Nanowire Arrays Research Articles

Nanoscale heterojunctions of InGaN/GaN photocathodes for electron sources

The design of the photocathode is crucial for generating high-quality electron beam in electron sources. In this study, InGaN/GaN heterojunction nanowire photocathodes were proposed, and the photoemission theoretical model was developed. The results demonstrate that the built-in electric field along the axis enables the heterojunction nanowire photocathode to achieve higher collection efficiency across the response spectrum compared to In0.5Ga0.5N nanowire photocathodes. The variation of incidence angle results in distinct peaks in quantum efficiency and collection efficiency for the heterojunction nanowire photocathode. Meanwhile, the “additional electric field” has the potential to decrease the number of laterally emitted electrons from the nanowires, consequently reducing the shielding effect of adjacent nanowires. With an incidence angle of 15° and an “additional electric field” of 2 V/μm, the collection efficiency of photoelectrons at the collection end can be maximized to 47.6 %. This indicates that the heterojunction nanowire array photocathode has potential for use in high-performance vacuum electron sources.

Effect of complexing agent concentration on photovoltaic performance of TiO2@MAPbI3 core-shell structured nanowire arrays

In TiO2@MAPbI3 core-shell nanowire array solar cells, the full use of incident light, rapid transportation of carrier, and enhancement of mutual properties are realized as a whole. However, the perovskite layer is prone to defects during the growth process, and the density of deep energy level defects on the surface of polycrystalline perovskite layers is 1–2 orders of magnitude higher than that of the bulk phase, so the surface composite mainly limits the carrier lifetime of perovskite layers. To address the interfacial defects of perovskite layers, it has been shown that modification of the ETL surface using complexing agents can eliminate or improve these defects by forming ionic and coordination bonds with the perovskite surface. However, the number of ligands and the number of unliganded ions will directly affect the degree of improvement of the hybridized perovskite defects. So we investigated the effect of complexing agent concentration on the photovoltaic performance of NWs array solar cells, and when TiO2 NWss were modified by complexing agent at a concentration of 0.3 mol/L the best performance of the devices was achieved with a PCE of 9.86 % and an increase of 37.1 %. It shows that the concentration of the complexing agent has a significant impact on the carrier transport characteristics and photovoltaic performance of the core-shell structure NWs array. This will provide some guidances for improving the photovoltaic performance of core-shell NWs array solar cells.

Insight into the Intra and Inter-wire Magnetic Interactions of Co Nanowire Arrays by FORC Diagrams

Insight into the Intra and Inter-wire Magnetic Interactions of Co Nanowire Arrays by FORC Diagrams

Emission surface improvement of In0.5Ga0.5N tilted nanowire array photocathode for vacuum electron sources

Photocathode has received increasing attention in scientific devices that require high-quality electron beams. A theoretical photoemission model for enhancing the performance of In0.5Ga0.5N tilted nanowire array photocathodes with negative electron affinity surface is proposed. Finite Element and finite difference methods are employed in simulation experiments to study the In0.5Ga0.5N tilted nanowire array photocathode. The results demonstrate that the photoelectric conversion performance of the In0.5Ga0.5N tilted nanowire array photocathode can be significantly enhanced through the combined impact of oblique incident light and an additional electric field. Specifically, when θ = 20°, β = −40°, and Eout = 4 V/μm, the total quantum efficiency and collection efficiency are 2.79 times and 4.27 times higher than compared to vertical nanowires without external assistance, respectively.

