Silica Nanowires Research Articles

Preparation of Nanowire Silica Inside Self-Assembled Sodium Bis(2-ethylhexyl) Sulfosuccinate (AOT) Gels.

In conventional sol-gel methods, gel formation occurs due to aggregation of particles into irregular shapes of larger size. In this study, we conducted hydrolysis-condensation reactions of tetraethyl orthosilicate (TEOS) within water-laden channels inside the space created by self-assembled AOT molecules to prepare regular and nanosized silica in self-assembled sodium bis(2-ethylhexyl) sulfosuccinate (AOT) gels. The AOT gels were obtained by adding small amounts of water to organic solvents containing high concentrations of AOT. Adding silica significantly influenced the rheological properties and microstructures of these AOT/silica gels. Rheological studies showed that the storage modulus G' and loss modulus G″ of the AOT gel systems became very close and even crossed, indicating that the gel is "weak"; however, for the AOT/silica gel systems, the rheological data demonstrated that G' is greater than G″ at all frequencies, indicative of a real gel with a G' of approximately 10(5) pa. Small-angle X-ray scattering (SAXS) results showed that the gels initially had a hexagonal close-packed cylindrical structure with long-range order and transitioned to nonclose-packed cylindrical structures without long-range order as the silica formed. The cylinder is expected to comprise stacks of silica molecules surrounded by AOT molecules, and the radius of the cylinder is close to the sum of the length of one AOT molecule and half the size of one silica molecule. The rheological and SAXS data show that silica in the AOT/silica systems grew in the axial direction due to the confinement of these cylindrical structures, leading to nanowire silica structures. After removal of the AOT components, the nanowire silica was approximately 5-10 nm in diameter, as observed using transmission electron microscopy (TEM).

Excess conductivity analysis in YBa2Cu3O7−d added with SiO2 nanoparticles and nanowires: Comparative study

The effect of nanosized silicon oxide nanoparticles (denoted NP-SiO2) and nanowires (denoted NW-SiO2) additions during the final processing stage on electrical fluctuation conductivity of polycrystalline YBa2Cu3O[Formula: see text] (Y-123 for brevity) in the mean field region has been reported. Series of samples were synthesized in air using a standard solid-state reaction technique by adding nanosized entities up to 0.5 wt.%. Phases, microstructure and superconductivity properties have been systematically investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM) and electrical measurements. TEM investigations show the presence of inhomogeneities embedded in the superconducting matrix along with the presence of columnar defects in the case of SiO2 nanoparticles added samples, however nanowires tend to agglomerate by entangling with each other in the intergrain regions. The fluctuation conductivity was analyzed as a function of reduced temperature using the Aslamazov–Larkin model. Using the Lawrence–Doniach equations, the Ginzburg–Landau (GL) number (NG) and equations, the coherence length, the effective layer thickness, the lower critical field [Formula: see text], the upper critical field [Formula: see text] and the critical current density [Formula: see text] were estimated. It was found that the addition of an optimum concentration of SiO2 nanomaterials, that depends on the shape, effectively controlled the microstructure, the grains coupling and hence improved the physical properties of Y-123 compound.

Brillouin scattering self-cancellation.

The interaction between light and acoustic phonons is strongly modified in sub-wavelength confinement, and has led to the demonstration and control of Brillouin scattering in photonic structures such as nano-scale optical waveguides and cavities. Besides the small optical mode volume, two physical mechanisms come into play simultaneously: a volume effect caused by the strain-induced refractive index perturbation (known as photo-elasticity), and a surface effect caused by the shift of the optical boundaries due to mechanical vibrations. As a result, proper material and structure engineering allows one to control each contribution individually. Here, we experimentally demonstrate the perfect cancellation of Brillouin scattering arising from Rayleigh acoustic waves by engineering a silica nanowire with exactly opposing photo-elastic and moving-boundary effects. This demonstration provides clear experimental evidence that the interplay between the two mechanisms is a promising tool to precisely control the photon–phonon interaction, enhancing or suppressing it.

