Growth Of Nanowire Arrays Research Articles

Epitaxial growth of bottom-crosslinked ZnGa2O4 nanowire arrays on c-plane GaN/Al2O3 substrate

The epitaxial growth of highly ordered ZnGa2O4 nanowire arrays and the construction of connectivity states between the individually segregated nanowires would significantly improve the performance of ZnGa2O4-based devices and expand their application fields. Herein, a strategy to construct high crystalline quality and well-aligned bottom-crosslinked ZnGa2O4 nanowire arrays along seven equivalent crystallographic directions of [111], [111̅], [11̅1], [1̅11], [11̅1̅], [1̅11̅] and [1̅1̅1] on Au-coated (0001) GaN/Al2O3 substrates using chemical vapor deposition (CVD) is proposed. The vapor-liquid-solid (VLS) mechanism dominates the entire growth process. The horizontal nanowires induced to nucleate and grow by catalyst droplets encountered and then turned towards inclined nanowires. Meanwhile, catalyst droplets that failed to move horizontally were enclosed by horizontal nanowires, resulting in the induction of perpendicular nanowire growth. The film-like horizontal nanowires connected all the inclined and perpendicular nanowires to form the bottom-crosslinked nanowire arrays. Additionally, the morphology, structure and optical properties of the ZnGa2O4 nanowire arrays, as well as the influence of Au layer thickness and growth time on the growth of ZnGa2O4 nanowires, were further characterized and thoroughly investigated. The proposed strategy achieved the growth of epitaxial well-aligned ZnGa2O4 nanowire arrays with bottom cross-linking, which is conducive to the application of ZnGa2O4 nanowires in optoelectronics.

Effect of gas diffusion layer surface property on platinum nanowire array electrode performance in proton exchange membrane fuel cells

3D-ordered catalyst electrodes have been recognized as one effective strategy to reach high current density operation for proton exchange membrane fuel cell (PEMFC) applications. Gas diffusion electrodes (GDEs) with platinum nanowire arrays in-situ grown on gas diffusion layer (GDL) surface is an important contribution in this area, but the performance is highly dependent on the GDL surface properties. In this study, the GDLs available in the market are systematically investigated, with a focus on the influence of the GDL surface properties on the in-situ growth of Pt nanowire arrays to fabricate GDEs as cathodes for PEMFCs. The experimental results indicate that mesopores especially micropores play a key role. They enable a hydrophilic surface for the isopropanol pretreated GDL, facilitating the in-situ growth of Pt nanowires to form a uniform array with a large electrochemical surface area (ECSA), finally leading to a high-power density. With Freudenberg H24CX483 carbon paper GDL, the highest power density of 0.9 W cm−2 is achieved. The understanding achieved here could be further used to develop novel GDLs for fabricating the next generation of electrodes for large current density operations.

Area-Selective Growth of Zinc Oxide Nanowire Arrays for Piezoelectric Energy Harvesting.

In this work, we present the area-selective growth of zinc oxide nanowire (NW) arrays on patterned surfaces of a silicon (Si) substrate for a piezoelectric nanogenerator (PENG). ZnO NW arrays were selectively grown on patterned surfaces of a Si substrate using a devised microelectromechanical system (MEMS)-compatible chemical bath deposition (CBD) method. The fabricated devices measured a maximum peak output voltage of ~7.9 mV when a mass of 91.5 g was repeatedly manually placed on them. Finite element modeling (FEM) of a single NW using COMSOL Multiphysics at an applied axial force of 0.9 nN, which corresponded to the experimental condition, resulted in a voltage potential of -6.5 mV. The process repeated with the same pattern design using a layer of SU-8 polymer on the NWs yielded a much higher maximum peak output voltage of ~21.6 mV and a corresponding peak power density of 0.22 µW/cm3, independent of the size of the NW array. The mean values of the measured output voltage and FEM showed good agreement and a nearly linear dependence on the applied force on a 3 × 3 µm2 NW array area in the range of 20 to 90 nN.

Ag-Coated Si nanowire arrays: A new route for the precise detection of fungicides by surface enhanced Raman scattering

In this study, we present an efficient method based on vertically oriented silicon nanowire arrays coated with silver nanoparticles to achieve significantly surface enhanced Raman scattering (SERS) signals. The method is applicable for the accurate detection of fungicides and related compounds. The substrates were obtained by a two-step process consisting of the growth of Si nanowire arrays on a silicon wafer by metal-assisted chemical etching and subsequent coating with Ag nanoparticles by the sputtering method. The effect of sputtering time on the growth of nanowires, their morphology and enhancement factor of the signals obtained from the SERS sensor were studied in detail. The final enhancement factor of Raman shift is 1.1 × 107, allowing the limit of trace detection for carbendazim to be as low as 0.1 ppm, with a relative standard deviation of less than 2.07%. This result opens up the potential for direct application of prepared substrates in ultra-fast chemical analysis.

