Fabrication Of Nanowires Research Articles

Controllable fabrication of nanoplate and nanowire determined by the surface/interface energy on high-temperature liquid metal

Nanomaterials and nanotechnology play an important role in engineering and science, and nanotechnology is constantly innovating. Fabrication of nano-sized oxides has been developed for a long time. As a member of nano-sized oxides, nano-sized transition metal oxides have been studied urgently for their promising applications in lithium-ion batteries. Many cutting-edge works have rendered tremendous smart routes to nanoflakes and nanowires, however a liquid metal strategy remains virgin land by far. Liquid metal has more special properties than other conventional solutions, so it has the foundation and prospect of fabricating nanomaterials. Here, liquid metal rotates speedily, keeping oxygen on surface to formations of Fe3O4 nanosheets and Co3O4 nanowires. The as-prepared nanomaterials can be used as favorable anode materials of lithium-ion batteries. Especially Co3O4 nanowires electrode has good cycle stability (497 ± 1.1 mAh g−1 at a current density of 1 A g−1 after 300 cycles) and favorable rate performance (428 ± 10 mAh g−1 at 1000 mA g−1).

Growth of PbTe nanowires by molecular beam epitaxy

Advances in quantum technology may come from the discovery of new materials systems that improve the performance or allow for new functionality in electronic devices. Lead telluride (PbTe) is a member of the group IV–VI materials family that has significant untapped potential for exploration. Due to its high electron mobility, strong spin–orbit coupling and ultrahigh dielectric constant it can host few-electron quantum dots and ballistic quantum wires with opportunities for control of electron spins and other quantum degrees of freedom. Here, we report the fabrication of PbTe nanowires by molecular beam epitaxy. We achieve defect-free single crystalline PbTe with large aspect ratios up to 50 suitable for quantum devices. Furthermore, by fabricating a single nanowire field effect transistor, we attain bipolar transport, extract the bandgap and observe Fabry–Pérot oscillations of conductance, a signature of quasiballistic transmission.

Ultra-high strength yet superplasticity in a hetero-grain-sized nanocrystalline Au nanowire

• Nanocrystalline nanowire always exhibits strength-ductility trade-off. Here, we provide in situ atomic-scale evidence that hetero-grain-sized nanocrystalline nanowires are simultaneously ultra-strong and ductile, with no strength-ductility trade-off. • The hetero-grain-sized nanocrystalline nanowire exhibits a super uniform elongation of ∼ 236% and high strength of ∼ 2.34 gigapascals at room temperature. • The in situ atomic-scale observations revealed that the dislocation activities, grain boundary plasticity, and surface atoms diffusion all contribute to the super elongation ability of hetero-grain-sized nanocrystalline nanowire. Nanocrystalline metals often display a high strength up to the gigapascal level, yet they suffer from poor plasticity. Previous studies have shown that the development of hetero-sized grains can efficiently overcome the strength-ductility trade-off of nanocrystalline metals. However, whether this strategy can lead to the fabrication of nanocrystalline nanowires exhibiting both high strength and superplasticity is unclear, similar to the atomistic deformation mechanism. In this paper, we show that ultra-small nanocrystalline Au nanowires comprising grains in both the Hall–Petch and inverse Hall–Petch grain-size regions can exhibit extremely high uniform elongation (236%) and high strength (2.34 gigapascals) at room temperature. In situ atomic-scale observations revealed that the plastic deformation underwent two stages. In the first stage, the super-elongation ability originated from the intergrain plasticity of small grains via mechanisms such as grain boundary migration and grain rotation. This intergrain plasticity caused the grains in the heterogeneous-structured nanowires to grow very large. In the second stage, the super-elongation ability originated from intragrain plasticity accompanied by the diffusion of surface atoms. Our results show that the hetero-grain-sized nanocrystalline nanowires, comprising grains with sizes both in the strongest Hall–Petch effect region and the inverse Hall–Petch effect region, were simultaneously ultra-strong and ductile. They displayed neither a strength-ductility trade-off nor plastic instability.

