Dual-coupling effect enables a high-performance self-powered UV photodetector.

Self-powered ultraviolet photodetectors generally operate by utilizing the built-in electric field within heterojunctions or Schottky junctions. However, the effectiveness of self-powered detection is severely limited by the weak built-in electric field. Hence, advances in modulating the built-in electric field within heterojunctions are crucial for performance breakthroughs. Here, we suggest a method to enhance the built-in electric field by taking advantage of the dual-coupling effect between heterojunction and the self-polarization field of ferroelectrics. Under zero bias, the fabricated AgNWs/TiO2/PZT/GaN device achieves a responsivity of 184.31 mA/W and a specific detectivity of 1.7 × 1013 Jones, with an on/off ratio of 8.2 × 106 and rise/decay times reaching 0.16 ms/0.98 ms, respectively. The outstanding properties are primarily attributed to the substantial self-polarization of PZT induced by the p-GaN and the subsequent enhancement of the built-in electric field of the TiO2/PZT heterojunction. Under UV illumination, the dual coupling of the enhanced heterojunction and the self-polarizing field synergistically boost the photo-generated carrier separation and transport, leading to breakthroughs in ferroelectric-based self-powered photodetectors.

High-Performance Piezoelectric Nanogenerator of BTO-PVDF Nanofibers for Wearable Sensing.

Piezoelectric nanogenerator (PENG) produces stable electrical signals in response to external mechanical stimuli and holds promise in the fields of flexible sensors and smart wearable devices. In practice, a high-performance PENG with a straightforward structure and exceptional reliability is deeply desired. This study optimally synthesizes piezoelectric composites comprising polyvinylidene fluoride (PVDF) incorporated with barium titanate (BTO) nanoparticles (NPs) and fabricated a PENG with heightened sensitivity by using the electrospinning technique. The polar ß-phase content of the dual-optimized BTO-PVDF (barium titanate and polyvinylidene fluoride) electrospun fiber reaches up to 82.39%. In the bending mode, it achieves a remarkable maximum open-circuit voltage of 19.152 V, a transferred charge of 8.058 nC, and an output voltage per unit area of 2.128 V cm- 2. Under vertical pressure conditions, the BP-PENG exhibits an impressive voltage of 12.361 V while the force is 2.156 N, demonstrating a notable pressure sensing sensitivity of 5.159 V kPa-1, with an excellent linear relationship. Furthermore, the BP-PENG displays sensitive sensing features in monitoring hand movements. The sensitive response and high performance make it promising for applications in human motion monitoring and smart wearable devices.

Optical and Structural Properties of Aluminum Nitride Epi-Films at Room and High Temperature.

The high-quality aluminum nitride (AlN) epilayer is the key factor that directly affects the performance of semiconductor deep-ultraviolet (DUV) photoelectronic devices. In this work, to investigate the influence of thickness on the quality of the AlN epilayer, two AlN-thick epi-film samples were grown on c-plane sapphire substrates. The optical and structural characteristics of AlN films are meticulously examined by using high-resolution X-ray diffraction (HR-XRD), scanning electron microscopy (SEM), a dual-beam ultraviolet-visible spectrophotometer, and spectroscopic ellipsometry (SE). It has been found that the quality of AlN can be controlled by adjusting the AlN film thickness. The phenomenon, in which the thicker AlNn film exhibits lower dislocations than the thinner one, demonstrates that thick AlN epitaxial samples can work as a strain relief layer and, in the meantime, help significantly bend the dislocations and decrease total dislocation density with the thicker epi-film. The Urbach's binding energy and optical bandgap (Eg) derived by optical transmission (OT) and SE depend on crystallite size, crystalline alignment, and film thickness, which are in good agreement with XRD and SEM results. It is concluded that under the treatment of thickening film, the essence of crystal quality is improved. The bandgap energies of AlN samples obtained from SE possess larger values and higher accuracy than those extracted from OT. The Bose-Einstein relation is used to demonstrate the bandgap variation with temperature, and it is indicated that the thermal stability of bandgap energy can be improved with an increase in film thickness. It is revealed that when the thickness increases to micrometer order, the thickness has little effect on the change of Eg with temperature.

UFO-Net: A Linear Attention-Based Network for Point Cloud Classification.

