Zn Nanowires Research Articles

Photobreeding Heterojunction on Semiconductor Materials for Enhanced Photocatalysis

AbstractConstruction of heterojunctions to photocatalysts is one of the most promising approaches to improve charge separation efficiency; however, the established constructing processes usually require high‐temperature conditions and/or the adding of highly concentrated or expensive exotic species, and the improvement of effective contact and charge exchange between heterojunction components remains a problem. This work proposes an unprecedented “photobreeding” method and realizes the direct growth of Zn nanowires and Mott–Schottky heterojunctions from ZnS or viologen‐coated ZnS microspheres through a photochemical reaction at room temperature without external species, while demonstrating the hypothesis proposed 140 years ago on the formation of Zn in the photochromic process of ZnS. After photobreeding of the heterojunctions, the hydrogen production efficiency of the photocatalysts increases by 2 orders of magnitude. This inexpensive, facile and efficient synthetic method will find applications in H2 production, organic synthesis, CO2 reduction, nitrogen fixation, and so on.

A Self-Healing Flexible Quasi-Solid Zinc-Ion Battery Using All-In-One Electrodes.

Self‐healing and flexibility are significant for many emerging applications of secondary batteries, which have attracted broad attention. Herein, a self‐healing flexible quasi‐solid Zn‐ion battery composing of flexible all‐in‐one cathode (VS2 nanosheets growing on carbon cloth) and anode (electrochemically deposited Zn nanowires), and a self‐healing hydrogel electrolyte, is presented. The free‐standing all‐in‐one electrodes enable a high capacity and robust structure during flexible transformation of the battery, and the hydrogel electrolyte possesses a good self‐healing performance. The presented battery remains as a high retention potential even after healing from being cut into six pieces. When bending at 60°, 90°, and 180°, the battery capacities remain 124, 125, and 114 mAh g−1, respectively, cycling at a current density of 50 mA g−1. Moreover, after cutting and healing twice, the battery still delivers a stable capacity, indicating a potential use of self‐healing and wearable electronics.

Direct synthesis of ACo2O4 (A = Ni, Cu, Fe, Zn) nanowires on carbon cloth as an oxygen electrode catalyst for rechargeable lithium-oxygen batteries

Developing a low-cost, stable and efficient oxygen electrode catalyst for use in lithium-oxygen batteries with a long cycling stability and a high discharge/charge capacity is very important for solving the energy crisis and reducing environmental pollution. In this study, ACo2O4 (A = Ni, Cu, Fe, Zn) nanowires grown on carbon cloth (CC) were readily synthesized via a hydrothermal method with a subsequent heat treatment. NiCo2O4 nanowires grew and crossed each other to randomly form many hedges with a three-dimensional network structure. The NiCo2O4/CC electrode has the higher specific surface area and more mesopores than the other ACo2O4/CC (A = Cu, Fe, Zn) electrodes. The NiCo2O4/CC electrode can cycle over 200 times under a limited capacity of 0.3 mA h cm−2 (500 mA h g−1) at 0.2 mA cm−2 (340 mA g−1) and show a discharge capacity of up to 6.2 mA h cm−2 (10541 mA h g−1) at 0.12 mA cm−2 and 4.75 mA h cm−2 (8076 mA h g−1) at 0.24 mA cm−2, reaching 2861.8 and 2674.5 Wh kg−1 at 0.12 and 0.24 mA cm−2, respectively.

Preparation of Ni nanotube-modified electrodes via galvanic displacement on sacrificial Zn templates: Solvent effects and attempts for non-enzymatic electrochemical detection of urea

In this study, Ni nanotube-modified stainless-steel electrode (SSE\\Nianodized) was prepared by galvanic displacement on tangled Zn nanowire-composed sacrificial template (SSE\\Zn) followed by anodization in 1 M NaOH. The tangled Zn nanowires were electrodeposited from an amide-type room temperature ionic liquid (RTIL) 1-butyl-1-methypyrrolidinium bis((trifluoromethyl)sulfonyl)amide ([BMP][TFSA]) containing ZnCl2, and then galvanic displacement was conducted in the same RTIL with [NiCl4]2−. The process was unable to be reproduced by using water or choline chloride-ethylene glycol deep eutectic solvent (ChCl-EG DES) as the reaction media, indicating the unique properties of RTILs. The cations of RTILs are critical to successfully retaining the skeleton of Zn-nanowire-template. SSE\\Nianodized showed high activity towards the oxidation of urea and possessed a detection limit of 3 μM, a sensitivity of 902.8 μA·mM−1·cm−2, and a dynamic range of 1–20000 μM. Most importantly, the electrode could be regenerated by anodization in 1 M NaOH to remove adsorbed urea without significantly altering the surface morphology and performance of the electrode. A low background current was achieved after the regeneration process, which is important for repeatedly using the same electrode in urea determination.

