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Hexagonal boron nitride is not only a promising functional material for the development of two-dimensional optoelectronic devices but also a good candidate for quantum sensing thanks to the presence of quantum emitters in the form of atom-like defects. Their exploitation in quantum technologies necessitates understanding their coherence properties as well as their sensitivity to external stimuli. In this work, we probe the strain configuration of boron vacancy centers (VB

Nonlinear optical activities (e.g., harmonic generations) in two-dimensional (2D) layered materials have attracted much attention due to the great promise in diverse optoelectronic applications such as nonlinear optical modulators, nonreciprocal optical device, and nonlinear optical imaging. Exploration of nonlinear optical response (e.g., frequency conversion) in the infrared, especially the mid-infrared (MIR) region, is highly desirable for ultrafast MIR laser applications ranging from tunable MIR coherent sources, MIR supercontinuum generation, and MIR frequency-comb-based spectroscopy to high harmonic generation. However, nonlinear optical effects in 2D layered materials under MIR pump are rarely reported, mainly due to the lack of suitable 2D layered materials. Van der Waals layered platinum disulfide (PtS2) with a sizable bandgap from the visible to the infrared region is a promising candidate for realizing MIR nonlinear optical devices. In this work, we investigate the nonlinear optical properties including third-and fifth-harmonic generation (THG and FHG) in thin layered PtS2 under infrared pump (1550-2510 nm). Strikingly, the ultrastrong third-order nonlinear susceptibility χ(3)(-3ω;ω,ω,ω) of thin layered PtS2 in the MIR region was estimated to be over 10-18 m2/V2, which is about one order of that in traditional transition metal chalcogenides. Such excellent performance makes air-stable PtS2 a potential candidate for developing next-generation MIR nonlinear photonic devices. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version This research was also supported partially by National Research Foundation Singapore program (NRFCRP19- 2017-01 and NRF-CRP22-2019-0007) and Ministry of Education Tier 2 program (MOE-T2EP50120-0009), and Singapore A*STAR funding (A18A7b0058 and A2090b0144).

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).

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.

A mono-bit digital receiver circuit for instantaneous frequency measurement is presented. The circuit is co-designed with Indium Phosphide Double Heterojunction Bipolar Transistor and complementary metal oxide semiconductor (CMOS) devices. The chip is fabricated by InP/CMOS three-dimensional (3D) heterogeneous integration using the wafer-level bonding technique. The measurable signal frequency within + 15 to − 25 dBm power is up to 7.5 GHz with a 14-GHz clock. Compared to an integrated circuit (IC) with a traditional InP or CMOS technologies, the proposed chip could benefit from both InP and CMOS technology. In the heterogeneous integration, InP devices provide high operating frequency, broad signal bandwidth, and large input signal dynamic range, while CMOS devices achieve complex function with low power consumption. In this way, the system FoM is improved for a mono-bit digital receiver while the system power consumption is kept the same. This work also shows the great potential of the 3D heterogeneous integration for the high-performance mixed-signal and multifunction radio-frequency ICs.

