Well-aligned Arrays Research Articles

Growth of ZnO nano-rods and its photoconductive characteristics on the photo-catalytic properties

Abstract Zinc oxide (ZnO) nano-rods has widely been investigated as a promising material for photo-catalysis, due to its high photocatalytic activity for the ambient gas molecules. Well-aligned ZnO nano-rods arrays were obtained by the two steps growth. Firstly, seeding layer deposition by RF magnetron sputtering, and secondly, nano-rods growth by hydrothermal processes were investigated. Moreover, after the samples were annealed at 450 °C, these samples were compared in crystalline characteristics and photo-electronic characteristics. The morphology of grown ZnO nano-rods were observed as the hexagonal nano-rods and XRD shows a (002) orientation in wurtzite crystals structure. Annealing processes shows a remarkable improvement of crystallinity. PL measurements showed a steep band edge emission and broad defect states emission and also fairly improvement in crystalline properties by the annealing process. The photoconductivity measurement could lead to investigate the photo-catalytic phenomena on the surface of ZnO nano-rods against the environmental gas molecules. The annealed samples showed a higher photo-conductivity and surface activity for the oxygen gas molecules comparing to the as grown samples.

Scratch to sensitize: scratch-induced sensitivity enhancement in semiconductor thin-film sensors.

Semiconductor gas sensors are advantageous in miniaturization and can be used in a wide range of applications, yet consume large power due to high operating temperature. Here we demonstrated the ability of nanoscale scratches produced with mechanical abrasion to enhance the chemical sensitivity of thin-film-type semiconductor sensors. Well-aligned arrays of scratches parallel to the electrical current direction between the source and drain electrodes were made, using typical polishing machines with diamond suspensions, on semiconductor thin films produced with various deposition methods such as atomic layer deposition (ALD), sputtering, and the sol-gel technique. Processing with sharp diamond microparticles left nano-grooves on the surface, together with changes in chemical composition. For all of the tested metal oxide thin films, the introduction of scratches yielded increased quantities of oxygen vacancies and metallic components. Scratched ZnO devices exhibited superior performance even at room temperature, as predicted by a computational simulation that showed increased binding energy of gas molecules on defects. The scratch technique shown in the present study may be used to produce dense arrays of nanometer-scale, chemically functionalized line patterns on substrates larger than a few tens of centimeters with minimum cost, which in turn may be used in a variety of applications including massive arrays of sensors displaying high sensitivity.

Dewetting mechanisms and their exploitation for the large-scale fabrication of advanced nanophotonic systems

ABSTRACTRecent progress in submicron- and nano-fabrication technologies has led to the emergence of novel photonic structures such as optical nanoantennas and metasurfaces. Real-life applications of these advanced photonic structures still require substantial improvement of the fabrication processes, in terms of their throughput and cost-effectiveness. Because of its simplicity and effectiveness, dewetting of a thin film has attained increasing attention as a feasible process for improving the scalability and productivity. Here, we provide an overview of the mechanisms and phenomenologies of dewetting to foster an improved fundamental understanding necessary for the optimisation of the dewetting process condition and template design. We then review the strategies demonstrating the use of templated-dewetting for producing well-aligned arrays of submicron- and nanostructures with great control over their size, shape and arrangement. Recent applications of dewetted structures in advanced nanophotonics are reviewed with an emphasis on the exploitation of dewetting mechanisms. Special attention is given to the fabrication of resonant optical nanoantennas and nanophotonic applications in which high repeatability and throughput are important parameters: sensing, colourisation, photovoltaics and nonlinear light frequency conversion. We expect this review to provide a basis for the use of thin-film dewetting to realise the industrial-level fabrication of various practical advanced photonic systems.

A practical-oriented NiFe-based water-oxidation catalyst enabled by ambient redox and hydrolysis co-precipitation strategy

