Nanotube Heterostructures Research Articles

Optimized Thermoelectric Performance of Carbon Nanoparticle-Carbon Nanotube Heterostructures by Tuning Interface Barrier Energy.

Herein, thermoelectric carbon nanoparticle (CNP)-carbon nanotube (CNT) heterostructures are introduced as a promising flexible thermoelectric material. The optimal barrier energy between the CNP and CNT increases the Seebeck coefficient (S) of the heterostructures through the energy filtering effect. For optimized thermoelectric performance, the CNP-CNT barrier energy can be effectively tuned by controlling the work function of the CNPs. The optimized p-type CNP-CNT heterostructures exhibited S and power factor (PF) of 50.6 ± 1.4 μV K-1 and 400 ± 26 μW m-1 K-2, respectively. The n-type CNP-CNT heterostructures, optimized for another work function of the CNPs, exhibited S and PF of up to -37.5 ± 3.4 μV K-1 and 214 ± 42 μW m-1 K-2, respectively. The energy harvesting capability of a thermoelectric generator prepared using p- and n-type CNP-CNT heterostructures with optimized barrier energies is demonstrated. The thermoelectric generator with 10 p-type and 9 n-type thermoelectric elements exhibited a maximum output power of 0.12 μW from a ΔT of 5 K. This work shows a facile strategy for synthesizing thermoelectric CNP-CNT heterostructures with optimized energy filtering effects. Application to the thermoelectric device on a paper substrate is also discussed.

Diversely Doped Uniform Silicon Nanotube Axial Heterostructures Enabled by "Dopant Reflection".

Here, we propose a novel method for the synthesis of extremely uniform, diversely doped silicon nanotube heterostructures. The method, comprising a simple two-step synthesis, exploits the use of a Ge nanowire sacrificial core upon which a multidoping axial pattern can be easily obtained, that is enclosed in an intrinsic Si shell. The Ge-Si core-shell structure is then heated to 750 °C, allowing the migration of dopant elements from the Ge core directly into the Si shell. Removal of the Ge core, via either wet or dry etch, does not impair the crystallinity of the Si shell nor its electrical characteristics, allowing for the formation of a multidoped axially patterned, conformal, and uniform Si nanotube. The precise dopant patterning allows for the extension of Si nanotube applications, which were unattainable because of the inability to precisely control the parameters and uniformity of the nanotubes while doping the structure simultaneously.

Binder-free Fe-doped NiCo2O4/Ni3S4 hollow heterostructure nanotubes for highly efficient overall water splitting.

For overall water splitting, a vital challenge is to design active sites at interfaces. Heterogeneous catalysts with enhanced mass/charge transfer and accelerated adsorption of intermediates have exhibited significantly enhanced activities. Herein, a Fe-doped NiCo2O4/Ni3S4 heterogeneous electrocatalyst is synthesized for the HER and OER. On account of the synergistic effect of heterostructures, Ni-O-S presents a low overpotential of 29.1 mV (10 mA cm-2), a relatively small Tafel slope of 53.3 mV dec-1 for the HER, and 259 mV at a current density of 100 mA cm-2 (33.1 mV dec-1) for the OER. What is more, Ni-O-S acts as a binder-free bi-functional electrode in an alkaline electrolyte for overall water splitting, exhibiting a cell voltage of 1.45 V (10 mA cm-2) with good stability. This work offers an efficient approach for designing stable and high-efficiency heterogeneous electrodes for overall water splitting.

