ZnO Nanowire Arrays Research Articles

(Invited) Solution-Processed Reorganization of Semiconductor Nanocrystals in Thin Films

Colloidal nanocrystals (NCs) have been attracted because of their strongly size-dependent luminous characteristics and solution processability. As prepared colloidal NCs covered with some bulky and long-chain organic ligands such as oleic acid, oleylamine (OAm), trioctylphosphine oxide, and so on are mostly dispersed in some solvents such as hexane, toluene, and so on. After preparation of thin films from the dispersed solutions of NCs, reduced inter NC distance (viz. NCs coming closer) with highly ordered alignment will lead to enhanced electronic coupling between adjacent NCs resulting in better wave function overlap and charge transport of the conducting solid materials.In this context, remarkable improvement of the alignment of the particles through solution-processed reorganization of AgInS2 quantum dots (QDs) covered with OAm by cast method was confirmed by bright-field TEM observation [1,2]. The interplanar spacing of the QDs was 0.33 nm, which corresponds to (112) crystal planes of the tetragonal phase of AgInS2.On the other hand, it was found that PbS colloidal QDs can be packed densely and infiltrated efficiently into the interrod space of vertically aligned ZnO nanowire arrays through convective deposition method, which is one of the meniscus coating techniques [3] as compared with spin-coating process, which brings many cracks and voids in the obtained thin films. As a result, a record power conversion efficiency of 9.92% has been demonstrated for ordered bulk heterojunction structured solar cells that are compatible with low-temperature and scalable manufacturing processes.While comparisons of perovskite CsPbBr3 NCs grafted on the surface of silica nanohelices as templates in dispersed state in toluene and dried state on quartz glass substrate revealed that the interparticle distance becomes shorter after the dryness by cast method from the dispersed state and the closely and helically packed NCs [4]. Tuning the conditions of solution-processed reorganization of CsPbBr3 NCs is crucial for reducing the inter NC distance with highly ordered alignment in the cast films with large circular dichroism and circularly polarized luminescence signals.On the basis of the above findings, reorganization of NCs with highly controlled crystal orientation and inter NC distance in thin films has deep influence on specific spectral characteristics and photovoltaic performances.[1] Kaewprajak, A.; Kumnorkaew, P.; Sagawa, T. Silver-indium-sulfide quantum dots in titanium dioxide as electron transport layer for highly efficient and stable perovskite solar cells. J. Mater. Sci.: Mater. Electron., 2019, 30, 4041-4055.[2] Kaewprajak, A.; Kumnorkaew, P.; Sagawa, T. Improved photovoltaic performance and device stability of planar heterojunction perovskite solar cells using TiO2 and TiO2 mixed with AgInS2 quantum dots as dual electron transport layers. Org. Electron., 2019, 69, 26-33.[3] Shi, G.; Kaewprajak, A.; Ling, X.; Hayakawa, A.; Zhou, S.; Song, B.; Kang, Y.-w.; Hayashi, T.; Altun, M. E.; Nakaya, M.; Liu, Z.; Wang, H.; Sagawa, T.; Ma, W. Finely interpenetrating bulk heterojunction structure for lead sulfide colloidal quantum dot solar cells by convective deposition. ACS Energy Lett., 2019, 4, 960-967.[4] Liu, P.; Chen, W.; Okazaki, Y.; Battie, Y.; Brocard, L.; Decossas, M.; Pouget, E.; M.-Buschbaum, P.; Kauffmann, B.; Pathan, S.; Sagawa, T.; Oda, R. Optically active perovskite CsPbBr3 nanocrystals helically arranged on inorganic silica nanohelices. Nano Lett., 2020, 20, 8453-8460.

A Portable and Flexible Self-Powered Multifunctional Sensor for Real-Time Monitoring in Swimming.

A portable and flexible self-powered biosensor based on ZnO nanowire arrays (ZnO NWs) and flexible PET substrate has been designed and fabricated for real-time monitoring in swimming. Based on the piezoelectric effect of polar ZnO NWs, the fabricated biosensor can work in both air and water without any external power supply. In addition, the biosensor can be easily attached to the surface of the skin to precisely monitor the motion state such as joint moving angle and frequency during swimming. The constant output piezoelectric signal in different relative humidity levels enables actual application in different sports, including swimming. Therefore, the biosensor can be utilized to monitor swimming strokes by attaching it on the surface of the skin. Finally, a wireless transmitting application is demonstrated by implanting the biosensor in vivo to detect angiogenesis. This portable and flexible self-powered biosensor system exhibits broad application prospects in sport monitoring, human–computer interaction and wireless sport big data.

