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A method based on few-layer MoS2 nanosheets for highly sensitive electrochemical detection of tumor marker ctDNA.

Strong light-matter interactions involved with photons and quasiparticles are fundamentally interesting to access the wealthy many-body physics in quantum mechanics. The emerging two-dimensional (2D) semiconductors with large exciton binding energies and strong quantum confinement allow to investigate exciton-photon coupling at elevated temperatures. Here we report room-temperature formation of Bragg polaritons in monolayer semiconductor on a dielectric mirror through the exciton-Bragg photon coupling. With the negative detuning energy of ∼ 30 meV, angle-resolved reflection signals reveal anti-crossing behaviors of lower and upper polariton branches at ±18° together with the Rabi splitting of 10 meV. Meanwhile, the strengthened photoluminescence appears in the lower polariton branch right below the anti-crossing angles, indicating the presence of the characteristic bottleneck effect caused by the slowing exciton-polariton energy relaxation towards the band minimum. The extracted coupling strength is between the ones of weak and distinct strong coupling regimes, where the eigenenergy splitting induced by the moderate coupling is resolvable but not large enough to fully separate two polaritonic components. Our work develops a simplified strategy to generate exciton-polaritons in 2D semiconductors and can be further extended to probe the intriguing bosonic characteristics of these quasiparticles, such as Bose-Einstein condensation, polariton lasing and superfluidity, directly at the material surfaces.[Figure not available: see fulltext.] Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version We thank the support of the Ministry of Education of Singapore (MOE 2019-T2-1-044), Singapore National Research Foundation under the Competitive Research Programs (No. NRF-CRP-21- 2018-0007), the Fundamental Research Funds for the Central Universities of China, National Natural Science Foundation of China (Nos. 61904151 and 51173081), Natural Science Foundation of Shaanxi (No. 2020JM-108), Joint Research Funds of Department of Science & Technology of Shaanxi Province and Northwestern Polytechnical University (No. 2020GXLHZ-020), Ministry of Education of China (IRT1148), and Zhejiang Provincial Natural Science Foundation of China (No. LGG19F040003).

Transition-metal dichalcogenides with intrinsic spin-valley degree of freedom have enabled great potentials for valleytronic and optoelectronic applications. However, the degree of valley polarization is usually low under nonresonant excitation at room temperature due to the phonon-assisted intervalley scattering. Here, achiral and chiral Au arrays are designed to enhance the optical response and valley polarization in monolayer and bilayer WS2. A considerable band edge emission with 7 times increment is realized under the resonant coupling with Au dimer-prism arrays. Valley polarization enhancement is quantitatively predicted by the inherent mechanisms from elevated electromagnetic field intensity and radiation efficiency and further realized in polarized photoluminescence. A tunable valley polarization up to 30.0% is achieved in bilayer WS2 under a nonresonant excitation at room temperature. All of these results provide a promising route toward the development of room-temperature valley-dependent optoelectronic devices.

Monolayer transition metal dichalcogenide (TMD) alloys have emerged as a unique material system for promising applications in electronics, optoelectronics, and spintronics due to their tunable electronic structures, effective masses of carriers, and valley polarization with various alloy compositions. Although spin-orbit engineering has been extensively studied in monolayer TMD alloys, the valley Zeeman effect in these alloys still remains largely unexplored. Here we demonstrate the enhanced valley magnetic response in Mo0.5W0.5Se2 alloy monolayers and Mo0.5W0.5Se2/WS2 heterostructures probed by magneto-photoluminescence spectroscopy. The large g factors of negatively charged excitons (trions) of Mo0.5W0.5Se2 have been extracted for both pure Mo0.5W0.5Se2 monolayers and Mo0.5W0.5Se2/WS2 heterostructures, which are attributed to the significant impact of doping-induced strong many-body Coulomb interactions on trion emissions under an out-of-plane magnetic field. Moreover, compared with the monolayer Mo0.5W0.5Se2, the slightly reduced valley Zeeman splitting in Mo0.5W0.5Se2/WS2 is a consequence of the weakened exchange interaction arising from p-doping in Mo0.5W0.5Se2via interlayer charge transfer between Mo0.5W0.5Se2 and WS2. Such interlayer charge transfer further evidences the formation of type-II band alignment, in agreement with the density functional theory calculations. Our findings give insights into the spin-valley and interlayer coupling effects in monolayer TMD alloys and their heterostructures, which are essential to develop valleytronic applications based on the emerging family of TMD alloys.

