Dynamic 3D phase-shifting profilometry based on a corner optical flow algorithm.

Real-time 3D reconstruction has been applied in many fields, calling for many ongoing efforts to improve the speed and accuracy of the used algorithms. Phase shifting profilometry based on the Lucas-Kanade optical flow method is a fast and highly precise method to construct and display the three-dimensional shape of objects. However, in this method, a dense optical flow calculation is required for the modulation image corresponding to the acquired deformed fringe pattern, which consumes a lot of time and affects the real-time performance of 3D reconstruction and display. Therefore, this paper proposes a dynamic 3D phase shifting profilometry based on a corner optical flow algorithm to mitigate this issue. Therein, the Harris corner algorithm is utilized to locate the feature points of the measured object, so that the optical flow needs to calculate for only the feature points which, greatly reduces the amount of calculation time. Both our experiments and simulations show that our method improves the efficiency of pixel matching by four times and 3D reconstruction by two times.

Silver nanowire network for flexible transparent electrodes based on spray coating at a low DC electric field and plasma treatment.

Flexible transparent electrodes have been fabricated successfully by using a metal nanowire network. Despite its higher conductivity and transparency, raw silver nanowire (AgNW) film suffers from the random arrangement and high surface roughness originating from the overlaps of a few tens of nanometer-thick AgNWs. In this work, a facile and environmentally friendly method is developed to form AgNW flexible transparent electrodes by spray coating at a low DC electric field (less than 6.0 V) and subsequent plasma treatment. The DC voltage, plasma power, and plasma treatment time of the AgNW network are optimized. The obtained electrodes fabricated by this technique exhibited excellent flexible, transparent, and flat junctions of AgNWs with a sheet resistance of 4.64 Ω · sq-1 and a specular transmittance of 87.3% at a wavelength of 550 nm. Furthermore, the AgNW electrodes are very flexible, highly durable, and moiré-free. The resistance remains almost unchanged over 500 cycles of mechanical deformation with a bending distance of 14 mm when its size is 20 × 20 mm. The as-prepared AgNW electrodes exhibited a root mean square roughness below 13.07 nm at a scan size of 5 × 5 µm. We propose that the improved properties can be attributed to the well-arranged AgNW network acheived by applying a DC electric field and a flat connection between the AgNW junctions induced by plasma treatment.

Homo-epitaxial secondary growth of ZnO nanowire arrays for a UV-free warm white light-emitting diode application.

The warm white homojunction light-emitting diode (LED) was fabricated by a doped ZnO nanowire array homojunction with homo-epitaxial secondary grown on a GaN substrate by the chemical vapor deposition method. Due to the high quality of the nanosized ZnO homojunction, the I-V characteristic curve of the ZnO homojunction shows good pn junction rectification characteristics, and the turn-on voltage is about 6 V. Under forward bias, bright yellow light was emitting from the homojunction LED. From the electroluminescence spectrum, the main luminescence peak is divided into a small part of blue light of about 420 nm and dominated yellow-green light of about 570 nm. The CIE color space chromaticity survey shows that the chromaticity coordinates of the homojunction LED are at (0.3358, 0.3341), which indicate that fabricated white LEDs have potential applications in efficient and healthy lighting and displaying fields.

Selenate Reduction and Selenium Enrichment of Tea by the Endophytic Herbaspirillum sp. Strain WT00C.

Herbaspirillum sp. WT00C is a tea-plant-specific endophytic bacterium. A genomic survey revealed an intact pathway for selenocompound metabolism in the genome of this bacterium. When it was cultured with sodium selenate, Herbaspirillum sp. WT00C was able to turn the culture medium to red. Electron microscopy and energy-dispersive X-ray spectroscopy confirmed that Herbaspirillum sp. WT00C reduced selenite (Se6+) to elemental selenium (Se0), and selenium nanoparticles (SeNPs) were secreted outside bacterial cells and grew increasingly larger to form Se-nanospheres and finally crystallized to form selenoflowers. Biochemical assays showed that selenospheres contained proteins but not carbohydrates or lipids. The improvement of selenium enrichment of tea plants by Herbaspirillum sp. WT00C was also tested. After Herbaspirillum sp. WT00C was inoculated into tea seedlings via needle injection and soaking tea-cutting methods, this endophytic bacterium markedly enhanced selenium enrichment of tea. When the tea seedlings inoculated by soaking tea-cutting mode were cultivated in the selenium-containing soils, selenium contents of tea leaves in three experimental groups were more than twofold compared to those of control groups. Our study demonstrates that the endophytic bacterium Herbaspirillum sp. WT00C has the ability to reduce selenate and improve selenium enrichment of tea.

