The ultimate strength of glass silica nanowires

Optical Microfiber Intelligent Sensor: Wearable Cardiorespiratory and Behavior Monitoring with a Flexible Wave-Shaped Polymer Optical Microfiber

With the advantages of high flexibility, strong real-time monitoring capabilities, and convenience, wearable devices have shown increasingly powerful application potential in medical rehabilitation, health monitoring, the Internet of Things, and human-computer interaction. In this paper, we propose a novel and wearable optical microfiber intelligent sensor based on a wavy-shaped polymer optical microfiber (WPOMF) for cardiorespiratory and behavioral monitoring of humans. The optical fibers based on polymer materials are prepared into optical microfibers, fully using the advantages of the polymer material and optical microfibers. The prepared polymer optical microfiber is designed into a flexible wave-shaped structure, which enables the WPOMF sensor to have higher tensile properties and detection sensitivity. Cardiorespiratory and behavioral detection experiments based on the WPOMF sensor are successfully performed, which demonstrates the high sensitivity and stability potential of the WPOMF sensor when performing wearable tasks. Further, the success of the AI-assisted medical keyword pronunciation recognition experiment fully demonstrates the feasibility of integrating AI technology with the WPOMF sensor, which can effectively improve the intelligence of the sensor as a wearable device. As an optical microfiber intelligent sensor, the WPOMF sensor offers broad application prospects in disease monitoring, rehabilitation medicine, the Internet of Things, and other fields.

Stretch tuning of dispersion in optical microfibers

Dispersion management is vital for nonlinear optics and ultrafast lasers. We demonstrate that group velocity dispersion (GVD, or second-order dispersion, i.e., β2) and group delay dispersion (GDD) in optical microfibers can be tuned simply by stretch due to their remarkable features of small diameter and diameter-dependent dispersion. We experimentally demonstrate that a pulling force of just a few mN would elongate the optical microfibers by up to 5%, bringing a significant change in the β2 and GDD. This change can be increment or decrement, lying on the diameter of optical microfibers. Therefore, 10-cm-long optical microfibers would provide a GDD change of 104 fs2 when elongated by 5%, well in the elastic limit. Remarkably, this change is equivalent to the GDD (not GDD change) provided by a 0.5-m-long single-mode fiber. Experimental results and simulations show that the GDD change is due to the interplay between elongation, diameter shrink, and refractive index decrease. Benefited from the easy manipulation, tiny pulling force required, and full integration with conventional optical fibers, stretch tuning of dispersion in optical microfibers would find applications in dispersion management for ultrafast lasers and nonlinear optics.

Superlubricity and Stress-Shielding of Graphene Enables Ultra Scratch-Resistant Glasses

Glasses, when subjected to scratch loading, incur damages affecting their optical and mechanical integrity. Here, it is demonstrated that silica glasses protected with mechanically exfoliated few-layer graphene sheets can exhibit remarkable improvement in scratch resistance. To this extent, the friction and wear characteristics of silica glasses with exfoliated graphene using atomic force microscopy (AFM) are explored. The friction forces recorded during AFM scratch tests of the graphene-glass surfaces at multiple loads exhibit ∼98% reduction compared to that of the bare silica glass, with the friction coefficient falling in the superlubricity regime. This dramatic reduction in friction achieved by the graphene sheets results in significantly lower wear of the graphene-glass surfaces postscratching. Further investigations employing atomistic simulations reveal that the stress-shielding mechanism is due to the reduced deformation of graphene-glass surfaces, thereby curtailing the overall damage. Altogether, the present work provides a new fillip toward the development of glasses with enhanced scratch resistance exploiting two-dimensional coatings.

Numerical analysis of the ultra-wide tunability of nanofiber Bragg cavities

Nanofiber Bragg cavities (NFBCs) are solid-state microcavities fabricated in optical tapered fiber. They can be tuned to a resonance wavelength of more than 20 nm by applying mechanical tension. This property is important for matching the resonance wavelength of an NFBC with the emission wavelength of single-photon emitters. However, the mechanism of the ultra-wide tunability and the limitation of the tuning range have not yet been clarified. It is important to comprehensively analyze both the deformation of the cavity structure in an NFBC and the change in the optical properties due to the deformation. Here, we present an analysis of the ultra-wide tunability of an NFBC and the limitation of the tuning range using three dimensional (3D) finite element method (FEM) and 3D finite-difference time-domain (FDTD) optical simulations. When we applied a tensile force of 200 μN to the NFBC, a stress of 5.18 GPa was concentrated at the groove in the grating. The grating period was extended from 300 to 313.2 nm, while the diameter slightly shrank from 300 to 297.1 nm in the direction of the grooves and from 300 to 298 nm in the direction orthogonal to the grooves. This deformation shifted the resonance peak by 21.5 nm. These simulations indicated that both the elongation of the grating period and the small shrinkage of the diameter contributed to the ultra-wide tunability of the NFBC. We also calculated the dependence of the stress at the groove, the resonance wavelength, and the quality Q factor while changing the total elongation of the NFBC. The dependence of the stress on the elongation was 1.68 × 10^-2 GPa/μm. The dependence of the resonance wavelength was 0.07 nm/μm, which almost agrees with the experimental result. When the NFBC, assumed to have the total length of 32 mm, was stretched by 380 μm with the tensile force of 250 μN, the Q factor for the polarization mode parallel to the groove changed from 535 to 443, which corresponded to a change in Purcell factor from 5.3 to 4.9. This slight reduction seems acceptable for the application as single photon sources. Furthermore, assuming a rupture strain of the nanofiber of 10 GPa, it was estimated that the resonance peak could be shifted by up to about 42 nm.