For the manufacture of graphene based electronic devices, graphene growth directly on SiO2/Si substrates is a prerequisite. However, the problem of metal contamination is a key issue that cannot be avoided when synthesizing graphene on SiO2/Si substrates. Additionally, the direct fabrication of patterned graphene still suffers from inefficient and low repeatable problems. In this article, an approach based on a germanium (Ge)-assisted chemical vapor deposition (CVD) is proposed. It can produce graphene directly on any dielectric substrates. Graphene is grown directly on Ge-covered SiO2/Si substrates due to the catalysis of Ge. By depositing the second Ge layer with a pattern by a designed hard mask onto the as-grown centimeter-scale and continuous graphene on SiO2/Si substrates followed by etching the graphene and removing the Ge, the monolayer graphene pattern was acquired. This process has the advantages of no metal pollution and high repeatability. Subsequently, the patterned and highly conductive graphene prepared on SiO2/Si substrates was used for gas sensor. The gas sensor exhibited well NO2 gas sensing properties because of large charge transferred from graphene to NO2 molecules.

Transition-metal dichalcogenides with intrinsic spin-valley degree of freedom have enabled great potentials for valleytronic and optoelectronic applications. However, the degree of valley polarization is usually low under nonresonant excitation at room temperature due to the phonon-assisted intervalley scattering. Here, achiral and chiral Au arrays are designed to enhance the optical response and valley polarization in monolayer and bilayer WS

Industrial gas leaks cause accidents and pose threats to the environment and human life. Thus, it is essential to detect gas leaks in time. Usually, the abnormal concentration signals are defined by a fixed concentration value, such as 25% of the lower explosive limit. However, it is difficult to accumulate to the fixed point quickly when the leak is small. In addition, the actual leak signals are seldom available, making many data classifications inoperable. To solve these problems, this paper proposes a detection approach using the auto-correlation function (ACF) of the normal concentration segment. The feature of each normal segment is obtained by calculating the correlation coefficients between ACFs. According to the features of statistical analysis, a nonconcentration threshold is determined to detect the real-time signals. In addition, the weighted fusion algorithm based on the distance between the sensors and virtual leak source is used to fuse multisensory data. The proposed method has been implemented in a field by building a wireless sensor network. It is confirmed that the system detection rate reaches as high as 96.7% and the average detection time delay is less than 30 s on the premise of low false alarm rate .

Two-dimensional transition-metal dichalcogenides (TMDCs) possess unique electronic and optical properties, which open up a new opportunity for atomically thin optoelectronic devices. Synthesizing l...

Controlled anisotropic growth of two-dimensional materials provides an approach for the synthesis of large single crystals and nanoribbons, which are promising for applications as low-dimensional semiconductors and in next-generation optoelectronic devices. In particular, the anisotropic growth of transition metal dichalcogenides induced by the substrate is of great interest due to its operability. To date, however, their substrate-induced anisotropic growth is typically driven by the optimization of experimental parameters without uncovering the fundamental mechanism. Here, the anisotropic growth of monolayer tungsten disulfide on an ST-X quartz substrate is achieved by chemical vapor deposition, and the mechanism of substrate-induced anisotropic growth is examined by kinetic Monte Carlo simulations. Results show that, besides the variation of substrate adsorption, the chalcogen to metal (C/M) ratio is a major contributor to the large growth anisotropy and the polarization of undergrowth and overgrowth; either perfect isotropy or high anisotropy can be expected when the C/M ratio equals 2.0 by properly controlling the linear relationship between gas flux and temperature.

