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Field emission property of vertically aligned nitrogen-doped multi-walled carbon nanotubes produced by chemical vapor deposition
摘要： Vertically aligned nitrogen-doped multi-walled carbon nanotubes (N-MWNTs) were synthesized by the chemical vapor deposition (CVD) at 900 °C using imidazole mixed with ferrocene as carbon and nitrogen sources, and catalyst, respectively. The effects of ammonia (NH3) and hydrogen (H2) flow rates on the growth of N-MWNTs were investigated (hereafter referred to A-N-MWNTs and H-N-MWNTs, respectively). Transmission electron microscopy (TEM) revealed the bamboo-like structure of the N-MWNTs, in which the separation between individual bamboo compartments decreased with increasing nitrogen concentration in N-MWNTs. X-ray photoelectron spectroscopy (XPS) analysis results supported that the nitrogen concentrations in N-MWNTs is 0.55 at.%, whereas A-N-MWNTs and H-N-MWNTs with the flow rate at 10 standard cubic centimeters per minute (sccm) (10A-N-MWNTs and 10H-N-MWNTs, respectively) showed 1.14 and 4.06 at.%, respectively. We found that the optimal conditions for the highest nitrogen-doped multi-walled carbon nanotubes (MWNTs) was a flow rate of NH3 and H2 at 10 sccm. Results from field emission measurements indicated that the turn-on fields of N-MWNTs, 10A-N-MWNTs and 10H-N-MWNTs were 6.7, 4.3 and 3.1 V/μm, respectively, while the field enhancement factors (β) were 5230, 10,805 and 20,390, respectively. Furthermore, the current density of N-MNWTs increased with increasing the nitrogen atoms in MWNTs. The results support that field emission based on N-MWNTs is a good emitter with low turn-on field and large field enhancement factor. Nitrogen doping in MWNTs makes them attractive candidates as high-performance field emitters.
关键词： Field emission,Nitrogen-doped multi-walled carbon nanotubes,Chemical vapor deposition
更新于2025-09-12 10:27:22
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Scalable Route toward Superior Photoresponse of UV-Laser-Treated TiO <sub/>2</sub> Nanotubes
摘要： Titanium dioxide nanotubes gain considerable attention as a photoactive material due to chemical stability, photocorrosion resistance, or low-cost manufacturing method. This work presents scalable pulsed laser modification of TiO2 nanotubes resulting in enhanced photoactivity in a system equipped with a motorized table, which allows for modifications of both precisely selected and any-large sample area. Images obtained from scanning electron microscopy along with Raman and UV?vis spectra of laser-treated samples in a good agreement indicate the presence of additional laser-induced shallow states within band gap via degradation of crystalline structure. However, X-ray photoelectron spectroscopy spectra revealed no change of chemical nature of the modified sample surface. Photoelectrochemical measurements demonstrate superior photoresponse of laser-treated samples up to 1.45-fold for an energy beam fluence of 40 mJ/cm2 compared to that of calcined one. According to the obtained results, optimal processing parameters were captured. Mott?Schottky analysis obtained from impedance measurements indicates an enormous (over an order of magnitude) increase of donor density along with a +0.74 V positive shift of flat band potential. Such changes in electronic structure are most likely responsible for enhanced photoactivity. Thus, the elaborated method of laser nanostructuring can be successfully employed to the large-scale modification of titania nanotubes resulting in their superior photoactivity. According to that, the results of our work provide a contribution to wider applications of materials based on titania nanotubes.
关键词： nanotubes,titanium dioxide,Mott?Schottky analysis,laser modification
更新于2025-09-12 10:27:22
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Screen-printed PEDOT:PSS/halloysite counter electrodes for dye-sensitized solar cells
摘要： In this work, water-based and viscous screen-printing inks composed of conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) and insulating halloysite nanotubes as a filler (HNTs) with different organic additives were prepared by simply homogenization process. PEDOT:PSS/HNTs inks were screen-printed onto FTO substrates and were used as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). Incorporation of HNTs leads to a significant increase in ink thermal stability evaluated by TGA. XPS results indicate that simple homogenization process of PEDOT:PSS and HNTs led to the formation of compact PEDOT:PSS/HNTs nanocomposite structure where components are linked by physical interactions. Screen-printed PEDOT:PSS/HNTs CEs with 1 wt% of HNTs reached the highest conductivity (381 S/cm). Moreover, the positive effect of HNTs filler in CEs was confirmed by electrochemical measurements (CV and EIS). DSSCs with screen-printed PEDOT:PSS/HNTs CEs have overall better photovoltaic properties with ≈15% increase in the conversion efficiency (η = 4.5%) compared to PEDOT:PSS CEs.