Integrated Gradient Cu Current Collector Enables Bottom-Up Li Growth for Li Metal Anodes: Role of Interfacial Structure.

3D Cu current collectors have been demonstrated to improve the cycling stability of Li metal anodes, however, the role of their interfacial structure for Li deposition pattern has not been investigated thoroughly. Herein, a series of 3D integrated gradient Cu-based current collectors are fabricated by the electrochemical growth of CuO nanowire arrays on Cu foil (CuO@Cu), where their interfacial structures can be readily controlled by modulating the dispersities of the nanowire arrays. It is found that the interfacial structures constructed by sparse and dense dispersion of CuO nanowire arrays are both disadvantageous for the nucleation and deposition of Li metal, consequently fast dendrite growth. In contrast, a uniform and appropriate dispersity of CuO nanowire arrays enables stable bottom Li nucleation associated with smooth lateral deposition, affording the ideal bottom-up Li growth pattern. The optimized CuO@Cu-Li electrodes exhibit a highly reversible Li cycling including a coulombic efficiency of up to ≈99% after 150 cycles and a long-term lifespan of over 1200h. When coupling with LiFePO4 cathode, the coin and pouch full-cells deliver outstanding cycling stability and rate capability. This work provides a new insight to design the gradient Cu current collectors toward high-performance Li metal anodes.

Three-dimensional porous AuNPs-decorated polyaniline array for ultrasensitive determination of trace Cd(II) and Pb(II) in drinking water

Herein, a three-dimensional porous nanomaterials AuNPs-decorated polyaniline nanowire arrays/carbon nanotube (Au-PANI-array@CNT) was constructed by modified dilute polymerization and redox reaction. The Au-PANI-array@CNT exhibited a larger specific surface area (50.03 m2 g−1) and abundant mesopores (average pore size: 19.6 nm), due to the vertical growth of PANI nanowire arrays on CNT. The Au-PANI-array@CNT composite with a three-dimensional interconnected porous structure exhibited abundant electroactive sites and high adsorption capacity, significantly enhancing the deposition and electrochemical reaction process of heavy metals. The AuNPs embedded on PANI nanowries can provide high catalytic activity and multidimensional electron transport channels, further improving the detection sensitivity. A sensing platform with ultra-high sensitivity (2091, 3890 μA μM−1 cm−2) and lower limit of detection (0.18, 0.15 nM) for Cd(II) and Pb(II) determination was developed based on the three-dimensional porous PANI composite. Furthermore, the sensing mechanism of Au-PANI-array@CNT with Cd(II) was explored by XPS and FTIR spectroscopy. The current response only decreased by 5% after being stored at room temperature for 2 months, indicating that the sensor has high reproducibility and stability. Finally, the analysis of drinking water samples verified the excellent practicability of the sensor for the simultaneous measurement of trace levels (nM) of Cd(II) and Pb(II).

Kinetics of Catalyst-Free and Position-Controlled Low-Pressure Chemical Vapor Deposition Growth of VO2 Nanowire Arrays on Nanoimprinted Si Substrates.

In the present article, the position-controlled and catalytic-free synthesis of vanadium dioxide (VO2) nanowires (NWs) grown by the chemical vapor deposition (CVD) on nanoimprinted silicon substrates in the form of nanopillar arrays was analyzed. The NW growth on silicon nanopillars with different cross-sectional areas was studied, and it has been shown that the NWs' height decreases with an increase in their cross-sectional area. The X-ray diffraction technique, scanning electron microscopy, and X-ray photoelectron spectroscopy showed the high quality of the grown VO2 NWs. A qualitative description of the growth rate of vertical NWs based on the material balance equation is given. The dependence of the growth rate of vertical and horizontal NWs on the precursor concentration in the gas phase and on the growth time was investigated. It was found that the height of vertical VO2 NWs along the [100] direction exhibited a linear dependence on time and increased with an increase in the precursor concentration. For horizontal VO2 NWs, the height along the direction [011] varied little with the growth time and precursor concentration. These results suggest that the high-aspect ratio vertical VO2 NWs formed due to different growth modes of their crystal faces forming the top of the growing VO2 crystals and their lateral crystal faces related to the difference between the free energies of these crystal faces and implemented experimental conditions. The results obtained permit a better insight into the growth of high-aspect ratio VO2 NWs and into the formation of large VO2 NW arrays with a controlled composition and properties.