Evaluation of carrier density and mobility in Mn ion-implanted GaAs:Zn nanowires by Raman spectroscopy

The fabrication of complex nanoscale electronics with reduced dimensions poses challenges on novel techniques to accurately determine fundamental electronic parameters. In this article, we present a universal contactless method based on Raman scattering for measuring the mobility and hole concentration independently in GaAs:Zn and Mn ion-implanted GaAs:Zn nanowires, potentially of great interest for spintronics applications. Clear coupled longitudinal optical phonon-plasmon modes were recorded and fitted with a dielectric function, based on the Drude model, which includes contributions from both plasmons and phonons. From the fitting, we extract accurate values of the plasma frequency and plasma damping constant from which we directly calculate the hole density and mobility, respectively. The extracted mobilities were also used as input data for analysis of complementary four-probe transport measurements, where the corresponding hole concentrations could be calculated and found to be in good agreement with those extracted directly from the Raman data. We also investigated the influence of annealing of the GaAs:Zn nanowires on the hole concentration and mobility and found strong indications of thermally activated defects related to a formed crystalline As/oxide shell around the nanowires. The method proposed here is extremely powerful for the characterization of nanoelectronics in general, and nanospintronics in particular for which Hall measurements are difficult to pursue due to problems related to contact formation, as well as to inherent magnetic properties of the devices.

Study on the Growth and Mechanism of Zinc Nanostructures on an Ionic Liquid Substrate

Compared with solid substrates, liquid substrates exhibit isotropic behavior due to the lack of a lattice and because the interaction between liquid substrates and metal atoms is weaker. Therefore, an in-depth understanding about the growth mechanism of metal atoms on liquid substrates is both fundamentally interesting and technically important. Herein, we report the growth of zinc nanocrystals, including hexagonal nanoplates and one-dimensional nanowires, on an ionic liquid substrate without catalyst using thermal deposition method. The average height of terraced steps is ∼18.6 nm with all steps height larger than 5.7 nm, corresponding to a critical value in determining the growth rate along [001] and [010] direction based on our theoretical calculations. Moreover, one-dimensional Zn nanowires can be also observed. The longest Zn nanowire can grow up to ∼35.2 μm. A theoretical model is then proposed to explain the formation of hexagonal zinc nanoplates and nanowires, qualitatively and quantitatively. The...

Zinc aluminate nanotubes fabrication based on heating-induced volatilization and Kirkendall effect in nanopores of anodic aluminum oxide template

The fabrication of zinc aluminate nanotubes attracted considerable attention due to their potential application as catalysts, catalyst supports, and electronics. In this paper, it is presented the influence of heating temperature and time on the Kirkendall effect-related evolution of Zn nanowires embedded in nanopores of anodic aluminum oxide (AAO) template. With increasing of the reaction temperature and heating time, zinc aluminate nanotubes can be gradually achieved from Zn nanowires embedded in AAO template under the air environment. In particular, ZnO was formed in the pores of AAO template by the volatilization and oxidation of Zn nanowires. And then through the solid-solid interfacial reaction of ZnO and AAO template, the nanostructures were transformed to zinc aluminate nanotubes conserving the shape of the corresponding ZnO nanostructures, which was induced by the nanoscale Kirkendall effect. Combined with the volatilization and oxidation time of Zn nanowires, the wall thickness of the formed nanotubes can be further precisely controlled. Our finding provides a simple and efficient pathway to fabricate the complex hollow zinc aluminate nanostructures, which are expected to have potential applications in catalytic related fields.

Highly luminescent Alq3: Zn nanowires

The present paper deals with the synthesis and characterization of Alq3 and Zn doped Alq3 (Alq3: Zn) nanowires. Zn has been incorporated in Alq3 matrix using ultrasonic assisted incorporation using ZnCl2. Nanowires of Alq3 and Alq3: Zn are synthesized using Thermal Vapor Transport or Chemical Vapor Deposition (CVD) method. The morphological, structural and optical characteristics of these nanowires are studied using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDAX), Fourier Transform Infrared (FTIR) Spectroscopy, UV-Visible Spectroscopy and Fluorescence Spectroscopy. These studies confirm the formation of fine and crystalline nanowires with the drastic enhancement in PL intensity on Zn incorporation. The PL intensity has been observed to increase with Zn concentration. The highest PL has been observed for Alq3: Zn nanowires having concentration ratio of Alq3: Zn = 1:0.9.