Novel Fabrication of Silver-Coated Copper Nanowires with Organic Compound Solution.

Copper nanowires and Cu-Ag nanowires have various potential applications, such as transparent conductive film, flexible electronics, and conductive filler. In this study, we developed a new green fabrication method for silver-coated copper nanowires using methylsulfonylmethane (DMSO2), which is an environmentally friendly chemical at the food-grade level, to replace toxic chemicals, including ammonia, in the silver coating process. Copper nanowires were synthesized under various reaction temperatures and concentrations of hydrazine (N2H4), ethylenediamine (EDA), sodium hydroxide (NaOH), and copper precursor. The reaction temperature higher than 70 °C caused the oxidation of copper products and evaporation of the sample solution. The optimal conditions to synthesize copper nanowires more than 18 µm in length and 25–45 nm in diameter were determined: 9 M of NaOH, 50 µL of EDA, 17 mM of CuCl2, 5.7 mM of N2H4, and 70 °C reaction temperature. Cu-Ag nanowires, which have about a 12 nm thick silver shell, were successfully fabricated at room temperature under 1 mM of silver nitrate (AgNO3) and 1 wt % of DMSO2. Synthesis conditions for copper and silver-coated copper nanowires have been optimized.

Wet-based digital etching on GaN and AlGaN

Many advanced III-nitride devices, such as micro-LEDs, vertical FinFETs, and field emitters, require the fabrication of high aspect ratio vertical pillars or nanowires. Two-step etchings combining dry and wet etching steps have been used on vertical devices in the past, but they show poor control in vertical nanostructures with sub-50 nm diameter. In this work, we demonstrate a wet-chemical digital etching on GaN and AlGaN and apply it to both vertical nanostructure scaling and planar etching along the c-axis. In this digital etching process, a mixture of H2SO4 and H2O2 is applied to oxidize the III-nitrides surface, and the oxide layer is then removed by dilute HCl. This digital etching approach can finely sharpen vertical structures and does not require any vacuum or plasma systems, which will enable advanced device structures in the future.

Ammonia sensing by silicon nanowires (SINWs) obtained through metal assisted electrochemical etching

Present work reports fabrication of silicon nanowires (SINWs) through metal-assisted electrochemical etching. The process of etching is carried out with the help of dc current supplied through Agilent 6634B dc power supply on silver electroplated silicon(Si) wafer. The method provides ordered SINWs with larger surface area. Morphology, as seen from FESEM shows vertically aligned bunched SINWs of average length of 23µm with porous structure of finely distributed pores over the surface. Electrochemically etched SINWs shows high sensitivity to gas/vapors due to its highly porous nature, by capturing the gas molecules through voids present on the surface. In the present work different vapors viz. acetone, chloroform and ammonia are tested. Among these SINWs are seen to be fairly selective to ammonia. Ammonia sensing measurements are done for gas concentrations from 10 to 100 ppm. Sensitivity of the sensor increases with increasing concentrations. Electrical conductivity of SINWs is reduced in presence of ammonia. The experimental results highlight fair response and recovery times with good correlation coefficient to ensure prospect of developing SINWs based gas sensor for possible utilization in the medical and environmental fields, for example.

Regioselective fabrication of gold nanowires using open-space laminar flow for attomolar protein detection.

Gold nanowires are expected to be applied to biosensing due to their advantages, such as high stability and biocompatibility. However, it is still inconvenient to fabricate a single gold nanowire at a precise position, and without a special demanding environment. In this study, we present an open-space laminar flow approach for fabricating a single gold nanowire at a precise position under normal conditions. The fabricated gold nanowire demonstrated excellent biosensing of IgA with an extremely low limit of detection (1 aM).

