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• A new strategy was developed to fabricate core-shell Mo nanocomposite powders. • Mo composite with high-density intragranular κ-Al 2 O 3 nanoparticles was prepared. • A coherent relationship was formed between the κ-Al 2 O 3 nanoparticles and Mo matrix. • The composite exhibited remarkably improved mechanical properties. Oxide dispersion strengthening (ODS) is an effective method to improve the mechanical properties of Mo-based materials. However, the mechanical properties of traditional ODS-Mo composites are always limited by the coarsening and intergranular distribution of second-phase particles. In this work, an effective nano-reinforcement dispersion strategy was developed to fabricate an ODS-Mo composite with ultrafine grain and intragranular distribution of second-phase particles. Core-shell structural Mo nanocomposite powders, with internally distributed sub-10 nm Al 2 O 3 dispersoids, were prepared by nano atomization doping (AD) followed by a chemical vapor transport growth strategy. Then, ODS-Mo composites with ultra-fine Mo grain (below 700 nm) and high-density intragranular κ-Al 2 O 3 (below 20 nm) nanoparticles were prepared via spark plasma sintering (SPS), in which a coherent interface between κ-Al 2 O 3 and Mo matrix was formed. The composites present remarkably improved hardness (above 500 HV), bend strength, and compressive yield strength (above 1664 MPa) at room temperature, with a suitable strain to fracture of 27.1 %. The calculation of strengthening mechanisms indicates that the enhancement was mainly attributed to the intragranular κ-Al 2 O 3 nanoparticles. This nano-sized reinforcement distributed within the grain can more effectively pin dislocations and achieve dispersion strengthening in ODS-Mo composites. Therefore, this strategy can efficiently construct intragranular second-phase nanoparticles and open up new avenues to fabricate high-performance ODS-Mo composites. [Display omitted] [ABSTRACT FROM AUTHOR]

In recent years, the exploitation of offshore wind resources has been attached with greater importance. As a result, semi-submersible floating wind turbines (FWTs) have gradually become a popular research topic, with the structural strength being a research hotspot as it can ensure the safe operation of FWTs. The severe sea conditions of freak waves result in enormous wave heights, extremely fast wave speeds, and concentrated energy. Thus, it is difficult to accurately simulate these effects on the loads of floating wind turbines using the potential flow theory and other theories. In this paper, the structural strength of a floating wind turbine under the action of freak waves is analyzed based on the CFD-FEA coupled method. The effects of the mooring system and the wind load are considered in the time domain, and the CFD method is applied to analyze the wave load of the floating wind turbine under the extreme sea state of freak waves. The strength and motion of the floating wind turbine float structure are analyzed by combining the CFD method and the FEA method, and the analytical results of the mutual transfer of these two methods are taken as the initial quantities for further analysis. The accuracy of the analytical model of the CFD-FEA method is verified by the results of the tank test analysis, and the structural strength analysis under freak wave conditions is carried out for a new type of floating wind turbine. The results of this research provide useful guidance and references for the design and engineering applications of offshore floating wind turbines.

Chalcophosphates are an important type of infrared nonlinear optical (NLO) candidates in view of their rich anionic motifs. Here, two copper chalcophosphates Cu3PSe4(CPSe) and Cs2CuP3S9(CCPS) were synthesized and studied as IR NLO materials. They both feature three-dimensional polyanionic frameworks constructed by similar T2-supertetrahedra, and the structure of CCPS can be derived from CPSe via introducing Cs and substituting Se with S. This structural evolution results in phase-matchable NLO behavior, enlarged optical band gap, and enhanced laser-induced damage threshold for CCPS. These results are elucidated by structure analysis and theoretical calculations, and the increased structural anisotropy contributes to the phase matchable behavior of CCPS. This work presents a case on how to adjust NLO properties via certain structure considerations, which may be extended to more systems for obtaining high-performance NLO materials.

