Role of Second Halogen Atoms of Dihalobenzene in Controlling the Photoluminescence Properties of Single-Walled Carbon Nanotubes by Reductive Arylation

In this paper,changing patterns of electronic velocity and effective mass of the lowest conduction band for various carbon nanotubes are calculated systematically. Based on these calculation results,low-bias transport properties of single-walled carbon nanotubes (SWCNTs) and deduced thoroughly. It is found that under a low bias,chiral metallic SWCNTs belonging to the same series ( i.e,having the same chiral angles) have the entirely identical transport properties and are independent of diameter of the SWCNT. But those that belong to different series have obviously distinguishable transport properties. While for chiral semi-conducting SWCNTs belonging to the same series,they have some different transport properties. But those that belong to different series have greatly different transport properties. Our findings suggest that low-bias transport properties of SWCNTs are intimately related to the series and the chiral angle is the most important geometry parameter for the determination of different low-bias transport properties of various SWCNTs.

Based on a method of molecular structural mechanics (MSM), the effect of environmental temperature on elastic properties of armchair and zigzag single-walled carbon nanotubes is investigated. Single-walled carbon nanotubes with different chiral vectors are considered as a molecular structural mechanics model, which is composed of the discrete molecular structures through the carbon-to-carbon bonds. By considering the effect of environmental temperature on force constant values of the bonds stretching, bonds angle bending and torsional resistance, the corresponding basic parameters of a truss of the single-walled carbon nanotubes are obtained in different environmental temperatures, respectively. Nanoscale structural mechanics simulation for the elastic properties of single-walled carbon nanotubes in different environmental temperatures reveals that the elastic modulus of single-walled carbon nanotubes decreases significantly with the increase of environmental temperature. It is noted that the Young's modulus of single-walled carbon nanotubes is more sensitive to environmental temperature than the shear modulus.

We compare the effects of O2, Ar, and H2 gases on the field-emission (FE) properties of single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs). We find that H2 and Ar gases do not significantly affect the FE properties of SWNTs or MWNTs. O2 temporarily reduces the FE current and increases the turn-on voltage of SWNTs. Full recovery of these properties occurs after operation in UHV. The higher operating voltages in an O2 environment cause a permanent decrease of the FE current and an increase in the turn-on field of MWNTs. The ratios of the slopes before and after O2 exposure are approximately 1.04 and 0.82 for SWNTs and MWNTs, respectively.

Establishing the relationship between the electrical transport properties of single-wall carbon nanotubes (SWCNTs) and their structures is critical for the design of high-performance SWCNT-based electronic and optoelectronic devices. Here, we systematically investigated the effect of the chiral structures of SWCNTs on their electrical transport properties by measuring the performance of thin-film transistors constructed by eleven distinct (n, m) single-chirality SWCNT films. The results show that, even for SWCNTs with the same diameters but different chiral angles, the difference in the on-state current or carrier mobility could reach an order of magnitude. Further analysis indicates that the electrical transport properties of SWCNTs have strong type and family dependence. With increasing chiral angle for the same-family SWCNTs, Type I SWCNTs exhibit increasing on-state current and mobility, while Type II SWCNTs show the reverse trend. The differences in the electrical properties of the same-family SWCNTs with different chiralities can be attributed to their different electronic band structures, which determine the contact barrier between electrodes and SWCNTs, intrinsic resistance and intertube contact resistance. Our present findings provide an important physical basis for performance optimization and application expansion of SWCNT-based devices.

Molecular mechanics has been widely used to analytically study mechanical behaviour of carbon nanotubes. However, explicit expressions for elastic properties of carbon nanotubes are so far confined to some special cases due to the lack of fully constructed governing equations for the molecular mechanics model. In this paper, governing equations for an analytical molecular mechanics model are fully established. The explicit expressions for five in-plane elastic properties of a chiral single-walled carbon nanotube are derived, which make properties at different length-scales directly connected. The effects of tube chirality and tube diameter are investigated. In particular, the present results show that the classic relationship from the isotropic elastic theory of continuum mechanics between Young's modulus and shear modulus of a single-walled carbon nanotube is not retained. The present analytical results are helpful to the understanding of elastic properties of carbon nanotubes, and also useful to the topic of linking molecular mechanics with continuum mechanics.

This paper focuses on the study of single-walled carbon nanotubes (SWNTs) filled with magnetic Fe nanoparticles. The magnetic properties of Fe-filled SWNTs are measured at various temperatures, and the results indicate that they exhibit a ferromagnetic characteristic at room temperature and superparamagnetic properties at low temperatures. In addition, the electrical transport properties of Fe-filled SWNTs are examined, and the results demonstrate that their electronic properties depend on the filling level of the encapsulated Fe particles. It is found that Fe-filled SWNTs can exhibit high-performance unipolar n-type semiconducting characteristics at high filling levels and p–n junction diode behavior at low filling levels.

The molecular dynamics method was used to investigate the elastic properties of armchair and zigzag single-walled carbon nanotubes grafted by hydroxyl on their ports. The results showed that the Young's moduli of ungrafted armchair (5, 5)，(10,10) and zigzag (9, 0) , (18,0) single-walled carbon nanotubes were 948，901 and 804, 860GPa, respectively. When the single-walled carbon nanotubes were grafted by 2 to 8 hydroxyl functional groups, the Young's modulus of the zigzag single-walled carbon nanotubes was little changed, while the Young's modulus of the armchair single-walled nanotubes first decreased significantly due to the grafting, then increased appreciably to some steady value with increasing of the grafts after having been grafted to certain numbers. The reasons were analyzed in terms of the isoline structure of deformation electron density, C—C bond-length and the system binding energy variation of the carbon nanotubes with different graft numbers.