Homogeneous ZnO nanowire arrays p-n junction for blue light-emitting diode applications.

ZnO is a promising short-wavelength light-emitting materials for its wide bandgap (3.37 eV) and large exciton binding energy (∼60 meV), however, practical p-type doped ZnO is the main challenge in this field. Here, Blue light-emitting diodes (LEDs) based on the homogeneous junctions of Sb doped ZnO nanowire arrays grown on Ga doped ZnO single crystal substrate are fabricated. Element analysis, FET and Hall-effect measurements demonstrate that the Sb atom has been successfully doped into ZnO nanowires to from p-type conductivity. On the benefit of high quality of nano-size homojunction, the fabricated LED shows low turn-on voltage turn-on voltage as low as 3.4 V and strong blue emission peak located at 425 nm at room temperature, which originate from interfacial recombination of ZnO nanowire p-n homojunctions. The present blue LED based on ZnO material may have potential applications in short-wavelength optoelectronic devices.

Influence of Structural Parameters on the Surface Enhanced Raman Scattering of Au Nanoarrays.

As an important research topic of surface enhanced Raman scattering (SERS), periodic metal nanoarrays have attracted remarkable attention due to their superior properties, such as excellent enhancing ability, and high structural homogeneity and stability. In this work, periodic Au nanostructures with variable repetitive unit size, Au nanoparticle size, and gap sizes are fabricated by electron beam lithography on SiO2/Si substrates to investigate the influence of these structural parameters on SERS performances. The SERS intensity is found to increase linearly with decreasing repetitive unit size (increase of Au nanoparticle number density), while shows no obvious dependence on the Au nanoparticle size. A SERS enhancement factor of 6.6 × 105 is obtained for Au arrays with a repetitive unit size of 200 nm. The gap size does not affect the SERS intensity when it is over 75 nm, and exhibits an obvious enhancement effect when it is below 25 nm. A linear quantitative relationship between the Raman intensity and analyte concentrations of R6G, as well as a limit of detection of 10-11 mol/L was achieved for an Au nanoparticle array with gap size of 25 nm.

Fabrication of CuO-Pt core-shell nanohooks by in situ reconstructing the Pt-shells.

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.

Bias-switchable negative and positive photoconductivity in 2D FePS3 ultraviolet photodetectors.

Metal-phosphorus-trichalcogenides (MPTs), represented by NiPS3, FePS3, etc, are newly developed 2D wide-bandgap semiconductors and have been proposed as excellent candidates for ultraviolet (UV) optoelectronics. In spite of having superior advantages for solar-blind UV photodetectors, including those free of surface trap states, being highly compatible with versatile integrations as well as having an appropriate band gap, to date relevant study is rare. In this work, the photoresponse characteristic of UV detectors based on few-layer FePS3 has been comprehensively investigated. The responsivity of the photodetector, which is observed to be determined by bias gate voltage, may achieve as high as 171.6 mAW-1 under the illumination of 254 nm weak light, which is comparable to most commercial UV detectors. Notably, both negative and positive photoconductivities exist in the FePS3 photodetectors and can be controllably switched with bias voltage. The eminent and novel photoresponse property paves the way for the further development and practical use of 2D MPTs in high-performance UV photodetections.

Ultraviolet Detectors Based on Wide Bandgap Semiconductor Nanowire: A Review.

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.

Remarkably Enhanced Room-Temperature Hydrogen Sensing of SnO2 Nanoflowers via Vacuum Annealing Treatment.

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.

A Free-Standing and Self-Healable 2D Supramolecular Material Based on Hydrogen Bonding: A Nanowire Array with Sub-2-nm Resolution.

In many 2D materials reported thus far, the forces confining atoms in a 2D plane are often strong interactions, such as covalent bonding. Herein, the first demonstration that hydrogen (H)-bonding can be utilized to assemble polydiacetylene (a conductive polymer) toward a 2D material, which is stable enough to be free-standing, is shown. The 2D material is well characterized by a large number of techniques (mainly different microscopy techniques). The H-bonding allows splitting of the material into ribbons, which can reassemble, similar to a zipper, leading to the first example of a healable 2D material. Moreover, such technology can easily create 2D, organic, conductive nanowire arrays with sub-2-nm resolution. This material may have potential applications in stretchable electronics and nanowire cross-bar arrays.

Visual detection of thrombin using a strip biosensor through aptamer-cleavage reaction with enzyme catalytic amplification.