Synthesis of Discrete Alkyl‐Silica Hybrid Nanowires and Their Assembly into Nanostructured Superhydrophobic Membranes

AbstractWe report the synthesis of highly flexible and mechanically robust hybrid silica nanowires (NWs) which can be used as novel building blocks to construct superhydrophobic functional materials with three‐dimensional macroporous networks. The hybrid silica NWs, with an average diameter of 80 nm and tunable length of up to 12 μm, are prepared by anisotropic deposition of the hydrolyzed tetraethylorthosilicate in water/n‐pentanol emulsions. A mechanistic investigation reveals that the trimethoxy(octadecyl)silane introduced to the water‐oil interface in the synthesis plays key roles in stabilizing the water droplets to sub‐100 nm and also growing a layer of octadecyl groups on the NW surface. This work opens a solution‐based route for the one‐pot preparation of monodisperse, hydrophobic silica NWs and represents an important step toward the bottom‐up construction of 3D superhydrophobic materials and macroporous membranes.

Synthesis of Discrete Alkyl-Silica Hybrid Nanowires and Their Assembly into Nanostructured Superhydrophobic Membranes.

We report the synthesis of highly flexible and mechanically robust hybrid silica nanowires (NWs) which can be used as novel building blocks to construct superhydrophobic functional materials with three-dimensional macroporous networks. The hybrid silica NWs, with an average diameter of 80 nm and tunable length of up to 12 μm, are prepared by anisotropic deposition of the hydrolyzed tetraethylorthosilicate in water/n-pentanol emulsions. A mechanistic investigation reveals that the trimethoxy(octadecyl)silane introduced to the water-oil interface in the synthesis plays key roles in stabilizing the water droplets to sub-100 nm and also growing a layer of octadecyl groups on the NW surface. This work opens a solution-based route for the one-pot preparation of monodisperse, hydrophobic silica NWs and represents an important step toward the bottom-up construction of 3D superhydrophobic materials and macroporous membranes.

Rigorous analysis of numerical methods: a comparative study

For any photonic device simulation, the accuracy of the numerical solution not only depends on the methods being used but also on the discretization parameters used in that numerical method. In this work, Finite Element Method and Finite Difference Time Domain Method based on Maxwell’s equations were used to simulate optical waveguides and directional couplers. As the solution accuracy may also depend on the index contrast used in such photonic devices, the characteristics of low-index contrast Germanium doped Silica and high-index contrast Silicon Nanowire Waveguides were analyzed, evaluated and benchmarked. Numerical results to benchmark Directional Couplers are also reported in this paper.

3D plasmonic transducer based on gold nanoparticles produced by laser ablation on silica nanowires

Silica two-dimensional substrates and nanowires (NWs) forests have been successfully decorated with Au nanoparticles (NPs) through laser ablation by using a pulsed ArF excimer laser, for sensor applications. A uniform coverage of both substrate surfaces with NPs has been achieved controlling the number of laser pulses. The annealing of the as-deposited particles resulted in a uniform well-defined distribution of spherical NPs with an increased average diameter up to 25 nm. The deposited samples on silica NWs forest present a very good plasmonic resonance which resulted to be very sensitive to the changes of the environment (ethanol/water solutions with increasing concentration of ethanol) allowing the detection of changes on the second decimal digit of the refractive index, demonstrating its potentiality for further biosensing functionalities.

Influence of substrate temperature on the morphology of silicon oxide nanowires synthesized using a tin catalyst

Silicon oxide nanowires SiOx were synthesized by the gas‐jet electron beam plasma chemical vapor deposition method. The synthesis of nanostructures was carried out on silicon substrates with thin tin film as a catalyst. The evolution in the morphology of the obtained structures was investigated while changing the substrate temperature in the range 200–415 °C. Dense array of aligned nanowire bundles (microropes) is formed at a temperatures of 335 and 415 °C. With decrease in the temperature to 270 and 245 °C arrays of microropes transform into cocoon‐like structures of nanowires. At a temperature 200 °С, array formed almost entirely consisting of cocoon‐like structures. The results of X‐ray energy dispersive spectroscopy (EDS) of the nanowires show that the ratio of oxygen to silicon is on average Si:O = 1:2.4. At the same time, Fourier Transform Infrared spectroscopy (FTIR) analysis of the obtained nanostructures showed that the synthesized nanowires consist of SiOx with x around 2. Moreover, the composition of the structures remains practically unchanged with the variation of the substrate temperature. The IR spectra show bands due to both Si–OH bonds and water molecules. Measurements of contact angles for water showed that the nanowire film surface synthesized in this work is hydrophilic in nature. When structuring involves the oriented growth microropes, the contact angle is about 20–35°. Decreasing of the substrate temperature and formation of cocoon‐like structures leads to a decrease in the contact angle to 4–12°. The photoluminescence (PL) spectra of nanostructures synthesized at the different substrate temperatures consist of a broad band with a maximum around 2.5 eV when using laser at 325 nm as the exciting source. We assume that the composition of the nanowires is close to SiO2, and the excess of oxygen in structures composition is due to the influence of adsorbed water molecules and hydroxyl groups with the formation of Si–OH bonds. Apparently, these bonds define the photoluminescence spectrum.