Although NiFe-based (oxy)hydroxides have been recognized as the most promising anode materials for industrial water splitting, the existed synthetic methods are difficult to fabricate NiFe-based (oxy)hydroxides simultaneously fulfilling the requirements of low-cost and ambient synthetic process, high performance, and easier realization of large-scale production. In this work, a simple while effective strategy was proposed to fabricate well-aligned Ni-Fe hydroxide nanosheets array on Ni foam (NiFe-OH NS/NF) by the ambient spontaneous redox reaction between Ni foam and Fe3+and accompanied hydrolysis co-deposition of the generated Ni2+, Fe2+/Fe3+, and OH−. The tailored highly-oriented amorphous and nanoporous nanosheets structure as well as the strong electronic interaction between Ni and Fe species endow this NiFe-OH NS/NF with excellent OER activity that a large current density of 500 mA cm−2 could be well afforded at a low overpotential of 292 mV. Importantly, the manufacturing and raw-materials cost to synthesize the NiFe-OH NS/NF by this strategy is estimated to be just $0.0165 per cm2, much lower than those for other reported self-supported Fe-containing catalyst materials. Also, this ambient means not only could be applicable to the large-scale production of size-tunable NiFe-OH NS/NF with stable nanoarray structure, but also could be easily used for the synthesis of NiCo NS/NF and NiCoFe NS/NF for applications.

N-doped CoO nanowire arrays as efficient electrocatalysts for oxygen evolution reaction

Abstract Rational design of cost-effective high-performance electrocatalysts for oxygen evolution reaction (OER) is of great significance for electrochemical water splitting. Herein, we adopt a nitrogen doping method to fabricate self-supported N-doped CoO nanowire arrays (N–CoO) as active electrocatalysts via a facile hydrothermal combined doping method. The N–CoO nanowires are strongly composited with the carbon cloth substrate forming free-standing electrode with reinforced stability and high electronic conductivity. Owing to the increased accessible and electroactive areas, rich/short pathways for charge transfer and enhanced electronic conductivity, the N–CoO electrode exhibits excellent electrocatalytic performance for OER with a low overpotential (319 mV at 10 mA cm−2 and 410 mV at 100 mA cm−2) and a low Tafel slope of 74 mV dec−1 as well as superior long-term stability with no decay in 24 h continuous test in alkaline solution. Our reported design and optimization strategy provide a promising way to construct interesting well-aligned arrays for application in energy storage and conversion.

Facile active control of a pulsed erbium-doped fiber laser using modulation depth tunable carbon nanotubes

Short pulsed fiber lasers have been widely made using single-walled carbon nanotubes as a saturable absorber (SA). However, most of the currently used devices can only operate in one determined operation state with an unchangeable modulation SA depth in the cavity, which significantly limits their application in photonic devices. In this paper, well-aligned carbon nanotube arrays are synthesized using zeolite AlPO4-5 as a template, which features anisotropic optical absorption. The linear optical absorption of the as-synthesized carbon nanotube arrays can easily be tuned by adjusting a polarization controller, thus providing a tunable modulation depth for the carbon nanotube SA. By exploiting this SA in an erbium-doped fiber laser cavity, both Q-switched and mode-locked pulsed lasers are achieved by simply adjusting a polarization controller under a fixed pump power of 330 mW. In addition, the repetition rate of the Q-switching and pulse duration of the mode-locking can be tuned according to the variation of modulation depth. Moreover, soliton molecules can be obtained when the modulation depth of the SA is 4.5%.

Template-free synthesis of nanoarrays SnO2 hollow microcubes with high gas-sensing performance to ether

Hierarchical nanoarrays SnO2 hollow microcubes were successfully synthesized by a simple one-pot template-free hydrothermal route without any substrates. The as-prepared products demonstrated novel hollow SnO2 microcubes with side length of 2–3 μm. Noticeably, the SnO2 cubic surfaces exhibited a hierarchical architecture of well-aligned nanorod arrays. The gas-sensing properties indicated that the nanoarrays SnO2 hollow microcubes possessed superior sensitivity towards ether at the heating voltage of 4.5 V. The formation and sensing mechanism of the nanoarrays SnO2 hollow microcubes were proposed in this paper.

Synergistic effect of silane and graphene oxide for enhancing the photoelectrochemical water oxidation performance of WO3NS arrays

Photoelectrochemical (PEC) water splitting using semiconductor-based photoelectrodes is a promising approach for renewable solar fuel production. One of the biggest challenge is that semiconductor electrodes suffer from lower utilization of photogenerated-carriers and sluggish surface water oxidation reaction. Herein, we report that a novel composite photoelectrode based on silane molecule/graphene oxide being modified on the surface of well-aligned WO3 nanosheet arrays (WO3 NS/Silane/GO), efficiently harvests holes from the semiconductor and provides more reactive surface for water oxidation owing to the synergistic effect. The results demonstrate that 1.8 times photocurrent enhancement of WO3 NS/Silane/GO electrode (1.25 mA cm−2 at 1.23 V vs RHE) can be obtained compared to that of the pristine WO3 NS (0.69 mA cm−2) electrode, and it is even much higher than the photocurrent sum of WO3 NS/Silane and WO3 NS/GO electrodes. The remarkably enhanced PEC performance mainly stems from the induced external electric field (EEF) created by silane acting as hole-storage spots and the efficient carrier migration channel provided by GO, dramatically suppress the recombination of photogenerated carriers. As a result, the synergistic effect of silane and GO leads to a steady and continuous hole-transfer pathway, and promotes water oxidation kinetic by the increased reactive site quantity and activity. This study indicates that it can be a general design strategy for the preparation of efficient PEC electrodes in solar water splitting.