关键词： Screen-printing,Printed electronics,Counter electrode,Halloysite nanotubes,PEDOT:PSS,Dye-sensitized solar cells
更新于2025-09-12 10:27:22
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First-principle study of SO2 adsorption on Fe/Co-doped vacancy defected single-walled (8, 0) carbon nanotubes in sensor applications
摘要： To explore the excellent sensor for detecting the pollution gas SO2, the adsorptions of SO2 molecule on the surfaces of Fe/Co-doped carbon nanotubes (CNTs) and single vacancy defected (8, 0) CNTs were investigated by using density functional theory (DFT). In addition, the adsorption energies, geometries, energy gaps and electronic structures were analyzed. The results showed that Fe/Co-doping and single-vacancy-defected can improve the adsorption and sensitiveness of CNTs toward SO2. Considering the changes of energy gap before and after the SO2 molecule adsorbed on each modiˉed CNTs and its adsorption strength, Fe-doped CNTs (Fe-CNTs) and Co-doped site-2 single-vacancy-defected CNTs performed better for detecting SO2 molecule. With the decreasing number of electrons of the doped atom (Fe, Co, Ni), the adsorption became more stable. The results of this paper are profound and meaningful for designing SO2 sensing devices.
关键词： SO2,adsorption,carbon nanotubes,co-doping,vacancy,Fe-doping
更新于2025-09-12 10:27:22
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Optical Voltammetry of Polymer-Encapsulated Single-Walled Carbon Nanotubes
摘要： The semiconducting single-walled carbon nanotube (SWCNT), noncovalently wrapped by a polymeric monolayer, is a nanoscale semiconductor?electrolyte interface under investigation for sensing, photonics, and photovoltaic applications. SWCNT complexes are routinely observed to sensitize various electrochemical/redox phenomena, even in the absence of an external ?eld. While the photoluminescence response to gate voltage depends on the redox potential of the functionalized nanotube, analogous optical voltammetry of carbon nanotubes could be conducted in suspension without applying voltage but by varying the solution conditions as well as the chemistry of the encapsulating polymer. Steady-state photoluminescence, absorbance, and in situ measurements of O2/H2O reactivity show correlation with the pH/pKa-dependent reactivity of π-rich coatings. The nanotube emission responses suggest that the presence of photogenerated potential may explain the observed coating electrochemical reactivity. This work ?nds that electronic and chemical interactions of the nanotube with the encapsulating polymer may play a critical role in applications that depend on radiative recombination, such as optical sensing.
关键词： redox phenomena,optical voltammetry,single-walled carbon nanotubes,photoluminescence,polymer encapsulation
更新于2025-09-12 10:27:22
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Thermodynamic control of quantum defects on single-walled carbon nanotubes
摘要： Single-walled carbon nanotubes with designed quantum defects are prepared and characterized. The photoluminescence (PL) of the nanotubes can be modified by thermal treatment from 1215–1224 to 1249–1268 nm. Theoretical calculations suggest that the change in the PL spectra by thermal treatment can be explained by isomerization from kinetic to thermodynamic products.
关键词： quantum defects,Single-walled carbon nanotubes,photoluminescence,thermal treatment,isomerization
更新于2025-09-12 10:27:22
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Bias Tunable Photocurrent in Metal-Insulator-Semiconductor Heterostructures with Photoresponse Enhanced by Carbon Nanotubes
摘要： Metal-insulator-semiconductor-insulator-metal (MISIM) heterostructures, with rectifying current-voltage characteristics and photosensitivity in the visible and near-infrared spectra, are fabricated and studied. It is shown that the photocurrent can be enhanced by adding a multi-walled carbon nanotube film in the contact region to achieve a responsivity higher than 100 mA W?1 under incandescent light of 0.1 mW cm?2. The optoelectrical characteristics of the MISIM heterostructures are investigated at lower and higher biases and are explained by a band model based on two asymmetric back-to-back Schottky barriers. The forward current of the heterojunctions is due to majority-carrier injection over the lower barrier, while the reverse current exhibits two different conduction regimes corresponding to the diffusion of thermal/photo generated carriers and majority-carrier tunneling through the higher Schottky barrier. The two conduction regimes in reverse bias generate two plateaus, over which the photocurrent increases linearly with the light intensity that endows the detector with bias-controlled photocurrent.
