On the applicability of cluster models to study the chemical reactivity of carbon nanotubes

We have performed a comparative study on the reactivity of metallic and semiconducting nanotubes using infinite and finite models. Infinite models were created using periodic boundary conditions while finite ones were constructed by means of hydrogen terminated nanotubes sections. Cluster models systematically underestimate the reactivity of metallic single wall carbon nanotube (SWCNT)s. We have confirmed that metallic nanotubes are more reactive than semiconducting species, in disagreement with previous works. The differences can be attributed to the presence of an instability in the singlet ground state of the wavefunction corresponding to semiconducting nanotubes clusters. When lower electronic states of the pristine cluster are considered, semiconducting nanotubes become less reactive as compared with metallic SWCNTs. Particularly, if an antiferromagnetic solution is considered for the semiconducting (10,0) SWCNT cluster, it becomes less reactive than the (5,5) SWCNT, as observed for infinite models. Because semiconducting nanotubes are less reactive than metallic counterparts, their reaction energies converge faster to the values observed for graphene. For a 1.6-nm diameter semiconducting nanotube, the addition energy is comparable with graphene. Thus, semiconducting nanotubes with diameters larger than 1.6 nm are going to be as reactive as graphene and the effects of curvature will be unimportant.     

Nerve agents interacting with single wall carbon nanotubes: Density functional calculations

First-principles calculations based on density functional theory (DFT) method are used to investigate the adsorption properties of nerve agent DMMP on typical zigzag (semiconducting) and armchair (metallic) single wall carbon nanotubes (SWCNTs). The adsorption energies for DMMP molecule on different adsorption sites on SWCNTs are obtained. The results indicate that DMMP is weakly bound to the outer surface of both the considered SWCNTs and the obtained adsorption energy values and binding distances are typical for the physisorption. We find that DMMP adsorptive capability of metallic CNTs is about twofold that of semiconducting one. The adsorption of DMMP on the higher chiral angle nanotubes was also investigated and the results indicate that nanotube’s chirality increases the adsorption capability of the tube but however the adsorption characteristic is typical for the physisorption. Furthermore, co-adsorption of two DMMP molecules on the SWCNTs as a single-layer/bi-layer of adsorbed molecules as well as the adsorption of one DMMP molecule on the CNT bundles consisting of three SWCNTs has also been examined. The obtained results reveal that for both the considered systems the binding energy was increased for the DMMP adsorption but it’s still typical for the physisorption, consistent with the recent experimental result. The study of the electronic structures and charge analysis indicate that no significant hybridization between the respective orbital takes place and the small interaction obtained quantitatively in terms of binding energies.     

有限长Y型碳纳米管结构和性质的第一性原理研究

采用密度泛函理论的GGA/PW91方法对有限长Y型碳纳米管的结构和性质进行了研究. 研究结果表明, 由于缺陷环的影响, Y型碳纳米管与直型管的性质明显不同, 而且, Y型碳纳米管的结构和性质与分支管长度存在一定的关系. 当分支管长度大于1 nm 时, Y型碳纳米管的结构、能隙和电学性质均出现周期性振荡变化的趋势.     

