Silica Nanowires Research Articles

Effect of Fe metal on the growth of silicon oxide nanowires

Silicon oxide (SiO x ) nanowires are generally grown on Si substrate under the catalysis of Au in N 2 atmosphere at elevated temperatures. Because the price of Au metal is quite high, Fe metal is then used to replace a part of Au for catalyzing the growth of SiO x nanowires. The results show that the Fe film can be used as the diffusion barrier of Au. SiO x nanowires are grown on Au/Fe/Si substrate at 1030°C. Under the catalysis of Fe/Au, the efficiency for the growth of SiO x nanowires is promoted.

The catalytic effect of Pt nanoparticles supported on silicon oxide nanowire

3.5 nm sized Pt nanocatalysts supported on silicon oxide nanowires (SiOXNWs) were fabricatedby decorating the SiOXNWs with Pt nanoparticles using a simple physical deposition system without anysurface pretreatment. High curvature of the nanowire surface together withthe weak metal–substrate interaction helped to maintain discrete particlemorphology with spherical shapes during deposition. Catalytic efficiency of theSiOXNWs coated with Pt nanoparticles was demonstrated through reduction of methylene blue in thepresence of sodium borohydride. It was demonstrated that the highly curved nanowiresurface allowed the Pt nanoparticles to be loaded with increased particle density, providinga larger surface area for the catalytic reaction. It was also shown that a simple heattreatment in vacuum improves the effectiveness of the Pt nanoparticles as a catalystwithout loss of catalytic activity when used repeatedly. We expect that this metalnanoparticle-decorated nanowire can be easily extended to other heterogeneous reactionsand can also be used as a template for building three-dimensional hierarchicalnanostructures.

In vitro proliferating cell models to study cytotoxicity of silica nanowires

Proliferating cells representing two disease models (HeLa and Panc 10.05 cells) and a more physiologically relevant cell model (3T3-L1 cells) were used to study the acute toxicologic effects of silica nanowires (NWs). Cellular responses to NW effects were determined over a 4- to 20-hour exposure time-course. Proliferation, viability, metabolic activity, and toxicologic mechanism (apoptosis vs. necrosis) data showed the following: 3 × 10 4 NWs per cell inhibited cell proliferation. The effect was rapid in HeLa cells, but 3T3-L1 and Panc 10.05 cells appeared to be more tolerant to NWs, effects being significant only after 20 or 16 hours, respectively. Cells of all three cell lines showed a significant reduction in cellular metabolic activity after 20 hours of treatment with NWs. Assay of NW-invoked mechanism of cell death (caspase 3/7 activity) indicated that apoptosis was minimally induced. Small but significant effects of NWs were detected in 3T3-L1 and HeLa cells after 20-hour treatment. No NW-induction of caspase 3/7 activity was detected for Panc 10.05 cells. Proliferating cells provide a sensitive model to study treatment with silica NWs. Silica NWs appeared to be well tolerated by these three cell lines at the doses tested. When effects were detected, cell necrosis and not apoptosis was the main mechanism of silica NW–induced cell death. From the Clinical Editor In this study, three relevant cell culture models were used to study the acute toxicological effects of silica nanowires (NW). All cell lines cells showed a significant reduction in cellular metabolic activity after 20 h of treatment with NW. Overall, silica NW appeared to be well-tolerated by these cell lines at the tested doses. Cell necrosis as opposed to apoptosis was the main mechanism of silica NW-induced cell death.

Toxic and teratogenic silica nanowires in developing vertebrate embryos

Silica-based nanomaterials show promise for biomedical applications such as cell-selective drug delivery and bioimaging. They are easily functionalized, which allows for the conjugation or encapsulation of important biomolecules. Although recent in vitro studies suggested that silica-derived nanomaterials are nontoxic, in vivo studies of silica nanomaterial toxicity have not been performed. Using the embryonic zebrafish as a model system, we show that silica nanomaterials with aspect ratios greater than 1 are highly toxic (LD 50 = 110 pg/g embryo) and cause embryo deformities, whereas silica nanomaterials with an aspect ratio of 1 are neither toxic nor teratogenic at the same concentrations. Silica nanowires also interfere with neurulation and disrupt expression of sonic hedgehog, which encodes a key midline signaling factor. Our results demonstrate the need for further testing of nanomaterials before they can be used as platforms for drug delivery. From the Clinical Editor Silica-based nanomaterials show promise for biomedical applications such as cell-selective drug delivery and bioimaging. Using an embryonic zebrafish model system silica nanomaterials with aspect ratios greater than one were found to be highly toxic; whereas silica nanomaterials with an aspect ratio of one are neither toxic nor teratogenic. These results demonstrate the need for testing “nanomaterials" before they can be used as platforms for drug delivery.