关键词： Schottky junctions,carbon nanotubes,photoconductivity,heterostructures,MISIM
更新于2025-09-12 10:27:22
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pH-Controlled fluorescence switching in water-dispersed polymer brushes grafted to modified boron nitride nanotubes for cellular imaging
摘要： pH-Switchable, fluorescent, hybrid, water-dispersible nanomaterials based on boron nitride nanotubes (BNNTs) and grafted copolymer brushes (poly(acrylic acid-co-fluorescein acrylate) – P(AA-co-FA)) were successfully fabricated in a two-step process. The functionalization of BNNTs was confirmed by spectroscopic, gravimetric and imaging techniques. In contrast to “pure” BNNTs, P(AA-co-FA)-functionalized BNNTs demonstrate intense green fluorescence emission at 520 nm. Under neutral or alkaline pH values, P(AA-co-FA)-functionalized BNNTs are highly emissive in contrast to acidic pH conditions where the fluorescent intensity is absent or low. No increase in the absorption was observed when the suspension pH was increased from 7 to 10. The functionalized BNNTs are easily taken up by human normal prostate epithelium (PNT1A) and human prostate cancer cell lines (DU145) and are suitable for further evaluation in cellular imaging applications.
关键词： pH switching,surface modification,cellular imaging,fluorescence,boron nitride nanotubes,polymer brushes
更新于2025-09-12 10:27:22
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Photoswitchable single-walled carbon nanotubes for super-resolution microscopy in the near-infrared
摘要： The design of single-molecule photoswitchable emitters was the first milestone toward the advent of single-molecule localization microscopy, setting a new paradigm in the field of optical imaging. Several photoswitchable emitters have been developed, but they all fluoresce in the visible or far-red ranges, missing the desirable near-infrared window where biological tissues are most transparent. Moreover, photocontrol of individual emitters in the near-infrared would be highly desirable for elementary optical molecular switches or information storage elements since most communication data transfer protocols are established in this spectral range. Here, we introduce a type of hybrid nanomaterials consisting of single-wall carbon nanotubes covalently functionalized with photoswitching molecules that are used to control the intrinsic luminescence of the single nanotubes in the near-infrared (beyond 1 mm). Through the control of photoswitching, we demonstrate super-localization imaging of nanotubes unresolved by diffraction-limited microscopy.
关键词： single-molecule localization microscopy,near-infrared,super-resolution microscopy,carbon nanotubes,photoswitchable emitters
更新于2025-09-12 10:27:22
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Excellent ambipolar gas sensing response of Eu[Pc(OC4H9)8]2/acidified multiwalled carbon nanotubes hybrid at room temperature
摘要： A new hybrid material has been developed by mixing a sandwich-type double-decker, Eu[Pc(OC4H9)8]2 = 2,3,9,10,16,17,23,24-octabutoxyphthalocyaninate] with acidified multiwalled carbon nanotubes (aMWCNTs) through non-covalent interactions. The UV-vis spectrum, X-ray diffraction and scanning electron microscope have been employed to reveal the J-aggregate mode and optimized morphology of Eu[Pc(OC4H9)8]2 molecules in the Eu[Pc(OC4H9)8]2/aMWCNTs hybrid material. The gas-sensing devices based on this hybrid material are fabricated by a simple solvent-processing quasi-Langmuir–Sh?fer (QLS) progress. The n-type and p-type response is shown by the Eu[Pc(OC4H9)8]2/aMWCNTs hybrid film at room temperature. The detection limit of the hybrid for ammonia and nitrogen dioxide gas is 0.5 ppm and 0.3 ppm, respectively.
关键词： phthalocyanine,gas sensing,multiwall carbon nanotubes,ambipolar organic semiconductor,europium complex
更新于2025-09-12 10:27:22