Green synthesis of CuO nanoparticles-loaded ZnO nanowires arrays with enhanced photocatalytic activity

Promoting the separation of photogenerated carriers and expanding the range of light absorption are critical factors for improving photocatalytic performance. Here, CuO nanoparticles-loaded ZnO nanowires arrays (CuO@ZnO NWAs)were synthesized via a three-step chemical approach on ITO glass. The morphology results demonstrate that CuO nanoparticles are dispersedly attached to the surface of the ZnO NWAs. Comparing with ZnO NWAs, the absorption peak of the CuO@ZnO NWAs extends to the visible region. In addition, CuO@ZnO NWAs exhibit the higher photocurrent response and photodegradation efficiency of methylene blue (MB) under visible light irradiation relative to pure ZnO NWAs, which can be caused by the enhanced efficiency and broadened range light absorption and the efficient generation and separation of photo-generated electrons and holes based on the CuO@ZnO (p-n) heterogeneous structure. The findings confirm that the hierarchical CuO nanoparticles-loaded ZnO NWAs hold a great potential candidate for wastewater treatment applications.

Controlled Synthesis of Oriented Zinc Oxide Nanowires Arrays by Electrochemical Deposition on Sputtered Layer

In this study, dense zinc oxide nanowires were electrochemically synthesized on sputtered zinc oxide buffer layers substrates using a solution of zinc chloride as a precursor. The control of nanowires density was studied. X-Ray Diffraction patterns revealed the formation of pure wurtzite zinc oxide structure. The mechanism of the formation of zinc oxide nanorods from the nucleation to the growth stage is proposed based on the study of the deposition parameters. Optical analysis reveals that these films can be involved in solar cells as window layers. Moreover, controlling structural properties of the buffer is an excellent way to control the formation of nanorods during the nucleation step. In fact, Scanning Electronic Microscopy images and reflectometry analysis showed that the buffer layer consists of dense nanoparticles, with a density that increases by increasing the radiofrequency frequency power, This can be explained by the densification of the nanorods deposited thereon.

A High-sensitivity Knock Sensor Based on ZnO Nanowires Array as Piezoelectric Nanogenerator

We develop a new ZnO nanowire (NWs) array knock sensor based on a piezoelectric nanogenerator. The ZnO NWs arrays generated by the hydrothermal method are deadlocked so that the tops of the two arr...

Dimensional Roadmap for Maximizing the Piezoelectrical Response of ZnO Nanowire-Based Transducers: Impact of Growth Method.

ZnO nanowires are excellent candidates for energy harvesters, mechanical sensors, piezotronic and piezophototronic devices. The key parameters governing the general performance of the integrated devices include the dimensions of the ZnO nanowires used, their doping level, and surface trap density. However, although the method used to grow these nanowires has a strong impact on these parameters, its influence on the performance of the devices has been neither elucidated nor optimized yet. In this paper, we implement numerical simulations based on the finite element method combining the mechanical, piezoelectric, and semiconducting characteristic of the devices to reveal the influence of the growth method of ZnO nanowires. The electrical response of vertically integrated piezoelectric nanogenerators (VING) based on ZnO nanowire arrays operating in compression mode is investigated in detail. The properties of ZnO nanowires grown by the most widely used methods are taken into account on the basis of a thorough and comprehensive analysis of the experimental data found in the literature. Our results show that the performance of VING devices should be drastically affected by growth method. Important optimization guidelines are found. In particular, the optimal nanowire radius that would lead to best device performance is deduced for each growth method.

ZnO nanowire arrays decorated with titanium nitride nanoparticles as surface-enhanced Raman scattering substrates

In this work, the potential of ZnO nanowire arrays decorated with titanium nitride (TiN) nanoparticles as surface-enhanced Raman scattering (SERS) substrates is demonstrated. ZnO nanowires were grown by hydrothermal synthesis while commercially obtained TiN powders were subjected to several hours of mechanical grinding to achieve 30–100 nm diameter nanoparticles. The nanoparticles were then dispersed in acetone and drop cast on the ZnO nanowire arrays for decoration. Scanning electron microscopy confirmed the presence of TiN nanoparticles on the ZnO nanowires. TiN nanoparticles exhibited multiple absorption features at 430, 520 and 600 nm. SERS experiments using Nile blue and methylene blue as the analyte molecules exhibited enhancement in the Raman signals. It is shown that the origin of the SERS effect is chemical in nature, with contribution from different interactions between the analyte molecule and the TiN nanoparticles. The current work, thus, represents a simple, cost-effective and facile method for the fabrication of TiN-based SERS substrates.