Removal of Ag remanence and improvement in structural attributes of silicon nanowires array via sintering

Metal-assisted chemical etching (MACE) is popular due to the large-area fabrication of silicon nanowires (SiNWs) exhibiting a high aspect ratio at a low cost. The remanence of metal, i.e., silver nanoparticles (AgNPs) used in the MACE, deteriorates the device (especially solar cell) performance by acting as a defect center. The superhydrophobic behavior of nanowires (NWs) array prohibits any liquid-based solution (i.e., thorough cleaning with HNO3 solution) from removing the AgNPs. Thermal treatment of NWs is an alternative approach to reduce the Ag remanence. Sintering temperature variation is chosen between the melting temperature of bulk-Ag (962 °C) and bulk-Si (1412 °C) to reduce the Ag particles and improve the crystallinity of the NWs. The melting point of NWs decreases due to surface melting that restricts the sintering temperature to 1200 °C. The minimum sintering temperature is set to 1000 °C to eradicate the Ag remanence. The SEM–EDS analysis is carried out to quantify the reduction in Ag remanence in the sintered NWs array. The XRD analysis is performed to study the oxides (SiO and Ag2O) formed in the NWs array due to the trace oxygen level in the furnace. The TG-DSC characterization is carried out to know the critical sintering temperature at which remanence of AgNPs removes without forming any oxides. The Raman analysis is studied to determine the crystallinity, strain, and size of Si nanocrystals (SiNCs) formed on the NWs surface due to sidewalls etching. An optimized polynomial equation is derived to find the SiNCs size for various sintering temperatures.

Fabrication and characterization of well-ordered PbS nanowires in aluminum oxide template by sulfurization and vacuum injection molding processes

Lead (Pb) nanowire arrays were fabricated with anodic aluminum oxide (AAO) templates of 30, 100 and 300 nm in pore diameters. Through vacuum injection molding process, Pb/AAO composite was obtained, and lead sulfide (PbS) could further be synthesized after exposing to sulfur gas. AAO templates with different pore sizes were fabricated by using pure aluminum in a two-step anodization. Three types of solutions, which are 10 vol% sulfuric acid, 3 wt% oxalic acid and 1 vol% phosphoric acid, were adopted to achieve AAO of various pore sizes. Different sulfurization temperatures and time spans were applied for studying on the formation mechanism of PbS. Finally, the morphology, composition, structure and elements distribution of the as-prepared Pb and PbS nanowires were confirmed through the use of scanning electron microscopy, energy dispersive x-ray spectroscopy, element-mapping, x-ray diffraction and transmission electron microscopy analysis. The results indicated that Pb nanowires were successfully obtained after applying vacuum injection molding process with 50 kgf cm−2 hydraulic pressure, and PbS nano arrays can be formed by sulfurization at 500 °C for 5 h. Furthermore, an optical property, ultraviolet–visible (UV–Vis) absorption, was also measured. The measurement of the PbS nanowires showed that a significant quantum confinement effect made the energy gap produce a blue shift from 0.41 eV to 1.65 eV or 1.72 eV.

Fabrication of MnO2 nanowires and their nanohybrid with flat conductive matrix for the treatment of industrial effluents

In recent times, nanostructured semiconductive materials and nanohybrid with flat (2D) MXene sheets have gained considerable attention for photocatalytic applications. Here, we fabricated MnO2 nanowires (NWs, 1D) and their nanohybrid with MXene, as an innovative photocatalyst, to remove organic pollutants (organic dyes) and bacteria from industrial effluents. Indeed, MXene has excellent surface properties, owing to its flat structure. However, it's higher affinity to restack and oxidize is the problem that masks its other inherent features. We developed an innovative design to improve the stability of MXene and to reduce the resistivity and photocorrosion of semiconductive photocatalysts. The crystalline structure, morphology, specific surface area, thermal stability, and nanohybrid formation between MnO2 and MXene have been analyzed and confirmed via well-established conventional and advanced techniques. The prepared materials' photocatalytic and antimicrobial properties were evaluated under solar illumination using crystal violet (CV) dye and a Staphylococcus aureus(S.aureus) bacterial strain, respectively. Compared to pure MnO2 and MXene/MnO2 nanohybrid photocatalysts, H2O2-supported MXene/MnO2 nanohybrid demonstrated significantly greater photocatalytic activity for CV dye elimination. After 50 min of continuous illumination, the MXene/MnO2@H2O2 photocatalyst demonstrated approximately 91.5% dye degradation at a rate constant (0.045 min−1) higher than MnO2 (0.025 min−1) and MXene/MnO2 (0.029 min−1). The current work demonstrates that the MXene/MnO2 nanohybrid photocatalyst is capable of photodegrading dyes efficiently and inhibiting the rapid growth of microbes found in industrial discharges.