Three-dimensional point cloud classification tasks have been a hot topic in recent years. Most existing point cloud processing frameworks lack context-aware features due to the deficiency of sufficient local feature extraction information. Therefore, we designed an augmented sampling and grouping module to efficiently obtain fine-grained features from the original point cloud. In particular, this method strengthens the domain near each centroid and makes reasonable use of the local mean and global standard deviation to extract point cloud's local and global features. In addition to this, inspired by the transformer structure UFO-ViT in 2D vision tasks, we first tried to use a linearly normalized attention mechanism in point cloud processing tasks, investigating a novel transformer-based point cloud classification architecture UFO-Net. An effective local feature learning module was adopted as a bridging technique to connect different feature extraction modules. Importantly, UFO-Net employs multiple stacked blocks to better capture feature representation of the point cloud. Extensive ablation experiments on public datasets show that this method outperforms other state-of-the-art methods. For instance, our network performed with 93.7% overall accuracy on the ModelNet40 dataset, which is 0.5% higher than PCT. Our network also achieved 83.8% overall accuracy on the ScanObjectNN dataset, which is 3.8% better than PCT.

The Spatial Correlation and Anisotropy of ß-(AlxGa1-x)2O3 Single Crystal.

The long-range crystallographic order and anisotropy in ß-(AlxGa1-x)2O3 (x = 0.0, 0.06, 0.11, 0.17, 0.26) crystals, prepared by optical floating zone method with different Al composition, is systematically studied by spatial correlation model and using an angle-resolved polarized Raman spectroscopy. Alloying with aluminum is seen as causing Raman peaks to blue shift while their full widths at half maxima broadened. As x increased, the correlation length (CL) of the Raman modes decreased. By changing x, the CL is more strongly affected for low-frequency phonons than the modes in the high-frequency region. For each Raman mode, the CL is decreased by increasing temperature. The results of angle-resolved polarized Raman spectroscopy have revealed that the intensities of ß-(AlxGa1-x)2O3 peaks are highly polarization dependent, with significant effects on the anisotropy with alloying. As the Al composition increased, the anisotropy of Raman tensor elements was enhanced for the two strongest phonon modes in the low-frequency range, while the anisotropy of the sharpest Raman phonon modes in the high-frequency region decreased. Our comprehensive study has provided meaningful results for comprehending the long-range orderliness and anisotropy in technologically important ß-(AlxGa1-x)2O3 crystals.

Performance Optimization of Pb0.97La0.03Sc0.45Ta0.45Ti0.1O3 Ceramics by Annealing Process.

The annealing effects on Pb0.97La0.03Sc0.45Ta0.45Ti0.1O3 (PLSTT) ceramics prepared by the solid-state reaction method are systemically investigated using experimental and theoretical techniques. Comprehensive studies are performed on the PLSTT samples by varying annealing time (AT) from t (=0, 10, 20, 30, 40, 50 and 60) h. The properties involving ferroelectric polarization (FP), electrocaloric (EC) effect, energy harvesting performance (EHP) and energy storage performance (ESP) are reported, compared and contrasted. All these features are seen to gradually improve with the increase in AT, and they all reach the climaxed-shaped values and then decrease by further increasing the AT. For t = 40 h, the maximum FP (23.2 µC/cm2) is attained at an electric field of 50 kV/cm, while the high EHP effects (0.297 J/cm3) and positive EC are achieved (for ΔT~0.92 K and ΔS~0.92 J/(K·kg)) at 45 kV/cm. The EHP value of the PLSTT ceramics increased by 21.7% while the polarization value was enhanced by 33.3%. At t = 30 h, the ceramics have attained the best ESP value of 0.468 J/cm3 with an energy loss of 0.05 J/cm3. We strongly believe that the AT plays a crucial role in the optimization of different traits of the PLSTT ceramics.

Enhancing the Output Performance of a Triboelectric Nanogenerator Based on Modified Polyimide and Sandwich-Structured Nanocomposite Film.

