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Theoretical investigation of electronic bandgaps of semiconducting single-walled carbon nanotubes using semi-empirical self-consistent tight binding and <i>ab-inito</i> density functional methods
摘要： We perform a comprehensive theoretical study of electronic band gaps of semiconducting single-walled carbon nanotubes (SWNTs) with different sets of chiral indices using semi-empirical tight binding and density functional (DFT) based ab-initio methods. In particular, self-consistent extended Huckel (EH-SCF) and self-consistent Slater Koster (SK-SCF) tight binding models are used as semi-empirical methods, whereas the DFT based LDA-1/2 and Tran-Blaha (TB09) meta-GGA schemes are used as ab-initio methods. The calculations are performed for 1) (n, m) chiral SWNTs for which experimental optical gaps have been reported 2) (9, 0), (12, 0) and (15, 0) ‘metallic’ zigzag SWNTs for which small bad gaps have been reported 3) Pairs of SWNTs having same diameters but different chiral angles 4) (n, 0) zigzag SWNTs with ? ?n 30. From the comparison of bands gaps of tubes with same diameter, the electronic band gaps are found to vary with chiral angles with opposing trend as compared to that reported for experimental optical band gaps. This result may be expected to have important implications for self-energy corrections and/or exciton binding energies and their dependence on chiral angles. The hopping parameter g0 obtained from ?tting EH-SCF and SK-SCF bandgap data, is found to be in good agreement with that obtained from ?tting experimental data. In general, the band gap values of SWNTs computed using semi-empirical EH-SCF and SK-SCF methods are quite close (within ～ 5%) to those computed using DFT-based LDA-1/2 and TB09 meta-GGA methods. The results suggest that self-consistent semi-empirical methods can be expected to provide similar accuracy in results as that expected from more computationally challenging ab-intio DFT based LDA-1/2 and TB09 meta-GGA methods.
关键词： self-consistent tight binding method,semiconducting carbon nanotubes,electronic structure,first principles calculations
更新于2025-09-16 10:30:52
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Broadening of van Hove Singularities Measured by Photoemission Spectroscopy of Single and Mixed Chirality Single-Walled Carbon Nanotubes
摘要： The occupied valence electronic states of single walled carbon nanotubes (SWCNTs) are responsible for their optoelectronic properties and are unique for each SWCNT chirality. Photoemission spectroscopy (PES) is one of the few methods capable of directly measuring the electron density in the valence states of materials but there are only few reports which have observed the valence states of SWCNTs and no examples for single-chirality SWCNTs. Here we prepare single and mixed chirality SWCNT films and characterise their valence states using PES. Chirality pure SWCNTs were isolated using both gel permeation chromatography and ssDNA facilitated aqueous two phase extraction from starting materials consisting of mixed chirality species. Chirality separation and purity was confirmed with UV-Vis-nIR absorption spectroscopy. SWCNT films were prepared for the single chirality species (10,3), (7,6), (7,3), (6,5), (8,3), (9,1) along with SWCNT chirality mixture of metallic and semiconducting SWCNTs, and as-synthesised mixtures possessing a range of SWCNT diameter. PES using synchrotron radiation was completed for all samples with survey and C 1s core level spectra obtained to confirm SWCNT coverage, defect level and purity. Valence band PES was obtained to characterise the valence electronic states and showed significant broadening of the signal, in comparison to calculated density of states, which could not be accounted for by instrument resolution. An inverse diameter dependence of the broadening was observed with greater broadening for smaller diameter SWCNTs. The broadening is hypothesised to be related to the photohole lifetime which was found to be significantly longer for wide diameter SWCNTs. The diameter dependence of the broadening and photohole lifetimes is discussed in terms of both Tomonaga-Luttinger and Landau theory of Fermi liquids.
关键词： chirality,valence electronic states,single-walled carbon nanotubes,van Hove singularities,photoemission spectroscopy
更新于2025-09-16 10:30:52
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Chirality-dependent growth of self-assembled diphenylalanine microtubes
摘要： The difference in crystal structure and growth kinetics of microtubes formed from L- and D- enantiomers of diphenylalanine dipeptide is investigated both experimentally and theoretically by computer simulation. The microtubes of L- and D- enantiomers grown simultaneously and under identical experimental conditions possess different crystallographic space groups, have essential difference in sizes and demonstrate different growth kinetics. Computer simulation by molecular mechanics methods revealed a fundamental difference in the interaction between structural units of microtubes of different chiralities. A model describing chirality-dependent growth of microtubes is proposed.
