Electronic Properties Of Single-walled Carbon Nanotubes Research Articles

Phemenology of Filling, Investigation of Growth Kinetics and Electronic Properties for Applications of Filled Single-Walled Carbon Nanotubes

This review discusses the phemenology of filling, the investigation of kinetics, and the electronic properties for applications of filled single-walled carbon nanotubes (SWCNTs), and summarizes five main achievements that were obtained in processing the spectroscopic data of SWCNTs filled with metal halogenide, metal chalcogenide, metal and metallocenes. First, the methods of processing kinetic data were developed to reveal precise trends in growth rates and activation energies of the growth of SWCNTs. Second, the metal-dependence of kinetics was revealed. Third, metallicity-sorted (metallic and semiconducting) SWCNTs were filled with a range of substances and the electronic properties were investigated. Fourth, new approaches to processing the data of spectroscopic investigations of filled SWCNTs were developed, which allowed more reliable and precise analysis of the experimental results. Fifth, the correlation between the physical and chemical properties of encapsulated substances and the electronic properties of SWCNTs were elucidated. These points are highlighted in the review.

Metal and Metal Halogenide-Filled Single-Walled Carbon Nanotubes: Kinetics, Electronic Properties, Engineering the Fermi Level

Here, we present a review of the major achievements in kinetics, electronic properties, and engineering in the Fermi level of single-walled carbon nanotubes (SWCNTs). Firstly, the kinetics of metal-filled SWCNTs were revealed with precision over several minutes. Secondly, the growth rates of nanotubes were calculated. Thirdly, the activation energies of nanotubes were measured. Fourthly, the methods of the quantitative analysis of the doping level were developed. Indeed, only qualitative analysis has been previously performed. The quantitative analysis allowed us to obtain quantitative data on charge transfer. Fifthly, the correlation between the physical properties, chemical properties, electronic properties of SWCNTs was elucidated.

Interactions of amine functional group with Stone-Wales defects on single-walled carbon nanotubes: A theoretical study

Spin-polarized density functional theory has been used to investigate the functionalization of single-walled carbon nanotubes (SWNT) with and without a Stone-Wales (SW) defect by amine (NH2) functional group. The reactivity of SW defects is compared to that of the pristine sidewalls of (5,0), (8,0), and (13,0) SWNT. Our calculations demonstrate that the adsorption of NH2 on SW defect sites is more energetically favorable than that on pristine SWNT sidewalls. All SW defect sites, and particularly the site S1, were considered low-energy adsorption sites for the functionalization process. Furthermore, the binding between the amine group and SW-SWNT is improved for tubes with smaller diameters. The adsorption of NH2 groups on defect sites has a significant influence on the electronic properties of SWNT, changing the electronic states around the Fermi level and converting nonmagnetic semiconductor SWNT to magnetic nanotubes, which is beneficial for the electrical conductivity.

Performance Evaluation of CNTFETs Fabricated with Carbon Nanotubes of Different Synthesis Methods

Single walled carbon nanotubes (SWCNTs) exhibit extraordinary electronic properties that render it as an exciting candidate to be applied as the active channel of high-performance carbon nanotube field effect transistors (CNTFETs). The electronic properties of SWCNTs have been demonstrated to be dependent on the tube intrinsic properties that includes structural defects, chirality and diameter. Structural tube defects can be affected by the synthesis method and therefore the latter should also affect the device performance. Hence, this paper aims to present the influence of SWCNTs source synthesis method towards the resulting CNTFET device characteristics. A total of four SWCNT samples were sourced from different synthesis methods in fabricating CNTFETs. The synthesis methods are arc-discharge and three different variation of chemical vapor deposition (CVD) processes, which are DIPS, HiPco and CoMoCAT, respectively. Prior to fabrication, the SWCNT samples were characterized via Raman spectroscopy to quantifythe tube defect levels of each sample, which are directly proportional to the G-peak to D-peak height ratio, G/D. Electrical characterization was carried out via 3-terminal field effect I-Vmeasurement to evaluate key device performance parameters such ason-off current ratio, ION/IOFF, transconductance, gm,subthreshold slope, Spand field effect mobility, μFE.Analysis shows that G/Daffects the IOFFmore significantly relative to ION, resulting in increasing ION/IOFF, and hence switching performance, when G/Dincreases. It is shown an increase of ~50% to the G/Dof the SWCNT source resulted in ~ 860% increase in μFE. Based on the correlation between the optical analysis and electrical measurement, weconclude that theSWCNT growth method cansignificantly affectthe CNTFET device performance.

