Surface engineering of ZnO electrocatalyst by N doping towards electrochemical CO_(2) reduction

The discovery of efficient,selective,and stable electrocatalysts can be a key point to produce the largescale chemical fuels via electrochemical CO_(2) reduction(ECR).In this study,an earth-abundant and nontoxic ZnO-based electrocatalyst was developed for use in gas-diffusion electrodes(GDE),and the effect of nitrogen(N)doping on the ECR activity of ZnO electrocatalysts was investigated.Initially,a ZnO nanosheet was prepared via the hydrothermal method,and nitridation was performed at different times to control the N-doping content.With an increase in the N-doping content,the morphological properties of the nanosheet changed significantly,namely,the 2D nanosheets transformed into irregularly shaped nanoparticles.Furthermore,the ECR performance of Zn O electrocatalysts with different N-doping content was assessed in 1.0 M KHCO_(3) electrolyte using a gas-diffusion electrode-based ECR cell.While the ECR activity increased after a small amount of N doping,it decreased for higher N doping content.Among them,the N:ZnO-1 h electrocatalysts showed the best CO selectivity,with a faradaic efficiency(FE_(CO))of 92.7%at-0.73 V vs.reversible hydrogen electrode(RHE),which was greater than that of an undoped Zn O electrocatalyst(FE_(CO)of 63.4%at-0.78 V_(RHE)).Also,the N:ZnO-1 h electrocatalyst exhibited outstanding durability for 16 h,with a partial current density of-92.1 mA cm^(-2).This improvement of N:ZnO-1 h electrocatalyst can be explained by density functional theory calculations,demonstrating that this improvement of N:ZnO-1 h electrocatalyst comes from(ⅰ)the optimized active sites lowering the free energy barrier for the rate-determining step(RDS),and(ⅱ)the modification of electronic structure enhancing the electron transfer rate by N doping.

High-efficiency ultra-fast all-optical photonic crystal diode based on the lateral-coupled nonlinear elliptical defect

An all-optical Fano-like diode featuring a nonlinear lateral elliptical micro-cavity and a reflecting column in the photonic crystal waveguide is proposed.The asymmetric micro-cavity is constructed by removing one rod and changing the shape of the lateral rod from a circle to an ellipse.A reflecting pillar is also introduced into the waveguide to construct an F-P cavity with the elliptical defect and enhance the asymmetric transmission for the incident light wave transmitting rightwards and leftwards,respectively.By designing the size of the ellipse and optimizing a reflecting rod at a suitable position,a maximum forward light transmittance of-1.14 dB and a minimum backward transmittance of-57.66 dB are achieved at the working wavelength of 1550.47 nm.The corresponding response time is about 10 ps when the intensity of the pump light beam resonant at 637 nm is 3.97 W/μm2.

Surface-functionalized hole-selective monolayer for high efficiency single-junction wide-bandgap and monolithic tandem perovskite solar cells

Carbazole moiety-based 2PACz([2-(9H-carbazol-9-yl)ethyl]phosphonic acid)self-assembled monolayers(SAMs)are excellent hole-selective contact(HSC)materials with abilities to excel the charge-transferdynamics of perovskite solar cells(PSCs).Herein,we report a facile but powerful method to functionalize the surface of 2PACz-SAM,by which reproducible,highly stable,high-efficiency wide-bandgap PSCs can be obtained.The 2PACz surface treatment with various donor number solvents improves assembly of 2PACz-SAM and leave residual surface-bound solvent molecules on 2PACz-SAM,which increases perovskite grain size,retards halide segregation,and accelerates hole extraction.The surface functionalization achieves a high power conversion efficiency(PCE)of 17.62%for a single-junction wide-bandgap(~1.77 e V)PSC.We also demonstrate a monolithic all-perovskite tandem solar cell using surfaceengineered HSC,showing high PCE of 24.66%with large open-circuit voltage of 2.008 V and high fillfactor of 81.45%.Our results suggest this simple approach can further improve the tandem device,when coupled with a high-performance narrow-bandgap sub-cell.