Recently, scientists have been facing major obstacles in terms of improving the performances of dielectric materials for triboelectric nanogenerators. The triboelectric nanogenerator (TENG) is one of the first green energy technologies that can convert random mechanical kinetic energy into electricity. The surface charge density of TENGs is a critical factor speeding up their commercialization, so it is important to explore unique methods to increase the surface charge density. The key to obtaining a high-performance TENG is the preparation of dielectric materials with good mechanical properties, thermal stability and output performance. To solve the problem of the low output performance of PI-based triboelectric nanogenerators, we modified PI films by introducing nanomaterials and designed a new type of sandwich-shaped nanocomposite film. Herein, we used polyimide (PI) with ideal mechanical properties, excellent heat resistance and flexibility as the dielectric material, prepared an A-B-A sandwich structure with PI in the outer layer and modified a copper calcium titanate/polyimide (CCTO/PI) storage layer in the middle to improve the output of a TENG electrode. The doping amount of the CCTO was tailored. The results showed that at 8 wt% CCTO content, the electrical output performance was the highest, and the open-circuit voltage of CCTO/PI was 42 V. In the TENG, the open-circuit voltage, short-circuit current and transfer charge of the prepared sandwich-structured film were increased by 607%, 629% and 672% compared to the TENG with the PI thin film, respectively. This study presents a novel strategy of optimizing dielectric materials for triboelectric nano-generators and has great potential for the future development of high output-performance TENGs.

Structural, Surface and Optical Studies of m- and c-Face AlN Crystals Grown by Physical Vapor Transport Method.

Bulk aluminum nitride (AlN) crystals with different polarities were grown by physical vapor transport (PVT). The structural, surface, and optical properties of m-plane and c-plane AlN crystals were comparatively studied by using high-resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Temperature-dependent Raman measurements showed that the Raman shift and the full width at half maximum (FWHM) of the E2 (high) phonon mode of the m-plane AlN crystal were larger than those of the c-plane AlN crystal, which would be correlated with the residual stress and defects in the AlN samples, respectively. Moreover, the phonon lifetime of the Raman-active modes largely decayed and its line width gradually broadened with the increase in temperature. The phonon lifetime of the Raman TO-phonon mode was changed less than that of the LO-phonon mode with temperature in the two crystals. It should be noted that the influence of inhomogeneous impurity phonon scattering on the phonon lifetime and the contribution to the Raman shift came from thermal expansion at a higher temperature. In addition, the trend of stress with increasing 1000/temperature was similar for the two AlN samples. As the temperature increased from 80 K to ~870 K, there was a temperature at which the biaxial stress of the samples transformed from compressive to tensile stress, while their certain temperature was different.

Angle-Dependent Raman Scattering Studies on Anisotropic Properties of Crystalline Hexagonal 4H-SiC.

Raman scattering spectroscopy (RSS) has the merits of non-destructiveness, fast analysis, and identification of SiC polytype materials. By way of angle-dependent Raman scattering (ADRS), the isotropic characteristics are confirmed for c-face 4H-SiC, while the anisotropic properties of a-face 4H-SiC are revealed and studied in detail via combined experiments and theoretical calculation. The variation functional relationship of the angle between the incident laser polarization direction and the parallel (perpendicular) polarization direction was well established. The selection rules of wurtzite 4H-SiC are deduced, and the intensity variations of the A1, E2, and E1 Raman phonon modes dependent on the incident angle are calculated, and well-matched with experimental data. Raman tensor elements of various modes are determined.

An Internal-Electrostatic-Field-Boosted Self-Powered Ultraviolet Photodetector.

Self-powered photodetectors are of significance for the development of low-energy-consumption and environment-friendly Internet of Things. The performance of semiconductor-based self-powered photodetectors is limited by the low quality of junctions. Here, a novel strategy was proposed for developing high-performance self-powered photodetectors with boosted electrostatic potential. The proposed self-powered ultraviolet (UV) photodetector consisted of an indium tin oxide and titanium dioxide (ITO/TiO2) heterojunction and an electret film (poly tetra fluoroethylene, PTFE). The PTFE layer introduces a built-in electrostatic field to highly enhance the photovoltaic effect, and its high internal resistance greatly reduces the dark current, and thus remarkable performances were achieved. The self-powered UV photodetector with PTFE demonstrated an extremely high on-off ratio of 2.49 × 105, a responsivity of 76.87 mA/W, a response rise time of 7.44 ms, and a decay time of 3.75 ms. Furthermore, the device exhibited exceptional stability from room temperature to 70 °C. Compared with the conventional ITO/TiO2 heterojunction without the PTFE layer, the photoresponse of the detector improved by 442-fold, and the light-dark ratio was increased by 8.40 × 105 times. In addition, the detector is simple, easy to fabricate, and low cost. Therefore, it can be used on a large scale. The electrostatic modulation effect is universal for various types of semiconductor junctions and is expected to inspire more innovative applications in optoelectronic and microelectronic devices.