Functionalization of Pristine, Metallic, and Semiconducting-SWCNTs by ZnO for Efficient Charge Carrier Transfer: Analysis through Critical Coagulation Concentration.

Noncovalent functionalization of single-walled carbon nanotubes (SWCNT) by semiconducting oxides is a majorly sought technique to retain individual properties while creating a synergetic effect for an efficient heterostructure charge transfer. Three types of electronically and optically different SWCNTs: metallic (m), semiconducting (s), and pristine (p) are functionalized by ZnO using a facile sonication method. The physicochemical and morphological properties of the ZnO-functionalized SWCNTs, m-SWCNT+ZnO, s-SWCNT+ZnO, and p-SWCNT+ZnO, are analyzed by advanced characterization techniques. Evidence of charge transfer between SWCNT and ZnO is observed with an increase in charge carrier lifetime from 3.31 ns (ZnO) to 4.76 ns (s-SWCNT+ZnO). To investigate the optimum interaction between SWCNTs and ZnO, critical coagulation concentrations (CCC) are determined using UV–vis absorption spectroscopy for m-SWCNT, s-SWCNT, and p-SWCNT using different molar concentrations of ZnO as the coagulant. The interaction and coagulation mechanisms are described by the modified DLVO theory. Due to the variation in dielectric values and electronic properties of SWCNTs, the CCC values obtained have differed: m-SWCNT (1.9 × 10–4), s-SWCNT (3.4 × 10–4), and p-SWCNT (2 × 10–4). An additional analysis of the aggregates and supernatants of the CCC experiments is also shown to give an insight into the interaction and coagulation processes, explaining the absence of influence exerted by sedimentation and centrifugation.

Nickelocene-Filled Purely Metallic Single-Walled Carbon Nanotubes: Sorting and Tuning the Electronic Properties.

We conducted the filling of single-walled carbon nanotubes (SWCNTs) with nickelocene molecules and separation of the filled SWCNTs by conductivity type by density-gradient ultracentrifugation. We tailored the electronic properties of nickelocene-filled purely metallic SWCNTs by thermal treatment in high vacuum. Our results demonstrated that annealing at low temperatures (360–600 °C) leads to n-doping of SWCNTs, whereas annealing at high temperatures (680–1200 °C) results in p-doping of SWCNTs. We found a correlation between the chemical state of the incorporated substances at different annealing temperatures and its influence on the electronic properties of SWCNTs.

Metallicity-Dependent Ultrafast Water Transport in Carbon Nanotubes.

Carbon nanotubes (CNTs) with hydrophobic and atomically smooth inner channels are promising for building ultrahigh-flux nanofluidic platforms for energy harvesting, health monitoring, and water purification. Conventional wisdom is that nanoconfinement effects determine water transport in CNTs. Here, using full-atomistic molecular dynamics simulations, it is shown that water transport behavior in CNTs strongly correlates with the electronic properties of single-walled CNTs (metallic (met) vs semiconducting (s/c)), which is as dominant as the effect of nanoconfinement. Three pairs of CNTs (i.e., (8,8)met , 10.85 Å vs (9,7)s/c , 10.88 Å; (9,8)s/c , 11.53 Å vs (10,7)met , 11.59 Å; and (9,9)met , 12.20 Å vs (10,8)s/c , 12.23 Å) are used to investigate the roles of diameter and metallicity. Specifically, the (9,8)s/c can restrict the hydrogen-bonding-mediated structuring of water and give the highest reduction in carbon-water interaction energy, providing an extraordinarily high water flux, around 250 times that of the commercial reverse osmosis membranes and approximately fourfold higher than the flux of the state-of-the-art boron nitrate nanotubes. Further, the high performance of (9,8)s/c is also reproducible when embedded in lipid bilayers as synthetic high-water flux porins. Given the increasing availability of high-purity CNTs, these findings provide valuable guides for realizing novel CNT-enhanced nanofluidic systems.