Plasma-enhanced low temperature growth of silicon nanowires and hierarchical structuresby using tin and indium catalysts

Plasma-enhanced low temperature growth (<300 °C)of silicon nanowires (SiNWs) and hierarchical structures via a vapor–liquid–solid (VLS) mechanismare investigated. The SiNWs were grown using tin and indium as catalysts prepared by in situ H2 plasmareduction of SnO2 and ITO substrates, respectively. Effective growth of SiNWs at temperatures as low as240 °C have been achieved, while tin is found to be more ideal than indium in achieving a bettersize and density control of the SiNWs. Ultra-thin (4–8 nm) silica nanowires, sprouting fromthe dendritic nucleation patterns on the catalyst’s surface, were also observed toform during the cooling process. A kinetic growth model has been proposed toaccount for their formation mechanism. This hierarchical structure combinesthe advantages of the size and position controllability from the catalyst-on-topVLS–SiNWs and the ultra-thin size from the catalyst-on-bottom VLS–ScNWs.

Large-scale synthesis, characterization and photoluminescence properties of amorphous silica nanowires by thermal evaporation of silicon monoxide

A single step non-catalytic process based on thermal evaporation of silicon monoxide has been established for large-scale synthesis of silica nanowires. Scanning electron microscopy, high-resolution transmission electron microscopy equipped with energy dispersive X-ray spectrometry (EDAX), X-ray diffractometry were used to characterize the morphology and structure of the material. The as-synthesized nanowires had amorphous structures with diameters in the range 30–100 nm and hundreds of micrometers in length. The EDAX analysis revealed that the nanowires consisted of mainly two elements Si and O in an atomic ratio of approximately 1:2 corresponding to silicon dioxide. Photoluminescence spectra of the silica nanowires showed strong blue emission around 393 nm. Nucleation and growth of silica nanowires has been discussed on the basis of tiny oxide cluster formation that acts as nucleation centers for the nanowires growth.

Direct deposition of size-tunable Au nanoparticles on silicon oxide nanowires

Silicon oxide nanowires (SiO X NWs) was decorated with 3- to 6-nm-sized Au nanoparticles by direct deposition of Au on the nanowire surface without any surface pretreatment. The nanowire surface was uniformly coated with Au nanoparticles with a density of 2 × 10 12 particles cm −2. It was found that the Au nanoparticles grown on the SiO X NWs was much finer in size compared to the Au nanoparticles deposited on a flat SiO 2 substrate because of the high curvature of the nanowires and abundant surface defects resulting from the oxygen non-stoichiometry. Moreover, the particle size as well as the particle density can be tuned at will by simply altering the growth condition of the SiO X NWs. The tuning of the Au particle provides an opportunity to tailor the Au nanoparticles for desired applications.

Luminescent silica nanotubes and nanowires: Preparation from cellulose whisker templates and investigation of irradiation-induced luminescence

Luminescent silica nanotubes and nanowires were fabricated from cellulose whisker templates by sol-gel processing. The cellulose templates were removed by calcination at 650 °C to generate silica nanotubes with diameters of 15 nm and lengths up to 500 nm. At temperatures of 900 °C the core region previously occupied by the cellulose template was closed yielding silica nanowires. Cathodoluminescence spectra of the silica nanotubes and nanowires were measured in the transmission electron microscope during irradiation with 150 keV electrons. A blue emission at 450 nm was observed for the silica nanowires calcined at 900 °C. This luminescence was found to be related to defects induced by electron irradiation and was investigated in situ as a function of irradiation dose. The as-synthesized and 650 °C calcined nanowires and nanotubes showed a fast decay of the signal. The observed irradiation dose dependent changes in the luminescence spectra will be discussed in terms of defect formation and transformation mechanisms.

Self-assembled silicon oxide nanojunctions

Novel silicon oxide nanojunction structures with various shapes, such as X type, Y type,T type, ringlike and treelike, are fabricated in a self-assembled manner by the hydrothermalmethod without any metallic catalyst. In the silicon oxide nanojunctions, both the siliconoxide nanowire part and the junction part consist of the same chemical composition,forming homogeneous homojunctions and being made suitable for application in nanoscaleoptoelectronics devices. The formation of silicon oxide nanojunctions may beinfluenced by the surrounding environment in the reaction kettle, growth space amongthe silicon oxide nanowires and the weight of SiO droplets at the growth tip.

Enhanced photoluminescence of silicon oxide nanowires brought by prolonged thermal treatment during growth

Silicon oxide nanowires synthesized during carbonization of polyimide thin film on a silicon substrate exhibited marked enhancement in photoluminescence (PL) at 420 nm by prolonging the growth period. Maximum intensity was recorded when the nanowire diameter coarsened from 70 to 165 nm by extending the growth period from 1 to 3 h. The enhancement was attributed to the increase in concentration of neutral oxygen vacancies on the surface of the nanowires. It was also demonstrated that the PL peak can be shifted to 600 nm while maintaining the enhanced intensity by postannealing the nanowires in a reducing atmosphere.

