Formation Of Nanowires Research Articles

Double loop-stem hairpins mediated hybridization chain reaction: A multifunctional DNA molecular tool to produce the intact aptamer for label-free biosensing

A DNA molecular tool based on the double loop-stem (DL) hairpins mediated hybridization chain reaction (D-HCR) system was proposed to produce the intact G-quadruplex (InG4) aptamers for enzyme-free and label-free biosensing. The D-HCR system was triggered by targets to produce the cross-sequential nanowires of double-stranded and single-stranded DNA (DS nanowire) through the alternating strand displacement events of DL hairpins. Unlike the split G4 (SpG4) aptamers in current HCR, the formation of DS nanowires was accompanied by the release of previously locked InG4 aptamers. Impressively, we tested that the fluorescence enhancement effect of InG4 aptamer on Thioflavin T (ThT) was16.49-fold higher than that of the SpG4 aptamer. To demonstrate the flexibility of the InG4 aptamer-based D-HCR system, we established a fluorescence biosensor depending on the fluorescence enhancement of InG4/ThT with a detection limit of 4.60 pM, and a colorimetric biosensor relying on the catalytic activity of InG4/Hemin with a detection limit of 13.60 pM. The abovementioned biosensors showed high specificity against interfering miRNAs and excellent detection performance in living cells and lysates. Our D-HCR system provides an avenue for preparing DS nanowires to produce the intact aptamer in each hairpin, which may be valuable to prompt the development of HCR-aptamer technique.

(Invited) The Impact of Interface Layer on Li Plating and Stripping Morphology

Li metal is the preferred anode material for high energy Li batteries. However, a stable plating and stripping of Li metal at the anode−solid electrolyte interface (SEI) remains a significant challenge, particularly at practically feasible current densities. The formation of the SEI layer can significantly change the Li-nucleation density and growth morphology. With multiscale modeling, these factors can be investigated in more detail. Upon, lithiation, while a classical nucleation and growth model can describe the nucleation density of Li clusters and the charging rates in ultrahigh vacuum, a trace amount of reactive gas (oxygen for example) can change Li growth morphology. Reactive molecular dynamics simulations revealed that the fine balance between Li growth rate and the reaction rate of the thin lithium-oxide shell on the surface of the metallic Li can lead to Li nanowire formation. During delithiation, the accumulation of Li vacancies can lead to void generation and interface delamination. A DFT-informed kinetic Monte Carlo (KMC) model was developed to investigate the impact of the SEI layer, stack pressure, and alloying effects. The contact area is then incorporated into a 1D Newman battery model to simulate the impact of the contact area on the battery performance.

The Diffusion Mechanism of Ge During Oxidation of Si/SiGe Nanofins.

A recently discovered, enhanced Ge diffusion mechanism along the oxidizing interface of Si/SiGe nanostructures has enabled the formation of single-crystal Si nanowires and quantum dots embedded in a defect-free, single-crystal SiGe matrix. Here, we report oxidation studies of Si/SiGe nanofins aimed at gaining a better understanding of this novel diffusion mechanism. A superlattice of alternating Si/Si0.7Ge0.3 layers was grown and patterned into fins. After oxidation of the fins, the rate of Ge diffusion down the Si/SiO2 interface was measured through the analysis of HAADF-STEM images. The activation energy for the diffusion of Ge down the sidewall was found to be 1.1 eV, which is less than one-quarter of the activation energy previously reported for Ge diffusion in bulk Si. Through a combination of experiments and DFT calculations, we propose that the redistribution of Ge occurs by diffusion along the Si/SiO2 interface followed by a reintroduction into substitutional positions in the crystalline Si.

Ultrasensitive p-n junction UV-C photodetector based on p-Si/β-Ga2O3 nanowire arrays

Ultrasensitive UV-C photodetector (PD) based on β-Ga2O3 nanowires (NWs) were fabricated on p-type Si substrate using glancing angle deposition technique inside RF/DC sputtering chamber. The formation of well-aligned NWs with an average length of ~ 270 nm was confirmed with the help of field emission scanning electron microscope (FE-SEM) images. Also, the fabricated β-Ga2O3 NWs array were polycrystalline in nature. Furthermore, a good photo absorption and photoemission were obtained from the fabricated sample. The PD fabricated using β-Ga2O3 NW operated in the UV-C region (275 nm) with a recorded responsivity of 31.71 A/W, detectivity of 1.37×1012 Jones and an NEP of 2.44×10−12 W at + 5 V. Additionally, the PD was able to respond at a very low power light of 6.37 µW/cm2. The transient response of the fabricated device shows a rise time and fall time of 0.18 s and 0.25 s respectively. The high performance was attributed to the strong p-n junction which could separate the photogenerated carriers efficiently.

