Ab initio calculations of electron affinity and ionization potential of carbon nanotubes

Electronic Structure of Pentagonal Carbon Nanocones: An ab Initio Study

In this work, we investigate the electronic structure of a particular class of carbon nanocones having a pentagonal tip and C5v symmetry. The ground-state nature of the wave function for these structures can be predicted by the recently proposed generalized Hückel rule that extends the original Hückel rule for annulenes to this class of carbon nanocones. In particular, the structures here considered can be classified as closed-shell or anionic/cationic closed-shells, depending on the geometric characteristics of the cone. The goal of this work is to assess the relationship between the electronic configuration of these carbon nanocones and their ability to gain or lose an electron as well as their adsorption capability. For this, the geometry of these structures in the neutral or ionic forms, as well as systems containing either one lithium or fluorine atom, was optimized at the DFT/B3LYP level. It was found that the electron affinity, ionization potential, and the Li or F adsorption energy present an intimate connection to the ground-state wave function character predicted by the generalized Hückel rule. In fact, a peculiar oscillatory energy behavior was discovered, in which the electron affinity, ionization energy, and adsorption energies oscillate with an increase in the nanocone size. The reasoning behind this is that if the anion is closed-shell, then the neutral nanocone will turn out to be a good electron acceptor, increasing the electron affinity and lithium adsorption energy. On the other hand, in the case of a closed-shell cation, this means that the neutral nanocone will easily lose an electron, leading to a smaller ionization potential and higher fluorine adsorption energy.

Additive Influence of Top Metal Contact and Alumina Deposition on the Threshold Voltage of Suspended Carbon Nanotube Field-Effect Transistors

One-dimensional nanostructures such as carbon nanotubes offer excellent properties useful for applications in gas sensors, piezoresistive devices, and radio frequency resonators. Considering their nanoscale form factor, carbon nanotubes (CNTs) are highly sensitive to surface adsorbents. This study presents the fabrication flow of CNT devices with extended passivated areas around electrical contacts between the CNT and source and drain electrodes. These types of structures could help in understanding the intrinsic CNT response by eliminating the analyte impact on the Schottky barrier regions of the CNT field-effect transistors (CNTFETs). The influence of multiple processing conditions on the electronic properties of CNTFETs with a suspended individual CNT used as the CNTFET channel is presented. Our findings show a threshold voltage shift in CNT ISD-Vg characteristics following the metal deposition and alumina atomic layer deposition.

Electrical Properties of Iodine-Doped Cu/f-CNT Coated Aluminum Wires by Electrophoresis with Copper Sulfate Solution

This work investigated the effects of iodine on copper/functionalized carbon nanotubes (Cu/f-CNT) that were used in the coating of 1350 Aluminum Alloy wires, using the process of electrophoretic exposure with a solution of copper sulfate and iodine, under an electrical current of 1.2 A and a voltage of 10 V. The Al@Cu/f-CNT was characterized by Scanning Electron Microscopy in Secondary Electron mode, X-ray Diffraction and Raman spectroscopy, in addition to electrical measurements, at room temperature and under heating, via kelvin bridge. The results showed an increase of approximately 18% in the electrical conductivity of the IACS compared to the standard aluminum conductor, due to the iodine doping of the outer walls of the f-CNT, causing an expansion between the layers, and reflecting the increase in the conduction channels. This method of electrodeposition of Cu/f-CNT on the surface of metallic wires shows promise for the production of nanostructured cables with high ampacity, lightness and high performance, for application in power transmission lines.

Impact of As-Prepared and Purifıed Multi-Walled Carbon Nanotubeson the Liquid-Phase Aerobic Oxidatıon of Hydrocarbons

The article presents simple kinetic approaches to study the effect of multi-walled carbon nanotubes (MWCNTs) additives on the aerobic oxidation of hydrocarbons and to propose real acceptable mechanisms of the process. The aerobic liquid phase low-temperature oxidation of ethylbenzene conducted in the presence of multi-walled carbon nanotubes has been used as a model pattern. Kinetic analysis established the catalytic action associated with the presence of the iron compounds in inner channels of MWCNTs. These compounds are identified as ferric carbides provoking decomposition of the ethylbenzene hydroperoxide and thereby suppressing the competitive route of alky-peroxide radicals addition to the nanocarbon cage. Thus the reaction finally proceeds in the autocatalytic mode.Contradictory conclusions on the effect of CNTs on the oxidation chain processes existing in the literature are associated with the lack of control over nature and content of metal impurities in channels of nanotubes.

