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Carbon Nanotubes - Recent Progress || Stability and Reliability of an Electrical Device Employing Highly Crystalline Single-Walled Carbon Nanotubes as a Field Emitter
摘要： Carbon nanomaterial is drawing keen interest from researchers as well as materials scientists. Carbon nanotubes (CNTs)—and their nanoscale needle shape—offering chemical stability, thermal conductivity, and mechanical strength exhibit unique properties as a quasi-one-dimensional material. Among the expected applications, field emission electron sources appear the most promising industrially and are approaching practical utilization. However, efforts to construct a field emission (FE) cathode with single-walled carbon nanotubes (SWCNTs) have so far only helped average out a non-homogeneous electron emitter plane with large FE current fluctuations and a short emission life-time because they failed to realize a stable emission current owing to crystal defects of the carbon network in CNTs. The utilization of CNTs to obtain an effective cathode, one with a stable emission and low FE current fluctuation, relies on the ability to disperse CNTs uniformly in liquid media. In particular, highly crystalline SWCNTs hold promise to obtain good stability and reliability. The author successfully manufactured highly crystalline SWCNTs-based FE lighting elements that exhibit stable electron emission, a long emission life-time, and low power consumption for electron emitters. This FE device employing highly crystalline SWCNTs has the potential for conserving energy through low power consumption in our habitats.
关键词： wet coating process,high crystallization,field emission,single-walled carbon nanotube,scratch,thin film,planar light source,cathode luminescence
更新于2025-09-23 15:21:01
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Enhanced Ferroelectric Photovoltaic Effect in Semiconducting Single-Wall Carbon Nanotubes/BiFeO <sub/>3</sub> Heterostructure Enabled by Wide-Range Light Absorption and Efficient Charge Separation
摘要： The interfacial electronic band structures of photovoltaic heterostructure devices greatly affect their light absorption and charge-transport properties and thus their photovoltaic performance. In this work, we report an enhanced ferroelectric photovoltaic effect in a semiconducting single-walled carbon nanotube (S-SWCNTs)/ferroelectric BiFeO3 (BFO) heterostructure. A wide range of light absorption was possible in this structure owing to the low bandgaps of the S-SWCNTs (0.2–2.1 eV) and BFO (2.2–2.7 eV). The heterostructure also enabled efficient charge separation owing to the strong built-in electric field resulting from the synergic effect of the formation of p–f–n junctions (p-type S-SWCNTs/ferroelectric (f) BFO/n-type Nb:SrTiO3) and the introduction of a polarization-mediated internal field in the ferroelectric BFO layer. Compared with a single-layer device (Pt/BFO/Nb:SrTiO3), the heterostructure device (Pt/S-SWCNTs/BFO/Nb:SrTiO3) exhibited substantial enhancement of the photovoltaic performance. The open-circuit photovoltage and short-circuit photocurrent density reached up to 0.23 V and ?7.52 mA cm?2 (corresponding to a photo-conversion efficiency of 4.40%) under one-sun illumination, respectively, after optimization of the ferroelectric layer thickness and appropriate interfacial band alignment. Moreover, by applying switchable electric polarization, this heterostructure could be tuned, enabling the development of controllable photovoltaic devices. Our findings demonstrate that the synergistic integration of materials with different functionalities is a promising approach for the design of photovoltaic devices with tunable performance.
关键词： BiFeO3,light absorption,single-walled carbon nanotube,heterostructure,charge separation,ferroelectric photovoltaic effect
更新于2025-09-23 15:21:01
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Efficiency of Charge-Transfer Doping in Organic Semiconductors Probed with Quantitative Microwave and Direct-Current Conductance
摘要： Although molecular charge-transfer doping is widely used to manipulate carrier density in organic semiconductors, only a small fraction of charge carriers typically escape the Coulomb potential of dopant counterions to contribute to electrical conductivity. Here, we utilize microwave and direct-current (DC) measurements of electrical conductivity to demonstrate that a high percentage of charge carriers in redox-doped semiconducting single-walled carbon nanotube (s-SWCNT) networks is delocalized as a free carrier density in the π-electron system (estimated as >46% at high doping densities). The microwave and four-point probe conductivities of hole-doped s-SWCNT films quantitatively match over almost 4 orders of magnitude in conductance, indicating that both measurements are dominated by the same population of delocalized carriers. We address the relevance of this surprising one-to-one correspondence by discussing the degree to which local environmental parameters (e.g., tube?tube junctions, the relative Coulombic stabilization, and local bonding environment) may impact magnitudes of each transport measurement.