Synthesis and morphology of silicon oxide nanowires from a free jet activated by electron-beam plasma

Silicon oxide nanowires were synthesized from monosilane–argon–hydrogen mixture by the gas-jet electron-beam plasma chemical deposition method with simultaneous oxygen injection into the vacuum chamber. The synthesis was performed on monocrystalline silicon substrates covered with micron and nanometer tin catalyst particles. The nanowires are formed the via vapor–liquid–solid mechanism in the “catalyst-on-bottom” mode, in which many nanowires grow from one catalyst particle. The process of synthesizing nanowires on a substrate with catalyst consists of three stages: heating to synthesis temperature, hydrogen plasma treatment, and nanowire growth. In the substrate region corresponding to the jet axis, different structures are formed depending on the catalyst particle size. For catalyst particles under 100 nm, there are formed structures of chaotically oriented and interlaced bundles of silica nanowires. For catalyst particles of 0.3–1 micron, there are formed oriented arrays of cylindrically shaped nanowire bundles (“microropes”). Cocoon-like structures are formed for catalyst particles of more than 1 micron.We propose a model of nanowire growth by this method, which is based on nonuniform heating of a catalyst particle by a directed plasma flow. It was found that for synthesis of oriented microrope arrays the initial tin film thickness should be less than 100 nm and the synthesis process should include a hydrogen plasma treatment stage.

A New Approach of the Synthesis of SiO2 Nanowires By Using Bulk Copper Foils As Catalyst

Silica nanowires (SiO2NWs) have attracted considerable attention over the last decades due to their diverse properties and broad range of applications. Among them, it is well-known the capacity of SiO2NWs to emit strong blue light. It is also widely recognized the versatility of this material as biosensor, since it can be easily functionalized in order to respond to several targets. Other applications include their potential use as anode electrode for lithium-ion batteries, or as protective layer against corrosion by exposure to the environment. In this regard, the use of a metal substrate is of paramount relevance; therefore, an adequate contact between the substrate and the nanostructures is required. Especially numerous and varied are the procedures for the growth of SiO2NWs, being one of the most employed the so-called vapor-liquid-solid (VLS) method. By this mechanism, the nanowires grow from a metal nanoparticle when the adequate gaseous precursor is added. However, the main drawback of this mechanism resides in the need of a Si substrate for the synthesis of the SiO2NWs. Apart from the original Au-Si system, a broad variety of other metals such as Fe, Co, Ni or Cu may act as catalysts for the growth. Particularly, of special interest is the case of copper, which is present in a large majority of electronic devices. Furthermore, the Cu–Si phase diagram shows a eutectic point at 802 ⁰C (16 wt% of silicon) promoting the formation of a liquid alloy at an accessible temperature for a relatively low concentration of silicon in copper. This work presents a novel procedure for the growth of SiO2 nanowires directly from polycrystalline copper foils. The single-step synthesis procedure consists of a thermal treatment at 900 ◦C without the need for additional catalysts. As a result, nanowires with an average diameter of 100 nm are synthesized. A systematic study undertaken at different stages of the SiO2NWs growth confirmed the generation of nucleation centers on the Cu surface as well as revealed the existence of an intermediate gaseous SiO species at the synthesis temperature, which promotes the growth of the SiO2NWs via a VLS mechanism. Figure 1 shows the dark field scanning transmission electron microscopy (DF-STEM) image of the as-synthesized SiO2NWs. As can be seen there, SiO2NWs growth is generated from substrate protrusions of around 200 nm in diameter, exceling from the Cu substrate. These protuberances produced during the thermal treatment could be the evidence of the formation of Cu-Si alloys required as initial step for generating the SiO2NWs. Figure 2a shows the detail of a protrusion of the Cu substrate (in bright contrast) just under the nanowire (in dark contrast). EDX elemental maps performed on the inset area confirms the presence of Cu at the bottom of the nanowire (Fig 2b). Meanwhile, Figs 2c and 2d show a homogeneous distribution of Si and O across the whole nanowire. This process with bulk Cu foils as catalytic agent allows the growth of SiO2NWs over metallic substrates, granting an adequate interconnection between both surfaces. Figure 1