Lubricant Depletion‐Resistant Slippery Liquid‐Infused Porous Surfaces via Capillary Rise Lubrication of Nanowire Array

AbstractDespite their promise in diverse applications, lubricant depletion over time presents an important challenge for slippery lubricant‐infused porous surfaces (SLIPS). The main source of lubricant depletion is the growth of a wetting ridge around a droplet of foreign liquid that removes the infused lubricant from the porous surface when the droplet slides off. This work describes the fabrication of liquid‐infused ZnO nanowire array by capillary rise lubrication and the effect of array morphology on suppressing wetting ridge formation. The orientation of nanowires strongly affects lubricant infiltration and the stability of SLIPS properties. The infiltrated lubricant in random ZnO nanowire arrays does not form a visible wetting ridge around a water droplet because of the strong capillarity that retains the lubricant confined in the nanoporous structure. The lack of wetting ridge gives rise to a stable SLIPS that exhibits self‐recovery of the infused lubricant. Such a structure retains lubricant under a strong centrifugal force, showing high stability. This study provides a straightforward, robust, and potentially scalable approach for making stable SLIPS that suppresses lubricant depletion by taking advantage of the unique morphology of the random nanowire arrays and capillary rise lubrication.

Significant enhancement of ZnO nanowires/ZnO/Mg0.2Zn0.8O ultraviolet photodetectors via light trapping effect

In order to optimize the performance of the ultraviolet photodetectors, a dual-band detector with light trapping effect is fabricated by using a hydrothermal method. By adding Mg into ZnO material can form Mg0.2Zn0.8O alloy which results the band gap increases and the detection region extends to the shorter wavelength. With the introduction of nanowires, the responsivity increases which is attributed to the light trapping effect of nanowires array structure. The ZnO nanowires photodetector significantly accelerate the performance where is observed along with higher responsivity, larger detectivity, and enhanced EQE of 15.1 A/W, 3.1 × 1012 jones and 5.0 × 103 % respectively. In conjunction with ZnO nanowires array, which shows strong light trapping effect, the ability of photodetectors is greatly enhanced. Controlled nanowires of ultraviolet photodetectors with light trapping effect can open the way for integrated ZnO technology for future optoelectronic applications.

A self-powered UV photodetector based on the hydrovoltaic and photoelectric coupling properties of ZnO nanowire arrays

We report a novel self-powered ultraviolet (UV) photodetector as sensor node in the internet of things (IoT). The working mechanism of the device relies on the coupling of hydrovoltaic and photoelectric effect of ZnO nanowire arrays. The photodetector can long-term work without any external batteries or power supply units, and the natural water (such as rain, river water and etc) can be used as the fuel to powering the system. Water flow and evaporation on the aligned ZnO nanowire arrays can generate power, and the outputting current is dependent on the UV illumination as photodetecting signal. The UV photodetector has rapid response/recovery processes, and the outputting current increases from 0.112 to 1.899 μA under UV illumination (365 nm, 20 mW cm−2). The UV photodetector as sensor nodes can be integrated with wireless transmitters, constructing self-powered smog monitoring systems in IoT. The self-powered photodetecting signal can reflect the smog degree, and the wireless transmitter can send the smog information to the mobile equipment or cloud. The present results can stimulate a new research trend on the next generation of photodetectors and promote the development of environment monitoring technique in IoT.

High Current Field Emission from Large-Area Indium Doped ZnO Nanowire Field Emitter Arrays for Flat-Panel X-ray Source Application.

Large-area zinc oxide (ZnO) nanowire arrays have important applications in flat-panel X-ray sources and detectors. Doping is an effective way to enhance the emission current by changing the nanowire conductivity and the lattice structure. In this paper, large-area indium-doped ZnO nanowire arrays were prepared on indium-tin-oxide-coated glass substrates by the thermal oxidation method. Doping with indium concentrations up to 1 at% was achieved by directly oxidizing the In-Zn alloy thin film. The growth process was subsequently explained using a self-catalytic vapor-liquid-solid growth mechanism. The field emission measurements show that a high emission current of ~20 mA could be obtained from large-area In-doped sample with a 4.8 × 4.8 cm2 area. This high emission current was attributed to the high crystallinity and conductivity change induced by the indium dopants. Furthermore, the application of these In-doped ZnO nanowire arrays in a flat-panel X-ray source was realized and distinct X-ray imaging was demonstrated.

