Heterojunction Nanowires Research Articles

Chiral 2D/Quasi‐2D Perovskite Heterojunction Nanowire Arrays for High‐Performance Full‐Stokes Polarization Detection

The realization of Stokes photodetectors accelerates the development of various modern optoelectronic applications. Chiral 2D perovskites with intrinsic chiral optical activity and superior carrier mobility are promising for next‐generation full‐Stokes polarization detection. So far, most of the chiral 2D metal‐halide perovskite‐based photodetectors suffer from limited discrimination of circularly polarized light due to the high exciton recombination rate in single‐phase perovskite, impeding the accurate measurement for Stokes parameters. Here, an on‐chip Stokes photodetector based on chiral 2D/quasi‐2D perovskite lateral heterojunction nanowire (NW) arrays with high polarization selectivity and photoresponsiveness is reported. The highly‐aligned heterojunction NW arrays not only build up a built‐in electric field for enhanced chiral discrimination, but also possess intrinsic anisotropy that enables outstanding linear polarization response. On this basis, the device exhibits reliable ability for polarization detection with a high anisotropy factor of 0.38, an outstanding polarized ratio of 1.5, and an excellent responsivity of 22.14 A W−1. These results will provide useful enlightenment for direct full‐Stokes polarization detection in optoelectronic integrated circuits.

In Situ Formation of CoP/Co3 O4 Heterojunction for Efficient Overall Water Splitting.

Electrochemical water splitting is an environmentally friendly and effective energy storage method. However, it is still a huge challenge to prepare non-noble metal based electrocatalysts that possess high activity and long-term durability to realize efficient water splitting. Here, we present a novel method of low-temperature phosphating for preparing CoP/Co3 O4 heterojunction nanowires catalyst on titanium mesh (TM) substrate that can be used for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting. CoP/Co3 O4 @TM heterojunction showed an excellent catalytic performance and long-term durability in 1.0 M KOH electrolyte. The overpotential of CoP/Co3 O4 @TM heterojunction was only 257 mV at 20 mA cm-2 during the OER process, and it could work stably more than 40 h at 1.52 V versus reversible hydrogen electrode (vs. RHE). During the HER process, the overpotential of CoP/Co3 O4 @TM heterojunction was only 98 mV at -10 mA cm-2 . More importantly, when used as anodic and cathodic electrocatalyst, they achieved 10 mA cm-2 at 1.59 V. The Faradaic efficiencies of OER and HER were 98.4 % and 99.4 %, respectively, outperforming Ru/Ir-based noble metal electrocatalysts and other non-noble metal electrocatalysts for overall water splitting.

Synergistic organic dye degradation and hydrogen production using Bi2Te3/Te/C single-catalyst nanowires

Over-consumption of limited fossil fuels has caused serious environmental pollution and a global energy crisis, threatening human life and biodiversity. As an ideal, environmentally friendly renewable energy, hydrogen can satisfy human clean energy requirements. Therefore, whether hydrogen can be catalytically generated in the wastewater treatment process is a highly meaningful investigation. Herein, Bi2Te3/Te/C heterojunction nanowires with high specific surface area and rich pore structure were successfully synthesized. The efficient catalytic degradation process is accompanied by the generation of hydrogen. The catalytic degradation of methylene blue and methyl orange was achieved in less than 20 s and 150 s, respectively. Meanwhile, in scaled-up degradation/hydrogen production experiments, fast and efficient H2 production from NaBH4 can be realized in the presence of Bi2Te3/Te/C nanowires. The mechanism of efficient synergistic organic dye degradation and hydrogen production is due to the efficient carrier transfers and accumulation at the hetero-interface. In contrast to previous work, rapid degradation of organic dyes and hydrogen production by decomposition of NaBH4 were achieved without the help of high-cost catalysts such as precious metals. This work could provide an alternative pathway for the future degradation of organic matter in synergistic heterogeneous catalytic wastewater and recovery of by-products including hydrogen.

Rational Design of Goethite-Sulfide Nanowire Heterojunctions for High Current Density Water Splitting.