2D Fractal Arrays of Ultrathin Silicon Nanowires as Cost‐Effective and High‐Performance Substrate for Supercapacitors

Silicon is the most diffused material in the industry; thus, considering its high capacity for energy storage, silicon‐based materials are well studied as battery anodes and supercapacitors. Si nanowires (NWs) emerge due to the high surface to volume ratio, its compatibility with a wafer processing typical of microelectronics, and are studied as anodes for lithium batteries as well as coupled with other materials for supercapacitor application. In this article, the synthesis and application are reported as a lithium anode of 2D fractal arrays of ultrathin Si NWs obtained by a thin‐film metal‐assisted chemical etching (MACE). These Si NWs exhibit a density of about 1012 NWs cm−2, maximizing the surface to volume ratio compared to silver‐salts MACE and other NW fabrication approaches. By using 2.7 μm long NWs, a pseudo‐capacitor behavior with a specific capacitance of about 274.2 μF cm−2 at a scan rate of 50 mV s−1 is obtained. This specific capacitance is two orders of magnitude higher than the one obtained in the same condition by using NWs synthesized by silver‐salt MACE. In this result, the route is opened toward the application of these fractal arrays of ultrathin Si NWs as substrate for supercapacitors with improved efficiency.

Improving Trace Detection of Methylene Blue by Designing Nanowire Array on Boron-Doped Diamond as Electrochemical Electrode

In this study, a boron-doped diamond nanowire array (BDD-NWA)-based electrode is prepared by using a microwave plasma chemical vapor deposition system and treated with inductively coupled plasma reactive ion etching. The BDD-NWA electrode is used for trace detection of methylene blue, which has a wide linear range of 0.04–10 μM and a low detection limit of 0.72 nM. Both the superhydrophilicity (contact angle ~0°) and the dense nanowire array’s structure after the etching process improve the sensitivity of the electrochemical detection compared to the pristine BDD. In addition, the electrode shows great repeatability (peak current fluctuation range of −3.3% to 2.9% for five detection/cleaning cycles) and stability (peak current fluctuation range of −5.3% to 6.3% after boiling) due to the unique properties of diamonds (mechanical and chemical stability). Moreover, the BDD-NWA electrode achieves satisfactory recoveries (93.8%–107.5%) and real-time monitoring in tap water.

Effect of gas diffusion layer surface property on platinum nanowire array electrode performance in proton exchange membrane fuel cells

3D-ordered catalyst electrodes have been recognized as one effective strategy to reach high current density operation for proton exchange membrane fuel cell (PEMFC) applications. Gas diffusion electrodes (GDEs) with platinum nanowire arrays in-situ grown on gas diffusion layer (GDL) surface is an important contribution in this area, but the performance is highly dependent on the GDL surface properties. In this study, the GDLs available in the market are systematically investigated, with a focus on the influence of the GDL surface properties on the in-situ growth of Pt nanowire arrays to fabricate GDEs as cathodes for PEMFCs. The experimental results indicate that mesopores especially micropores play a key role. They enable a hydrophilic surface for the isopropanol pretreated GDL, facilitating the in-situ growth of Pt nanowires to form a uniform array with a large electrochemical surface area (ECSA), finally leading to a high-power density. With Freudenberg H24CX483 carbon paper GDL, the highest power density of 0.9 W cm−2 is achieved. The understanding achieved here could be further used to develop novel GDLs for fabricating the next generation of electrodes for large current density operations.

Construction of core-shell heterostructures Co3S4@NiCo2S4 as cathode and covalent organic framework derived carbon as anode for hybrid supercapacitors

Structured design helps to play out the coordination advantage and optimize the performance of electrochemical reactions. In this work, hierarchical hollow microspheres (Co3S4@NiCo2S4) with unique core-shell heterostructure were successfully prepared through simple template and solvothermal methods. Thanks to the hollow structure, cross-linked nanowire arrays, and in-situ coating of zeolite imidazole framework (ZIF), Co3S4@NiCo2S4 demonstrated excellent electrochemical performance with a specific capacitance of up to 2697.7 F g−1 at 1 A g−1 and cycling stability of 80.5% after 5000 cycles. The covalent organic framework (COF) derived nano carbon, which had undergone secondary calcination and ZnCl2 activation, also exhibited excellent double-layer energy storage performance. Compared to a single calcination, the incredible increase in capacitance was up to 208.5 times greater, reaching 291.9 F g−1 at 1 A g−1 while maintaining ultra-high rate performance (81.0% at 20 A g−1). The hybrid supercapacitor, assembled with Co3S4@NiCo2S4 as the cathode and COF-derived carbon as the anode, exhibited an extremely high energy density (79.7 Wh kg−1 at 693.5 W kg−1) and excellent cyclic stability (maintained 79.3% after 10,000 cycles of 20 A g−1), further explaining the reliable and practical characteristics. This work provided reference for the structural optimization of transition metal sulfides and the high-temperature activation of COF-derived carbon.