Dual-Phasic, Well-Aligned, and Strong Flexible Hydrophobic Ceramic Membranes for Efficient Thermal Insulation in Extreme Conditions

The inherent brittleness and hydrophilicity of ceramics pose a great challenge to designing a reliable structure that can resist mechanical loads and moisture in extreme conditions with high temperature and high humidity. Here, we report a two-phase hydrophobic silica-zirconia composite ceramic nanofiber membrane (H-ZSNFM) with exceptional mechanical robustness and high-temperature hydrophobic resistance. For the dual-phasic nanofibers, the amorphous silica blocked the connection of zirconia nanocrystals, and the lattice distortion was observed due to Si in the ZrO2 lattice. H-ZSNFM has strong strength (5-8.4 MPa), high hydrophobic temperature resistance (450 °C), high porosity (89%), low density (40 mg/cm3), low thermal conductivity (30 mW/m·K), and excellent thermal radiation reflectivity (90%). By simulating the actual high-temperature and high-humidity environment, 10-mm-thick H-ZSNFMs can reduce the heat source from 1365 to 380 °C and maintain complete hydrophobicity even in a water vapor environment of 350 °C. This means that it has superior insulation and waterproof performance even in a high-temperature water environment. For firefighting clothing, H-ZSNFM displayed waterproof and insulation layers, which have excellent thermal protection performance and achieve incompatibility between water and fire, providing valuable time for fire rescue and a safety line of defense for emergency personnel. This design strategy with mechanical robust and hydrophobic temperature resistance applies to the development of many other types of high-performance thermal insulation materials and presents a competitive material system for thermal protection in extreme conditions.

Advancing the Mechanical Performance of Glasses: Perspectives and Challenges

Glasses are materials that lack a crystalline microstructure and long-range atomic order. Instead, they feature heterogeneity and disorder on superstructural scales, which have profound consequences for their elastic response, material strength, fracture toughness, and the characteristics of dynamic fracture. These structure-property relations present a rich field of study in fundamental glass physics and are also becoming increasingly important in the design of modern materials with improved mechanical performance. A first step in this direction involves glass-like materials that retain optical transparency and the haptics of classical glass products, while overcoming the limitations of brittleness. Among these, novel types of oxide glasses, hybrid glasses, phase-separated glasses, and bioinspired glass-polymer composites hold significant promise. Such materials are designed from the bottom-up, building on structure-property relations, modeling of stresses and strains at relevant length scales, and machine learning predictions. Their fabrication requires a more scientifically driven approach to materials design and processing, building on the physics of structural disorder and its consequences for structural rearrangements, defect initiation, and dynamic fracture in response to mechanical load. In this article, a perspective is provided on this highly interdisciplinary field of research in terms of its most recent challenges and opportunities.

Fire-Resistant and Hierarchically Structured Elastic Ceramic Nanofibrous Aerogels for Efficient Low-Frequency Noise Reduction

Traffic noise has been regarded as one of the most annoying pollutions that induce severe hazards to human health, both physiological and psychological. The commonly used fibrous noise absorption materials are limited by their large density, poor sound absorption ability at low frequencies, and unsatisfactory fire-resistant ability. Here, we develop hierarchically structured elastic ceramic electrospun nanofibrous aerogels, which possess lightweight properties (density of 13.29 mg cm^-3) and superior low-frequency sound absorption ability (NRC value of 0.59). Specifically, the obtained ceramic electrospun nanofibrous aerogel is nonflammable on exposure to fire and can be compressed and quickly recover to its original height without any visible damage. Moreover, the resultant aerogels could be facilely and efficiently manufactured into designed shapes on a large scale, demonstrating their potential for industrialization. The successful design of such ceramic-based bulk materials may provide new insights for the further development of the next-generation high-efficiency sound-absorbing products.