Engineering atomic-scale defects has become an important strategy for the future application of transition metal dichalcogenide (TMD) materials in next-generation electronic technologies. Thus, providing an atomic understanding of the electron–defect interactions and supporting defect engineering development to improve carrier transport is crucial to future TMDs technologies. In this work, we utilize low-temperature scanning tunneling microscopy/spectroscopy (LT-STM/S) to elicit how distinct types of defects bring forth scattering potential engineering based on intervalley quantum quasiparticle interference (QPI) in TMDs. Furthermore, quantifying the energy-dependent phase variation of the QPI standing wave reveals the detailed electron–defect interaction between the substitution-induced scattering potential and the carrier transport mechanism. By exploring the intrinsic electronic behavior of atomic-level defects to further understand how defects affect carrier transport in low-dimensional semiconductors, we offer potential technological applications that may contribute to the future expansion of TMDs.

Background: Bile duct leaks (BDLs) are serious complications that occurs after hepatobiliary surgery and trauma, leading to rapid clinical deterioration. Endoscopic retrograde cholangiopancreatography (ERCP) is the first-line treatment for BDLs, but it is not clear which patients will respond to this therapy and which patients will require additional surgical intervention. The aim of our study was to explore the predictors of successful ERCP for BDLs. Methods: A retrospective analysis was conducted using data from six centers' databases. All consecutive patients who were clinically confirmed as BDLs were included in the study. Collected data were demographics, disease severity, and ERCP procedure characteristics. Univariate and multivariate analysis were used to select independent predictive factors that affect the outcome of ERCP for BDLs, and a nomogram was established. Calibration and ROC curves were used to evaluate the models. Results: Four hundred and forty-eight consecutive patients were clinically confirmed as BDLs and 347 were excluded. In the 101 patients included patients, clinical success was achieved in 78 patients (77.2%). In logistic multivariable regression, two independent factors were negatively associated with the success of ERCP: SIRS (OR, 0.183; 95% CI 0.039–0.864; P= 0.032) and high-grade leak (OR 0.073; 95% CI 0.010–0.539; P= 0.010). Two independent factors were positively associated with the success of ERCP: leak-bridging drainage (OR 4.792; 95% CI 1.08–21.21; P= 0.039) and cystic duct leak (OR 6.193; 95% CI 1.03–37.17; P= 0.046). The prediction model with these four factors was evaluated using a receiver-operating characteristic (ROC) curve, which demonstrated an area under the curve of 0.9351. The calibration curve showed that the model had good predictive accuracy. Conclusion: Leak-bridging drainage and cystic duct leak are positive predictors for the success of ERCP, while SIRS and high-grade leak are negative predictors. This prediction model with nomogram has good predictive ability and practical clinical value, and may be helpful in clinical decision-making and prognostication. Graphical abstract:

As one of the potential candidates of nonlinear-optical (NLO) materials, rare-earth chalcophosphates have demonstrated promising properties. Here, KREP2S6(RE = Sm, Gd, Tb, Dy) were synthesized using the facile RE2O3-B-S solid-state method. They crystallize with a monoclinic chiral P21structure, and their layer structures are built by isolated ethane-like P2S6dimers and RES8bicapped trigonal prisms built {[RE2S15]24–}∞layers. By comparing the structures with related ones, the change of the alkali metal or RE3+ions can cause structural transformation. Their band gaps are tunable between 2.58 and 3.79 eV, and their powder samples exhibit good NLO properties. Theoretical calculations suggest that the NLO properties are mainly contributed by P2S6units and {[RE2S15]24–}∞layers synergistically, in which {[RE2S15]24–}∞layers and P2S6units dominate the contribution to the band gap and second-harmonic-generation response, respectively. This work enriches the application of rare-earth chalcophosphates as NLO materials.