关键词： microwave conductivity,organic semiconductors,single-walled carbon nanotube,charge-transfer doping,DC conductivity
更新于2025-09-23 15:21:01
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MATHEMATICAL ANALYSIS AND MODELING OF SINGLE-WALLED CARBON NANOTUBE COMPOSITE MATERIAL FOR ANTENNA APPLICATIONS
摘要： In this paper, the mathematical analysis of a single-walled carbon nanotube composite material (SWCNT-composite) is presented in order to estimate its e?ective conductivity model and other important parameters. This composite material consists of SWCNT coated by other di?erent materials. The e?ects of the radius of SWCNT and average thickness of coating layer on this e?ective conductivity model are investigated. The e?ects of using di?erent types of coating materials with di?erent radii of SWCNTs on the behavior of this composite material are also presented. An investigation of electromagnetic properties of SWCNT-composite material was carried out based on designing and implementing the dipole antenna con?guration using a common electromagnetic engineering tool solver CST (MWS). The results obtained from comparisons between SWCNT and SWCNT-composite materials are presented, based on their electromagnetic properties.
关键词： dipole antenna,CST (MWS),electromagnetic properties,effective conductivity model,single-walled carbon nanotube composite material
更新于2025-09-19 17:13:59
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Raman Spectroscopic Evidence of the Selective Extraction of Metallic Single-Walled Carbon Nanotubes by Polymethyl(1-undecylic acidy)Silane
摘要： The selective extraction behavior of a water soluble polysilane derivative, polymethyl(1-undecylic acidyl)silane, towards metallic single-walled carbon nanotubes from the primarily purified arc-discharged sample is confirmed by Raman spectroscopy recorded with varying excitation laser wavelength. In line with the wavelength of the excitation laser the full assignment (n, m) for individual single-walled carbon nanotubes is made by referencing a Kataura plot, and these selectively extracted metallic carbon nanotubes are assigned to be of (13, 1), (14, 5), (15, 3), (21, 0) and (19, 1) chiral indices, which have larger diameters and smaller chiral angles than those reported previously. Moreover, it is evidenced that the width of Breit–Wigner–Fano G? band is directly correlated with the diameter distribution of metallic carbon nanotubes, and that metallic carbon nanotubes normally exhibit much enhanced D-band relative to semiconducting ones. It is also found that the G+, second order M and none dispersive IFM bands are largely up-shifted in comparison with those reported previously, which might be a result of the release of tube–tube interaction, the close helix wrapping of SWNTs by polymethyl(1-undecylic acidyl)silane and charge transfer between polymethyl(1-undecylic acidyl)silane and carbon nanotubes. Additionally, the dispersive IFM bands show a “step-like dispersive behavior,” offering another support for the success in selective extraction of SWNTs with small chiral angles.
关键词： Polymethylsilane Derivative,Single-Walled Carbon Nanotube,Selective Extraction,Raman Scattering,Excitation Laser Wavelength
更新于2025-09-16 10:30:52
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Tunable Assembly of Superfine Single-Walled Carbon Nanotube Fibers
摘要： We have developed a method of spinning super?ne single-walled carbon nanotube (SWNT) ?bers to facilitate their assembly in 2D counter microelectrode array via alternating current (AC) dielectrophoresis (DEP) by using clean, combination of ionic surfactants, and stable SWNT aqueous high-quality solutions. Our method can attract metallic SWNTs (M_SWNTs) toward a counter microelectrode array, resulting in an opposite movement of semiconducting SWNTs (S_SWNTs) and leaving S_SWNTs in the suspension by taking advantages of the differences in the relative dielectric constants of M_SWNTs and S_SWNTs with respect to the suspension and substrate-bent AC DEP structure. Our method can also control the stretching or relaxed extent and diameters of the suspended SWNT ?bers by tuning the bending degree of a ?exible substrate, AC frequency, peak value of AC voltage, and time. The effectiveness of the method is proven by the electrical measurement result, scanning electron microscopy image, atomic force microscope image and Raman spectroscopy on test samples.