Raman characterization of single-crystalline Ga0.96Mn0.04As:Zn nanowires realized by ion-implantation

Recent progress in the realization of magnetic GaAs nanowires (NWs) doped with Mn has attracted a lot of attention due to their potential application in spintronics. In this work, we present a detailed Raman investigation of the structural properties of Zn doped GaAs (GaAs:Zn) and Mn-implanted GaAs:Zn (Ga0.96Mn0.04As:Zn) NWs. A significant broadening and redshift of the optical TO and LO phonon modes are observed for these NWs compared to as-grown undoped wires, which is attributed to strain induced by the Zn/Mn doping and to the presence of implantation-related defects. Moreover, the LO phonon modes are strongly damped, which is interpreted in terms of a strong LO phonon-plasmon coupling, induced by the free hole concentration. Moreover, we report on two new interesting Raman phonon modes (191 and 252 cm−1) observed in Mn ion-implanted NWs, which we attribute to Eg (TO) and A1g (LO) vibrational modes in a sheet layer of crystalline arsenic present on the surface of the NWs. This conclusion is supported by fitting the observed Raman shifts for the SO phonon modes to a theoretical dispersion function for a GaAs NW capped with a dielectric shell.

Structural Analysis and Growth Mechanism of Zn/ZnO Nanowires in AAO Template by Electrodeposition

To fully understand the mechanism of forming Zn and ZnO nanowires in electrodeposition, Anodic Alumina Oxide (AAO) membrane was used to electrodeposit Zn/ZnO nanowires by varying the potential. The structure of electrodeposited Zn/ZnO nanowires is studied by means of X-ray diffraction and scanning electron microscopy. Different deposition parameters were used to obtain different structure of electrodeposited nanowires. At -1.4 V with pH2.5, the pure Zn nanowires are electrodeposited. By lowering the potential to -1.0 V with same electrolytic concentration and pH, the formed nanowires are mixture of Zn and ZnO. Further decrease in potential to -0.6V, electrodeposited nanowires are of pure ZnO. The size of the critical cluster decreases with increasing the over potential. The formation of pure ZnO nanowires can be attributed to the formation of large size critical Zn nuclei, the larger size of nuclei favors the formation of pure zinc oxides nanowires.

Shape, size and temperature dependency of thermal expansion, lattice parameter and bulk modulus in nanomaterials

A theoretical model is described here for studying the effect of temperature on nanomaterials. The thermodynamic equation of state (EoS) proposed by Goyal and Gupta in High Temp.-High Press. 45, 163 (2016); Oriental J. Chem. 32(4), 2193 (2016), is extended in the present study using Qi and Wang model [Mater. Chem. Phys. 88, 280 (2004)]. The thermal expansion coefficient is expressed in terms of shape and size and used to obtain the isobaric EoS of nanomaterials for the change in volume $$V/{V_0}$$ . The variation in $$V/{V_0}$$ with temperature is estimated for spherical nanoparticles, nanowires and nanofilms. It is found that the volume thermal expansivity decreases as size of the nanomaterial increases, whereas $$V/{V_0}$$ increases with temperature across nanomaterials of different sizes. The lattice parameter variation with temperature is studied in Zn nanowires, Se and Ag nanoparticles. It is found that lattice constant increases with increase in temperature. Also, bulk modulus is found to increase with temperature in nanomaterials. The results obtained from the present model are compared with the available experimental data. A good consistency between the compared results confirms the suitability of the present model for studying thermal properties of the nanomaterials.

Modification of the Electrolyte/Electrode Interface for the Template-free Electrochemical Synthesis of Metal Nanowires from Ionic Liquids.