Because of the intrinsic low carrier density of monolayer two-dimensional (2D) materials, doping is crucial for the performance of underlap top-gated 2D devices. However, wet etching of a high-k(dielectric constant) dielectric layer is difficult to implement without causing performance deterioration on the devices; therefore, finding a suitable spacer doping technique for 2D devices is indispensable. In this study, we developed a remote doping (RD) method in which defective SiOxcan remotely dope the underlying high-kcapped 2D regions without directly contacting these materials. This method achieved a doping density as high as 1.4 × 1013cm–2without reducing the mobility of the doped materials; after 1 month, the doping concentration remained as high as 1.2 × 1013cm–2. Defective SiOxcan be used to dope most popular 2D transition-metal dichalcogenides. The low-kproperties of SiOxrender it ideal for spacer doping, which is very attractive from the perspective of circuit operation. In our experiments, MoS2and WS2underlap top-gate devices exhibited 10× and 200× increases in their on-currents, respectively, after being doped with SiOx. These results indicate that SiOxdoping can be conducted to manufacture high-performance 2D devices.

In large group decision-making, participators with different knowledge structures, backgrounds, and other characteristics are unlikely to accurately evaluate alternatives. For this, it is necessary to decompose alternatives into several elements, and consider the participators’ preferences for elements of alternatives and the multiple classifications for participators according to their characteristics. However, related studies are still scarce. The objective of this paper is to propose a multi-elemental large group decision-making method, in which the desirable alternative(s) are selected from a set of feasible alternatives according to the preference information on multiple elements of alternatives provided by participators from multiple subgroups, and multiple classifications for participators are considered. In the method, according to the strict preference ordering of elements provided by participators, the percentage distributions on preferences of each subgroup concerning each element are firstly presented under each classification for participators. Secondly, the decision weight of each subgroup is determined by three factors, i.e., the consensus of preferences provided by each subgroup, the organizer’s preference for each subgroup, and the number of participators in each subgroup. Then, the comprehensive preference concerning each element is determined by combing the preference information from multiple subgroups and the decision weights of multiple subgroups, the overall preference vector can be obtained under each classification, and the virtual alternatives are determined by normalizing the overall preference vector. Further, considering multiple classifications for participators, the overall dominant degrees of alternatives can be obtained by calculating the similarity degrees between each virtual alternative and each alternative, thus the ranking order of alternatives can be obtained based on the overall dominant degrees of alternatives. Finally, an example is given to confirm the feasibility of the proposed method. The results of the sensitivity and comparative analyses show that the proposed method is applicable and effective. The proposed method can further enrich and improve the theory and approach of large group decision-making with multiple elements considering multiple classifications for participators.

Resolving the momentum degree of freedom of photoexcited charge carriers and exploring the excited-state physics in the hexagonal Brillouin zone of atomically thin semiconductors have recently attracted great interest for optoelectronic technologies. We demonstrate a combination of light-modulated scanning tunneling microscopy and the quasiparticle interference (QPI) technique to offer a directly accessible approach to reveal and quantify the unexplored momentum-forbidden electronic quantum states in transition metal dichalcogenide (TMD) monolayers. Our QPI results affirm the large spin-splitting energy at the spin-valley-coupled Q valleys in the conduction band (CB) of a tungsten disulfide monolayer. Furthermore, we also quantify the photoexcited carrier density-dependent band renormalization at the Q valleys. Our findings directly highlight the importance of the excited-state distribution at the Q valley in the band renormalization in TMDs and support the critical role of the CB Q valley in engineering the quantum electronic valley degree of freedom in TMD devices.

In the underwater waveguide, the conventional adaptive subspace detector (ASD), derived by using the generalized likelihood ratio test (GLRT) theory, suffers from a significant degradation in detection performance when the samplings of training data are deficient. This paper proposes a dimension-reduced approach to alleviate this problem. The dimension reduction includes two steps: firstly, the full array is divided into several subarrays; secondly, the test data and the training data at each subarray are transformed into the modal domain from the hydrophone domain. Then the modal-domain test data and training data at each subarray are processed to formulate the subarray statistic by using the GLRT theory. The final test statistic of the dimension-reduced ASD (DR-ASD) is obtained by summing all the subarray statistics. After the dimension reduction, the unknown parameters can be estimated more accurately so the DR-ASD achieves a better detection performance than the ASD. In order to achieve the optimal detection performance, the processing gain of the DR-ASD is deduced to choose a proper number of subarrays. Simulation experiments verify the improved detection performance of the DR-ASD compared with the ASD.

