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1.
ACS Nano ; 2020 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-32083843

RESUMO

Mixed-dimensional van der Waals (vdW) heterostructures composed of one-dimensional (1D) and two-dimensional (2D) materials have exhibited great potential in nanoelectronics and nano-optoelectronics. In this study, we present a vertical point p-n junction (VPpnJ), in which a vertical stacked molybdenum disulfide/tungsten diselenide p-n junction is sandwiched between two cross-stacked metallic carbon nanotubes (CNTs). The device can be transformed from p-n junction to n-n junction via gate modulation. As a photodetector, the VPpnJ device can work in three different modes by setting the appropriate gating voltages. The photosensitive areas are localized around the top CNT, bottom CNT, and the cross point at VG = -10 V, 10 V, and ∼0 V, respectively. In the p-n regime at the negative gate voltage, the VPpnJ device showed an obvious photovoltaic effect. The external quantum efficiency of the VPpnJ can reach 42.7%. The electrical control of the electronic and optoelectronic characteristics can be mainly attributed to the gate-tunable interfacial built-in electric fields in the heterostructures. The progress also reveals the functional diversity of such 1D/2D mixed-dimensional heterostructures, which will be prospects for future nanoelectronics and nano-optoelectronics.

2.
Phys Chem Chem Phys ; 22(2): 556-563, 2020 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-31840700

RESUMO

Recently, MnBi2Te4 has been discovered as the first intrinsic antiferromagnetic topological insulator (AFM TI), and it will become a promising material to discover exotic topological quantum phenomena. In this work, we have realized the successful synthesis of high-quality MnBi2Te4 single crystals by solid-state reactions. The as-grown MnBi2Te4 single crystal exhibits a van der Waals layered structure, which is composed of septuple Te-Bi-Te-Mn-Te-Bi-Te sequences as determined by X-ray diffraction and high-resolution high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The magnetic order below 25 K as a consequence of A-type antiferromagnetic interaction between Mn layers in the MnBi2Te4 crystal suggests the unique interplay between antiferromagnetism and topological quantum states. Moreover, the transport measurements of MnBi2Te4 single crystals further confirm its magnetic transition. This study on the first AFM TI of MnBi2Te4 will guide the future research on other potential candidates in the MBixTey family (M = Ni, V, Ti, etc.).

3.
Soft Matter ; 15(47): 9788-9796, 2019 Dec 04.
Artigo em Inglês | MEDLINE | ID: mdl-31746933

RESUMO

Spiral configurations and helical curlings of plant tendrils and seed pods are very common in nature. Many researchers have tried to develop spirally deformable actuators to mimic these natural spirals through several approaches, such as preforming helical shapes, processing diagonal stripes and employing anisotropic organic layers. However, these methods are usually complex and time-consuming. Here, we used an efficient method to produce a highly oriented carbon nanotube (CNT) film and develop a series of spirally deformable soft actuators which perform various controllable helical actuations. The actuator consists of a CNT layer with strong anisotropy and a silicone layer. By simply adjusting the orientations of the aligned CNTs, the prepared actuators can accomplish left- or right-handed spiral deformations with different helical forms when driven by electricity. Finite element analyses and simulations were conducted to investigate the mechanism. It is confirmed that it is the anisotropic moduli of the CNT film that regulate the internal stress distributions of the actuators and lead to helical actuations. Moreover, complex actuator designs and functional applications were also carried out. A V-shaped actuator can simultaneously achieve left- and right-handed curling with large angles (630°), which vividly imitates the spiral winding of a tendril. A Y-shaped actuator performed three-dimensional movements, which can manipulate lightweight objects deftly. By virtue of easy preparation and flexible function design, the spirally deformable actuators based on the oriented CNT film will be very promising in artificial muscles and bionic soft robots.

4.
Small ; : e1902719, 2019 Sep 29.
Artigo em Inglês | MEDLINE | ID: mdl-31565872

RESUMO

Carbon nanotubes (CNTs) are regarded as one of the most promising materials to manufacture high-performance lithium batteries. This prospect is closely related to the construction of macroscopic architectures of CNTs. The superaligned CNT (SACNT) array is a unique kind of vertically aligned CNT array. Its highly oriented feature and strong intertube force facilitate the fabrication of macroscopic SACNT structures with various forms, including unidirectional films, buckypapers, and aerogels, etc. The as-produced SACNT macroscopic architectures are successfully introduced into lithium batteries due to their outstanding electrical and mechanical properties. Herein, an overview of the functions of macroscopic SACNTs in lithium batteries is proposed, including their applications in composite electrodes, current collectors, interlayers, and flexible full cells.

