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Lead-free K0.5Na0.5NbO3 (KNN) nanotube arrays were synthesized by a sol-gel method with anodic aluminum oxide templates. The obtained KNN nanotubes exhibited a polycrystalline and monoclinic perovskite structure with diameters of ∼200 nm and wall thickness of ∼30-40 nm, respectively. The polarization-electric loop curve of the nanotubes array were examined showing the values of 2Pr and 2Ec at about 3.4 μC/cm2 and 13 kV/cm, respectively, under a maximum electric field of 12.5 kV/cm. The piezoelectric characteristics of individual KNN nanotube array was also identified through piezoresponse force microscopy. [ABSTRACT FROM AUTHOR]

Neodymium-modified bismuth titanate, Bi4-xNdxTi3O12 (BNdT), nanotube arrays were fabricated by sol-gel method utilizing experimentally prepared porous anodic aluminum oxide (AAO) templates with pore diameters of about 200 nm and 100 nm, respectively. The as-prepared nanotube arrays exhibit orthorhombic perovskite polycrystalline structure of BNdT, which have outer diameters of about 200 and 100 nm, corresponding to the pores diameters of the AAO templates employed, and with wall thicknesses of about 9.7 nm and 12 nm, respectively. The phonon vibration modes corresponding to the Bi atoms in the Bi2O2 layers weaken and broaden with increasing Nd content. The changes of Raman internal modes originated from the vibrations of atoms inside the TiO6 octahedral indicate the increase in octahedron tilting and structural distortion. The leakage current and polarization-electric field response curves of BNdT nanotube arrays were measured, and the hysteresis loop illustrates a good ferroelectric property of as-prepared BNdT nanotube array at room temperature. The dielectric constant and dissipation factor were measured in the frequency region from 1 kHz to 1 MHz indicating polarization relaxation phenomenon. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) detectors have attracted considerable attention in the past decade due to their extensive applications in the civil and military fields. Wide bandgap semiconductor-based UV detectors can detect UV light effectively, and nanowire structures can greatly improve the sensitivity of sensors with many quantum effects. This review summarizes recent developments in the classification and principles of UV detectors, i.e., photoconductive type, Schottky barrier type, metal-semiconductor-metal (MSM) type, p-n junction type and p-i-n junction type. The current state of the art in wide bandgap semiconductor materials suitable for producing nanowires for use in UV detectors, i.e., metallic oxide, III-nitride and SiC, during the last five years is also summarized. Finally, novel types of UV detectors such as hybrid nanostructure detectors, self-powered detectors and flexible detectors are introduced. [ABSTRACT FROM AUTHOR]

In this work, SnO2 nanoflowers synthesized by a hydrothermal method were employed as hydrogen sensing materials. The as-synthesized SnO2 nanoflowers consisted of cuboid-like SnO2 nanorods with tetragonal structures. A great increase in the relative content of surface-adsorbed oxygen was observed after the vacuum annealing treatment, and this increase could have been due to the increase in surface oxygen vacancies serving as preferential adsorption sites for oxygen species. Annealing treatment resulted in an 8% increase in the specific surface area of the samples. Moreover, the conductivity of the sensors decreased after the annealing treatment, which should be attributed to the increase in electron scattering around the defects and the compensated donor behavior of the oxygen vacancies due to the surface oxygen adsorption. The hydrogen sensors of the annealed samples, compared to those of the unannealed samples, exhibited a much higher sensitivity and faster response rate. The sensor response factor and response rate increased from 27.1% to 80.2% and 0.34%/s to 1.15%/s, respectively. This remarkable enhancement in sensing performance induced by the annealing treatment could be attributed to the larger specific surface areas and higher amount of surface-adsorbed oxygen, which provides a greater reaction space for hydrogen. Moreover, the sensors with annealed SnO2 nanoflowers also exhibited high selectivity towards hydrogen against CH4, CO, and ethanol. [ABSTRACT FROM AUTHOR]