Ingeniously designed Silica nanostructures as an exceptional support: Opportunities, potential challenges and future prospects for viable degradation of pesticides

Despite significant advancements in modern agricultural practices, efficient handling of pesticides is a must as they are continuously defiling our terrestrial as well as aquatic life. During the last couple of decades, substantial efforts by various research groups have been devoted to find innovative solutions to remove pesticides from our environment in a greener way. In this regard, functionalized silica nanoparticles (NPs) have gained considerable attention of scientific community due to their notable properties such as amenable design, large surface area as well as fine-tunable and uniform pore structures which make them an ideal material for pesticides removal. The present review aims to proffer current scientific progress attained by silica-based nanostructures as an excellent material for effective removal of noxious agrochemicals. Further, a brief discussion on the synthetic strategies as well as intrinsic benefits associated with different morphologies of silica have also been highlighted in this article. It also summarizes the recent reports on silica assisted degradation of pesticides via enzymatic, chemical as well as advanced oxidation protocols. Additionally, it presents a critical analysis of different support materials for decontamination of our ecosystem. The review concludes with potential challenges, their possible solutions along with key knowledge gaps and future research directions for successful deployment of silica supported materials in degradation of pesticides at commercial scale.

Silica optical fiber integrated with two-dimensional materials: towards opto-electro-mechanical technology

In recent years, the integration of graphene and related two-dimensional (2D) materials in optical fibers have stimulated significant advances in all-fiber photonics and optoelectronics. The conventional passive silica fiber devices with 2D materials are empowered for enhancing light-matter interactions and are applied for manipulating light beams in respect of their polarization, phase, intensity and frequency, and even realizing the active photo-electric conversion and electro-optic modulation, which paves a new route to the integrated multifunctional all-fiber optoelectronic system. This article reviews the fast-progress field of hybrid 2D-materials-optical-fiber for the opto-electro-mechanical devices. The challenges and opportunities in this field for future development are discussed.

Flexible welding of SiOx nanowire to macroporous carbon film and underlying new insights

With the continuous decreasing in sizes of functional materials and devices, people are being asked to perform a flexible, accurate, in-situ and non-thermal welding of nanowires at the nanoscale. In this work, a well deliberated procedure including three typical stages: sharpening, hooking and welding, was carried out in sequence by in-situ TEM to realize the high demand welding of SiOx nanowire to macroporous carbon film. It was found that the brittle SiOx nanowire was non-thermally softened under energetic e-beam irradiation, and the flexibility and accuracy of welding could be achieved by adjusting the beam spot size, irradiation location and irradiation time. It was demonstrated that the nanocurvature effect of SiOx nanowire and the ultra-fast energy deposition effect induced by energetic e-beam irradiation dominated the diffusion, evaporation and plastic flow of atoms and the resulting nanowire re-shaping and nanowelding processes. In contrast, the traditional knock-on mechanism and e-beam heating effect are inadequate to explain these phenomena. Therefore, such a study is crucial not only to the flexible technical controlling but also to the profound fundamental understanding of energetic e-beam-induced nanowire re-shaping and nanowelding.

Optical Micro/Nanofiber-Enabled Compact Tactile Sensor for Hardness Discrimination

Optical micro/nanofibers (MNFs) can be applied for ultrasensitive tactile sensing with fast response and compact size, which are attractive for restoring tactile information in minimally invasive robotic surgery and tissue palpation. Herein, we present a compact tactile sensor (CTS) with a diameter of 1.5 mm enabled by an optical MNF. The CTS provides continuous readouts for high-fidelity transduction of touch and pressure stimuli into interpretable optical signals, which permit instantaneous sensing of contact and pressure with pressure-sensing sensitivity as high as 0.108 mN^-1 and a resolution of 0.031 mN. Working in pressing mode, the CTS can discriminate the difference in the hardness of two poly(dimethylsiloxane) (PDMS) slats (with shore A of 36 and 40) directly, a hardness resolving ability even beyond the human hands. Benefitting from the fast response feature, the CTS can also be operated in either scanning or tapping mode, making it feasible for hardness identification by analyzing the shape of the response curve. As a proof of concept, the hardness discrimination of a pork liver and an adductor muscle was experimentally demonstrated. Such MNF-enabled compact tactile sensors may pave the way for hardness sensing in tissue palpation, surgical robotics, and object identification.

Tunable Anelasticity in Amorphous Si Nanowires

In situ bending tests of amorphous Si nanowires (a-Si NWs) found different elastic behavior depending on whether they were straight or curved to begin with. The axially straight NWs exhibit pure elastic deformation; however, the axially curved NWs exhibit obvious anelastic behavior when they are bent in the direction of original curvature. On the basis of STEM-EELS analysis, we propose that the underlying mechanism for this anelastic behavior is a bond-switching assisted redistribution of the nonuniform density (structure) in the curved NWs under the inhomogeneous stress field. This mechanism was further supported by the fact that the originally straight a-Si NWs also display similar anelasticity with the as-grown curved NWs after focused ion beam irradiation that can cause nonuniform structure distribution. As compared to what has been reported in other 1D materials, the anelasticity of a-Si NWs can be tuned by modifying their morphology, controlling the loading direction, or irradiating them via ion beam. Our findings suggest that a-Si NWs could be a promising material in the nanoscale damping systems, especially the semiconductor nanodevices.

