Silica Nanowires Research Articles

Mechanical and structural properties of helical and non-helical silica nanowire

Energetically favorable configurations of silica nanowires with helical and non-helical structures and diameters ranging from 0.4 to 1.5nm were obtained by using the simulated annealing basing-hopping (SABH) method with penalty function in our previous work. Those nanowires include five non-helical (2MR, 2MR-2O, 3MR-3O, 4MR-4O, and 5MR-5O) and three helical structures (4MR-3f, 4MR-4f, and 4MR-5f). In this study, their mechanical properties and structural characteristics were carried out by molecular dynamics simulation, specifically the temperature and diameter effect on the tensile strength, yielding strain, and Young’s modulus. Results show that diameter significantly affects Young’s modulus and yielding stress, whereas the temperature mainly influences yielding strain and yielding stress. The elastic deformation allows the variation of θO–Si–O to be about >16°. For comparison and insight, the mechanical property and deformation behaviors in the tensile loading are compared to those in the compression loading. Buckle deformation was observed on both helical and non-helical nanowires under the compression process, demonstrating that the nanowires exhibit a higher yielding strain and Young’s modulus in the compression loading than in the tensile loading. In both the tensile and compression tests, the helical angle structures of silica nanowires lower the yielding strain and only slightly affect the yielding stress and Young’s modulus.

Morphology and Photoluminescence of Silica Nanowires Synthesized by Thermal Evaporation

Gallium was intentionally used to catalyze the growth of brushhead-like and feather-like silica nanowires through thermal evaporation. Due to the different amount of Ga element deposited on the two silicon substrates, the growth of brushhead-like structures was catalyzed by Ga on one silicon substrate, while the feather-like structures were self-assembled on the other silicon substrate. Photoluminescence analysis shows that the brushhead-like structures have two emission peaks centered at 397 nm and 457 nm, and the feather-like structures have only one emission peak centered at 406 nm. The growth rate determined by the Ga catalyst of the brushhead-like and feather-like structures would affect the structure defects in the silica nanowires, which are responsible for their difference in optical properties.

Synthesis of Mesoporous Silica from Poly(ethylene oxide)/Polystyrene Copolymers: Influence of Block Architecture and Each Copolymer Block on Porous Size

Several well defined block copolymers PEO-b-PS and PS-b-PEO-b-PS were synthesized by atom transfer radical polymerization using PEO-Br and Br-PEO-Br as macroinitiators. These copolymers were characterized by GPC and 1H NMR. Mesoporous silicas with large and tunable accessible pores were successfully synthesized by evaporation-induced self-assembly using block copolymers as templates. The structures of these materials were characterized by BET and TEM. When block copolymers possess similar hydrophobic block length but different block architecture, the pore size of mesoporous silica templated by triblock copolymers is larger than that templated by diblock copolymers. For diblock copolymers, with the increasing of PEO block, the mesoporous size decreases; and with the increasing of PS block, the mesoporous size increases. The increase in the degree of polymerization of the PS block leads to a loss of pore organization. When PS block reaches long enough, the product was not mesoporous silica but silica nanowire. In addition, a method of a preparation of block copolymers vesicles by EISA approach was accidentally found.

Silicon Oxide Nanowires: Facile and Controlled Large Area Fabrication of Vertically Oriented Silicon Oxide Nanowires for Photoluminescence and Sensor Applications

We describe a technique for the fabrication of dense and patterned arrays of aligned silicon oxide nanowires for applications in surface modification, optoelectronic, and electromechanical based devices. Conventional techniques for the fabrication of silicon oxide nanowires based on the vapor-liquid-solid (VLS) chemical vapor deposition (CVD) processes involve the use of high temperatures and catalysts. We demonstrate a technique that extends the use of a plasma thermal reactive ion etching for the fabrication of aligned silicon oxide nanowires with aspect ratios extending up to 20 and lengths exceeding 1 μm. The process incorporates phase separated PS-b-P4VP block copolymer loaded with an iron salt. The iron salt preferentially segregates into the P4VP layer and during an O2 etch is not removed but forms a hexagonally packed array on the silicon oxide substrate. Further etching with CHF3/O2 gas mixture over time can generate nanodots, to nanopillars, and then nanowires of silicon oxide. The photoluminescence property of the as-fabricated nanowire arrays as well as the parasitic ferromagnetic effect from the iron oxide-tipped section of the wires resulting in coalescence under an scanning electron microscope (SEM) are demonstrated. This technique is simpler compared to existing VLS fabrication approaches and can be used for the direct fabrication of patterned arrays of nanowires when a laser interference ablation step is incorporated into the fabrication procedure.

