Nanowire Clusters Research Articles

Enhanced bubble nucleation and liquid rewetting for highly efficient boiling heat transfer on two-level hierarchical surfaces with patterned copper nanowire arrays

Enhancing boiling heat transfer by surface modification is of critical interest for improving the efficiency of many energy systems and for addressing thermal management bottlenecks in electronics. However, the improvement of all boiling heat transfer characteristics including the critical heat flux, heat transfer coefficient and onset of nucleate boiling, usually has conflicting requirements on surface wettability and morphology. In this work, we develop a two-level hierarchical surface with patterned copper nanowire arrays for boiling heat transfer enhancement. By surrounding long nanowire arrays with short nanowires where microcavities are formed between short nanowire clusters, a novel strategy is reported to improve all the boiling heat transfer characteristics through increasing bubble nucleation site density, capillary-induced liquid rewetting, and the separation of liquid-vapor pathways. Compared to boiling heat transfer performance on the plain copper surface, a 71% higher critical heat flux, a 185% higher heat transfer coefficient as well as a 37% lower onset of nucleate boiling are demonstrated on such two-level hierarchical surfaces. In addition, we correctly predict the effect of surface structure on the boiling heat transfer performance by an analytical model. Through distinguishing the role of different structure morphologies including the improved nucleation site by microcavities, enhanced liquid wicking by nanowires, and continuous liquid supply by long nanowire arrays, we have established a comprehensive understanding on the relation between the surface structures and boiling heat transfer characteristics.

Carbon monoxide gas sensing using zinc oxide deposited by successive ionic layer adhesion and reaction

This study was aimed to determine the carbon monoxide (CO) gas sensing capability of zinc oxide (ZnO) film fabricated by successive ionic layer adsorption and reaction (SILAR) on glass substrate. Films consisting of a mixture of flower-like clusters of ZnO nanorods and nanowires were observed using scanning electron microscopy (SEM). Current-voltage characterization of the samples showed an average resistivity of 13.0 Ω-m. Carbon monoxide gas was synthesized by mixing the required amount of formic acid and excess sulfuric acid to produce CO gas concentrations of 100, 200, 300, 400, and 500 parts per million (ppm) v/v with five trials for each concentration. Two sets of data were obtained. One set consisted of the voltage response of the single film sensor while the other set were obtained from the double film sensor. The voltage response for the single film sensor and the double film sensor showed an average sensitivity of 0.0038 volts per ppm and 0.0024 volts per ppm, respectively. The concentration the single film can detect with a 2V output is 526 ppm while the double film sensor can detect up to 833 ppm with a 2V output. This shows that using the double film sensor is advantageous compared to single film sensor, because of its higher concentration range due to the larger surface area for the gas to interact. Moreover, the measured average resistance for the single film sensor was 10 MΩ while for the double film sensor the average resistance was 5 MΩ.

Preparation of aligned W18O49 nanowire clusters with high photocatalytic activity

The aligned W18O49 nanowire clusters were synthesized via a facile and economic ethanol-assisted hydrothermal method using peroxopolytungstic acid as precursor. Results show that the as-prepared W18O49 exhibits a high yield and ultrathin structure with preferential growth direction along [010]. The amount of peroxopolytungstic acid and reaction time play significant role on the morphology of W18O49 nanowires. The nanowires have unique structure, high degree of crystallinity, large specific surface area, and large number of defects such as oxygen vacancies, which are responsible for their high photocatalytic performance for degradation of methylene blue. The photocatalytic conversion of methylene blue can reach above 98% after degradation. W18O49 also exhibits good photodegradation stability after five cycles of reuse. The results demonstrate that the as-prepared W18O49 nanowire clusters are expected to be a promising material for applications in the field of environment.

Increased absorption in InAsSb nanowire clusters through coupled optical modes

Nanowires can act as efficient light absorbers where waveguide modes are resonant to specific wavelengths. This resonant wavelength can easily be tuned by the nanowire dimensions, but the absorption of infrared radiation requires diameters of hundreds of nm, which is difficult to achieve using epitaxial growth. Here, we demonstrate that infrared absorption in InAsSb nanowires with the diameters of only 140 nm grown on Si substrates can be enhanced resonantly by placing them closely packed in clusters of different sizes. We find that coating the nanowires with a dielectric to optically connect them results in an efficient absorption diameter far exceeding the diameter of the constituent nanowires and that the cut-off wavelength is redshifted with an increasing cluster diameter. Numerical simulations are in agreement with the experimental results and demonstrate that if nanowires are positioned in clusters, a peak absorptance of 20% is possible at 5.6 μm with only 3% surface coverage. This absorptance is 200 times higher than for wires placed in an equidistant pattern. Our findings have direct implications for the design of efficient nanowire based photodetectors and solar cells.