5.
ACS Appl Mater Interfaces ; 11(45): 42172-42178, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31617341

RESUMO

Planar supercapacitors (SCs) have been regarded as promising energy devices for on-chip electronics and they should be evaluated by areal performances due to the very limited available areas. However, these SCs usually suffer from inevitable size increase for the requirement of substrates, current collectors, and sealants. This work presents a kind of freestanding, foldable, and quasi-solid-state SCs that single SC units were stacked in the thickness direction with a common electrode to reduce their occupied areas. The foldable SCs can be fabricated in desired patterns by laser graving and their areal performances increase linearly with the assembled units. The energy density of a 5-unit foldable SC is 177.9 µWh cm-2 at the power density of 2.78 mW cm-2, and it outperforms most planar SCs. Therefore, this work provides a new reference to improve the areal properties of on-chip SCs from the device design aspect.

6.
Nano Lett ; 19(10): 6756-6764, 2019 10 09.
Artigo em Inglês | MEDLINE | ID: mdl-31203631

RESUMO

In extreme environments, such as at ultrahigh or ultralow temperatures, the amount of tape used should be minimal so as to reduce system contamination and unwanted residues. However, tapes made from conventional materials typically lose their adhesiveness or leave residues difficult to remove under such conditions. Thus, the development of more versatile, lightweight, and easily removable tapes for applications in such extreme environments has received considerable attention. Here, we report that horizontally superaligned carbon nanotube (SACNT) tapes can be used to provide perfect van der Waals (vdW) interface contacts over a wide range of temperatures (from -196 to 1000 °C), yielding outstanding adhesiveness with specific adhesion strengths up to ∼1.1 N/µg. With a surface density of only 0.5-5 µg/cm2, hundreds of times lighter than the vertically aligned CNT adhesives, the SACNT tapes can be cost-effectively provided in hundreds of meters. They have multipurpose adhesive abilities for versatile materials and are also easily separated from samples even after exposure to extreme temperature regimes. First-principles calculations confirm the mechanism of vdW adhesion and reveal that ultraflat and nanometer-thick SACNT tapes may yield far greater adhesive abilities. These SACNT tapes show great potential for use in mechanical bonding, electrical bonding, and thermal dissipation in electronic devices.

7.
J Phys Chem Lett ; 10(9): 2113-2120, 2019 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-30990711

RESUMO

A high-performance exciton-localized surface plasmon (LSP) coupling system consisting of well-designed plasmonic nanostructures and CdSe/ZnS quantum dots (QDs) was fabricated by first introducing a Ta2O5 layer as both an adhesive coating and coupling medium. It is shown that a larger emission enhancement factor of 6 from CdSe/ZnS QDs can be obtained from the strong coupling effect between QDs and triprism Au nanoarrays and the high scattering efficiency of LSPs without damping. This can be attributed to the matching conditions and a low extinction coefficient with little damping absorption of the Ta2O5 layer in the system. The radiative scattering rate of ΓLSPs can make a contribution to the spontaneous emission rate Γ and thus improve the internal quantum yield of the QDs. This strategy could be promising for practical application of metal-modified fluorescence enhancement.

8.
Proc Natl Acad Sci U S A ; 116(14): 6586-6593, 2019 04 02.
Artigo em Inglês | MEDLINE | ID: mdl-30890635

RESUMO

Low-dimensional nanomaterials, such as one-dimensional (1D) nanomaterials and layered 2D materials, have exhibited significance for their respective unique electronic and optoelectronic properties. Here we show that a mixed-dimensional heterostructure with building blocks from multiple dimensions will present a synergistic effect on photodetection. A carbon nanotube (CNT)-[Formula: see text]-graphene photodetector is representative on this issue. Its spatial resolution can be electrically switched between high-resolution mode (HRM) and low-resolution mode (LRM) revealed by scanning photocurrent microscopy (SPCM). The reconfigurable spatial resolution can be attributed to the asymmetric geometry and the gate-tunable Fermi levels of these low-dimensional materials. Significantly, an interference fringe with 334 nm in period was successfully discriminated by the device working at HRM, confirming the efficient electrical control. Electrical control of spatial resolution in CNT-[Formula: see text]-graphene devices reveals the potential of the mixed-dimensional architectures in future nanoelectronics and nano-optoelectronics.

