Well-aligned Arrays Research Articles

Orthogonal Anisotropic Sensing and Actuating Characteristics of a 1-3 PZT Piezoelectric Microfiber Composite

Orthogonal anisotropic sensing plays an important role in determining driver and sensor properties, while the fiber diameter directly affects the sensitivity of piezoelectric fiber composites. However, few studies have been carried out on fibers at the micron level. Here, well-aligned piezoelectric fiber arrays approximately 10 μm in diameter were prepared using an activated carbon template. A 1-3 lead zirconate titanate (PZT) piezoelectric microfiber composite was obtained by infiltrating epoxy resin into fibers. The microfibers were embedded orderly and well distributed in the epoxy matrix. The orthogonal anisotropy of the sensing and actuating performance was investigated and evaluated. The 1-3 PZT piezoelectric microfiber composite was clearly anisotropic with a much better piezoelectric sensitivity along the longitudinal direction of the fibers. The highest output voltage in the longitudinal direction was twice as large as that in the transverse direction. The highest strain in the longitudinal sensitivity direction was about four times the strain of the transverse direction.

Aligning dense carbon nanotube arrays

Device Technology Although semiconducting carbon nanotubes (CNTs) are promising candidates to replace silicon in transistors at extremely small dimensions, their purity, density, and alignment must be improved. Liu et al. combined a multiple dispersion sorting process, which improves purity, and a dimension-limited self-alignment process to produce well-aligned CNT arrays on a 10-centimeter silicon wafer. The density is sufficiently high (100 to 200 CNTs per micrometer) that large-scale integrated circuits could be fabricated. With ionic liquid gating, the performance metrics exceeded those of conventional silicon transistors with similar dimensions. Science , this issue p. [850][1] [1]: /lookup/doi/10.1126/science.aba5980

Aligned, high-density semiconducting carbon nanotube arrays for high-performance electronics.

Single-walled carbon nanotubes (CNTs) may enable the fabrication of integrated circuits smaller than 10 nanometers, but this would require scalable production of dense and electronically pure semiconducting nanotube arrays on wafers. We developed a multiple dispersion and sorting process that resulted in extremely high semiconducting purity and a dimension-limited self-alignment (DLSA) procedure for preparing well-aligned CNT arrays (within alignment of 9 degrees) with a tunable density of 100 to 200 CNTs per micrometer on a 10-centimeter silicon wafer. Top-gate field-effect transistors (FETs) fabricated on the CNT array show better performance than that of commercial silicon metal oxide-semiconductor FETs with similar gate length, in particular an on-state current of 1.3 milliamperes per micrometer and a recorded transconductance of 0.9 millisiemens per micrometer for a power supply of 1 volt, while maintaining a low room-temperature subthreshold swing of <90 millivolts per decade using an ionic-liquid gate. Batch-fabricated top-gate five-stage ring oscillators exhibited a highest maximum oscillating frequency of >8 gigahertz.

Flexible 3D Electrodes of Free-Standing TiN Nanotube Arrays Grown by Atomic Layer Deposition with a Ti Interlayer as an Adhesion Promoter.

Nanostructured electrodes and their flexible integrated systems have great potential for many applications, including electrochemical energy storage, electrocatalysis and solid-state memory devices, given their ability to improve faradaic reaction sites by large surface area. Although many processing techniques have been employed to fabricate nanostructured electrodes onto flexible substrates, these present limitations in terms of achieving flexible electrodes with high mechanical stability. In this study, the adhesion, mechanical properties and flexibility of TiN nanotube arrays on a Pt substrate were improved using a Ti interlayer. Highly ordered and well-aligned TiN nanotube arrays were fabricated on a Pt substrate using a template-assisted method with an anodic aluminum oxide (AAO) template and atomic layer deposition (ALD) system. We show that with the use of a Ti interlayer between the TiN nanotube arrays and Pt substrate, the TiN nanotube arrays could perfectly attach to the Pt substrate without delamination and faceted phenomena. Furthermore, the I-V curve measurements confirmed that the electric contact between the TiN nanotube arrays and substrate for use as an electrode was excellent, and its flexibility was also good for use in flexible electronic devices. Future efforts will be directed toward the fabrication of embedded electrodes in flexible plastic substrates by employing the concepts demonstrated in this study.

