Enhancing multifunctional photocatalysis with acetate-assisted cesium doping and unlocking the potential of Z-scheme solar water splitting

Graphitic carbon nitride(g-C_(3)N_(4))has been extensively doped with alkali metals to enlarge photocatalytic output,in which cesium(Cs)doping is predicted to be the most efficient.Nevertheless,the sluggish diffusion and doping kinetics of precursors with high melting points,along with imprecise regulation,have raised the debate on whether Cs doping could make sense.For this matter,we attempt to confirm the positive effects of Cs doping on multifunctional photocatalysis by first using cesium acetate with the character of easy manipulation.The optimized Csdoped g-C_(3)N_(4)(CCN)shows a 41.6-fold increase in visible-light-driven hydrogen evolution reaction(HER)compared to pure g-C_(3)N_(4) and impressive degradation capability,especially with 77%refractory tetracycline and almost 100%rhodamine B degradedwithin an hour.The penetration ofCs+is demonstrated to be a mode of interlayer doping,and Cs–N bonds(especially with sp^(2) pyridine N in C═N–C),along with robust chemical interaction and electron exchange,are fabricated.This atomic configuration triggers the broadened spectral response,the improved charge migration,and the activated photocatalytic capacity.Furthermore,we evaluate the CCN/cadmium sulfide hybrid as a Z-scheme configuration,promoting the visible HER yield to 9.02 mmol g^(−1) h^(−1),which is the highest ever reported among all CCN systems.This work adds to the rapidly expanding field of manipulation strategies and supports further development of mediating served for photocatalysis.

Investigation of helicity-dependent photocurrent of surface states in(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplate

Helicity-dependent photocurrent(HDPC)of the surface states in a high-quality topological insulator(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplate grown by chemical vapor deposition(CVD)is investigated.By investigating the angle-dependent HDPC,it is found that the HDPC is mainly contributed by the circular photogalvanic effect(CPGE)current when the incident plane is perpendicular to the connection of the two contacts,whereas the circular photon drag effect(CPDE)dominates the HDPC when the incident plane is parallel to the connection of the two contacts.In addition,the CPGE of the(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplate is regulated by temperature,light power,excitation wavelength,the source–drain and ionic liquid top-gate voltages,and the regulation mechanisms are discussed.It is demonstrated that(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplates may provide a good platform for novel opto-spintronics devices.

Investigation of reflection anisotropy induced by micropipe defects on the surface of a 4H-SiC single crystal using scanning anisotropy microscopy

Optical reflection anisotropy microscopy mappings of micropipe defects on the surface of a 4H-SiC single crystal are studied by the scanning anisotropy microscopy(SAM)system.The reflection anisotropy(RA)image with a'butterfly pattern'is obtained around the micropipes by SAM.The RA image of the edge dislocations is theoretically simulated based on dislocation theory and the photoelastic principle.By comparing with the Raman spectrum,it is verified that the micropipes consist of edge dislocations.The different patterns of the RA images are due to the different orientations of the Burgers vectors.Besides,the strain distribution of the micropipes is also deduced.One can identify the dislocation type,the direction of the Burgers vector and the optical anisotropy from the RA image by using SAM.Therefore,SAM is an ideal tool to measure the optical anisotropy induced by the strain field around a defect.

Effect of drying methods on perovskite films and solar cells

The high efficiency,solution processibility,and flexibility of perovskite solar cells make them promising candidates for the photovoltaic industry[1−8].The deposition method is one of the most critical factors that affect the performance of perovskite films.Various deposition methods have been developed to make perovskite films,including spin-coating,slotdie coating.