Interaction of narrow carbon nanotubes with nitronium tetrafluoroborate salts

Density functional calculations have been performed to investigate the destruction of narrow carbon nanotubes (CNTs) under the attack of nitronium tetrafluoroborate salts. The dissociation of these salts in a solvent produces nitronium and tetrafluoroborate ions which coadsorb on the external surface of the tubes. It is shown that the ions bind strongly to both metallic and semiconducting narrow nanotubes, although stronger to the metallic ones. The nitronium cations bind to the CNTs through a charge transfer mechanism, whereas the tetrafluoroborate anions remain negatively charged upon adsorption on the nanotubes. The surface of the nanotubes gets substantially deformed around the adsorption site of the nitronium ion, but it is hardly changed around the adsorption site of the tetrafluoroborate ion. These results are the theoretical basis to explain the destruction of the narrow CNTs found in the experiments and also to unravel, in agreement with the experimental interpretation, the distinct role played by the nitronium and the tetrafluoroborate ions. The tetrafluoroborate ions contribute to separate the CNTs from the bundles into individual tubes, without affecting the tubes. The nitronium ions, in contrast, modify the electronic and geometrical structures of the narrow tubes leading eventually to their destruction. The implications for the selective removal of intermediate diameter metallic CNTs found in the experiments are also discussed. The adsorption of the neutral nitrogen dioxide molecule is also studied, and the results show that the weak interactions of this molecule with both metallic and semiconducting tubes cannot be used as a model for the strong attack of the nitronium ions to the narrow tubes. The sensor effect of the nanotubes toward adsorption of nitrogen dioxide is also discussed.     

A first principles study of NO2 chemisorption on silicon carbide nanotubes

Using methods based on first principles, we find that an NO₂ molecules can be chemisorbed on silicon carbide nanotubes (SiCNTs) with an appreciable binding energy (∼−1.0 eV), and that this is not the case for either carbon nanotubes (CNTs) or boron nitride nanotubes (BNNTs). A detailed analysis of the energetics, geometry, and electronic structure of various isomers of the complexes was performed. The SiCNT–NO₂ complex can be metallic or nonmetallic depending on the type of adsorption site and the chirality of the tube. However, our analysis of the electronic structure predicts that a strong p-type effect of the adsorption turns semiconducting systems into metallic ones at room temperature, irrespective of the chirality of the tube.     

单壁碳纳米管的电子速度及有效质量

利用单壁碳纳米管(SWCNTs)能量色散关系, 计算了最低导带的电子速度和有效质量, 重点讨论了SWCNTs中最低导带电子速度和有效质量与波矢及管径大小的关系. 结果表明, 半导体型锯齿SWCNTs的电子速度和有效质量与其结构参量(管径)有直接的关系. 各种椅型SWCNTs(金属型)和金属型锯齿SWCNTs最低导带电子速度和有效质量随波矢的变化规律分别相同, 各种半导体型锯齿SWCNTs最低导带电子速度和有效质量随波矢的变化规律则有明显差别. 这意味着在低偏压下, 不同管径的椅型SWCNTs和金属型锯齿SWCNTs输运性能相同, 而各种不同管径半导体型锯齿SWCNTs输运性能有明显差别.     

The effect of 3<Emphasis Type="Italic">d</Emphasis>-metal dopants on the electronic structure of carbon nanotubes

In the course of synthesis of nanotubes, atoms of transition metals used as a catalyst can be substituted for carbon atoms. The electronic properties of semiconducting (13,0) and metallic (5,5) nanotubes doped with Co and Ni atoms have been calculated by ab initio quantum-chemical methods. The total and partial densities of states have been determined. The conclusion has been made that Co and Ni substituted for carbon disturb the electronic structure of metallic and semiconducting nanotubes. Such dopants can be detected by spectral and electrical measurements.     

自组装半导体碳纳米管薄膜的光电特性

采用自组装的方法制备99%高纯度半导体碳纳米管平行阵列条带,以金属钯和钪为非对称接触电极制备碳纳米管(CNT)薄膜晶体管(TFTs)器件.主要研究不同沟道长度碳纳米管薄膜晶体管器件的电输运特性和红外光电响应特性,分析了其中的载流子输运和光生载流子分离的物理机制.我们发现薄膜晶体管器件的电学性能和光电性能依赖于器件沟道长度(L)和碳纳米管的平均长度(LCNT).当沟道长度小于碳纳米管的平均长度时,器件开关比最低;当沟道长度超过碳纳米管平均长度时,随着沟道长度的增加,器件开关比增加,光电流减小.相关研究结果为高纯碳纳米管薄膜晶体管器件在红外光探测器方面的进一步应用提供参考依据.     