Thrust characteristics of nano-carbon/Al/oxygenated salt nanothermites for micro-energetic applications

Combustion within small motors is key in the application-specific development of nanothermite-based micro-energetic systems. This study evaluates the performance of nanothermite mixtures in a converging-diverging nozzle and an open tube. Mixtures were prepared using nano-aluminum(n-Al),potassium perchlorate(KClO_(4)), and different carbon nanomaterials(CNMs) including graphene-oxide(GO), reduced GO, carbon nanotubes(CNTs) and nanofibers(CNFs). The mixtures were packed at different densities and ignited by laser beam. Performance was measured using thrust measurement,high-speed imaging, and computational fluid dynamics modeling, respectively. Thrust, specific impulse(ISP), volumetric impulse(ISV), as well as normalized energy were found to increase notably with CNM content. Two distinctive reaction regimes(fast and slow) were observed in combustion of low and high packing densities(20% and 55%TMD), respectively. Total impulse(IFT) and ISPwere maximized in the 5%GO/Al/KClO_4 mixture, producing 7.95 m N·s and 135.20 s respectively at 20%TMD, an improvement of 57%compared to a GO-free sample(5.05 m N·s and 85.88 s). CFD analysis of the motors over predicts the thrust generated but trends in nozzle layout and packing density agree with those observed experimentally;peak force was maximized by reducing packing density and using an open tube. The numerical force profiles fit better for the nozzle cases than the open tube scenarios due to the rapid nature of combustion. This study reveals the potential of GO in improving oxygenated salt-based nanothermites,and further demonstrates their applicability for micro-propulsion and micro-energetic applications.

Effects of Adaptive Random Deceleration on Traffic Flow

Based on the Nagel-Schreckenberg model, an improved cellular automaton traffic flow model is proposed, in which the random deceleration probability of each vehicle is no longer fixed, but is adaptively adjusted according to the local traffic density in its vision and its current velocity. The numerical simulation results show that the maximum traffic capacity of the improved model under the same parameters is greater than that of the Nagel-Schreckenberg model, and is closer to the measured data. In addition, the traffic flow and vehicle velocity under different meteorological conditions are simulated by using the improved model, and the synchronized flow phenomenon consistent with the actual traffic is reproduced. Meanwhile, the results show that under the same parameters, when the traffic density is equal to 0.3, the traffic flow of the improved model increases by about 11% compared with the original model, and when the traffic density increases to 0.6, the traffic flow increases by about 27%. .

Annealing temperature dependent catalytic water oxidation activity of iron oxyhydroxide thin films

Nanostructured iron oxyhydroxide（Fe OOH） thin films have been synthesized using an electrodeposition method on a nickel foam（NF） substrate and effect of air annealing temperature on the catalytic performance is studied. The as-deposited and annealed thin films were characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）, field emission scanning electron microscopy（FE-SEM） and linear sweep voltammetry（LSV） to determine their structural, morphological, compositional and electrochemical properties, respectively. The as-deposited nanostructured amorphous Fe OOH thin film is converted into a polycrystalline Fe;O;with hematite crystal structure at a high temperature. The Fe OOH thin film acts as an efficient electrocatalyst for the oxygen evolution reaction（OER） in an alkaline 1 M KOH electrolyte. The film annealed at 200 °C shows high catalytic activity with an onset overpotential of 240 m V with a smaller Tafel slope of 48 m V/dec. Additionally, it needs an overpotential of 290 mV to the drive the current density of 10 m A/cm;and shows good stability in the 1 M KOH electrolyte solution.

High performance silicon-based GeSn p–i–n photodetectors for short-wave infrared application

An investigation of germanium-tin(GeSn) on silicon p–i–n photodetectors with a high-quality Ge0.94 Sn0.06 absorbing layer is reported. The Ge Sn photodetector reached a responsivity as high as 0.45 A/W at the wavelength of 1550 nm and 0.12 A/W at the wavelength of 2 μm. A cycle annealing technology was applied to improve the quality of the epitaxial layer during the growth process by molecular beam epitaxy. A low dark-current density under 1 V reverse bias about 0.078 A/cm2 was achieved at room temperature. Furthermore, the Ge Sn photodetector could detect a wide spectrum region and the cutoff wavelength reached to about 2.3 μm. This work has great importance in silicon-based short-wave infrared detection.