Realizing van der Waals (vdW) epitaxy in the 1980s represents a breakthrough that circumvents the stringent lattice matching and processing compatibility requirements in conventional covalent heteroepitaxy. However, due to the weak vdW interactions, there is little control over film qualities by the substrate. Typically, discrete domains with a spread of misorientation angles are formed, limiting the applicability of vdW epitaxy. Here, the epitaxial growth of monocrystalline, covalent Cr5 Te8 2D crystals on monolayer vdW WSe2 by chemical vapor deposition is reported, driven by interfacial dative bond formation. The lattice of Cr5 Te8 , with a lateral dimension of a few tens of micrometers, is fully commensurate with that of WSe2 via 3 × 3 (Cr5 Te8 )/7 × 7 (WSe2 ) supercell matching, forming a single-crystalline moiré superlattice. This work establishes a conceptually distinct paradigm of thin-film epitaxy, termed "dative epitaxy", which takes full advantage of covalent epitaxy with chemical bonding for fixing the atomic registry and crystal orientation, while circumventing its stringent lattice matching and processing compatibility requirements; conversely, it ensures the full flexibility of vdW epitaxy, while avoiding its poor orientation control. Cr5 Te8 2D crystals grown by dative epitaxy exhibit square magnetic hysteresis, suggesting minimized interfacial defects that can serve as pinning sites. M.B., C.H., A.M., and H.Z. acknowledge support from the US National Science Foundation (Grant Nos. ECCS-2042085, MRI-1229208, MRI-1726303, CBET-1510121), and the University at Buffalo VPRED seed grant. M.B. and Y.H. acknowledge support from the National Key R & D Program of China (Grant No. 2017YFA0206301), the National Natural Science Foundation of China (Grant Nos. 52027801, 51631001, 52101280), the China–German Collaboration Project (Grant No. M-0199), and the China Postdoctoral Science Foundation (Grant No. 2020M670042). L.Z. and J.L. acknowledge the support from the National Natural Science Foundation of China (Grant No. 11974156), the Guangdong International Science Collaboration Project (Grant No. 2019A050510001), the Science, Technology and Innovation Commission of Shenzhen Municipality (Grant No. ZDSYS20190902092905285), and also the assistance of SUSTech Core Research Facilities. J.C. and S.A.C. acknowledge the support from the National Science Foundation (Grant No. DMR-1644779), the State of Florida, and the U.S. Department of Energy. X.W. and X.M.C. acknowledge the support from the US National Science Foundation (Grant No. DMR-1708790). S.Z. acknowledges the support from the Grant No. NSF ECCS-2042126. R.F.S. acknowledges the support from the NU Collaborative Research and NSF-DMREF (Grant No. 1729288).

Two-dimensional (2D) atomically thin transition-metal dichalcogenides (TMD) and their van der Waals (vdW) heterostructures offer a platform with tightly bound intralayer/interlayer excitons for the on-chip fabrication of ultracompact nanolasers. Excitons in 2D TMD materials present a considerable binding energy of up to hundreds of meV, which permits a high Mott transition density of 1014 cm-2 and stable excitonic lasing under room-temperature operation and high pump fluences. Here, we review the recent progress on the lasing emission from intralayer excitons in TMD monolayers and interlayer excitons in vdW heterostructures incorporated with various high-quality optical cavities, including photonic-crystal, whispering-gallery-mode, distributed-feedback, distributed-Bragg-reflector cavities. Lasing emissions in TMD monolayers and heterostructures have been demonstrated by narrow emission peaks, a clear threshold for nonlinear amplification, time- and spatial coherence under either continuous-wave or pulsed light pumping. Finally, prospective and frontier research topics, including large-scale on-chip integration of TMD nanolasers, electrically pumped lasers, spin-polarized nanolasers, and exciton-polariton Bose-Einstein condensation (BEC) are highlighted. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This work is supported by the Ministry of Education of Singapore (MOE 2019-T2-1-044). This work is supported by the Singapore National Research Foundation (NRF) under the Competitive Research Programs (NRF-CRP-21-2018-0007).

In monolayer group‐VI transition metal dichalcogenides (TMDs), valley splitting features have received a lot of attention since it can be potentially utilized for information storing and processing. Among the known two‐dimensional (2D) TMDs, monolayer WSe2 or MoSe2 has been mostly selected for excitonic and valleytronic physics studies because of its sharp and well‐resolved excitonic spectral features. Meanwhile, their high optical quality leads to a tremendous desire for developing promising WSe2‐ and MoSe2‐based valleytronic devices. Toward this goal, exploring the uniformity of valley features crossing an entire piece of monolayer becomes necessary and critical. Here, we performed the systematic magneto‐photoluminescence mapping measurements on mechanically exfoliated monolayer WSe2 and observed unconventional spatial variations of valley splitting. The observed nonuniformity is attributed to the modulated doping, which is probably due to the different distributions of unintentional absorbates across the sample. Such an unexpected doping effect shows the nonnegligible influence on the valley Zeeman splitting of the trion emission (XT) while affecting that of the neutral exciton emission (X0) trivially, evidencing for the large valleytronic sensitivity of the charged exciton. This work not only enriches the understanding of the doping effect on valley splitting but also is meaningful for developing 2D valleytronics. Ministry of Education (MOE) Published version National Natural Science Foundation of China, Grant/Award Numbers: 61774040, 11774170; Singapore Ministry of Education (MOE) Tier 1, Grant/Award Number: RG199/17; The Fudan University-CIOMP Joint Fund, Grant/Award Number: FC2018-002; The National Key R&D Program of China, Grant/Award Number: 2018YFA0703700; The National Young 1000 Talent Plan of China; The Shanghai Municipal Natural Science Foundation, Grant/Award Number: 16ZR1402500; The Shanghai Municipal Science and Technology Commission, Grant/Award Number: 18JC1410300.