Controllable synthesis of BiPr composite oxide nanowires electrocatalyst for sensitive L-cysteine sensing properties

BiPr composite oxide nanowires with rhombodedral Bi1.35Pr0.65O3, monoclinic Bi2O3 and monoclinic Pr5O9 phases were synthesized via a facile sodium dodecyl sulfate (SDS) assisted hydrothermal route. The obtained nanowires were characterized by x-ray diffraction, electron microscopy, x-ray photoelectron spectroscopy and electrochemical measurements. The BiPr composite oxide nanowires possess poly-crystalline structure, semi-circular tips, diameter and length of 20–100 nm and several micrometers, respectively. SDS is essential for the formation of the BiPr composite oxide nanowires which can be explained by a SDS assisted hydrothermal growth process. Electrochemical impedance spectroscopy shows that the electrons are easier to transfer by the surface of the BiPr composite oxide nanowires modified glassy carbon electrode (GCE) than bare GCE. The BiPr composite oxide nanowires modified GCE possesses good electro-catalytic activity for L-cysteine detection with a pair of quasi-reversible cyclic voltammetry peaks at +0.04 V and –0.72 V for the oxidation and reduction of L-cysteine, respectively. The roles of the scan rate, electrolyte species and L-cysteine concentration on the electrochemical responses of L-cysteine at the nanowires modified GCE were systematically analyzed. The BiPr composite oxide nanowires modified GCE presents a linear response range from 0.001 to 2 mM and detection limit of 0.27 μM, good reproducibility and stability.

High Performance UV-A Detector Using Axial n-ZnO/p-CuO p-n Junction Heterostructure Nanowire Arrays

UV-A photodetector (PD) based on axial n-ZnO/p-CuO heterostructure (HS) nanowires (NWs) array was fabricated using GLAD (glancing angle deposition) technique. The high resolution transmission electron microscope (HR-TEM) images confirmed the formation of axial HS NWs. The PD shows a high rectification ratio of ~ 278, with low dark current of 0.49 nA (at –1V) and fast photoresponse with rise time and fall time of 0.18 ms and 0.24 ms respectively. A high detectivity of (0.05 TJones) and low noise equivalent power of (70 pW) was also observed at +3 V for the proposed device.

A Facile Method for the Fabrication of Luminescent Eu3+-Doped SiO2 Nanowires.

Europium trivalent ion (Eu3+)-doped silica nanowires were prepared, and the positioning of Eu3+ in the silicon dioxide nanowire matrix was researched. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD) and energy-dispersive X-ray spectroscope analysis (EDX) were used to characterize the product’s morphology and structure. The representation of Fourier transform infrared spectra (FT-IR) and X-ray photoelectron spectroscopy (XPS) were indicative of the presence of a covalent Eu-O-Si bond. The results suggest that Eu3+ was successfully doped into amorphous silica. Furthermore, a sol-gel inorganic−organic co-assembly mechanism model was proposed to illuminate the formation of the rare-earth ion-doped nanowires. In addition, photoluminescent emission of europium ions in a silica matrix was further discussed. It was demonstrated that a 10% content of Eu3+ resulted in a quenching effect and after annealing at 650 °C, the europium ions in the nanowires had a high luminescence intensity due to the silica network structure.

Формування одновимірних оксидних наноструктур шляхом проміжного осадження благородних металів

A method for forming the geometry of one-dimensional nanostructures (nanowires) of copper oxide is proposed, which allows for a significant increase in the ratio of their length to diameter, which is critical for certain practical applications. The essence of the method is that after reaching the saturation regime of the dependence of the length of the nanowire on the time of its growth, the stage of deposition of precious metal (gold) is realized, the nanoparticles of which are fixed on the side surface of the nanowire. In the saturation mode, the entire flow of copper atoms moving from the root to the top of the nanowire reacts on the side surface of the nanowire due to collisions with oxygen molecules adsorbed by this surface. But the presence of a metal that does not react with oxygen significantly reduces the concentration of the latter on the side surface of the nanowire. The presence of a noble metal, which covers most of the nanowire, significantly reduces the intensity of the oxidation reaction of copper on the side of the nanowire, thus lengthening the diffusion path of copper from root to tip of the nanowire, thereby increasing its length. Therefore, after the stage of intermediate deposition, the growth process of the nanowires is restored. The process of intermediate deposition of unreacted metal can be applied more than once, which allows for flexible control of the process of nanowire formation. From the viewpoint of the general productivity of the process, it is critical to use plasma to implement the process of nanowire growth because it is the processes in the plasma environment that are characterized by the rapid achievement of the saturation mode of time dependence, which is proven experimentally. As a result, the overall productivity of the combined process using the intermediate deposition of the noble metal can be accelerated up to five times compared to the currently common thermal growth processes. Calculations using a modified mathematical model of growth of one-dimensional nanostructures of copper oxide in a thermal reactor, which is used to predict growth in plasma under atmospheric pressure (radiofrequency, capacitive, etc.), where conditions are similar to thermal growth. The method is general and can be applied to other growth processes that depend on the reactions on the surfaces of nanostructures.