Monolayer transition metal dichalcogenide (TMD) alloys have emerged as a unique material system for promising applications in electronics, optoelectronics, and spintronics due to their tunable electronic structures, effective masses of carriers, and valley polarization with various alloy compositions. Although spin-orbit engineering has been extensively studied in monolayer TMD alloys, the valley Zeeman effect in these alloys still remains largely unexplored. Here we demonstrate the enhanced valley magnetic response in Mo

Traffic intersections are hubs in the transportation network, but traffic intersections have become areas with a high incidence of traffic accidents due to their many branch intersections, dense vehicles, and complex traffic conditions. However, the use of Internet of Vehicles related technologies to solve such problems has Think it is an effective program. Although many collision warning schemes based on the Internet of Vehicles have been proposed, most of the schemes still have problems that need to be improved. The purpose of this article is to study the vehicle collision warning method based on trajectory prediction. This article introduces the improved vehicle collision warning algorithm based on trajectory prediction, and introduces the framework and composition of the vehicle collision warning system. Then we use the characteristics of vehicle driving to establish trajectory models for straight vehicles and turning vehicles, and use the established trajectories for the model, we calculate the trajectory prediction and collision warning of the vehicle at a traffic intersection for a period of time in the future. Aiming at how to make the collision warning performance better, we propose a collision warning method based on trajectory prediction, and then carry out the improved algorithm proposed. Simulation and performance evaluation, and finally design and realize an anti-collision safety early warning system combining vision and hearing. Experimental research shows that the CICW early warning algorithm in this paper has a collision hit rate of more than 80%, which can basically guarantee the accuracy of early warning of collisions between vehicles in the case of heavy traffic.

Traffic accidents cause huge casualties and economic losses every year. The main causes of traffic accidents are the untimely response and improper disposal of drivers. The Internet of vehicles (IOT) system is a large system network based on the intranet, Internet and mobile Internet. According to the agreed communication protocol and data exchange standard, it carries out wireless communication and information exchange between vehicles and roads. It provides technical support for the realization of vehicle danger identification and creates new opportunities for safety early warning. Therefore, from the perspective of assistant driving, this paper discusses the dangerous state identification and safety warning methods of vehicles in different traffic scenes in the environment of Internet of vehicles. In this paper, low order car following model is studied for road traffic scene, and response time and following distance characteristic parameters are obtained by using different calculation methods. Through the above parameters, the curve of vehicle speed and following distance can be obtained. This paper analyzes the speed and following distance curves of all vehicles in the fleet, discusses the representativeness of different mean values to the data as a whole, and determines the safety threshold of following distance in normal driving. When the following distance of vehicles is less than the safety threshold, it is judged as a dangerous state; and according to the relationship between the actual value and the safety threshold, it uses the piecewise function to calculate the probability of vehicle collision accident. The algorithm is verified by the traffic data provided by ngsim project, and the results show that the method can accurately describe the dangerous state of vehicles and the possibility of collision accidents. The experimental results show that in the two traffic scenarios of road section and intersection, this paper uses the low-order car following model and the dangerous state recognition method combining time conflict zone with space conflict zone to realize the dangerous state recognition of vehicles, and expresses it by probability. The dispersion coefficient of arithmetic mean is 0.1840. The utility based early warning method can reduce vehicle collision accidents.