Magnetically Recoverable Pd/Fe3 O4 Core-Shell Nanowire Clusters with Increased Hydrogenation Activity.

Core-shell nanostructures are promising candidates for the next generation of catalysts due to synergistic effects which can arise from having two active species in close contact, leading to increased activity. Likewise, catalysts displaying added functionality, such as a magnetic response, can have increased scientific and industrial potential. Here, Pd/Fe3 O4 core-shell nanowire clusters are synthesized and applied as hydrogenation catalysts for an industrially important hydrogenation reaction: the conversion of acetophenone to 1-phenylethanol. During synthesis, the palladium nanowires self-assemble into clusters which act as a high-surface-area framework for the growth of a magnetic iron oxide shell. This material demonstrates excellent catalytic activity due to the presence of palladium while the strong magnetic properties provided by the iron oxide shell enable facile catalyst recovery.

Efficient intracellular delivery of biomacromolecules employing clusters of zinc oxide nanowires.

Zinc oxide (ZnO) nanocomposites have been widely applied in biomedical fields due to their multifunctionality and biocompatibility. However, the physicochemical properties of ZnO nanocomposite involved in nano-bio interactions are poorly defined. To assess the potential applicability of ZnO nanowires for intracellular delivery of biomolecules, we examined the dynamics of cellular activity of cells growing on densely packed ZnO nanowire arrays with two different physical conformations, vertical (VNW) or fan-shaped (FNW) nanowires. Although a fraction of human embryonic kidney cells cultured on VNW or FNW underwent rapid apoptosis, peaking at 6 h after incubation, cells could survive and replicate without significant apoptosis on the foreign substrate after 12 h of lag phase. In addition, the cells formed lamellipodia to wrap FNW, and efficiently took up peptides non-covalently coated on VNW and FNW within 30 min of incubation. Moreover, FNW could mediate intracellular delivery of associated DNAs and their gene expression, suggesting that ZnO nanowires transiently penetrate membranes to mediate intranuclear delivery of exogenous DNA. These results indicate that ZnO nanowire arrays can serve as nanocomposites for manipulating nano-bio interfaces if appropriately modified in a 3-dimensional conformation.

UV-assisted, template-free electrodeposition of germanium nanowire cluster arrays from an ionic liquid for anodes in lithium-ion batteries

The structure of Ge nanowire cluster arrays is beneficial for capacity retention of the electrode.

Gel-combustion synthesized vanadium pentoxide nanowire clusters for rechargeable lithium batteries

Gel-combustion by a bio-fuel, processed starch of the root tuber of cassava (Manihot esculenta), was used to prepare vanadium pentoxide nanowire clusters (V2O5NWC). The as-synthesized product was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) UV–Visible spectroscopy and Photoluminescence (PL) spectroscopy. The electrochemical performance of V2O5NWC has been evaluated by cyclic voltammetry (CV), galvanostatic cycling (GC) and electrochemical impedance spectroscopy (EIS). The V2O5NWC had a discharge capacity of 188 mAh g−1with better capacity retention of 90% at the end of the 50th cycle, which corresponds to a coulombic efficiency of around 99%. The rate performance of the compound is also carried out and it has shown excellent performance. EIS was used to study the kinetic properties of Li+ ions for V2O5NWC and the fitted resistance and capacitance values are discussed in detail.

PTH-028 How About Resurrecting The Research of Mechanically Actuated Robotic Capsule Endoscopy by Designing Novel Pressure Crystallised Self-Powering Composite Structures?