Diagonal 4-in ZnO Nanowire Cold Cathode Flat-Panel X-Ray Source: Preparation and Projection Imaging Properties

Uniform large-area flat-panel X-ray sources have potential applications in projection imaging. Achieving such a source has remained a challenge. A diagonal 4-in cold cathode flat-panel X-ray source device has been fabricated using ZnO nanowire field emitter arrays. A large-area uniform X-ray emission was produced, and projection imaging with a resolution of more than 5.0 lp/mm was realized. Its projection imaging resolution and its dependence on geometric imaging parameter settings were studied along with the imaging performance of the device. Simulations using the fast ray-tracing algorithm were performed, yielding results consistent with those from experiments. Optimal parameter settings for high-resolution projection imaging using the flat-panel X-ray source are presented. This study has significance in the application of this cold cathode flat-panel X-ray source in X-ray imaging.

Piezoelectric potential enhanced photocatalytic performance based on ZnO with different nanostructures

In this paper, two novel nanostructures with ZnO nanowire and nanosheet arrays vertically growing on the FTO and Al foil have been synthesized by a hydrothermal method, which exhibit both the piezoelectric and photocatalytic properties. These nanostructures have typical wurtzite structures based on the XRD results. From the SEM results, the average diameter and length of nanowire have been measured to be about 150 nm and 4.5 μm, the thickness of ZnO nanosheet is about 50 nm and the width is about 5 μm. In the photocatalytic test, the photodegradation of RhB under 365 nm illumination for nanowire and nanosheet is about 25% and 37% in 80 min reaction. With stirring, the degradation rate is increased to 61% and 85%. Finally, the photocurrent test and finite element method were used to analyze the piezo-photodegradation mechanism.

Light trapping in ZnO nanowires to control ultraviolet photodetection responsivity

The ZnO planar thin-layer usually suffers from low-light absorbing ability because of its short transmission path of incident light. Herein, we demonstrate a series of high-performance ZnO nanowires array ultraviolet photodetectors via hydrothermal synthesis. In conjunction with ZnO nanowires array, which shows strong light trapping effect, the light absorbing ability of ZnO photodetectors is greatly enhanced. Using optical transmission and photocurrent measurements on ZnO photodetectors, it is shown that the ordered arrays of ZnO nanowires increase the light responsivity. Furthermore, in the case of nanowires length growth, it is confirmed that the photon path length and path length enhancement factor also increases, thus reducing the loss of light, and reflecting a large amount of light on ZnO film, which is then collected. The light trapping effect of ZnO nanowires ultraviolet photodetectors exhibits higher photo-to-dark current ratio above 104, where photoresponsivity reaches 14.50 A W−1 and excellent detectivity (~1012 Jones). The light trapping effect of nanomaterials is applied to the research of photoelectric detectors, which provides a new perspective for photoelectric materials.

Digitally aligned ZnO nanowire array based synaptic transistors with intrinsically controlled plasticity for short-term computation and long-term memory.

Digitally aligned long continuous ZnO NWs with distinct widths and microstructures are prepared and used for tuning the plasticity of synaptic transistors (STs) for the first time. Intrinsically controlled synaptic plasticity, i.e. short-term plasticity (STP) and long-term plasticity (LTP), was achieved using the same source material and post-fabrication condition for the first time, which is essential for simple and low-cost fabrication. Moreover, these versatile properties of ZnO STs enable the integration of STP and LTP as realized by multiplexed neurotransmission of different neurotransmitters: dopamine and acetylcholine, which promote learning and memory in organisms, so the device may utilize these processes in neuroelectronic devices. Devices with well-controlled synaptic plasticity can simulate the "learning-forgetting-erase" and "instant display" processes. ZnO NWs may enable the development of neuromorphic computers that can use the same material to achieve both short-term computation and long-term memory.

Effect of Sputtered Pressure on Au Nanoparticles Formation Decorated ZnO Nanowire Arrays

Abstract The hybrids nanostructure of gold nanoparticles (Au NPs) decorated on zinc oxide nanowires (ZnO NWs) was developed through sequential hydrothermal process and magnetron sputtering. The ZnO NWs grown on silicon wafer substrate via hydrothermal method at 90 °C using zinc acetate and hexamethylenetramine. Subsequently, the Au NPS were sputtering on to the ZnO NWs surfaces at 5-20 mTorr sputtering pressure. The morphology of the Au NPs grown on ZnO NW arrays was investigated by scanning electron microscopy and transmission electron microscopy. The results indicated that size and distribution of the Au NPs on ZnO NWs strongly depended on the sputtering pressure due to the mean free part and rate of gas phase collisions. The current work will be useful to develop high order hybrid nanostructure for nanosensor devices