A New Mitigation Method for Space Robot Charging Effect Based on CNTs

Autonomous space robot will be widely used to complete various space missions in future. Unfortunately electrostatic surface discharge (ESD) induced by space plasma environment may produce one of the most common anomaly in space robots. Liquid Metal Ion Source (LMIS) is one of the effective mitigation methods for space robot charging effect. But as a devices for space-robots charging mitigation equipment, has strict requirements to its weight and volume. The present LMIS can only work at a very high voltage, so the weight and volume of LMIS isn’t suitable for space robot. Here we propose that carbon nanotubes (CNTs) can be used as capillary-type emitters in LMIS to meet the challenge. Well-aligned CNT arrays are synthesized on self-ordered hexagonal porous anodic aluminum oxide (AAO) template using chemical vapor deposition (CVD) method. The CNTs obtained are monodispersed and have open tip, which indicates that they have the similar geometry to the present capillary-type emitters in LMIS. So the LMIS made of CNTs can emit ions at a very lower voltage. A new mitigation device for space robot charging effects with very small weight and volume can be developed. The key steps for fabricating CNT emitters are presented.

TiO2 nanorod array film decorated with rGO nanosheets for enhancing photocatalytic and photoelectrochemical properties

A well-aligned TiO2 nanorod array film decorated with reduced graphene oxide(rGO/TNR) was constructed on fluorine-doped tin oxide (FTO) via a one-pot hydrothermal route with the aim of improving the photocatalytic and photoelectrochemical performances. The optimal ratio of components was investigated by changing the GO content that was added to the TiO2 precursor solution. The structure, morphology, composition, optical, photocatalytic and photoelectrochemical properties of the rGO/TNR films were investigated in detail. The resulting rGO/TNR films had a unique microstructure, apparent red shift of the absorption edge and low recombination rate of photoinduced charge carriers. For the degradation of methylene orange (MO) under UV light, the 5 wt%-rGO/TNR film exhibited the best photogradation efficiency of 95.8% in 120 min compared to bare TNR, which had a photogradation efficiency of 41.4%. Moreover, the 5 wt%-rGO/TNR film also showed the highest photocurrent of 110 μA/cm2, which was 6 times higher than that of bare TNR (16 μA/cm2). The excellent performance of the rGO/TNR film may be caused by the synergistic effect of the extended photoresponse range, high adsorption of target molecules and effective photogenerated electron-hole separation via rGO nanosheets as electron collectors and transporters.

Preparation of Well-Aligned TiO₂ Nanotubes with High Length-Diameter Aspect Ratio by Anodic Oxidation Method.

This paper focused on the influence of various oxidation parameters such as electrolyte composition, reaction time, calcination temperature and current change on the morphology and structure of TiO2 nanotube arrays. It was found that ammonium fluoride with a high viscosity reduced the diffusion rate of fluoride ions and significantly increased the length of TiO2 nanotubes, creating nanotubes with ordered arrays and uniform diameters. Meanwhile, the time of anodic oxidation determined the length of TiO2 nanotube arrays. Well-aligned nanotube arrays could be obtained after 0.5-2.5 h of oxidation. In addition, when the oxidation temperature was about 30 °C, the TiO2 nanotube arrays achieved the optimal uniformity and the maximum length-diameter aspect ratio. The morphology and quality of the TiO2 nanotubes fabricated were estimated through current as a function of reaction time. Consequently, formation mechanism of TiO2 nanotube arrays was investigated undergoing three major periods. The findings of this study can shed some light on the optimal conditions for preparing well-aligned TiO2 nanotube arrays with high length-diameter aspect ratio.

Bottom-Up Synthesis of Heteroatom-Doped Chiral Graphene Nanoribbons.

