Structure Of Nanowire Arrays Research Articles

Cu2S‐Cu3P Nanowire Arrays Self‐Supported on Copper Foam as Boosting Electrocatalysts for Hydrogen Evolution

With the rapid electrochemical development of hydrogen evolution, the search for low‐cost and high activity electrocatalysts for hydrogen evolution has received extensive attention. The fabrication of self‐supported Cu2S‐Cu3P nanowire (Cu2S‐Cu3P NW) arrays on a commercial copper foam by a liquid–solid reaction and subsequent phosphatation at low temperature is reported. The corresponding scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results indicate that the Cu2S‐Cu3P NW arrays have a dense nanowire (NW) structure with sulfur and phosphorous uniformly distributed on the surface of the nanowires. Interestingly, the Cu2S‐Cu3P NW arrays act as a hydrogen‐evolving cathode that when operated in 1.0 m KOH electrolyte only require a low overpotential of 158 mV to achieve a current density of 10 mA cm−2 and show a small Tafel slope of 45 mV dec−1. The activity decrease is negligible after holding at −500 mA cm–2 for 75 h, which thus demonstrates excellent stability. This could be due to the structure of nanowire arrays and synergistic effects between S and P, which could increase the specific surface area, reduce the charge transfer resistance, facilitate mass diffusion and electron transfers, and increase the active sites. This work therefore provides a simple method to prepare low‐cost and self‐supported electrocatalysts with high catalytic activity for hydrogen evolution.

Fabrication of a Silicon Nanowire Solar Cell on a Silicon-on-Insulator Substrate

This study proposes metal-assisted chemical etching (MAE) as a facile method to fabricate silicon nanowire (SiNW) array structures, with high optical confinement for thin crystalline silicon solar cells. Conventional SiNW arrays are generally fabricated on Si wafer substrates. However, tests on conventional SiNW-based solar cells cannot determine whether the photo-current is derived from SiNWs or from the Si wafer. Herein, SiNW arrays were fabricated on a silicon-on-insulator substrate with a 10-μm-thick silicon layer for measuring the photocurrent of the SiNW only. The 9 μm-long p-type SiNW arrays were applied to a solar cell structure fabricated using an n-type H-doped amorphous Si layer, thereby confirming the photovoltaic effect. However, the device exhibited a conversion efficiency of 0.0017% because of a low short-circuit current (Jsc) and a low open-circuit voltage (Voc). The low Jsc resulted from a high series resistance and high absorption loss from the amorphous Si layer, whereas the low Voc resulted from the high surface recombination velocity of the SiNW array structure. Therefore, reducing the surface recombination of SiNW-based solar cells can improve their conversion efficiency.

Broadband Ultraviolet Photodetector Based on Vertical Ga2O3/GaN Nanowire Array with High Responsivity

AbstractBroadband ultraviolet (BUV) photodetectors responding to the multiband spectrum can effectively reduce false alarm rates and improve the accuracy and versatility of detection systems in various situations. A high‐responsivity BUV photodetector based on vertical Ga2O3/GaN nanowire array is proposed and demonstrated. Ga2O3/GaN nanowires are obtained by partially thermally oxidizing GaN nanowires grown by molecular beam epitaxy and used to combine with a monolayer graphene film to form graphene/Ga2O3/GaN heterojunction. Moreover, the oxidation mechanism of GaN nanowires is further investigated by the developed thermal oxidation model. The fabricated devices exhibit excellent performance with a broadband spectral response of exceeding 550 A W−1 at −5 V and a fast‐response speed in the millisecond range, which can be attributed to the optical properties of vertical nanowire array structure and the internal gain mechanism of graphene/Ga2O3/GaN heterojunction.