A High-Density Array of Size-Controlled Silicon Nanodots in a Silicon Oxide Nanowire by Electron-Stimulated Oxygen Expulsion

Methods of producing Si nanodots embedded in films of silicon oxide and silicon nitride abound, but fabrication of Si nanodots in a nanowire of these materials is very rare despite the fact that nanowire architecture enhances the charge collection and transport efficiencies for solar cells and field-effect transistors. We report a novel fabrication method for a high-density array of size-controlled sillicon nanodots from a silicon oxide nanowire using electron-beam irradiation. Our results demonstrate that a highly dense phase of Si nanodots with a narrow size distribution can be made from a silicon oxide nanowire with a core-shell structure of crystalline silicon-rich oxide (c-SRO)/amorphous silicon oxide (a-SiO(2)). This new nanomaterial shows the carrier transport characteristics of a semiconductor. The initially produced amorphous Si nanodots can be readily turned into crystalline Si (c-Si) nanodots by thermal annealing. Key characteristics of c-Si nanodots such as their size, number density, and rate of nucleation and growth are easily controlled by varying the electron radiation dose and annealing temperature. Nanodot formation is mechanistically initiated by electron trapping at the c-SRO core as well as at the core-shell interface, which leads to out-diffusion of the negatively charged oxygen through Coulomb repulsion, fostering the aggregation of Si atoms.

Patterned growth of silicon oxide nanowires from iron ion implantedSiO2 substrates

We demonstrate experimentally a simple and efficient approach for silicon oxide nanowire growth, by implantingFe+ ions intothermally grown SiO2 layers on Si wafers and subsequently annealing in argon and hydrogen to nucleate thenanowires. We study the effect of implantation dose and energy, growth temperature,H2 gas flow, and growth time on the silicon oxide nanowire growth. We find thatsufficiently high implant dose, high growth temperature, and the presence ofH2 gas flow are crucial parameters for silicon oxide nanowire growth.We also demonstrate the patterned growth of silicon oxide nanowires inlocalized areas by lithographic patterning and etching of the implantedSiO2 substrates before growth. We propose a simple physical model to explain the growthresults. This works opens up the possibility of growing silicon oxide nanowires directly fromsolid substrates, controlling the location of nanowires at the submicron scale, andintegrating them into nonplanar three-dimensional nanoscale device structures.

Synthesis of Superhydrophobic Silicon Oxide Nanowires Surface on Silicon Wafer

High roughness of several hundreds of nanometers and low free energy introduced the superhydrophobic surface with a high water contact angle of approximatelt 160 degrees for the chemically modified silicon oxide nanowires on silicon wafer. Particularly, a very small rolling angle of < 5 degrees with the annealed sample was observed. The nano-structure with high roughness and organic perfluoroalkysilane coating with CF2/CF3 groups contributed the superhydrophobicity. The present superhydrophobic nanowires surface on silicon wafer suggests the potential applications in self-cleaning semiconductor devices such as radar surface, solar cell.

Low-temperature vapour–liquid–solid (VLS) growth of vertically aligned silicon oxidenanowires using concurrent ion bombardment

Vertically aligned silicon oxide nanowires can be synthesized over a large area by alow-temperature, ion-enhanced, reactive vapour–liquid–solid (VLS) method. Synthesis ofthese randomly ordered arrays begins with a thin indium film deposited on a Si orSiO2 surface. At theprocessing temperature of 190 °C, the indium film becomes a self-organized seed layer of molten droplets, receiving atomicsilicon from a DC magnetron sputtering source rather than from the gaseous precursorsused in conventional VLS growth. Simultaneous vigorous ion bombardment aligns theobjects vertically and expedites mixing of oxygen and silicon into the indium. Silicon oxideprecipitates from each droplet in the form of multiple thin strands having diameters assmall as 5 nm. These strands form a single loose bundle growing normal to the surface,eventually consolidating to form one nanowire. The vertical rate of growth can reach300 nm min−1 in an environment containing argon, hydrogen, and traces of water vapour. This paperdiscusses the physical and chemical factors leading to the formation of the nanostructures.It also demonstrates how the shape of the resulting nanostructures can be furthercontrolled by sputtering, during both VLS growth and post-VLS processing. Keytechnological advantages of the developed process are nanowire growth at low substratetemperatures and the ability to form aligned nanostructure arrays, without the use oflithography or templates, on any substrate onto which a thin silicon film can be deposited.