Electronic structures and band alignment transition in double-wall MoS2/WS2 nanotubes for optoelectronic applications

Band alignment caused by discontinuous band structures of two different materials plays a central role in semiconductor heterojunctions and interface physics. We investigate the electronic structures and band alignments of double-wall MoS2/WS2 nanotubes with different chirality and geometry. We find that the band gap of both armchair and zigzag nanotubes obeys with being the band gap of the inner nanotube and the spacing distance between the inner and outer nanotubes. When placing MoS2 in the inner and WS2 in the outer of the nanotubes, the band alignment belongs to type-I because the conduction band minimum (CBM) of the inner MoS2 nanotube is lower than that of the outer WS2 nanotube, and the valence band maximum (VBM) of MoS2 nanotube is higher than that of WS2 nanotube. While putting the WS2 nanotube in the inner and MoS2 nanotube in the outer, the CBM and VBM of MoS2 nanotube are both lower than the corresponding band extreme points of WS2 nanotube when their diameter is small. Therefore, type-II to type-I band alignment transition occurs, originating from charge transfer with increasing spacing distance. Due to the adjustable band gap and electronic structures, we expect that these double-wall hetero-structured nanotubes will have great potential in optoelectronic devices.

High‐Performance Quasi‐2D Perovskite/Single‐Walled Carbon Nanotube Phototransistors for Low‐Cost and Sensitive Broadband Photodetection

Quasi‐2D Ruddlesden–Popper perovskites (RPPs) have emerged as promising functional materials for optoelectronics due to the highly tunable optoelectronic properties and have been considered as alternative candidates for semiconductors in photodetectors. However, RPPs normally show low carrier mobilities, which is unfavorable for the performance of photodetectors. Herein, a solution‐processed hybrid phototransistor based on RPP/single‐walled carbon nanotube (SWCNT) heterostructure is reported. A vertical composition gradient is formed upon RPP film preparation, which leads to a gradient type‐II heterojunction in the film. More importantly, the high carrier mobility of SWCNTs can result in ultrahigh responsivity and detectivity of 2 × 106 A W−1 and 7 × 1014 Jones, respectively. In addition, high on/off ratio of ≈103 can be achieved in the phototransistors. Herein, the high potential of RPP/SWCNT hybrid phototransistors as next‐generation photodetectors with superior sensitivity is demonstrated.

Fabrication of heterostructured UIO-66-NH2 /CNTs with enhanced activity and selectivity over photocatalytic CO2 reduction

Developing photocatalysts with superior efficiency and selectivity is an important issue for photocatalytic converting CO2. Hierarchically heterostructured one-dimensional nanomaterials represent a kind of promising catalysts for photocatalytic CO2 reduction on account of the high surface area and synthetic effect between different components. Herein, we synthesized UIO-66-NH2/carbon nanotubes (CNTs) heterostructures via a hydrothermal method, and investigated their photocatalytic performance. The element mapping, X-ray diffraction, and X-ray photoelectron spectroscopy collectively confirmed that the UIO-66-NH2 was successfully loaded on the surface of the CNTs. The specific surface area of the UIO-66-NH2/CNTs is 1.5 times higher than that of UIO-66-NH2. The photocurrent and electrochemical impedance spectroscopy measurements showed that the CNTs could enhance the electron mobility and reduce the recombination of photogenerated electron-hole pairs, which was also confirmed by the Photoluminescence spectroscopy (PL). The CNTs can improve the conductivity of composites and the dispersion of UIO-66-NH2, exposing more active sites, therefore the UIO-66-NH2 can increase the absorption of carbon dioxide and thus enhance the selectivity. The composites remarkably promoted the separation and transition of electrons and thus improved the photocatalytic efficiency of CO2 reduction. More importantly, it was found that the as-prepared composites suppress the hydrogen generation reaction during the CO2 reduction process.

Fe-doped CoP nanotube heterostructure enhanced the catalytic activity of Pt nanoparticles towards methanol oxidation reaction