关键词： Growth kinetics,Enantiomers,Dipeptide,Computer modeling,Nanotubes,Self-assembly
更新于2025-09-16 10:30:52
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The In-Depth Studies of Pulsed UV Laser-Modified TiO2 Nanotubes: The Influence of Geometry, Crystallinity, and Processing Parameters
摘要： The laser processing of the titania nanotubes has been investigated in terms of morphology, structure, and optical properties of the obtained material. The length of the nanotubes and crystallinity, as well as the atmosphere of the laser treatment, were taken into account. The degree of changes of the initial geometry of nanotubes were checked by means of scanning electron microscopy, which visualizes both the surface and the cross-section. The phase conversion from the amorphous to anatase has been achieved for laser-treated amorphous material, whereas modification of calcined one led to distortion within the crystal structure. This result is confirmed both by Raman and grazing incident XRD measurements. The latter studies provided an in-depth analysis of the crystalline arrangement and allowed also for determining the propagation of laser modification. The narrowing of the optical bandgap for laser-treated samples has been observed. Laser treatment of TiO2 nanotubes can lead to the preparation of the material of desired structural and optical parameters. The usage of the motorized table during processing enables induction of changes in the precisely selected area of the sample within a very short time.
关键词： laser treatment,TiO2 nanotubes,phase transformation,surface modification
更新于2025-09-16 10:30:52
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Ni3S2@MWCNTs films for effective counter electrodes of dye-sensitized solar cells
摘要： Composite films nickel sulfide (Ni3S2) nanoparticles were grown on multiwall carbon nanotubes (MWCNTs) and in situ coated onto conducting glass substrates by the hydrothermal process at 170 °C. These Ni3S2@MWCNTs films were applied for counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). In this work, nanostructure, crystalline structure, electrochemical activities and electron-charge transfer resistance of CEs were studied. In addition, the effective surface areas of CEs were analyzed and discussed as well. The power conversion efficiency (PCE) enhancement of up to 7.48%, compared with that of Ni3S2-DSSC, was demonstrated for a Ni3S2@MWCNTs DSSC.
关键词： Counter electrode,Ni3S2,Dye-sensitized solar cell,Hydrothermal method,Multiwall carbon nanotubes
更新于2025-09-16 10:30:52
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Covalent Surface Modification Effects on Singlea??Walled Carbon Nanotubes for Targeted Sensing and Optical Imaging
摘要： Optical nanoscale technologies often implement covalent or noncovalent strategies for the modification of nanoparticles, whereby both functionalizations are leveraged for multimodal applications but can affect the intrinsic fluorescence of nanoparticles. Specifically, single-walled carbon nanotubes (SWCNTs) can enable real-time imaging and cellular delivery; however, the introduction of covalent SWCNT sidewall functionalizations often attenuates SWCNT fluorescence. Recent advances in SWCNT covalent functionalization chemistries preserve the SWCNT’s pristine graphitic lattice and intrinsic fluorescence, and here, such covalently functionalized SWCNTs maintain intrinsic fluorescence-based molecular recognition of neurotransmitter and protein analytes. The covalently modified SWCNT nanosensor preserves its fluorescence response towards its analyte for certain nanosensors, presumably dependent on the intermolecular interactions between SWCNTs or the steric hindrance introduced by the covalent functionalization that hinders noncovalent interactions with the SWCNT surface. These SWCNT nanosensors are further functionalized via their covalent handles with a targeting ligand, biotin, to self-assemble on passivated microscopy slides, and these dual-functionalized SWCNT materials are explored for future use in multiplexed sensing and imaging applications.
关键词： single-walled carbon nanotubes,biosensing,fluorescence,imaging,surface functionalization
更新于2025-09-16 10:30:52
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Fabrication of Durable Ordered Ta2O5 Nanotube Arrays Decorated with Bi2S3 Quantum Dots
摘要： One of the most important challenges in the fabrication of ordered tantalum pentaoxide (Ta2O5) nanotube arrays (NTs) via the electrochemical method is the formation of nanotubes that adhere well to the Ta substrate. In this paper, we propose a new protocol that allows tight-fitting Ta2O5 nanotubes to be obtained through the anodic oxidation of tantalum foil. Moreover, to enhance their activity in the photocatalytic reaction, in this study, they have been decorated by nontoxic bismuth sulfide (Bi2S3) quantum dots (QDs) via a simple successive ionic layer adsorption and reaction (SILAR) method. Transmission electron microscopy (TEM) analysis revealed that quantum dots with a size in the range of 6–11 nm were located both inside and on the external surfaces of the Ta2O5 NTs. The effect of the anodization time and annealing conditions, as well as the effect of cycle numbers in the SILAR method, on the surface properties and photoactivity of Ta2O5 nanotubes and Bi2S3/Ta2O5 composites have been investigated. The Ta2O5 nanotubes decorated with Bi2S3 QDs exhibit high photocatalytic activity in the toluene degradation reaction, i.e., 99% of toluene (C0 = 200 ppm) was degraded after 5 min of UV-Vis irradiation. Therefore, the proposed anodic oxidation of tantalum (Ta) foil followed by SILAR decorating allows a photocatalytic surface, ready to use for pollutant degradation in the gas phase, to be obtained.