Synthesis of silicon oxide nanowires by the GJ EBP CVD method using different diluent gases

Nanowires of silicon oxide SiOx (x ≤ 2) were synthesized from a mixture of monosilane and hydrogen (helium, argon) by gas‐jet electron beam plasma chemical vapor deposition (GJ EBP CVD) method with simultaneous supply of oxygen into the vacuum chamber. The synthesis was performed on monocrystalline silicon and glass substrates coated with micron‐sized particles of a tin catalyst. In particular, aligned arrays of nanowire bundles (microropes) were synthesized from a mixture of monosilane and hydrogen (argon). A bundle of amorphous silicon oxide nanowires, each of which is about 15 nm in diameter, grows from a catalyst particle. The growth rate of the microropes is about 25 nm s−1 at a synthesis temperature of 320–330 °C. The morphology of the nanostructures was investigated by transmission and scanning electron microscopy, their composition by X‐ray energy dispersive spectroscopy and optical properties by photoluminescence spectroscopy. The synthesis was carried out using the well‐known vapor–liquid–solid (VLS) mechanism. A model is proposed for the synthesis of the nanostructures by the above method, including the formation of aligned bundles of nanowires (microropes) due to nonuniform heating of the catalyst particle by directed plasma flow. The obtained nanostructures have intense photoluminescence in the visible region of the spectrum at room temperature.

Haemocompatibility evaluation of silica nanomaterials using hemorheological measurements

Silica nanomaterials (NMs) are widely used in semiconductor, agriculture, cosmetics, and biomedical applications, in addition to other industries. We investigated the toxic effect of silica NMs on rheological characteristics of human red blood cells (RBCs), including hemolysis, deformability, aggregation, and morphological changes. Red blood cells were exposed to silica nanoparticles (d =∼200 nm) or silica nanowires (d =∼200 nm, l = 1μm or 10μm) at a range of concentrations and incubation times. Rheological characteristics were measured using microfluidic-laser diffractometry and aggregometry. Overall, at a concentration greater than 12.5 μg/ml, the hemolytic activity was shown to be in the order of nanoparticles, short nanowires, and long nanowires. Elongation index (EI) values were insignificant in the RBCs exposed to each of the silica NMs at a concentration of 12.5 μg/ml. Aggregation index (AI) values decreased in the short silica nanowires at a concentration of 12.5 μg/ml compared to other silica NMs. Therefore, the safe concentration of silica NMs for toxicity, in this study, was considered less than 12.5 μg/ml. These hemorheological results provided insight into the interaction between RBCs and silica NMs; they will also help assess the risk of NMs' toxicity in the blood.

Morphology controlling method for amorphous silica nanoparticles and jellyfish-like nanowires and their luminescence properties.

Uniform silica nanoparticles and jellyfish-like nanowires were synthesized by a chemical vapour deposition method on Si substrates treated without and with Ni(NO3)2, using silicon powder as the source material. Composition and structural characterization using field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and fourier-transform infrared spectroscopy showed that the as-prepared products were silica nanoparticles and nanowires which have amorphous structures. The form of nanoparticles should be related to gas-phase nucleation procedure. The growth of the nanowires was in accordance with vapour-liquid-solid mechanism, followed by Ostwald ripening to form the jellyfish-like morphology. Photoluminescence and cathodoluminescence measurements showed that the silica products excited by different light sources show different luminescence properties. The emission spectra of both silica nanoparticles and nanowires are due to the neutral oxygen vacancies (≡Si-Si≡). The as-synthesized silica with controlled morphology can find potential applications in future nanodevices with tailorable photoelectric properties.

Upcycling spent petroleum cracking catalyst: pulsed laser deposition of single-wall carbon nanotubes and silica nanowires

From waste to single-wall carbon nanotubes and silica nanowires: the first high-tech outlet for FC3R.

Artificial synapses based on biopolymer electrolyte-coupled SnO2nanowire transistors

Synaptic transistors coupled by proton neurotransmitters with a multiple in-plane gate structure were fabricated for the first time using silicon oxide nanowires.