Comparative study of quantum confinements effect present in Silicon Nanowires using absorption and Raman spectroscopy

Silver-induced chemical etching (SIE) has been widely explored for developing silicon (Si) based photovoltaic devices with its benefits for low-cost and large-area fabrication of silicon nanowires (SiNWs) of high aspect ratios. Structures and optical properties of SiNWs fabricated through chemical etching are significantly affected by experimental as well as environmental conditions of etching. A comparative study of quantum confinement (QC) effect due to variation in nano crystallite size (NCS) of SiNWs samples, fabricated by SIE technique has been investigated here using ultraviolet visible (UV-VIS) spectroscopy and Raman spectroscopy. An enhanced optical band gap has been observed from the samples under UV excitation at room temperature due to QC effect. To improve the understanding of basic mechanism of QC effect present in samples has been analyzed through characteristic features of Raman line-shape like red shift, asymmetry ratio and broadening as compared to its bulk counterpart. The NCS of SiNWs present in the samples has been calculated by QC based Brus model, bond polarizability (BP) model and Raman line-shape fitting model. This study prove itself to explore a new direction towards a systematic building block for fabricating optoelectronic devices based on light - matter interactions present at the nano-scale. • Silicon nanowires (Si-NWs) onn type-Si(100) by silver-induced chemical etching. • Results obtained, indicate that the fabrication of size controlled Si-NWs. • Quantum confinements effectobserved in Si-NWs using Brus, bond polarizability and line shape model. • Estimated size from Brus and bond polarizability model using PL and Raman data were around 1.7–3.2 nm. • Theoretical estimation of size from line shape model were 2.66–3.16 nm.

Fabrication of GaN nanowires containing n+-doped top layer by wet processes using electrodeless photo-assisted electrochemical etching and alkaline solution treatment

We attempted to fabricate GaN nanowires by electrodeless photo-assisted electrochemical (PEC) etching and successive alkaline solution treatment. The sample consisting of n+-doped and unintentionally doped GaN grown on a GaN substrate was selectively etched using a Ti mask in a mixed solution of K2S2O8 and KOH under UV light radiation. This specific layer structure required a relatively concentrated KOH solution for etching. The PEC etching resulted in the formation of a tapered cone structure of GaN with its top diameter determined by the mask size. Successive KOH treatment after PEC etching yielded GaN nanowires with diameters of about 220 nm.

Fabrication and field emission properties of vertical, tapered GaN nanowires etched via phosphoric acid

The controlled fabrication of vertical, tapered, and high-aspect ratio GaN nanowires via a two-step top-down process consisting of an inductively coupled plasma reactive ion etch followed by a hot, 85% H3PO4 crystallographic wet etch is explored. The vertical nanowires are oriented in the direction and are bound by sidewalls comprising of semipolar planes which are at a 12° angle from the [0001] axis. High temperature H3PO4 etching between 60 °C and 95 °C result in smooth semipolar faceting with no visible micro-faceting, whereas a 50 °C etch reveals a micro-faceted etch evolution. High-angle annular dark-field scanning transmission electron microscopy imaging confirms nanowire tip dimensions down to 8–12 nanometers. The activation energy associated with the etch process is 0.90 ± 0.09 eV, which is consistent with a reaction-rate limited dissolution process. The exposure of the type planes is consistent with etching barrier index calculations. The field emission properties of the nanowires were investigated via a nanoprobe in a scanning electron microscope as well as by a vacuum field emission electron microscope. The measurements show a gap size dependent turn-on voltage, with a maximum current of 33 nA and turn-on field of 1.92 V nm−1 for a 50 nm gap, and uniform emission across the array.