The application of perovskite materials in solar water splitting

Solar water splitting is a promising strategy for sustainable production of renewable hydrogen,and solving the crisis of energy and environment in the world.However,large-scale application of this method is hampered by the efficiency and the expense of the solar water splitting systems.Searching for non-toxic,low-cost,efficient and stable photocatalysts is an important way for solar water splitting.Due to the simplicity of structure and the flexibility of composition,perovskite based photocatalysts have recently attracted widespread attention for application in solar water splitting.In this review,the recent developments of perovskite based photocatalysts for water splitting are summarized.An introduction including the structures and properties of perovskite materials,and the fundamentals of solar water splitting is first provided.Then,it specifically focuses on the strategies for designing and modulating perovskite materials to improve their photocatalytic performance for solar water splitting.The current challenges and perspectives of perovskite materials in solar water splitting are also reviewed.The aim of this review is to summarize recent findings and developments of perovskite based photocatalysts and provide some useful guidance for the future research on the design and development of highly efficient perovskite based photocatalysts and the relevant systems for water splitting.

Tuning Properties of External Cavity Violet Semiconductor Laser

A tunable grating-coupled external cavity(EC)laser is realized by employing a GaN-based laser diode as the gain device.A tuning range of 4.47 nm from 403.82 to 408.29 nm is achieved.Detailed investigations reveal that the injection current strongly influences the performance of the EC laser.Below the free-running lasing threshold,EC laser works stably.While above the free-running lasing threshold,a Fabry–Pérot(F-P)resonance peak in the emission spectrum and a smooth kink in the output power-injection current characteristic curve are observed,suggesting the competition between the inner F-P cavity resonance and EC resonance.Furthermore,the tuning range is found to be asymmetric and occurs predominantly on the longer wavelength side.This is interpreted in terms of the asymmetric gain distribution of GaN-based quantum well material.

Recent progress and future prospect of novel multi-ion storage devices

Rechargeable batteries,especially lithium-ion batteries(LIBs),have made rapid development since the 21st century,greatly facilitating people's lives[1−6].Based on considerations of cost and existing problems(such as safety issues due to LIBs stacking strategy and unsatisfactory performance for various applications),researchers have explored alternative technologies to LIBs to meet the needs for wide application scenarios[5].Among them,multi-ion storage devices such as dual-ion batteries(DIBs)and metal-ion hybrid capacitors(MIHCs)are considered promising alternative energy storage devices of LIBs due to their unique multi-ion storage mechanism.In a multi-ion storage device,cations and anions carry charges back and forth between the electrolyte and the electrodes at the same time,unlike the rocking chair mechanism of LIBs[7].Generally,the anodes of DIBs and MIHCs work in a similar mechanism to LIBs,storing charge through redox reactions.The main difference among them is the mechanism of the cathodes during charging and discharging[8].In DIBs,the battery-type cathode stores anions through the Faraday reaction.

4‑Terminal Inorganic Perovskite/Organic Tandem Solar Cells Offer 22%Efficiency

After fast developing of single-junction perovskite solar cells and organic solar cells in the past 10 years,it is becoming harder and harder to improve their power conversion efficiencies.Tandem solar cells are receiving more and more attention because they have much higher theoretical efficiency than single-junction solar cells.Good device performance has been achieved for perovskite/silicon and perovskite/perovskite tandem solar cells,including 2-terminal and 4-terminal structures.However,very few studies have been done about 4-terminal inorganic perovskite/organic tandem solar cells.In this work,semi-transparent inorganic perovskite solar cells and organic solar cells are used to fabricate 4-terminal inorganic perovskite/organic tandem solar cells,achieving a power conversion efficiency of 21.25%for the tandem cells with spin-coated perovskite layer.By using drop-coating instead of spin-coating to make the inorganic perovskite films,4-terminal tandem cells with an efficiency of 22.34%are made.The efficiency is higher than the reported 2-terminal and 4-terminal inorganic perovskite/organic tandem solar cells.In addition,equivalent 2-terminal tandem solar cells were fabricated by connecting the sub-cells in series.The stability of organic solar cells under continuous illumination is improved by using semi-transparent perovskite solar cells as filter.