9.
ACS Appl Mater Interfaces ; 11(12): 11612-11617, 2019 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-30838844

RESUMO

Transition-metal dichalcogenides are promising challengers to conventional semiconductors owing to their remarkable electrical performance and suppression of short-channel effects (SCEs). In particular, monolayer molybdenum disulfide has exhibited superior suppression of SCEs owing to its atomic thickness, high effective carrier mass, and low dielectric constant. However, difficulties still remain in large-scale stable fabrication of nanometer-scale channels. Herein, a method to fabricate electrodes with sub-10 nm gaps was demonstrated using horizontally aligned single-walled carbon nanotubes as an evaporation mask. The widths of the nanogaps exhibit robust stability to various process parameters according to the statistical results. Based on these nanogaps, ultrashort-channel length monolayer MoS2 field-effect transistors were produced. Monolayer MoS2 devices with a 7.5 nm channel length and a 10 nm thick HfO2 dielectric layer exhibited excellent performances with an ON/OFF ratio up to 107, a mobility of 17.4 cm2/V·s, a subthreshold swing of about 120 mV/dec, and a drain-induced barrier lowering of about 140 mV/V, all of which suggest a superior suppression of SCEs. This work provides a universal and stable method for large-scale fabrication of ultrashort-channel 2D-material transistors.

10.
ACS Nano ; 13(3): 3106-3116, 2019 Mar 26.
Artigo em Inglês | MEDLINE | ID: mdl-30776213

RESUMO

Thin films with large compressive residual stress and low interface adhesion can buckle and delaminate from relatively rigid substrates, which is a common failure mode of film/substrate interfaces. Current studies mainly focused on the geometry of various buckling patterns and related physical origins based on a static point of view. However, fundamental understanding of dynamic propagation of buckles, particularly for the complicated web buckles, remains challenging. We adopt strained two-dimensional MoS2 thin films to study the phenomenon of web buckling because their interface adhesion, namely van der Waals interaction, is naturally low. With a delicately site-controlled initiation, web buckles can be triggered and their dynamic propagation is in situ observed facilely. Finite element modeling shows that the formation of web buckles involves the propagation and multilevel branching of telephone-cord blisters. These buckled semiconducting films can be patterned by spatial confinement and potentially used in diffuse-reflective coatings, microfluidic channels, and hydrogen evolution reaction electrodes. Our work not only reveals the hidden mechanisms and kinematics of propagation of web buckles on rigid substrates but also sheds light on the development of semiconducting devices based on buckling engineering.

11.
Nanoscale ; 11(10): 4489-4495, 2019 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-30806420

RESUMO

A novel method is proposed to realize coordinated stress management and dislocation control in GaN growth on Si (111) substrates. This method is facilely implemented by using a unique carbon nanotube (CNT) mask with a nanoscale diameter and a high fill factor. It is found that most dislocations are directly blocked by high-density nanovoids formed around CNTs within 150 nm from the GaN/AlN interface. In this way, without dislocation inclination, the threading dislocation density (TDD) of the GaN epilayer is dramatically reduced. Thus the compressive stress relaxation due to dislocation inclination during GaN growth is significantly decreased and more compressive stress can be preserved. In addition, the high-density nanovoids also contribute to decreasing the thermal tensile stress during cooling down. As a result, coordinated stress management and dislocation control are realized and a 3.5 µm-thick crack-free GaN epilayer with a homogeneously low TDD of 2.51 × 108 cm-2 is obtained. With the facile fabrication of the CNT mask and a simple epitaxy procedure, the quality of the GaN epilayer grown on Si substrates is greatly improved, which extends the application of the nanomaterial in the GaN epitaxy on the Si substrate and demonstrates great application potential for high-performance electronic devices.