Sandwich nanoporous framework decorated with vertical CuO nanowire arrays for electrochemical glucose sensing

Increasing demands for electrochemical glucose sensors with high overall performance have recently attracted intensive attention. Herein, we report a novel sandwich-like nanoarchitecture composed of uniform CuO nanowire array layers grown on the nanoporous Cu2O film, which was synthesized via annealing the nanoporous copper thin film obtained by dealloying Cu-based metallic glass precursors. The glucose sensor based on the newly developed CuO/Cu2O nanocomposite exhibits prominent overall electrocatalytic performance towards the oxidation of glucose with a wide linear dynamic detection range from 0.1 to 6 mM, high sensitivity up to 1.95 mA/cm2·mM, fast response time of less than 1.5 s, low detection limit of 1 μM (S/N = 3) as well as excellent selectivity. The enhanced electrocatalytic property of the nanocomposite is attributed to the high surface area originating from the in-situ grown CuO nanowire array structure and synergetic bi-continuous nanoporous Cu2O substrate. This finding not only provides promising candidates for blood glucose sensing, but also opens a new avenue to designing nanostructured catalysts for engineering applications in general.

All-Solid-State Fiber-Shaped Asymmetric Supercapacitors with Ultrahigh Energy Density Based on Porous Vanadium Nitride Nanowires and Ultrathin Ni(OH)2 Nanosheet Wrapped NiCo2O4 Nanowires Arrays Electrode

Fiber-shaped supercapacitors (FSC), among the most promising next-generation flexible energy storage devices, attract tremendous attention due to their high power density and rapid charging and discharging. However, their practical application is hindered by the low energy density that results from inferior specific capacitance and a limited voltage window. Herein, we design a flexible fiber-shaped asymmetric supercapacitor (FASC) with high energy density using vanadium nitride (VN) nanowires (NWs) on carbon nanotube fiber (CNTF) as negative electrode and ultrathin Ni(OH)2 nanosheet wrapped nickel cobalt oxide (NiCo2O4) to form a hierarchical nanowire array (HNWA) structure on CNTF as positive electrode. As-assembled FASC device has a maximum operational voltage of 1.6 V, with a highest areal capacitance of 291.9 mF/cm2 (106.1 F/cm3) and an energy density of 103.8 μWh/cm2 (37.7 mW/cm3). The FASC device possesses excellent reliability and achieves a retaining capacitance of more than 90% after 3000 bending...

A Novel Bimetallic Nickel–Molybdenum Carbide Nanowire Array for Efficient Hydrogen Evolution

The design and fabrication of noble-metal-free hydrogenevolution electrocatalysts with high activity is significant to future renewable energy systems. In this work, self-supported NiMo carbide nanowires on carbon cloth (Ni3 Mo3 C@NPC NWs/CC; NPC=N,P-doped carbon) were developed through an electropolymerization-assisted procedure. During the synthesis process, NiMoO4 nanowires were first grown on CC through a hydrothermal reaction that was free of any polymer binder such as Nafion. By use of electropolymerization, the as-prepared NiMoO4 NWs/CC sample was then coated by a layer of polypyrole (PPy) that served as the carbon source for subsequent conversion into Ni3 Mo3 C@NPC NWs/CC by carbothermal reduction. The experimental results indicated that judicious choices of the amount of coated PPy and the pyrolysis temperature were essential for obtaining the pure-phase, nanowire array structure of Ni3 Mo3 C@NPC NWs/CC. Benefitting from the pure phase of the bimetallic carbide, the unique architecture of the nanowire array, and its self-supported nature, the optimized Ni3 Mo3 C@NPC NWs/CC electrode exhibited excellent performance in the hydrogen evolution reaction (HER) in both acidic and alkaline media. Low overpotentials of 161 and 215 mV were required to afford a high current density of 100 mA cm-2 toward the HER in acidic and alkaline media, respectively, and the catalytic activity was maintained for at least 48 h, which puts Ni3 Mo3 C@NPC NWs/CC among the best HER electrocatalysts based on metallic carbides yet reported.

Plasmonic Au Array SERS Substrate with Optimized Thin Film Oxide Substrate Layer.

