en Investigación 2019 Grant N. 11190934 (Chile). A.A. acknowledge financial support by the European Commission from the NRG-STORAGE project (GA 870114). K.E., C.P. and D.P. acknowledge the Swiss National Science Foundation under Grant No. 200020_182015 and No. 200021_172527, and the NCCR MARVEL funded by the Swiss National Science Foundation (51NF40-182892). The Swiss National Supercomputing Centre (CSCS) under project ID s746 and s904 is acknowledged for computational resources.

We have investigated the magnetic field dependence of transfer characteristics of a device fabricated in a configuration of a field-effect transistor with a conduction channel formed by a semiconducting multiwalled carbon nanotube. Our results unambiguously indicate that an axial magnetic field suppresses the band gap of the nanotube. Quantitative analysis of the data indicates linear dependence of the band gap on magnetic field as well as a linear splitting between the K and K' subbands of the band structure of the nanotube.

In a recent experiment [A. Donarini et al., Nat Comms 10, 381 (2019)], electronic transport through a carbon nanotube quantum dot was observed to be suppressed by the formation of a quantum-coherent ``dark state''. In this paper we consider theoretically the counting statistics and waiting-time distribution of this dark-state-limited transport. We show that the statistics are characterised by giant super-Poissonian Fano factors and long-tailed waiting-time distributions, both of which are signatures of the bistability and extreme electron bunching caused by the dark state., 9 pages; 10 figures. Updated version with new section on experimental signatures

We show that quantum confinement in the valence and conduction bands of semiconducting single-walled carbon nanotubes can be engineered by means of artificial defects. This ability holds potential for designing future nanotube-based quantum devices such as electrically driven room-temperature single-photon sources emitting at telecom-wavelength. Using Ar$^{+}$ and N$^{+}$ ion-induced defects, intrananotube quantum dots with sub-10 nm lateral sizes are created, giving rise to quantized electronic bound states with level spacings of the order of 100 meV and larger. Using low-temperature scanning tunneling spectroscopy, we resolve the energy and real space properties of the quantized states and compare them with theoretical model calculations. By solving the Schr\"odinger equation over a one-dimensional piecewise constant potential model, the effects of inhomogeneous defect scattering strength as well as surface variations in the Au(111) substrate on the quantized states structure are remarkably well reproduced. Furthermore, using ab-initio calculations, we demonstrate that defect structures such as vacancies, di-vacancies and chemisorbed nitrogen ad-atoms constitute strong scattering centers able to form quantum dots with clear signatures of discrete bound states as observed experimentally. The ab-initio simulations also allowed to study the scattering strength profile as a function of energy for different defect combinations, supporting the potential of highly stable double vacancies for practical applications at room temperature., Comment: Supplementary Informations can be downloaded at the following link: http://dario-bercioux.eu/download/SM/Supp_info.pdf

In a quantum dot hybrid superconducting junction, the behavior of the supercurrent is dominated by Coulomb blockade physics, which determines the magnetic state of the dot. In particular, in a single level quantum dot singly occupied, the sign of the supercurrent can be reversed, giving rise to a π -junction. This 0 − π transition, corresponding to a singlet-doublet transition, is then driven by the gate voltage or by the superconducting phase in the case of strong competition between the superconducting proximity effect and Kondo correlations. In a two-level quantum dot, such as a clean carbon nanotube, 0– π transitions exist as well but, because more cotunneling processes are allowed, are not necessarily associated to a magnetic state transition of the dot. In this proceeding, after a review of 0– π transitions in Josephson junctions, we present measurements of current-phase relation in a clean carbon nanotube quantum dot, in the single and two-level regimes. In the single level regime, close to orbital degeneracy and in a regime of strong competition between local electronic correlations and superconducting proximity effect, we find that the phase diagram of the phase-dependent transition is a universal characteristic of a discontinuous level-crossing quantum transition at zero temperature. In the case where the two levels are involved, the nanotube Josephson current exhibits a continuous 0 − π transition, independent of the superconducting phase, revealing a different physical mechanism of the transition.