12.
Nanoscale ; 10(42): 19972-19978, 2018 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-30349918

RESUMO

Ultra-stretchable carbon nanotube (CNT) composite electrodes for lithium-ion batteries are fabricated by coating CNT films and active material powders on biaxially pre-strained polydimethylsiloxane (PDMS) substrates. The wrinkled structures that form during the pre-straining and release process extend along the strain axis to protect the CNT composite structures from fracture. The CNT composites demonstrate excellent stability and high durability with resistance increase of less than 12% after 2000 cycles at 150% strain. Both CNT/Li4Ti5O12 (LTO) anodes and CNT/Li(Ni1/3Co1/3Mn1/3)O2 (NCM) cathodes maintain excellent electrochemical properties at cyclic 150% strain in different axes. The full lithium-ion battery consisting of the stretchable CNT/LTO anode and CNT/NCM cathode is able to withstand 150% strain in different axes without large decreases in performance. Stretchable batteries fabricated by the scalable, highly efficient, and low-cost biaxial pre-strain process with excellent durability and electrochemical properties will have potential applications in flexible devices.

13.
ACS Appl Mater Interfaces ; 10(41): 35273-35280, 2018 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-30240567

RESUMO

Based on porous carbon nanotube/polyaniline composite (CNT/PANI) and poly(vinyl alcohol) gel, we fabricated centimeter-sized hydrocapacitors with dual functions of energy conversion and storage with an efficient low-cost method. Owning to excellent hydrophily and large specific capacitance of CNT/PANI, the hydrocapacitors can easily convert energy from water movement induced by capillarity, gravity, or air pressure difference into electricity and store the generated electricity. Especially, sandwich-like hydrocapacitors outputted large current of 1.65 mA through an external load of 100 Ω, and hydrocapacitors showed good extendibility by connecting in series. To explain the mechanism of hydrocapacitors in this work, a possible model based on capillarity and traditional streaming potential was proposed and discussed. Hydrocapacitors here also provide a reference for future integration of nanogenerators and energy storage parts.

14.
ACS Appl Mater Interfaces ; 10(42): 36058-36066, 2018 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-30260205

RESUMO

Black phosphorus (BP) is a promising electrode material with high energy density for lithium-ion batteries. However, volumetric expansion of BP upon lithiation leads to rapid capacity fading of the electrode. Herein, BP composite electrodes are prepared by mixing microsized BP particles with carbon nanotubes and KetjenBlack as dual conducting agents, which facilitate the construction of stable and conductive networks in the electrodes. An ultrathin TiO2 nanocoating is deposited on the surface of the BP composite electrode by electron-beam evaporation. The TiO2 nanocoating acts as a protective layer to prevent the BP particles from directly contacting the electrolyte by forming a Li xTi yO z passivation coating on the electrode surface. The Li xTi yO z passivation layer suppresses propagation of the formed irreversible solid electrolyte interlayer on the BP particles, resulting in an improved Coulombic efficiency of the BP electrode. Moreover, the Li xTi yO z passivation layer facilitates lithium-ion diffusion and electron transfer and thus superior cycling and rate performance of the BP electrode are achieved.

15.
Nano Lett ; 18(8): 4691-4696, 2018 08 08.
Artigo em Inglês | MEDLINE | ID: mdl-29975842

RESUMO

A superaligned carbon nanotube (SACNT) film can act as an ideal gate electrode in vacuum electronics due to its low secondary electron emission, high electron transparency, ultrasmall thickness, highly uniform electric field, high melting point, and high mechanical strength. We used a SACNT film as the gate electrode in a thermionic emission electron tube and field emission display prototype. The SACNT film gate in a thermionic emission electron tube shows a larger amplification factor. A triode tube with the SACNT film gate is used in an audio amplification circuit. The SACNT film gate electrode in field emission devices shows better field uniformity. The field emission display prototype is demonstrated to dynamically display Chinese characters.

16.
Nanotechnology ; 29(34): 345601, 2018 Aug 24.
Artigo em Inglês | MEDLINE | ID: mdl-29775440

RESUMO

Using super-aligned carbon nanotube (CNT) film, we have fabricated van der Waals crystalline multiwall CNTs (MWCNT) by adopting high pressure and high temperature processing. The CNTs keep parallel to each other and are distributed uniformly. X-ray diffraction characterization shows peaks at the small angle range, which can be assigned to the spacing of the MWCNT crystals. The mechanical, electrical and thermal properties are all greatly improved compared with the original CNT film. The field emission properties of van der Waals crystalline MWCNTs are tested and they show a better surface morphology stability for the large emission current. We have further fabricated a field emission x-ray tube and demonstrated a precise resolution imaging ability.