This work studies the effect of a plasmonic array structure coupled with thin film oxide substrate layers on optical surface enhancement using a finite element method. Previous results have shown that as the nanowire spacing increases in the sub-100 nm range, enhancement decreases; however, this work improves upon previous results by extending the range above 100 nm. It also averages optical enhancement across the entire device surface rather than localized regions, which gives a more practical estimate of the sensor response. A significant finding is that in higher ranges, optical enhancement does not always decrease but instead has additional plasmonic modes at greater nanowire and spacing dimensions resonant with the period of the structure and the incident light wavelength, making it possible to optimize enhancement in more accessibly fabricated nanowire array structures. This work also studies surface enhancement to optimize the geometries of plasmonic wires and oxide substrate thickness. Periodic oscillations of surface enhancement are observed at specific oxide thicknesses. These results will help improve future research by providing optimized geometries for SERS molecular sensors.

SERS effect of Rhodamine 6G molecular probe on AgAu alloy nanowire arrays by a solid-state ionics method

AgAu alloy nanowire arrays were prepared by a solid-state ionics method under a direct current electric field (DCEF) using fast ionic conductor RbAg4I5 films. The surface morphology and chemical composition of the AgAu alloy nanowire arrays were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), respectively. Raman enhancement performance of the AgAu alloy nanowire arrays substrates was detected by Rhodamine 6G (R6G) aqueous solutions as molecular probe. Long-range order and short-range order AgAu alloy nanowire arrays with the length of 1 cm were prepared by a solid-state ionics method. The nanowires were bamboo-shaped and the diameters of nanowires ranged from 20 to 80 nm. The molar ratio of Ag to Au is 15:1. The limiting concentrations of R6G for the prepared AgAu alloy nanowire arrays SERS substrates is 10−17 mol/L. The long-range and short-range orderly arrangement, high roughness and alloy structure of AgAu alloy nanowire arrays result in the substantial SERS effect.

A simple and transparent well-aligned ZnO nanowire array ultraviolet photodetector with high responsivity

Well-aligned zinc oxide (ZnO) nanowire arrays were grown on an interdigital patterned fluorine tin oxide (FTO)-coated glass substrate by a facile chemical bath deposition at low temperature. Morphology, crystalline structure, and optical properties of the ZnO nanowire arrays were analyzed in detail. The results revealed that the ZnO nanowires had wurtzite structure, typically ∼40–60 nm in diameter, and ∼700–800 nm in length, a great number of highly uniform and dense nanowires grew vertically on the substrate to form the well-aligned ZnO nanowire arrays, which had very high optical transmission (>86%) in the visible light region. In addition, the performance of ZnO nanowire arrays ultraviolet (UV) photodetector was systematically examined. The photosensitivity (S), responsivity (R), response and decay time of the photodetector were 703 at +0.2 V, 113 A/W at +5 V, 23 s and 73 s respectively. Also, the photoresponse mechanism of the UV photodetector was illuminated in terms of the oxygen adsorption-photodesorption process.

Photovoltaic Performance of a Nanowire/Quantum Dot Hybrid Nanostructure Array Solar Cell

An innovative solar cell based on a nanowire/quantum dot hybrid nanostructure array is designed and analyzed. By growing multilayer InAs quantum dots on the sidewalls of GaAs nanowires, not only the absorption spectrum of GaAs nanowires is extended by quantum dots but also the light absorption of quantum dots is dramatically enhanced due to the light-trapping effect of the nanowire array. By incorporating five layers of InAs quantum dots into a 500-nm high-GaAs nanowire array, the power conversion efficiency enhancement induced by the quantum dots is six times higher than the power conversion efficiency enhancement in thin-film solar cells which contain the same amount of quantum dots, indicating that the nanowire array structure can benefit the photovoltaic performance of quantum dot solar cells.

Piezotronic Effect on Rashba Spin-Orbit Coupling in a ZnO/P3HT Nanowire Array Structure.