Introduction Mechanically actuated robotic capsule endoscopes for active locomotion have demonstrated considerable clinical potential for conducting biopsies or therapeutic intervention in human gastrointestinal (GI) tract.1 Nevertheless, the research began to slow down owing to on-board power limitations and mechanical complexity in miniaturising electronic elements incorporated in the capsule body.2 Ideally, such swallowable capsules should be self-powered in vivo by converting the numerous GI-providing energy, such as the energy from the peristalsis near gastroesophageal junction and the high shear intestinal fluid flow.3 Methods Graphene nanoplatelet (GNP), consisting of stacked layers of graphene to enable the delivery of a broad range of therapeutics, was pre-mixed and then melt blended with poly (vinylidene fluoride) (PVDF). The as fabricated binary composites were crystallised at pressure with a piston-cylinder apparatus. Results Controllable rapid growth of unique self-powering 3 D hybrid nanoarchitectures, assembled from 1 D PVDF micro/nanowires on GNPs, was achieved by the pressure crystallisation of GNP/PVDF composites (Figure 1 a-c). By controlling the crystallisation conditions, the PVDF nanowires, with piezoelectric crystalline beta phase, were obtained respectively with folded- and extended-chain lamellae as their substructures. The GNPs may play the role as a catalyst in the composite system, due to their size effect, which catalysed the self-assembly of the PVDF molecules into nanowires and then resulted in the radial nanowire clusters. Although the original surfaces of GNP/PVDF composites were high hydrophobic, they were successfully converted into hydrophilic surfaces through the pressure treatment followed by appropriate etching process (Figure 1 d and e). Conclusion The pressure crystallised GNP/PVDF composites may permit niche applications in the fabrication of a new-generation of self-powering robotic capsule endoscopes to meet the environmental conditions of each section of GI tract for energy scavenging. This study was funded by the National Natural Science Foundation of China (51373139). References 1 Munoz F, Alici G, Li WH. Adv Drug Deliver Rev 2014;71:77–85. 2 Slawinski PR, Obstein KL, Valdastri P. World J Gastroentero 2015;21:10528–41. 3 Wang ZL, Song J. Science 2006;312:242–6. Disclosure of Interest None Declared

Hydrogen sensing properties of Pt/Pd bimetal decorated on highly hydrophobic Si nanowires

This paper describes the synthesis of Pt/Pd bimetal decorated highly hydrophobic rough silicon nanowires (Si NWs) by using a facile metal assisted chemical etching and pulse laser deposition (PLD) process. In addition, the potential of the Si NWs as a new hydrogen (H2) detection matrix was investigated. The Pt/Pd bimetal was coated as a discrete ultra-thin film manner in a semi-dense configuration over the basal podium and along the length of vertical-standing and semi-densely distributed rough Si NW clusters. The resulting structure showed significant advantages in H2 sensing performances such as a large detection range of 1–40,000 ppm, high response magnitude of nearly 5.02%, and fast response-recovery time of 7/7 s to 10,000 ppm (1 vol%) hydrogen concentration at an optimum operating temperature of 75 °C. The observed characteristics of fast response-recovery time could relate to the enhanced hydrogen-induced changes in the work function of the Pt/Pd bimetal decorated Si NWs (Pt/Pd–Si NWs), which were configured as an array matrix comprising of many nanowire clusters with variable distances between the two electrodes. Finally, the fabricated sensor showed excellent repeatability towards (1 vol%) hydrogen concentration.

Study on Field Emission Characteristics of Ti-based Chrysanthemum-like Nano-ZnO Cathode by Electrophoresis Deposition

Abstract Chrysanthemum-like ZnO nanowire clusters were prepared by hydrothermal process, then were transferred to Ti substrate by electrophoresis method, and uniform ZnO nano-film with certain thickness was formed. Finally ZnO field emission cathode sample was fabricated after vacuum heat treatment. The microstructure and the morphology of chrysanthemum-like ZnO nanowire clusters were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Field emission tests were conducted for cathode samples after heat treatment, results reveal that the low turn-on field is 2.0 V/μm for the chrysanthemum-like ZnO, and the threshold field is 5.5 V/μm. Moreover, the field emission current density is 200 μA/cm2 under the condition of electric field of 7.5 V/μm, and the field emission current density and its stability can be effectively improved by appropriate enlarging the thickness of the ZnO coating. The field emission mechanism was also explored.