The Effects of Hydrogen Annealing on Carbon Nanotube Field-Effect Transistors

We have systematically investigated the effects of hydrogen annealing on Ni- and Al-contacted carbon nanotube field-effect transistors (CNTFETs), whose work functions have not been affected by hydrogen annealing. Measured results show that the electronic properties of single-walled carbon nanotubes are modified by hydrogen adsorption. The Ni-contacted CNTFETs, which initially showed metallic behavior, changed their p-FET behavior with a high on-current over 10 µA after hydrogen annealing. The on-current of the as-made p-FETs is much improved after hydrogen annealing. The Al-contacted CNTFETs, which initially showed metallic behavior, showed unipolar p-FET behavior after hydrogen annealing. We analyzed the energy band diagrams of the CNTFETs to explain experimental results, finding that the electron affinity and the bandgap of single-walled carbon nanotubes changed after hydrogen annealing. These results are consistent with previously reported ab initio calculations.

Probing Laser Plasma Dynamics Using High-Order Harmonics Generation in Carbon-Containing Nanomaterials

We study high-order harmonics generation from plasmas generated from graphite, fullerenes, carbon nanotubes, carbon nanofibers, diamond nanoparticles, and graphene. Our approach utilizes a heating nanosecond laser pulse to produce plasmas that serve as the media for high harmonic generation from a subsequent driven femtosecond laser pulse. High harmonics are generated at different time delays following the plasma formation, which allows us to analyze the spreading of species with different masses. We analyze the harmonic yields from species of single carbon atom, 60 atoms (fullerene), 106 atoms (diamond nanoparticles), 109 atoms (CNTs and CNFs), and even much larger species of graphene sheets. The harmonic yields are analyzed in the range of 100 ns–1 ms delays. The harmonic yields were significantly higher within the 200 ns–0.5 µs range, but no harmonic is observed between 10 µs–1 ms. Our observations show that, at the optimal ablation of atoms and clusters, the laser-induced plasmas produced on the surfaces of different carbon-contained species spread out from targets with the comparable velocities.

Carbon and germanium nanocages as anode electrodes in sodium-ion and potassium-ion batteries

Here, the potential of C₃₆, C₄₈, and Ge₄₈ nanocages as anodes of Na-ion battery (IB) and K-IB are investigated by DFT/M06-2X and DFT/B3LYP in gas and solvent. The E_Formation and E_Gap of C₃₆, C₄₈, and Ge₄₈ nanocages are investigated by theoretical methods. The vertical and adiabatic EA and IP of C₃₆, C₄₈, and Ge₄₈ nanocages are examined in gas and solvent. The E_ad of Na⁺ and K⁺ on inner and outer positions of C₃₆, C₄₈, and Ge₄₈ nanocages are investigated. The V_cell and C_Theory of C₃₆, C₄₈, and Ge₄₈ as anodes of batteries are investigated. The results of this paper proposed the nano materials (C₄₈ and Ge₄₈ nanocage) as anodes of Na-IB and K-IB with higher C_Theory and V_cell than graphene nanosheet.

Langmuir-Scheaffer Technique as a Method for Controlled Alignment of 1D Materials

A widely applicable method for aligning 1D materials, and in particular carbon nanotubes (CNTs), independent of their preparation would be very useful as the growth methods for these materials are substance-specific. Langmuir-Schaefer (LS) deposition could be such an approach for alignment, as it aligns a large number of 1D materials independently of the desired substrate. However, the mechanism and required conditions for alignment of 1D nanomaterials in a Langmuir trough are still unclear. Here we show, relying on numerical simulations of the Langmuir film compression, that the LS method is a powerful tool to achieve maximal alignment of 1D material in a controllable manner. In particular, 1D materials terminated with a suitable surfactant can align only if the velocity induced by the attraction between individual 1D entities is low enough relative to the flow speed. To validate this model, we achieved an efficient LS alignment of single-walled carbon nanotubes covered with a suitable surfactant relying on the numerical simulations. In situ polarized Raman microspectroscopy during the compression of Langmuir film revealed good quantitative agreement between the numerical simulations and the experiment. This suggests the applicability of the LS technique as a versatile method for the controlled alignment of 1D materials.