A key concept in the emerging field of spintronics is the voltage-gate control of spin precession via the effective magnetic field generated by the Rashba spin-orbit coupling (SOC). Traditional external gate voltage usually needs a power supply, which can easily bring about background noise or lead to a short circuit in measurement, especially for nanoscale spintronic devices. Here, we present a study on the circular photogalvanic effect (CPGE) in a ZnO/P3HT nanowire array structure with the device excited under oblique incidence. We demonstrate that a strong Rashba SOC is induced by the structure inversion asymmetry of the ZnO/P3HT heterointerface. We show that the Rashba SOC can be effectively tuned by inner-crystal piezo-potential created inside the ZnO nanowires instead of an externally applied voltage. The piezo-potential can not only ensure the stability of future spin-devices under a static pressure or strain but also work without the need of extra energy; hence this room-temperature generation and piezotronic effect control of spin photocurrent demonstrate a potential application in large-scale flexible spintronics in piezoelectric nanowire systems.

Sea urchin-like architectures and nanowire arrays of cobalt–manganese sulfides for superior electrochemical energy storage performance

Cobalt–manganese (Co–Mn)-based bimetallic compounds (such as Co–Mn oxides, hydroxides) have been investigated as a new type of high-performance electroactive materials for energy storage device. Nevertheless, Co–Mn sulfides are seldom investigated, especially for those with hierarchical architectures and structures. Herein, we first adopt a facile two-step hydrothermal route and synthesize Co–Mn sulfides with sea urchin-like architecture and nanowire array structure. The anion-exchange sulfuration process gives rise to hierarchical structure with numerous nanosheets grown on the surface. Benefiting from the attractive structures and the high electrochemical activity of Co–Mn sulfides, the Co–Mn sulfides show improved performance than Co–Mn oxides with similar morphology. Especially, the Ni foam-supported Co–Mn sulfide nanowire arrays exhibit superior performance of 502 C g−1 at 1 A g−1 as well as excellent cycling stability with 107% of capacity retention after 2000 cycles. In addition, a hybrid supercapacitor Co–Mn sulfide nanowire arrays/RGO displays an energy density of 18.4 Wh kg−1 at 375 W kg−1. More importantly, an ultrahigh power density (22.5 kW kg−1 at 9.5 Wh kg−1) and outstanding cycling stability can also be achieved. The excellent electrochemical performance can be ascribed to the attractive structure and high electrochemical activity of Co–Mn sulfide.

Vertically oriented CoO@FeOOH nanowire arrays anchored on carbon cloth as a highly efficient electrode for oxygen evolution reaction

Developing high efficiency electrocatalysts for electrocatalytic oxygen evolution reaction (OER) is a key to water splitting. In this work, we demonstrate the preparation of CoO@FeOOH core-shell nanowire (NWs) grown on three-dimensional (3D) carbon cloth (CC@CoO@FeOOH-NWAs) by hydrothermal method followed by electrodeposition process as well as its highly efficient activity for water oxidation. In this hybrid structure, CoO@FeOOH-NWs with an average diameter of 100nm is vertically grown on the surface of carbon fibers of the carbon cloth. The combination of CoO@FeOOH catalyst with good electron transfer substrate exhibits exceptionally good electrocatalytic activity and long-term durability towards oxygen evolution reaction in alkaline solution. It needs an overpotential as low as 255mV to achieve the current density of 10mAcm−2, with a Tafel slope of 82mVdec−1 and also exhibits a good stability in 20h. In addition, the nanowire array structure is well retained after the durability test with high current density of 50mAcm−2. Our strategy provides a guide to rational design of micro-structures of the materials to achieve their high performance.