Efficient photon management with Ag nanoparticles coated TiO2 nanowire clusters for photodetector application

TiO2 nanowire clusters (NWCs) covered with Ag nanoparticles (NPs) were synthesized on Si substrates using GLAD technique. Ag NPs/TiO2 NWCs showed enhanced optical absorption all over the spectrum compared to bare TiO2 NWCs. The leakage current of the TiO2 NWCs device (−10.8 μA) was reduced by ∼9 × 103 times for Ag NPs/TiO2 NWCs detector (−1.2 nA) at −1 V applied bias. Ag NPs/TiO2 NWCs detector exhibited maximum photoresponsivity ∼2.4 times (−2 V) as compared to the bare TiO2 NWCs detector. Using 10 K photocapacitance measurement, a sharp peak at 355 nm (∼3.5 eV) was detected due to the main band transition. The other sub band gap defects were observed within 410–490 nm along with a broad hump between 595–700 nm. The light dependent capacitance-time (I-T) characteristic of the Ag/TiO2 NWCs detector shows rise-time (T r ) of 9.6 s and decay time (T d ) of 10 s.

Performance Enhancements for Chemiresistive Electronic Noses Based upon Materials, Temperature Modulation and Signal Processing

Chemical sensors capable of detecting, identifying and quantifying trace chemical species in the air would be beneficial for a broad range of application areas from the laboratory, to workplace safety, to medical diagnostics, to homeland security and environmental monitoring, and even extending to planetary exploration. Our recent research has focused on studying the analytical capabilities of electronic nose-type sensors that utilize arrays of chemiresistive microsensor elements. In particular, we have explored the utility of microsensor arrays populated with varied sensing materials and employing temperature modulation to further enhance the analytical content of the measured signal streams. It is important that these aspects work together to improve the performance of the electronic nose, and we will illustrate that with several examples. One scenario demonstrates the discrimination of several volatile organic compounds at varied concentrations using a temperature-modulated electronic nose. We have studied both inorganic and polymer-based sensing materials in the past, which were integrated with the microsensor array using a variety of approaches [1]. Here, the materials that we employed in the arrays are based upon metal oxide semiconductors with varied morphologies (including: tin oxide nanowire clusters, copper oxide films, and porous indium oxide films) deposited using semi-automated microcapillary pipetting. While each material is cross-selective to the targeted analytes, their ensemble performance with temperature modulation shows enhancements for analyte and concentration discrimination when evaluated using Linear Discriminant Analysis. Concentrations for the analytes (acetone, toluene and chlorobenzene) range from 1 µmol/mol to 80 µmol/mol, and these chemicals are presented to the microsensor array in air backgrounds either alone or in mixtures with varied levels of humidity. A second example demonstrates different temperature-modulation approaches to improve the performance characteristics of the microsensors. We have expanded our use of a relatively simple bi-level program to enhance the speed of the sensor responses [2], testing the approach for use with different materials and different types of analyte molecules. The utility of the approach for attaining faster responses is shown in Figure 1. Here the raw data collected from a microsensor element based upon a porous indium oxide film are shown for two operating conditions: fast temperature modulation and isothermal. As seen, the response time for the modulated operation is ≈ 2× faster (t 90 = (2.0 ± 0.2) s vs. (4.1 ± 0.2) s) than for the isothermal operation when responding to 40 µmol/mol of chlorobenzene in dry air. Finally, we conclude by touching on several examples of using more complex ramp/base temperature programs that cover a broader range of temperature-induced sensor-analyte interactions. Here, we examine the potential of the different temperatures in the modulation program for yielding sensor responses that show resilience versus confounding chemicals (e.g., humidity, other analytes) or aging and drift, or those temperatures that maximize the overall response magnitude for particular analytes. This work emphasizes our collaborative research efforts, which have examined a variety of approaches, including those inspired by biological olfaction, to enhance the analytical capabilities of the chemiresistive electronic noses. Ultimately, for the flexibility needed to impact different applications, as well as for obtaining optimized performance, it is important the materials selections, operational mode and data analysis work together synergistically.

Superhydrophobic surface based on self-aggregated alumina nanowire clusters fabricated by anodization

The hierarchical micro/nano structures were designed and successfully fabricated on the alumina surface by a facile anodization method. Different morphologies of these surfaces could be obtained by adjusting anodization time and voltage, which revealed remarkable superhydrophobicity after the modification of stearic acid. The maximum contact angle of 158° could be easily obtained by this simple method and the sliding angle (SA) was near to 0°. Moreover, the superhydrophobic surface showed good corrosive effect and stability in 3.5% NaCl solution and good self-cleaning ability as well. This investigation would provide a simple, cost-effective, and highly efficient approach to design stable superhydrophobicity, anticorrosion, and self-cleaning surfaces.