The fluorescence intensities of CdSe/ZnS quantum dots on a silver nanowire and a gold-silver alloy nanotube with different molar ratios of gold and silver are investigated under excitation with different polarization angles. The ratio of the fluorescence intensity of perpendicular and parallel polarization excitations is measured to be 4.05 for a silver nanowire and decreases to 1.30, 1.10 and 1.07 for nanotube with Au:Ag molar ratios of 1:4.0, 1:2.5 and 1:1.5, respectively. The numerical simulation results show that the aforementioned experimental phenomena can be attributed to the variation in the distribution of the surface plasmon electromagnetic field under perpendicular polarized light excitation. The electromagnetic field is primarily distributed on the outer surface of the silver nanowire, while the field partially penetrates the interior of the silver nanotube and becomes completely concentrated at the interior of the gold nanotube. This research also found that the productivity and robustness of the chemical synthesis of the alloy nanotubes can be greatly improved by using a microwave reactor.

The present paper shows that a carbon nanotube filled with a mass chain behaves like a metamaterial which exhibits negative effective mass density within a certain range of frequencies. Unlike the known elastic metamaterials proposed in literature which are all based on artificial design of their microstructure, a filled carbon nanotube offers an already fabricated metamaterial which exhibits negative effective mass density and achieves desirable metamaterial dynamic properties even without any artificial design of microstructure. To demonstrate metamaterial dynamic behaviors of such a filled carbon nanotube, a simple continuum model is used to study flexural vibration of a hinged filled carbon nanotube. It is confirmed that the locally resonant bandgap of a filled carbon nanotube is determined by the mass of the inserted mass chain and the van der Waals interaction coefficient between the inserted mass chain and the surrounding carbon nanotube, and the expected metamaterial behavior can be demonstrated by remarkable vibration isolation. Actually, our results show clearly that when the applied excitation frequency is within the bandgap, forced vibration of a filled carbon nanotube is highly restricted to a narrow region around the site of the applied external excitation whose width is only a few times the outer diameter of the carbon nanotube.

The inception of the plasmonic laser or spaser (surface plasmon amplification by stimulated emission of radiation) concept in 2003 provides a solution for overcoming the diffraction limit of electromagnetic waves in miniaturization of traditional lasers into the nanoscale. From then on, many spaser designs have been proposed. However, all existing designs use closed resonators. In this work, we use cavity quantum electrodynamics analysis to theoretically demonstrate that it is possible to design an electric spaser with an open resonator or a closed resonator with much weak feedback in the extreme quantum limit in an all-carbon platform. A carbon nanotube quantum dot plays the role of a gain element, and Coulomb blockade is observed. Graphene nanoribbons are used as the resonator, and surface plasmon polariton field distribution with quantum electrodynamics features can be observed. From an engineering perspective, our work makes preparations for integrating spasers into nanocircuits and/or photodynamic therapy applications.

Two vertically stacked quantum dots that are electronically coupled, so called quantum dot molecules, are of great interest for the realization of solid state building blocks for quantum communication networks. We present a modified gradient approach to realize InAs quantum dot molecules with a low areal density so that single quantum dot molecules can be optically addressed. The individual quantum dot layers were prepared by solid source molecular beam epitaxy depositing InAs on GaAs(100). The bottom quantum dot layer has been grown without substrate rotation resulting in an In-gradient across the surface, which translated into a density gradient with low quantum dot density in a certain region of the wafer. For the top quantum dot layer, separated from the bottom quantum dot layer by a 6 nm thick GaAs barrier, various InAs amounts were deposited without an In-gradient. In spite of the absence of an In-gradient, a pronounced density gradient is observed for the top quantum dots. Even for an In-amount slightly below the critical thickness for a single dot layer, a density gradient in the top quantum dot layer, which seems to reproduce the density gradient in the bottom layer, is observed. For more or less In, respectively, deviations from this behavior occur. We suggest that the obvious influence of the bottom quantum dot layer on the growth of the top quantum dots is due to the strain field induced by the buried dots.