Most research works emphasized on the acoustic sensor miniaturization are not optimized for applications under high surrounding pressure. For underwater acoustic sensing, measuring the small acoustic pressure from the huge hydrostatic pressure makes the design of the sensor challenging. In this paper, we attempt to solve the problem by adopting a center-embossed diaphragm as the sensitive structure. The deformation angular error is defined to evaluate the optical performance degradation and the optical sensitivity reduction under hydrostatic pressure. Simulations indicate that the central embossment is beneficial to maintain optics-related properties, although the structural sensitivity is reduced. Then, the diaphragm design guideline for underwater acoustic sensing is regulated. An optical fiber extrinsic Fabry-Perot interferometer probe based on the diaphragm, which was micromachined by double-side etching of the silicon on insulator, was designed and assembled. Experimental results show that the interferometric fringe preserves similar shapes at any tested depth from 0 (in air) to 50 cm. The recovered signal detected by the sensor coincides well with the corresponding transmitted signal. The pressure sensitivity response is flat in frequency range from 10 to 2 kHz, of which value is about -154.6 dB re. 1/μPa. It agrees well with the theoretical predication. These results demonstrated that the designed sensor according to the guideline can be used as an underwater acoustic sensor. Moreover, the sensor has potential applications in smart unmanned platforms and swiftly deployable arrays. [ABSTRACT FROM PUBLISHER]

Mode instability acts as a common feature in single-frequency fiber ring lasers. The mechanism of coherence collapse by mode instability is theoretically analyzed and demonstrated with an unbalanced fiber Michelson interferometer utilizing phase modulation, which is illuminated by a single-frequency erbium-doped fiber ring laser. Multiform mode instability phenomena accompanied with coherence collapse are observed and discussed in detail by tracing the dynamics of the interference fringe visibility. The results show that mode instability would introduce extra phase noises like a false alarm to interferometric fiber optic sensing systems. [ABSTRACT FROM AUTHOR]

An integrated polarization maintaining fiber polarized Bragg grating is proposed, which achieves reflecting and polarizing functions simultaneously. This integrated polarized grating was designed to replace the traditional fiber polarizer and Bragg grating by a single fiber device, which may induce enormous performance promotion to optical fiber systems incorporating the two devices, such as fiber ring laser, some fiber sensing networks, etc. An integrated fiber polarized grating was fabricated, and the polarization states of both the reflection and transmission were measured. The temperature and strain responses were also tested which indicated sufficient stability. The integrated fiber polarized grating was then applied to the fiber ring laser, and results indicated that a robust single-longitudinal and single-polarization mode laser can be realized by utilizing this design type of integrated polarized grating. [ABSTRACT FROM AUTHOR]

Fiber Bragg grating written in polarization-maintaining fiber is strongly polarization-dependent, and its spectral character depends on the polarization state of light that interrogates the grating. We propose a novel and practical method to test the spectra character of the polarization-maintaining fiber Bragg grating (PM-FBG) interrogated by a linearly polarized light with a different azimuth for the first time. We specially designed a splice with a different angle in the system to alter the azimuth of the input linearly polarized light. Using this method, we got the transmission and reflection spectra of the PM-FBG measured at different splice angles and then the experimental results were analyzed originally. The analysis result shows that the relationship between the transmission dip and the splice angle obeys the Gaussian distribution. The reflectivity of the two wavelengths of the PM-FBG depends on the azimuth of the input linearly polarized light. [ABSTRACT FROM AUTHOR]

Fascicular KNbO3 nanowires with tetragonal perovskite structures and ultrasmall diameters are synthesized by hydrothermal route at about 150° C for 24 hours. The concentrations of medium alkalinity have influenced phase structures and the final morphologies of the products significantly by modifying the conditions in process. The as-prepared KNbO3 nanowires exhibit three phase transitions at about 343,454.7, and 623 K as the temperature increases from 250 to 700 K. The band gap is about 3.78 eV for KNbO3 nanowires. Photoluminescence study at room temperature reveals two visible light emission bands peaking at ~551 and 597 nm, respectively, which may be due to the oxygen vacancies, site niobium (occupy the location of Nb), and antisite niobium (occupy the location of K) in KNbO3, nanowires. [ABSTRACT FROM AUTHOR]

Polarization fluctuation in polarization maintaining fiber (PMF) resonator is one of the major noise sources in resonant fiber optic gyroscope (R-FOG). 90-deg polarization-axis rotated splicing in R-FOG is an effective way to suppress the polarization-fluctuation induced noise. 90-deg polarization-axis rotated splicing error influences the noise suppression effect. Here, a polarization-coupling testing system based on white-light interferometry is designed to control 90-deg splicing error in double-coupler PMF resonator first time and a result of 0.37-deg splicing error is obtained for the first time. Then the resonant characteristics of the double-coupler PMF resonator are tested using the saw-tooth waveform scanning method. The finesse of this double-coupler PMF resonator is 24.0 and the phase interval of the two eigenstates of polarization (ESOPs) is π. [ABSTRACT FROM AUTHOR]