自组装半导体碳纳米管薄膜的光电特性

采用自组装的方法制备99%高纯度半导体碳纳米管平行阵列条带,以金属钯和钪为非对称接触电极制备碳纳米管（CNT）薄膜晶体管（TFTs）器件. 主要研究不同沟道长度碳纳米管薄膜晶体管器件的电输运特性和红外光电响应特性,分析了其中的载流子输运和光生载流子分离的物理机制. 我们发现薄膜晶体管器件的电学性能和光电性能依赖于器件沟道长度（L）和碳纳米管的平均长度（L_CNT）. 当沟道长度小于碳纳米管的平均长度时,器件开关比最低;当沟道长度超过碳纳米管平均长度时,随着沟道长度的增加,器件开关比增加,光电流减小.相关研究结果为高纯碳纳米管薄膜晶体管器件在红外光探测器方面的进一步应用提供参考依据.     

Separation and/or selective enrichment of single-walled carbon nanotubes based on their electronic properties

Single-walled carbon nanotubes (SWNTs) possess unique electronic properties that make them very promising materials for use in both nano-electronics and thin film devices. However, SWNTs are always produced as a mixture of metallic and semiconducting nanotubes, which is a major roadblock to their widespread application. This tutorial review provides a brief summary of ways of separating single-walled carbon nanotubes into metallic and semiconducting fractions. Various methods including selective growth, selective removal, selective adsorption and band structure modulation--all of which aim to produce pure SWNTs with well-defined electronic properties--are systematically discussed. The main problems in this field, the outlook for separation techniques and some views of future developments are presented.     

Electronic properties of single-walled carbon nanotubes inside cyclic supermolecules

Possible ways for manipulating carbon nanotubes (CNTs) with cyclic supermolecules are studied using density functional theory. Electronic structure calculations with structure optimizations have been performed for the (4,4) and (8,0) single-walled carbon nanotubes (SWNTs) complexed with crown ethers as well as for the (4,0) SWNT with beta-cyclodextrin. A slight polarization of charge in both the nanotube and the supermolecule is observed upon rotaxane complexation, but the interaction is mainly repulsive, and the systems stay 2.8-3.5 A apart. The supermolecule does not affect the electronic band structure of the nanotube significantly within such a configuration. The situation differs noticeably for chemically cross-linked SWNTs and crown ethers, where a peak arises at the Fermi energy in the density of states. As a result, the band gap of semiconducting CNT(8,0) (0.5 eV) vanishes, and a new conduction channel opens for the metallic CNT(4,4).     

Anisotropic Photoluminescence of Poly(3-hexyl thiophene) and Their Composites with Single-Walled Carbon Nanotubes Highly Separated in Metallic and Semiconducting Tubes

In this work, the effect of the single-walled carbon nanotubes (SWNTs) as the mixtures of metallic and semiconducting tubes (M + S-SWNTs) as well as highly separated semiconducting (S-SWNTs) and metallic (M-SWNTs) tubes on the photoluminescence (PL) of poly(3-hexyl thiophene) (P3HT) was reported. Two methods were used to prepare such composites, that is, the chemical interaction of the two constituents and the electrochemical polymerization of the 3-hexyl thiophene onto the rough Au supports modified with carbon nanotubes (CNTs). The measurements of the anisotropic PL of these composites have highlighted a significant diminution of the angle of the binding of the P3HT films electrochemical synthetized onto Au electrodes covered with M + S-SWNTs. This change was attributed to metallic tubes, as was demonstrated using the anisotropic PL measurements carried out on the P3HT/M-SWNTs and P3HT/S-SWNTs composites. Small variations in the angle of the binding were reported in the case of the composites prepared by chemical interaction of the two constituents. The proposed mechanism to explain this behavior took into account the functionalization process of CNTs with P3HT. The experimental arguments of the functionalization process of CNTs with P3HT were shown by the UV-VIS-NIR and FTIR spectroscopy as well as surface-enhanced Raman scattering (SERS). A PL quenching process of P3HT induced both in the presence of S-SWNTs and M-SWNTs was reported, too. This process origins in the various de-excitation pathways which can be developed considering the energy levels diagram of the two constituents of each studied composite.     