Self-supported CuS nanowire array: an efficient hydrogen-evolving electrode in neutral media

A self-supported copper sulfide (CuS) nanowire array (NWA) of hierarchical and porous structure has been developed on Cu foil via two consecutive liquid-solid reactions at room temperature. The composition, structure and morphology of the as-prepared CuS NWA samples have been systematically investigated by a series of techniques. When applied as cathode for the hydrogen evolution reaction (HER) in neutral solution, the optimized CuS NWA electrode exhibits excellent HER performance with high long-term stability. To achieve current densities of 10 and 100mAcm−2, it requires overpotentials of only ∼97 and ∼226mV, respectively. The excellent catalytic performance of CuS NWA toward HER is attributable to the binder-free electrode construction strategy, the unique porous nanowire array structure, and the small solubility product (Ksp) value of CuS that guarantees the high catalyst stability.

Dye gain gold NW array of surface plasmon polariton waveguide

Plasmon lasers can support ultrasmall mode confinement and ultrafast dynamics with device feature sizes below the diffraction limit. At present in the single visible light frequency, the optical gain method of constraint SPP on metal nanowires structure reported less. We design the gold nanowire array structure, consisting of PMMA and R6G dye molecules as gain, by 488nm pump in the middle of the nanowires position for wide range of light, use symmetry broken overcome that momentum does not match the photonic and SPP energy conversion. Theoretical analysis shows that dyes provide coherent optical feedback, resulting in nanowires face will observe laser properties of surface plasmons. Feature analysis: the incident light and pump joint strength is greater than the sum of strength which is the incident light, pump respectively. Under the effect of dye molecules gain effective, length of SPP transmission can increase 1µm. The results achieved in a single optical frequency of stimulated radiation, application of dye optical gain can achieve continuous gain effect. This is for the future development of plasma amplifier and the wavelength laser.

Site-Selective Controlled Dealloying Process of Gold-Silver Nanowire Array: a Simple Approach towards Long-Term Stability and Sensitivity Improvement of SERS Substrate.

Limitations of achieving highly sensitive and stable surface-enhanced Raman scattering (SERS) substrate greatly concern the suitable method for fabrication of large-area plasmonic nanostructures. Herein we report a simple approach using template-based synthesis to create a highly ordered two-dimensional array of gold-silver alloy nanowires, followed by the controlled dealloying process. This particular step of mild acid etching (15%v/v nitric acid for 5 min) allowed the formation of Raman hot spots on the nanowire tips while maintaining the integrity of highly active alloy composition and rigid nanowire array structure. Full consideration of SERS substrate performance was accomplished using 4-mercaptobenzoic acid (4-MBA) as a probe molecule. Exceedingly higher SERS signal (150-fold) can be achieved with respect to typical gold film substrate. Moreover, an excellent stability of SERS substrate was also determined for over 3 months storage time. In contrast to the previous studies which stability improvement was accomplished at a cost of sensitivity reduction, the simultaneous improvement of sensitivity and stability makes the controlled dealloying process an excellent choice of SERS substrate fabrication. In addition, uniformity and reproducibility studies indicated satisfactory results with the acceptable values of relative standard deviation.

Nanowire Array Structures for Photocatalytic Energy Conversion and Utilization: A Review of Design Concepts, Assembly and Integration, and Function Enabling

The increasing human demand for clean and renewable energy and a cleaner environment has stimulated various materials related research and development for efficient solar energy conversion and utilization, photocatalytic environmental remediation, and photoassisted selective conversion of organic compounds. Among the various candidate solutions to improving the efficiency of these processes, semiconductor nanowire (NW) and nanorod (NR) array structures have been offering a unique tool box combining desirable characteristics in structure, function, and applicability. Efficient photocatalytic energy conversion requires excellent light absorption, readily charge separation, transport, and collection, as well as fast kinetics of interfacial reactions and mass transport of reactants. The long axis of the NW enables adequate light absorption, while the radical axis provides short electron–hole separation distance. Additionally, the NW arrays have relatively high surface area to facilitate interfacial kinetics while their open pore structure allows good mass transport properties. This study reviews the current status of research on NW and NR array structures of some most popular semiconducting materials for photocatalytic energy conversion and utilization including photocatalytic water splitting and CO2 reduction/fixation, dye/quantum dot sensitized solar cells, and other photoassisted reactive applications such as pollutant degradation, selective conversion of organic compounds, and biological disinfection.