Developing the efficient and stable anode catalysts of direct methanol fuel cell has been a pivotal requirement for its extensive commercial application. Herein, we design the Fe-doped CoP nanotube heterostructure as the co-catalyst of Pt-based catalyst via combining a facile hydrothermal with phosphorization process, subsequently, the traditional NaBH4 reduction method is utilized to deposit Pt nanoparticles. As anticipated, Fe species have been successfully doped into CoP to generate the Fe-doped CoP nanotube heterostructure, and the involved characterizations identify that Pt–C/Fe2–CoP catalyst exhibits admirable mass activity (1237 mA·mg−1Pt) towards methanol oxidation reaction, which is approximately 2.04 and 3.66 times as high as the Pt–C/CoP (607 mA·mg−1Pt) and Pt–C–H (338 mA·mg−1Pt). After stability test, the decline ratio of mass activity for Pt–C/Fe2–CoP (83.43%) is markedly preferable to Pt–C/CoP (94.92%) and Pt–C–H (98.67%) catalysts. The enhanced catalytic activity and durability can be imputed to the formation of uniform Pt nanoparticles and co-catalysis effect of Fe-doped CoP nanotube heterostructure since the introduction of hetero-metal cations is able to effectively accelerate the charge transfer rate and adjust the electronic structure of material. Therefore, the fabrication of nanotube heterostructure and introduction of hetero-metal may provide a new direction to the development of other high-efficiency electrocatalysts.

MoS2-carbon nanotube heterostructure as efficient hole transporters and conductors in perovskite solar cells

We demonstrate the excellent hole-transporting ability of molybdenum disulfide (MoS2) by applying one-dimensional (1D) and two-dimensional (2D) mixed MoS2-single-walled carbon nanotube (MoS2-SWCNT) heterostructures to perovskite solar cells. The CVD-synthesized MoS2-SWCNT functions as both the hole transport layer and anode at the same time. Compared with bare SWCNT, the wrapping of 1D/2D MoS2 around SWCNT improved the power conversion efficiency (PCE) by almost 20%, owing to the substantial enhancement of the fill factor. A PCE of 15.0% has been achieved after the application of 2,2′,7,7′-Tetrakis-9,9′-spirobifluorene (spiro-MeOTAD).

Ultra-sensitive glycol sensing performance with rapid-recovery based on heterostructured ZnO-SnO2 hollow nanotube

In this work, we successfully synthesized heterostructured ZnO-SnO2 composite nanotubes for high performance glycol gas sensor combined with certain calcination treatment. The as-prepared sample was characterized by various technologies. The sensor based on this hybrid nanotube displayed high response (47.71) toward 150 ppm glycol at 210 °C with response/recovery time of approximately 55 and 13 s respectively, even to 5 ppm glycol with a response of about 2.16. It also showed excellent repeatability and long-term stability. These good sensing properties are mainly attributed to the ZnO-SnO2 hollow heterostructure which possesses a large surface area and porosity. Besides, the sensing mechanism was elaborated at length.

Circuit Level Modeling of Electrically Doped Adenine–Thymine Nanotube Based Field Effect Transistor

We investigate the gate-controlled, electrically doped tunnelling current in Adenine-Thymine heterojunction nanotube-based Field Effect Transistor (FET). This analytical model FET is designed by Density Functional Theory (DFT) and Non-Equilibrium Green's Function (NEGF) based First principle formalisms. It is demonstrated that Band to Band Tunnelling (BTBT) is possible in relaxed Adenine-Thymine heterostructure nanotube. The evaluation of BTBT tunnelling probability to estimate tunnelling current for only ±0.01V applied bias voltage is calculated using Wentzel-Kramers-Brillouin approximation. Electrical doping is introduced to eliminate the probability of fault generation. By keen observation on the shift of energy levels in the band structure, the availability of high transmission co-efficient peaks and current-voltage response we demonstrate the Schottky barrier nature for this geometrically pre-optimized bio-molecular FET. The doping concentration is varied from 0.0001V to 0.1V to achieve a substantially large amount of tunnelling current when the electronic temperature is kept at 300K. The E-k diagram or complex band structure of this heterostructure nanotube ensures its in-direct semi-conducting nature. This is a first attempt to present a circuit-level demonstration using this Adenine-Thymine nanotube-based bio-molecular FET and validate the obtained results with the existing approaches.