An ab initio study of ground state, electronic and thermodynamical properties of GaP and Ga2P

In the present paper, we report an ab initio calculation of the ground state, electronic and thermodynamical properties like constant volume lattice specific heat, vibrational energy, internal energy, and entropy for GaP and Ga₂P is presented. These properties are obtained after calculating the phonon spectrum over the entire Brillouin zone. The calculations were performed using the ABINIT program package, which is based on density functional theory (DFT) method and the use of pseudopotentials and plane wave expansion. Difference in the ground state properties such as electronic structure and thermodynamical properties are discussed. The thermodynamical properties follow the expected trend. There is a good agreement between present theoretical and limited available experimental data in the case of ground state such as lattice constant and bulk modulus and electronic properties. With the increase of Ga atoms in the unit cell the semiconducting nature of Ga₂P turns to metallic. There is a noticeable difference in the thermodynamical properties in the case of both gallium compounds.     

A First-Principles Study of C3N Nanostructures: Control and Engineering of the Electronic and Magnetic Properties of Nanosheets,Tubes and Ribbons

Using first-principles calculations we systematically investigate the atomic, electronic and magnetic properties of novel two-dimensional materials (2DM) with a stoichiometry C₃N which has recently been synthesized. We investigate how the number of layers affect the electronic properties by considering monolayer, bilayer and trilayer structures, with different stacking of the layers. We find that a transition from semiconducting to metallic character occurs which could offer potential applications in future nanoelectronic devices. We also study the affect of width of C₃N nanoribbons, as well as the radius and length of C₃N nanotubes, on the atomic, electronic and magnetic properties. Our results show that these properties can be modified depending on these dimensions, and depend markedly on the nature of the edge states. Functionalization of the nanostructures by the adsorption of H adatoms is found induce metallic, half-metallic, semiconducting and ferromagnetic behavior, which offers an approach to tailor the properties, as can the application of strain. Our calculations give insight into this new family of C₃N nanostructures, which reveal unusual electronic and magnetic properties, and may have great potential in applications such as sensors, electronics and optoelectronic at the nanoscale.     

Electrochemistry and electroanalytical applications of carbon nanotubes: a review.

This review addresses recent developments in electrochemistry and electroanalytical chemistry of carbon nanotubes (CNTs). CNTs have been proved to possess unique electronic, chemical and structural features that make them very attractive for electrochemical studies and electrochemical applications. For example, the structural and electronic properties of the CNTs endow them with distinct electrocatalytic activities and capabilities for facilitating direct electrochemistry of proteins and enzymes from other kinds of carbon materials. These striking electrochemical properties of the CNTs pave the way to CNT-based bioelectrochemistry and to bioelectronic nanodevices, such as electrochemical sensors and biosensors. The electrochemistry and bioelectrochemistry of the CNTs are summarized and discussed, along with some common methods for CNT electrode preparation and some recent advances in the rational functionalization of the CNTs for electroanalytical applications.     

Induced ferromagnetism in one-side semihydrogenated silicene and germanene

The intriguing electronic and magnetic properties of one-side semihydrogenated silicene and germanene are investigated by means of first-principles calculations. Both one-side semihydrogenated silicene and germanene are confirmed as dynamically stable in the ground state based on phonon-mode analysis. Moreover, we find that semihydrogenation from only one side causes localized and unpaired 3p (4p) electrons in the unhydrogenated Si (Ge) sites and then introduces ferromagnetism to silicene (germanene) sheet with no need for doping, cutting, or etching. One-side semihydrogenated silicene and germanene are both identified as semiconductors with direct energy gaps: their gap values obtained from the HSE06 functional are estimated to be 1.74 eV and 1.32 eV, much greater than the PBE-GGA results of 0.94 eV and 0.41 eV, respectively. From pristine to one-side semihydrogenated and then to fully hydrogenated systems, silicene and germanene change from metallic to magnetic semiconducting and then to nonmagnetic semiconducting. The hydrogenation process provides a novel method to tune the properties of silicene and germanene with unprecedented potentials for future nanoelectronics.     