A high-performance hybrid supercapacitor with NiO derived NiO@Ni-MOF composite electrodes

Metal-organic framework (MOF) is a class of porous material, which has been gradually applied in supercapacitor fields but remains a significant challenge owing to their intrinsic instability and poor conductivity. Herein, we design a new strategy for synthesizing a well-aligned porous NiO@Ni-MOF/NF cylindrical cage-shape structure derived from NiO self-sacrificed template and precursor. Particularly, this unique construction structure could not only boost the conductivity of the electrode, but also endow the Ni-MOF with a good orientation to promote the transport of electrons and ion in electrochemical energy storage process. The as-prepared NiO@Ni-MOF/NF delivers an amazing specific capacity (1853 C cm−2 at 1 mA cm−2) superior to NiO/NF (242 C cm−2), as well as a relatively low impedance. The hybrid supercapacitor (HSC) is composed of the NiO@Ni-MOF/NF and carbon nanotube (CNT) as the positive and negative electrode, respectively. This HSC exhibits a specific capacitance of 144 F g−1 at 1 A g−1. The maximum energy and power densities of this HSC device reach to 39.2 W h kg−1 and 7000 W kg−1, respectively, showing good cycling stability with 94% capacity retention over 3000 cycles. This work proposes an innovative strategy for rational preparation well-aligned MOF arrays, which could serve as a promising method in the asymmetric supercapacitor devices field.

Well-aligned periodic germanium nanoisland arrays with large areas and improved field emission performance induced by femtosecond laser

Si-based field emitters with high and stable current densities have gained increasing attention owing to their relevant compatibility with other silicon-based microelectronic and photonic devices. Currently, well-aligned Ge nanostructure arrays can be used in fabrication of Si-based field emitters with excellent performance. In this study, large-area well-aligned Ge nanoisland arrays are induced by femtosecond laser (120 fs, 800 nm, 1 kHz). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman analyses, and X-ray photoelectron spectroscopy (XPS) reveal that well-aligned Ge nanoisland arrays with good quality. Field emission (FE) measurements indicate Ge nanoisland arrays with high emission current densities and good stability. Overall, the excellent FE properties of the proposed Ge nanoisland arrays will make them potential for applications in high-performance field emitters integrated with Si nanodevices.

Long-Range Order Self-Assembly of Conjugated Block Copolymers at Inclined Air-Liquid Interfaces.

Here, we report that long-range order, direction-controlled, ultrathin conjugated polymer films can be formed by the self-assembly of conjugated block copolymers (i.e., poly(3-hexylthiophene)-block-poly(ethylene glycol)) at inclined air-water interfaces. Structure analyses revealed well-aligned nanowire arrays of poly(3-hexylthiophene) with a dramatically increased ordered domain size compared to the polymer films formed on a flat water surface. The improved degree of order was attributed to the flow field created by the enhanced solvent evaporation at the top of the water contact line. Note that it is challenging to prepare such well-ordered and molecularly thin films of conjugated polymers by conventional fabrication methods. The long-range order polymer film showed hole mobility an order of magnitude higher than polymer films formed on a flat interface when implemented as an active layer of field-effect transistor devices. This study demonstrates that a simple interface modification can significantly impact the self-assembly process, structure, and function of polymer films formed at the air-liquid interface.

In situ growth of well-aligned Ni-MOF nanosheets on nickel foam for enhanced photocatalytic degradation of typical volatile organic compounds.