17.
Nanoscale ; 10(32): 15195-15204, 2018 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-29845168

RESUMO

A flexible and transparent film assembled from the cross-nanoporous structures of Au on PET (CNS of Au@PET) is developed as a versatile and effective SERS substrate for rapid, on-site trace analysis with high sensitivity. The fabrication of the CNS of Au can be achieved on a large scale at low cost by employing an etching process with super-aligned carbon nanotubes as a mask, followed by metal deposition. A strongly enhanced Raman signal with good uniformity can be obtained, which is attributed to the excitation of "hot spots" around the metal nanogaps and sharp edges. Using the CNS of Au@PET film as a SERS platform, real-time and on-site SERS detection of the food contaminant crystal violet (CV) is achieved, with a detection limit of CV solution on a tomato skin of 10-7 M. Owing to its ability to efficiently extract trace analytes, the resulting substrate also achieves detection of 4-ATP contaminants and thiram pesticides by swabbing the skin of an apple. A SERS detection signal for 4-ATP has a relative standard deviation of less than 10%, revealing the excellent reproducibility of the substrate. The flexible, transparent and highly sensitive substrates fabricated using this simple and cost-effective strategy are promising for practical application in rapid, on-site SERS-based detection.

18.
Nanotechnology ; 29(17): 175503, 2018 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-29438104

RESUMO

Electro-active polymer (EAP) actuators, such as electronic, ionic and electrothermal (ET) actuators, have become an important branch of next-generation soft actuators in bionic robotics. However, most reported EAP actuators could realize only simple movements, being restricted by the small area of flexible electrodes and simple designs. We prepared large-area flexible electrodes of high anisotropy, made of oriented carbon nanotube (CNT) paper, and carried out artful graphic designs and processing on the electrodes to make functional ET bimorph actuators which can realize large bending deformations (over 220°, curvature > 1.5 cm-1) and bionic movements driven by electricity. The anisotropy of CNT paper benefits electrode designs and multiform actuations for complex actuators. Based on the large-area CNT paper, more interesting and functional actuators can be designed and prepared which will have practical applications in the fields of artificial muscles, complicated actuations, and soft and bionic robotics.

19.
Nano Lett ; 18(3): 1770-1776, 2018 03 14.
Artigo em Inglês | MEDLINE | ID: mdl-29481093

RESUMO

Carbon nanotubes (CNTs) and other related CNT-based materials with a high thermal conductivity can be used as promising heat dissipation materials. Meanwhile, the miniaturization and high functionality of portable electronics, such as laptops and mobile phones, are achieved at the cost of overheating the high power-density components. The heat removal for hot spots occurring in a relatively narrow space requires simple and effective cooling methods. Here, an auxiliary passive cooling approach by the aid of a flat plate (aluminum-magnesium alloy) is investigated to accommodate heat dissipation in a narrow space. The cooling efficiency can be raised to 43.5%. The cooling performance of several CNT-based samples is compared under such circumstances. Heat dissipation analyses show that, when there is a nearby plate for cooling assistance, the heat radiation is weakened and natural convection is largely improved. Thus, improving heat radiation by increasing emissivity without reducing natural convection can effectively enhance the cooling performance. Moreover, the decoration of an auxiliary cooling plate with sprayed CNTs can further improve the cooling performance of the entire setup.

20.
Small ; 14(8)2018 02.
Artigo em Inglês | MEDLINE | ID: mdl-29280267

RESUMO

A multifunctional interlayer, composed of molybdenum diphosphide (MoP2 ) nanoparticles and a carbon nanotube (CNT) film, is introduced into a lithium-sulfur (Li-S) battery system to suppress polysulfide migration. Molybdenum diphosphide acts as the catalyst and can capture polysulfides and improve the polysulfide conversion activity during the discharge/charge processes. The CNT film acts as a conductive skeleton to support the MoP2 nanoparticles and to ensure their uniform distribution. The CNT film physically hinders polysulfide migration, acts as a current collector, and provides abundant electron pathways. The Li-S battery containing the multifunctional MoP2 /CNT interlayer exhibits excellent electrochemical performance. It delivers a reversible specific capacity of 905 mA h g-1 over 100 cycles at 0.2 C, with a capacity decay of 0.152% per cycle. These results suggest the introduction of the multifunctional CNT/MoP2 interlayer as an effective and practical method for producing high-performance Li-S batteries.

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