Silver nanoparticles with vanadium oxide nanowires loaded into electrospun dressings for efficient healing of bacterium-infected wounds

Silver nanoparticles (AgNPs) have been widely recognised as effective antibacterial materials in textiles for enhancing wound healing. However, high loadings of AgNPs are toxic and expensive. Thus, it is ideal to prepare AgNPs in a favourable nanostructure for stable and effective conjugation with the textile carrier by selecting a reductant and stabiliser that contributes to the antibacterial effect. Here, silver nanoparticles/vanadium oxide nanowires (Ag/VOx NWs) were prepared via a one-step reduction strategy using vanadium oxide quantum dots (VOx QDs) as both the reductant and stabiliser. VOx QDs possess antibacterial properties, which aid in minimising the applied silver content while enhancing bactericidal performance. Silver can self-aggregate into nanoparticles as well as promote the formation of vanadium oxide nanowires (VOx NWs). Accordingly, the Ag/VOx NWs exhibited remarkable antibacterial effects against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The nanowire structure of the Ag/VOx NWs was favourable for effective loading into a sodium alginate (SA) gel fabric to form a wound dressing. The effective loading of Ag/VOx NWs on SA was conducive to the complete dispersion of the bacteriostatic agent and enhanced the antibacterial activity of AgNPs. The wound dressing efficiently suppressed the growth of wound bacteria and promoted wound healing in vivo.

Chemical Vapor Deposition-Fabricated Manganese-Doped and Potassium-Doped Hexagonal Tungsten Trioxide Nanowires with Enhanced Gas Sensing and Photocatalytic Properties.

Owing to its unique and variable lattice structure and stoichiometric ratio, tungsten oxide is suitable for material modification; for example, doping is expected to improve its catalytic properties. However, most of the doping experiments are conducted by hydrothermal or multi-step synthesis, which is not only time-consuming but also prone to solvent contamination, having little room for mass production. Here, without a catalyst, we report the formation of high-crystallinity manganese-doped and potassium-doped tungsten oxide nanowires through chemical vapor deposition (CVD) with interesting characterization, photocatalytic, and gas sensing properties. The structure and composition of the nanowires were characterized by transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS), respectively, while the morphology and chemical valence were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. Electrical measurements showed that the single nanowires doped with manganese and potassium had resistivities of 1.81 × 0−5 Ω·m and 1.93 × 10−5 Ω·m, respectively. The doping contributed to the phase transition from monoclinic to metastable hexagonal for the tungsten oxide nanowires, the structure of which is known for its hexagonal electron channels. The hexagonal structure provided efficient charge transfer and enhanced the catalytic efficiency of the tungsten oxide nanowires, resulting in a catalytic efficiency of 98.5% for the manganese-doped tungsten oxide nanowires and 97.73% for the potassium-doped tungsten oxide nanowires after four hours of degradation of methylene blue. Additionally, the gas sensing response for 20 ppm of ethanol showed a positive dependence of doping with the manganese-doped and potassium-doped responses being 14.4% and 29.7%, respectively, higher than the pure response at 250 °C. The manganese-doped and potassium-doped tungsten oxide nanowires are attractive candidates in gas sensing, photocatalytic, and energy storage applications, including water splitting, photochromism, and rechargeable batteries.

A novel high performance photodetection based on axial NiO/β-Ga2O3 p-n junction heterostructure nanowires array

Axial NiO/β-Ga2O3 heterostructure (HS) nanowires (NWs) array was fabricated on Si substrate by catalytic free and controlled growth process called glancing angle deposition technique. The field emission scanning electron microscope image shows the formation of well aligned and vertical NWs. A typical high resolution transmission electron microscope image confirms the formation of axial HS NWs consisting of β-Ga2O3 NW at the top and NiO NW at the bottom with an overall length ∼213 nm. A large photo absorption and also photoemission was observed for axial NiO/β-Ga2O3 HS NW as compared to the NiO/β-Ga2O3 HS thin film sample. Moreover, x-ray photoelectron spectroscopy analysis prove that there are higher oxygen vacancies with no deviation in electronic state after the formation of axial HS NW. Also, a high performance photodetector (PD) with a very low dark current of 6.31 nA and fast photoresponse with rise time and fall time of 0.28 s and 0.17 s respectively at +4 V was achieved using the axial NiO/β-Ga2O3 HS NWs. The type-II HS p-n junction formation and efficient charge separation at the small wire axis also makes this design to operate in self-powered mode.