Experimental and Theoretical Comparable Study of Pure and Zinc Porphyrin Surface Modified ZnO Nanorod Arrays for Hybrid Solar Cell Applications

Experimental and theoretical study Porphyrin-grafted ZnO nanowire arrays were investigated for organic/inorganic hybrid solar cell applications. Two types of porphyrin – Tetra (4-carboxyphenyle) TCPP and meso-Tetraphenylporphine (Zinc-TPP)were used to modify the nanowire surfaces. The vertically aligned nanowires with porphyrin modifications were embedded in graphene-enriched poly (3-hexylthiophene) [G-P3HT] for p-n junction nanowire solar cells. Surface grafting of ZnO nanowires was found to improve the solar cell efficiency. There are different effect for the two types of porphyrin as results of Zn existing. Annealing effects on the solar cell performance were investigated by heating the devices up to 225 °C in air. It was found that the cell performance was significantly degraded after annealing. The degradation was attributed to the polymer structural change at high temperature as evidenced by electrochemical impedance spectroscopy measurements.

Field enhancement in microfluidic semiconductor nanowire array.

Nano-material integrated microfluidic platforms are increasingly being considered to accelerate biological sample preparation and molecular diagnostics. A major challenge in this context is the generation of high electric fields for electroporation of cell membranes. In this paper, we have studied a novel mechanism of generating a high electric field in the microfluidic channels by using an array of semiconductor nanowires. When an electrostatic field is applied across a semiconductor nanowire array, the electric field is localized near the nanowires and the field strength is higher than what was reported previously with various other micro-geometries. Nanowires made of ZnO, Si, and Si-SiO2 and their orientation and array spacing are considered design parameters. It is observed that for a given ratio of the spacing between nanowires to the diameter, the electric field enhancement near the edges of ZnO nanowires is nearly 30 times higher compared to Si or Si-SiO2 nanowire arrays. This enhancement is a combined effect of the unique geometry with a pointed tip with a hexagonal cross section, the piezoelectric and the spontaneous polarization in the ZnO nanowires, and the electro-kinetics of the interface fluid. Considering the field localization phenomena, the trajectories of E. coli cells in the channel are analyzed. For a given inter-nanowire spacing and an applied electric field, the channels with ZnO nanowire arrays have a greater probability of cell lysis in comparison to Si-based nanowire arrays. Detailed correlations between the cell lysis probability with the inter-nanowire spacing and the applied electric field are reported.

Tailoring zinc oxide nanowire architectures collectively by catalytic vapor-liquid-solid growth, catalyst-free vapor-solid growth, and low-temperature hydrothermal growth

We present a comprehensive study of the fabrication of zinc oxide (ZnO) nanowires (NWs) with tailored structural morphologies and functional features by utilizing three major growth methods based on vapor-liquid-solid (VLS), vapor-solid (VS), and hydrothermal growth mechanisms. The vertically aligned ZnO NW (ZNW) array can be constructed with tailored length, diameter, and density by controlled catalytic epitaxial VLS growth; the catalyst-free VS growth can create a hierarchical ZNW assembly onto complementary topological frameworks, such as transparent conducting oxides and carbon nanotubes; and the hydrothermal growth practically enables low-temperature growth of conformal ZNWs on large-area and flexible substrates. The growth mechanism and tailoring of the ZNW architectures for each growth strategy were investigated in detail, combined with rational analyses and parametric experiments. This study provides a critical route to the purposeful tailoring of ZNW architectures toward targeted ZnO-driven applications that require specific ZNW morphologies, assembly configurations, and substrate materials for many diverse fields including energy conversion and harvesting, electronics, photonics, and smart and wearable sensors.

Experimental evaluation of ZnO nanowire array based dynamic pressure sensor

This paper presents the synthesis of ZnO nanowire array on metallic alloy substrate, its packaging and experimental evaluation for dynamic pressure sensing applications. Vertically aligned dense nanowire array was synthesized using hydrothermal method. Crystal structure, morphology and chemical composition analysis were carried out using X-ray diffraction, field emission scanning electron microscopy and energy dispersive spectroscopy respectively. ZnO nanowires were grown to an average height of 2.2 µm with an average diameter of 200 nm. The as-synthesised nanowire array was packaged as a pressure sensor and was evaluated for its sensing properties. The sensor responded to shock pressure input with a sensitivity 1.65 ± 0.15 mV/bar, rise time 1.38 ms and discharge time 1.79 ms. ZnO nanowire array demonstrated highly promising features which are desirable for a dynamic pressure sensor.