Metallic Carbon Nanotubes Research Articles

Neural Stimulation In Vitro and In Vivo by Photoacoustic Nanotransducers

Summary Neuromodulation is an invaluable approach for the study of neural circuits and clinical treatment of neurological diseases. Here, we report semiconducting polymer nanoparticles based photoacoustic nanotransducers (PANs) for neural stimulation in vitro and in vivo. Our PANs strongly absorb the nanosecond pulsed laser in the near-infrared second window (NIR-II) and generate localized acoustic waves. PANs are shown to be surface modified and selectively bind onto neurons. PAN-mediated activation of primary neurons in vitro is achieved with ten 3-ns laser pulses at 1,030 nm over a 3-ms duration. In vivo neural modulation of mouse brain activities and motor activities is demonstrated by PANs directly injected into brain cortex. With submillimeter spatial resolution and negligible heat deposition, PAN stimulation is a new non-genetic method for precise control of neuronal activities, opening up potentials in non-invasive brain modulation.

A tight-binding model of a carbon nanotube interacting with TiO2 rutile (110) surface

The electronic and the spatial structure of an armchair carbon nanotube (CNT) deposited on a (110) surface of titanium dioxide (rutile) is studied with a help of the density functional theory (DFT) and using a tight binding model. It is shown that an electrostatic potential due to an ionic surface of the rutile crystal may induce an energy gap at the Fermi level in the electronic structure of the nominally metallic CNT. The gap may reach a magnitude 0.02 eV depending on a symmetry of an arrangement of the CNT at the surface. The electron site occupations obtained from the DFT computations are used to deduce an analytic form of the external potential applied in the model. It is shown that the potential induces a substantial lattice distortion which contributes to an enhancement of the energy gap. The electronic structure obtained from the calculation based on the model is in a good quantitative agreement with the DFT results.

Propagation of an electromagnetic wave based on a continuum model of kp-type in an almost circular bundle of packed metal nanotubes

A continuum model of kp-type for the approximate calculation of the characteristics of electromagnetic waves propagating in an almost circular (azimuthally symmetric), closely packed bundle of parallel, identical, and metal carbon nanotubes (CNTs) yields results in reasonably good agreement with the equivalent-multishell approach and with a many-body technique, for infinitely long bundles when the number of CNTs is moderately high. The slow-wave coefficients for azimuthally symmetric guided waves increase with the number of metallic CNTs in the bundle, tending for these bundles to unity, which is characteristic of macroscopic metallic wires. The existence of an azimuthally asymmetric guided wave at low frequencies in a bundle of a large number of finite-length CNTs stands in contrast to the characteristics of guided-wave propagation in a single CNT. A continuum model of kp-type yields the polarizability scalar and the antenna efficiency of a bundle of finite-length CNTs in the long-wavelength regime over a wide frequency range spanning the terahertz and the near-infrared regimes. Edge effects give rise to geometric resonances in such bundles. • The slow-wave coefficients for azimuthally symmetric directed waves. • The characteristics of electromagnetic waves propagating in an almost circular, bundle of carbon nanotubes (CNTs). • Contrast of characteristics of a guided-wave at low frequencies in a bundle of a large number of CNTs and in single CNT.

Wide application feasibility report on graphene

In 2005, Dennard scaling, which had hitherto delivered the performance enhancement of integrated circuit (IC) chips, completely collapsed. Hence, the need for new materials and material research emerged. Two-dimensional (2D) graphene emerged as a device material, and two-dimensional hexagonal boron nitride (BN) has emerged as the ideal substrate material. For the ongoing digital revolution to be sustained, petabit/second and exabit/second transmission links are needed. Graphene technology has matured to the level where functional graphene ICs on the wafer scale can be implemented, such as frequency multipliers, high-frequency graphene analog amplifiers and quaternary digital modulation circuits. These functional graphene ICs can be fabricated at the wafer scale because of the development of the imperfection-immune paradigm called very-large-scale-integration-compatible metallic carbon (C) nanotube removal technique. To harness the exotic properties of graphene nanomaterials in real-life applications at the macro scale, three-dimensional graphene-based monoliths have been developed, which could become the basis of future batteries and solar cells. Terahertz graphene chips will herald peta- and exabit rate optical fiber communication, which is the answer to the large data workload of the Internet. Graphene is emerging as an important thermoelectric material that is capable of converting temperature difference into electric current.