An in-depth understanding of photophysics in organic photocatalysts

The urgent need to replace conventional fossil fuels with clean energy has stimulated a large number of research efforts on photocatalytic hydrogen evolution[1−4].Alternatively,organic semiconductors with tunable light absorption,well-positioned band edges,and excellent charge separation are highly expected[5−8].Conventionally,a semiconductor material with a wide band gap has a larger exciton binding energy,while a semiconductor material with a narrow band gap has a smaller exciton binding energy[9].Since smaller exciton binding energies are favorable for exciton separation,choosing a semiconductor with a suitable bandgap seems to be the first step toward high solar-to-hydrogen efficiency.The tunable light-harvesting ability determines the advantage and potential of organic semiconductors as photocatalysts.However,the insufficient external quantum efficiency(EQE)and the un-derlying photophysical mechanism remain restricting the orientation toward industrialization[10].

Space Materials Science in China:Ⅱ.Ground-based Researches and Academic Activities

Activities of space materials science research in China have been continuously supported by two main national programs.One is the China Space Station(CSS)program since 1992,and the other is the Strategic Priority Program(SPP)on Space Science since 2011.In CSS plan in 2019,eleven space materials science experimental projects were officially approved for execution during the construction of the space station.In the SPP Phase Ⅱ launched in 2018,seven pre-research projects are deployed as the first batch in 2018,and one concept study project in 2019.These pre-research projects will be cultivated as candidates for future selection as space experiment projects on the recovery of scientific experimental satellites in the future.A new apparatus of electrostatic levitation system for ground-based research of space materials science and rapid solidification research has been developed under the support of the National Natural Science Foundation of China.In order to promote domestic academic activities and to enhance the advancement of space materials science in China,the Space Materials Science and Technology Division belong to the Chinese Materials Research Society was established in 2019.We also organized scientists to write five review papers on space materials science as a special topic published in the journal Scientia Sinica to provide valuable scientific and technical references for Chinese researchers.

Investigation of Ga_(2)O_(3)/diamond heterostructure solar-blind avalanche photodiode via TCAD simulation

A Ga_(2)O_(3)/diamond separate absorption and multiplication avalanche photodiode(SAM-APD)with mesa structure has been proposed and simulated.The simulation is based on an optimized Ga_(2)O_(3)/diamond heterostructure TCAD physical model,which is revised by repeated comparison with the experimental data from the literature.Since both Ga_(2)O_(3)and diamond are ultra-wide bandgap semiconductor materials,the Ga_(2)O_(3)/diamond SAM-APD shows good solar-blind detection ability,and the corresponding cutoff wavelength is about 263 nm.The doping distribution and the electric field distribution of the SAM-APD are discussed,and the simulation results show that the gain of the designed device can reach 5×10^(4)and the peak responsivity can reach a value as high as 78 A/W.

Influence of Frohlich Interaction on Intersubband Transitions of InGaAs/InAlAs-Based Quantum Cascade Detector Structures Investigated by Infrared Modulated Photoluminescence

We demonstrate the use of an infrared modulated photoluminescence(PL)method based on a step-scan Fourier-transform infrared spectrometer to analyze intersubband transition(ISBT)of InGaAs/InAlAs quantum cascade detector(QCD)structures.By configuring oblique and parallel excitation geometries,high signal-to-noise ratio PL spectra in near-to-far-infrared region are measured.With support from numerical calculations based on the k·p perturbation theory,the spectra is attributed to intraband and interband transitions of InGaAs/InAlAs QCD structures.Temperature evolution results show that the k-dependent transitions caused by longitudinal optical phonon-assisted scattering(Frohlich interaction)plays an important role in the ISBT.These results suggest that this infrared modulated-PL method has great potential in characterizing QCD devices and conducting performance diagnostics.