Platinum diselenide (PtSe2) is a group-10 two-dimensional (2D) transition metal dichalcogenide that exhibits the most prominent atomic-layer-dependent electronic behavior of “semiconductor-to-semimetal” transition when going from monolayer to bulk form. This work demonstrates an efficient photoelectrochemical (PEC) conversion for direct solar-to-hydrogen (H2) production based on 2D layered PtSe2/Si heterojunction photocathodes. By systematically controlling the number of atomic layers of wafer-scale 2D PtSe2films through chemical vapor deposition (CVD), the interfacial band alignments at the 2D layered PtSe2/Si heterojunctions can be appropriately engineered. The 2D PtSe2/p-Si heterojunction photocathode consisting of a PtSe2thin film with a thickness of 2.2 nm (or 3 atomic layers) exhibits the optimized band alignment and delivers the best PEC performance for hydrogen production with a photocurrent density of −32.4 mA cm–2at 0 V and an onset potential of 1 mA cm–2at 0.29 V versus a reversible hydrogen electrode (RHE) after post-treatment. The wafer-scale atomic-layer controlled band engineering of 2D PtSe2thin-film catalysts integrated with the Si light absorber provides an effective way in the renewable energy application for direct solar-to-hydrogen production.

Two-dimensional transition metal dichalcogenide nanoribbons are touted as the future extreme device downscaling for advanced logic and memory devices but remain a formidable synthetic challenge. Here, we demonstrate a ledge-directed epitaxy (LDE) of dense arrays of continuous, self-aligned, monolayer and single-crystalline MoS2nanoribbons on β-gallium (iii) oxide (β-Ga2O3) (100) substrates. LDE MoS2nanoribbons have spatial uniformity over a long range and transport characteristics on par with those seen in exfoliated benchmarks. Prototype MoS2-nanoribbon-based field-effect transistors exhibit high on/off ratios of 108and an averaged room temperature electron mobility of 65 cm2V−1s−1. The MoS2nanoribbons can be readily transferred to arbitrary substrates while the underlying β-Ga2O3can be reused after mechanical exfoliation. We further demonstrate LDE as a versatile epitaxy platform for the growth of p-type WSe2nanoribbons and lateral heterostructures made of p-WSe2and n-MoS2nanoribbons for futuristic electronics applications.

A core-shell g-C3N4/SiO2nanocomposite was successfully synthesized by depositing g-C3N4, obtained from the sublimation of melamine and subsequent polymerization reaction in the gaseous phase, on the nano-silica. The as-prepared g-C3N4/SiO2was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, N2adsorption–desorption, UV-vis diffuse reflectance spectroscopy. The visible-driven photocatalytic activity of g-C3N4/ SiO2was evaluated by the degradation of tetracycline. The results indicate that the specific surface area of g-C3N4/SiO2is 97.32 m2/g, which is 6.74 times as high as that of bulk g-C3N4(14.44 m2/g). Compared to bulk g-C3N4, g-C3N4/SiO2composite exhibits significantly enhanced photocatalytic activity for degradation of tetracycline and can degrade 72.7% of tetracycline within 60 min under visible-light irradiation. The photodegradation rate constant of tetracycline over g-C3N4/SiO2is 7.2 times as high as that over bulk g-C3N4. The greatly enhanced photocatalytic activity of g-C3N4/SiO2is due to coupling enlarged surface areas with the contribution of SiO2in inhibition of the recombination of photo-induced electron-hole pair.