Nanomechanics driven by Andreev tunneling

We predict and analyze mechanical instability and corresponding self-sustained mechanical oscillations occurring in a nanoelectromechanical system composed of a metallic carbon nanotube (CNT) suspended between two superconducting leads and coupled to a scanning tunneling microscope (STM) tip. We show that such phenomena are realized in the presence of both the coherent Andreev tunneling between the CNT and superconducting leads, and an incoherent single electron tunneling between the voltage biased STM tip and CNT. Treating the CNT as a single-level quantum dot, we demonstrate that the mechanical instability is controlled by the Josephson phase difference, relative position of the electron energy level, and the direction of the charge flow. It is found numerically that the emergence of the self-sustained oscillations leads to a substantial suppression of DC electric current.

Preparation and Thermoelectric Properties of Semiconducting Single-Walled Carbon Nanotubes/Regioregular Poly(3-dodecylthiophene) Composite Films.

Single-walled carbon nanotubes (SWNTs) have been widely used as leading additives for improving the thermoelectric properties of organic materials, due to their unique structure and excellent electronic transport properties. However, the as-synthesized SWNTs are mixtures (mix-SWNT) of semiconducting (sc-SWNT) and metallic (met-SWNT) carbon nanotubes. The significantly different surface character and transport behavior of sc-SWNT and met-SWNT frequently raise the difficulty of modifying microstructures, and tuning transport properties of SWNTs/organic composites, when using mix-SWNTs as dispersion phase. Herein, we prepared high quality sc-SWNTs/rr-P3DDT composite film by presorting pure sc-SWNT from the raw mix-SWNTs using regioregular poly(3-dodecylthiophene) (rr-P3DDT). Both the smoothness and compactness of sc-SWNTs/rr-P3DDT are great improved, as compared with the mix-SWNTs/rr-P3DDT films, and the sc-SWNTs are well-dispersed and uniformly wrapped by rr-P3DDT with diameter less than 50 nm. The significantly enhanced Seebeck coefficients and power factors are obtained in the sc-SWNT/rr-P3DDT samples. As the result, the maximum power factor of 60 μW/mK2 in 50 wt% sc-SWNTs sample is 70% higher than that of mix-SWNTs/P3DDT sample. This work reveals the effectiveness of pure semiconductor SWNTs as fillers to optimize the thermoelectric properties of CNT/polymer nano-composites.

Transport Properties of Ordered and Disordered Doped Metallic Nanotubes

We have studied the transport properties of ordered and disordered doped metallic nanotubes. We have presented these properties in periodic chemically metallic nitrogen doped metallic nanotubes. Transport properties with long range correlation have been studied using the Green’s function formalism in the frame work of the tight binding approach with effective parameters. Resonant conduction behaviour and ballistic transport have been demonstrated for particular positions of the dopant. These doping patterns have been shown to preserve the Bloach like transport properties and then to avoid Anderson localisation. The conductance response was almost changed because one of the two conductance channels remains true for both armchair and chiral nanotubes. These result reproduce the electronic properties of periodic nitrogen doped graphene. The present result has been drawn for specific chemical substitution of carbon atoms by nitrogen. These remain qualitatively valid for other local modifications of the nanotube by other chemical species by covalent or noncovalent functionalization. The energy of the quasi bound state depend on the specific local modification. We have shown that both axial and screw periodicities gave rise to such a behaviour and that specific disorder preserve their ballistic transport in doped metallic carbon nanotube.

Decay, amplification and absorption of initial terahertz pulse in resonant two-level medium based on noninteracting array of zigzag nanotubes and armchair nanoribbons

Theoretical investigation and computer simulation of the evolution of terahertz (THz) radiation in a two-level resonance gain medium was carried out on the basis of Maxwell–Bloch equations, using the slowly varying amplitude approximation. The gain medium is based on a system of noninteracting parallel-oriented metallic carbon nanotubes and nanoribbons. Considering the Maxwell–Garnett theory (MGT), the effective dielectric function (EDF) of the medium was obtained. Due to the large nanotube dipole moment (or large value of oscillator strength) not only THz radiation occurs, but also a totality of periodic pulses generation. Results of simulation totally coincide with the theoretical ones. The equation for the phase by analogy with the self-induced transparency (SIT), taking into account the dissipative processes, was obtained. The obtained equation describes a mathematical pendulum, where friction force is proportional to the velocity and directed to the opposite of particle movement. The friction leads to the fact that the pendulum makes a full rotation around the axis or decays, depending on the absorption properties of a gain medium. It was shown that at the certain properties of a gain medium, the equation coincides with the well-known Sine-Gordon equation. It was obtained, that at the initial pumping [Formula: see text] m[Formula: see text] and at the volume fraction of nanoparticles about 10[Formula: see text], the stationary value of radiation energy in a resonator is about 1 J/m3.