Fabrication and characterization of CdS nanowires templated in tobacco mosaic virus with improved photocatalytic ability.

Using a virus as a template to synthesize nanomaterial is a simple, green, and controllable method to acquire unique structure nanoparticles. In this study, CdS nanowires were synthesized using the tobacco mosaic virus (TMV) as a template and for deposition in the inner center channel of TMV. TMV/CdS was successfully characterized, with the results showing a diameter of 4.0 nm, a cubic-phase composition, and strong fluorescence emission peaks, with an absorption edge of 566 nm and bandgap energy of 2.28 eV. The bandgap energy is narrower than that of template-free CdS. Furthermore, TMV/CdS exhibited an increased transient photocurrent, which was attributed to the effective separation of electron-hole pairs. The photoactivities of TMV/CdS and template-free CdS were tested; the results showed that the TMV/CdS had a better performance in methylene blue (MB) photodegradation, indicating that the photoactivity of TMV/CdS was higher than that of the template-free CdS. Further research on TMV/CdS regarding the photocatalytic mechanism showed that O2•- and •OH were the major species involved in photocatalysis, rather than holes (h+). Therefore, TMV/CdS might have applications as a novel visible-light-responsive photocatalyst. KEY POINTS: • CdS nanowires were firstly synthesized in the inner center channel of TMV • TMV/CdS presented higher photocatalytic efficiency compared with template-free CdS • The O2•- and •OH were responsible for the photocatalytic reaction of TMV/CdS.

Fabrication, Characterization and Photocatalytic Activity of Copper Oxide Nanowires Formed by Anodization of Copper Foams.

In recent paper anodization of copper foams in 0.1 M K2CO3 is reported. Anodization was performed in the voltage range of 5–25 V and in all the cases oxides with a developed surface area were obtained. However, anodizing only at 20 and 25 V resulted in the formation of nanostruc-tures. In all the cases, the products of anodizing consisted of crystalline phases like cuprite (Cu2O), tenorite (CuO), parameconite (Cu4O3) as well as spertiniite (Cu(OH)2). Copper foams after ano-dizing were applied as catalysts in the photocatalytic decolorization of a model organic compound such as methylene blue. The highest photocatalytic activity was observed for samples anodized at 25 V and closely followed by samples anodized at 5 V. The anodized copper foams proved to be a useful material in enhancing the photocatalytic efficiency of organic dye decomposition.

Fabrication of Needle-Like Silicon Nanowires by Using a Nanoparticles-Assisted Bosch Process for Both High Hydrophobicity and Anti-Reflection.

In this work, a modified Bosch etching process is developed to create silicon nanowires. Au nanoparticles (NPs) formed by magnetron sputtering film deposition and thermal annealing were employed as the hard mask to achieve controllable density and high aspect ratios. Such silicon nanowire exhibits the excellent anti-reflection ability of a reflectance value of below 2% within a broad light wave range between 220 and 1100 nm. In addition, Au NPs-induced surface plasmons significantly enhance the near-unity anti-reflection characteristics, achieving a reflectance below 3% within the wavelength range of 220 to 2600 nm. Furthermore, the nanowire array exhibits super-hydrophobic behavior with a contact angle over ~165.6° without enforcing any hydrophobic chemical treatment. Such behavior yields in water droplets bouncing off the surface many times. These properties render this silicon nanowire attractive for applications such as photothermal, photocatalysis, supercapacitor, and microfluidics.

Surface-Tailored InP Nanowires via Self-Assembled Au Nanodots for Efficient and Stable Photoelectrochemical Hydrogen Evolution.