Crystallinity modulation and microenvironment engineering synergistically manipulate ROS generation on Ni single-atom photocatalysts

The microenvironment modulation of metal-based catalysis sites plays a critical role in single-atom photocatalysis, and remains a grand challenge yet. Herein, the single-atom Ni anchored crystalline carbon nitride (Ni/CCN) nanowire arrays are reported. The obtained Ni/CCN nanowire arrays exhibit an impressive photocatalytic activity (>96% degradation of pharmaceuticals and personal care products (PPCPs) in only 5 min) and photocatalytic rate (maximum 0.5941 min−1) with only clean solar energy input. The Ni/CCN catalyst attached on microfiltration membrane in the continuous flow experiments exhibits >90% PPCPs degradation efficiency over 10 h, demonstrating the ultrahigh activity and long-term operation of the Ni/CCN catalysts. The results of electron spin resonance analysis, probe experiment and theoretical calculations demonstrate that the promoted generation of reactive oxygen species (ROS) highly relies on the crystallinity regulation and microenvironment engineering of active metal sites, which are consequently utilized to trigger the rapid degradation of PPCPs. The introduced Ni-N4 moiety disrupts the uniform distribution of delocalized electrons and precisely tunes the electronic distribution of the microenvironment in CCN, providing an electron-rich region coupled with strong electron transfer effect between Ni and adsorbed O, thus optimizing the crucial step for molecular oxygen activation. This work offers a new idea of photocatalysis from theoretical design towards broad applications through the perspective about modulating microenvironment of active metal sites and optimizing intrinsic electronic properties.

Constructing a Built-In Electric Field To Accelerate Water Dissociation for Efficient Alkaline Hydrogen Evolution.

The alkaline hydrogen evolution reaction (HER) is intricately linked to the water dissociation kinetics. The quest for new strategies to accelerate this step is a pivotal aspect of enhancing the HER performance. Herein, we designed and synthesized a heterogeneous nickel phosphide/cobalt phosphide nanowire array grown on nickel foam (Ni2P/CoP/NF) to form a p-n junction structure. The built-in electric field (BEF) in the p-n junction optimizes the binding ability of hydrogen and hydroxyl intermediates, efficiently promoting water dissociation for the alkaline HER. Consequently, Ni2P/CoP/NF exhibits a lower overpotential of 58 and 118 mV at 30 and 100 mA cm-2, respectively, and high stability over 40 h at 300 mA cm-2 for the HER in 1 M KOH. Computational calculations combined with experiment results testify that the BEF presence in the p-n junction of Ni2P/CoP/NF effectively promotes water dissociation, regulates intermediate adsorption/desorption, and boosts electron transport. This study presents a rational design approach for high-performance heterogeneous electrocatalysts.

Titanium-coated high-density Fe2O3 single crystal nanowire array for solar water splitting

Fe2O3 holds promising n-type semiconductor material in the field of solar water splitting due to its excellent photocatalytic properties. However, the photoelectrochemical performance of Fe2O3 is limited by its inherent properties such as poor conductivity, and charge separation efficiency owing to its recombination rate. Therefore, researchers are more focused on nanostructuring, doping, and surface coating to overcome these issues of Fe2O3. In this study, we have investigated a low-cost way to fabricate a Ti coating layer on a high-density Fe2O3 single-crystal nanowire array for solar water splitting. Firstly, we have prepared a high-density single-crystal Fe2O3 nanowire array at lower temperatures by a new approach stress-induced atomic diffusion method. Thereafter, the prepared nanowire array was coated by Ti film using RF sputtering. The optimal film thickness of 13 nm titanium coatings layer into Fe2O3 single crystal nanowire array exhibited a high photocurrent density of 1.36 mA/cm2 at 1.23 V versus RHE and solar to hydrogen conversion efficiency (STH) of 1.67%, which could be resulting from adjusted optoelectronic properties of the nanowires.