Recently, the hydrogen gas sensing properties of semiconductor oxide (SMO) nanostructures have been widely investigated. In this article, we provide a comprehensive review of the research progress in the last five years concerning hydrogen gas sensors based on SMO thin film and one-dimensional (1D) nanostructures. The hydrogen sensing mechanism of SMO nanostructures and some critical issues are discussed. Doping, noble metal-decoration, heterojunctions and size reduction have been investigated and proved to be effective methods for improving the sensing performance of SMO thin films and 1D nanostructures. The effect on the hydrogen response of SMO thin films and 1D nanostructures of grain boundary and crystal orientation, as well as the sensor architecture, including electrode size and nanojunctions have also been studied. Finally, we also discuss some challenges for the future applications of SMO nanostructured hydrogen sensors. [ABSTRACT FROM AUTHOR]

This paper reports a new-style all-polarization-maintaining optical fiber vector hydrophone (OFVH) that is composed of a three-component optical fiber accelerometer and an optical fiber hydrophone. In order to make the OFVH small and compact in volume, the orthogonal and unitized structure of the three-component optical fiber accelerometer is adopted. The sensitivity and the operating frequency band of the accelerometer are increased by this proposed structure. The signal fading caused by the random phase shift in the interferometer is eliminated by phase-generated carrier technology. Calibration results show that the acceleration sensitivity is 32.6 dB re rad/g and its fluctuation is less than 1.4 dB over the frequency range of 20-2000 Hz. The phase sensitivity of the optical fiber accelerometer is dB re rad/ Pa at 1000 Hz. This OFVH has an excellent directivity; its maximum asymmetric index is less than 0.4 dB and its directivity index is greater than 45 dB. The excellent performance of this new-style OFVH for use in source localization measurements is also proved by the sea trial. [ABSTRACT FROM PUBLISHER]

Nanoparticles (NPs) of multiferroic bismuth ferrite (BiFeO3) with narrow size distributions were synthesized via a wet chemical route using bismuth nitrate and iron nitrate as starting materials and excess tartaric acid and citric acid as chelating agent, respectively, followed by thermal treatment. It was found that BiFeO3 NPs crystallized at ~350°C when using citric acid as chelating agent. Such crystallization temperature is much lower than that of conventional chemical process in which other types of chelating agent are used. BiFeO3 NPs with different sizes distributions show obvious ferromagnetic properties, and the magnetization is increased with reducing the particle size. [ABSTRACT FROM AUTHOR]

(K1−xNax)NbO3(KNN) nanomaterials with various morphologies, including nanorods, step-like structures etc.were synthesized through a hydrothermal route. For KNN nanomaterials, the phase structures changed from orthorhombic to monoclinic as the xvalue increased from 0.27 to 0.66. Oriented attachment and aggregation are the major formation mechanism of the nanorods and the step-like structures, respectively. The compositional change in KNN induced a series of shifts of the Raman bands, of which the mechanisms are briefly discussed. A UV/vis absorption study shows that, for K0.50Na0.50NbO3nanorods, two interband transitions from O2pelectron states to empty Nb4delectron states and two intraband transitions in relation to Nb5熫抢 are revealed, and the band gap is about 3.09 eV. [ABSTRACT FROM AUTHOR]

Abstract  Single crystalline nanowires of lead titanate (PbTiO3) were fabricated by hydrothermal method at 200C using lead acetate and n-tetrabutyl titanate as starting materials, where sodium hydroxide was served as a mineralizer. Crystalline phases, microstructure and optical properties of PbTiO3 nanowires were investigated. The PbTiO3 nanowires were uniform and continuous along the long axis, and were composed of single crystalline PbTiO3 with a tetragonal perovskite structure. The diameter of a single nanowire was around 12 nm and the length reached up to 3 μm. The chemical composition of the samples and the valence states of elements were determined by X-ray photoelectron spectroscopy (XPS). The ultraviolet/visible absorption spectroscopic investigation suggested that the absorption edge of optical transition of the first excitonic state occurred at around 320 nm. A blue-green light emission peaking at about 471 nm (2.63 eV) is observed at room temperature, and the intensity of this emission increased with increasing excitation wavelength. Oxygen vacancies are responsible for the light emission of PbTiO3 nanowires. [ABSTRACT FROM AUTHOR]