Purification of Single‐Walled Carbon Nanotubes Using Acid Treatment and Magnetic Separation

A detailed analysis of TUBALL single‐walled carbon nanotubes (SWCNTs) after two‐step purification involving acid purification treatment with concentrated HCl, HNO3, H2SO4 and solution of HNO3:H2SO4 followed by magnetic processing is presented. The purity degree from iron higher than 99% is achieved, and the yield obtained by the above process is about 75 wt.%. Such high purity of the resultant sample is achieved by removing of the external iron nanoparticles by acid treatment and following extraction of nanotubes containing encapsulated nanoparticles under applied magnetic field. A comprehensive characterization of SWCNTs by Raman, optical absorption, and X‐ray photoelectron spectroscopies reveals purification‐induced changes in the integrity, composition, and electronic properties of SWCNT.

Density functional calculations of nickel, palladium and cadmium adsorption onto (10,0) single-walled carbon nanotube.

Adsorption of three heavy metals (Ni, Pd, Cd) onto (10,0) single-walled carbon nanotube (SWCNT) was investigated using density functional theory (DFT). Metals were adsorbed to both inside and outside of SWCNT and their structures and electronic properties [e.g., band structures and density of states (DOS)] were calculated and compared. The effects of substituting one carbon atom of the nanotube with these metals were also investigated. Formation energy results showed that adsorption inside and outside the nanotube is energetically favored. Significant changes were observed in the electronic properties of SWCNT after Ni and Pd adsorptions, and the nanotube changes from being a semi-conductor to a metallic conductor. However, the conductivity did not change markedly after Cd adsorption, indicating its physical adsorption to the nanotube. Spin polarized calculations showed that nickel adsorption inside and outside SWCNT induces magnetization of the system. Different electronic properties were obtained after adsorption of Pd atoms to different sides of SWCNT. Partial DOS were also applied to interpret the changes in electronic properties more precisely.

Excitons in Single-Walled Carbon Nanotubes and Their Dynamics.

Understanding exciton dynamics in single-walled carbon nanotubes (SWCNTs) is essential to unlocking the many potential applications of these materials. This review summarizes recent progress in understanding exciton photophysics and, in particular, exciton dynamics in SWCNTs. We outline the basic physical and electronic properties of SWCNTs, as well as bright and dark transitions within the framework of a strongly bound one-dimensional excitonic model. We discuss the many facets of ultrafast carrier dynamics in SWCNTs, including both single-exciton states (bright and dark) and multiple-exciton states. Photophysical properties that directly relate to excitons and their dynamics, including exciton diffusion lengths, chemical and structural defects, environmental effects, and photoluminescence photon statistics as observed through photon antibunching measurements, are also discussed. Finally, we identify a few key areas for advancing further research in the field of SWCNT excitons and photonics.

COMPUTER SIMULATION OF FUNCTIONALIZED CARBON NANOTUBES AND GRAPHENE

Nanomaterials based on carbon nanotubes (CNT) and graphenes attract a lot of attention of researchers as the materials capable to raise the development of various industries to the new level, and first of all, of the chemical and electronic sectors. In addition to known experimental methods, new nanosystems are widely studied using advanced tools of quantum-chemical approaches. Modern theoretical methods are of great interest due to their ability to interpret known experimental facts and predict properties of non-synthesized compounds yet. This paper reviews results of theoretical studies performed using the density functional theory (DFT) methods to obtain data on the structure and electronic properties of single-walled CNT and graphene, modified with various impurities, with covalent-ionic and non-covalent binding mechanisms. New computational methods are briefly described that are currently employed to treat the dispersion interaction and enhance possibilities of DFT tools in systems where the van der Waals forces play a significant role. Particular attention is paid to the characteristics of carbon nanomaterials containing technologically important hydroxyl, carboxyl and amino groups. It is shown that the specific peculiarity of band structures of discussed in the literature CNT functionalized by OH, COOH, NHn and CONH2 groups is the partially occupied band in the neighborhood of the Fermi level, which directly affects the CNT conductivity. Modification of graphene layers is analyzed that interact with hydrogen, fluorine, bases of nucleic acids and the metal substrate surface. We also provide accuracy estimates for the calculations of interatomic bond lengths, interaction energy and band gap carried out in the literature using a variety of DFT approximations.