Structural Characterization of Carbon-implanted GaSb

Ion implantation induced damage in GaSb and its removal by rapid thermal annealing(RTA)have been investigated by Raman spectroscopy.The evolution of the Raman modes as a function of implantation fluence,annealing temperature and time has been analyzed.Results indicate that a lattice quality that is close to as-grown GaSb has been obtained by annealing the implanted samples at 500℃for 45 s.However,consequent surface analyses by scanning electron microscope(SEM)and atomic force microscope(AFM)show that a heavily perturbed layer contains voids due to the outdifiusion of Sb atoms on the surface remains.Mechanism of the damage recovery and the structure of the implanted layer are discussed based on the experimental results.

Helicity-dependent photoconductance of the edge states in the topological insulator Bi_(2)Te_(3)

The helicity-dependent photoconductance of the edge states in three-dimensional topological insulator Bi_(2)Te_(3)films is investigated.It is revealed that the helicity-dependent photoconductivity current on the left edge of the Bi_(2)Te_(3)film shows an opposite sign with that on the right edge.In addition,the helicity-dependent photoconductivity current increases linearly with the applied longitudinal electric field,and it reverses the sign with the reversal of the electric field.As the thickness of the Bi_(2)Te_(3)film increases,the helicity-dependent photoconductivity current also increases.Theoretical analysis suggests that the helicity-dependent photo-conductivity current may come from the intrinsic spin orbit coupling(SOC)or the SOC introduced by the chiral impurities or defects.

Flat Top Optical Frequency Combs Based on a Single-Core Quantum Cascade Laser at Wavelength of~8.7μm

We present optical frequency combs with a spectral emission of 48 cm-1and an output power of 420 m W based on a single-core quantum cascade laser at λ ~ 8.7μm. A flat top spectrum sustains up to 130 comb modes delivering ~ 3.2 m W of optical power per mode, making it a valuable tool for dual comb spectroscopy. The homogeneous gain medium, relying on a slightly diagonal bound-to-continuum structure, promises to provide a broad and stable gain for comb operating. Remarkably, the dispersion of this device is measured within 300 fs2/mm to ensure stable comb operation over 90% of the total current range. The comb is observed with a narrow beatnote linewidth around 2 k Hz and has weak dependence on the applied current for stable comb operation.

The measurement of responsivity of infrared photodetectors using a cavity blackbody

For the measurement of responsivity of an infrared photodetector,the most-used radiation source is a blackbody.In such a measurement system,distance between the blackbody,the photodetector and the aperture diameter are two parameters that contribute most measurement errors.In this work,we describe the configuration of our responsivity measurement system in great detail and present a method to calibrate the distance and aperture diameter.The core of this calibration method is to transfer direct measurements of these two parameters into an extraction procedure by fitting the experiment data to the calculated results.The calibration method is proved experimentally with a commercially extended InGaAs detector at a wide range of blackbody temperature,aperture diameter and distance.Then proof procedures are further extended into a detector fabricated in our laboratory and consistent results were obtained.

State-of-the-art advances in vacancy defect engineering of graphitic carbon nitride for solar water splitting

Developing low-cost,efficient,and stable photocatalysts is one of the most promising methods for large-scale solar water splitting.As a metal-free semiconductor material with suitable band gap,graphitic carbon nitride(g-C_(3)N_(4))has attracted attention in the field of photocatalysis,which is mainly attributed to its fascinating physicochemical and photoelectronic properties.However,several inherent limitations and shortcomings—involving high recombination rate of photocarriers,insufficient reaction kinetics,and optical absorption—impede the practical applicability of g-C_(3)N_(4).As an effective strategy,vacancy defect engineering has been widely used for breaking through the current limitations,considering its ability to optimize the electronic structure and surface morphology of g-C_(3)N_(4) to obtain the desired photocatalytic activity.This review summarizes the recent progress of vacancy defect engineered g-C_(3)N_(4) for solar water splitting.The fundamentals of solar water splitting with g-C_(3)N_(4) are discussed first.We then focus on the fabrication strategies and effect of vacancy generated in g-C_(3)N_(4).The advances of vacancy-modified g-C_(3)N_(4) photocatalysts toward solar water splitting are discussed next.Finally,the current challenges and future opportunities of vacancy-modified g-C_(3)N_(4) are summarized.This review aims to provide a theoretical basis and guidance for future research on the design and development of highly efficient defective g-C_(3)N_(4).