The development of GaN-on-diamond devices offers bright prospects for the creation of high-power density electronics. This article presents a process of fabricating GaN-on-diamond structure by depositing diamond films on dual sides, including heat dissipation diamond film and sacrificial carrier diamond film. Prior to heat dissipation diamond film layer preparation, aluminum nitride (AlN) is chosen as a dielectric layer and pretreated by nanodiamond (ND) particles, to enhance the nucleation density. Zeta potential measurements and X-ray photoelectron spectroscopy are used to analyze the AlN surface after each treatment. The results show that oxygen-terminated ND particles tend to adhere to an AlN surface because the oxygen-terminated NDs have–COOH and–OH groups, and hold a negative potential. On the contrary, fluorine-terminated AlN prefers to attract the hydrogen-terminated ND seeds, which resulted in higher diamond nucleation density. Based on this preliminary study, a dense high-quality GaN-on-diamond wafer is successfully produced by using AlN as the dielectric layer and a diamond film as the sacrificial carrier.

Light-matter interactions in two-dimensional transition metal dichalcogenides (TMDs) are sensitive to the surrounding dielectric environment. Depending on the interacting strength, weak and strong exciton-photon coupling effects can occur when the exciton energy is resonant with the one of photon. Here we report angle-resolved spectroscopic signatures of monolayer tungsten disulfide (1L-WS2) in weak and strong exciton-photon coupling environments. Inherent optical response of 1L-WS2 in the momentum space is uncovered by employing a dielectric mirror as substrate, where the energy dispersion is angle-independent while the amplitudes increase at high detection angles. When 1L-WS2 sits on top of a dielectric layer on silicon, the resonant trapped photon weakly couples with the exciton, in which the minimum of reflection dip shifts at both sides of the crossing angle while the emitted exciton energy remains unchanged. The unusual shift of reflection dip is attributed to the presence of Fano resonance under white-light illumination. By embedding 1L-WS2 into a dielectric microcavity, strong exciton-photon coupling results in the formation of lower and upper polariton branches with an appreciable Rabi splitting of 34 meV at room temperature, where the observed blueshift of the lower polariton branch is indicative of the enhanced polariton-polariton scattering. Our findings highlight the effect of dielectric environment on angle-resolved optical response of exciton-photon interactions in a two-dimensional semiconductor, which is helpful to develop practical TMD-based architectures for photonic and polaritonic applications. [Figure not available: see fulltext.] National Research Foundation (NRF) Submitted/Accepted version J. Z. S. thanks the support of the Fundamental Research Funds for the Central Universities of China, the National Natural Science Foundation of China (No. 61904151), the Natural Science Foundation of Shaanxi (No. 2020JM-108), the Joint Research Funds of the Department of Science & Technology of Shaanxi Province and Northwestern Polytechnical University (No. 2020GXLH-Z-020). T. Y thanks the support of the Singapore National Research Foundation (NRF) under the Competitive Research Programs (No. NRF-CRP-21-2018-0007). X. W. Z. thanks the support of National Natural Science Foundation of China (No. 12174422).

This letter presents the fabrication of InP double heterojunction bipolar transistors (DHBTs) on a 3-inch flexible substrate with various thickness values of the benzocyclobutene (BCB) adhesive bonding layer, the corresponding thermal resistance of the InP DHBT on flexible substrate is also measured and calculated. InP DHBT on a flexible substrate with 100 nm BCB obtains cut-off frequency f T = 358 GHz and maximum oscillation frequency f MAX = 530 GHz. Moreover, the frequency performance of the InP DHBT on flexible substrates at different bending radii are compared. It is shown that the bending strain has little effect on the frequency characteristics (less than 8.5%), and these bending tests prove that InP DHBT has feasible flexibility.

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

In this work, we demonstrate heterogeneous integration of InP DHBT and Si CMOS on the same Silicon substrate based on 30μm Au-In microbump bonding technology, InP DHBTs are vertical stacked at the top of the Si CMOS wafer. Meanwhile, we exhibit a InP-on-Si CMOS 14Gbps 1:16 demultiplexer as example, which shows the potential to integrate InP and Si CMOS on the same chip to take advance of the two different material systems.