Micro-/Nanofiber Optics: Merging Photonics and Material Science on Nanoscale for Advanced Sensing Technology

Micro-/nanofibers (MNFs) are optical fibers with diameters close to or below the wavelength of the guided light. These tiny fibers can offer engineerable waveguiding properties including optical confinement, fractional evanescent fields, and surface intensity, which is very attractive to optical sensing on the micro-/nano scale. In this review, we first introduce the basics of MNF optics and MNF optical sensors from physical and chemical to biological applications and review the progress and current status of this field. Then, we review and discuss hybrid MNF structures for advanced optical sensing by merging MNFs with functional structures including chemical indicators, quantum dots, dye molecules, plasmonic nanoparticles, 2-D materials, and optofluidic chips. Thirdly, we introduce the emerging trends in developing MNF-based advanced sensing technology for ultrasensitive, active, and wearable sensors and discuss the future prospects and challenges in this exciting research field. Finally, we end the review with a brief conclusion.

Silica Glass Toughened by Consolidation of Glassy Nanoparticles

The brittleness of oxide glasses has dramatically restricted their practical applications as structural materials despite very high theoretical strength. Herein, using molecular dynamics simulations, we show that silica glass prepared by consolidating glassy nanoparticles exhibit remarkable tensile ductility. Because of dangling bonds at surfaces and high contact stresses, the pressure applied for consolidating glassy nanoparticles to achieve ductility is significantly lower than that required to toughen bulk glass via permanent densification. We have identified 5-fold silicon, with a higher propensity to carry out local shear deformation than 4-fold silicon, as the structural origin for the observed tensile ductility. Interestingly, the work hardening effect has been, for the first time, observed in thus-prepared silica glass, with its strength increasing from 4 GPa to ∼7 GPa upon cold work. This is due to stress-assisted relaxation of 5-fold silicon to 4-fold during cold work, analogous to transformation hardening.

Optically Levitated Nanodumbbell Torsion Balance and GHz Nanomechanical Rotor

Levitated optomechanics has great potential in precision measurements, thermodynamics, macroscopic quantum mechanics, and quantum sensing. Here we synthesize and optically levitate silica nanodumbbells in high vacuum. With a linearly polarized laser, we observe the torsional vibration of an optically levitated nanodumbbell. This levitated nanodumbbell torsion balance is a novel analog of the Cavendish torsion balance, and provides rare opportunities to observe the Casimir torque and probe the quantum nature of gravity as proposed recently. With a circularly polarized laser, we drive a 170-nm-diameter nanodumbbell to rotate beyond 1 GHz, which is the fastest nanomechanical rotor realized to date. Smaller silica nanodumbbells can sustain higher rotation frequencies. Such ultrafast rotation may be used to study material properties and probe vacuum friction.

An atomic-scale evaluation of the fracture toughness of silica glass

Using an atomistic technique consistent with continuum balance laws and drawing on classical fracture mechanics theory, we estimate the resistance to fracture propagation of amorphous silica. We discuss correspondence and deviations from classical linear elastic fracture mechanics theory including size dependence, rigid/floppy modes of deformation, and the effects of surface energy and stress.

Micro/Nanofibre Optical Sensors: Challenges and Prospects

Micro/nanofibres (MNFs) are optical fibres with diameters close to or below the vacuum wavelength of visible or near-infrared light. Due to its wavelength- or sub-wavelength scale diameter and relatively large index contrast between the core and cladding, an MNF can offer engineerable waveguiding properties including optical confinement, fractional evanescent fields and surface intensity, which is very attractive to optical sensing on the micro and nanometer scale. In particular, the waveguided low-loss tightly confined large fractional evanescent fields, enabled by atomic level surface roughness and extraordinary geometric and material uniformity in a glass MNF, is one of its most prominent merits in realizing optical sensing with high sensitivity and great versatility. Meanwhile, the mesoporous matrix and small diameter of a polymer MNF, make it an excellent host fibre for functional materials for fast-response optical sensing. In this tutorial, we first introduce the basics of MNF optics and MNF optical sensors, and review the progress and current status of this field. Then, we discuss challenges and prospects of MNF sensors to some extent, with several clues for future studies. Finally, we conclude with a brief outlook for MNF optical sensors.

A Review of Microfiber-Based Temperature Sensors

Optical microfiber-based temperature sensors have been proposed for many applications in a variety of industrial uses, including biomedical, geological, automotive, and defense applications. This increasing demand for these micrometric devices is attributed to their large dynamic range, high sensitivity, fast-response, compactness and robustness. Additionally, they can perform in-situ measurements remotely and in harsh environments. This paper presents an overview of optical microfibers, with a focus on their applications in temperature sensing. This review broadly divides microfiber-based temperature sensors into two categories: resonant and non-resonant microfiber sensors. While the former includes microfiber loop, knot and coil resonators, the latter comprises sensors based on functionally coated/doped microfibers, microfiber couplers, optical gratings and interferometers. In the conclusions, a summary of reported performances is presented.