Implementing the Reactor Geometry in the Modeling of Chemical Bath Deposition of ZnO Nanowires.

The formation of nanowires by chemical bath deposition is of great interest for a wide variety of optoelectronic, piezoelectric, and sensing devices, from which the theoretical description of their elongation process has emerged as a critical issue. Despite its strong influence on the nanowire growth kinetics, reactor size has typically not been taken into account in the theoretical modeling developed so far. We report a new theoretical description of the axial growth rate of nanowires in dynamic conditions based on the solution of Fick’s diffusion equations, implementing a sealed reactor of finite height as a varying parameter. The theoretical model is applied in various chemical bath deposition conditions in the case of the growth of ZnO nanowires, from which the influence of the reactor height is investigated and compared to experimental data. In particular, it is found that the use of reactor heights smaller than 2 cm significantly decreases the ZnO nanowires’ axial growth rate in typical experimental conditions due to the faster depletion of reactants. The present approach is further used predictively, showing its high potential for the design of batch reactors for a wide variety of chemical precursors and semiconductor materials in applied research and industrial production.

Influence of reaction temperature on phase assemblage and morphologies of SiC nanowires by a carbothermal reduction method

3C-SiC nanowires were synthesized using Si, SiO2, and active carbon as raw materials at different reaction temperatures without additional metal catalysts. The influence of reaction temperature on the phase assemblage and morphologies of the products were investigated by XRD and SEM. The experimental results indicate that a suitable reaction temperature is essential for the final products. When the reaction temperature was not high enough (1400 and 1450∘C), the raw materials were not reacted completely, and a small amount of targeted nanowires were formed. When reaction temperature increased to 1500∘C, the nanowires were mainly composed of 3C-SiC phase, and they were straight, curved, and needle-shaped. The straight nanowires ranged from several to tens of microns, but the diameters were not uniform. The vapor-solid mechanism dominantly governed the formation of SiC nanowires.

Low-temperature-fabrication and the preferred growth mechanism of Ag nanowires for stabling SnO2 film

A low-temperature-fabrication of Ag nanowires (NWs) was introduced for cost cutting and safety. Nucleating at room temperature (RT) for about 6 h and growing at 50–70 ℃ favored the formation of Ag NWs with the aspect ratio of more than 1000. The preferred growth mechanism of Ag NWs was the stacking of (220) or (2 2¯ 0) planes, which were the twinning planes of high-density twin crystals. Coating the as-prepared Ag NWs on the surface of SnO2 transparent semiconductor film and heat treating the bilayer film at 200–300 °C, the adhesion property and conductive performance of SnO2 film were significantly enhanced.

Atomistic mechanism effects on the growth of GaAsBi and GaAs nanowires

Kinetic Monte Carlo (KMC) simulations were developed to describe all the kinetic processes occurring during epitaxial growth on vicinal surfaces and to interpret the formation of one-dimensional structures on vicinal surface. Moreover, we know that whatever the considered mechanism, it allows the attachment of deposited atoms in the step edge of the substrate surface. Among these mechanisms that can be studied as adjustable parameters by KMC, are the Ehrlich-Schwoebel (ES) barrier, and inverse (iES), have been considered in this work and shown to play a key role in the formation of perfect nanowires (NWs) on substrate surface. We also assessed the effect of the terrace width of substrate surface on the quality of NWs. The results show that the GaAsBi NWs have a better quality than the GaAs NWs. This work provides experimentalists with optimum growth parameters and atomistic mechanisms governing the creation of a uniform distribution of wires on vicinal surfaces.

Effect of mask-film properties on the initial GaAs nanowire growth stages

The initial self-catalyze GaAs nanowire (NW) growth stages were studied using Monte Carlo simulation. We analyzed the effect of the mask-film etching rate with liquid gallium for different thicknesses on the initial nanowire formation stages. At a high etching rate NWs do not form on thick mask-films. A high etching rate of a thin film-mask can lead to lateral Ga drop motion over the crystalline substrate surface, which delays the nanowire formation onset. It is shown that, for the NW formation, it is necessary to maintain the correct ratio between the film thickness, etching rate, Ga and As2 flux intensities.