Bottom-up synthesis of graphene nanoribbons (GNRs) has significantly advanced during the past decade, providing various GNR structures with tunable properties. The synthesis of chiral GNRs, however, has been underexplored and only limited to (3,1)-GNRs. We report herein the surface-assisted synthesis of the first heteroatom-doped chiral (4,1)-GNRs from the rationally designed precursor 6,16-dibromo-9,10,19,20-tetraoxa-9a,19a-diboratetrabenzo[ a, f, j, o]perylene. The structure of the chiral GNRs has been verified by scanning tunneling microscopy, noncontact atomic force microscopy, and Raman spectroscopy in combination with theoretical modeling. Due to the presence of oxygen-boron-oxygen (OBO) segments on the edges, lateral self-assembly of the GNRs has been observed, realizing well-aligned GNR arrays with different modes of homochiral and heterochiral inter-ribbon assemblies.

Conductive Leaflike Cobalt Metal–Organic Framework Nanoarray on Carbon Cloth as a Flexible and Versatile Anode toward Both Electrocatalytic Glucose and Water Oxidation

Transition metal-organic frameworks (MOFs), on account of their unique inherent properties of large pore volume, high specific surface area, tunable pores, and good catalytic activity, have been highly regarded as superior catalysts recently for water electrolysis, supercapacitors, batteries, sensors, and so on. Herein, we report on a cobalt MOF phase with 3D well-aligned nanosheets array architecture on carbon cloth (Co-MOF NS/CC), fabricated by a facile ambient liquid-phase deposition, could serve as a self-standing Janus catalytic electrode toward both glucose and water oxidation. It shows good glucose-sensing performance with low determination limit and large detection range. Also, it exhibits high water-oxidation efficiency with low overpotential and good durability. This work demonstrates the potential of utilizing transition-metal based well-aligned MOF nanoarrays for electrocatalytic oxidation.

Epitaxial growth of horizontally aligned single-crystal arrays of perovskite

Well-aligned single-crystal nanowire arrays of CH3NH3PbI3 have shown potentials in laser sources and photovoltaic applications. Here we developed a solution based epitaxial method to grow CH3NH3PbI3 nanowire arrays. By confining the precursor solution between a silicon wafer and ST-cut quartz, the evaporation rate of the solvent was slowed down which brings a more stable and controllable solution environment. Relying on the lattice match between CH3NH3PbI3 and ST-cut quartz, arrays of single-crystal nanowires of CH3NH3PbI3 have been grown epitaxially. The densities and lengths of CH3NH3PbI3 nanowires can be tuned. The lengths of the resultant crystals range from several microns to over one millimeter. Such CH3NH3PbI3 arrays with good alignment and crystallinity were then applied to fabricate photovoltaic devices with good performances.

FeP@C Nanotube Arrays Grown on Carbon Fabric as a Low Potential and Freestanding Anode for High-Performance Li-Ion Batteries.

An anode of self-supported FeP@C nanotube arrays on carbon fabric (CF) is successfully fabricated via a facile template-based deposition and phosphorization route: first, well-aligned FeOOH nanotube arrays are simply obtained via a solution deposition and in situ etching route with hydrothermally crystallized (Co,Ni)(CO3 )0.5 OH nanowire arrays as the template; subsequently, these uniform FeOOH nanotube arrays are transformed into robust carbon-coated Fe3 O4 (Fe3 O4 @C) nanotube arrays via glucose adsorption and annealing treatments; and finally FeP@C nanotube arrays on CF are achieved through the facile phosphorization of the oxide-based arrays. As an anode for lithium-ion batteries (LIBs), these FeP@C nanotube arrays exhibit superior rate capability (reversible capacities of 945, 871, 815, 762, 717, and 657 mA h g-1 at 0.1, 0.2, 0.4, 0.8, 1.3, and 2.2 A g-1 , respectively, corresponding to area specific capacities of 1.73, 1.59, 1.49, 1.39, 1.31, 1.20 mA h cm-2 at 0.18, 0.37, 0.732, 1.46, 2.38, and 4.03 mA cm-2 , respectively) and a stable long-cycling performance (a high specific capacity of 718 mA h g-1 after 670 cycles at 0.5 A g-1 , corresponding to an area capacity of 1.31 mA h cm-2 at 0.92 mA cm-2 ).