Achieving a high speed, unidirectional water flow through carbon nanotubes (CNTs) is a key factor in designing novel nanofluidic devices. In this study, utilizing molecular dynamics (MD) simulations, we propose a novel nanoscale water pump for directed water transportation using charged rotating CNTs. Two basic conditions for stable water flow, including thermodynamic nonequilibrium and spatial asymmetry, are provided by introducing partial charges on carbon atoms of the channel with asymmetric patterns and its rotation, respectively. We demonstrate that the performance of the water pump is proportional to the gradient of a linear charge distribution and angular velocity of the rotation. Our results indicate that, in a constant total charge, there is a linear relationship between water flux and charge difference of the nanotube ends. In addition there is a logarithmic relationship between the water flux and the nanotube angular velocity. In fact, there is no considerable flux when the nanotube is rotating...

In this paper, we engineered the physical properties of the isolated single-walled SiC nanotube (NT) such as (7,7). Through bundling the nanotube to tetragonal crystalline structure or creating the inherent point defects of both Si and C, the physical properties of the isolated single-walled SiC nanotube (7,7) will change notably. In use of the data calculated from the density functional theory using the Quantum SPRESSO Software, we studied the physical properties including the lattice constants, stability, band gap and the direction of translation point, charge density, bulk modulus, magnetization, symmetry number, radial buckling, effective mass and the velocity of carriers. All the data were compared with the pure isolated single-walled SiC nanotube.

First principles investigations are performed on understanding the spin-polarized transport in carbon nanotubes and carbon nanotube bundles consisting of ( 8 , 0 ) and ( 17 , 0 ) SWCNTs kept in vertical (out-of-plane) arrangement and contacted by two CrO2 Half-Metallic-Ferromagnetic (HMF) electrodes. On comparison of the results for all the structures, it is observed that carbon nanotube bundle consisting of ( 17 , 0 ) CNT offers high TMR ∼100% and the transport phenomenon is tunneling, since there are no transmission states near Fermi level. However, in individual ( 8 , 0 ) and ( 17 , 0 ) CNT the transport is not because of tunneling, since there are significant number of transmission states near Fermi level. High Magneto Resistance (MR) 96% and 99% is observed in individual ( 8 , 0 ) and ( 17 , 0 ) CNTs respectively. Both TMR and Spin Injection Efficiency η (Spin-Filtration) are higher in ( 17 , 0 ) carbon nanotube bundle structure, which is due to carbon nanotube bundle acting as a perfect barrier in vertical (out-of-plane) arrangement resulting in negligible spin-down current (I↓) in both Parallel Configuration (PC) and Antiparallel Configuration (APC).

In this paper, we discuss the transmission properties of weak probe laser field propagate through slab cavity with defect layer of carbon-nanotube quantum dot (CNT-QD) nanostructure. We show that due to spin-orbit coupling, the double electromagnetically induced transparency (EIT) windows appear and the giant Kerr nonlinearity of the intracavity medium can lead to manipulating of transmission coefficient of weak probe light. The thickness effect of defect layer medium has also been analyzed on transmission properties of probe laser field. Our proposed model may be useful for integrated photonics devices based on CNT-QD for applications in all-optical systems which require multiple EIT effect.

A model to simulate the atomistic properties of the field emission (FE) from a zigzag-single walled carbon nanotube (Z-SWCNT) is presented. By a modification of the self-energy in non-equilibrium Green's function (NEGF) method, we simulated the field emission current, considering the quantum transport of electrons within the CNT. The paper involves investigation on the effect of the n index of the ( n , 0 ) Z-SWCNT and the number of carbon dimers in the length direction as well as the anode–cathode separation on the FE current. Effect of additional gate voltage and substitutional impurities on the FE current is also studied. A comparison between the experimental data and simulation results are also included in the paper. The model can be used to consider different quantum effects of the atomistic emitter structure on the FE current.