Sustainable Nanomaterials: A Greener Future Avenue?

The field of nanoscience has experienced a staggering number of advances in recent years with regards to a wide range of disciplines including physics, chemistry, materials science, biology and medicine [1]. Although most of these are still closely related to laboratory practices and yet far from entrepreneurial activities, many of these nanomaterials are currently commercially available (e.g. silica nanowires, silicon wafers, carbon nanotubes, graphene and derivatives) and have paved the way to enormous developments in the preparation of functional nanomaterials for various applications [1,2]. Generally speaking, environment and sustainable considerations around the synthetic protocols currently in place for the fabrication of nanoentities are scarce and nanosafety procedures in terms of toxicity, handling of nanomaterials and their environmental impact are still not yet sufficiently developed (in the available cases). Considering the synthesis of some of these nanomaterials, protocols often involve high temperatures and pressures, the use of hazardous reagents and/or solvents or include little details to be accounted for in terms of environmental considerations (e.g. environmental impact, green metrics, handling risks, toxicity). Taking into account the essentially different nature and properties (often unknown) of such nanoentities, an increasing number of restrictions, handling practices and safety procedures are currently present in several laboratories and working places in which nanomaterials are handled on a daily basis [3,4]. A complete set of new and updated information on characteristics and properties (as well as risks and toxicity issues in their manipulation) is truly needed to better understand and establish the most acceptable working practices for nanotechnologies. However, a benign by design concept should be promoted in all nano-related practices, aiming to target the development of future sustainable nanoprotocols and environmentally compatible nanomaterials [5,6]. This editorial contribution advocates for more thoughtful and carefully design methodologies that take into account environmentally sound protocols for nanomaterials development. These should range from low temperature ambient pressure methods, avoidance of hazardous chemicals, solvent-free protocols to alternative greener technologies such as mechanochemistry-ball milling-[7], microwave irradiation [2,8,9] and sonication [10] as well as life cycle and risks assessments (whenever possible and appropriate) [11] to analyse and considerate toxicity, risks and environmental impact of the synthesis, handling and utilization of nanomaterials in our daily practices in view of a future implementation of nanotechnologies in our future society [12].

Formation of silicon oxide nanowires in nanomaterial synthesis experiments based on the usage of tube furnace

In an effort to synthesize doped ZnO nanowires, SiOx nanowires were obtained accidently. In the experiment, mixed powders containing chemicals such as ZnO, graphite, Ga2O3, and In2O3 were placed in the center of a tube furnace, where the temperature was set to 1200 °C and the vacuum was approximately 27 Pa. Silicon wafers were placed around the vicinity of the furnace exit to collect the expected nanomaterials. After prolonged heating, grey layers were found on top of one wafer located inside the furnace. The layer showed no adhesion to the substrate. Characterization by using Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and Energy Dispersive X-ray Spectroscopy (EDS) revealed that this layer consisted of SiOx nanowires. Formation of Si-containing liquid drop and the subsequent growth of SiOx nanowires out of it are suggested as the growth mechanism.

Study of ultrafine grains formed on the microsized catalyst surface induced growth of aligned SiO2 nanowires

In this study, beard-like and sea cucumber-like silica structures have been successfully synthesized on the Si substrate by a novel and simple water assisted method. The investigation of SEM and TEM reveals that the as-grown products possess many similar features like that they all have a very big, nearly spherical microsized body and uncountable, high density and highly oriented silica nanowire antennas. It is proved that ultrafine nanosized metal catalysts could be generated on the surface of one microsized catalyst during their growth process due to the indications of surface local softening and different elastic deformation along different crystal plane taking place on the catalyst surface during growth process. Our results could introduce a new way to control the growth of high-density and well-oriented functional nanowire arrays with desired morphologies.