Exploitation of highly efficient catalysts for photocatalytic degradation of volatile organic compounds (VOCs) under visible light irradiation is highly desirable yet challenging. Herein, well-aligned 2D Ni-MOF nanosheet arrays vertically grown on porous nickel foam (Ni-MOF/NF) without lateral stacking were successfully prepared via a facile in situ solvothermal strategy. In this process, Ni foam could serve as both a skeleton to vertically support the Ni-MOF nanosheets and a self-sacrificial template to afford Ni ions for MOF growth. The Ni-MOF/NF nanosheet arrays with highly exposed active sites and light harvesting centres as well as fast mass and e- transport channels exhibited excellent photocatalytic oxidation activity and mineralization efficiency to typical VOCs emitted from the paint spray industry, which was almost impossible for their three-dimensional (3D) bulk Ni-MOF counterparts. A mineralization efficiency of 86.6% could be achieved at 98.1% of ethyl acetate removal. The related degradation mechanism and possible reaction pathways were also attempted based on the electron paramagnetic resonance (EPR) and online Time-of-Flight Mass Spectrometer (PTR-ToF-MS) results.

Synthesizing molybdenum-doped bismuth vanadate nanoneedle array as photocatalyst for water oxidation using bifunctional molybdenum as dopant and structure directing agent

Developing one-dimensional nanostructures is one of the efficient strategies for improving short charge diffusion path and serious charge recombination of bismuth vanadate (BiVO4) as the photocatalyst for water oxidation. The well-aligned molybdenum-doped (Mo-doped) BiVO4 nanoneedle array is synthesized on transparent conducting glass via the facile one-step solution process. The Mo ion cannot only act as the dopant for enhancing the carrier density but also play the role of the structure directing agent for promoting the formation of the well-defined nanoneedle array. The highest photocurrent density of 1.62 mA/cm2 at 1.23 VRHE and the smallest onset potential of 0.34 VRHE are obtained for the 6% Mo-doped BiVO4 electrode, while the pristine BiVO4 electrode only shows the photocurrent density of 0.78 mA/cm2 and the onset potential of 0.64 VRHE at the same conditions. The better photocatalytic ability for the Mo-doped BiVO4 electrode is owing to the preferable charge-transfer path and the higher carrier density induced by the doping of Mo in BiVO4. This work firstly demonstrates that Mo-doping can attain an extra benefit of producing the well-aligned nanoneedle array. Realizing heteroatom-doping and morphology design simultaneously using the simple solution process is promising for synthesizing the efficient photocatalyst toward water oxidation. The relation between the metal dopant and the morphology evolution is expected to be developed in the future work to more understand the principle of designing photocatalysts using the heteroatom-doping technique.

Construction of porous interface on CNTs@NiCo-LDH core-shell nanotube arrays for supercapacitor applications

Carbon-based materials have always been a research hotspot in the field of supercapacitors due to their unique stability under a wide range of potential. However, most of carbon-based materials used in supercapacitors cannot maximize the intrinsic capacitance performance due to the limited internal mass transfer. Herein, hierarchical well-aligned nanotube arrays with porous diffusive interfaces are in-situ fabricated by the self-templated effect of ZnO nanorod and ZIF-8 nano-shell. In this unique architecture, the well-aligned carbon nanotubes (CNTs) growing firmly on carbon fibers (CFs) can not only improve the mass transfer of ions onto the NiCo-LDHs surfaces, but also used as good backbones for the subsequent loading of NiCoLDHs nanosheets with high capacity. The optimized core-shell electrode displays an excellent capacity of 176.33 mAh g−1 at 1 A g−1. The as-prepared CNTs@NiCo-LDH//ZIF-8 derived carbon asymmetric supercapacitor (ASC) exhibits a high energy density of 37.38 Wh kg−1 at 800 W kg−1 and an outstanding cycling stability (90.22% retention after 5200 cycles), which offers a new synthesis strategy for design of carbon-based materials in superior electrochemical energy storage applications.