The First-Principle Study on Tuning Optical Properties of MA2Z4 by Cr Replacement of Mo Atoms in MoSi2N4.

Recently, with the successful preparation of MoSi2N4, an emerging family of two-dimensional (2D) layered materials has been predicted with a general formula of MA2Z4 (M: an early transition metal, A: Si or Ge and Z: N, P, or As). In terms of this new type of 2D material, how to effectively tune its light absorption properties is unclear. We systematically discuss the effects of replacing Mo with Cr atoms on the lattice structure, energy bands, and light absorption properties of 2D monolayer MoSi2N4 using density functional theory (DFT) and the Vienna Ab initio Simulation Package (VASP). Additionally, the results show that the single replacement of the atom Cr has no significant effect on the lattice structure of the outermost and sub-outer layers but plays a major role in the accumulation of electrons. In addition, the 2D MoSi2N4, Mo0.5Cr0.5Si2N4, and CrSi2N4 all have effective electron-hole separation properties. In the visible region, as the excited state increases, the required excitation energy is higher and the corresponding wavelength of light is shorter. It was found that the ultraviolet (UV)-visible spectra are red-shifted when Cr atoms replace Mo atoms in MoSi2N4; when Cr atoms and Mo atoms coexist, the coupling between Cr atoms and Mo atoms achieves modulation of the ultraviolet (UV)-visible spectra. Finally, we reveal that doping M-site atoms can effectively tune the light absorption properties of MA2Z4 materials. These results provide a strategy for the design of new 2D materials with high absorption properties.

Self-Powered Resistance-Switching Properties of Pr0.7Ca0.3MnO3 Film Driven by Triboelectric Nanogenerator.

As one of the promising non-volatile memories (NVMs), resistive random access memory (RRAM) has attracted extensive attention. Conventional RRAM is deeply dependent on external power to induce resistance-switching, which restricts its applications. In this work, we have developed a self-powered RRAM that consists of a Pr0.7Ca0.3MnO3 (PCMO) film and a triboelectric nanogenerator (TENG). With a traditional power supply, the resistance switch ratio achieves the highest switching ratio reported so far, 9 × 107. By converting the mechanical energy harvested by a TENG into electrical energy to power the PCMO film, we demonstrate self-powered resistance-switching induced by mechanical movement. The prepared PCMO shows excellent performance of resistance switching driven by the TENG, and the resistance switch ratio is up to 2 × 105, which is higher than the ones ever reported. In addition, it can monitor real-time mechanical changes and has a good response to the electrical signals of different waveforms. This self-powered resistance switching can be induced by random movements based on the TENG. It has potential applications in the fields of self-powered sensors and human-machine interaction.

Interferometrical single-molecule localization based on dynamic PSF engineering: publisher's note.

This publisher's note contains a correction to Opt. Lett.47, 1770 (2022)10.1364/OL.453113.

Interferometrical single-molecule localization based on dynamic PSF engineering.

We present a method for interferometric single-molecule localization based on dynamic point spread function (PSF) engineering. By using two galvo mirrors, a hexagonal PSF is constructed and the fluorescent signal under different illumination patterns could be acquired simultaneously. This method was evaluated using simulation, fluorescent nanosphere imaging, and single-molecule imaging. The study indicates a twofold improvement in localization precision while maintaining the same photon budget. This strategy, we believe, is a cost-effective way to increase the resolution of single-molecule localization microscopy.

Alternate-Layered MXene Composite Film-Based Triboelectric Nanogenerator with Enhanced Electrical Performance.