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).

Metallic layered transition metal dichalcogenides (TMDs) host collective many-body interactions, including the competing superconducting and charge density wave (CDW) states. Graphene is widely employed as a heteroepitaxial substrate for the growth of TMD layers and as an ohmic contact, where the graphene/TMD heterostructure is naturally formed. The presence of graphene can unpredictably influence the CDW order in 2D CDW conductors. This work reports the CDW transitions of 2H-NbSe

In recent cryogenic measurements, narrow photoluminescence (PL) peaks due to diverse quantum emitters have been found at random locations of monolayer transition metal dichalcogenides (TMDs), which impedes precise optoelectronic applications. Thus, it is of great importance to truly regulate these localized exciton emissions by deterministic spatial and spectral control. Here, such desired emission is primarily demonstrated in monolayer WS2 nanodisks. The size-dependent PL studies indicate the clear evolution from the broad defect-band emission to a set of spectrally isolated narrow peaks (linewidth of ≈ sub nm) at 4.2 K, which is associated with the prevailing effect of edge defects with the shrinkage of the disk diameter, providing a narrow emission energy range for bound excitons. When the disk diameter is reduced to 300 nm, more than 80% of emitter peaks are located between 610 and 616 nm, verifying the effective control of emission wavelength of these photon emitters. Furthermore, the strategy is extended to prepare scalable WS2 nanodisk arrays based on flakes of hundreds of µm, and size-dependent narrow emissions of WSe2 nanodisks are testified. This work develops a defect-engineering strategy to generate localized exciton emitters toward the promising TMD-based optoelectronic applications. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version S.F. and C.Z. contributed equally to this work. S.F. is supported by a Marie Skłodowska-Curie Individual Fellowship H2020-MSCA-IF-2020 SingExTr (No. 101031596). This work was supported by the Singapore Ministry of Education (MOE) Tier 1 (No. RG199/17, RG93/19) and the Singapore National Research Foundation (NRF) under the Competitive Research Programs (NRF-CRP-212018-0007) and NRF QEP programme, National Natural Science Foundation of China (Nos. 61774040, 11774170, and 61904151), the National Young 1000 Talent Plan of China, the Shanghai Municipal Natural Science Foundation (No. 16ZR1402500), the Opening project of State Key Laboratory of Functional Materials for Informatics (Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences), 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). J.Z. thanks the support from National Natural Science Foundation of China (NSFC) under the Grant No. 12174384.

Organoarsenic arsanilic acid (ASA) contamination of paddy soil is a serious but less concerned hazard to agriculture and health of people consuming rice as staple food, for rice is one major pathway of arsenic (As) exposure to human food. To date little research has studied the effect of ASA on biochemical process of rice. Silicon (Si) application is able to reduce the toxicities of heavy metals in numerous plants, but little information about ASA. This work investigated whether and how Si influenced alleviation of ASA toxicity in rice at biochemical level to have a better understanding of defense mechanism by Si against ASA stress. Results showed that ASA reduced rice growth, disturbed protein metabolism, increased lipid peroxidation but decreased the efficiencies of antioxidant activities compared to control plants, more severe in roots than in shoots. The addition of Si in ASA-stressed rice plants noticeably increased growth and development as well as soluble protein contents, but decreased malondialdehyde (MDA) contents in ASA-stressed rice plants, suggesting that Si did have critical roles in ASA detoxification in rice. Furthermore, increased superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities along with elevated glutathione (GSH) and ascorbic acid (AsA) contents implied the active involvement of ROS scavenging and played, at least in part, to Si-mediated alleviation of ASA toxicity in rice, and these changes were related to rice genotypes and tissues. The study provided physio-chemical mechanistic evidence on the beneficial effect of Si on organoarsenic ASA toxicity in rice seedlings.