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

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

(Invited) Fullerene Nanostructures: Preparation and Application

During the past two decades, the self-assembly of spherical fullerene molecules has attracted intensive attention for their definite structures, high electronic affinity and three-dimensional (3D) electron transporting property. We report herein the systematical investigation of the self-assembly behavior of C60 molecules to form various polyhedron microstructures and well-aligned arrays together with their extraordinary optical properties.[ 1 ] Furthermore, a solution-processible co-assembly strategy taking advantage of charge-transfer interaction is developed to prepare C70/porphyrin supramolecular architectures, which possess excellent electrical conductivity and high thermal resistance, and charge separation characteristics.[ 2,3 ] More practically, porous carbon materials with abundant functional moieties are readily obtained by KOH activation of C70 microtubes, which exhibit excellent supercapacitor performances.[ 4 ] References [1] S. Zheng, et al., Carbon 201 8, DOI:10.1016/j.carbon.2017.10.012. [2] S. Zheng, et al., Nano Res. 201 8, DOI:10.1007/s12274-017-1809-7. [3] B. Wang, S. Zheng, et al., J. Am. Chem. Soc. 2017, 139, 10578. [5] S. Zheng, H. Ju, X. Lu, Adv. Ener. Mater. 2015, 1500871.

Comparative study on drain current conduction mechanisms of (100)- and (111)-silicon nanowire using a quantitative current model

Over the years, semiconductor nanowires have been extensively researched due to their electrical properties for implementation of nano-to-microscale field-effect transistors (FETs). In order to implement a nanowire integrated device, well-aligned arrays of silicon nanowire are necessary for scalable and repeatable mass production. Although there has been much research on various fabrication processes to implement arrayed silicon-nanowires, few studies on channel conduction mechanism and theoretical modeling have been conducted on top-down fabricated silicon nanowires. In this paper, a comparative study on electrical characteristics of (100)- and (111)-silicon nanowire using a quantitative current model is presented for high-performance silicon-nanowire devices. Compared to silicon nanowire using (100)-silicon, one of the advantages of using (111)-silicon is that it can control the height and width of silicon nanowire through a sequential deep-silicon-etching process. According to the operation mechanism of the silicon-nanowire FET, the height of the silicon nanowire needs to be minimized to achieve high on/off-current ratio and low power consumption at off-state. Using (111)-silicon, it is possible to define height and width independently, which can result in higher performance characteristics.

Rapid Synthesis of Semipolar ZnO Nanorod Arrays on M-Sapphire by Microwave-Assisted Chemical Bath Deposition

Microwave-assisted chemical bath deposition (CBD) is a newly developed technique for fast growth of single-crystalline ZnO nanorods in a solution containing zinc nitrate at temperature below 100°C. ZnO nanorods have many applications for devices, however, semipolar oriented ZnO nanorods have been rarely reported. In this study, epitaxial growth of well-aligned arrays of inclined semipolar ZnO nanorods on a ZnO seed layer on m-plane sapphire substrates is successfully fabricated by using microwave-assisted chemical bath deposition for 10 min at 90 °C. TEM analysis reveals that The ZnO nanorods have an inclined angle about 30° with m-sapphire surface and an average length about 500 nm which gives a growth rate of 3 μm/h. Micro-photoluminescence measurements show that ZnO nanorods are of a reasonably good quality.

Hierarchically-structured Co3O4 nanowire arrays grown on carbon nanotube fibers as novel cathodes for high-performance wearable fiber-shaped asymmetric supercapacitors

Fiber-shaped supercapacitors (FSCs) are lightweight and flexible energy storage devices that have potential applications in portable and wearable electronics. However, FSCs have flawed energy density stemming from a small specific capacitance and low operating voltage, which limits their practical application. This study puts forth a simple and effective approach to grow well-aligned three-dimensional cobalt oxide nanowire arrays (Co3O4 NWAs) directly on carbon nanotube fibers (CNTFs). The hybrid fibers obtained an ultrahigh specific capacitance of 734.25 F cm−3 (2210 mF cm−2) in a three-electrode system. Benefiting from their intriguing features, we successfully fabricated an all-solid-state fiber-shaped asymmetric supercapacitor (FASC) prototype with a stable potential window of 1.6 V. Where the vanadium nitride nanowires/carbon nanotube fibers (VN NWAs/CNTFs) acted as negative electrode and the KOH poly(vinyl alcohol) (PVA) worked as the gel electrolyte. The electrochemical results suggested that the device possessed a high energy density of 13.2 mWh cm−3 at a current density of 1.0 A cm−3. Besides, the FASC exhibited excellent mechanical flexibility and structural stability. Therefore, this device has great potential for next-generation wearable energy-storage devices.