Single-chirality ( n , m ) carbon nanotubes exhibit the same richness in physics of graphene including an additional phenomenon: the quantum confinement of electrons and phonons along the nanotubes circumference. Raman spectroscopy has been employed for almost 20 years to study carbon nanotubes, but the effect of the quantum confinement on the double-resonance (DR) Raman process in a single-chirality carbon nanotube was not yet understood. In this work, Raman spectra of the 2D band in enriched nanotube samples were measured using more than 70 laser excitation lines in the visible range (1.87–2.71 eV), and simulations of the D and 2D Raman spectra of single-chirality nanotubes were performed considering the quantum confinement along the nanotube circumference. We show that each single-chirality nanotube exhibits a series of non-dispersive D and 2D Raman peaks, which are not necessarily enhanced by resonances with optical transitions between van Hove singularities. Our results provide a complete explanation of the DR Raman spectrum, including the D and 2D bands, at the specificity level of a single-chirality nanotube, and will allow for the correct interpretation of the DR spectra of carbon nanotubes in samples containing a distribution of different ( n , m ) nanotube species.

Here we report a quantum mechanical molecular dynamics (QM/MD) study of a fusion process of an open-ended carbon nanotube on a graphene hole, which results in the formation of a so-called pillared graphene structure – a three-dimensional nanomaterial consisting entirely of sp2-carbons. The self-consistent-charge density-functional tight-binding potential was adopted in this study. Two different sizes of graphene holes with 12 or 24 central carbon atoms removed from a graphene flake, and a (6,6) carbon nanotube with a compatible diameter were adopted. Formations of 6–7–6/5–8–5 defect structures were found on the fusion border between tube and graphene hole. The 6–7–6 structure was found to bear less curvature-induced strain energy and therefore to be more stable and much easier to form than the 5–8–5 structure.

To study the charge transfer between cadmium selenide (CdSe) quantum dots (QDs) and double-walled nanotubes (DWNTs), various sizes of CdSe–ligand–DWNT structures are synthesized, and field-effect transistors from individual functionalized DWNTs rather than networks of the same are fabricated. From the electrical measurements, two distinct electron transfer mechanisms from the QD system to the nanotube are identified. By the formation of the CdSe–ligand–DWNT heterostructure, an effectively n-doped nanotube is created due to the smaller work function of CdSe as compared with that of the nanotube. In addition, once the QD–DWNT system is exposed to laser light, further electron transfer from the QD through the ligand, specifically, 4-mercaptophenol (MTH), to the nanotube occurs and a clear QD size-dependent tunneling process is observed. The detailed analysis of a large set of devices and the particular methodology employed here for the first time allowed for extracting a wavelength and quantum dot size-depen...

Carbon Nanotube (CNT) is the substitution of silicon material for designing of transistor device due to the shortcoming of silicon properties. In this study, 1.95 nm diameter of CNT is fabricated and characterized by analyzing of depletion width and I-V characteristics by realizing the p-n junction behavior. The p-n junction behavior of carbon nanotube is realized by applying self-consistency of the electrostatic potential and charge of CNT. The result shows that the variation of doping concentration happens in p-n junction due to the different cylindrical size of the carbon nanotube. Finally, the p-n junction current voltage transfer characteristics shows low current required for CNT device.

Photoelectrochemical splitting of water for chemical fuel production utilizing solar energy is regarded as an effective strategy to resolve crisis of energy. Self assembled and highly ordered titanium dioxide nanotube arrays offers considerable interest for hydrogen generation, since ordered structural design of titania nanotubes provides a unidirectional charge transfer channel for electron's transport. Here, we report the hydrogen generation by self assembled and vertically oriented carbon doped titania nanotube array. Carbon doped titania nanotube array photoelectrodes were synthesized by electrochemical method through the anodization of Titanium (Ti) foil in ethylene glycol bath consisting of 0.3 wt.% NH4F and 2 vol.% water by varying the anodization potential and time. The increase in length of carbon doped titania nanotube array increases the efficiency of photo conversion. However very higher lengths of carbon doped titania nanotube array results into decrease in the efficiency mainly due to recombination of charge carriers. The photocurrent density and hydrogen generation rate was found to be 4.0 mAcm−2 and 150 μmol cm−2 h−1 for carbon doped titania nanotube array of lengths 13.5 μm in 1 M NaOH electrolyte solution under 1.5AM solar irradiance of white light with illumination intensity of 100 mWcm−2.