Alkynyl ligands-induced growth of ultrathin nanowires arrays

Ligands are almost essential in the synthesis of nanostructures. In this work, we introduce the alkynyl ligands into the synthesis of ultrathin gold (Au) nanowires arrays. The strong binding affinity of the alkynyl ligands enables one-dimensional (1D) growth via the active surface growth mechanism. The scope of the ligand generality was systematically investigated, and the alkynyl ligand-induced nanowire growth processes were compared and contrasted with those involving thiolated ligands. While strong ligands are usually difficult to dissociate from the nanostructure surface and therefore problematic for post-synthetic processing, the alkynyl ligands are readily dissociable, making the alkynyl ligand-stabilized Au nanowires potentially more modifiable and applicable. As a demonstration, direct palladium (Pd) deposition on the Au nanowires was successfully carried out without any ligand exchange process.

Air Nanocolumn-SiO2 composite film with adjustable anisotropic refractive index

Low refractive index (RI) porous dielectrics at optical frequencies, serving as subwavelength effective media for versatile photonic utilization, still face great challenges in realizing flexible refractive index adjustment, and balancing low RI performance and material robustness. These mainly stem from difficulty in precisely controlling their porosity, as well as high porosity (excessive air exposure) induced refractive index shift and weakened rigidity. To address these issue, ultrafine vertically aligned and perforated air nanocolumn-SiO2 composite films are elaborately designed and fabricated, namely, ultrafine (the diameter <10 nm) nanoholes embedded in the SiO2 matrix. The simple preparation process refers to self-organization growth of Ag nanowire (NW) arrays in SiO2 matrix followed by chemical etching for silver removal. Owing to high aspect ratio-induced depolarization effect and porosity modulation, their RIs not only possess anisotropic feature, but also are continuously tunable (from 1.40 to 1.15 for ordinary component and 1.41 to 1.19 for extraordinary component). Due to their low-RI nature and nanoscale microstructural characteristic, broadband (380 nm–1700 nm) high transmittance properties are demonstrated with ultralow (<0.5%) haze. More importantly, our proposed films are mechanically robust with water-proof and antifouling in nature. This work provides a new scheme for constructing anisotropic low RI materials that should be intriguing for diverse photonic applications.

Homogeneous and well-aligned GaN nanowire arrays via a modified HVPE process and their cathodoluminescence properties.

In this work, we demonstrate the growth of homogeneous and well-aligned [0001]-oriented 1-D GaN nanoarrays via a modified hydride vapor phase epitaxy (HVPE) process using GaCl3 and NH3 as precursors. The density and length of the grown nanowires can be easily controlled by the process parameters. It was found that the growth technique provides Cl-rich growth conditions, which lead to special morphology and optical properties of the GaN nanoarrays. Different from reported GaN nanowires, the as-synthesized GaN nanoarrays in this study exhibit a hollow bamboo-like structure. Also, the cathodoluminescence spectrum shows strong visible luminescence between 400 and 600 nm wavelengths centered at 450 nm, and the disappearance of an intrinsic emission peak, which has been investigated in detail with the assistance of first-principles calculations. The strategy proposed in this work will pave a solid way for the controlled nucleation and growth of well-aligned GaN nanowire arrays which are significant for applications in large-scale integrated optoelectronic nanodevices, functionalized sensors and photoelectrocatalysis.

Epitaxial growth of aligned MgO nanowire arrays on a single crystalline substrate.

MgO nanostructures with different morphologies were fabricated by regulating the composition of raw materials, using the chemical vapor deposition method with gold as a catalyst. Polycrystalline MgO nanopillars were prepared using only Mg3N2 as the raw material. Single crystalline nanowire arrays can be obtained by adding carbon powder into the raw material. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used for the detailed characterization of (100) nanowire arrays. Besides the vertical growth direction [100], the nanowires change into two kinds of orientations after growing to a certain length: 〈111〉 and 〈001〉. The epitaxial growth was attributed to the lattice match and regulation of the concentration of the Mg source. The variation of growth orientations was probably caused by the difference in surface energy and reaction temperature.

Unveiling low-temperature thermal oxidation growth of W18O49 nanowires with metastable β-W films.

