Silica Nanowires Research Articles

Secondary growth and photoluminescence from erbium implanted silica nanowires

Gold-catalyzed silica nanowires were grown using vapor from the active oxidation of the silicon substrate and then implanted with erbium and annealed. During prolonged annealing at 1100 °C, where the concentration of vapor-phase reactants is sufficient to support nanowire growth, the erbium rich precipitates act as catalysts for the growth of a second generation of nanowires. These secondary nanowires increase in photoluminescence as they grow, suggesting that a fraction of the optically active erbium is incorporated into the growing wire. The resulting luminescent nanostructures have a very large surface-to-volume fraction and are well suited for optical-sensing applications.

Comparative Flow Cytometric Analysis of Immunofunctionalized Nanowire and Nanoparticle Signatures

Flow cytometry is one of the gold-standard techniques used in clinical medicine for quantitative immunoassaying. The continuous development of its probes, commonly fluorescent nanoparticles, is important. Lately, the introduction of quantitative multiplexed immunoassay has challenged the use of nanoparticles as probes. Functionalized fluorescent silica-based magnetic nanowires are investigated under flow cytometry as a novel probe category. The preparation and full characterization of these multimodal nanowires is reported and compared to those of silica-based magnetic nanoparticles by flow cytometry. Full characterization includes transmission electron microscopy and fluorescence microscopy imaging, flow cytometric assaying, superconducting quantum interference device (SQUID) magnetization, and Mössbauer spectroscopy measurements. This work shows that loaded silica nanowires have intrinsic geometrical advantages when compared to similar spherical particles due to their unique "flow cytometry fingerprint" when utilized as magnetic carriers for immunodetection applications. These advantages account for a 17% yield in detecting the functional binding between THP-1 and ICAM-1, by utilizing a much lower concentration than that required for the nanoparticles.

Manufacturing aspects of oxide nanowires

Exploring the mass manufacturing aspects of nanostructures can enable the transition from laboratory-based research into a commercial product. Among the several one-dimensional nanostructures, oxide nanomaterials have a wide variety of applications including energy harvesting, photonics and biosensing applications. In this article, mass manufacturing aspects of bottom-up grown silica nanowires on silicon (Si) by metal thin film catalysis have been detailed. The investigation reports on (a) a growth model derived from studying nanowire nucleation as a function of heating time, (b) nanowire growth rate estimation via weight differential of the Si substrate before and after growth, and (c) reusability of the Si substrate for nanowire growth. Silica nanowires were found to grow on Pd coated Si substrate in an open tube furnace at 1100 °C with Ar as a carrier gas and a Si support wafer. Nanowires nucleated following a combination of Vapor Liquid Solid (VLS) and Oxide Assisted Growth (OAG) mechanisms conducive for mass manufacturing. The role of SiO vapor was found to be critical in the growth of the wires. Further, five distinct growth regimes were identified while estimating the growth rate. Experimental observations indicated the non-reusability of the Si substrate after one time growth due to depletion of catalyst.

Carbon-assisted lateral self-assembly of amorphous silica nanowires

Amorphous silica nanowires generally grow in either a metal-catalyzed vapour–liquid–solid (VLS) process or a solid–liquid–solid (SLS) process. So far, ordered alignment of impurity-free SiOx (1 < x < 2) nanowires has not been achieved. In this study, without using metal catalysts, laterally aligned amorphous silica nanowire arrays have been successfully synthesized on a Si(100) substrate surface at ∼700–1100 °C. These amorphous silica nanowires have diameters of ∼100–350 nm and lengths of ∼1–20 μm, which are uniformly decorated with ∼4–11 nm SiO nanocrystals as a result of possible thermal decomposition of amorphous silica at high temperature. A carbon-assisted and lattice strain driven mechanism might be responsible for the lateral alignment of these SiO nanocrystal decorated amorphous silica nanowires.

Control of amorphous silica nanowire growth by oxygen content of Si-rich oxide

Ni-coated Si-rich oxide (SRO, SiOx) on a p-type Si wafer has been annealed with Si powder to growsilica nanowires (NWs), which have a composition of stoichiometricSiO2, irrespectiveof x. The diameters of the NWs are well controlled from 82 to 23 nm by increasingx from 0.4 to 1.2 and they have a uniform distribution at a fixedx. These results suggest that the oxygen content (x) plays a crucial role in determining the diameter of the NWs at the early stage of the NWformation. The growth behaviors of the NWs are explained well based on a modifiedvapor–liquid–solid mechanism.

The preparation of silver nanoparticle decorated silica nanowires on fused quartz asreusable versatile nanostructured surface-enhanced Raman scattering substrates

We introduce a platform, comprised of silver nanoparticle decorated silica nanowires(SiONWs) dispersed on fused quartz substrates, for high sensitivity surface-enhancedRaman scattering (SERS) measurements using both frontal (through the analytes) andback-face (through the transparent substrate) excitation. Quasi-quantitative SERSperformances on the specialized substrate, vis-à-vis a silver deposited bare fusedquartz plate, showed: (i) the suitability of the Ag modified SiONW substrate forfrontal as well as back-face excitation; (ii) a wider detection range with highsensitivity to Rhodamine 6G; and (iii) good underwater metal–oxide adhesion of thespecialized substrates. Capable of surviving ultrasonic cleaning, the substrateintroduced is one of the few reusable low-cost Ag-based nanostructured SERSsubstrates, requiring only a simple silver reload process (the silver mirror reaction).