Possessing a valley degree of freedom and potential in information processing by manipulating valley features (such as valley splitting), group-VI monolayer transition metal dichalcogenides have attracted enormous interest. This valley splitting can be measured based on the difference between the peak energies of σ+ and σ− polarized emissions for excitons or trions in direct band gap monolayer transition metal dichalcogenides under perpendicular magnetic fields. In this work, a well-prepared heterostructure is formed by transferring exfoliated WSe2 onto a EuS substrate. Circular-polarization-resolved photoluminescence spectroscopy, one of the most facile and intuitive methods, is used to probe the difference of the gap energy in two valleys under an applied out-of-plane external magnetic field. Our results indicate that valley splitting can be enhanced when using a EuS substrate, as compared to a SiO2/Si substrate. The enhanced valley splitting of the WSe2/EuS heterostructure can be understood as a result of an interfacial magnetic exchange field originating from the magnetic proximity effect. The value of this magnetic exchange field, based on our estimation, is approximately 9 T. Our findings will stimulate further studies on the magnetic exchange field at the interface of similar heterostructures. MOE (Min. of Education, S’pore)

Two-dimensional (2D) semiconductors, represented by 2D transition metal dichalcogenides (TMDs), exhibit rich valley physics due to strong spin-orbit/spin-valley coupling. The most common way to probe such 2D systems is to utilize optical methods, which can monitor light emissions from various excitonic states and further help in understanding the physics behind such phenomena. Therefore, 2D TMDs with good optical quality are in great demand. Here, we report a method to directly grow epitaxial WS2 and MoS2 monolayers on hexagonal boron nitride (hBN) flakes with a high yield and high optical quality; these monolayers show better intrinsic light emission features than exfoliated monolayers from natural crystals. For the first time, the valley Zeeman splitting of WS2 and MoS2 monolayers on hBN has been visualized and systematically investigated. This study paves a new way to produce high optical quality WS2 and MoS2 monolayers and to exploit their intrinsic properties in a multitude of applications. MOE (Min. of Education, S’pore)

Two-dimensional transition metal dichalcogenides (2D TMDs) possess a tunable excitonic light emission that is sensitive to external conditions such as electric field, strain, and chemical doping. In this work, we reveal the interactions between DNA nucleobases, i.e., adenine (A), guanine (G), cytosine (C), and thymine (T) and monolayer WS2 by investigating the changes in the photoluminescence (PL) emissions of the monolayer WS2 after coating with nucleobase solutions. We found that adenine and guanine exert a clear effect on the PL profile of the monolayer WS2 and cause different PL evolution trends. In contrast, cytosine and thymine have little effect on the PL behavior. To obtain information on the interactions between the DNA bases and WS2, a series of measurements were conducted on adenine-coated WS2 monolayers, as a demonstration. The p-type doping of the WS2 monolayers on the introduction of adenine is clearly shown by both the evolution of the PL spectra and the electrical transport response. Our findings open the door for the development of label-free optical sensing approaches in which the detection signals arise from the tunable excitonic emission of the TMD itself rather than the fluorescence signals of label molecules. This dopant-selective optical response to the DNA nucleobases fills the gaps in previously reported optical biosensing methods and indicates a potential new strategy for DNA sequencing.

Two-dimensional (2D) layered lead halide perovskites with large exciton binding energies, efficient radiative recombination, and outstanding environmental stability are regarded as supreme candidates for realizing highly compact and ultralow threshold lasers. However, continuous-wave (CW) pumped lasing of 2D lead halide perovskites, as the precondition for the electrically pumped lasing, is still challenging. Here, we tackled this challenge by demonstrating lasing emission in phenylethylammonium lead iodide [(PEA)2PbI4] embedded in a vertical microcavity under continuous pumping at room temperature. The millimeter-sized (PEA)2PbI4 single crystal was obtained from a two-step seed-growth method, showing high crystallization, excellent thermal stability, and outstanding optical properties. We used the exfoliated (PEA)2PbI4 thin flake as the gain medium to construct a vertical-cavity surface-emitting laser (VCSEL), showing robust single-mode CW lasing operation with an ultra-low threshold of 5.7 W cm−2 at room temperature, attributed to strong optical confinement in the high-Q cavity. Our findings provide a strategy to design and fabricate solution-based 2D perovskite VCSELs and mark a significant step toward the next-generation of coherent light sources. Ministry of Education (MOE) Published version