Catalyst Electrodes with PtCu Nanowire Arrays In Situ Grown on Gas Diffusion Layers for Direct Formic Acid Fuel Cells.

The excellent performance and safety of direct formic acid fuel cells (DFAFCs) promote them as potential power sources for portable electronic devices. However, their real application is still highly challenging due to the poor power performance and high complexity in the fabrication of catalyst electrodes. In this work, we demonstrate a new gas diffusion electrode (GDE) with ultrathin PtCu alloy nanowire (NW) arrays in situ grown on the carbon paper gas diffusion layer surface. The growing process is achieved by a facile template- and surfactant-free self-growth assisted reduction method at room temperature. A finely controlled ion reduction process tunes the nucleation and crystal growth of Pt and Cu leading to the formation of alloy nanowires with an average diameter of about 4 nm. The GDE is directly used as the anode for DFAFCs. The results in the half-cell GDE measurement indicate that the introduction of Cu in PtCu NWs boosts the direct oxidation pathway for formic acid. The Pt3Cu1 NW GDE shows a 2.4-fold higher power density compared to the Pt NW GDE in the membrane electrode assembly test in single cells.

Luminescence-Tunable ZnS-AgInS2 Nanocrystals for Cancer Cell Imaging and Photodynamic Therapy.

A highly luminescent I-III-VI group of semiconductor nanocrystals (NCs) has attracted considerable attention for applications in biomedical engineering and design of novel optoelectronic devices. In this work, high quality ZnS-AgInS2 (ZAIS) solid solution NCs were synthesized by thermal decomposition of a organometallic diethyldithiocarbamate precursor complex of (AgIn)xZn2(1-x) (S2CN(C2H5)2)4 in the presence of specific stabilizing and structure directing agents. By changing the composition of the precursor complex (value of x), the structure and optical property could easily be adjustable, thus leading to the formation of nanowire, nanorod, and tetrapod-like NCs and highly luminescent green to yellow to red color tunable NCs. The ZAIS NCs were further transferred to aqueous medium by 3-mercaptopropionic acid (MPA) capping without losing any optical properties. The color-tunable, water-soluble, and biocompatible ZAIS NCs were utilized for the in vitro cellular imaging of human cervical cancer cells (HeLa cells) and showed intense localization in the cell cytoplasm after 6 h of incubation. In addition, the inherent photocatalytic property of ZAIS NCs under light illumination showed promising photodynamic therapy of cancer cells, and thus, ZAIS NCs could be a promising candidate for future biomedical applications.

On the formation of Si nanowires by molecular beam epitaxy

Abstract Silicon nanowires can be successfully grown by applying the vapor – liquid – solid process. In the case of the commonly used chemical vapor deposition technique, a Si containing gas/precursor is cracked at Au droplets acting as seeds. Si adatoms are subsequently dissolved in the liquid metal. Due to a supersaturation within this droplet, Si precipitates predominantly at the liquid – solid interface – a nanowire grows. A different situation occurs if nanowires are grown by molecular beam epitaxy via the vapor– liquid – solid mechanism. The difference consists, for example, of the role of the metal seed, the morphology of the nanowires and their aspect ratio. In particular, surface diffusion including the metal used as well as Si, strongly influences the growth process. This article describes molecular beam epitaxy growth experiments of Si nanowires under ultra-high vacuum conditions and compares the results with other growth techniques.

Formation of Nanowires of Various Types in the Process of Galvanic Deposition of Iron Group Metals into the Pores of a Track Membrane.

The processes of formation of one-dimensional nanostructures by the method of matrix synthesis was studied in this work. Nanowires (NWs) from magnetic metals of iron-group and copper (3-d metals) were synthesized in the pores of matrix-track membranes by galvanic deposition. NWs with both homogeneous elemental distribution (alloys) and with periodically alternating parts with different composition (layers) were obtained in matrices with different pore diameters and under different parameters of the galvanic process. The transport of ions, which determined the growth of wires, in pores of different sizes was analyzed. The influence of the size of pore channels on the features of NWs growth, the correlation between the elemental composition of the NWs and the growth electrolyte, as well as the influence of the growth conditions (voltage and pore diameter) were investigated. Approaches to formation of thin layers in layered NWs were studied. This included the choice of methods for controlling the pulse duration, slowing down the growth rate by the dilution of the solution, the use of additives and the work with reference electrode. The study of NWs was carried out using visualization and analysis of their structure using transmission and scanning electron microscopy, electron diffraction, energy dispersive analysis, and elemental mapping. For the studied types of samples, a relationship was established between the growth conditions and the structure. This data raises the possibility of varying the magnetic properties of NWs.