Graphene shell on silica nanowires toward a nanostructured electrode with controlled morphology

We report a direct growth of highly conductive nanocrystalline graphene on dielectric SiO2 nanowires. Graphene structure on the nanowire surface is easily controlled by adjusting the growth conditions. In addition, highly dense ZnO nanorods are electrochemically grown on graphene/dielectric nanowire, which demonstrates potential for the nanostructured electrode with controlled morphology.

Cross-Domain Model Building and Validation (CDMV): A New Modeling Strategy to Reinforce Understanding of Nanomanufacturing Processes

Understanding nanostructure growth faces issues of limited data, lack of physical knowledge, and large process uncertainties. These issues result in modeling difficulty because a large pool of candidate models almost fit the data equally well. Through the Integrated Nanomanufacturing and Nanoinformatics (INN) strategy, we derive the process models from physical and statistical domains, respectively, and reinforce the understanding of growth processes by identifying the common model structure across two domains. This cross-domain model building strategy essentially validates models by domain knowledge rather than by (unavailable) data. It not only increases modeling confidence under large uncertainties, but also enables insightful physical understanding of the growth kinetics. We present this method by studying the weight growth kinetics of silica nanowire under two temperature conditions. The derived nanowire growth model is able to provide physical insights for prediction and control under uncertainties.

Nanowire-based refractive index sensor on the tip of an optical fiber

This letter presents a refractive index sensor created at the tip of an optical fiber that utilizes silica nanowire within a radius of between 225 nm and 600 nm, as a sensing element. Sensitivity in excess of 800 nm/RIU was demonstrated within an aquatic medium, while the entire sensor structure was shorter than 1 mm with a diameter equal to or less than the standard fiber diameter. The presented sensor structure is made entirely from silica and provides the mechanical protection of sensitive nanowire. The proposed sensor is thus a robust and self-sustained structure, which does not require any complex packing.

Surface plasmon-enhanced gas sensing in single gold-peapodded silica nanowires

An intriguing system featuring a wide band gap silica nanowire (SiOx NW) that absorbs visible light (532 nm) via the surface plasmons (SPs) of embedded gold nanoparticles (Au NPs) is reported for sensing applications. We report SP resonance-enhanced molecular oxygen sensing by single Au-NPs@SiOx NWs under 532-nm illumination (visible light) at room temperature. Excellent selectivity of the Au-NPs@SiOx NWs to molecular oxygen in air has been demonstrated. Illumination improved the sensing properties in terms of response and fast recovery time, which can be attributed to the photogenerated hole-mediated oxygen desorption. A general strategy of light-modulated sensing, vis-à-vis dark, is demonstrated in a wide band gap single NW system that could potentially open up routes for biosensing, because silica and Au both lack biotoxicity.

Nanowire liquid pumps

The ability to form tiny droplets of liquids and control their movements is important in printing or patterning, chemical reactions and biological assays. So far, such nanofluidic capabilities have principally used components such as channels, nozzles or tubes, where a solid encloses the transported liquid. Here, we show that liquids can flow along the outer surface of solid nanowires at a scale of attolitres per second and the process can be directly imaged with in situ transmission electron microscopy. Microscopy videos show that an ionic liquid can be pumped along tin dioxide, silicon or zinc oxide nanowires as a thin precursor film or as beads riding on the precursor film. Theoretical analysis suggests there is a critical film thickness of ∼10 nm below which the liquid flows as a flat film and above which it flows as discrete beads. This critical thickness is the result of intermolecular forces between solid and liquid, which compete with liquid surface energy and Rayleigh-Plateau instability.

ZrB2–SiC coating to protect carbon/carbon composites against ablation

To improve the ablation resistance of carbon/carbon (C/C) composites, a ZrB2–SiC coating was prepared by pack-cementation. The phase composition, microstructure and element distribution of the coating were analyzed using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The coated sample exhibits a dense structure and has an outstanding ablation property. During exposure to the oxyacetylene flame at about 2000K for 40s, the coated sample had a linear ablation rate of 4.4×10−3mm/s and a mass ablation rate of 6.2×10−5g/s. Compared with the uncoated C/C composites, the linear and mass ablation rate decreased by 49% and 97%, respectively. During the oxyacetylene torch test, a silica-scale glass was generated on the surface of the coating, and the embed ZrO2 could provide pinning effect to avoid cracking and spalling of the silica-scale glass. After the ablation test, some silica nanowires (SiONWs) were found in the ablation edge region of the sample. The growth mechanism of SiONWs consists of oxide-assisted growth (OAG) and vapor-liquid-solid (VLS) formation.