We present a novel photovoltaic self-powered gas sensor based on a p-type single-walled carbon nanotube (SWNT) and n-type silicon (n-Si) heterojunction. The energy from visible light suffices to drive the device owing to a built-in electric field (BEF) induced by the differences between the Fermi levels of SWNTs and n-Si.

We have studied the effect of AuCl4 functionalization on the conductivity of carbon nanotube networks by first-principles electronic structure calculations. The functionalization results from treating carbon nanotube networks by dissolved AuCl3. Band structures and electronic transmission functions for single-walled semiconducting carbon nanotubes with physisorbed AuCl4 anions are computed using the density functional theory. The resulting p-type doping of nanotubes accompanied by a downshift of the Fermi level and balanced by negatively charged AuCl4 anions make the nanotubes metallic. Moreover, the influence of AuCl4 functionalization on the conductance of the junction between two semiconducting carbon nanotubes is considered. Increasing the AuCl4 coverage lowers the Fermi level rapidly until it is pinned by a van Hove singularity of the nanotube electronic structure. For these doping levels our calculations based on the density-functional nonequilibrium Green’s function method show a significant increa...

Three-dimensional polyaniline nanowire arrays are vertically grown on free-standing acidized carbon nanotube paper, and further carbonized to nitrogen doped carbon for supercapacitor electrodes. The three-dimensional porous structure of the as-prepared nitrogen doped carbon can increase the specific surface area and benefit ion transport into the interior of the electrode materials. Nitrogen doping can effectively improve the wettability of the carbon surface in the electrolyte and enhance the specific capacitance by a pseudocapacitive effect. Thus, free-standing nitrogen doped carbon nanowires on conductive carbon nanotube paper show excellent electrochemical performance as a supercapacitor electrode material. At a current density of 2 A g −1 , the specific capacitance reaches 210 F g −1 with 94% capacitance retention after 10,000 cycles.

Carbon nanotube thin film transistors (TFTs) with characteristics resembling those of TFTs constructed on amorphous silicon, low-temperature polycrystalline silicon and metal oxides were fabricated on (6,5) single chirality single-walled carbon nanotube (SWCNT) thin film deposited from electronically pure semiconducting (6,5) single chirality single-walled carbon nanotube (SWCNT) ink. This ink was extracted in industrial scale from raw SWCNTs produced using high pressure carbon monoxide conversion, and deposited on pretreated substrates to form uniform and consistent (6,5) HiPCO SWCNT thin film using solution process. The (6,5) HiPCO SWCNT thin films were characterized as pure semiconductor without metallic impurities showing classic nonlinear current-bias curves in Schottky-type diodes. Both N-type and P-type (6,5) HiPCO SWCNT TFTs were fabricated with femto Ampere off-current and ION/IOFF ratio of 108 by depositing SiNx and HfO2 dielectrics on the top of (6,5) HiPCO SWCNT thin films, respectively. The (6,5) HiPCO SWCNT inverter with voltage gain of 52 was also demonstrated by wire-bonding one P-type HiPCO SWCNT TFT to one N-type HiPCO SWCNT TFT.

A supercell of a nanotube formed by a carbon nanotube (CNT) and a silicon nanotube (SiNT) is established. The electronic structure and optical properties are implemented through the first-principles method based on the density functional theory (DFT) with the generalized gradient approximation (GGA). The calculated results show that (6, 6) - (6, 6) silicon/carbon nanotubes (Si/CNTs) presented a direct band gap of 0.093 eV, (4, 4) - (6, 6) silicon/carbon nanotubes presented a direct band gap of 0.563 eV. The top of valence band was fundamentally determined by the Si-3p states and C-2p states, and the bottom of conduction band was primarily occupied by the C-2p states and Si-3p states in the Si/CNTs. It was found that (6, 6) - (6, 6) Si/CNTs have smaller energy band gap and better conductivity. Besides, Si/CNTs have satisfactory absorption characteristics and luminous efficiency in ultraviolet band.