Differences and Similarities of Photocatalysis and Electrocatalysis in Two-Dimensional Nanomaterials:Strategies,Traps,Applications and Challenges

Photocatalysis and electrocatalysis have been essential parts of electrochemical processes for over half a century.Recent progress in the controllable synthesis of 2D nanomaterials has exhibited enhanced catalytic performance compared to bulk materials.This has led to significant interest in the exploitation of 2D nanomaterials for catalysis.There have been a variety of excellent reviews on 2D nanomaterials for catalysis,but related issues of differences and similarities between photocatalysis and electrocatalysis in 2D nanomaterials are still vacant.Here,we provide a comprehensive overview on the differences and similarities of photocatalysis and electrocatalysis in the latest 2D nanomaterials.Strategies and traps for performance enhancement of 2D nanocatalysts are highlighted,which point out the differences and similarities of series issues for photocatalysis and electrocatalysis.In addition,2D nanocatalysts and their catalytic applications are discussed.Finally,opportunities,challenges and development directions for 2D nanocatalysts are described.The intention of this review is to inspire and direct interest in this research realm for the creation of future 2D nanomaterials for photocatalysis and electrocatalysis.

Development of long-wavelength infrared detector and its space-based application requirements

Infrared detection technology has greatly expanded the ability of mankind to study the earth and the universe. In recent years, the demand for long-wavelength infrared detectors is increasing for their advantages in exploring the earth and the universe. A variety of long-wavelength infrared detectors have been made based on thermal resistive effect, photoelectric effect, etc., in the past few decades. Remarkable achievements have been made in infrared materials, device fabrication,readout circuit, and device package. However, high performance long-wavelength infrared detectors, especially those for large format long-wavelength infrared detector focus plane array, are still unsatisfactory. Low noise, high detectivity, and large format long-wavelength infrared detector is necessary to satisfy space-based application requirements.

A new 3-dB bandwidth record of Ge photodiode on Si

Si photonics is a promising technological approach to realize a photonic integrated circuits on Si substrate with small footprint,high performance,low cost,and being highly compatible with Si complementary metal oxide semiconductor(CMOS)technology[1].Because of good compatibility of Si and the relatively high absorption coefficient in the near-infrared region,Ge waveguide photodiode on Si is almost the only option for optical receiving in Si photonic integrated circuits.For a high performance Ge photodiode,the critical parameters are optical responsivity,3-dB bandwidth,and dark current.

Fully-inorganic strontium incorporated CsPbI_(2)Br perovskite solar cells with promoted efficiency and stability

In the present investigation, we fabricated strontium (Sr2+) incorporated CsPbI2Br-based inorganic perovskite solar cells in ambient conditions. The morphology, crystallinity, absorption, elemental composition and photoluminescence analysis of the bare CsPbI2Br and CsPb1-xSrxI2Br perovskite thin films were studied systematically to investigate the role of Sr2+ incorporation. It is observed that the surface morphology of the CsPbI2Br perovskite thin film has been improved by partial substitution of Pb2+ by Sr2+ which facilitates photoactive black phase-stabilization and defect passivation. The champion device having CsPb0.98Sr0.02I2Br composition exhibited a power conversion efficiency (PCE) of 16.61% which is much higher than the bare device (13.65%). Furthermore, our CsPb0.98Sr0.02I2Br-based devices maintain > 85% of its initial efficiency over 100 h in ambient conditions.

Silica-based microcavity fabricated by wet etching

Silica whispering gallery mode（WGM） microcavities were fabricated by the buffered oxide etcher and potassium hydroxide wet etching technique without any subsequent chemical or laser treatments. The silicon pedestal underneath was an octagonal pyramid, thus providing a pointed connection area with the top silica microdisk while weakly influencing the resonance modes. The sidewalls of our microdisks were wedge shaped, which was believed to be an advantage for the mode confinement. Efficient coupling from and to the 60 μm diameter microdisk structure was achieved using tapered optical fibres, exhibiting a quality factor of 1.5×10^4 near a wavelength of 1550 nm. Many resonance modes were observed, and double transverse electric modes were identified by theoretical calculations. The quality factor of the microdisks was also analysed to deduce the cavity roughness. The wet etching technique provides a more convenient avenue to fabricate WGM microdisks than conventional fabrication methods.