In electrochemistry, the electrode/electrolyte interface (EEI) governs the charge/mass-transfer processes and controls the nucleation/growth phenomena. The EEI in ionic liquids (ILs) can be controlled by changing the cation/anion of the IL, salt concentration, electrode potential, and temperature. Here, we show that adding a dopant salt leads to the deposition of nanowires. To illustrate, zinc nanowires were electrodeposited from ZnCl2/1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate in the presence of GaCl3 as a dopant salt. The choice of Zn salt and its ratio to GaCl3 were found to be crucial for Zn nanowires formation. AFM studies revealed that the solvation structure of Au(111)/IL changes significantly in the presence of GaCl3 and ZnCl2. Chronoamperometry showed changes in the nucleation/growth process, consequently leading to the formation of nanowires. A similar approach was adopted to synthesize Sn nanowires. Thus, modification of the EEI by adding a dopant to ILs can be a viable method to obtain nanowires.

Large-Area Schottky Junctions between ZnO and Carbon Nanotube Fibres.

In this study, large-area (10 cm2 ) samples of heterojunctions between zinc oxide and carbon nanotube (CNT) fibre arrays were synthesised. A two-step hydrothermal treatment was used to grow Zn nanowires (NWs) in situ directly onto the CNT array. This resulted in a bulk heterojunction that consisted of a five-micron layer of ZnO crystals in contact with the built-in CNT fabric current collector, with preferential orientation of the ZnO c axis perpendicular to the CNT sheet. The electrical properties of the heterojunction corresponded to a Schottky junction with a barrier height of 0.26 eV and an ideality factor of 2.9. Photoconductivity measurements indicated charge transfer through the ZnO/CNT interface, thus leading to a gain factor of approximately 100 and a responsivity as high as 5000 mA w-1 under UV irradiation. The resulting ZnO/CNT fibre hybrid was both piezoresistive and piezoelectric under transverse compression with an attractive format for energy-harvesting applications.

Ultrathin Pt–Zn Nanowires: High-Performance Catalysts for Electrooxidation of Methanol and Formic Acid

Herein, we have developed a Zn2+ ion induced reduction strategy (ZIRS) for synthesizing ultrathin Pt–Zn nanowires (NWs) with average size of ∼2.2 nm. The precise selection of solvent and the addition of ZnCl2 precursor are of crucial significance to preparing bimetallic NWs. The NWs exhibited electrocatalytic performance compared with commercial catalysts, such as electrooxidation of methanol (MOR) and formic acid (FAOR). Moreover, the prepared Pt–Zn NWs can be adopted as a template to prepare Pt-based trimetallic ultrathin NWs.

Effect of size and shape on melting and superheating of free standing and embedded nanoparticles

A simple model is proposed to study the size and shape dependence of melting and superheating of nanomaterials. The size dependence of melting temperature of free standing spherical nanosolids viz. Ag, Au, Al and Zn nanowire as well as embedded nanoparticles Pb and Ag is reported. The formulation is used to study the effect of shape on melting temperature during reduction of size. The different shapes of nanomaterials viz. film, icosahedral, wire, spherical, hexahedral, octahedral and tetrahedral are considered. The size and shape dependence of surface atoms, total number of atoms and their ratio is computed. The results obtained are compared with the available experimental data and discussed in the light of recent investigations. A good agreement between model predictions and experimental data supports the validity of the formulation developed. It is concluded that in addition to the size, the shape of nanomaterials also plays an important role during the behaviour of nanomaterials.

Direct Electrical Probing of Periodic Modulation of Zinc-Dopant Distributions in Planar Gallium Arsenide Nanowires.

Selective lateral epitaxial (SLE) semiconductor nanowires (NWs), with their perfect in-plane epitaxial alignment, ability to form lateral complex p-n junctions in situ, and compatibility with planar processing, are a distinctive platform for next-generation device development. However, the incorporation and distribution of impurity dopants in these planar NWs via the vapor-liquid-solid growth mechanism remain relatively unexplored. Here, we present a detailed study of SLE planar GaAs NWs containing multiple alternating axial segments doped with Si and Zn impurities by metalorganic chemical vapor deposition. The dopant profile of the lateral multi-p-n junction GaAs NWs was imaged simultaneously with nanowire topography using scanning microwave impedance microscopy and correlated with infrared scattering-type near-field optical microscopy. Our results provide unambiguous evidence that Zn dopants in the periodically twinned and topologically corrugated p-type segments are preferentially segregated at twin plane boundaries, while Si impurity atoms are uniformly distributed within the n-type segments of the NWs. These results are further supported by microwave impedance modulation microscopy. The density functional theory based modeling shows that the presence of Zn dopant atoms reduces the formation energy of these twin planes, and the effect becomes significantly stronger with a slight increase of Zn concentration. This implies that the twin formation is expected to appear when a threshold planar concentration of Zn is achieved, making the onset and twin periodicity dependent on both Zn concentration and nanowire diameter, in perfect agreement with our experimental observations.