Multilayer graphene nanobelts on SWCNT films for high current interconnect applications

In this work we propose multilayer graphene (MLG) nanobelts for high current interconnections with single wall carbon nanotubes (SWCNT) and compare these with metal contacts. MLG contacts were directly printed on the SWCNT, without any additional metal parts, demonstrating the possibility to use these materials as interconnections in microelectronics. Different work function metals Al, Ti and Pd were probed for the lowest contact resistance with the SWCNT. Ti contacts demonstrated the best results among the metals owing to its work function being closest to the SWCNT and therefore giving the lowest Schottky barrier. Even though Ti contacts show the lowest contact resistance, the current density for MLG contacts was higher, giving the best results for high current interconnection applications. Moreover, MLG contacts show a stable and repeatable resistance decrease under high current conditions. Heat treatment of the MLG and metal contacts was completed in vacuum, in order to further reduce the contact resistance and optimal heat treatment conditions were found at 600 °C.

GaN nanowire field emitters with the adsorption of Pt nanoparticles

We report Pt NP coated GaN NWs through CVD method and the fabrication of their field emitters.

Computational Studies on the Encapsulation of 1,4-Dihydropyridine Derivatives into CNT(10,10)

Semiempirical and density functional theory (DFT) methods were herein used to study the encapsulation process of 1,4-dihydropyridine (DHP) derivatives into (10,10) armchair carbon nanotube (CNT(10,10)). The encapsulated DHPs do not affect the overall structural and electronic properties of the CNT(10,10). The following binding energy was obtained from DFT-D3 calculations: DHP_Cl2@CNT(10,10) (–62.36 kcal mol–1) < DHP_Ph@CNT(10,10) (–54.71 kcal mol–1) < DHP_OH@CNT(10,10) (–43.92 kcal mol–1) < DHP_NO2@CNT(10,10) (–41.71 kcal mol–1) < DHP_H@CNT(10,10) (–32.74 kcal mol–1). The increase in the dipole moment for all DHPs@CNT(10,10) indicates their partial solubility in water. Our results play a promising role as a guide for future experiments using CNTs as a vehicle to transport DHP derivatives.

Predicting the binding properties of single walled carbon nanotubes (SWCNT) with an ADP/ATP mitochondrial carrier using molecular docking, chemoinformatics, and nano-QSBR perturbation theory

Interactions between single walled carbon nanotubes (SWCNT) family with mitochondrial ADP/ATP carrier (ANT-1) were evaluated using constitutional and electronic nanodescriptors defined by (n, m)-Hamada indexes (armchair, zig-zag and chiral).

Covalent Functionalization of Boron Nitride Nanotubes via Reduction Chemistry

Boron nitride nanotubes (BNNTs) exhibit a range of properties that hold great potential for many fields of science and technology; however, they have inherently low chemical reactivity, making functionalization for specific applications difficult. Here we propose that covalent functionalization of BNNTs via reduction chemistry could be a highly promising and viable strategy. Through density functional theory calculations of the electron affinity of BNNTs and their binding energies with various radicals, we reveal that their chemical reactivity can be significantly enhanced via reducing the nanotubes (i.e., negatively charging). For example, a 5.5-fold enhancement in reactivity of reduced BNNTs toward NH2 radicals was predicted relative to their neutral counterparts. The localization characteristics of the BNNT π electron system lead the excess electrons to fill the empty p orbitals of boron sites, which promote covalent bond formation with an unpaired electron from a radical molecule. In support of our theoretical findings, we also experimentally investigated the covalent alkylation of BNNTs via reduction chemistry using 1-bromohexane. The thermogravimetric measurements showed a considerable weight loss (12-14%) only for samples alkylated using reduced BNNTs, suggesting their significantly improved reactivity over neutral BNNTs. This finding will provide an insight in developing an effective route to chemical functionalization of BNNTs.

Self-Trapping of Charge Carriers in Semiconducting Carbon Nanotubes: Structural Analysis

The spatial extent of charged electronic states in semiconducting carbon nanotubes with indices (6,5) and (7,6) was evaluated using density functional theory. It was observed that electrons and holes self-trap along the nanotube axis on length scales of about 4 and 8 nm, respectively, which localize cations and anions on comparable length scales. Self-trapping is accompanied by local structural distortions showing periodic bond-length alternation. The average lengthening (shortening) of the bonds for anions (cations) is expected to shift the G-mode frequency to lower (higher) values. The smaller-diameter nanotube has reduced structural relaxation due to higher carbon-carbon bond strain. The reorganization energy due to charge-induced deformations in both nanotubes is found to be in the 30-60 meV range. Our results represent the first theoretical simulation of self-trapping of charge carriers in semiconducting nanotubes, and agree with available experimental data.

Controlled covalent binding of antiferromagnetic tetramanganese complexes to carbon nanotubes

Tetramanganese complexes are covalently attached to carbon nanotubes such, that the magnetic properties of the antiferromagnetic molecules are preserved.