Optically tuned dielectric characteristics of SrTiO_(3)/Si thin film in the terahertz range

Active control of the optical parameters in strontium titanate(SrTiO_(3),STO)thin films is highly desirable for tunable terahertz(THz)integrated devices such as filters,phase modulators,and electro-optical devices.In this work,optically tuned dielectric parameters of a STO thin film epitaxially grown on a silicon wafer were characterized in the THz region with an 800 nm laser pump-THz detection system.The refractive index,extinction coefficient,and complex dielectric constant of the STO thin film were calculated using thin-film parameter extraction.Owing to carrier transportation and soft-mode oscillation,the above optical parameters changed notably with the pump power of the external laser.This study is of great significance for rapid and non-contact THz phase-modulation technology and may serve as a powerful tool to tune the dielectric properties of the STO thin films.

Bilayer tellurene-metal interfaces

Tellurene, an emerging two-dimensional chain-like semiconductor, stands out for its high switch ratio, carrier mobility and excellent stability in air. Directly contacting the 2D semiconductor materials with metal electrodes is a feasible doping means to inject carriers. However, Schottky barrier often arises at the metal–semiconductors interface, impeding the transport of carriers. Herein, we investigate the interfacial properties of BL tellurene by contacting with various metals including graphene by using ab initio calculations and quantum transport simulations. Vertical Schottky barriers take place in Ag, Al, Au and Cu electrodes according to the maintenance of the noncontact tellurene layer band structure. Besides, a p-type vertical Schottky contact is formed due to the van der Waals interaction for graphene electrode. As for the lateral direction, p-type Schottky contacts take shape for bulk metal electrodes(hole Schottky barrier heights(SBHs) ranging from 0.19 to 0.35 eV). Strong Fermi level pinning takes place with a pinning factor of 0.02. Notably, a desirable p-type quasi-Ohmic contact is developed for graphene electrode with a hole SBH of 0.08 eV. Our work sheds light on the interfacial properties of BL tellurene based transistors and could guide the experimental selections on electrodes.

Toward stable photoelectrochemical water splitting using NiOOH coated hierarchical nitrogen-doped ZnO-Si nanowires photoanodes

Photoelectrochemical(PEC)water splitting is regarded as the most promising method to generate“green hydrogen”,and zinc oxide(ZnO)has been identified as one of the promising candidates for PEC water splitting owing to its straddling band alignment with the water redox level.However,its PEC performance is limited due to its wide bandgap and anticipated by photocorrosion in an aqueous medium.In this work,we present strategic improvements in the PEC water splitting performance of ZnO nanowires(NWs)by nitrogen(N)-doping along with photostability by the core–shell deposition of a NiOOH cocatalyst.Highly crystalline hierarchical ZnO NWs were fabricated on Si NWs(ZnO-Si HNWs)using a metal organic chemical vapor deposition approach.The NWs were then N-doped by annealing in an NH_(3) atmosphere.The N-doped ZnO-Si HNWs(N:ZnO-Si HNWs)showed enhanced visible light absorption,and suppressed recombination of the photogenerated carriers.As compared to ZnO-Si HNWs(0.045 m A cm^(-2) at 1.23 V vs RHE),the N:ZnO-Si HNWs(0.34 m A cm^(-2) at 1.23 V vs RHE)annealed in NH^(3) ambient for 3 h at 600℃showed 7.5-fold enhancement in the photocurrent density.NiOOH-deposited N:ZnO-Si HNW photoanodes with a photostability of 82.21%over 20000 s showed 10.69-fold higher photocurrent density(0.48 m A cm^(-2) at 1.23 V vs RHE)than ZnO-Si HNWs.

A New Mixed-metal Monophosphate:Ba2Bi2Co(PO4)4

A new member of mixed-metal Ba2Bi2M-Ⅱ（PO4）4 monophosphate, namely Ba2Bi2Co（PO4）4, was synthesized by solid state method and characterized by X-ray single-crystal diffraction and powder diffraction for the first time. It crystallizes in the orthorhombic system with space group Pnma（No. 62） and features a 3D architecture built up of adjacent zig-zag linear structures of [CoP4O（16）]∞ along [100], and further connected by [Bi2O（11）] dimers to form a 3D framework, where the Ba2＋ are located in the free space. The stereochemical activity of the Bi3＋ lone pair has also been discussed. The result of magnetic property measurement confirms the antiferromagnetic property of Ba2Bi2Co（PO4）4.