关键词： Bi2S3 quantum dots,ordered Ta2O5 nanotubes,heterogeneous photocatalysis
更新于2025-09-16 10:30:52
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Sonication-Enhanced Alignment Relay Technique for the Orientation of Single-Walled Carbon Nanotubes
摘要： The high demand for thin, lightweight yet fast and e?cient devices is a driving force behind the miniaturization trend in the electronics industry. Speci?cally, the advancement of semiconducting single-walled carbon nanotubes (SWNTs) can continue to revolutionize transistors, although there are still many challenges ahead. We have previously reported an alignment relay technique (ART) that is capable of simultaneously controlling the alignment, length, and diameter of surface deposited SWNTs. However, the current technique yields inconsistencies in orientation, lengths of tubes, and their density. Here, we present a reviewed ART protocol that includes sonication for improved selectivity. We show that the SWNTs average alignment increased from 40% to 77% within a 10° range in orientation with sonication times as low as 5 min. Sonication generated larger diameter nanotubes on the surface, with a preference for semiconducting chiral tubes in the range of 1.44?1.61 nm in diameter. Consequently, simple alterations to the standard alignment relay technique can prove to be prosperous in improving selectivity and orientational control of single-walled carbon nanotubes. This work has direct impact for the simultaneous control of nanotube alignment and nanotube chiralities.
关键词： alignment relay technique,iptycenes,alignment,sonication,single-walled carbon nanotubes,surface chemistry,liquid crystals
更新于2025-09-16 10:30:52
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Fabrication of architectural structured polydopamine-functionalized reduced graphene oxide/carbon nanotube/PEDOT:PSS nanocomposites as flexible transparent electrodes for OLEDs
摘要： High performance, flexible transparent conductive films with a structure similar to that of reinforced concrete and constructed by sandwiching single-walled carbon nanotubes (SWCNT) between poly (3,4-ethylene dioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) and polydopamine functionalized reduced graphene oxide (PDA-RGO) were fabricated using simple spray coating. Mussel-inspired polydopamine was introduced as a graphene oxide reducing agent and modifier; the obtained PDA-RGO improved the interfacial adhesion between the conductive coating layers and substrate, and an effective post fabrication treatment method was performed on the hybrid film to achieve better conductivity. It was found that the resulting electrode exhibited a low sheet resistance of 52.2 Ω/sq. with a high optical transmittance of 88.7% at 550 nm. Moreover, the transparent film exhibited long-term stability with a relatively low roughness (ca. 2.41 nm), and its architectural structure sustained the flexibility of the film during bending. The organic light emitting diodes which using PDA-RGO/SWCNT/PEDOT:PSS film as anode was successfully fabricated, the luminance of the device was 2032 cd/cm2 at 15 V and the maximum current efficiency was 2.13 cd/A at 14 V, indicating the strong potential of this type of transparent electrode for flexible electroluminescent devices.
关键词： OLEDs,Polydopamine Functionalized Reduced Graphene Oxide,PEDOT:PSS,Flexible transparent conductive films,Carbon nanotubes
更新于2025-09-16 10:30:52
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Fine-tuning of spark-discharge aerosol CVD reactor for single-walled carbon nanotube growth: the role of ex situ nucleation
摘要： We report a development of recently designed apparatus equipped with a spark discharge generator of catalytic nanoparticles for robust aerosol CVD synthesis of single-walled carbon nanotubes. We achieve a profound control over the diameter distribution and the defectiveness of carbon nanotubes produced. By providing a justified comparison of the apparatus with the most abundant aerosol CVD reactor utilizing ferrocene as a catalyst precursor, we reveal the role of the activation procedure: while spark-discharge generator provides aerosol of nanoparticles (ex situ route), the ferrocene vapor decomposes in the nanotube growth zone providing an in situ formation of the catalyst. With other parameters being equal, we reveal the differences in the nanotube growth (diameter and length distribution, yield, defectiveness) employing a comprehensive set of methods (the analysis of differential mobility of the aerosol particles, optical spectroscopy, scanning and transmission electron microscopy, Raman spectroscopy, and atomic force microscopy). We show the ex situ activation in the spark discharge reactor to provide a lower utilization degree of the nanoparticles due to over-coagulation. However, the same method provides an independence of the key performance parameters of the nanotubes opening a room for scaling the apparatus.
关键词： spark-discharge generator,differential mobility analyzer,aerosol CVD synthesis,catalyst activation,floating catalyst,single-walled carbon nanotubes
更新于2025-09-16 10:30:52