Synthesis and enhanced light-emission of Si nanocrystals embedded in silicon oxidenanowires

In this paper, we report the synthesis of silicon oxide nanowire-embedded silicon (SONW-Si) nanocrystals (NCs) and their light emission characteristics. The SONW-Si NCs were formed by thermally annealing silicon-rich oxide nanowires (NWs) grown at low temperatures. The well-defined Si NCs were found to have grown in (111) direction and clearly displayed a higher density distribution at the center of the NWs. Photoluminescence (PL) measurements of the SONW-Si NCs showed an enhanced PL intensity compared to the silicon oxide film-embedded Si NCs, which may be related to the difference between the Si diffusion characteristics of SiOx NWs andfilms.

Reactive molecular dynamics simulations on SiO2-coated ultra-small Si-nanowires

The application of core-shell Si-SiO(2) nanowires as nanoelectronic devices strongly depends on their structure, which is difficult to tune precisely. In this work, we investigate the formation of the core-shell nanowires at the atomic scale, by reactive molecular dynamics simulations. The occurrence of two temperature-dependent oxidation mechanisms of ultra-small diameter Si-NWs is demonstrated. We found that control over the Si-core radius and the SiO(x) (x≤ 2) oxide shell is possible by tuning the growth temperature and the initial Si-NW diameter. Two different structures were obtained, i.e., ultrathin SiO(2) silica nanowires at high temperature and Si core|ultrathin SiO(2) silica nanowires at low temperature. The transition temperature is found to linearly decrease with the nanowire curvature. Finally, the interfacial stress is found to be responsible for self-limiting oxidation, depending on both the initial Si-NW radius and the oxide growth temperature. These novel insights allow us to gain control over the exact morphology and structure of the wires, as is needed for their application in nanoelectronics.

Special Issue on Cold Atmospheric Plasmas for Thin Films and Nanomaterials

Non-equilibrium cold atmospheric plasmas (CAPs) are, starting with the discovery of ozone production in a silent discharge by Werner von Siemens in the year 1857, the longest serving man-made plasmas in the history of the human race. They can generate high densities of reactive and internally excited species at very low or moderate gas temperatures, which can be utilized in many surface treatment processes. They can effectively charge surfaces, which resulted in application in dust precipitators or photocopiers, or they can emit photons in the ultraviolet and vacuum ultraviolet range, which is very effectively used in plasma displays. The low gas temperature and the atmospheric pressure operation make them attractive for the surface processing of materials and very friendly to many non-standard substrates such as fabrics, wood, liquids, or even living tissues. Several special issues in this journal have already been dedicated to CAPs: two special issues devoted to Plasma Medicine in years 20081 and 2010,2 a Cold Atmospheric Plasma issue in 2008,3 the special issue “Highlights from the 10th International Symposium on High Pressure, Low Temperature Plasma Chemistry” published in 20074 and a Plasma Sterilisation and Decontamination issue in this year3 with several contributions presenting effects of CAPs.5 This demonstrates the growing interest of the plasma-science community in this type of technology. This interest is, however, accompanied by the awareness of the intrinsic limitations of CAPs. Very high collisional rate and several instabilities lead to preferential filamentation of the plasma. Homogeneous discharge is usually achieved only under very limited range of process parameters, in confined volumes (microplasmas) and/or with special design of both the plasma source and the power supply. Additionally, due to the atmospheric operation, collisional sheaths prevent ion bombardment of the surface and frequent collisions lead also to fast cluster formation. All this limits the application of CAPs for large-scale deposition of high quality and homogeneous thin films or for anisotropic etching and they will very probably never replace low-pressure plasmas in these areas. On the other hand, and this double special issue is a convincing argument for it, there are still many exciting and often unexplored areas, where the CAPs can be used successfully for material synthesis in the gas phase, liquid phase and at the surface. The purpose of this special issue is to show recent progress in this multifaceted field by many of the most distinguished plasma-scientists and provide the overview for somebody who wants to start the research or is looking for plasma application in this area. In this special issue, one review article and three feature articles provide the state-of-the-art and identify key future challenges of the CAP deposition of thin films by dielectric barrier discharges and microplasmas, as well as of nanoparticles synthesis and functionalization by microplasmas in the liquid phase. Moreover, this special issue includes another eight full articles covering the topics from the deposition of coatings for biomedical interest, over the fundamental studies of SiO2 film deposition mechanism, to the synthesis of membrane-electrode assembly for fuel cells and the deposition in microfluidic channels. The issue also contains three original contributions on the continually growing area of nanomaterials production such as the synthesis of silica nanowires, carbon nanotubes or metal nanoparticles. We, the guest editors, are very happy that we could with this special issue attract so much interest from all the authors, and we thank them very much for their excellent contributions. Our thanks go also to all reviewers for their valuable time and effort in securing the highest scientific standards possible. We would like to express our sincere gratitude to the Editors-in-Chief for offering us the privilege to prepare this special issue and to the Managing Editor Dr. Renate Förch for helping us with its coordination.