With features of innate tunnels and oxygen vacancies derived from a unique geometrical structure and sub-stoichiometric compositions, W18O49 nanowires have been explored as multifunctional materials with diverse applications. Though thermal oxidation offers a facile method to synthesize patterned W18O49 nanowires, the relatively high growth temperature (≳500 °C) hinders their emerging applications in flexible or wearable electronics. In this work, aiming to lower the growth temperature of W18O49 nanowires by thermal oxidation, the temperature and oxygen partial pressure dependent growth has been systematically investigated for both W films and powders. W18O49 nanowires could be steadily obtained with appropriate temperature and oxygen pressure ranges for both cases, while the growth temperature of a W film (metastable β phase dominant) could be much lower than that of W powder (α phase). The structural analysis indicates that metastable β-W is susceptible to oxidation in comparison with α-W and thus generates oxidation-induced chemical compression for nanowire growth. The growth temperature of W18O49 nanowires could be reduced to ca. 400 °C, which paves the way for the in situ patterning of W18O49 nanowires on indium-tin-oxide (ITO) glass substrates and flexible substrates.

Single-Crystal Nanostructure Arrays Forming Epitaxially through Thermomechanical Nanomolding.

For nanostructures in advanced electronic and plasmonic systems, a single-crystal structure with controlled orientation is essential. However, the fabrication of such devices has remained challenging, as current nanofabrication methods often suffer from either polycrystalline growth or the difficulty of integrating single crystals with substrates in desired orientations and locations to create functional devices. Here we report a thermomechanical method for the controlled growth of single-crystal nanowire arrays, which enables the simultaneous synthesis, alignment, and patterning of nanowires. Within such diffusion-based thermomechanical nanomolding (TMNM), the substrate material diffuses into nanosized cavities under an applied pressure gradient at a molding temperature of ∼0.4 times the material's melting temperature. Vertically grown face-centered cubic (fcc) nanowires with the [110] direction in an epitaxial relationship with the (110) substrate are demonstrated. The ability to control the crystal structure through the substrate takes TMNM a major step further, potentially allowing all fcc and body-centered cubic (bcc) materials to be integrated as single crystals into devices.

Co-electrophoretic deposition of Mn2O3/activated carbon on CuO nanowire array growth on copper foam as a binder-free electrode for high-performance supercapacitors

Co-electrophoretic deposition of Mn2O3/activated carbon on CuO nanowire array growth on copper foam as a binder-free electrode for high-performance supercapacitors

Growth of high-crystallinity uniform GaAs nanowire arrays by molecular beam epitaxy* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61674021, 11674038, 61704011, 61904017, 11804335, and 12074045), the Developing Project of Science and Technology of Jilin Province, China (Grant No. 20200301052RQ), the Project of Education Department of Jilin Province, China (Grant No. JJKH20200763KJ), and the Youth Foundation

The self-catalyzed growth of GaAs nanowires (NWs) on silicon (Si) is an effective way to achieve integration between group III–V elements and Si. High-crystallinity uniform GaAs NW arrays were grown by solid-source molecular beam epitaxy (MBE). In this paper, we describe systematic experiments which indicate that the substrate treatment is crucial to the highly crystalline and uniform growth of one-dimensional nanomaterials. The influence of natural oxidation time on the crystallinity and uniformity of GaAs NW arrays was investigated and is discussed in detail. The GaAs NW crystallinity and uniformity are maximized after 20 days of natural oxidation time. This work provides a new solution for producing high-crystallinity uniform III–V nanowire arrays on wafer-scale Si substrates. The highly crystalline uniform NW arrays are expected to be useful for NW-based optical interconnects and Si platform optoelectronic devices.

Novel fabrication method of hierarchical planar micro-supercapacitor via laser-induced localized growth of manganese dioxide nanowire arrays

Micro-supercapacitors are enormously needed, owing to increasing energy demands in miniaturizing mobile electronic devices. Manganese dioxide (MnO2) is one of the most popular micro-supercapacitor electrode materials that can be applied with various fabrication methods. However, in case of the conventional fabrication of MnO2-based micro-supercapacitor, fabrication methods require complex multiple steps or sophisticated patterning techniques for MnO2 selective micro-patterning. Thus, it is difficult to improve space utilization of micro-supercapacitor and apply them to further another application. In this study, we introduce a novel fabrication method of hierarchical planar micro-supercapacitor using MnO2 nanowire (NW) arrays. Using laser-induced hydrothermal growth (LIHG) process, MnO2 NW arrays are vertically grown on selective area in the desired location under ambient conditions. For the stable growth of vertically aligned MnO2 NW array using LIHG process, various laser parameters, including irradiation time and power, are adjusted. Afterward, the vertically grown MnO2 NW arrays are applied to fabricate hierarchical planar micro-supercapacitor, showing high areal capacitance of 227 mF cm−2 (at 1 mA cm−2) in terms of footprint area on tiny 2D plane. Thus, the proposed approach can be considered as a new fabrication method for capacitance enhancement of planar micro-supercapacitor.