Fe-doped SrBi2Nb2O9 precursor solution was synthesized using bismuth nitrate Bi(NO3)3·5H2O, strontium nitrate Sr(NO3)2, iron nitrate Fe(NO3)3·9H2O, and niobium ethoxide Nb(OC2H5)5 as starting materials, ethylene glycol monomethyl ether (C3H8O2) as the solvent. 0.1BiFeO3-0.9SrBi2Nb2O9 thin films were prepared on fused quartz substrates using sol-gel processing. The surface morphology and crystal structure and optical properties of the thin films were investigated. The thin film annealing at 400°C were found to be amorphous, and the thin films crystallize to a perovskite structure after a post-deposition annealing at 600°C for 1 h in air. The grain of thin film was evenly distributed. The thin films exhibit the designed optical transmission, while the optical transition is indirect in nature. Their optical band gap is about 2.5 eV. [ABSTRACT FROM AUTHOR]

PbTiO3 nanowires have been successfully fabricated by a hydrothermal method at 200 °C. X-ray diffraction result shows that the PbTiO3 nanowires have a tetragonal perovskite structure without any other impurity phase. Scanning electron microscopy and transmission electron microscopy investigations exhibit that the as-prepared samples are made up of large quantity nanowires with diameters of about 10–20 nm and lengths reaching up to 3 μm and single crystalline in nature. Photoluminescence study at room temperature for wavelength between 400 and 650 nm reveals a strong blue-green emission band peaking at ca. 471.4 nm (2.63 eV). Raman spectroscopy study of the nanowires at room temperature demonstrates that the lifetime of the phonons is shorter compare to that of bulk materials. [ABSTRACT FROM AUTHOR]

The design of various nanostructures with specific compositions and shapes is highly demanded due to the widespread use of micro/nano electro-mechanical systems. In this work, one-dimensional CuO–Pt core–shell nanowires (NWs) are acquired by depositing Pt nanoparticles onto CuO NWs and then mechanically-shaped into nanohooks. Subsequently, the hook-like shape is maintained by the Pt-shell which is reconstructed via Joule heat and re-solidified after cooling down, during which the elastic strain energy is stored in the CuO-core. The results provide a simple strategy to design nanostructures with various compositions and shapes, implying the potential applications in mechanical energy storage and shape memory nanodevices. [ABSTRACT FROM AUTHOR]

The development of self-powered vibration sensors using polymeric piezoelectric nanomaterials has attracted great attention owing to their outstanding flexibility and energy harvesting behaviours. In this study, ultra-long poly (vinylidene fluoride) (PVDF) nanofibres with optimised β-phase content were synthesised through electrospinning method with different DC voltages. The increase in the β-phase content of the PVDF nanofibres greatly enhanced their piezoelectric response with nearly tripled output voltage and current under the same strain condition. Moreover, the output voltage exhibited linear correlations with both the amplitude and frequency of the strain. Under a fixed frequency of 1.54 Hz, the output voltage exhibited a linear correlation to the strain amplitude with strain sensitivity up to 0.92 V rad−1 and 0.61 V mm−1. The frequency-dependent strain sensing behaviour also confirmed the necessity for frequency calibration to the measured results of vibration. Accordingly, the sensor can be used for self-powered monitoring of the vibration state of a metal foil and measuring the intrinsic resonance frequency of the objects without any powering source. [ABSTRACT FROM AUTHOR]

The inline time division multiplexing (TDM) fiber Fabry–Pérot (FFP) sensor array based on fiber Bragg gratings (FBGs) is attractive for many applications. But the intrinsic multi-reflection (MR) induced crosstalk limits applications especially those needing high resolution. In this paper we proposed an expandable method for MR-induced crosstalk reduction. The method is based on complexing-exponent synthesis using the phase-generated carrier (PGC) scheme and the special common character of the impulse responses. The method could promote demodulation stability simultaneously with the reduction of MR-induced crosstalk. A polarization-maintaining 3-TDM experimental system with an FBG reflectivity of about 5 was set up to validate the method. The experimental results showed that crosstalk reduction of 13 dB and 15 dB was achieved for sensor 2 and sensor 3 respectively when a signal was applied to the first sensor and crosstalk reduction of 8 dB was achieved for sensor 3 when a signal was applied to sensor 2. The demodulation stability of the applied signal was promoted as well. The standard deviations of the amplitude distributions of the demodulated signals were reduced from 0.0046 to 0.0021 for sensor 2 and from 0.0114 to 0.0044 for sensor 3. Because of the convenience of the linear operation of the complexing-exponent and according to the common character of the impulse response we found, the method can be effectively extended to the array with more TDM channels if the impulse response of the inline FFP sensor array with more TDM channels is derived. It offers potential to develop a low-crosstalk inline FFP sensor array using the PGC interrogation technique with relatively high reflectivity FBGs which can guarantee enough light power received by the photo-detector. [ABSTRACT FROM AUTHOR]