The output power of the triboelectric nanogenerator (TENG) strongly depends on the performance of triboelectric materials, especially microstructures and functional groups of them. In this work, aiming at the excellent triboelectric ability, alternate-layered MXene composite films-based TENG with abundant fluorine groups(-F) through layer-by-layer stacking are designed and fabricated. Benefitting from the uniform intrinsic microstructure and increased dielectric constant, when the amount of the Nb2CTx nanosheets increases to 15 wt%, the TENG based on Nb2CTx/Ti3C2Tx composite nanosheets films achieves the maximum output. The short-circuit current density of 8.06 µA/cm2 and voltage of 34.63 V are 8.4 times and 3.5 times over that of pure Ti3C2Tx films, and 3.3 times and 4.3 times over that of commercial poly(tetrafluoroethylene) (PTFE) films, respectively. Furthermore, the fabricated TENG could be attached to human body to harvest energy from human motions, such as typing, texting, and hand clapping. The results demonstrate that the alternate-layered MXene composite nanosheet films through layer-by-layer stacking possess remarkably triboelectric performance, which broaden the choice of negative triboelectric materials and supply a new choice for high output TENG.

A Polymeric Bilayer Multi-Legged Soft Millirobot with Dual Actuation and Humidity Sensing.

There are numerous works that report wirelessly controlling the locomotion of soft robots through a single actuation method of light or magnetism. However, coupling multiple driving modes to improve the mobility of robots is still in its infancy. Here, we present a soft multi-legged millirobot that can move, climb a slope, swim and detect a signal by near-infrared irradiation (NIR) light or magnetic field dual actuation. Due to the design of the feet structure, our soft millirobot incorporates the advantages of a single actuation mode of light or magnetism. Furthermore, it can execute a compulsory exercise to sense a signal and analyze the ambience fluctuation in a narrow place. This work provides a novel alternative for soft robots to achieve multimode actuation and signal sensing.

Dielectric and energy storage properties of Bi2O3-B2O3-SiO2 doped Ba0.85Ca0.15Zr0.1Ti0.9O3 lead-free glass-ceramics.

A sol-gel method is employed for preparing high quality lead-free glass-ceramic samples (1 - x)BCZT-xBBS-incorporating Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) powder and Bi2O3-B2O3-SiO2 (BBS) glass-doped additives with different values of x (x = 0, 0.05, 0.1, 0.15). Systematic investigations are performed to comprehend the structural, dielectric and energy storage characteristics using X-ray diffraction, field-emission scanning electron microscopy, impedance and ferroelectric analyser methods. With appropriate BBS doping (x), many fundamental traits including breakdown strength, dielectric loss and energy storage density have shown significant improvements. Low doping-level samples x < 0.1 have retained the pure perovskite phase while a second glass phase appeared in samples with x ≥ 0.1. As the doping level (0.1 ≥ x > 0) is increased, the average grain size decreased to become better homogeneous materials with improved breakdown energy strengths. Excessive addition of BBS (x = 0.15) causes negative effects on microstructures and other traits. The glass-ceramic sample 0.95BCZT-0.05BBS exhibits excellent dielectric permittivity and temperature stability, with the highest energy storage density of 0.3907 J cm-3 at 130 kV cm-1. These results provide good reference to develop lead-free ceramics of high energy storage density.

Low-angle optical vortex coronagraphic scatterometer.

The important, but difficult-to-measure zero and low-angle scattering spectrum, as well as the broader angular spectrum, was obtained by use of an optical vortex coronagraphic scatterometer (patent pending). The experimental measurements agreed well with the predictions from the Mie scattering theory. High contrast discrimination allowed us to remove the unscattered coherent illumination, revealing a low-angle superimposed scattered signal.

White-light imaging analysis of bi-grating systems.

Two gratings consist of an imaging system that forms a no-dispersion image of an object that is illuminated by white light. The process of double diffraction of the actual system is analyzed using the Fresnel diffraction approximation. One grating generates a number of spectral images of the diffraction orders of an object. The other grating combines one-order dispersive images into one and reconstructs a clear image. A bi-grating system in this case shows the same imaging capability as the lens, but its principle is completely different. An expression of the imaging rule is deduced that agrees well with experiments.

Mutual alignment errors due to wave-front aberrations in intersatellite laser communications.

We analyze mutual alignment errors due to wave-front aberrations. To solve the central obscured problem, we introduce modified Zernike polynomials, which are a set of complete orthogonal polynomials. It is found that different aberrations have different effects on mutual alignment errors. Some aberrations influence only the line of sight, while some aberrations influence both the line of sight and the intensity distributions.