Structural Engineering of Dispersed Graphene Flakes into ZnO Nanotubes on Discontinues Ultra‐Nanocrystalline Diamond Substrates for High‐Performance Photodetector with Excellent UV Light to Dark Current Ratios

AbstractIn this work, ultraviolet (UV) photodetectors based on ultra‐nanocrystalline diamond (UNCD) and dispersed graphene flakes (GrF) with ZnO nanotubes (ZnTs) heterostructures are investigated. Unique hybrid nanostructure of dispersed GrF into ZnTs on discontinuous UNCD substrates using scalable techniques is presented. It is revealed from microstructural analysis that the addition of GrF into highly uniform ZnTs grown on UNCD substrates results outstanding UV photodetection properties. Thus, the GrF‐ZnTs/UNCD nanostructure reveals superior UV diode performance, with an ultrahigh UV switching ratio of 19 708 at 5 V, which is excellently better than those of ZnO nanostructures. It is perceived that the perfect distribution of GrF into ZnTs on UNCD substrates results in ultrafast electron–hole recombination. The distribution of GrF and UNCD interlayer enables the new energy levels on the conduction band, which reduces the barrier height to allow fast charge carrier transportation during the UV illumination. It is believed that the addition of GrFs and UNCD layer increase the UV adsorptivity and sufficient amount of conducting path within ZnTs. Therefore, the present GrF‐ZnTs/UNCD photodetector can be used as an efficient UV photodetection device with high performance and opening up new opportunities for future optoelectronic devices.

Self-supported Hierarchical Fe(PO3)2@Cu3P nanotube arrays for efficient hydrogen evolution in alkaline media

Developing high-efficient and Earth-abundant electrocatalysts toward hydrogen evolution reaction (HER) is strongly desired for electrochemical water splitting but remains a considerable challenge. Herein, we propose a 3D hierarchical Fe(PO3)2@Cu3P heterostructure nanotube arrays on Cu foams for promising HER catalysts. The HER performance can be tuned by changing FeCl3 concentrations and the optimized cathode exhibits excellent HER activity in 1 M KOH with a low overpotentials of 108 mV @ 10 mA cm−2 and a small Tafel slope of 84 mV dec−1. Furthermore, this electrode delivers high electrochemical durability with stable operation for 24 h. Such high performance can be ascribed to the unique hierarchical heterostructure with large electrochemical surface area, synergistic effect and fast electron transport. Our study can provide new inspiration for rational construction of copper-based hierarchical nanomaterials for HER electrodes and other energy-related applications.

From Highly Purified Boron Nitride to Boron Nitride‐Based Heterostructures: An Inorganic Precursor‐Based Strategy

AbstractThe current approaches used to fabricate hexagonal boron nitrides (h‐BN) from boron trioxide and urea always results in contamination of the h‐BN product with carbon/oxygen. Thus, discovering a facile way of mass producing high‐purity h‐BN remains a challenge. A simple yet highly efficient thermal treatment approach to large‐scale fabrication of nanoporous h‐BN with high yield, high purity, and high crystallinity is described using NaNH2 and NaBH4 as the oxygen‐ and carbon‐free precursors. The unique properties of inorganic metal salts, i.e., high melting point and strong electrostatic interaction with carbon substrates, render this strategy suitable for the production of homogeneous h‐BN/mesoporous carbon and h‐BN/carbon nanotube heterostructures of high crystallinity, high h‐BN dispersity, and with a strong interfacial effect. These unique features make them promising candidates for supercapacitor applications, resulting a significantly enhanced specific capacitance. This study provides new insight into the fabrication of high‐purity h‐BN and h‐BN‐based heterostructures thus expanding their application in the field of energy storage and transformation.