关键词： Tunable assembly,single-walled carbon nanotube (SWNT) ?bers,alternating current (AC) dielectrophoresis,substrate-bent
更新于2025-09-16 10:30:52
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Single-walled carbon nanotube growth at low temperature by alcohol gas source method using Co catalyst: enhancement effects of Al<sub>2</sub>O<sub>3</sub> buffer layer on carbon nanotube yield
摘要： Using an alcohol gas source chemical vapor deposition method, we attempted to grow single-walled carbon nanotube (SWCNT) growth using Co catalysts on Al2O3 buffer layers. Reducing the growth temperature decreased the optimal ethanol pressure to obtain the highest SWCNT yield. By optimizing the ethanol pressure, we succeeded in growing SWCNTs at 400oC. Irrespective of the growth temperature, SWCNT yields from Co catalysts on Al2O3 buffer layers were higher than those on SiO2/Si substrates, but the enhancing effects of Al2O3 buffer layers on SWCNT yield were reduced below 500oC. Taking into account both in-plane X-ray diffraction results and decrease of catalyst aggregation in the low temperature region, we concluded that the density of Co particles suitable for SWCNT growth increased on SiO2 surface at low temperature, resulting in the reduction of difference in SWCNT yield at low temperature between Al2O3 buffer layers and SiO2/Si substrates.
关键词： catalyst,CVD,low-temperature growth,single-walled carbon nanotube,Co
更新于2025-09-16 10:30:52
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Model for electroluminescence in single-walled carbon nanotube field effect transistor under transverse magnetic field
摘要： Electroluminescence spectrum and radiative recombination rate of short channel single-walled carbon nanotube field effect transistor in presence of transverse magnetic field is calculated by using non-equilibrium Green’s function method. Significant enhancement in radiative recombination rate and red shift in electroluminescence spectrum are observed with increase in the strength of magnetic field. The band gap suppression estimated from energy position resolved local density of states calculation plays a dominant role in transport mechanism under the influence of external magnetic field. The tuning of electroluminescence spectrum of single-walled carbon nanotube by transverse magnetic field can be employed as nanoscale optical source in next generation optoelectronic and photonic devices.
关键词： electroluminescence,single-walled carbon nanotube,optoelectronics,radiative recombination rate,plasmonics,field effect transistor
更新于2025-09-16 10:30:52
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Ideal <i>pn</i> Diodes from Single-Walled Carbon Nanotubes for Use in Solar Cells: Beating the Detailed Balance Limit of Efficiency
摘要： Though many technologies exist for improving solar cell efficiencies, there remains an unexplored fundamental parameter, the diode ideality factor (??), that we can exploit. The Shockley-Queisser limit states that the maximum solar conversion efficiency in a single pn junction is achievable only when it is operated in the ideal diode limit of ?? = 1. Generation and recombination losses correlate directly to an increase in the dark saturation current and ??, both of which have competing effects on the open-circuit voltage. Here, we demonstrate a new approach to improving the efficiency of solar cells beyond the detailed balance limit by gate modulation of the diode’s ideality factor in ideal carbon nanotube pn diodes. We show that the open-circuit voltage can be tuned in direct proportion to ?? without impacting the reverse bias leakage current or the short circuit current. We show that our approach is similar to the enhancement from solar concentrators without actually using them. We achieve an open-circuit voltage that is ~300% higher than that given by the detailed balance limit.
关键词： pn junction,photovoltaic effect,open-circuit voltage,gate-tunable diodes,Single-walled carbon nanotube,detailed balance limit
更新于2025-09-16 10:30:52
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Semiconducting single-walled carbon nanotube/graphene van der Waals junctions for highly sensitive all-carbon hybrid humidity sensors
摘要： Van der Waals (vdW) heterojunctions composed of diverse atomic-thin nanomaterials have great potential as building blocks for innovative nanodevices due to the unique electron coupling effect. However, previous researches have mainly focused on the light-mater interactions and charge transfer process, and the interactions between gas/vapor and vdW heterojunctions still remain to be verified. Herein, we firstly demonstrate the charge transfer based on the interaction between water (H2O) molecules and the all-carbon vdW junctions, which are formed by stacking non-carboxylated (6, 5) single-walled carbon nanotube (SWCNT) on the surface of chemical vapor deposition synthesized graphene. Based on these interaction mechanism and charge transfer process, a proof-of-concept all-carbon vdW junction humidity sensor has been fabricated. The device exhibits good reproducibility and high sensitivity of 24% per 1% RH change in a wide relative humidity range of 5~80 % with short response/recovery time of 198/110 ms. Furthermore, the effect of H2O molecule absorption on the charge transfer dynamics at the SWCNT/graphene vdW junctions has been demonstrated via Raman spectra, giving a novel humidity sensing mechanism. Our finding provides a new strategy to fabricate high performance humidity sensors using vdW heterojuctions as sensing layers.
关键词： humidity sensor,single-walled carbon nanotube,graphene,charge transfer,van der Waals heterojunctions
更新于2025-09-16 10:30:52