Growth of self-aligned single-crystal vanadium carbide nanosheets with a controllable thickness on a unique staked metal substrate

The single-crystal α-Mo2C nanosheets was first achieved on liquid copper by chemical vapor deposition in 2015. However, the other single-crystal transition-metal carbide nanosheets have not been reported yet. Here, we demonstrate the chemical vapor deposition of single-crystal VC nanosheets with the maximum size of 77 μm on a unique stacked metal substrate. The thickness of VC crystals can be controlled from 12 to 227 nm by changing the deposition pressure (Pd). The reduced Pd decreased the growth rate parallel and perpendicular to the [0 1¯ 1] zone axis. When the Pd was 5000 Pa, the well-aligned single-crystal VC arrays with the thickness of 12 ± 4 nm was obtained. The effect of the hydrogen flow (f) on VC morphology was also discussed. Due to the growth of VC complied to the mass-transport-limited process under high f, the VC crystals tended to be dendrite with the increase of the f. This study could pave a new way for controlling growth of transition-metal carbide nanosheets with tunable thickness and morphology.

Fabrication of Ag2S quantum dots sensitized CdSe photoelectrodes and its photoelectric performance

Well-aligned wheat-like CdSe nanorods array was fabricated by electrodeposition method, which was sensitized with Ag2S quantum dots (QDs) by using successive ionic layer adsorption and reaction (SILAR) method. The combination of five successive layers Ag2S QDs with CdSe shows maximum short-circuit photocurrent density of 36.88 mA/cm2. Compared with TiO2-based photoelectrode, the wheat-like CdSe nanorods array modified with Ag2S QDs exhibit improved photoelectrochemical (PEC) performance. The main reason for the enhancement of PEC is to use narrow band-gap semiconductor CdSe instead of the conventional wide band-gap oxide as the sensitized substrate of Ag2S QDs. In addition, the synthetic nanocomposites are characterized by analytical techniques such as XRD, UV–vis absorption spectroscopy, FESEM, HRTEM, EDX, XPS and EIS. The results indicate that Ag2S QDs are well grown on the surface of CdSe photoelectrodes. Meantime, the PEC performance of CdSe photoelectrodes has also been improved.

Membrane/Electrode Interface Design for Effective Water Management in Alkaline Membrane Fuel Cells.

The recent development of ultrathin anion exchange membranes and optimization of their operating conditions have significantly enhanced the performance of alkaline-membrane fuel cells (AMFCs); however, the effects of the membrane/electrode interface structure on the AMFC performance have not been seriously investigated thus far. Herein, we report on a high-performance AMFC system with a membrane/electrode interface of novel design. Commercially available membranes are modified in the form of well-aligned line arrays of both the anode and cathode sides by means of a solvent-assisted molding technique and sandwich-like assembly of the membrane and polydimethylsiloxane molds. Upon incorporating the patterned membranes into a single-cell system, we observe a significantly enhanced performance of up to ∼35% compared with that of the reference membrane. The enlarged interface area and reduced membrane thickness from the line-patterned membrane/electrode interface result in improved water management, reduced ohmic resistance, and effective utilization of the catalyst. We believe that our findings can significantly contribute further advancements in AMFCs.

Optimization of All Figure-of-Merits in Well-Aligned GaN Microwire Array Based Schottky UV Photodetectors by Si Doping

GaN nano/microwires, due to their large surface-to-volume ratio and the reduced dimensionality, have been widely used in high-performance ultraviolet (UV) photodetectors (PDs). However, there has been a fundamental trade-off between the photocurrent gain and the speeds of PDs, which have limited their practical applications. In this work, highly ordered GaN microwire array based Schottky UV PDs have been fabricated, and optimizing Si doping concentrations can entirely improve the performances of the devices. The results show that output photocurrent increases monotonously as increasing doping concentration, while the dark current experiences a decrease followed by an increase, resulting in an optimized value under a certain doping concentration. At doping concentration of 1 × 1018 cm–3 with 2.2 mW cm–2 illuminating intensity, the sensitivity, responsivity, and detectivity of the devices are greatly enhanced by 1.84 × 104%, 163%, and 2103%, respectively. Meanwhile, the time-dependent response in Si-doped d...