Assessing the interaction of alcohol homologs with InAs nanowires in contact with gas-permeable SWCNT electrode: Towards a novel sensing platform

We report the approach to designing the hybrid gas sensor based on the array of vertically-oriented InAs nanowires and gas-permeable film made of single-walled carbon nanotubes (SWCNTs). We probe the sensor performance at room temperature towards isopropyl alcohol analyte, whose highest occupied molecular orbital energy to be in-between the Fermi levels of SWCNTs and InAs, to check the main contributing mechanism. Our theoretical analysis revealed that electronic systems of both materials contribute to sensor response. Our findings indicate that the sensor response to isopropyl alcohol in a mixture with dry and humid air primarily stems from its interaction with carbon nanotubes, although it also involves an interplay between the electron energy states of SWCNTs and InAs. We also test the sensor response to methanol, ethanol, and butanol analytes and demonstrate that it enhances with a molecule weight. The proposed sensor design can be further optimized to capture vector signals under a multivariate approach to selectively determine various analytes.

The effect of micro-nanostructural changes on the absorption and emission characteristics of InGaAsP photocathodes

In this paper, three structures (cylinder, square column, and hexagonal prism) of InGaAsP nanowire arrays are designed based on the excellent light trapping effect of nanostructures. The effects of nanowire aperture, array period, and nanowire height on the light absorption properties are simulated and analyzed using the finite-domain time-difference (FDTD) method. The photoelectron emission capacity of the nanowire arrays was also calculated using MATLAB. The results show that the cylindrical nanowire array has phenomenon of resonance enhancement (absorption peak) in the near-infrared band of 820–1000[Formula: see text]nm, and the shift of absorption peaks can be achieved by adjusting the geometric parameters. Meanwhile, the quantum efficiency is taken to 9.98%. These simulation results provide some reference for the photocathode design of InGaAsP in the near-infrared band.

Design of a high-resolution magneto-plasmonic biosensor for analyte detection

This paper introduces the design of a magneto-plasmonic refractometric sensor aimed at achieving high resolution. This sensor consists of arrays of gold nanowires and layers of SiO2 and Co6Ag94, where the analyte is placed on the gold nanowires. A p-polarized optical field with a wavelength of 631 nm is used to excite the structure, which is applied in the range of 1° to 45°. A magnetic field is applied to z-axis to create the magneto-optical effect. The reflected optical field of the samples is used to calculate the signal of the transverse magneto-optical Kerr effect, which shows significant changes in the refractive index of the samples and the direction of the magnetic field. The highest displacement is 4°. The highest value of the figure of merit is 3611 RIU−1, and the maximum sensitivity is obtained as 71 °/RIU.

Evolution of 2D MoO3 layer structures on Pd(100): interplay of interfacial interactions and polarity

Abstract We explore the structural evolution of two-dimensional (2D) MoO3 films beyond the monolayer (ML), which have been prepared by physical vapor deposition and post-oxidation onto a Pd(100) surface, and characterized by the tools of surface science and density functional theory (DFT) calculations. According to DFT, the most stable oxide layers are stoichiometric, and derive their energetic stability from the low cost of creating 2D freestanding layers from the orthorhombic bulk phase, good matching to Pd, and the particularly strong adhesion to the substrate. The observed 2D MoO3 layers are distinguished by well-ordered linear defects, such as domain boundaries in the ML, and misfit dislocations in the bilayer (BL). Applying reactive oxidation preparation conditions results in the formation of ordered arrays of nanostructures, nanowires and nanoclusters, in the MoO3 BL. The formation of such linear structures is accounted for in the DFT by models of missing row defects of various orientations and stoichiometries. Their relative stability is rationalized in terms of the number of broken Mo–O bonds, the polar character of the nanostructure edges and the interaction strength with the Pd substrate. Comparison with similar WO3 layers on Pd(100) is provided.