Twisted van der Waals homo- and hetero-structures have aroused great attentions due to their unique physical properties, providing a new platform to explore the novel two-dimensional (2D) condensed matter physics. The robust dependence of phonon vibrations and electronic band structures on the twist angle has been intensively observed in transition metal dichalcogenide (TMD) homo-structures. However, the effects of twist angle on the lattice vibrational properties in the TMD heterostructures have not caused enough attention. Here, we report the distinct evolutions of Raman scattering and the underlying interlayer interactions in the twisted WS2/MoS2 heterostructures. The shifts and linewidths of E2g(Γ) and A1g(Γ) phonon modes are found to be twist angle dependent. In particular, analogous to that of the twisted TMD homostructures, the frequency separations between E2g(Γ) and A1g(Γ) modes of MoS2 and WS2 in the twisted heterostructures varying with twist angle correlate with the interlayer mechanical coupling, essentially originating from the spacing-related repulsion between sulfur atoms. Moreover, the opposite shift behaviors and broadening of A1g(Γ) modes caused by charge transfer are also observed in the twisted heterostructures. The calculated interlayer distances and band alignment of twisted WS2/MoS2 through density functional theory further evidence our interpretations on the roles of the interlayer mechanical coupling and charge transfer in variations of Raman features. Such understanding and controlling of interlayer interaction through the stacking orientation are significant for future optoelectronic device design based on the newly emerged 2D heterostructures. [Figure not available: see fulltext.] Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This work was mainly supported by the National Key R&D Program of China (Grant No. 2018YFA0703700) and the Ministry of Education, Singapore, MOE Tier 1 RG93/19, NRF-CRP-21-2018-0007, MOE2018-T2-2-072, and MOE2019- T2-1-004. C. X. C. also thanks the support of the National Natural Science Foundation of China (Grant No. 61774040), the Shanghai Municipal Science and Technology Commission (Grant No. 18JC1410300), the Fudan University-CIOMP Joint Fund (Grant No. FC2018-002), the National Young 1000 Talent Plan of China, and the Shanghai Municipal Natural Science Foundation (No. 16ZR1402500). J. Z. S. appreciates the support of the Fundamental Research Funds for the Central Universities of China, National Natural Science Foundation of China under Grant No. 61904151, Natural Science Foundation of Shaanxi under Grant No. 2020JM-108, and the Joint Research Funds of Department of Science & Technology of Shaanxi Province and Northwestern Polytechnical University (No. 2020GXLH-Z-020). Z. L. acknowledges the support of MOE Tier 1 grant RG164/15, Tier 2 grant MOE2016-T2-2-153, and MOE2015-T2-2-007, and Singapore National Research Foundation under NRF award No. NRF-NRFF2013-08. W. H. Y. acknowledges the support of the National Natural Science Foundations of China (Grant No. 61704040). This research was also supported by Zhejiang Provincial Natural Science Foundation of China (Grant No. LGG19F040003).

We report tunable optical performances of gallium selenide (GaSe) layers in phonon vibrations, band edge emission, circular polarization, and anisotropic response via strain manipulation. By applying a uniaxial tensile strain, frequency shift and peak broadening are observed in Raman spectra. A shrink in bandgap is demonstrated in photoluminescence (PL) spectra and confirmed by first-principles calculations. A continuously growing circular polarization from 3.8% to 37.9% is detected at room temperature when the tensile strain is increased from 0% to 0.35%, which is almost a ten-fold enhancement compared with that under the non-resonant excitation. Through the theoretical calculations, the decrease in exciton lifetime is revealed to be responsible for the overwhelming enhanced circular polarization. By deforing the lattices of GaSe layers, the Raman intensity was found to be suppressed in the strain direction. The intrinsic fourfold-symmetry of the E2g1 mode in angle-dependent Raman spectra is tuned to a two-fold symmetry. An anisotropic PL response is further regulated by changing the structural symmetry of GaSe lattices. A maximal polarization of 66.0% is achieved when the detection polarizations are perpendicular to the strain direction. All the findings in this study suggest a route for tuning the optical properties, particularly the polarized response in two-dimensional (2D) materials, and provide a strategy for developing flexible and anisotropic 2D optical devices.

Correction for ‘A highly sensitive silicon nanowire array sensor for joint detection of tumor markers CEA and AFP’ by Ke Lu et al., Biomater. Sci., 2022, https://doi.org/10.1039/D2BM00555G.

Group-IIIA metal-monochalcogenides with the enticing properties have attracted tremendous attention across various scientific disciplines. With the aim to satisfy the multiple demands of device applications, here we report a design framework on GaSe monolayer in an effort to tune the electronic and magnetic properties through a dual modulation of vacancy doping and electric field. A half-metallicity with a 100% spin polarization is generated in a Ga vacancy doped GaSe monolayer due to the nonbonding 4p electronic orbital of the surrounding Se atoms. The stability of magnetic moment is found to be determined by the direction of applied electric field. A switchable magnetic configuration in Ga vacancy doped GaSe monolayer is achieved under a critical electric field of 0.6 V/A. Electric field induces redistribution of the electronic states. Finally, charge transfers are found to be responsible for the controllable magnetic structure in this system. The magnetic modulation on GaSe monolayer in this work offers some references for the design and fabrication of tunable two-dimensional spintronic device.