Ultra‐High Capacity Lithium‐Ion Batteries with Hierarchical CoO Nanowire Clusters as Binder Free Electrodes

Although transition metal oxide electrodes have large lithium storage capacity, they often suffer from low rate capability, poor cycling stability, and unclear additional capacity. In this paper, CoO nanowire clusters (NWCs) composed of ultra‐small nanoparticles (≈10 nm) directly grown on copper current collector are fabricated and evaluated as an anode of binder‐free lithium‐ion batteries, which exhibits an ultra‐high capacity and good rate capability. At a rate of 1 C (716 mA g−1), a reversible capacity as high as 1516.2 mA h g−1 is obtained, and even when the current density is increased to 5 C, a capacity of 1330.5 mA h g−1 could still be maintained. Importantly, the origins of the additional capacity are investigated in detail, with the results suggesting that pseudocapacitive charge and the higher‐oxidation‐state products are jointly responsible for the large additional capacity. In addition, nanoreactors for the CoO nanowires are fabricated by coating the CoO nanowires with amorphous silica shells. This hierarchical core–shell CoO@SiO2 NWC electrode achieves an improved cycling stability without degrading the high capacity and good rate capability compared to the uncoated CoO NWCs electrode.

Pd nanoparticles decorating flower-like Co3O4 nanowire clusters to form an efficient, carbon/binder-free cathode for Li–O2 batteries

A novel high-performance flower-like Co3O4 nanowire cluster decorated with Pd nanoparticles to form a carbon/binder-free cathode for Li–O2 batteries.

In situ SERS interrogation of catalytic reaction on three-dimensional gold nanowire carpeted polycarbonate membranes

Direct monitoring of a catalytic process is essential to elucidate the underlying chemical principles and to expedite the design of next generation catalysts. The in situ SERS approach on three-dimensional gold nanowire ensembles was investigated in this study, which have a double role as an optical enhancer for Raman scattering and as a catalytic active center over many chemical reactions. The nanowire cluster was first electrolessly deposited using a porous polymer template, producing a SERS-active substrate with massive optical enhancement with an average factor of ∼105. This established system, integrating a heterogeneous catalysis and real-time SERS detection, is assessed by monitoring the catalytic reduction of 4-nitrophenol in the presence of excessive amount of NaBH4, during which the gradual increase of Raman intensity from the signature peak of 4-aminophenol is clearly recorded, implying the successful chemical transformation of gold nanowires. Therefore, this integrated system, synchronizing reaction and detection, is an ideal candidate for the in situ study of catalytic reactions on a relatively large scale as it balances technological and economical advantages.

A Facile Synthesis of Graphene-WO3Nanowire Clusters with High Photocatalytic Activity for O2Evolution

In the present work, graphene-WO3nanowire clusters were synthesizedviaa facile hydrothermal method. The obtained graphene-WO3nanowire clusters were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy (DRS) techniques. The photocatalytic oxygen (O2) evolution properties of the as-synthesized samples were investigated by measuring the amount of evolved O2from water splitting. The graphene-WO3nanowire clusters exhibited enhanced performance compared to pure WO3nanowire clusters for O2evolution. The amount of evolved O2from water splitting after 8 h for the graphene-WO3nanowire clusters isca.0.345 mmol/L, which is more than 1.9 times as much as that of the pure WO3nanowire clusters (ca.0.175 mmol/L). The high photocatalytic activity of the graphene-WO3nanowire clusters was attributed to a high charge transfer rate in the presence of graphene.

Synthesis and properties of single crystal TbMn2O5 nanostructures

Single crystal nanowire clusters of multiferroic material TbMn2O5 were obtained through a simple two-step method.

Contact Angle Hysteresis on Textured Surfaces with Nanowire Clusters

Nanowire arrays with various agglomeration patterns were synthesized by adjusting the solvent evaporation rates. Nanowires with 200 nm diameter and 2-25 microm in length were fabricated from an anodic aluminum oxide (AAO) porous template. Various drying treatments were applied to develop nanostructured surfaces with topological differences. Due to surface tension forces, copper nanowires after thermal and evaporative drying treatments agglomerated into clusters, while supercritical drying technique provided excellent bundled-free and vertically-standing nanowire arrays. Although all dried surfaces exhibited hydrophobic nature, the contact angle hysteresis, or the difference between advancing and receding angles, was found to be larger on those surfaces with bundled nanowire clusters. To explain the difference, the wetted solid fraction on each surface was calculated using the Cassie-Baxter model to show that the hysteresis was contributed by liquid/solid contact area on the textured surfaces.