Ultrafast Photophysics of Single‐Walled Carbon Nanotubes

Single‐walled carbon nanotubes (SWNTs) are nanocylinders obtained by wrapping one layer of graphene; due to their very high aspect ratio, they are the prototypical quantum confined one‐dimensional systems. The unique mechanical, electronic, and optical properties of SWNTs open up transversal application possibilities in many fields of science and technology, with particular emphasis on optoelectronics and photonics. A prerequisite for many of these applications is a thorough understanding of the nature and dynamics of their elementary excitations. This review aims at summarizing the current understanding of the ultrafast photophysics of SWNTs, based on two decades of experimental investigations. After discussing the morphological and electronic properties of SWNTs and introducing the different photogenerated species, we will briefly describe the ultrafast spectroscopic techniques most commonly used for their characterization. Finally, we present the experimental evidence that has led to establish the nature (singlet and triplet excitons, bi‐excitons, trions, and free charges) and the relaxation pathways of photoexcitations in SWNTs.

Diameter dependence of the optoelectronic properties of single walled carbon nanotubes determined by ellipsometry

We report ellipsometric measurement on single walled carbon nanotube (SWCNT) films performed in a large spectral range from 0.07 to 4.97eV. The complex dielectric functions of SWCNTs are correlated to their diameter distribution extracted from transmission electron microscopy. Here we show that the transition energies between Van Hove singularities are directly related to the strong one dimensional confinement. In the infrared spectral range, the real part of the dielectric function becomes negative. The electronic properties of SWCNTs are extracted from ellipsometry by using a Drude model. The mobility and the mean free path of charge carriers are limited by the high number of SWCNT contacts. In accordance with tight binding simulation, the conductivity and the charge carrier concentration increase with the SWCNT diameter. Finally, we demonstrate that the π-plasmon energy depends on the charge carrier concentration.

Relative ordering between bright and dark excitons in single-walled carbon nanotubes.

The ordering and relative energy splitting between bright and dark excitons are critical to the optical properties of single-walled carbon nanotubes (SWNTs), as they eventually determine the radiative and non-radiative recombination processes of generated carriers. In this work, we report systematic high-field magneto-optical study on the relative ordering between bright and dark excitons in SWNTs. We identified the relative energy position of the dark exciton unambiguously by brightening it in ultra-high magnetic field. The bright-dark excitonic ordering was found to depend not only on the tube structure, but also on the type of transitions. For the 1st sub-band transition, the bright exciton appears to be higher in energy than its dark counterpart for any chiral species and is robust against environmental effect. While for the 2nd sub-band, their relative ordering was found to be chirality-sensitive: the bright exciton can be either higher or lower than the dark one, depending on the specific nanotube structures. These findings provide new clues for engineering the optical and electronic properties of SWNTs.

Molybdenum-encapsulation modified the optical property of single walled carbon nanotubes

Changes in the optical properties of single walled carbon nanotubes (SWNTs) caused by the encapsulation of molybdenum (Mo) clusters were investigated in the current research. Detailed transmission electron microscope observations showed that the encased Mo clusters within the hollow core of SWNTs exhibited in the form of short rod-like structure, indicating the growth of the clusters within the confined nano space. The upshifted G-band frequency as well as the quenched photoluminescence and absorption signals signified the modulation in the electronic properties of SWNTs caused by a strong coupling interaction between the nanotube and the Mo clusters.

Fullerene peapods: In-situ conductivity study during synthesis

We report in-situ measurement of the conductivity during the synthesis of C60-filled single-walled carbon nanotubes (SWNTs), so-called fullerene peapods. The synthesis was performed in a sealed quartz tube at 773 K by using the sublimation of C60 into the hollow space of the SWNTs. The change in the resistance in the SWNT buckypaper was monitored during the C60-filling process, and the temperature dependence of the resistance was compared to that for empty SWNTs and fullerene peapods. The SWNT networks became more metallic due to the encapsulation of C60, and a reduced temperature dependence of the resistivity was observed in the peapods, with an overall decrease in the resistivity. The interaction between the SWNT and C60 molecules, changing the electronic properties of SWNTs, can provide a way to functionalize the SWNTs.