First-principles calculations were performed to investigate the interaction of small gas molecules, including H2, O2, H2O, NH3, NO, NO2, and CO, with monolayer GaSe. The energetics, charge transfer and band structures were evaluated by considering the Grimme-D2 correction. Due to the low adsorption energies and the moderate charge transfer, monolayer GaSe could be a promising candidate as a sensor for O2 and NO2. The theoretical results for adsorption of O2 on monolayer GaSe are consistent well with the most recent experimental observation. Diverse projected band structures of these gas molecule-adsorbed systems demonstrate that there exist two kinds of charge transfer mechanisms: traditional and orbital mixing theories. Based on the proposed charge transfer mechanisms, external strain exerted different influences on the charge transfer for gas molecules adsorbed on the GaSe monolayer. The present study provides theoretical insight leading to a better understanding of the novel two-dimensional materials, such as graphene, phosphorene, and transition metal dichalcogenides.

The mechanisms of interaction between the layers of transition metal dichalcogenide (TMD) heterostructures, i.e., WS2/MoS2 and WSe2/MoSe2, were investigated based on density functional theory calculations to deepen the understanding of TMD-based electronic devices. Based on the evolution of the energies of the states at the high-symmetric points (KC1, KV2, ΓV2, KC2, KV1, and ΓV1) and the distributions of the differential charge densities, two interaction mechanisms, interlayer orbital coupling and interlayer polarization field, were found to be operative at the interface of the investigated TMD/TMD systems. Due to the interlayer polarization effect, two energetically close band-edge states at the KC1 and KC2 points or at the KV2 and KV1 points become closer with decreasing interlayer distance. Therefore, the two interaction mechanisms exert opposite effects on the band structures of the investigated TMD/TMD systems. Interlayer orbital coupling tends to split two energetically close band-edge states, whereas the interlayer polarization field tends to bring two energetically close band-edge states closer together. Thus, the observation of the interlayer polarization field in this calculation completes the explanation of the influence of the interlayer interaction in the WS2/MoS2 and WSe2/MoSe2 heterostructures and can be helpful for evaluating the performance of TMD-based electronic devices.

Inspired by the profound physical connotations and potential application prospects of the valleytronics, we design a two-dimensional (2D) $\mathrm{W}{\mathrm{S}}_{2}/h\ensuremath{-}\mathrm{VN}$ magnetic van der Waals (vdW) heterostructure and study the control of valley degrees of freedom through the first-principles calculations. A considerable spin splitting of 627 meV is obtained at the $K$ valley, accompanied with a strong suppression of that at the ${K}^{\ensuremath{'}}$ valley. An intrinsic large valley splitting of 376 meV is generated in the valence band, which corresponds to an effective Zeeman magnetic field of 2703 T. Besides the valence band, the conduction band of $\mathrm{W}{\mathrm{S}}_{2}$ possesses a remarkable spin splitting also, leading to the possible formation of valley-labeled dark exciton states at the ${K}^{\ensuremath{'}}$ valley. The strengths of spin and valley splitting relying on the interfacial orbital hybridization are further tuned continually by the in-plane strain and interlayer spacing. Maximum spin and valley splitting of 654 and 412 meV are finally achieved, respectively, and the effective Zeeman magnetic field can be enhanced to 2989 T with a \ensuremath{-}3% strain. Time-reversal symmetry breaking and the sizable Berry curvature in the heterostructure lead to a prominent anomalous Hall conductivity at the $K$ and ${K}^{\ensuremath{'}}$ valleys. Based on these finding, a prototype filter device for both the valley and spin is proposed.

Two-dimensional transition-metal dichalcogenides (TMDCs) possess unique electronic and optical properties, which open up a new opportunity for atomically thin optoelectronic devices. Synthesizing large-scale monolayer TMDCs on the SiO