Catalytic Growth of Ionic Conductive Lithium Nitride Nanowire Array for Dendrite‐Free Lithium Metal Anode

AbstractThe development of an artificial solid‐electrolyte interphase (SEI) has been recognized as the most efficient strategy to overcome the safety concerns associated with the lithium metal anode (LMA). Inorganic‐rich SEIs on the LMA are crucial for suppressing Li dendrites. Among the prevalent SEI inorganic compounds observed for LMA, lithium nitride (Li3N) is often found in the SEIs of high‐performance LMA. Herein, the Li3N nanowire array is successfully synthesized and the catalytic base‐growth mechanism is thoroughly investigated. The fast ionic conductor Li3N nanowires act as pillars to control the nucleation and growth of lithium metal along the vertical direction of the nanowire by bottom‐up self‐lubrication, which fundamentally prevents the dendrite growth. The Li3N is characterized by abundant lithiophilic nucleation sites, which effectively reduces the local current density, and facilitates homogeneous Li+ flux. Symmetric cells utilizing the Li3N@Li anode have demonstrated excellent stability, featuring uniform deposition without dendrite formation. Additionally, high‐capacity retentions of 98% at 0.5 C after 400 cycles and impressive high‐rate performance at 31.1 mA cm−2 have been realized in high‐loading Li3N@Li||LFP cells. The universal preparation of the Li3N nanowires with various precursors and substrates is further explored, which is expected to be applied in solid‐state batteries and hydrogen storage.

In-situ stabilization of metal-nitride sites in sprouted 2D cMOF@LDHs hetero-nano petals on metaloxynitrides nanostems for enhanced water splitting

Addressing the challenges of enhancing water-splitting efficiency necessitates the exploration and rational design of high-performance and durable electrocatalysts with appealing nanoarchitectures. In this study, we present the design and fabrication of conjugated cMOF/LDH hetero-nano petals decorated with monodispersed Metal-N sites, which are uniformly shelled over tungsten oxynitride (WNO) nanowire arrays to form a unique core–shell architecture. For this rational engineering, WNO nanowire arrays were grown on carbon cloth. Then, a thin-layered Ru-Co-Fe layered double hydroxide (RuCoFe/LDH) was deposited around these wires, resulting in a highly porous three-dimensional array of hierarchical hetero RuCoFe-LDHs@WNO-NWs core–shell nanowires (RuCoFe-NSs@WNO-NWs). Subsequently, the linkers coordinated with the RuCoFe-LDH nanosheets and transformed them in-situ into the RuCoFe-cMOF nano petals (RuCoFe-NPs@WNO-NWs). Notably, the linker’s amino groups functioned as hooks for precisely anchoring and stabilizing metal sites, forming the metal nitride (M-N) moieties. Interestingly, the designed bi-functional catalyst exhibited superior catalytic activities for both OER (230 mV @ 10 mAcm−2) and HER (49 mV @ 10 mAcm−2) in an alkaline medium. Additionally, an electrolyzer cell employing Ru-CoFe-NPs@WNO-NWs as a bi-functional electrocatalyst required 1.49V to reach a current density of 10 mA cm−2. These remarkable catalytic performances can be attributed to several key factors, including opulent exposed active sites, an efficient charge/mass transport pathway, an optimized electronic structure, and an interfacial synergy effect. Hence, this study provides a new perspective for the design of efficient bi-functional electrocatalysts for use in the energy related electrochemical devices.