Rational construction of triangle-like nickel-cobalt bimetallic metal-organic framework nanosheets arrays as battery-type electrodes for hybrid supercapacitors

Reasonably designing self-supported metal-organic framework (MOF) nanoarrays is profound for applications in energy storage and conversion. Herein, we construct a triangle-like nickel-cobalt bimetallic metal-organic framework nanosheet array on nickel foam (NiCo-MOF/NF) via facile one-step hydrothermal reaction, served as battery-like electrode material for hybrid supercapacitors. By adjusting the molar ratio of Ni and Co, the optimal NiCo-MOF/NF with Ni/Co = 3:2 (3-2 NiCo-MOF/NF) produces an impressive specific capacity of 1003.5 C/g (2230 F/g) at 1 A/g, surpassing most of the previously reported MOF based electrode materials. The superior electrochemical performances may be related to their 3D well-aligned MOF nanosheets arrays, which provides enlarged electroactive areas. Meanwhile, the tight junction of electrode materials and conductive substrate nickel foam (NF) can guarantee their sufficient electric contact, contributing to fast electron transfer from electrodes to conductive substrates. Finally, a hybrid supercapacitor fabricated by the 3-2 NiCo-MOF/NF against active carbon (AC) delivers an advantageous energy density of 34.3 Wh/kg at a power density of 375 W/kg. These results certificate that such bimetallic NiCo-MOF nanosheets arrays hold great potential as novel electrode materials for hybrid supercapacitors.

Hierarchical cobalt oxide@Nickel-vanadium layer double hydroxide core/shell nanowire arrays with enhanced areal specific capacity for nickel–zinc batteries

The aqueous Nickel–Zinc batteries have advantages of high safety and environmental benignity. However, their low energy density and poor cycling stability hinder their widespread applications. To address these issues, we demonstrate here a well-aligned hierarchical nanowires array as an advanced cathode for Nickel–Zinc batteries, which is composed of Nickel-vanadium layered double hydroxide decorated on cobalt oxide with a core/sheath configuration featuring merits of high electrical conductivity, large specific surface area, and short diffusion pathway for ions and electrons. Benefiting from the hierarchy structure design and component synergistic effect, the nanowires array electrode with high mass-loading of 11.1 mg cm−2 exhibits high areal capacity of 1.98 mAh cm−2 at 5 mA cm−2, 61.8% capacity retention at 50 mA cm−2 and excellent cycling stability with 100% retention after 1000 cycles. Moreover, full cell of the as-fabricated nanowiress arrays//Zinc configuration delivers high operating voltage of 1.71 V, energy density up to 2.2 mWh cm−2, power density up to 82.0 mW cm−2 and remarkable cycling stability of 89% capacity retention after 1500 cycles, showing great potential for practical applications. This work may also bring new design opportunities for the well-defined nanoarrays electrode in other energy storage devices.

Hierarchical CoP3/NiMoO4 heterostructures on Ni foam as an efficient bifunctional electrocatalyst for overall water splitting

Abstract Controllable synthesis strategies of the cost-effective and high-active non-noble metal bifunctional electrocatalysts for overall water splitting are imperatively required. Herein, the hierarchical heterostructure CoP3/NiMoO4 nanosheets on Ni foam (CoP3/NiMoO4–NF) are synthesized by hydrothermal, annealing and phosphorization treatment. The synergistic effect between CoP3 and NiMoO4 remarkably promotes the HER intrinsic activity. Moreover, the Ni foam promotes the vertical growth of well-aligned nanosheet arrays, which expose more active sites for HER and OER. The CoP3/NiMoO4–NF-2 (Co/Mo = 1/1) electrocatalyst reveals a low overpotential of 92 mV for HER and 347 mV for OER at 10 mA cm−2 in 1.0 M KOH. Especially, the CoP3/NiMoO4–NF-2 exhibits exceptional performance for overall water splitting which presents a low cell voltage of 1.57 V at 10 mA cm−2, and outstanding durability which could maintain over 12 h. The design strategy and controllable synthesis of the hierarchical heterostructure bifunctional electrocatalyst will be beneficial for efficient overall water splitting.