Electronic and electrical properties of several single-walled carbon nanotubes as well as their derived structures with multi-dichlorocarbene addition are investigated by using self-consistent field crystal orbital method based on density functional theory. The addition can convert metallic tubes into semiconducting ones and increase their carrier mobilities, which are comparable with those of the pristine semiconducting tube. With small amount of dichlorocarbenes, the mobility of semiconducting single-walled carbon nanotube does not decrease. The dichlorocarbene addition can be a good pathway for processing high mobility electronic devices for mixtures of semiconducting and metallic single-walled carbon nanotubes.

A comparative study, for the first time, was conducted on thermophysical and rheological properties of single-walled carbon nanotubes (SWCNT) and graphene nanoplatelets (GNP) nanofluids. Highly stable aqueous 0.5, 1.0, and 2.0 wt% SWCNT and GNP nanofluids were successfully prepared with no surfactant, through ultrasound technology. The preparation was explained in detail, adjusting pH to around 8 where nanofluids would be expected to be stable. The highest zeta potential of −60.5 mV was obtained for 2.0 wt% SWCNT nanofluids. Shear thinning was observed for all nanofluids at low shear rates. Unlike shear thickening of GNP, Newtonian behavior of SWCNT nanofluids was detected at high shear rate region. The effect of ultrasound technology was directly verified by scanning electron microscopy (SEM), resulting in GNP size reduction and separation of bundles for SWCNT. The results revealed that SWCNT nanofluids showed a remarkable zeta potential value for heat transfer systems compared to GNP nanofluids.

In this work we present a systematic density functional theory study of the electronic properties of single-walled carbon nanotubes (SWNT) with diameters ranging from 3 to 5 A. In this work meta-generalized-gradient approximation, hybrid, and screened exchange hybrid functionals are utilized to compute energy band gaps in these narrow SWNT. Our calculations using hybrid functionals show that the only true exceptions to the zone folding predictions are the (4,0) and (5,0) SWNT. The remaining chiral SWNT are semiconducting with band gaps that can be as large as 1.7 eV. However, the calculated energy band gaps are significantly smaller than those predicted by the zone folding scheme. This difference is primarily attributed to the sigma-pi hybridization present in such narrow SWNT.

Harnessing the unique optical properties of chirality-enriched single-walled carbon nanotubes (SWCNTs) is the key to unlocking the application of SWCNTs in photonics. Recently, it has been discovered that chemical modification of SWCNTs greatly increases their potential in this context. Despite the dynamic progress in this area, the mechanism of the chemical modification of SWCNTs and the impact of the reaction conditions on the properties of the obtained functional nanomaterials remain unclear. In this study, we demonstrate how the reaction environment influences the observed fluorescence pattern of SWCNTs after modification with benzoyloxy radicals generated in situ. The obtained results reveal that each diacyl peroxide molecule can generate either one or two radicals by two different mechanisms, i.e., induced or spontaneous decomposition. Through proper selection of the reactant concentration, process temperature, and solvent, we were able to activate one or both radical decay pathways. In addition, the choice of a solvent, such as tetrahydrofuran or acetonitrile, allowed drastic changes in the functionalization process. Consequently, the SWCNT surface was grafted with functional groups via C-C bonds using radicals derived from the solvent molecules instead of attaching an aromatic moiety from the reactant present in the system through the expected C-O linkage. Verification of the structure of the chemically bound functional groups through hydrolysis opens the route to further modification of SWCNT surfaces using the labile ester connection. By gaining a better understanding of the emergence and behavior of the generated radicals, we demonstrate the possibility of controlling the density of introduced defects, as well as the selectivity of the functionalization process. The identification of the underlying chemical pathways responsible for the functionalization of SWCNTs paves the way for the design of precise methods of SWCNT modification to adjust their photonic characteristics for specific applications.

The effects of attaching COOH groups at different sites and in various concentrations on electronic and structural properties of (8,0) single-walled carbon nanotubes (SWNT) were investigated using ab initio calculations. The binding energies and the charge transfers between the COOH functional groups and the tube were calculated for several configurations and a novel feature in the electronic structure of these groups was observed. The electronic character of these systems can be modulated by playing with the concentration and the position of the carboxyl groups bonded on the tube wall. The carboxyl groups bound to different carbon atom sub-lattices are more hybridized than those bound in the same one. These results suggested that SWNT-COOH systems are a playground for engineering electronic properties through a proper chemical functionalization which exploit both the attachment site and concentration of functional groups.

Density functional theory investigation of the mechanical properties of single-walled carbon nanotubes

Carbon nanotube (CNT) is promising to revolutionise several fields in material science and is a major component of nanotechnology. In this study, molecular dynamics simulation is used to investigate the elastic properties of single-walled carbon nanotubes. Comprehensive numerical calculations are carried out for different armchair and zigzag carbon nanotubes with various geometric dimensions to assess the effects of tube radius, tube length and tube chirality on the elastic properties of single-walled carbon nanotubes (SWCNTs). The results show that, the axial Young’s modulus of both armchair and zigzag SWCNTs decreases with increasing tube radius which is also in good agreement with experimental observation. The results also reveal that, the value of the axial Young’s modulus of the SWCNTs is independent of the tube length and tube chirality.

We report theoretical investigations on the changes in optical and electronic properties of single-walled carbon nanotubes (SWNTs) induced by chemical doping with organic molecules or fullerene C60. It is found that doping alters the electronic and optical properties of parent SWNTs and both p- and n-type doping can be realized on SWNTs by encapsulating organic molecules which have large electron affinities or small ionization energies. The doping-induced optical features and additions of donor∕acceptor states to the density of states provide compelling evidence that the standard rigid-band model breaks down and the band-structure changes play an important role on the solid state properties of doped SWNTs.