Hierarchical Porous Structured SiO2/SnO2 Nanofibrous Membrane with Superb Flexibility for Molecular Filtration

The separation and purification of chemical molecules from organic media under harsh chemical environments are of vital importance in the fields of water treatment, biomedical engineering, and organic recycling. Herein, we report the preparation of a flexible SiO₂/SnO₂ nanofibrous membrane (SiO₂/SnO₂ NFM) with high surface area and hierarchical porous structure by selecting poly(vinyl butyral) as pore-forming agent and embedding crystalline phase into amorphous matrix without using surfactant as sacrificial template. Benefiting from the uniform micropore size on the fibers and negatively charged properties, the membranes exhibit a precise selectivity toward molecules based on electrostatic interaction and size exclusion, which could separate organic molecule mixtures with the same electrostatic charges and different molecular sizes with a high efficiency of more than 97%. Furthermore, the highly tortuous open-porous structures and high porosity give rise to a high permeate flux of 288 000 L m^-2 h^-1. In addition, the membrane also displays excellent stability and can be reused for ten consecutive filtration-regeneration cycles. The integration of high filtration efficiency, large permeate flux, good reutilization, and easy to industrialization provides the SiO₂/SnO₂ NFM for potential applications in practical molecular purification and separation science.

Exceptional room-temperature plasticity in amorphous alumina nanotubes fabricated by magnetic hard anodisation

Crystalline aluminum oxide is a brittle ceramic material. Here we show that individual alumina nanotubes with internal and external radii of ∼15 nm and ∼50 nm, respectively and lengths of the order of 100 μm can be readily separated from amorphous alumina membranes fabricated by a hard anodisation process under a magnetic field of up to 1.5 T. The ceramic nanotubes are extremely flexible and exhibit an exceptional plasticity of ±70% at room temperature without breaking. Elastic properties investigated by the double clamped beam method include a tensile strength of 4.1 GPa, corresponding to a breaking strain of 5%. These values are respectively 17 and 70 times greater than those of polycrystalline alumina fibres. The plasticity of anodic amorphous alumina helps explain the formation of ordered arrays of nanopores in the alumina membranes.

The Mechanical Properties of Nanowires

Applications of nanowires into future generation nanodevices require a complete understanding of the mechanical properties of the nanowires. A great research effort has been made in the past two decades to understand the deformation physics and mechanical behaviors of nanowires, and to interpret the discrepancies between experimental measurements and theoretical predictions. This review focused on the characterization and understanding of the mechanical properties of nanowires, including elasticity, plasticity, anelasticity and strength. As the results from the previous literature in this area appear inconsistent, a critical evaluation of the characterization techniques and methodologies were presented. In particular, the size effects of nanowires on the mechanical properties and their deformation mechanisms were discussed.

Superplastic behavior of silica nanowires obtained by direct patterning of silsesquioxane-based precursors

Silica nanowires spanning 10 μm-deep trenches are fabricated from different types of silsesquioxane-based precursors by direct e-beam patterning on silicon followed by release through deep reactive ion etching. Nanowire aspect ratios as large as 150 are achieved with a critical dimension of about 50 nm and nearly rectangular cross-sections. In situ bending tests are carried out inside a scanning electron microscope, where the etch depth of 10 [Formula: see text] provides sufficient space for deformation. Silica NWs are indeed observed to exhibit superplastic behavior without fracture with deflections reaching the full etch depth, about two orders of magnitude larger than the nanowire thickness. A large-deformation elastic bending model is utilized for predicting the deviation from the elastic behavior. The results of forty different tests indicate a critical stress level of 0.1-0.4 GPa for the onset of plasticity. The study hints at the possibility of fabricating silica nanowires in a monolithic fashion through direct e-beam patterning of silsesquioxane-based resins. The fabrication technology is compatible with semiconductor manufacturing and provides silica nanowires with a very good structural integrity.

Study on fracture behavior of individual InAs nanowires using an electron-beam-drilled notch

The mechanical properties and fracture behavior of individual InAs nanowires (NWs) were investigated under uniaxial tensile loading in a transmission electron microscope.

Microstructure provides insights into evolutionary design and resilience of Coscinodiscus sp. frustule

We conducted in situ three-point bending experiments on beams with roughly square cross-sections, which we fabricated from the frustule of Coscinodiscus sp. We observe failure by brittle fracture at an average stress of 1.1 GPa. Analysis of crack propagation and shell morphology reveals a differentiation in the function of the frustule layers with the basal layer pores, which deflect crack propagation. We calculated the relative density of the frustule to be ∼30% and show that at this density the frustule has the highest strength-to-density ratio of 1,702 kN⋅m/kg, a significant departure from all reported biologic materials. We also performed nanoindentation on both the single basal layer of the frustule as well as the girdle band and show that these components display similar mechanical properties that also agree well with bending tests. Transmission electron microscopy analysis reveals that the frustule is made almost entirely of amorphous silica with a nanocrystalline proximal layer. No flaws are observed within the frustule material down to 2 nm. Finite element simulations of the three-point bending experiments show that the basal layer carries most of the applied load whereas stresses within the cribrum and areolae layer are an order of magnitude lower. These results demonstrate the natural development of architecture in live organisms to simultaneously achieve light weight, strength, and exceptional structural integrity and may provide insight into evolutionary design.