Silver-loaded In2S3-CdIn2S4@X(X=Ag, Ag3PO4, AgI) ternary heterostructure nanotubes treated by electron beam irradiation with enhanced photocatalytic activity

Ternary heterostructure nanotubes of In2S3-CdIn2S4@X(X = Ag, Ag3PO4, AgI) were synthesized with enhanced photocatalytic activity for efficiently degrading pollutants. Electron beam irradiation was employed to artificially introduce interface defects to the heterostructure nanotubes. The experimental results for degrading carmine and Cr6+ under visible light irradiation showed that the photocatalytic efficiency of In2S3-CdIn2S4 was improved to some extent by the introduction of silver compounds. DRS results confirmed that the band gaps of In2S3-CdIn2S4 were reduced to 1.62 eV and 1.58 eV by introducing Ag3PO4 and AgI, respectively. Interestingly, the band gap of In2S3-CdIn2S4@AgI after electron beam irradiation was further reduced to 1.56 eV, resulting in that the degradation time of both Cr6+ and carmine by In2S3-CdIn2S4@AgI after high-energy electron beam irradiation was shortened to only 5 min. The XRD spectra of the photocatalysts after five cycles could maintain the original crystal form to a large extent. The OH stretching vibration peaks of In2S3-CdIn2S4@AgI after electron beam irradiation at 3387 cm−1 became wider and sharper, thus indicating that the number of free hydroxyl groups on the heterostructure surface significantly increased. PL results showed that electron beam irradiation could significantly reduce the PL emission peak and enhance the utilization of photogenerated charge carriers. EIS results further confirmed that In2S3-CdIn2S4@AgI processed by electron beam irradiation had higher photogenerated electron-hole separation efficiency. Based on the experimental results, a feasible reaction pathway and photocatalytic mechanism for the degradation of carmine was investigated. ESR results showed that the main active groups in the whole photocatalytic system were •O2– and h+.

A Computational Study of a Heterostructure Tunneling Carbon Nanotube Field-Effect Transistor

In this paper a heterostructure tunneling carbon nanotube field-effect transistor, namely H-T-CNTFET, is introduced. In the proposed structure, a carbon nanotube with a different chirality is used for the drain side compared to the source and the channel region. Characteristics of the proposed structure are numerically simulated by a mode-space non-equilibrium Green’s function formulism in the ballistic limit. Simulation results show that, compared to a conventional tunneling carbon nanotube field-effect transistor, the proposed structure has higher ON-current, better ambipolar behavior and better switching characteristics. In addition, the analog characteristics of the device, such as the transconductance (gm) and unity-gain frequency (fT), are also improved.

Covalent bonding of ZnO nanostructures with dispersible carbon nanotubes for self-assembly photocatalytic heterostructures

Abstract This work demonstrates the fabrication of zinc oxide‑carbon nanotube (ZnO/CNT) heterostructures with tunable photocatalytic activity via microstructure modulation. The ZnO/CNT heterostructures are constructed in one-step hydrothermal procedure consisting of in situ anchoring of ZnO nanostructures with dispersible CNTs in an aqueous alkali solution containing bile salts as a dispersant. Observation via scanning (SEM) and transmission (TEM) electron microscopy reveals self-assembled heterostructures of monodispersible CNTs tightly surrounding ZnO nanostructures with multimorphology. The XRD, FT-IR, Raman and XPS analysis confirm that the CNTs were successfully incorporated into the ZnO nanostructures with strong interfacial contact of covalent bonding rather than simple mixing. A series of ZnO/CNT heterostructures, which varies according to their degree of doping with dispersible CNTs, exhibit distinct sunlight-induced photocatalytic activity onto the degradation of Rhodamine B (RhB). The superior photocatalytic performance of ZnO/CNT heterostructures originates from synergistic effects of sufficient interfacial bonding, self-assembly microstructures, and continuous conducting pathways between ZnO nanostructures and CNTs, which acquires better sunlight utilization and more efficient separation of electron-hole pair, confirmed by UV–Visible diffuse reflectance spectra as well as photocurrent and photovoltage analysis. This study also proposes a photocatalytic degradation mechanism of RhB dyes through detection of active species confirmed by electron-spin-resonance analysis.