Facile synthesis of RuOx/SiC/C for photoelectrocatalysis

The rapid growth of quasi-aligned SiC nanowire arrays on carbon paper was achieved by an induction heating technique without catalyst assistance. RuOx/SiC/C results in enhanced performance compared to SiC/C toward the photoelectrochemical oxygen evolution reaction.

Control of the asymmetric growth of nanowire arrays with gradient profiles.

A novel electrochemical methodology for the growth of arrays of Ni and Co nanowires (NWs) with linear and non-linear varying micro-height gradient profiles (μHGPs), has been developed. The growth mechanism of these microstructures consists of a three-dimensional growth originating from the allowed electrical contact between the electrolyte and the edges of the cathode at the bottom side of porous alumina membranes. It has been shown that the morphology of these microstructures strongly depends on electrodeposition parameters like the cation material and concentration and the reduction potential. At constant reduction potentials, linear Ni μHGPs with trapezoid-like geometry are obtained, whereas deviations from this simple morphology are observed for Co μHGPs. In this regime, the μHGPs average inclination angle decreases for more negative reduction potential values, leading as a result to more laterally extended microstructures. Besides, more complex morphologies have been obtained by varying the reduction potential using a simple power function of time. Using this strategy allows us to accelerate or decelerate the reduction potential in order to change the μHGPs morphology, so to obtain convex- or concave-like profiles. This methodology is a novel and reliable strategy to synthesize μHGPs into porous alumina membranes with controlled and well-defined morphologies. Furthermore, the synthesized low dimensional asymmetrically loaded nanowired substrates with μHGPs are interesting for their application in micro-antennas for localized electromagnetic radiation, magnetic stray field gradients in microfluidic systems, non-reciprocal microwave absorption, and super-capacitive devices for which a very large surface area and controlled morphology are key requirements.

3D growth of silicon nanowires under pure hydrogen plasma at low temperature (250 °C)

The synthesis of silicon nanowires (SiNWs) is carried out at 250 °C under pure hydrogen plasma from monocrsytalline silicon substrates or amorphous silicon thin film, using indium as a catalyst. Studies have been carried out in function of the duration of the hydrogen plasma. The results showed a growth of smooth surface nanowire arrays (diameter 100 nm, length 500 nm) from an indium thickness of 20 nm and a hydrogen plasma duration of 30 min. The growth of nanowires for longer hydrogen plasma durations has led to SiNWs with larger diameters and rougher surfaces, revealing the onset of secondary nanowire growth on these surfaces, probably due to the presence of indium residues. The results present a new procedure for the 3D solid liquid solid growth mode of SiNWs.

Fishnet-like superstructures constructed from ultrafine and ultralong Ni-MOF nanowire arrays directionally grown on highly rough and conductive scaffolds: synergistic activating effect for efficient and robust alkaline water oxidation activity

The water oxidation efficiency driven by electrocatalysts is related to the energy conversion efficiency of water electrolysis and other systems. It is the key to expose active sites as possible, to fully and firmly contact with other components, and to deliver superior conductivity for the development of high-performance electrocatalysts. Herein, we have fabricated self-supporting Ni-MOF electrode containing three-dimensional (3D) fishnet-like superstructures, which are constructed from in-situ growth of amorphous or poor crystalline Ni-MOF nanowire arrays on highly rough and conductive scaffolds of metallic Ni/carbon cloth (Ni-MOF/Ni/CC). The Ni-MOF/Ni/CC electrode delivers an overpotential of 250 mV at the current density of 10 mA cm−2 (η10). The η10 is maintained at 240 mV after a constant current electrolysis for 32 h, which is much smaller than those of Ni-MOF/CC (423 mV) and Ni/CC (281 mV). The superior activity and robust durability can be attributed to the synergistic activating effect of each component in the superstructures with high density of coordination unsaturated active sites, intimate connection and excellent conductivity. This work can provide a new strategy to develop high-efficiency MOFs-based electrocatalysts for electrocatalytic water oxidation.