Modeling adsorbate‐induced property changes of carbon nanotubes

Because of their potential for chemical functionalization, carbon nanotubes (CNTs) are promising candidates for the development of devices such as nanoscale sensors or transistors with novel gating mechanisms. However, the mechanisms underlying the property changes due to functionalization of CNTs still remain subject to debate. Our goal is to reliably model one possible mechanism for such chemical gating: adsorption directly on the nanotubes. Within a Kohn–Sham density functional theory framework, such systems would ideally be described using periodic boundary conditions. Truncating the tube and saturating the edges in practice often offers a broader selection of approximate exchange–correlation functionals and analysis methods. By comparing the two approaches systematically for NH₃ and NO₂ adsorbates on semiconducting and metallic CNTs, we find that while structural properties are less sensitive to the details of the model, local properties of the adsorbate may be as sensitive to truncation as they are to the choice of exchange–correlation functional, and are similarly challenging to compute as adsorption energies. This suggests that these adsorbate effects are nonlocal. © 2017 Wiley Periodicals, Inc.     

Liquid Metals and Liquid Semiconductors

Numerous liquid systems have electrical properties which resemble those of crystalline and amorphous semiconductors. The existence of “semiconducting” behavior in these liquids is mostly related to a continuous transition from a metallic to a “semiconducting” state when a thermodynamic variable such as temperature, density or concentration is changed. Changes in the nature of the chemical interaction and the associated changes in the structure of the liquid are of fundamental importance for the transition to a “semiconducting” state. This will be demonstrated for the ionic liquid CsAu, for covalent liquid selenium, and for expanded liquid metals.     

Characterisation of Nanohybrids of Porphyrins with Metallic and Semiconducting Carbon Nanotubes by EPR and Optical Spectroscopy

Single‐walled carbon nanotubes (SWCNTs) are noncovalently functionalised with octaethylporphyrins (OEPs) and the resulting nanohybrids are isolated from the free OEPs. Electron paramagnetic resonance (EPR) spectroscopy of cobalt(II)OEP, adsorbed on the nanotube walls by π–π‐stacking, demonstrates that the CNTs act as electron acceptors. EPR is shown to be very effective in resolving the different interactions for metallic and semiconducting tubes. Moreover, molecular oxygen is shown to bind selectively to nanohybrids with semiconducting tubes. Water solubilisation of the porphyrin/CNT nanohybrids using bile salts, after applying a thorough washing procedure, yields solutions in which at least 99 % of the porphyrins are interacting with the CNTs. Due to this purification, we observe, for the first time, the isolated absorption spectrum of the interacting porphyrins, which is strongly red‐shifted compared to the free porphyrin absorption. In addition a quasi‐complete quenching of the porphyrin fluorescence is also observed.     

Biomolecule-functionalized carbon nanotubes: applications in nanobioelectronics.

Carbon nanotubes (CNTs) revealing metallic or semiconductive properties depending on the folding modes of the nanotube walls represent a novel class of nanowires. Different methods to separate semiconductive CNTs from conductive CNTs have been developed, and synthetic strategies to chemically modify the side walls or tube ends by molecular or biomolecular components have been reported. Tailoring hybrid systems consisting of CNTs and biomolecules (proteins and DNA) has rapidly expanded and attracted substantial research effort. The integration of biomaterials with CNTs enables the use of the hybrid systems as active field-effect transistors or biosensor devices (enzyme electrodes, immunosensors, or DNA sensors). Also, the integration of CNTs with biomolecules has allowed the generation of complex nanostructures and nanocircuitry of controlled properties and functions. The rapid progress in this interdisciplinary field of CNT-based nanobioelectronics and nanobiotechnology is reviewed by summarizing the present scientific accomplishments, and addressing the future goals and perspectives of the area.