Size-Dependent Brittle-to-Ductile Transition in Silica Glass Nanofibers

Silica (SiO2) glass, an essential material in human civilization, possesses excellent formability near its glass-transition temperature (Tg > 1100 °C). However, bulk SiO2 glass is very brittle at room temperature. Here we show a surprising brittle-to-ductile transition of SiO2 glass nanofibers at room temperature as its diameter reduces below 18 nm, accompanied by ultrahigh fracture strength. Large tensile plastic elongation up to 18% can be achieved at low strain rate. The unexpected ductility is due to a free surface affected zone in the nanofibers, with enhanced ionic mobility compared to the bulk that improves ductility by producing more bond-switching events per irreversible bond loss under tensile stress. Our discovery is fundamentally important for understanding the damage tolerance of small-scale amorphous structures.

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.

Silica Nanowires Templated by Amyloid-like Fibrils

Many peptides self‐assemble to form amyloid fibrils. We previously explored the sequence propensity to form amyloid using variants of a designed peptide with sequence KFFEAAAKKFFE. These variant peptides form highly stable amyloid fibrils with varied lateral assembly and are ideal to template further assembly of non‐proteinaceous material. Herein, we show that the fibrils formed by peptide variants can be coated with a layer of silica to produce silica nanowires using tetraethyl‐orthosilicate. The resulting nanowires were characterized using electron microscopy (TEM), X‐ray fiber diffraction, FTIR and cross‐section EM to reveal a nanostructure with peptidic core. Lysine residues play a role in templating the formation of silica on the fibril surface and, using this library of peptides, we have explored the contributions of lysine as well as arginine to silica templating, and find that sequence plays an important role in determining the physical nature and structure of the resulting nanowires.

Silica Nanowires Templated by Amyloid-like Fibrils

Many peptides self-assemble to form amyloid fibrils. We previously explored the sequence propensity to form amyloid using variants of a designed peptide with sequence KFFEAAAKKFFE. These variant peptides form highly stable amyloid fibrils with varied lateral assembly and are ideal to template further assembly of non-proteinaceous material. Herein, we show that the fibrils formed by peptide variants can be coated with a layer of silica to produce silica nanowires using tetraethyl-orthosilicate. The resulting nanowires were characterized using electron microscopy (TEM), X-ray fiber diffraction, FTIR and cross-section EM to reveal a nanostructure with peptidic core. Lysine residues play a role in templating the formation of silica on the fibril surface and, using this library of peptides, we have explored the contributions of lysine as well as arginine to silica templating, and find that sequence plays an important role in determining the physical nature and structure of the resulting nanowires.

Optical Microfibre Based Photonic Components and Their Applications in Label-Free Biosensing

Optical microfibre photonic components offer a variety of enabling properties, including large evanescent fields, flexibility, configurability, high confinement, robustness and compactness. These unique features have been exploited in a range of applications such as telecommunication, sensing, optical manipulation and high Q resonators. Optical microfibre biosensors, as a class of fibre optic biosensors which rely on small geometries to expose the evanescent field to interact with samples, have been widely investigated. Due to their unique properties, such as fast response, functionalization, strong confinement, configurability, flexibility, compact size, low cost, robustness, ease of miniaturization, large evanescent field and label-free operation, optical microfibres based biosensors seem a promising alternative to traditional immunological methods for biomolecule measurements. Unlabeled DNA and protein targets can be detected by monitoring the changes of various optical transduction mechanisms, such as refractive index, absorption and surface plasmon resonance, since a target molecule is capable of binding to an immobilized optical microfibre. In this review, we critically summarize accomplishments of past optical microfibre label-free biosensors, identify areas for future research and provide a detailed account of the studies conducted to date for biomolecules detection using optical microfibres.

Robust scaling of strength and elastic constants and universal cooperativity in disordered colloidal micropillars

We study the uniaxial compressive behavior of disordered colloidal free-standing micropillars composed of a bidisperse mixture of 3- and 6-μm polystyrene particles. Mechanical annealing of confined pillars enables variation of the packing fraction across the phase space of colloidal glasses. The measured normalized strengths and elastic moduli of the annealed freestanding micropillars span almost three orders of magnitude despite similar plastic morphology governed by shear banding. We measure a robust correlation between ultimate strengths and elastic constants that is invariant to relative humidity, implying a critical strain of ∼0.01 that is strikingly similar to that observed in metallic glasses (MGs) [Johnson WL, Samwer K (2005) Phys Rev Lett 95:195501] and suggestive of a universal mode of cooperative plastic deformation. We estimate the characteristic strain of the underlying cooperative plastic event by considering the energy necessary to create an Eshelby-like ellipsoidal inclusion in an elastic matrix. We find that the characteristic strain is similar to that found in experiments and simulations of other disordered solids with distinct bonding and particle sizes, suggesting a universal criterion for the elastic to plastic transition in glassy materials with the capacity for finite plastic flow.