Palladium diselenide (PdSe2), a peculiar noble metal dichalcogenide, has emerged as a new two-dimensional material with high predicted carrier mobility and a widely tunable band gap for device applications. The inherent in-plane anisotropy endowed by the pentagonal structure further renders PdSe2promising for novel electronic, photonic, and thermoelectric applications. However, the direct synthesis of few-layer PdSe2is still challenging and rarely reported. Here, we demonstrate that few-layer, single-crystal PdSe2flakes can be synthesized at a relatively low growth temperature (300 °C) on sapphire substrates using low-pressure chemical vapor deposition (CVD). The well-defined rectangular domain shape and precisely determined layer number of the CVD-grown PdSe2enable us to investigate their layer-dependent and in-plane anisotropic properties. The experimentally determined layer-dependent band gap shrinkage combined with first-principle calculations suggest that the interlayer interaction is weaker in few-layer PdSe2in comparison with that in bulk crystals. Field-effect transistors based on the CVD-grown PdSe2also show performances comparable to those based on exfoliated samples. The low-temperature synthesis method reported here provides a feasible approach to fabricate high-quality few-layer PdSe2for device applications.

The heating mechanism of electric and magnetic loss materials under microwave irradiation is expounded. The heating rate, material composition and road performance of four kinds of microwave ice and snow roads including carbon fiber, magnetite ore, steel fiber and ferrite are reviewed. And analyze their respective characteristics and applicable conditions. The problems existing in microwave melting ice and snow technology are discussed, and the application prospects of electromagnetic wave absorbing materials in microwave melting ice and snow road are prospected.

Identifying the point defects in 2D materials is important for many applications. Recent studies have proposed that W vacancies are the predominant point defect in 2D WSe2, in contrast to theoretical studies, which predict that chalcogen vacancies are the most likely intrinsic point defects in transition metal dichalcogenide semiconductors. We show using first-principles calculations, scanning tunneling microscopy (STM), and scanning transmission electron microscopy experiments that W vacancies are not present in our CVD-grown 2D WSe2. We predict that O-passivated Se vacancies (OSe) and O interstitials (Oins) are present in 2D WSe2, because of facile O2dissociation at Se vacancies or due to the presence of WO3precursors in CVD growth. These defects give STM images in good agreement with experiment. The optical properties of point defects in 2D WSe2are important because single-photon emission (SPE) from 2D WSe2has been observed experimentally. While strain gradients funnel the exciton in real space, point defects are necessary for the localization of the exciton at length scales that enable photons to be emitted one at a time. Using state-of-the-art GW-Bethe-Salpeter-equation calculations, we predict that only Oinsdefects give localized excitons within the energy range of SPE in previous experiments, making them a likely source of previously observed SPE. No other point defects (OSe, Se vacancies, W vacancies, and SeWantisites) give localized excitons in the same energy range. Our predictions suggest ways to realize SPE in related 2D materials and point experimentalists toward other energy ranges for SPE in 2D WSe2.

When one is trying to maintain original advantageous properties of molecule without increasing the difficulty of synthesis and processing, simultaneously, adding more predictable properties is a preferred choice for designing promising molecules. Here, we report the photovoltaic performance of bistricyclic aromatic enes (BAE) derivative acceptors as a function of heteroatom substitutions (O, S, Se, Te), and the range they can maintain. Beyond that, by combining singlet–triplet exciton conversion with singlet fission (SF), an additional perspective to characterize molecules performance is predicted by employing T1-excitation. Theoretical calculation results showed that for small molecules (BAEs), heavy atom substitution of the same group could increase conformation stability, electron acceptability, and spin–orbit coupling. After expansion of the molecular size (DPP-BAE-DPP), the difference in molecular properties is mainly due to the conformation type for singlet states excitation. For triplet states excitation, the degree of negative correlation between SF and singlet–triplet exciton conversion decreases, which is conducive to obtaining more T1excitons, thus improving the organic photovoltaic performances. As a result, A-S-DPP, A-Te-DPP, T-S-DPP, T-Se-DPPand T-Te-DPPnot only have superior single-excitation performance but also potential triple-excitation possibilities; they are promising acceptors. These results provided some new evidence for designing nonfullerene acceptors and demonstrating the role of heavy atoms substitution in photovoltaic performance.