LCAO-TDDFT-k-ω: spectroscopy in the optical limit

Understanding, optimizing, and controlling the optical absorption process, exciton gemination, and electron–hole separation and conduction in low dimensional systems is a fundamental problem in materials science. However, robust and efficient methods capable of modelling the optical absorbance of low dimensional macromolecular systems and providing physical insight into the processes involved have remained elusive. We employ a highly efficient linear combination of atomic orbitals (LCAOs) representation of the Kohn–Sham (KS) orbitals within time dependent density functional theory (TDDFT) in the reciprocal space (k) and frequency (ω) domains, as implemented within our LCAO-TDDFT-k-ω code, applying either a priori or a posteriori the derivative discontinuity correction of the exchange functional Δx to the KS eigenenergies as a scissors operator. In so doing we are able to provide a semi-quantitative description of the photoabsorption cross section, conductivity, and dielectric function for prototypical 0D, 1D, 2D, and 3D systems within the optical limit (‖q‖ → 0+) as compared to both available measurements and from solving the Bethe–Salpeter equation with quasiparticle G0W0 eigenvalues (G0W0-BSE). Specifically, we consider 0D fullerene (C60), 1D metallic (10, 0) and semiconducting (10, 10) single-walled carbon nanotubes, 2D graphene (Gr) and phosphorene (Pn), and 3D rutile (R-TiO2) and anatase (A-TiO2). For each system, we also employ the spatially and energetically resolved electron–hole spectral density to provide direct physical insight into the nature of their optical excitations. These results demonstrate the reliability, applicability, efficiency, and robustness of our LCAO-TDDFT-k-ω code, and open the pathway to the computational design of macromolecular systems for optoelectronic, photovoltaic, and photocatalytic applications in silico.

High-field electromagnetic radiation converts carbon nanotubes to nanoribbons embedded with carbon nanocrystals

One-dimensional carbon nanomaterials such as carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) are promising for future applications in nanoelectronics and nanophotonics due to their unique characteristics such as topological edge states, chirality, and quantum confinement. Despite the chemical unzipping method of producing GNRs from CNTs, using energetic photons to control light–matter interaction and shape materials at the nanoscale has great promise, especially for chemical-free and on-demand manufacturing. Here, we exploit the high electromagnetic field from a Ti:Sapphire femtosecond laser to interact with CNTs, causing ultrafast energy transfer between the photons and the nanotubes and converting them to GNRs and carbon nanocrystals. Probed with scattering-type scanning near-field optical microscopy, the nanoribbons are identified as semiconducting and/or insulating, a strikingly different electronic phase compared with the original metallic CNTs. Our method of employing high-field and nonequilibrium processes with an ultrafast laser to alter the shape and transform the electronic properties is scalable, does not necessitate high-temperature processes, and is highly spatially controllable—conditions that pave the way for manufacturing nanoscale hybrid materials and devices.

Monolithic 3D Carbon Nanotube Memory for Enhanced Yield and Integration Density

Carbon nanotube field effect transistor (CN-MOSFET) is attractive for the realization of future monolithic three-dimensional (M3D) memory circuits with ultra-high integration density, capacity, efficiency, and speed. However, the yield of each vertically-stacked active layer can be significantly degraded by the presence of metallic carbon nanotubes (m-CNs) caused by process imperfections. The potential integration density benefits of M3D circuits also may not be fully realized by the large area skews between different layers within standard cells. In this paper, ultra-high density and robust M3D static random-access memory (SRAM) cells are proposed for tolerance to the removal of m-CNs. By minimizing the skew and area of each device layer, the 16Kibit memory arrays with the proposed SRAM cells enhance the integration density by up to 82.92% as compared to the carbon-based traditional 2D and previously published M3D memory arrays. While achieving high functional yield and maintaining robust read/write operations, the proposed SRAM circuits enhance the overall electrical quality by up to 27.41x as compared to the alternative 2D and M3D memory arrays.