Facile conversion of Zn nanowires to Zn nanotubes by heating-induced volatilization in nanopores of anodic aluminum oxide template

In this work, a new template assisted synthesis strategy for the preparation of Zn nanotubes is demonstrated. By means of the heating-induced volatilization, Zn nanotubes can be successfully converted from Zn nanowires embedded in anodic aluminum oxide (AAO) template. The morphology and crystal structure of as-prepared Zn nanotubes are examined by transmission electron microscopy, X-ray diffraction, and selected-area electron diffraction. The related results can systemically reveal the synthesis process of Zn nanotubes. The heating temperature and time have effect on the structure morphology of Zn nanotubes. The extension of heating time and increase of heating temperature are conducive to the formation of Zn nanotubes. The volatilization of metal Zn and the confinement of AAO nanochannels play key roles in the formation of Zn nanotubes. This synthesis strategy may become a universal method to obtain the low melting point metal or metal oxide nanotubes.

Fabrication of ZnO Nanowires Arrays by Anodization and High-Vacuum Die Casting Technique, and Their Piezoelectric Properties.

In this investigation, anodic aluminum oxide (AAO) with arrayed and regularly arranged nanopores is used as a template in the high-vacuum die casting of molten zinc metal (Zn) into the nanopores. The proposed technique yields arrayed Zn nanowires with an aspect ratio of over 600. After annealing, arrayed zinc oxide (ZnO) nanowires are obtained. Varying the anodizing time yields AAO templates with thicknesses of approximately 50 μm, 60 μm, and 70 μm that can be used in the fabrication of nanowires of three lengths with high aspect ratios. Experimental results reveal that a longer nanowire generates a greater measured piezoelectric current. The ZnO nanowires that are fabricated using an alumina template are anodized for 7 h and produce higher piezoelectric current of up to 69 pA.

Zinc Oxide Wire-Like Thin Films as Nitrogen Monoxide Gas Sensor

We present an excellent detection for nitrogen monoxide (NO) gas using polycrystalline ZnO wire-like films synthesized via a simple method combined with sputtering of Zn metallic films and subsequent thermal oxidation of the sputtered Zn nanowire films in dry air. Structural and morphological characterization revealed that it would be possible to synthesize polycrystalline hexagonal wurtzite ZnO films of a wire-like nanostructure with widths of 100-150 nm and lengths of several microns by controlling the sputtering conditions. It was found from the gas sensing measurements that the ZnO wire-like thin film gas sensor showed a significantly high response, with a maximum value of 29.2 for 2 ppm NO at , as well as a reversible fast response to NO with a very low detection limit of 50 ppb. In addition, the ZnO wire-like thin film gas sensor also displayed an NO-selective sensing response for NO, , , , and CO gases. Our results illustrate that polycrystalline ZnO wire-like thin films are potential sensing materials for the fabrication of NO-sensitive high-performance gas sensors.

Electrodeposition of Zinc–Copper and Zinc–Tin Films and Free‐Standing Nanowire Arrays from Ionic Liquids

AbstractThe electrodeposition of Cu–Zn and Zn–Sn films as well as free‐standing nanowires from ionic liquids 1‐ethyl‐3‐methylimidazolium trifluoromethylsulfonate and 1‐butyl‐1‐methylpyrrolidinium trifluoromethylsulfonate is reported. The nanowire arrays were obtained by using polycarbonate membranes. The study includes cyclic voltammetry, chronoamperometry, X‐ray diffraction, and scanning electron microscopy–energy‐dispersive X‐ray analyses. The results show that the morphology and the composition of the electrodeposited Cu–Zn alloys are dependent on the deposition potential. Free‐standing Cu–Zn nanowires with average diameters and lengths of approximately 100 nm and 5 μm, respectively, were prepared. The morphology of Zn–Sn deposits shows coarse Zn particles on a Sn‐rich layer, indicating the formation of Zn/Sn co‐deposits. The XRD results reveal the co‐deposition of Zn–Sn films. Zn–Sn nanowires with average diameters of approximately 100 nm and lengths of 5 μm were synthesized. Free‐standing Zn–Sn nanowires with different lengths and a diameter of approximately 200 nm were also synthesized.