Oxychalcogenides are receiving increasing interest as nonlinear-optical (NLO) materials because of the possible combination of advantages from oxides and chalcogenides. Here, two new pentanary oxythiogermanates Eu2MGe2OS6[M = Zn (1), Cd (2)] were obtained by the facile metal oxide–boron–sulfur solid-state route. They crystallize with a melilite-type structure and feature {[MGe2OS6]4–}∞layers built by Ge2OS6dimers and MS4tetrahedra. Their optical band gaps are 2.37 and 2.38 eV. As the first NLO rare-earth (RE)/d10dual-metal oxychalcogenides, they exhibit phase-matchable NLO responses and enhanced laser-induced damage thresholds. Theoretical calculations show that the NLO responses are predominantly contributed by the EuOS7motifs. This work provides the potential of RE/d10dual-metal-based NLO materials.

Two-dimensional transition metal dichalcogenides (TMDCs) have shown great promise in electronics and optoelectronics due to their unique electrical and optical properties. Heterostructured TMDC layers such as the laterally stitched TMDCs offer the advantages of better electronic contact and easier band offset tuning. Here, we demonstrate a photoresist-free focused ion beam (FIB) method to pattern as-grown TMDC monolayers by chemical vapor deposition, where the exposed edges from FIB etching serve as the seeds for growing a second TMDC material to form desired lateral heterostructures with arbitrary layouts. The proposed lithographic and growth processes offer better controllability for fabrication of the TMDC heterostrucuture, which enables the construction of devices based on heterostructural monolayers.

Noncentrosymmetric chalcogenides are promising candidates for infrared nonlinear-optical (NLO) crystals, and exploring high-performance ones is a hot topic and challengeable. Herein, the combination of AgQ4, InQ4, and SiQ4(Q = S, Se) units with different S/Se ratios resulted in the discovery of the tetrahedral chalcogenides Ag2In2SiS4Se2(1) and Ag2In2SiS5Se (2). They both crystallize in the monoclinic Ccspace group with different local structures. Co-occupied S/Se sites only exist in 2, and the arrangement of [In2SiQ3] six-membered rings builds different helical chains and 3D [(In2SiQ6)2–]npolyanionic frameworks in 1and 2. They show balanced NLO performances, including phase-matchable moderate NLO responses (0.7 and 0.5 × AGS) and enhanced laser-induced damage thresholds (4.5 and 5.1 × AGS). Theoretical calculations reveal that their NLO responses are predominantly contributed by the AgQ4and InQ4units.

Acupuncture has been proven to improve the pregnancy rate in infertile women. Endometriosis is a common cause of infertility. So far, there are no studies of the efficacy of acupuncture on endometriosis-associated infertility (EAI). Therefore, we will conduct a randomized controlled trial (RCT) to investigate whether acupuncture could have higher pregnancy rates in patients with EAI compared with sham acupuncture. The study protocol is reported in this paper.

Integration of high performance n-type and p-type field-effect transistors with complementary device operation in the same kind of layered materials is highly desirable for pursuing low power and flexible next-generation electronics. In this work, we have shown a well-mannered growth of MoS2on a fin-shaped oxide structure and integration of both n-type and p-type MoS2by using a traditional implantation technique. With the advance of the fin-shaped structure, the maxima and the effective ON current density for the MoS2fin-shaped field-effect transistors are respectively obtained to be about 50 μA μm−1(normalized by the circumference of the fin) and around 500 μA μm−1(only normalized by the fin size), while its ON/OFF ratio is more than 106with low OFF current of a few pA. Based on our n-type and p-type MoS2fin-shaped field-effect transistors, the complementary MoS2inverter with a high DC voltage gain of more than 20 is acquired. Our results provide evidence for complementary 2D material operation in the same materials, a promising avenue for the development of high performance and high-density complementary 2D electronic devices.

3D printing has been getting increasing attention from both industry and academy in recent years. Unlike traditional construction processes, 3D cementitious material printing requires more accurate control on the pumping flow rate, which is known to be affected by the material rheology. In this paper, the effect of fresh rheology on the flow rate of cementitious material was studied experimentally in 3D cementitious material printing process. The material viscosity was measured via a large gap vane viscometer at different time points after mixing, and printing tests were conducted at the same time period to measure the flow rate based on volume conservation principle. Experiments showed that the flow rate was significantly affected by rheology change with respect to time. An open loop control method was then implemented to harmonize the flow volume per unit length during printing processes to improve printing quality.