Synthesis and characterization of amorphous silicon oxide nanowires embedded with Ni nanoparticles

The growth of silicon oxide nanowires (SiOxNWs) was obtained by thermal process of nickel (Ni) nanoparticles (NPs) deposited on silicon (Si) wafer in mixed gases of nitrogen (N2) and hydrogen (H2). TEM analysis showed that SiOxNWs had diameters ranging from 100 to 200 nm with lengths extending up to a few μm and their structure was amorphous. SiOxNWs were grown by the reaction between Ni NPs and Si wafer and Ni NPs acted as catalysts. Ni silicides (NixSi) were also formed inside the wafer by Ni diffusion into Si wafer.

A Novel Way to Prepare Silicon Oxide Nanomaterials with White Light Emission by Reactive Ladder Polyhydrosilsesquioxane

In the present work, we describe a simple and template-free preparation method of silicon oxide nanowires (SiOx-NWs) and silicon oxide nanotubes (SiOx-NTs) from a reactive ladder polyhydrosilsesquioxane (H-LPSQ) precursor. SiOx-NWs and SiOx-NTs were synthesized in large scale by high temperature (1100°C) reaction of ladder HLPSQ on silicon wafer substrate under wet hydrogen and argon (nitrogen) atmosphere. The SiOx-NWs and SiOx-NTs have a uniform diameter and long length. The as-prepared SiOx-NWs exhibits a particular white light emission rather than blue or green light emission found before. Keywords: Ladder polysilsesquioxanes, nanotubes, nanowires, silicon oxide, chemical vapor deposition (CVD), anodic aluminium, carboxylate crystals, sol-gel, Eclipse spectrometer, Si-OH groups, calorimetry, lamella

A Novel Way to Prepare Silicon Oxide Nanomaterials with White Light Emission by Reactive Ladder Polyhydrosilsesquioxane

In the present work, we describe a simple and template-free preparation method of silicon oxide nanowires (SiOx-NWs) and silicon oxide nanotubes (SiOx-NTs) from a reactive ladder polyhydrosilsesquioxane (H-LPSQ) precursor. SiOx-NWs and SiOx-NTs were synthesized in large scale by high temperature (1100°C) reaction of ladder HLPSQ on silicon wafer substrate under wet hydrogen and argon (nitrogen) atmosphere. The SiOx-NWs and SiOx-NTs have a uniform diameter and long length. The as-prepared SiOx-NWs exhibits a particular white light emission rather than blue or green light emission found before. Keywords: Ladder polysilsesquioxanes, nanotubes, nanowires, silicon oxide, chemical vapor deposition (CVD), anodic aluminium, carboxylate crystals, sol-gel, Eclipse spectrometer, Si-OH groups, calorimetry, lamella

General approach to splicing optical microfibers via polymer nanowires

We demonstrate a general approach to splicing microfibers via polymer nanowires. Chloroform dissolved polystyrene nanowires are used to splice silica, tellurite glass, and semiconductor microfibers or nanowires, with splicing loss down to 0.51 dB. Using spliced microfiber structures, we also demonstrate microfiber ring resonators and Mach-Zehnder interferometers with high robustness. The splicing technique demonstrated here promises high potentials for robust optical integration of microfibers or nanowires for functional circuits or devices.