With a band gap close to the Shockley-Quiesser limit and excellent conduction band alignment with the water reduction potential, InP is an ideal photocathode material for photoelectrochemical (PEC) water reduction. Here, we develop facile self-assembled Au nanodots based on dewetting phenomena as a masking technique to fabricate wafer-scale InP nanowires (NWs) via a top-down approach. In addition, we report dual-function wet treatment using sulfur-dissolved oleylamine (S-OA) to remove a plasma-damaged surface in a controlled manner and stabilize InP NWs against surface corrosion in harsh electrolyte solutions. The resulting InP NW photocathodes exhibit an excellent photocurrent density of 33 mA/cm2 under 1 sun illumination in 1 M HCl with a highly stabilized performance without needing additional protection layers. Our approach combining large-area NW fabrication and surface engineering synergistically enhances light harvesting and PEC performance and stability, thereby providing a pathway for the development of efficient and durable InP photoelectrodes in a scalable manner.

Controllable fabrication of polymeric nanowires by NIL technique and self-assembled AAO template for SERS application

A controllable strategy to fabricate the polymeric nanowires with high throughput and low cost is developed by using the thermal nanoimprint lithography (NIL) technique and self-assembled anodic aluminum oxide (AAO) template. The length of polymeric nanowires can be controlled by adjusting the duration of thermal NIL. A fill mechanism of thermoplastic intermediate polymer stamp (IPS) polymer pressed into the AAO nanopores is closely studied. The as-prepared IPS polymeric nanowire-based Surface-Enhanced Raman Scattering (SERS)-active substrate exhibits a remarkable reproducibility. The effective adsorption of the R6G as probe molecule near to hotspots generated at 3D vertically aligned polymeric nanowire SERS active substrates shows extraordinary enhancement of Raman signal with an enhancement factor (EF) of 105–106. The present strategy is of great guiding significance to broaden the use of thermal NIL technique and AAO template for the fabrication of other nanomaterials, especially for the flexible and transparent polymer-based nanomaterials.

Evaluation of 1-dimensional nanomaterials release during electrospinning and thermogravimetric analysis.

The growing research interests with engineered nanomaterials in academic laboratories and manufacturing facilities pose potential safety risks to students and workers. New nanoparticle substances, compositions, and processing approaches are developed regularly, creating new health risks which may not have been addressed previously. Accordingly, the Institute of Occupational Medicine conducted field studies at Texas A&M University (TAMU) to characterize possible particle emissions during processing and fabrication of carbon nanotubes, copper nanowires, and polymeric fibers. The nature of the monitoring work carried out at TAMU was to investigate the potential release of 1D nanomaterials to air from activities associated with synthesis, handling, thermal gravimetric analysis, and electrospinning processes, and evaluate the effectiveness of the utilized control measures. The potential nanoparticle release to air from each activity was investigated using a combination of particle detection instrumentations, coupled with standard filter-based sampling techniques. The analyses indicated that a measurable quantity of free carbon nanosphere aggregates was detected during these activities; however, no free MWCNTs or nanowires were detected. Scanning electron microscopy identified the presence of carbon nanospheres aggregates on the filters. While the control measures used at TAMU are effective in containing the nanomaterial release during processing, poor handling and occupational hygiene practices can increase the risk of employee exposure to the nanomaterials.

Sensitive pH measurement using EGFET pH-microsensor based on ZnO nanowire functionalized carbon-fibers

Herein, we report the fabrication of zinc oxide nanowire (ZnO NW) coated carbon fiber (CF) ultra-microelectrodes (UME). ZnO NWs were grown on commercial multifilament CFs through hydrothermal process in a teflon-lined autoclave at 90 °C for 4 h. X-ray diffraction (XRD), Raman and scanning electron microscopy characterizations showed that crystalline and well oriented NW structures were successfully obtained. The fabrication of the pH sensitive UME was carried out by a novel approach which allowed controlling the protruding length of the modified CF surface. The UME was then integrated with a metal-oxide-semiconductor field effect transistor (MOSFET) for the construction of an EGFET pH-microsensor. The present pH microsensor is expected to be useful for localized pH measurement in small volumes such single cell analysis.