A new class of strip biosensors has been established based on well-distributed thrombin aptamer-linked gold nanoparticle aggregates, which will undergo a cracking reaction when the target recognizes its homologous aptamer. Combining the aptamer-cleavage reaction with the enzyme catalytic amplification system, our proposed lateral flow strip biosensor (LFB) is capable of visually detecting 6.4 pM of thrombin without instrumentation within 12 minutes. Under the optimal conditions, the quantitative detection of thrombin by a portable strip reader exhibited a linear relationship between the peak area and the concentration of thrombin in the range of 6.4 pM-500 nM with a detection limit of 4.9 pM, which is three orders of magnitude lower than that of the aptamer-functionalized gold nanoparticle-based LFB (2.5 nM, Xu et al., Anal. Chem., 2009, 81, 669-675). As the aptamers have no special requirements and the gold nanoparticles can also be replaced by other metallic nanoparticles, this method for strip sensing is expected to be generally applicable in point of care testing, home testing, medical diagnostics, clinical diagnosis, and environmental monitoring.

Intercrossed carbon nanorings with pure surface states as low-cost and environment-friendly phosphors for white-light-emitting diodes.

As an important energy-saving technique, white-light-emitting diodes (W-LEDs) have been seeking for low-cost and environment-friendly substitutes for rare-earth-based expensive phosphors or Pd(2+)/Cd(2+)-based toxic quantum dots (QDs). In this work, precursors and chemical processes were elaborately designed to synthesize intercrossed carbon nanorings (IC-CNRs) with relatively pure hydroxy surface states for the first time, which enable them to overcome the aggregation-induced quenching (AIQ) effect, and to emit stable yellow-orange luminescence in both colloidal and solid states. As a direct benefit of such scarce solid luminescence from carbon nanomaterials, W-LEDs with color coordinate at (0.28, 0.27), which is close to pure white light (0.33, 0.33), were achieved through using these low-temperature-synthesized and toxic ion-free IC-CNRs as solid phosphors on blue LED chips. This work demonstrates that the design of surface states plays a crucial role in exploring new functions of fluorescent carbon nanomaterials.

Ultrathin Boundary-Less SnO2 Films with Surface-Activated Two-Dimensional Nanograins Enable Fast and Sensitive Hydrogen Gas Sensing.

Fast and reliable semiconductor hydrogen sensors are crucially important for the large-scale utilization of hydrogen energy. One major challenge that hinders their practical application is the elevated temperature required, arising from undesirable surface passivation and grain-boundary-dominated electron transportation in the conventional nanocrystalline sensing layers. To address this long-standing issue, in the present work, we report a class of highly reactive and boundary-less ultrathin SnO2 films, which are fabricated by the topochemical transformation of 2D SnO transferred from liquid Sn-Bi droplets. The ultrathin SnO2 films are purposely made to consist of well-crystallized quasi-2D nanograins with in-plane grain sizes going beyond 30 nm, whereby the hydroxyl adsorption and grain boundary side-effects are effectively suppressed, giving rise to an activated (101)-dominating dangling-bond surface and a surface-controlled electrical transportation with an exceptional electron mobility of 209 cm2 V-1 s-1. Our work provides a new cost-effective strategy to disruptively improve the gas reception and transduction of SnO2. The proposed chemiresistive sensors exhibit fast, sensitive, and selective hydrogen sensing performance at a much-reduced working temperature of 60 °C. The remarkable sensing performance as well as the simple and scalable fabrication process of the ultrathin SnO2 films render the thus-developed sensors attractive for long awaited practical applications in hydrogen-related industries.

Ferroelectric mechanism of croconic acid: a first-principles and Monte Carlo study.

The ferroelectric mechanism of croconic acid in terms of the electronic structure and the molecular structure was studied by first principles using the density functional theory with the generalized gradient approximation. The spontaneous polarization (Ps) was simulated by the Berry phase method. It is found that the large polarization originates from charge transfer due to the strong "push-pull" effect of electron-releasing and -withdrawing groups along the hydrogen bond. According to the characteristics of polarization of croconic acid, we constructed a one-dimensional ferroelectric Hamiltonian model to describe the ferroelectric properties of croconic acid. Based on the Hamiltonian model, the thermal properties of the ferroelectricity of croconic acid were studied by Monte Carlo method. The simulated Curie temperature is 756 K, and the spontaneous polarization keeps well temperature range stability up to 400 K. These results are in good agreement with the experimental data.

TiO2-modified MoS2 monolayer films enable sensitive NH3 sensing at room temperature.