Assembly of large-area helical nanowire and nanosphere superstructures by PS-b-P2VP/S-mandelic acid via interfacial nanoarchitectonics

Chiral supramolecules have attracted great research interest due to their unique properties and functions. How to assemble them into the ordered superstructures, however, remains a challenge. In this paper, two methods have been developed to fabricate such superstructures. In method I, polystyrene-b-poly (2-vinylpyridine) (PS-b-P2VP) and S-mandelic acid (S-MA) diffused from the oil and aqueous phases respectively to the oil/water interface, combined and self-assembled into helical nanowires and nanospheres with monochirality, and formed parallel-aligned nanowire arrays and close-packed arrays at the liquid/liquid interface. In method II, PS-b-P2VP in DMF droplets was introduced into the aqueous solution of S-MA through a liquid/liquid interfacial phase transfer process. Then the polymer molecules self-assembled into helical nanowires and nanospheres with monochirality in the aqueous phase, which adsorbed at the air/liquid interface and organized into superstructures. The formation of chiral aggregates should be attributed to the induction of S-MA, while the superstructures at the interfaces were considered to result from the modulation by the interfacial pressures. This study has developed one-step techniques to assemble the chiral aggregates and superstructures, which is expected to become universal for fabrication of functional superstructures.

CoSe2 nanowire array enabled highly efficient electrocatalytic reduction of nitrate for ammonia synthesis

The electrocatalytic reduction of nitrate (NO3–) not only facilitates the environmentally sustainable production of ammonia (NH3) but also purifies water by removing NO3–, thereby transforming waste into valuable resources. The process of converting NO3– to NH3 is complex, involving eight electron transfers and multiple intermediates, making the choice of electrocatalyst critical. In this study, we report a cobalt selenide (CoSe2) nanowire array on carbon cloth (CoSe2/CC) as an effective electrocatalyst for the NO3– to NH3 conversion. In an alkaline medium with 0.1 mol/L NO3–, CoSe2/CC demonstrates exceptional NH3 Faradaic efficiency of 97.6 % and a high NH3 yield of 517.7 µmol h–1 cm–2 at –0.6 V versus the reversible hydrogen electrode. Furthermore, insights into the reaction mechanism of CoSe2 in the electrocatalytic NO3– reduction are elucidated through density functional theory calculations.

Highly uniform organic nanowire synaptic arrays with excellent performance for associative memory

Synaptic devices of optoelectronic nature, which combine light-detection and data-storage capabilities, hold significant promise in the realm of neuromorphic computing. They are especially beneficial for the processing of visual data and the execution of intricate cognitive functions akin to learning, memory retention, and logical reasoning. However, current research is mostly confined to the level of individual devices, with corresponding studies on synaptic arrays being relatively scarce. Type II heterojunctions are widely used in optoelectronics. Bandgap engineering enables efficient separation and trapping of photogenerated excitons in selected materials, reducing carrier recombination. This prolongs carrier retention in the channel, delaying photocurrent decay, crucial for artificial optoelectronic synapses. We designed an organic nanowire/perovskite Type II heterojunction where CsPbBr3 perovskite films and TIPS nanowires serve as the photosensitive and channel layers, respectively. The composite synaptic array was successfully fabricated by in-situ growth of TIPS nanowires on the surface of perovskite thin films. It was further used to fabricate a photonic synapse array that exhibits characteristic photocurrent and stable optical response. Achieving high-performance photonic synapses was facilitated by characteristics such as high mobility and high on/off ratios, stemming from the formation of complete single-crystal nanowires on the perovskite films. Exhibiting synaptic behaviors such as photo-induced enhancements and paired-pulse facilitation, the device enabled a visual sensing system with a 5 × 5 pixel array for simulating memory processes and restoring associative memories. A novel photocurrent model was established for understanding device characteristics. This work provides valuable insights for future utilization of composite organic nanowire arrays in simulating brain-like computations and realizing large-scale intelligent visual sensing systems.