Phase-locked single-mode terahertz quantum cascade lasers array

We demonstrated a scheme of phase-locked terahertz quantum cascade lasers(THz QCLs)array,with a single-mode pulse power of 108 mW at 13 K.The device utilizes a Talbot cavity to achieve phase locking among five ridge lasers with first-order buried distributed feedback(DFB)grating,resulting in nearly five times amplification of the single-mode power.Due to the optimum length of Talbot cavity depends on wavelength,the combination of Talbot cavity with the DFB grating leads to better power amplification than the combination with multimode Fabry-Perot(F-P)cavities.The Talbot cavity facet reflects light back to the ridge array direction and achieves self-imaging in the array,enabling phase-locked operation of ridges.We set the spacing between adjacent elements to be 220μm,much larger than the free-space wavelength,ensuring the operation of the fundamental supermode throughout the laser's dynamic range and obtaining a high-brightness far-field distribution.This scheme provides a new approach for enhancing the single-mode power of THz QCLs.

Influence of Yb_2O_3 doping on microstructural and electrical properties of ZnO-Bi_2O_3-based varistor ceramics

ZnO-Bi2O3-based varistor ceramics doped with Yb2O3 in the range from 0 to 0.4% （molar fraction） were obtained by a solid reaction route. The X-ray diffractometry （XRD） and scanning electron microscopy （SEM） were applied to characterize the phases and microstructure of the varistor ceramics, and a DC parameter instrument for varistor ceramics was applied to investigate their electrical properties and V-I characteristics. The XRD analysis of the samples shows that the ZnO phase, Bi2O3 phase, ZnTSbaOl2-type spinel phase and Zn2Bi3Sb3O14-type pyrochlore are present, and the Yb2O3 phases and Sb2O4 phases are found in varistor ceramics with increasing amounts of Yb2O3. The average size of ZnO grain firstly increases and then decreases with the increase of Yb2O3 content. The result also shows that the threshold voltage is between 656 V/nun and 1 232 V/mm, the nonlinear coefficient is in the range of 14.1-22.3, and the leakage current is between 0.60 μA and 19.6 μA. The 0.20% Yb2O3-added ZnO-Bi2O3-based varistor ceramics sintered at 900 ℃ have the best electrical characteristics.

Comparative characteristics of yttrium oxide and yttrium nitric acid doping in ZnO varistor ceramics

The effect of different molar ratios of Y2O3 and Y（NO3）3 on the microstructure and electrical response of ZnO-Bi203-based varistor ceramics sintered at 1 000 ℃ was investigated, and the mechanism by which this doping improves the electrical characteristics of ZnO-Bi203-based varistor ceramics was discussed. With increasing amounts of Y（NO3）3 or Y2O3 in the starting composition, Y2O3, Sb204 and Y-containing Bi-rich phase form, and the average grain size significantly decreases. The average grain size significantly decreases as the contents of rare earth compounds of Y（NO3）3 or Y2O3 increase. The maximum value of the nonlinear coefficient is found at 0.16% Y（NO3）3 or 0.02% YaO3 （molar fraction） doped varistor ceramics, and there is an increase of 122% or 35% compared with the varistor ceramics without Y（NO3）3 or Y2O3. The threshold voltage VT of Y（NO3）3 and Y2O3 reaches at 1 460 V/mm and 1 035 V/ram, respectively. The results also show that varistor sample doped with Y（NO3）3 has a remarkably more homogeneous and denser microstructure in comparison to the sample doped with Y2O3.