We performed numerical studies for the conductance of a heterojunction carbon nanotube quantum dot (QD) with an extra spin orbital quantum number and a conventional QD in which the electron state is determined only by the spin quantum number. Our computational approach took into account the spin-orbit interaction and the Coulomb repulsion both between electrons on a QD as well as between the QD electron and the contacts. We utilized an approach based on the Keldysh non-equilibrium Green's function formalism as well as the equation of motion technique. We focused on the case of a finite Coulombic on-site repulsion and considered two possible cases of applied voltage: spin bias and conventional bias. For the system of interest we obtained bias spectroscopy diagrams, i.e. contour charts showing dependence of conductivity on two variables - voltage and the energy level position in a QD - which can be controlled by the plunger gate voltage. The finite Coulombic repulsion splits the density of states into two distinct maxima with the energy separation between them controlled by that parameter. It was also shown that an increase of either the value of the on-site Coulomb repulsion in a QD or the parameter of the Coulomb repulsion between the electrons in the QD and the contacts leads to an overall shift of the density of electronic states dependence toward higher energy values. Presence of the QD-lead interaction yields formation of a new pair of peaks in the differential conductance dependence. We also show that existence of four quantum states in a QD leads to abrupt changes in the density of states. These results could be beneficial for potential applications in nanotube-based amperometric sensors.

A new fully carbon nanocomposite material is synthesized by the immersion of carbon nanotubes in a fullerene solution in carbon disulfide. The presence of a dense layer of fullerene molecules on the outer nanotube surface is demonstrated by TEM and XPS. Fullerenes are redistributed on the nanotube surface during a long-term action of an electron beam, which points to the existence of a molecular bond between a nanotube and fullerenes. Theoretical calculations show that the formation of a fullerene shell begins with the attachment of one C60 molecule to a defect on the nanotube surface.

Thin films of multi-walled carbon nanotubes forming random networks were produced by vacuum filtration method, and their broadband electromagnetic radiation transmittance spectra are presented. Thickness of the nanotube films was between 100 nm and 1 μm, and the transmission properties are demonstrated for the wavelength range from 300 nm to 400 μm. It is observed that transmittance is an increasing function of a radiation wavelength, and for the thickest films it almost saturates above 1 μm wavelength. To explain the experimental results in the ultraviolet–near infrared range, we employed effective medium theory (in the form of symmetric Bruggeman model) correlating properties of multi-walled carbon nanotubes with the effective dielectric function of a nanotube network. The optical properties of a single multi-walled carbon nanotube that were used for calculations were based on ordinary and extraordinary dielectric functions of bulk graphite. The proposed theoretical model has been successfully fitted to the experimental results. It has been also found that despite the fact that radiation undergoes multiple internal reflections at the film interfaces, the transmittance–thickness relation can be still described by exponential decay.

We present a simple fabrication process of heterojunction solar cells from single-walled carbon nanotubes (SWCNTs) and n -type silicon wafer. SWCNTs were synthesized from alcohol-catalytic chemical vapor deposition and were made into a film with transmittance of 70% by vacuum filtration. The mean diameter of the nanotube was about 1.1 nm. The patterned silicon substrate was prepared by a simple wet-etching process with hydrofuric acid utilizing a hand-made physical mask. The nanotube film was transferred onto the patterned silicon substrate. Power-conversion efficiency value of 4.3% with fill factor of 0.67 can be achieved. Abstract code: BO21.

In this work, a facile strategy of ultrasound-assisted successive ionic layer adsorption and reaction was successfully employed to modify TiO 2 nanotube arrays with BiFeO 3 nanoparticles. An enhanced positive surface photovoltage was observed with the obtained BiFeO 3 /TiO 2 nanotube arrays as well as a longer lifetime of charges separation state, as probed by transient photovoltage technique. The higher photocurrent density produced by BiFeO 3 /TiO 2 nanotube arrays further indicated that BiFeO 3 nanoparticles contributed to photo conversion and promoted the generation of photo-induced charge carriers over TiO 2 nanotube arrays. Besides, the prepared BiFeO 3 /TiO 2 electrode exhibited a much enhanced photoelectrocatalytic performance in removing methyl blue compared with bare TiO 2 nanotube arrays.