The research and development of high-performance NH3 sensors are of great significance for environment monitoring and disease diagnosis applications. Two-dimensional (2D) MoS2 nanomaterials have exhibited great potential for building room-temperature (RT) NH3 sensors but still suffer from relatively low sensitivity. Herein, the TiO2-modified monolayer MoS2 films with controllable TiO2 loading contents are fabricated by a facile approach. A remarkable enhancement in the RT NH3 sensing performance is achieved after the n-n hetero-compositing of the TiO2/MoS2 system. The device with 95% surface coverage of TiO2 shows enhanced sensor response, low detection limit (0.5 ppm), wide detection range (0.5-1000 ppm), good repeatability, and superior selectivity against other gases. In situ Kelvin potential force microscopy results revealed that the TiO2 modification not only improved the surface reactivity of the sensing layers but also contributed to the NH3 sensing performance by serving as the "gas-gating" layers that modulated the electron depletion layer and the conductivity of the MoS2 films. Such an n-n hetero-compositing strategy can provide a simple and cost-effective approach for developing high-performance NH3 sensors based on 2D semiconductors.

Gas sensing performance of In2O3 nanostructures: A mini review.

Effective detection of toxic and hazardous gases is crucial for ensuring human safety, and high-performance metal oxide-based gas sensors play an important role in achieving this goal. In2O3 is a widely used n-type metal oxide in gas sensors, and various In2O3 nanostructures have been synthesized for detecting small gas molecules. In this review, we provide a brief summary of current research on In2O3-based gas sensors. We discuss methods for synthesizing In2O3 nanostructures with various morphologies, and mainly review the sensing behaviors of these structures in order to better understand their potential in gas sensors. Additionally, the sensing mechanism of In2O3 nanostructures is discussed. Our review further indicates that In2O3-based nanomaterials hold great promise for assembling high-performance gas sensors.

Giant Piezoelectric Output and Stability Enhancement in Piezopolymer Composites with Liquid Metal Nanofillers.

Integrating nanomaterials into the polymer matrix is an effective strategy to optimize the performance of polymer-based piezoelectric devices. Nevertheless, the trade-off between the output enhancement and stability maintenance of piezoelectric composites usually leads to an unsatisfied overall performance for the high-strength operation of devices. Here, by setting liquid metal (LM) nanodroplets as the nanofillers in a poly(vinylidene difluoride) (PVDF) matrix, the as-formed liquid-solid/conductive-dielectric interfaces significantly promote the piezoelectric output and the reliability of this piezoelectric composite. A giant performance improvement featured is obtained with, nearly 1000% boosting on the output voltage (as high as 212 V), 270% increment on the piezoelectric coefficient (d33 ∼51.1 pC N-1 ) and long-term reliability on both structure and output (over 36 000 cycles). The design of a novel heterogenous interface with both mechanical matching and electric coupling can be the new orientation for developing high performance piezoelectric composite-based devices.

Hydrogen gas sensors based on semiconductor oxide nanostructures.

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.

Wearable Piezoelectric Nanogenerators Based on Core-Shell Ga-PZT@GaOx Nanorod-Enabled P(VDF-TrFE) Composites.

High-output flexible piezoelectric nanogenerators (PENGs) have achieved great progress and are promising applications for harvesting mechanical energy and supplying power to flexible electronics. In this work, unique core-shell structured Ga-PbZrxTi1-xO3 (PZT)@GaOx nanorods were synthesized by a simple mechanical mixing method and then were applied as fillers in a poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) matrix to obtain highly efficient PENGs with excellent energy-harvesting properties. The decoration of gallium nanoparticles on PZT @GaOx nanorods can amplify the local electric field, facilitate the increment of polar ß-phase fraction in P(VDF-TrFE), and strengthen the polarizability of PZT and P(VDF-TrFE). The interfacial interactions of GaOx and P(VDF-TrFE) are also in favor of an increased ß-phase fraction, which results in a remarkable improvement of PENG performance. The optimized Ga-PZT@GaOx/P(VDF-TrFE) PENG delivers a maximum open-circuit voltage of 98.6 V and a short-circuit current of 0.3 µA with 9.8 µW instantaneous power under a vertical force of 12 N at a frequency of 30 Hz. Such a PENG exhibits a stable output voltage after 6 000 cycles by the durability test. Moreover, the liquid gallium metal offers a mechanical matching interface between rigid PZT and the soft polymer matrix, which benefits the effective, durable mechanical energy-harvesting capability from the physical activities of elbow joint bending and walking. This research renders a deep association between a liquid metal and piezoelectric ceramics in the field of piezoelectric energy conversion, offering a promising approach toward self-powered smart wearable devices.