Silicon oxide nanowire growth mechanisms revealed by real-time electron microscopy.

Growth of one-dimensional materials is possible through numerous mechanisms that affect the nanowire structure and morphology. Here, we explain why a wide range of morphologies is observed when silicon oxide nanowires are grown on silicon substrates using liquid gallium catalyst droplets. We show that a gallium oxide overlayer is needed for nanowire nucleation at typical growth temperatures, and that it can decompose during growth and, hence, dramatically alter the nanowire morphology. Gallium oxide decomposition is attributed to etching caused by hydrogen that can be supplied by thermal dissociation of H2O (a common impurity). We show that H2O dissociation is catalyzed by silicon substrates at temperatures as low as 320 °C, identify the material supply pathways and processes that rate-limit nanowire growth under dry and wet atmospheres, and present a detailed growth model that explains contradictory results reported in prior studies. We also show that under wet atmospheres the Ga droplets can be mobile and promote nanowire growth as they traverse the silicon substrate.

Influence of thin fluoropolymer film deposition on wettability of the silicon oxide nanowires array

In this work, we studied influence of fluoropolymer thin film deposition on wettability of the silicon oxide nanowires array. Deposition of fluoropolymer coating on the silicon oxide nanowires array changes the surface properties from hydrophilic to hydrophobic, and micro and nano scale surface roughness does not change significantly. In addition, it was shown that the deposition of fluoropolymer coating on nanowires protects the nanostructures from bundling together as a result of the attractive capillary forces that arise during evaporative drying.

A New Synthesis and Analysis of Silica Nanowire Periodically Wrapped by Nano-spheres

A New Synthesis and Analysis of Silica Nanowire Periodically Wrapped by Nano-spheres

Au nanoparticles decoration of silica nanowires for improved optical bio-sensing

In this work we study the potential of silica nanowires (NWs) decorated with Au nanoparticles (NPs) as novel optical platform for plasmonic biosensing. These composite materials combine the high white-light scattering of silica NWs with the selective absorption of the localized surface plasmon resonances (LSPRs) of the metal NPs, generating efficient light trapping just at the LSPR wavelengths. In addition, the NWs offer a macroporous framework for a three-dimensional (3D) distribution of the Au NPs, easily accessible by biomolecules. These optical and morphological pecularities, make the decoration of silica NWs with metal NPs a promising strategy for improved plasmonic biosensing. We fabricated silica NWs by thermal oxidation of silicon (Si) NWs, grown by plasma enhanced chemical vapor deposition (PECVD). The silica NWs were decorated with Au NPs by evaporating and then de-wetting via thermal annealing Au thin films. The biosensing ability of these materials was studied and compared with the performances of similar Au NPs deposited on glass substrate, forming a planar (two-dimensional, 2D) distribution. A careful morphological analysis about the NWs and their Au NP coverage, including their vertical distribution across the NW film, was performed by high resolution scanning electron microscopy (HR-SEM) and energy dispersive X-ray spectroscopy (EDS) experiments. The morphological information was used for building a theoretical model through 2D finite element modeling (FEM) able to describe the optical behavior of the new transducers and their functional properties, as well as to predict the evolution of the sensing performance of the transducer when passing from a 2D to a 3D distribution of plasmonic NPs. The Au NPs decorated NWs were finally modified with a self-assembled monolayer of BSA (bovin serum albumin) and the specific binding with the related antibody monitored during the time.

Dynamics of Fracture in Silica and Soda-Silicate Glasses: From Bulk Materials to Nanowires

Classical molecular dynamics simulations are used to investigate the fracture mechanism, intrinsic strength, strain at failure and elastic modulus of silica and soda-silicate bulk glasses and nanowires. The latter have been generated by using a new casting approach described in this paper for the first time. The results show that large systems have to be used to reproduce the brittle fracture mechanism of silicate glasses; the appropriate dimensions of the simulation boxes depend on the glass composition. Whereas for silica glass an ideal brittle fracture is observed with models containing 30k atoms, for soda-silicate glasses models with more than 60k atoms should be used. Glasses containing nanovoids and atomic defects (such as under- and overcoordinated silicon and oxygen atoms) are less brittle than flaw-free bulk glasses. The main finding, shown here for the first time, is that the presence of atomic defects and/or modifier cations allows the material to rearrange its structure and absorb the stresses...