Anomalous surface states modify the size-dependent mechanical properties and fracture of silica nanowires

Molecular dynamics simulations of amorphous silica nanowires under tension were analyzed for size and surface stress effects on mechanical properties and for structural modifications via bond angle distributions. Their fracture behavior was also investigated beyond the elastic limit. The Young's moduli of silica nanowires were predicted to be about 75-100 GPa, depending on the nanowire size. The ultimate strength was calculated to be ∼10 GPa, depending on the diameter, which is in excellent agreement with the experiments. The dependence of the Young's modulus on nanowire diameter is explained in terms of surface compressive stress effects. The fracture behavior of nanowires was also found to be influenced by surface compressive stresses. Bond angle distribution analysis of various nanowires reveals significant compressive surface states, as evidenced by the appearance of a secondary peak in the Si-O-Si bond angle distribution at ∼97°, which is absent in bulk silica. The strain rate was found to have a negligible effect on the Young's modulus of the silica nanowires, but it has a critical role in determining their fracture mode.

Photonic nanowires: from subwavelength waveguides to optical sensors

Nanowires are one-dimensional (1D) nanostructures with comparatively large aspect ratios, which can be useful in manipulating electrons, photons, plasmons, phonons, and atoms for numerous technologies. Among various nanostructures for low-dimensional photonics, the 1D nanowire is of great importance owing to its ability to route tightly confined light fields in single-mode with lowest space and material requirements, minimized optical path, and high mechanical flexibilities. In recent years, nanowire photonics have increasingly been attracting scientists' interests for both fundamental studies and technological applications because 1D nanowires have more favorable properties than many other structures, such as 0D quantum dots (QDs) and 2D films. As subwavelength waveguides, free-standing nanowires fabricated by either chemical growth or physical drawing techniques surpass nanowaveguides fabricated by almost all other means in terms of sidewall smoothness and diameter uniformity. This conveys their low waveguiding losses. With high index contrast (typically higher than 0.5) between the core and the surrounding or with surface plasmon resonance, a nanowire can guide light with tight optical confinement. For example, the effective mode area is less than λ(2)/10 for a dielectric nanowire or less than λ(2)/100 for a metal nanowire, where λ is the vacuum wavelength of the light. As we increase the wavelength-to-diameter ratio (WDR) of a nanowire, we can enlarge the fractional power of the evanescent fields in the guiding modes to over 80% while maintaining a small effective mode area, which may enable highly localized near-field interaction between the guided fields and the surrounding media. These favorable properties have opened great opportunities for optical sensing on the single-nanowire scale. However, several questions arise with ongoing research. With a deep-subwavelength cross-section, how can we efficiently couple light into a single nanowire? How can we fabricate a nanowire with low optical loss? How can we activate a passive nanowire for optical sensing? And lastly, how can we adapt mature optical measurement technology onto a nanowire? In this Account, we highlight our initial attempts to address the above-mentioned challenges. First, we introduce the fabrication and functionalization of low-loss photonic nanowires. We show that nanowires fabricated by either top-down physical drawing (e.g., for amorphous nanowires) or bottom-up chemical growth (e.g., for crystalline nanowires) can yield excellent geometric and structural uniformities with surface roughness down to atomic level and minimize the scattering loss for subwavelength optical or plasmonic waveguiding. Then, relying on a near-field fiber-probe micromanipulation, we demonstrate optical launching of single nanowires by evanescent coupling, with coupling efficiency up to 90% for dielectric nanowires and 80% for plasmonic nanowires. Third, we discuss the waveguiding properties of nanowires and emphasize their outstanding capability of waveguiding tightly confined optical fields with high fractional evanescent fields. In addition, we briefly show a balance between the loss, confinement, and bandwidth in a waveguiding nanowire. Fourthly, we present promising approaches to single-nanowire optical sensors. By measuring optical absorption or spectral transmission of a nanowire and activating nanowires with sensitive dopants, we demonstrate a single-nanowire optical sensor with high sensitivity, fast response, and low optical power. This may lead to a novel platform for optical sensing at nanoscale. Finally, we conclude with an outlook for future challenges in the light manipulation and sensing applications of photonic nanowires.

Synthesis of very small diameter silica nanofibers using sound waves

Silica nanofibers of an average diameter of 30 nm were synthesized using sound waves.

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.

Concentration gradient induced morphology evolution of silica nanostructure growth on photoresist-derived carbon micropatterns

The evolution of silica nanostructure morphology induced by local Si vapor source concentration gradient has been investigated by a smart design of experiments. Silica nanostructure or their assemblies with different morphologies are obtained on photoresist-derived three-dimensional carbon microelectrode array. At a temperature of 1,000°C, rope-, feather-, and octopus-like nanowire assemblies can be obtained along with the Si vapor source concentration gradient flow. While at 950°C, stringlike assemblies, bamboo-like nanostructures with large joints, and hollow structures with smaller sizes can be obtained along with the Si vapor source concentration gradient flow. Both vapor-liquid-solid and vapor-quasiliquid-solid growth mechanisms have been applied to explain the diverse morphologies involving branching, connecting, and batch growth behaviors. The present approach offers a potential method for precise design and controlled synthesis of nanostructures with different features.