Characterization of Silica Nanowires for Optical Sensing

In this paper, the optical properties of silica nanowires in a Mach-Zehnder-based optical sensor for detecting biomaterial specimens have been studied using the full vectorial H-field formulation of the finite element method. The variation of the propagation constant, the power fraction in the composite nanowires with the variation of the nanowire size and the specimen refractive index, temperature, and wavelength are also presented.

Preparation of Ultrafine Silica Nanowires Using an Iron Based Surfactant

Silica nanowires have been shown to have exceptional mechanical properties. However, to date, their preparation with diameters less than 20 nm by an easily implemented colloidal method has been problematic. In this work, we show how a novel iron based surfactant readily forms rodlike micelle structures which may be used to template the formation of silica nanowires with diameters less than 5 nm.

Preparation of highly aligned silicon oxide nanowires with stable intensive photoluminescence

In this work we report the successful formation of highly aligned vertical silicon oxide nanowires. The source of silicon was from the substrate itself without any additional source of silicon. X-ray measurement demonstrated that our nanowires are amorphous. Photoluminescence measurements were conducted through 18 months and indicated that there is a very good intensive emission peaks near the violet regions. The FTIR measurements indicated the existence of peaks at 463, 604, 795 and a wide peak at 1111 cm −1 and this can be attributed to Si–O–Si and Si–O stretching vibrations. We also report the formation of the octopus-like silicon oxide nanowires and the growth mechanism of these structures was discussed.

Room temperature photoluminescence in the visible range from silicon nanowires grown by a solid-state reaction

The solid-liquid-solid method (also known as the solid-state method) is used to produce silicon nanowires at the core of silica nanowires with a support catalyst layer structure of nickel and titanium layers sputtered on oxide-coated silicon wafers. This silane-free process is low cost and large-area compatible. Using electron microscopy and Raman spectroscopy we deduce that the wires have crystalline silicon cores. The nanowires show photoluminescence in the visible range (orange), and we investigate the origin of this band. We further show that the nanowires form a random mesh that acts as an efficient optical trap, giving rise to an optically absorbing medium.

Dielectric Properties of Novel Polyurethane/Silica Nanowire Composites

An aliphatic isocyanate, polyether, polyol thermoplastic polyurethane, Tecoflex SG-85A, was solution processed with the varying amounts of silica nanowire. The dielectric permittivity (epsilon') and loss factor (epsilon") were measured via Dielectric Analysis (DEA) in the frequency range 1 Hz to 100 kHz and between the temperature -150 to 150 degrees C. The electric modulus formalism was used to reveal alpha, beta and conductivity relaxations. The activation energies for the relaxations are presented. Nanocomposites were also characterized by differential scanning calorimetry (DSC) to determine glass transition temperatures. The onset of decomposition temperature was measured by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) provided images of the polymer-nanocomposites.

Microelectrical sensors as emerging platforms for protein biomarker detection in point-of-care diagnostics

Current methods used to measure protein expression on microarrays, such as labeled fluorescent imaging, are not well suited for real-time, diagnostic measurements at the point of care. Studies have shown that microelectrical sensors utilizing silica nanowire, impedimetric, surface acoustic wave, magnetic nanoparticle and microantenna technologies have the potential to impact disease diagnosis by offering sensing characteristics that rival conventional sensing techniques. Their ability to transduce protein binding events into electrical signals may prove essential for the development of next-generation point-of-care devices for molecular diagnostics, where they could be easily integrated with microarray, microfluidic and telemetry technologies. However, common limitations associated with the microelectrical sensors, including problems with sensor fabrication and sensitivity, must first be resolved. This review describes governing technical concepts and provides examples demonstrating the use of various microelectrical sensors in the diagnosis of disease via protein biomarkers.

Hierarchical Nanostructure Produced by Growing Carbon Nanotubes on Silicon Oxide Nanowires

It was demonstrated that an array of carbon nanotubes (CNT) can be grown using plasma-enhanced chemical vapor deposition on silicon oxide nanowires (SiOxNWs) to construct one-dimensional hierarchical heterostructure. In order to grow the CNTs on the SiOxNWs, the nanowire surface was decorated with Ni seed particles by direct physical deposition without any surface pretreatment. Nano-sized Ni seed particles allowed the CNTs to nucleate on the nanowire surface. Scanning and transmission electron microscopy verified the branches of CNTs projecting from the SiOxNWs. All CNTs were multi-walled and have an average diameter of 20 nm. These CNTs cover the entire length of the individual SiOxNWs. The CNT-coated SiOxNWs can be potentially used as a nanowire-supported catalyst with high active surface area.