A simple and facile route to oriented Bi2Al4O9 nanowire arrays and their photoluminescence properties

A new route based on the developed “MID” method is presented for the synthesis of oriented mullite-type Bi2Al4O9 nanowire arrays. The fabrication process is simple and facile, which only utilizes bismuth nitrate as the starting material and exploits a porous anodic aluminum oxide membrane as a reactive template. The obtained sample was carefully characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, respectively and the results indicate that it’s well-crystalized and display oriented nanowire morphology. A possible mechanism based on the Kirkendall effect was also discussed for the formation of the well-aligned nanowire arrays. Room temperature photoluminescence measurement of the nanowires exhibits a broad emission band centered at about 500 nm, 550 nm and 660 nm. Such supported and well-allied Bi2Al4O9 nanowire arrays may have advantages in future applications.

Morphology Controlled Synthesis of ZnO Nanorods for Glucose Enzymatic Biosensor

The use of zinc oxide nanorods is a promising option to increase the specific area for efficient glucose oxidase immobilization which further enhance the signal performance of glucose detection. In this work ZnO nanorods were prepared via hydrothermal process on sol-gel ZnO seed layer. The effects of different temperature of annealed seed layer on the morphology and properties of grow ZnO nanorods were investigated. The ZnO seed layers were annealed at various temperatures ranging from 300 to 600 °C for 2 h. The study demonstrated that the process condition of ZnO seed layer had a strong influence on the morphology and crystallinity of ZnO nanorods grow. X-ray diffraction analysis and scanning electronic microscopy were employed to characterize the crystal structure and morphology of the prepared ZnO seed layer and grow ZnO nanorods. The performance of different aspect ratio of ZnO nanorods on glucose detection were measured by using electrochemical analysis. With optimized ZnO nanorods, the glucose biosensor exhibited an enhanced in signal performance with a high sensitivity of 11.36 μA mM-1 cm-2 in the range of 0.05-1 mM. Such high performance was due to more immobilization on the well-aligned ZnO nanorods array and direct electron conduction between the nanorods and the electrodes

Realizing Controllable Carbon Nanotube Arrays for Soft Devices by Asymmetric Langmuir–Blodgett and Hydrophilization Process

Well-aligned Carbon nanotube (CNT) arrays are expected by flexible and stretchable devices. In this paper, an asymmetric Langmuir-Blodgett (LB) method and inorganic hydrophilization method have been proposed, with which well-aligned CNT arrays on soft substrates like polyethylene naphthalate, polyimide and polydimethylsiloxane have been realized. After depositing 50 nm SiO2 for hydrophilization, the water contact angle has been significantly reduced for different substrates. The surface roughness and flexibility have also been characterized to analyze their effect on device performance. The nanotube density in the arrays can be controlled to 10-25 tubes/μm 2 , 25-35 tubes/μm 2 or 35-45 tubes/μm 2 by tuning the surface pressure during the LB process. With aligned semiconducting CNT arrays as channel and anisotropic metallic CNT network as gate/source/drain electrodes, all-carbon nanotube transistors on PI substrate have been fabricated for demonstration. The fabricated devices show a subthreshold swing of 92.9 mV/dec, a carrier mobility of 15.32 cm 2 /Vs, and an on/off current ratio of 4.51 × 10 2 . More importantly, with 50 nm thick gate dielectrics, the changes of threshold voltage and carrier mobility are within 16.62% and 28.78%, respectively, even after bending 1000 times under a curvature radius of 3.66 mm.