Synthesis,Single-crystal Structure,and Computational Studies of a Yavapaiite Structure Compound:Pb(Sb0.5Fe0.5)(PO4)2

The single crystals and powder of a Yavapaiite Structure phosphate,namely,PbSb0.5Fe0.5（PO4）2,were synthesized by solid state method and characterized by X-ray single-crystal diffraction and powder diffraction.The title compound crystallizes in the monoclinic system,space group C2/c（No.15） with a = 16.716（4）,b = 5.186（7）,c = 8.130（2）A,β = 114.93（6）°,Z = 4,R（I 〉 2s（I）） = 0.0430,R indices（all data） = 0.0460,and T = 293（2） K.The title compound belongs to the Yavapaiite Structure A^（Ⅱ）M^（Ⅳ）（PO4）2 compounds,and the Sb1 atom and Fe1 atoms occupy the same site（M） and their occupancy factors are refined to be 0.5 and 0.5 having a sum occupancy factor of 1.0.Its structure consists of [M（PO）4]n^2n- layers running parallel to the（b,c） plane built up of cornerconnected MO6 octahedra and PO4 tetrahedra.Additionally,the calculations of energy band structure,and density of states have been performed with the density functional theory method.The studies of computational calculation and UV experimental results show that the new compound is an indirect band-gap insulator.

Effect of In Diffusion on the Property of Blue Light-Emitting Diodes

In diffusion to blue light-emitting diode （LED） wafers is performed by the inductive coupled plasma （ICP） treatment of a covering layer of indium tin oxide （ITO） on the wafer surface. The electrical property of the p- type contact is improved and the redshift of photoluminescence （PL） from the InGaN quantum well of the wafer is found. Measurements by x-ray photoelectron spectroscopy （XPS） demonstrate that In atoms have diffused into p-GaN. Reflectance spectra of the sample surface reveal the variation caused by the ICP treatment. A model of compensation of the in-plane strain of the InGaN layer is used to explain the redshift of the PL data. Finally, LEDs are fabricated by using as-grown and ICP-treated wafers and their properties are compared. Under an injection current of 20mA, LEDs with ICP-induced In doping show a decrease of 0.3 V in the forward voltage and an increase of 23% in the light output, respectively.

Temperature Dependence of Emission Properties of Self-Assembled InGaN Quantum Dots

Emission properties of self-assembled green-emitting InGaN quantum dots （QDs） grown on sapphire substrates by using metal organic chemical vapor deposition are studied by temperature-dependent photoluminescence （PL） measurements. As temperature increases （15-300K）, the PL peak energy shows an anomalous V-shaped （redshift blueshift） variation instead of an S-shaped （redshift-blueshift-redshift） variation, as observed typically in green-emitting InGaN/GaN multi-quantum wells （MOWs）. The PL full width at half maximum （FWHM） also shows a V-shaped （decrease-increase） variation. The temperature dependence of the PL peak energy and FWHM of QDs are well explained by a model similar to MOWs, in which carriers transferring in localized states play an important role, while the confinement energy of localized states in the QDs is significantly larger than that in MOWs. By analyzing the integrated PL intensity, the larger confinement energy of localized states in the QDs is estimated to be 105.9meV, which is well explained by taking into account the band-gap shrinkage and carrier thermalization with temperature. It is also found that the nonradiative combination centers in QD samples are much less than those in QW samples with the same In content.

Ionizing terahertz waves with 260 MV/cm from scalable optical rectification

Terahertz(THz)waves,known as non-ionizing radiation owing to their low photon energies,can actually ionize atoms and molecules when a sufficiently large number of THz photons are concentrated in time and space.Here,we demonstrate the generation of ionizing,multicycle,15-THz waves emitted from large-area lithium niobate crystals via phase-matched optical rectification of 150-terawatt laser pulses.A complete characterization of the generated THz waves in energy,pulse duration,and focal spot size shows that the field strength can reach up to 260 megavolts per centimeter.In particular,a single-shot THz interferometer is employed to measure the THz pulse duration and spectrum with complementary numerical simulations.Such intense THz pulses are irradiated onto various solid targets to demonstrate THz-induced tunneling ionization and plasma formation.This study also discusses the potential of nonperturbative THz-driven ionization in gases,which will open up new opportunities,including nonlinear and relativistic THz physics in plasma.