Tunable electronic and optical properties of the MoS2/MoSe2 heterostructure nanotubes

The electronic and optical properties of the MoS 2 /MoSe 2 heterostructure nanotubes (NTs) with different ratios are systematically investigated by first principles calculations. It is found that the zigzag and armchair MoS 2 /MoSe 2 heterostructure NTs retain direct and indirect band gap under different MoSe 2 ratios, respectively. It is interesting that the band gap of the armchair NTs decreases firstly and then increases with the increase of MoSe 2 ratios, while the band gap of the zigzag NTs decreases gradually with the increase of MoSe 2 ratios. Moreover, the dielectric function, absorption coefficient , refractive index and reflectivity coefficient of the MoS 2 /MoSe 2 heterostructure NTs exhibit red shift with the increase of MoSe 2 ratios. Especially, the static dielectric constant ε 1 ( 0 ) and static refractive index n ( 0 ) increase monotonously with the increase of MoSe 2 ratios. These results suggest that the MoS 2 /MoSe 2 heterostructure NTs may serve as promising building blocks for optoelectronic nanodevices . • The band structures of MoS 2 /MoSe 2 heterostructure nanotubes can be modulated. • The variation trends of the band gaps are dependent on chirality. • The optical parameters exhibit red shift with the increase of MoSe 2 ratios. • The static dielectric constant and static refractive index change monotonously.

Excellent visible light-driven photocatalytic performance and band alignment of g-C3N4/TiO2 nanotube heterostructures

Visible-light-driven graphite-like carbon nitride/TiO2 nanotubes (g-C3N4/TNTs) heterostructures were synthesized by hydrothermal and calcination processes. The g-C3N4/TNTs heterostructures with the different weight ratios of g-C3N4 to TNTs, from 0.5 wt% to 5 wt%, were characterized by modern methods of physical-chemical analysis. The photocatalytic activity of materials was evaluated by the degradation of methylene blue (MB) dye in aqueous under the visible light. Results showed that the MB photocatalytic degradation performance of the g-C3N4/TNTs heterostructures was enhanced, and that of the 2% g-C3N4/TNTs witnessed the highest efficiency (81%, 180 min). The photocatalytic activity was improved, thanks to the extended optical absorption range and enhanced separation of the photoinduced electron-hole pairs. Furthermore, the band alignment of the g-C3N4/TNTs heterostructures was determined by the preliminary calculation.

The preparation of high quality heterostructure photonic crystals by using pulse anodization and their enhanced photocatalytic property

Abstract The TiO2 nanotube heterostructure photonic crystals (HPCs) with high quality photonic band gap (PBG) and more photonic band edges have been prepared by using the pulse anodization with compensation voltage. It is found that when the hetero-structure is introduced on the top of the whole HPC, its structure becomes more uniform and more band edges with high quality PBG appear in the whole visible range, which greatly enhance the light absorption of PC photocatalyst due to the higher photonic state density, and further improve its photocatalytic performance. Furthermore, the matching of PBG red and blue edges with the RhB absorption peak also has effect on the photocatalytic performance. And the HPC has two closely adjoining PBGs and their band edges are simultaneously matched with the RhB absorption peak, which make the HPC have the strongest photocatalytic enhancement.

Tunable Mechanical and Electrical Properties of Coaxial BN‐C Nanotubes

Heterostructures provide a great chance to tune the properties and functions of a nanomaterial, e.g., its mechanical and electrical properties, and thus allowing for the design and realization of novel nanoelectromechanical devices. Boron nitride and carbon nanotubes, with similar structure and mechanical properties but dramatically different electrical properties, are ideal candidates for investigating nanoscale heterostructured materials. In this work, graphitic C‐coated BN nanotubes (BN‐C NTs) were synthesized and their mechanical and electrical properties were simultaneously measured using in situ high‐resolution transmission electron microscopy (TEM). As a function of the coated carbon content, the elastic modulus obtained from second order harmonic resonance of heterostructured nanotubes could be tuned from ∼140 to ∼700 GPa, and their electrical resistivity could be adjusted within three orders of magnitude from ∼0.16 to ∼2.5×10−4 Ω · m. This work opens the way for making custom‐designed heterostructures for the requirements of specific applications.