High current density electron wind forces in metallic graphene nanoribbons

In this study electric current-induced wind forces on a unit lattice of a 10-dimer zigzag graphene nanoribbon (ZGNR) are calculated under different magnitudes of electric field and temperatures. Wind forces are calculated using a semi-classical method where quantum mechanics is integrated into ensemble Monte Carlo simulations by considering energy and momentum conservation in both the transverse and longitudinal directions of graphene nanoribbon (GNR) during the electron-phonon scattering process. First order perturbation theory using the deformation potential approximation was used in the calculation of the scattering rates. The results show that under the same electric field, Joule heating power in a 10-dimer ZGNR is around 3 magnitudes higher than that in metallic single-walled carbon nanotubes and the wind forces are 1 magnitude higher. According to the calculated results, the wind force in the 10-dimer ZNGR is in the order of 0.0073 eV Å−1 under 20 kV at 300 K and it is much lower than the fracture strength of ZGNR based on the results of molecular dynamics simulations. Thus the failure of GNR under an electric current is considered to be mainly due to the Joule heating.

Noncontact Spin Pumping by Microwave Evanescent Fields.

The angular momentum of evanescent light fields has been studied in nano-optics and plasmonics but not in the microwave regime. Here we predict noncontact pumping of electron spin currents in conductors by the evanescent stray fields of excited magnetic nanostructures. The coherent transfer of the photon to the electron spin is proportional to the g factor, which is large in narrow gap semiconductors and surface states of topological insulators. The spin pumping current is chiral when the spin susceptibility displays singularities that indicate collective states. However, 1D systems with linear dispersion at the Fermi energy, such as metallic carbon nanotubes, are an exception since spin pumping is chiral even without interactions.

The kinetic inductance of single-walled carbon nanotube metal type

The results of theoretical studies of the kinetic inductance Lk metallic single-walled carbon nanotube type, taking into account the electron-electron interaction in the approximation of a right circular cylinder are presented. The system under consideration is a cylindrically symmetric potential well with a final height of the wall. As part of the response of the theory of two-dimensional electron gas in the external electromagnetic disturbance obtained in the form of kinetic inductance depending on the nanotube diameter, frequency and intensity of the radiation. Established that Lk value increases with increasing frequency, and decreases with increasing radiation intensity.

A unified electrical model based on experimental data to describe electrical transport in carbon nanotube-based materials

Understanding the electrical transport in carbon nanotube (CNT) materials is one key to reach very high electrical conductivities. All CNT material resistivity (?? (T)) as function of the temperature are fully apprehended by their reduced activation $$W(T) = \frac{{d\ln (\rho )}}{{d\ln (T)}}$$ curves. Up to now, no model accurately fits W(T) curves, thus preventing from precisely describing the CNT material electrical transport. We present a new electrical transport model that perfectly fits all W(T) curves found in the literature and in our own data. CNT material resistivities are modeled by ??(T)= ??0(T????? + M(1 + ??T??T2)). Our model has few enough parameters (??, M, ??, ??) to relate them to the CNT physics. Below 70 K, we experimentally show that CNT material resistivity follows the Luttinger Liquid theory justifying the T????? term in our model. Above 70 K, the polynomial part becomes dominant and depends on the two different CNT fabrication techniques which lead to two very different yarn structures. For yarns made from floating catalyst chemical vapor deposition CNTs, the polynomial is explained by the percolation of metallic CNT walls. Whereas, the polynomial of yarns spun from CNT arrays is explained by the electrical transport in CNT bundles which are the basic building blocks of this type of yarns.

Free-standing ZnO nanorod arrays modified with single-walled carbon nanotubes for betavoltaics and photovoltaics

A full-duplex radiant energy converter based on both betavoltaic and photovoltaic effects in an easy-to-implement way is an attractive alternative for the autonomous wireless sensor microsystem. Here, we report a novel beta/photovoltaic cell based on free-standing ZnO nanorod arrays (ZNRAs) modified with metallic single-walled carbon nanotubes (m-SWCNTs), using radioisotope 63Ni as beta-emitting source. The ZNRAs were grown on Al-doped ZnO (AZO) conductive glass using hydrothermal method. The optimum length and diameter of ZnO nanorods were determined by Monte Carlo simulation for beta energy deposition in ZNRAs. The m-SWCNTs were anchored into the ZNRAs to form a three-dimensional (3-D) Schottky junction structure for effectively separating the beta/photo-excited electron-hole pairs. Experimentally, the betavoltaic and photovoltaic effects were confirmed through the I–V measurements of beta/photovoltaic cells under beta/UV/Vis irradiations, respectively. It is suggested that the m-SWCNTs play key role for the enhancement of beta/photovoltaic performance through the formation of extensive 3-D Schottky junction, the conductive network for hole transport, and the surface plasmon resonance exciton absorption for visible light.