The lithiation mechanisms that occur in silicon nanotube lithium-ion battery electrodes are not well understood at the atomic level. In this study, first-principles calculations were carried out to investigate the mechanism responsible for the insertion of lithium in armchair and zigzag nanotubes. The size dependence of the formation energy and the Young’s modulus was investigated for the placement of a single Li atom. Our simulations showed that the elastic softening of a zigzag nanotube will occur when a single Li atom was placed, and that the lithiated configuration will transform from a crystalline structure to an amorphous structure with increasing Li concentration for both armchair and zigzag nanotubes. Formation energy and voltage analyses also demonstrated that zigzag nanotubes exhibit a much steeper descending trend compared with armchair nanotubes. It was found that, under uniaxial tension, the corresponding fracture strength of a silicon nanotube will decrease with increasing Li concentration, and that the ductility of such a nanotube will be improved greatly with increasing Li concentration, meaning that plastic deformation will occur relatively easily. This understanding of the lithiation mechanisms will provide useful guidelines for the designing of silicon nanotube electrodes in lithium-ion batteries.

The influence of point defect on the electronic and spatial structure of carbon nanotubes (8.0) have been studied depending on the placement vacancies in the structure of nanotubes. On the basis of quantum-chemical calculations and using semi-empirical and ab initio approaches the maps of the distribution of molecular electrostatic potential were builds in the planes which are perpendicular to the main axis of the nanotubes. It is shown that defects such as vacancy, are placed outside the first hexagonal carbon belt no effect on the topology of the distribution of molecular electrostatic potential in the vicinity of the entrance to the carbon nanotube. Instead, reactivity of port’s atoms such nanotubes may determinated point defects of the vacancy type to be placed in first hexagonal belt. Keywords: carbon nanotubes, molecular electrostatic potential, point defect, quantum-chemical calculations.

In this paper we report the effect of external magnetic field and core radius on the excited quantum state energies of an electron confined in the core of a double walled carbon nanotube. The goal is accomplished by using Wentzel–Kramers–Brillioun (WKB) approximation method within the effective mass approximation and confinement potential. All numerical analysis were carried out in a strong confinement regime. The results show that the electron energy increases with the increase in external magnetic field at a given core radii. The electron energy is also found to increase as the core radius of the CNT decreases and for core radius a > 5 n m the energy becomes almost zero. The effect of magnetic field on the excited state energies of the confined electron is more evident for smaller core radius a [1] .

The sensitivity of shot noise to the interplay between Kondo correlations and superconductivity is investigated in a carbon nanotube quantum dot connected to superconducting electrodes. Depending on the gate voltage, the SU(2) and SU(4) Kondo unitary regimes can be clearly identified. We observe enhancement of the shot noise via the Fano factor in the superconducting state. Its divergence at low bias voltage, which is more pronounced in the SU(4) regime than in the SU(2) one, is larger than what is expected from proliferation of multiple Andreev reflections predicted by the existing theories. Our result suggests that the Kondo effect is responsible for this strong enhancement.

Theoretical investigations using density functional theory have been carried out to examine the interactions between armchair 4,4 gallium nitride nanotube (GaNNT) with NH 3 (NO 2 ) toxic gas molecule. Binding energy of NH 3 and NO 2 on nanotube surface lies within strong physisorption range. Mulliken, NBO and PDOS analysis suggests significant amount of charge transfer between molecular and nanotube fragments. The Transmission spectra evaluated through non equilibrium Green's function (NEGF) at different biasing voltage, across nanotubes are used to analyse the current voltage relationship. Further, the sensitivity of nanotube for NH 3 and NO 2 adsorption are validated through respective reduction and enhancement in conductivity.