Based on a device-first transfer process, a 3-inch polycrystalline diamond substrate is bonded within $1.5~\mu \text{m}$ of the junction in GaN high electron mobility transistors (HEMTs) to enhance heat removal of the high-power RF devices. Highly preserved electrical performance is demonstrated by comparison exactly on the same HEMT device prior and after substrate transfer. The residual compressive strain relaxation of the whole GaN epilayer does not reduce the 2-D electron gas sheet density. The dc characteristics show weakened self-heating in the GaN-on-diamond HEMT with maximum current density increasing from 968 to 1005 mA/mm. The power density increases from 4.8 to 5.5 W/mm with the PAE slightly reducing from 50.9% to 50.5%. On-wafer infrared measurement is performed on a 1.25-mm GaN HEMT at power dissipation of 10 W/mm, and the peak juncture temperature of the device decreases from 241 °C to 191 °C after transferring to the diamond substrate.

Boron (B) is an essential microelement for higher plants, and plays a role in cell wall formation. Citrange seedlings with different amounts of B were studied through Fourier-transform infrared spectroscopy (FTIR) analyses. The results showed that the growth and development of new roots were evidently inhibited by B deficiency. Boron-deficiency significantly increased cell wall biomass (CWB) as a percentage of root fresh weight and the ratio of B concentration in cell wall to the total B in roots. The findings from CWB FTIR spectra showed the band at 3429 cm−1 under control condition was shifted to 3442 cm−1 after being B deprived, suggesting that the mode of hydrogen bonding was changed by B deficiency. Boron deficiency clearly decreased the peak height of carboxylic ester band around 1741 cm−1, but increased that of COO− stretching band around 1400 cm−1, suggesting that the relative amount and degree of esterification of carboxylic groups was decreased and pectin content and structure was altere...

Site-specific nitrogen (N) fertilizer strategy based on soil mineral N (Nmin) test is crucial for maintaining high crop yield and high N-use efficiency. A two-year field experiment was conducted to develop a site-specific N fertilizer management for winter oilseed rape in the 2011–12 and 2012–13 seasons in Wuhan, central China. In contrast to fixed N fertilizer recommendation (FN), the use of the Nmin test could optimize the N fertilizer inputs in time to fulfill crop N uptake during different growth stages and achieve high seed yield. Despite annual variations in seed yields and N fertilizer recommendations, the N recovery efficiency of the site-specific N fertilizer (SN) treatment was higher than that of the FN treatment. Consequently, the soil-based N strategy matches crop N uptake and soil N supply and achieves high yield depending on the site-specific soil-crop conditions.

Thermal expansion coefficients measurements of AgGa 0.7 In 0.3 Se 2 with the direction of c- and a- axis are made in the temperature range between 300 and 900 K. It is obviously that AgGa 0.7 In 0.3 Se 2 is with a reverse thermal expansion behavior along the c -axis, and variation of directional coefficient at different temperatures as a function of cos2φ has been discussed in this work. It’s found that the crystal would expand with increasing temperature if the angle between the direction [ hkl ] and the c-axis is greater than 42.71°. In addition, Gruneisen parameters at different temperatures have been calculated and also exhibit anisotropic behavior ( γ a > γ c ). At last, by a modified formula, variation of lattice thermal conductivity with temperature have been deduced. And the calculation value at room temperature is a little larger than the measurement value of thermal conductivity with [100] direction at room temperature which is found to be 0.751 W/m K.

The emerging field of valleytronics has boosted intensive interests in investigating and controlling valley polarized light emission of monolayer transition metal dichalcogenides (1L TMDs). However, so far, the effective control of valley polarization degree in monolayer TMDs semiconductors is mostly achieved at liquid helium cryogenic temperature (4.2 K), with the requirements of high magnetic field and on-resonance laser, which are of high cost and unwelcome for applications. To overcome this obstacle, it is depicted that by electrostatic and optical doping, even at temperatures far above liquid helium cryogenic temperature (80 K) and under off-resonance laser excitation, a competitive valley polarization degree of monolayer WS

This letter reports on the first demonstration of wafer scale flexible InP double heterogeneous bipolar transistors (DHBTs) with record cut-off frequency (f T) and maximum oscillation frequency (f MAX). The as-fabricated DHBTs on 3-inch InP bulk substrate are separated by epitaxial layer lift-off, followed by adhesive bonding onto flexible substrate. Radio frequency measurements reveal that the InP DHBTs on flexible substrate exhibit a f T of 337 GHz and f MAX of 485 GHz, representing the highest f T and f MAX ever reported in flexible electronics. Moreover, InP DHBTs on flexible substrate have good consistency and the functional transistor yield is more than 73%. The results provide ways to accelerate the time for flexible electronics toward future applications working at multi-gigahertz range.