The preparation of efficient and stable bifunctional electrocatalysts for electrochemical overall water splitting (OWS) to scale up commercial hydrogen production remains a great challenge. Here, we synthesized heterojunction structures consisting of Co9S8/Ni3S2 nanowire arrays and amorphous goethite (FeOOH, α-phase) particles as efficient OWS catalysts using an interface engineering strategy. The interfacial charge inhomogeneity caused by the heterojunction contact leads to the generation of a built-in electric field, which makes the electron-deficient FeOOH and electron-rich Co9S8/Ni3S2 favorable for hydrogen/oxygen evolution reaction, respectively, thus ensuring the excellent activity of FeOOH/Co9S8/Ni3S2 as a bifunctional catalyst. FeOOH/Co9S8/Ni3S2 exhibits impressive catalytic activity for the oxygen evolution reaction, achieving an ultralarge current density of 1000 mA cm-2 needed as low as 265 mV overpotential, and its stability was tested up to 1440 h. Furthermore, an excellent OWS output (1.55 V to generate 10 mA cm-2) is achieved by the bifunctional FeOOH/Co9S8/Ni3S2 catalysts.

Piezotronic and Piezo-Phototronic Effects-Enhanced Core-Shell Structure-Based Nanowire Field-Effect Transistors.

Piezotronic and piezo-phototronic effects have been extensively applied to modulate the performance of advanced electronics and optoelectronics. In this study, to systematically investigate the piezotronic and piezo-phototronic effects in field-effect transistors (FETs), a core-shell structure-based Si/ZnO nanowire heterojunction FET (HJFET) model was established using the finite element method. We performed a sweep analysis of several parameters of the model. The results show that the channel current increases with the channel radial thickness and channel doping concentration, while it decreases with the channel length, gate doping concentration, and gate voltage. Under a tensile strain of 0.39‱, the saturation current change rate can reach 38%. Finally, another core-shell structure-based ZnO/Si nanowire HJFET model with the same parameters was established. The simulation results show that at a compressive strain of -0.39‱, the saturation current change rate is about 18%, which is smaller than that of the Si/ZnO case. Piezoelectric potential and photogenerated electromotive force jointly regulate the carrier distribution in the channel, change the width of the channel depletion layer and the channel conductivity, and thus regulate the channel current. The research results provide a certain degree of reference for the subsequent experimental design of Zn-based HJFETs and are applicable to other kinds of FETs.

Constructing a Si-CuO core-shell nanowire heterojunction photoanode for enzyme-free and highly-sensitive glucose sensing

Constructing novel heterojunctions has become an effective strategy to improve the performance of photoelectrochemical (PEC) biosensors, but most of the glucose-sensing photoelectrodes involve enzyme modification and disordered or semi-closed surface topography which restricts the working environment and sensing performance. Herein, the dense and burr-like CuO nanospikes (CuONSs) are grown on all over the whole surfaces of the relatively-sparse and ordered Si nanowires (SiNWs) by a combination of magnetron sputtering and hydrothermal growth. The optimized SiNWs-CuONSs heterojunction with a core–shell structure achieves the enzyme-free PEC detection of glucose with a sensitivity of 2324.09 μA mM−1 cm−2 in the concentration range of 0–1.0 mM and a detection limit of 0.74 μM (Signal/Noise = 3). The excellent sensing performance is ascribed to that (1) the SiNWs with a large specific surface area acting as host have open-style surface topography, ensuring the analyte flowability; (2) the CuONSs with a desired glucose-catalytic activity are hierarchical, providing a great number of active sites; and (3) the SiNWs-CuONSs heterojunction has a satisfactory optical absorption and a high efficiency of the photogenerated-hole transfer. This work demonstrates that the enzyme-free and highly-sensitive glucose detection can be realized by morphology-controllable heterojunction, and provides an alternative route to noninvasive sensing.

0D/1D CuFeO2/CuO nanowire heterojunction arrays for improved photoelectrocatalytic reduction of CO2 to ethanol

CuO material with a bandgap of 1.2–1.9 eV and suitable energy level is a promissing material for photoelectrocatalytic reduction of CO2. However, the serious photocorrosion limits its performance improvement. Herein, an in-situ synthesis route is designed to fabricate 0D/1D CuFeO2/CuO nanowire heterojunction arrays with large specific surface. The nanowire heterojunction arrays presented excellent activity for photoelectrochemical reduction of CO2 to ethanol with an optimal faradaic efficiency of 66.73% at - 0.6 V (vs. Ag/AgCl). A heterojunction is formed between CuFeO2 and CuO, and the enhanced charge transfer mechanism is proposed based on the measurement of energy band structures. Under the action of interfacial built-in electric field of heterojunction, photogenerated holes are transferred from the valence band of CuO to CuFeO2, and photogenerated electrons are transferred from the conduction band of CuFeO2 to CuO with high selective reduction of CO2 to ethanol.