Electronics and Structural Properties of Single-Walled Carbon Nanotubes Interacting with a Glucose Molecule: ab initio Calculations

The adsorption of glucose molecule on single-walled carbon nanotubes (SWCNTs) is investigated by density functional theory calculations. Adsorption energies and equilibrium distances are evaluated, and glucose binding to the typical semiconducting and metallic nanotubes with various diameters and chirality are compared. We also investigated the role of the structural defects on the adsorption capability of the SWCNTs. We could observe larger adsorption energies for the larger diameters semiconducting CNTs, while the story is paradoxical for the metallic CNTs. The obtained results reveal that the adsorption energy is significantly higher for nanotubes with higher chiral angles. Finally, the adsorption energies are calculated for defected nanotubes for various configurations such as glucose molecule approaching to the pentagon, hexagon, and heptagon sites in the tube surface. We find that the respected defects have a minor contribution to the adsorption mechanism of the glucose on SWNTs. The calculation of electron transfers and the density of states supports that the electronic properties of SWCNTs do not change significantly after the gluycose molecular adsorption. Consequently, one can predict that presence of glucose would neither modify the electronic structure of the SWCNTs nor direct to a change in the conductivity of the intrinsic nanotubes.

Single-walled carbon nanotube field-effect transistors with graphene oxide passivation for fast, sensitive, and selective proteindetection

We report a novel technique to design an insulating membrane with attachment sites on top of single-walled carbon nanotubes (SWNTs) for achieving high sensitivity and selectivity in an SWNT field-effect transistor (FET) biosensor. Because electronic properties of SWNTs are extremely sensitive to the surface state, direct immobilization of proteins or DNAs onto SWNTs will generate surface defects through chemical reactions or physical adsorption, resulting in degradation of performance and instability of SWNT-FET biosensor devices. Here we demonstrate fabrication of novel FET biosensor devices using SWNTs as semiconducting channels, and a monolayer of graphene oxide (GO) membrane covered on the SWNTs as a passivating layer to avoid direct attachment of biomaterials on SWNTs, thereby preserving intrinsic electrical properties of SWNTs. Gold nanoparticles (Au NPs) are decorated on the GO layer for the covalent attachment of biotin, which is then used to selectively detect the target avidin. The passivation with GO layers can effectively lead to enhanced sensitivity of biosensor devices through increasing the on/off ratio of FET sensors.

The growth mechanism of single-walled carbon nanotubes with a controlled diameter

Understanding the growth mechanism of carbon nanotube is important to control the structure and properties of carbon nanotubes. We examined several aspects of the single wall carbon nanotubes (SWCNTs) prepared by chemical vapor deposition (CVD) processes using ethanol with the additions of ferrocene and thiophene, focusing on the potential mechanisms leading to the differences in the diameters, structures, and conductivities of the SWCNTs formed. The diameter of SWCNTs could be controlled from ∼1.0 to ∼5.8nm by adjusting the concentration of thiophene used. The larger diameter SWCNTs has a higher thermal stability than smaller-diameter SWCNTs. With increasing diameter, the electrical properties of the SWCNT change from mainly semi-conducting to metallic-like. The growth mechanism of SWCNTs was subsequently studied to understand the mechanism of thiophene controlled SWCNTs formation. This study could lead to improved control over the diameter and electronic properties of SWCNTs.

Carbon Nanotubes Doped with Nitrogen, Pyridine-like Nitrogen Defects, and Transition Metal Atoms

Dopants and defects can be introduced as well as the intercalation of metals into single wall carbon nanotubes (SWCNTs) to modify their electronic and magnetic properties, thus significantly widening their application areas. Through spinpolarized density functional theory (DFT) calculations, we have systemically studied the following: (i) (10,0) and (5,5) SWCNT doped with nitrogen (), (ii) (10,0) and (5,5) SWCNT with pyridine-like defects (3NV-), and (iii) chemical functionalization of (10,0) and (5,5) 3NV- with 12 different transition metals (TMs) (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, and Pt). Attention was done in searching for the most stable configurations, deformation, calculating the formation energies, and exploring the effects of the doping concentration of nitrogen and pyridine-like nitrogenated defects on the electronic properties of the nanotubes. Also, calculating the corresponding binding energies and effects of chemical functionalization of TMs on the electronic and magnetic properties of the nanotubes has been made. We found out that the electronic properties of SWCNT can be effectively modified in various ways, which are strongly dependent not only on the concentration of the adsorbed nitrogen but also to the configuration of the adsorbed nitrogen impurities, the pyridine-like nitrogenated defects, and the TMs absorbed; due to the strong interaction between the d orbitals of TMs and the p orbitals of N atoms, the binding strengths of TMs with the two 3NV- are significantly enhanced when compared to the pure SWCNTs.