Chemical Vapor Deposition of Silica Nanowires using Heteroleptic Bis(ethylmethylamino)silane Precursor

In the present study, silica nanowires were synthesized by employing inherent directionality of chemical vapor reaction between heteroleptic bis(ethylmethylamino)silane ((H2Si[N(C2H5)(CH3)]2) precursor and water without a metal catalyst at room temperature. The conceptual scheme used here is that the difference in the oxidation reactivities between Si-H and Si-N groups with water leads the formation of linear shaped products. The optimized pressure and temperature to obtain straight silica nanowires were 7 Torr and 25oC. The diameter and length of the silica nanowires were ~ 60-80 nm and ~ 1.9 µm, respectively. TEM revealed that nanowire is amorphous. FTIR, XPS, and EDX analyses indicated that the estimated composition was very close to SiO2.

Direct synthesis of silicon oxide nanowires on organic polymer substrates

A nanowire growth model assisted by polymer reconstruction was discovered and used toachieve the direct synthesis of amorphous silicon oxide nanowires (SiONWs) onpolyethylene terephthalate (PET) substrates at low growth temperatures (no more than150 °C) usingplasma-enhanced chemical vapor deposition (PECVD). The reconstructed polymers were generatedfrom the scission and recombination of polymer chains on the surface of PET substrates under activeAr:O2 plasma in the PECVD process. The highly ordered nanowire arraysexhibited an excellent geometrical configuration that is comparable tothat of SiONWs grown on Si substrates at temperatures higher than1000 °C by using conventional vapor deposition methods with various metal catalysts. A promisingoptical property—strong photoluminescence in the violet–blue spectral range at roomtemperature—was detected in the nanowires. This might lead to breakthroughs in thefabrication of electronic and optical nanoscale devices on flexible polymer substrates.

Preparation and growth mechanism of clustered one-dimensional SiO x amorphous nanowires by catalytic pyrolysis of a polymer precursor

Large-scale synthesis of clustered one-dimensional amorphous silica nanowires was achieved by simple thermal pyrolysis of an amorphous preceramic powder from perhydropolysilazane on alumina wafers coated with catalyst FeCl 2. Scanning electron microscopy and transmission electron microscopy observations showed that the silica nanowires had smooth surface, and lengths of hundreds of micrometers and diameters in the range of 30–40 nm. Energy dispersive X-ray spectroscopy revealed that these nanowires consisted of Si and O elements in an atomic ratio of approximately 1:2, consistent with the stoichiometric formula SiO 2. The two amorphous bulges in Raman spectrum at the centers of around 260 cm −1 and 800 cm −1 were identified to be those of amorphous silica. The growth mechanism of the as-produced silica nanowires could be attributed to vapor–liquid–solid mechanism. These results provide an alternative and simple preparation procedure for nanostructures with controlled morphology, and it will be helpful to understand the growth mechanism of one-dimensional SiO 2 nanostructures.

Hierarchical Nanostructure Produced by Growing Carbon Nanotubes on Silicon Oxide Nanowires

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Waveguiding properties and applications of silica nanowires in various environments

Waveguiding properties of silica nanowires in various environments are studied by solving the eigenvalue equations of a circular cross-section waveguide numerically in cylindrical coordinates. The single-mode condition, propagation constants, poynting vector and power distribution inside and outside silica nanowire are calculated. The results show that silica nanowires in water, compared with silica nanowires in air, have higher fraction of the evanescent fields. Due to the sensitivity to surrounding environment, silica nanowires are very suitable for sensing elements, which can be used to implement a single-mode fiber optic evanescent wave sensing element of highly sensitive and accurate measurement.

Influence of the Atmosphere on the Growth by CVD of Silicon Based Nanostructures

Silica nanowires (phi = 70-80 nm) and core crystalline silicon carbide/amorphous silica coaxial nanocables (phi = 30-50 nm) have been grown on Ni (5 nm) covered silicon substrates by thermal CVD at 950 degrees C. Heating the sample in different atmospheres and the addition of methane lead to the growth of the nanostructures. The as-grown product was characterized by Scanning Electron (SEM) and Transmission Electron (TEM) Microscopies, Infrared (IR) and Glow Discharge Optical Emission (GDOES) Spectroscopies. High contents of Ni, O and Si have been detected in the surface layer for argon and nitrogen treatments and in both cases silica based nanostructures grew. However, no nanostructures were obtained in hydrogen environment probably due to the detected Ni migration inward the substrate making the nanostructures nucleation more difficult. In this work we have studied and proven that previous processes on the substrate surface affect significantly the nanostructures growth.

Endface reflectivities of optical nanowires

Endface reflectivities (ERs) of optical nanowires are investigated using three-dimensional finite-difference time-domain simulations. Typical ERs of both free-standing and substrate-supported silica, tellurite, PMMA and semiconductor nanowires or nanofibers are obtained. Unlike in conventional waveguides such as optical fibers, ERs of nanowires are usually considerably lower when operated in single mode. Dependences of ER on the diameter and the refractive index of the nanowire, and the wavelength of the guided light are also investigated. These results are helpful for estimating and understanding ERs in optical nanowires with diameters close to or smaller than the wavelengths of the light, and may offer valuable references for practical applications such as nanowire or nanofiber-based resonators and lasers.