Polychiral semiconducting carbon nanotube-fullerene solar cells

Single-walled carbon nanotubes (SWCNTs) have highly desirable attributes for solution-processable thin-film photovoltaics (TFPVs), such as broadband absorption, high carrier mobility, and environmental stability. However, previous TFPVs incorporating photoactive SWCNTs have utilized architectures that have limited current, voltage, and ultimately power conversion efficiency (PCE). Here, we report a solar cell geometry that maximizes photocurrent using polychiral SWCNTs while retaining high photovoltage, leading to record-high efficiency SWCNT-fullerene solar cells with average NREL certified and champion PCEs of 2.5% and 3.1%, respectively. Moreover, these cells show significant absorption in the near-infrared portion of the solar spectrum that is currently inaccessible by many leading TFPV technologies.

Low-frequency noise in individual carbon nanotube field-effect transistors with top, side and back gate configurations: effect of gamma irradiation

We report on the influence of low gamma irradiation (10(4) Gy) on the noise properties of individual carbon nanotube (CNT) field-effect transistors (FETs) with different gate configurations and two different dielectric layers, SiO2 and Al2O3. Before treatment, strong generation-recombination (GR) noise components are observed. These data are used to identify several charge traps related to dielectric layers of the FETs by determining their activation energy. Investigation of samples with a single SiO2 dielectric layer as well as with two dielectric layers allows us to separate traps for each of the two dielectric layers. We reveal that each charge trap level observed in the side gate operation splits into two levels in top gate operation due to a different potential profile along the CNT channel. After gamma irradiation, only reduced flicker noise is registered in the noise spectra, which indicates a decrease of the number of charge traps. The mobility, which is estimated to be larger than 2 × 10(4) cm(2) V(-1) s(-1) at room temperature, decreases only slightly after radiation treatment, demonstrating high radiation hardness of the CNTs. Finally, we study the influence of Schottky barriers at the metal-nanotube interface on the transport properties of FETs, analyzing the behavior of the flicker noise component.

Graphene nanoribbon electrical decoupling from metallic substrates

We address the structural and electronic properties of graphene nanoribbons (GNRs) covalently immobilized on a metallic substrate by means of an organic layer. The GNR-organic layer and organic layer-metal interfaces can be thought of as constituents of a nanodevice and have been accurately studied using large-scale density functional theory calculations. Our results demonstrate the possibility of combining nanopatterned metal-organic layer substrates with selected GNRs to obtain well ordered and stable structures while preserving the GNR energy band gap, an essential requirement for any switching nanodevice.

Electrical transport and field-effect transistors using inkjet-printed SWCNT films having different functional side groups

The electrical properties of random networks of single-wall carbon nanotubes (SWNTs) obtained by inkjet printing are studied. Water-based stable inks of functionalized SWNTs (carboxylic acid, amide, poly(ethylene glycol), and polyaminobenzene sulfonic acid) were prepared and applied to inkjet deposit microscopic patterns of nanotube films on lithographically defined silicon chips with a back-side gate arrangement. Source-drain transfer characteristics and gate-effect measurements confirm the important role of the chemical functional groups in the electrical behavior of carbon nanotube networks. Considerable nonlinear transport in conjunction with a high channel current on/off ratio of approximately 70 was observed with poly(ethylene glycol)-functionalized nanotubes. The positive temperature coefficient of channel resistance shows the nonmetallic behavior of the inkjet-printed films. Other inkjet-printed field-effect transistors using carboxyl-functionalized nanotubes as source, drain, and gate electrodes, poly(ethylene glycol)-functionalized nanotubes as the channel, and poly(ethylene glycol) as the gate dielectric were also tested and characterized.

Finite size effects on the gate leakage current in graphene nanoribbon field-effect transistors

The finite size effects in nanoribbon graphene field-effect transistors (FETs) make the energy distribution of the channel electrons very different from that when neglecting finite size effects. Such an effect is especially obvious when the width of the graphene ribbon is a few nanometers. Thus, it results in more high-energy electrons in a nanoribbon graphene FET than in a two-dimensional graphene FET for the same device structure and parameters. Furthermore, such an energy distribution of channel electrons results in a change in the gate leakage current of a nanoribbon graphene FET. The numerical calculations demonstrate that the tunneling current rapidly increases with decreasing width of the graphene ribbon. This implies that a workable graphene FET after considering gate oxide reliability should have a channel width larger than 100 nm.