Gas‐Phase Anion Exchange for Multisegment Heterostructured CsPb(Br1−xClx)3 Perovskite Nanowires

AbstractMetal‐halide perovskites (MHPs) are promising as active optoelectronic materials for a diverse range of devices. Anion exchange is a post‐growth modification of MHP materials that allows tuning of the band gap and crystal structure by exposure to alternative halides, normally using solution methods. Here, low temperature gas‐phase anion exchange for the conversion of CsPbBr3 nanowires (NW) into CsPb(Br1−xClx) NWs using two media, fuming HCl and Cl2 gas, is systematically investigated. It is found that both methods can be used to tune the composition in the full range with excellent control. While fuming HCl is the simplest process, Cl2 gives similar results with no surface damage and better process control. Based on a simple solid diffusion model, an average diffusivity of 1.4 × 10−12 cm2s−1 is extracted for Cl‐anions inside CsPbBr3. By combining the Cl2 exchange process with electron‐beam lithography patterning, heterojunction NWs with varying halide compositions are produced, including complex barcode‐like NWs with segment lengths as short as 500 nm. Designed heterostructures provide an important basis for optoelectronic device applications of MHPs, and gas‐phase anion exchange should be suitable for any MHP morphology.

A Fast-Response Ultraviolet Phototransistor with a PVK QDs/ZnO Nanowire Heterostructure and Its Application in Pharmaceutical Solute Detection.

The sensitivity and photoelectric noise of UV photodetectors are challenges that need to be overcome in pharmaceutical solute detection applications. This paper presents a new device concept for a CsPbBr3 QDs/ZnO nanowire heterojunction structure for phototransistors. The lattice match of the CsPbBr3 QDs and ZnO nanowire reduces the generation of trap centers and avoids carrier absorption by the composite center, which greatly improves the carrier mobility and high detectivity (8.13 × 1014 Jones). It is worth noting that by using high-efficiency PVK quantum dots as the intrinsic sensing core, the device has a high responsivity (6381 A/W) and responsivity frequency (300 Hz). Thus, a UV detection system for pharmaceutical solute detection is demonstrated, and the type of solute in the chemical solution is estimated by the waveform and the size of the output 2f signals.

Synergistic Tuning of CoO/CoP Heterojunction Nanowire Arrays as Efficient Bifunctional Catalysts for Alkaline Overall Water Splitting.

Bifunctional electrocatalysts with superior activity and durability are of great importance for electrocatalytic water splitting. Herein, hierarchical structured CoO/CoP heterojunctions are successfully designed as highly efficient and freestanding bifunctional electrocatalysts toward overall water splitting. The unique microstructure combining two-dimensional nanosheets with one-dimensional nanowires enables numerous exposed active sites, shortened ion-diffusion pathways, and enhanced conductivity, significantly improving performance. Such freestanding electrodes achieve high current density over 400mA cm-2 at low overpotentials and have exceptional electrocatalytic activity as well as long-term durability for both hydrogen and oxygen evolution reactions under alkaline conditions. Remarkably, a high current density of 20mA cm-2 is generated at a low cell voltage of 1.56V in an alkaline water electrolyzer, originating from synergistic interactions between CoO and CoP exposing active sites and facilitating charge transfer and enhancing kinetics. This work provides new insight into designing low-cost but high-performance bifunctional electrocatalysts for practical water splitting.

2D Ruddlesden-Popper Sn-Based Perovskite Weak Light Detector for Image Transmission and Reflection Imaging.

2D Ruddlesden-Popper Sn-based perovskite has excellent optoelectronic properties and weak halide ion migration characteristics, making it an ideal candidate for weak light detection, which has great potential in light communication, and medical applications. Although Sn-based perovskite photodetectors are developed, weak light detection is not demonstrated yet. Herein, a high-performance self-powered photodetector with the capability to detect ultra-weak light signals is designed based on vertical PEA2 SnI4 /Si nanowires heterojunction. Due to the low dark current and high light absorption efficiency, the devices present a remarkable responsivity of 42.4mA W-1 , a high detectivity of 8 × 1011 Jones, and an ultralow noise current of 2.47 × 10-13 A Hz-1/2 . Especially, the device exhibits a high on-off current ratio of 18.6 at light signals as low as 4.60 nW cm-2 , revealing the capacity to detect ultra-weak light. The device is applied as a signal receiver and realized image transmission in light communication system. Moreover, high-resolution reflection imaging and multispectral imaging are obtained using the device as the sensor in the imaging system. These results reveal that 2D PEA2 SnI4 -based self-powered photodetectors with low-noise current possess enormous potential in future weak light detection.