The tribocorrosion behavior of 304 stainless steel was studied through comparing the damage behavior of 304 stainless steel in dilute sulfuric acid to that in distilled water by a reciprocating tribotester. The re-passivation behavior, the surface and sectional morphological features, as well as the change of microhardness of samples were studied, and the tribocorrosion mechanism was also discussed. The experimental results reveal that the damage of stainless steel in dilute sulfuric acid was caused by the steel’s mechanical removal and electrochemical dissolution. The wear mechanism of stainless steel is abrasive wear, which mainly consists of micro-cutting and peeling. The synergetic action between corrosion and wear is notable. The corrosive environment leads to the embrittlement of the surface layer, and the wear destroys the passivation film and causes galvanic corrosion.

Studies of the ultrafast carrier dynamics of transition metal dichalcogenides have employed spatially averaged measurements, which obfuscate the rich variety of dynamics that originate from the structural heterogeneity of these materials. Here, we employ femtosecond time-resolved photoemission electron microscopy (TR-PEEM) with sub-80 nm spatial resolution to image the ultrafast subpicosecond to picosecond carrier dynamics of monolayer tungsten diselenide (WSe2). The dynamics observed following 2.41 eV pump and 3.61 eV probe occurs on two distinct time scales. The 0.1 ps process is assigned to electron cooling via intervalley scattering, whereas the picosecond dynamics is attributed to exciton–exciton annihilation. The 70 fs decay dynamics observed at negative time delay reflects electronic relaxation from the Γ point. Analysis of the TR-PEEM data furnishes the spatial distributions of the various time constants within a single WSe2flake. The spatial heterogeneity of the lifetime maps is consistent with increased disorder along the edges of the flake and the presence of nanoscale charge puddles in the interior. Our results indicate the need to go beyond spatially averaged time-resolved measurements to understand the influence of structural heterogeneities on the elementary carrier dynamics of two-dimensional materials.

Nanomaterials are interesting for a variety of applications, such as optoelectronics and photovoltaics. However, they often have spatial heterogeneity, i.e., composition change or physical change in the topography or structure, which can lead to varying properties that would influence their applications. New techniques must be developed to understand and correlate spatial heterogeneity with changes in electronic properties. Here we highlight the technique of surface photovoltage Kelvin probe force microscopy (SPV-KFM), which is a modified version of noncontact atomic force microscopy capable of imaging not only the topography and surface potential but also the surface photovoltage on the nanoscale. We demonstrate its utility in probing monolayer WSe2–MoS2lateral heterostructures, which form an ultrathin p–n junction promising for photovoltaic and optoelectronic applications. We show surface photovoltage maps highlighting the different photoresponse of the two material regions as a result of the effective charge separation across this junction. Additionally, we study the variations between different heterostructure flakes and emphasize the importance of controlling the synthesis and transfer of these materials to obtain consistent properties and measurements.

Controlling circularly polarized (CP) states of light is critical to the development of functional devices for key and emerging applications such as display technology and quantum communication, and the compact circular polarization-tunable photon source is one critical element to realize the applications in the chip-scale integrated system. The atomic layers of transition metal dichalcogenides (TMDCs) exhibit intrinsic CP emissions and are potential chiroptical materials for ultrathin CP photon sources. In this work, we demonstrated CP photon sources of TMDCs with device thicknesses approximately 50 nm. CP photoluminescence from the atomic layers of tungsten diselenide (WSe2) was precisely controlled with chiral metamolecules (MMs), and the optical chirality of WSe2was enhanced more than 4 times by integrating with the MMs. Both the enhanced and reversed circular dichroisms had been achieved. Through integrations of the novel gain material and plasmonic structure which are both low-dimensional, a compact device capable of efficiently manipulating emissions of CP photon was realized. These ultrathin devices are suitable for important applications such as the optical information technology and chip-scale biosensing.