(Invited) Synthesis of Monochiral CNTs

The conductivity of CNT yarn or wire depends on chirality, alignment, doping, lack of contamination, residual amorphous carbon, and twist angle. All these factors must be well controlled to obtain good conductivity. This talk addresses one of these issues, the synthesis of all metallic tubes, and as it happens these tend to be of predominately the same chirality. The synthesis and characterization of monochiral tubes are difficult due to variable bundle strain and the consequent shift in the Radial Breathing Mode Peaks. In this presentation, we present a method for compensating for this strain phenomenon that utilizes the known strain-free position of the G band. We also present TEM data of SWCNT metallic carbon nanotube material as is, and with amorphous carbon removed. The latter is important to analytically determine the crystal structure and diameter of the tubes. We found that: (1) the tubes are remarkably consistent in diameter, (2) the diameters ranged from about 1.2 to 2.5 nm but most bundles were about 1.7nm consistent with our TEM and Raman findings, and finally (3) We found that all the tubes resided in bundles that vary in size. We used both acetylacetonate and benzyl alcohol as carbon sources. We showed by TEM the bundles are monochiral.

Subthermionic field-effect transistors with sub-5 nm gate lengths based on van der Waals ferroelectric heterostructures

Overcoming the sub-5 nm gate length limit and decreasing the power dissipation are two main objects in the electronics research field. Besides advanced engineering techniques, considering new material systems may be helpful. Here, we demonstrate two-dimensional (2D) subthermionic field-effect transistors (FETs) with sub-5 nm gate lengths based on ferroelectric (FE) van der Waals heterostructures (vdWHs). The FE vdWHs are composed of graphene, MoS2, and CuInP2S6 acting as 2D contacts, channels, and ferroelectric dielectric layers, respectively. We first show that the as-fabricated long-channel device exhibits nearly hysteresis-free subthermionic switching over three orders of magnitude of drain current at room temperature. Further, we fabricate short-channel subthermionic FETs using metallic carbon nanotubes as effective gate terminals. A typical device shows subthermionic switching over five-to-six orders of magnitude of drain current with a minimum subthreshold swing of 6.1 mV/dec at room temperature. Our results indicate that 2D materials system is promising for advanced highly-integrated energy-efficient electronic devices.

Structural effects on carrier doping in carbon nanotube thin-film transistors

Based on density functional theory, we studied the electronic properties of carbon nanotube (CNT) thin films under an external electric field. The carrier accumulation resulting from an electric field depends slightly on the CNT species that form the thin films and their arrangement with respect to the electrode. Although most of the carriers are accumulated in the CNTs located at the electrode side, wave function hybridization between semiconducting CNTs slightly enhances the carrier penetration into the opposite CNT layer. Metallic CNTs strongly depress or enhance the carrier penetration for the thin films when they are located at the electrode side or not, respectively.

Metallic Carbon Nanotube Nanocavities as Ultracompact and Low-loss Fabry-Perot Plasmonic Resonators.

Plasmonic resonators enable deep subwavelength manipulation of light matter interactions and have been intensively studied both in fundamental physics as well as for potential technological applications. While various metallic nanostructures have been proposed as plasmonic resonators, their performances are rather limited at mid- and far-infrared wavelengths. Recently, highly confined and low-loss Luttinger liquid plasmons in metallic single-walled carbon nanotubes (SWNTs) have been observed at infrared wavelengths. Here, we tailor metallic SWNTs into ultraclean nanocavities by advanced scanning probe lithography and investigate plasmon modes in these individual nanocavities by infrared nanoimaging. The dependence of mode evolutions on cavity length and excitation wavelength can be captured by a Fabry-Perot resonator model of a plasmon nanowaveguide terminated by highly reflective ends. Plasmonic resonators based on SWNT nanocavities approach the ultimate plasmon confinement limit and open the door to the strong light-matter coupling regime, which may enable various nanophotonic applications.