Selective-area growth of β-Ga2O3 nanowire films on nano-patterned Si(111) substrate by metal-organic chemical vapor deposition

β-Ga2O3 nanowire films were prepared on Si(111) substrate by selective area growth (SAG) using metal-organic chemical vapor deposition (MOCVD). A large-area periodic nano-hole array TiN mask was fabricated. The effects of MOCVD process parameters on SAG were discussed by calculating Ga supersaturation. It was found that the SAG is closely related to the selective area nucleation and inhibition of lateral growth. Transmission electron microscopy confirmed that β-Ga2O3 nanowires have a preferential orientation of the (002) crystal plane. The sample after in-situ O2 annealing showed an x-ray diffraction intensity increase of (400), (002), and (-111) crystal planes. On this basis, P–Si/β‐Ga2O3 nanowire heterojunctions were fabricated and presented high resistance of the films. At a bias voltage of 20 V, the current decreased from 6.14 × 10−6 to 2.25 × 10−6 A. The MOCVD-based SAG paves a novel way to fabricate β-Ga2O3 nanowire films with high surface-to-volume ratio and homogeneity.

Enhanced Photocurrent Performance of Flexible Micro‐Photodetector Based on PN Nanowires Heterojunction using All‐Laser Direct Patterning

AbstractUV micro‐photodetectors (mPDs) have received significant attention owing to the increasing demand for application in wearable healthcare devices. However, mPDs often suffer from tiny signals owing to their small size. Although this problem can be overcome by using low‐dimensional nanomaterials with high surface‐to‐volume ratios, such as nanowires (NWs), selective synthesis of functional NWs on the desired position of the specific substrate is challenging. This study introduces, for the first time, the laser‐induced hydrothermal growth (LIHG) process, in which a strongly focused laser beam generates a localized high‐temperature field, enabling the localized growth of CuO NWs on the desired position of the specific substrate. Also, an all‐laser direct patterning process for the fabrication of a flexible mPD based on a p‐CuO NW/n‐ZnO NW heterojunction is demonstrated. The PN NWs heterojunction exhibits remarkable photocurrent enhancement compared to a homojunction with a single semiconductor material. Furthermore, the all‐laser direct patterning process of the flexible PN NWs heterojunction can be applied for the fabrication of other flexible optoelectronic applications.

3D hierarchically branched Cu2S/ZnO heterojunction nanowire arrays for enhanced solar water splitting

3D hierarchically branched Cu2S/ZnO heterojunction nanowire arrays for enhanced solar water splitting

Self-powered (In,Ga)N-nanowire-based photodetector with fast response speed for under-seawater detection.

Due to the requirements of oceanography exploration and detection, self-powered photodetectors (PDs) with low-power consumption are essential for the next-generation optoelectronic applications. In this work, we successfully demonstrate a self-powered photoelectrochemical (PEC) PD in seawater based on the (In,Ga)N/GaN core-shell heterojunction nanowires. Compared to those of the PD in pure water, it is found that the upward and downward overshooting features of current can be the key reason contributing to the much faster response speed of the PD in seawater. Thanks to the enhanced response speed, the rise time of PD can be reduced more than 80%, and the fall time remains only 30% by applying in seawater instead of pure water. The key factors of generating these overshooting features should be the instantaneous temperature gradient, carrier accumulation and elimination on the semiconductor/electrolyte interfaces at the moments of light on and off. By the analysis of experimental results, the Na+ and Cl- ions are proposed to be the main factors affecting the PD behavior in seawater, which can enhance the conductivity and accelerate the oxidation-reduction reaction significantly. This work paves an effective way to develop the new self-powered PDs for the wide applications in under-seawater detection and communication.

Manganese cobalt sulfide/molybdenum disulfide nanowire heterojunction as an excellent bifunctional catalyst for electrochemical water splitting