High-Resolution p-Type Metal Oxide Semiconductor Nanowire Array as an Ultrasensitive Sensor for Volatile Organic Compounds.

The development of high-performance volatile organic compound (VOC) sensor based on a p-type metal oxide semiconductor (MOS) is one of the important topics in gas sensor research because of its unique sensing characteristics, namely, rapid recovery kinetics, low temperature dependence, high humidity or thermal stability, and high potential for p-n junction applications. Despite intensive efforts made in this area, the applications of such sensors are hindered because of drawbacks related to the low sensitivity and slow response or long recovery time of p-type MOSs. In this study, the VOC sensing performance of a p-type MOS was significantly enhanced by forming a patterned p-type polycrystalline MOS with an ultrathin, high-aspect-ratio (∼25) structure (∼14 nm thickness) composed of ultrasmall grains (∼5 nm size). A high-resolution polycrystalline p-type MOS nanowire array with a grain size of ∼5 nm was fabricated by secondary sputtering via Ar(+) bombardment. Various p-type nanowire arrays of CuO, NiO, and Cr2O3 were easily fabricated by simply changing the sputtering material. The VOC sensor thus fabricated exhibited higher sensitivity (ΔR/Ra = 30 at 1 ppm hexane using NiO channels), as well as faster response or shorter recovery time (∼30 s) than that of previously reported p-type MOS sensors. This result is attributed to the high resolution and small grain size of p-type MOSs, which lead to overlap of fully charged zones; as a result, electrical properties are predominantly determined by surface states. Our new approach may be used as a route for producing high-resolution MOSs with particle sizes of ∼5 nm within a highly ordered, tall nanowire array structure.

TiO2(B) nanowire arrays on Ti foil substrate as three-dimensional anode for lithium-ion batteries

TiO2(B) nanowire arrays (TBNA) were synthesized directly on Ti foil substrate as a three-dimensional (3D) anode for lithium ion batteries. The crystal phase of TiO2(B) in the products was confirmed by X-ray diffraction and Raman spectroscopy. Observations from electron microscopy revealed uniform nanowires that were distributed regularly on the surface of the Ti metal foil forming an unique 3D nanowire array structure. TBNA exhibits promising electrochemical performance, the discharge capacity is extremely high even over the theoretical capacity of TiO2(B) at C/20, though it decays gradually, it is still high as 124.9mAh/g at 2C. The dramatic improvement in reversible capacity is ascribed to the unique structure of 3D nanowire array, which provides good electronic conductivity and accessible lithium ion paths, as well as a large surface area.

New Insights into the Origins of Sb-Induced Effects on Self-Catalyzed GaAsSb Nanowire Arrays.

Ternary semiconductor nanowire arrays enable scalable fabrication of nano-optoelectronic devices with tunable bandgap. However, the lack of insight into the effects of the incorporation of Vy element results in lack of control on the growth of ternary III-V(1-y)Vy nanowires and hinders the development of high-performance nanowire devices based on such ternaries. Here, we report on the origins of Sb-induced effects affecting the morphology and crystal structure of self-catalyzed GaAsSb nanowire arrays. The nanowire growth by molecular beam epitaxy is changed both kinetically and thermodynamically by the introduction of Sb. An anomalous decrease of the axial growth rate with increased Sb2 flux is found to be due to both the indirect kinetic influence via the Ga adatom diffusion induced catalyst geometry evolution and the direct composition modulation. From the fundamental growth analyses and the crystal phase evolution mechanism proposed in this Letter, the phase transition/stability in catalyst-assisted ternary III-V-V nanowire growth can be well explained. Wavelength tunability with good homogeneity of the optical emission from the self-catalyzed GaAsSb nanowire arrays with high crystal phase purity is demonstrated by only adjusting the Sb2 flux.