A novel apparatus for in situ compression of submicron structures and particles in a high resolution SEM

We report on the development and characterization of a novel in situ manipulation device to perform stressing experiments on the submicron scale inside a high resolution field emission scanning electron microscope. The instrument comprises two main assembly groups: an upper part for positioning and moving a mounted probe and a force sensor as well as a specimen support as lower part. The upper part consists of a closed loop tripod piezoelectric scanner mounted on a self-locking coarse positioning stage. Two interlocked steel springs and a linear variable differential transformer measuring the springs' deflections compose the lower part of the instrument. This arrangement acts as force-sensor and sample support. In comparison to already well-established concepts a wide measuring range is covered by adjusting the spring constant between 30 N/m and 50000 N/m. Moreover, the new device offers striking advantages with respect to force calibration and sample deformation measurements. Force calibration is performed using the eigenfrequency of the force detection system directly inside the SEM. Deformation data are obtained with high accuracy by simultaneously recording displacements above and below the specimen. The detrimental apparatus compliance is determined, and the influence on measured data subsequently minimized: an easy to validate two-springs-in-series model is used for data correction. A force resolution in normal direction of 100 nN accompanied by a sample deformation resolution of 5 nm can be achieved with the instrument using an appropriate load cell stiffness. The capabilities and versatility of this instrument are exemplified by compression experiments performed on submicron amorphous silica particles.

Ultimate bending strength of Si nanowires

Test platforms for the ideal strength of materials are provided by almost defect-free nanostructures (nanowires, nanotubes, nanoparticles, for example). In this work, the ultimate bending strengths of Si nanowires with radii in the 20-60 nm range were investigated by using a new bending protocol. Nanowires simply held by adhesion on flat substrates were bent through sequential atomic force microscopy manipulations. The bending states prior to failure were analyzed in great detail to measure the bending dynamics and the ultimate fracture strength of the investigated nanowires. An increase in the fracture strengths from 12 to 18 GPa was observed as the radius of nanowires was decreased from 60 to 20 nm. The large values of the fracture strength of these nanowires, although comparable with the ideal strength of Si, are explained in terms of the surface morphology of the nanowires.

Phyto-inspired silica nanowires: characterization and application in lipase immobilization

Silica nanostructures were phyto-fabricated on different surfaces by using pomegranate (Punica granatum) leaf extracts. On zinc films, nanowires were obtained. On other surfaces such as silica, alumina, zinc oxide, and glass, spherical aggregates, cubic assemblies, microflakes, and acicular structures, respectively, were observed. The nanowires developed on Zn surfaces were characterized by scanning electron microscope-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD), photoluminescence, and Fourier transform infrared (FTIR) spectroscopic analysis. XRD profiles displayed peaks at 2.4, 4.9, and 12.1° indicating the presence of silica nanostructures. When excited at 340 nm, the reaction mixtures displayed a characteristic blue luminescence at 404 nm. FTIR spectra showed the existence of Si-OH and Si-O-Si bonds. The nanowires were functionalized with amine groups and used for the covalent immobilization of Candida rugosa lipase. The immobilized enzyme displayed better pH and temperature stability and retained 80% activity after 20 cycles. This paper highlights a novel route for the phyto-mediated growth of silica nanowires on Zn surfaces, their characterization and effective use as a matrix for enzyme immobilization.

Understanding the growth of amorphous SiO2 nanofibers and crystalline binary nanoparticles produced by laser ablation

The pulsed-laser evaporation synthesis of silica nanofibers and crystalline binary nanoparticles is investigated in detail. By careful adjustment of the synthesis parameters one can tailor the product to form high yield nanofibers or binary nanoparticles. Some control on their diameters is also possible through the synthesis parameters. Oxidation of the nanofibers occurs upon exposure to air after the reaction.

Stable low-loss optical nanofibres embedded in hydrophobic aerogel

Nanofibres, optical fibres narrower than the wavelength of light, degrade in hours on exposure to air. We show that encapsulation in hydrophobic silica aerogel (refractive index 1.05) provides protection and stability (over 2 months) without sacrificing low attenuation, strong confinement and accessible evanescent field. The measured attenuation was <0.03 dB/mm, over 10 × lower than reported with other encapsulants. This enables many nanofibre applications based on their extreme small size and strong external evanescent field, such as optical sensors, nonlinear optics, nanofibre circuits and high-Q resonators. The aerogel is more than a waterproof box, it is a completely-compatible gas-permeable material in intimate contact with the nanofibre and hydrophobic on both the macroscopic and molecular scales. Its benefits are illustrated by experiments on gas sensing (exploiting the aerogel's porosity) and supercontinuum generation (exploiting its ultra-low index).