Heterointerface engineering enhances catalytic active centers and charge transfer capabilities to increase oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) kinetics. In this study, a novel heterostructure of manganese cobalt sulfide-molybdenum disulfide on nickel foam (MnCo2S4-MoS2/NF) was synthesized via a two-step hydrothermal process. The nanowire-shaped MnCo2S4-MoS2 on NF displayed accelerated charge transfer ability and multiple integrated active sites. When tested in one molar (1 M) potassium hydroxide (KOH) electrolyte, it furnished low overpotentials of 105 and 171 mV for the HER and 220 and 300 mV for the OER at the current densities of 20 and 50 mA cm−2, respectively. An electrolyzer based on MnCo2S4-MoS2/NF required low operating potentials of 1.41 and 1.49 V to yield the current densities of 10 and 20 mA cm−2, respectively, surpassing commercial and previously reported catalysts. Density functional theory (DFT) analysis revealed that the MnCo2S4-MoS2 heterostructure possesses the optimal adsorption free energies for the reactants, an extended electroactive surface area, good charge transfer ability, and reasonable density of electronic states close to the Fermi level, all of which contribute to the high activity of catalyst. Thus, heterointerface engineering is a promising strategy for creating efficient catalysts for overall water splitting.

Self‐Powered, Flexible Ultraviolet Photodetector Based on ZnO/Te All Nanowires Heterojunction Structure

Self‐powered and flexible photodetectors exhibit great potential in the application of optical communication, deep space exploration, and other related fields. Herein, a self‐powered ultraviolet photodetector based on ZnO nanowires/Te nanowires heterojunction has been prepared by two‐step vacuum filtration method, which also has superior flexibility and fast response speed. The obtained photodetector has a high photocurrent (about 1 μA) at 5 V bias under 365 nm UV light illumination and a fast response speed (3.47/0.13 s). Even if the bending angle reaches 90°, its photocurrent still maintains about 0.5 μA under 5 V bias, showing superior flexibility. Under 0 V bias, the photocurrent of the photodetector is 0.18 nA and the response time is 65/140 ms, displaying its good self‐powered characteristic and fast response speed. These superior properties are caused by the flexibility of ZnO nanowire film and Te nanowire film, and the heterojunction is formed between ZnO and Te. The obtained results provide a solid foundation for the further development of flexible optoelectronic devices based on ZnO nanostructures.

Tuning interfacial thermal conductance of GaN/AlN heterostructure nanowires by constructing core/shell structure

The ability to tune the interfacial thermal conductance of GaN/AlN heterojunction nanowires (NWs) with a core/shell structure is shown using molecular dynamics and non-equilibrium Green’s functions method. In particular, an increase in the shell thickness leads to a significant improvement of interfacial thermal conductance of GaN/AlN core/shell NWs. At room temperature (300 K), the interfacial thermal conductance of NWs with specific core/shell ratio can reach 0.608 nW K−1, which is about twice that of GaN/AlN heterojunction NWs due to the weak phonon scattering and phonon localization. Moreover, changing the core/shell type enables one to vary interfacial thermal conductance relative to that of GaN/AlN heterojunction NWs. The results of the study provide an important guidance for solving the thermal management problems of GaN-based devices.

3D Printing of Arbitrary Perovskite Nanowire Heterostructures

AbstractDeterministic integration of arbitrary semiconductor heterostructures opens a new class of modern electronics and optoelectronics. However, the realization of such heterostructures continues to suffer from impracticality, requiring energy‐ and labor‐intensive, time‐consuming fabrication processes. Here a 3D printing approach to fabricate freestanding metal halide perovskite nanowire heterostructures with a high degree of control over shape and composition is demonstrated. These features arise from freeform guiding of evaporation‐driven perovskite crystallization by a femtoliter precursor meniscus formed on a printing nozzle. By using a double‐barreled nanopipette as a printing nozzle, “all‐at‐once” heterostructure fabrication is achieved within seconds. The 3D‐printed perovskite nanowire heterojunctions with multiple emission colors provide exciting optical functionalities such as programmable color mixing and encryption at the single nanopixel level. This “lithography‐free” additive approach opens up the possibility to freely design and realize heterostructure‐based devices without the constraints of traditional manufacturing processes.

Metal assisted chemical etching of silicon and solution synthesis of Cu-=SUB=-2-=/SUB=-O/Si radial nanowire array heterojunctions

Cu2O/Si radial nanowire (NWs) array heterojunctions were prepared by depositing Cu2O nanoparticles via chemical bath deposition on n-Si nanowire arrays that were fabricated by metal-assisted electroless etching. After 20 cycles of deposition, large numbers of Cu2O nanoparticles with form shells that wrap the upper segment of each Si nanowire. This method of etching offers exceptional simplicity, flexibility, environmental friendliness, and scalability for the fabrication of three-dimensional silicon nanostructures with considerable depths, because of replacement of harsh oxidants such as H2O2 and AgNO3. Keywords: Cu2O/Si NWs heterojunctions, Cu2O nanoparticles, metal-assisted electroless etching.