Gold bead-strings in silica nanowires: a simple diffusion model

Silica nanowires grown from gold droplets deposited on the surface of a silicon crystalsometimes develop within them a regular series of gold beads distributed along the wireaxis in what is often called either a bead-string or a pea-pod structure. This is generallyattributed to a ‘Rayleigh instability’ driven by the surface free energy of theincluded gold core. Here a new model is proposed in which quasi-conical goldinclusions are developed by the diffusion-limited growth process and are subsequentlymodified to spherical shape by another diffusion process that is driven by surface freeenergy. This model provides a possible basis for detailed numerical calculations.

The Ultimate Strength of Glass Silica Nanowires

In the past decade nanowires have attracted an increase interest because of their extraordinary mechanical strength. In fact, material properties in the nanoregime are extremely different from those found in macroscopic samples: few crystalline materials have shown a tensile strength in excess of 10 GPa in the form of nanowires. Still the length of defect-free crystalline nanowires is limited to a few millimeters and the strength of long nanowires is compromised by defects. The strength of glass nanowires is less affected by single defects. In this paper we present the ultimate strength of glass silica nanowires manufactured by a top-down fabrication technique; this is the highest value reported for glass materials. The measured ultimate strength is in excess of 10 GPa and increases for decreasing nanowire diameters. Scanning electron micrographs of the broken fragments showed a fragile rupture.

The mechanical behavior and nanostructure of silica nanowires via simulations

Atomistic simulations of vitreous silica nanowires under compression were evaluated for size effects on stiffness and for structural transformations using ring distributions. Results from nanowires (diameters 1.4–20.0 nm) bridge the gap between experiments and simulations. Ultrathin nanowires (diameter 4.3 nm, length 14.3 nm) show no change in structure through 25% strain. Thicker nanowires resemble bulk glass in structure and Young’s modulus while longer nanowires (length ∼57 nm) display buckling modes. Ultrathin nanowire results are consistent with predictions using elasticity calculations.

Ion Implanted SiO2 Substrates for Nucleating Silicon Oxide Nanowire Growth

AbstractWe experimentally demonstrate a simple and efficient approach for silicon oxide nanowire growth by implanting Fe+ ions into thermally grown SiO2 layers on Si wafers and subsequently annealing in argon and hydrogen to nucleate silicon oxide nanowires. We study the effect of implantation dose and energy, growth temperature, and H2 gas flow on the SiOx nanowire growth. We find that sufficiently high implant dose, high growth temperature, and the presence of H2 gas flow are crucial parameters for silicon oxide nanowire growth. We also demonstrate the patterned growth of silicon oxide nanowires in localized areas by lithographic patterning and etching of the implanted SiO2 substrates before growth. This works opens up the possibility of growing silicon oxide nanowires directly from solid substrates, controlling the location of nanowires at the submicron scale, and integrating them into nonplanar three-dimensional nanoscale device structures.

Hierarchical Nanostructure Produced by Growing Carbon Nanotubes on Silicon Oxide Nanowires

Carbon nanotubes (CNTs) were grown using plasma-enhanced chemical vapor deposition on silicon oxide nanowires (SiO x NWs) to construct one-dimensional hierarchical heterostructures. To grow the CNTs on the SiO x NWs, the nanowire surface was decorated with Ni seed particles by direct physical deposition. The nanosized Ni seed particles allowed the CNTs to nucleate on the nanowire surface. Scanning- and transmission electron microscopy verified that branches of CNTs project from the SiO,NWs throughout the entire length of the individual SiO x NWs. The initial Ni seed size can be used as one of the process parameters to control the CNT length and density on the nanowire surface.

Synthesis of silicon oxide nanocluster and C-Si-O nanospheres morphology and photoluminscence Fourier transform infrared spectroscopy study

Silicon oxide nanocluster and C-Si-O nanospheres are fabricated by the chemical vapor deposition method at 1100℃，in flowing N2/H2 atmosphere using the ferrcene and the silicon oil （201） as the raw material and the catalyzer, respcetively. The silicon oxide nanowires are uniform with diameter of 5—40 nm and length up to hundreds of nanometer. The diameter of the C-Si-O solid-nanospheres is 100—300 nm. SEM，TEM，EDS，FTIR and PL were used to characterize the microstructure，composition and optical propertics of the nanocluster and the C-Si-O nanospheres. Energy dispersive X-ray spectrum analysis reveals that the C-Si-O nanospheres consist of C，Si and O elements in an atomic ratio of approximately 1.13∶1∶2.35. The nanoclusters show IR absorption peaks at 474，802 and 1100 cm-1. The PL peak of the nanoclusters is at 440 nm. It is very curious that the PL of the C-Si-O solid-nanospheres possesses the red，green and blue——trichromic luminescent peeks.