Boron (B) is a microelement required for higher plants, and B deficiency has serious negative effect on metabolic processes. We concentrated on the changes in metabolite profiles of trifoliate orange leaves and roots as a consequence of B deficiency at the initial stage of growth by gas chromatography-mass spectrometry (GC-MS)-based metabolomics. Enlargement and browning of root tips were observed in B-deficient plants, while any obvious symptom was not recorded in the leaves after 30 days of B deprivation. The distinct patterns of alterations in metabolites observed in leaves and roots due to B deficiency suggest the presence of specific organ responses to B starvation. The accumulation of soluble sugars was occurred in leaves, which may be attributed to down-regulated pentose phosphate pathway (PPP) and amino acid biosynthesis under B deficiency, while the amount of most amino acids in roots was increased, indicating that the effects of B deficiency on amino acids metabolism in trifoliate orange may be a consequence of disruptions in root tissues and decreased protein biosynthesis. Several important products of shikimate pathway were also significantly affected by B deficiency, which may be related to abnormal growth of roots induced by B deficiency. Conclusively, our results revealed a global perspective of the discriminative metabolism responses appearing between B-deprived leaves and roots and provided new insight into the relationship between B deficiency symptom in roots and the altered amino acids profiling and shikimate pathway induced by B deficiency during seedling establishment.

Metallic layered transition metal dichalcogenides (TMDs) host collective many-body interactions, including the competing superconducting and charge density wave (CDW) states. Graphene is widely employed as a heteroepitaxial substrate for the growth of TMD layers and as an ohmic contact, where the graphene/TMD heterostructure is naturally formed. The presence of graphene can unpredictably influence the CDW order in 2D CDW conductors. This work reports the CDW transitions of 2H-NbSe2 layers in graphene/NbSe2 heterostructures. The evolution of Raman spectra demonstrates that the CDW phase transition temperatures (TCDW ) of NbSe2 are dramatically decreased when capped by graphene. The induced anomalous short-range CDW state is confirmed by scanning tunneling microscopy measurements. The findings propose a new criterion to determine the TCDW through monitoring the line shape of the A1g mode. Meanwhile, the 2D band is also discovered as an indicator to observe the CDW transitions. First-principles calculations imply that interfacial electron doping suppresses the CDW states by impeding the lattice distortion of 2H-NbSe2 . The extraordinary random CDW lattice suggests deep insight into the formation mechanism of many collective electronic states and possesses great potential in modulating multifunctional devices.

The emerging 2D semiconductors have aroused increasing attention due to their fascinating fundamental properties and application prospects. Technical investigation of 2D semiconductor–based electronics and optoelectronics is paving the way to realizing practical applications, which opens up new opportunities to reshape the current semiconductor industry. Particularly, 2D semiconductor–based optoelectronics can be extensively utilized in the promising semiconductor and information industries, such as solid‐state lighting, on‐chip optical interconnects, quantum computing, and communication. Here, the research progress regarding the fabrication and characterization of rapidly growing light‐emitting devices and photodetectors enabled by 2D semiconductors is reviewed. According to different emission mechanisms, 2D semiconductor–activated light sources are classified into four types: excitonic light‐emitting diodes (LEDs), quantum LEDs, valley LEDs, and lasers. Moreover, photodetecting devices based on atomically thin MoS2, other 2D semiconductors, and van der Waals heterostructures are discussed, where diverse device structures, performance parameters, and working principles are compared. Furthermore, the remaining challenges in the realization of practical devices with desirable features are outlined and new research opportunities for 2D semiconductor optoelectronics are proposed. MOE (Min. of Education, S’pore)

Transition-metal disulfide with its layered structure is regarded as a kind of promising host material for sodium insertion, and intensely investigated for sodium-ion batteries. In this work, a simple solvothermal method to synthesize a series of MoS2 nanosheets@nitrogen-doped graphene composites is developed. This newly designed recipe of raw materials and solvents leads the success of tuning size, number of layers, and interplanar spacing of the as-prepared MoS2 nanosheets. Under cut-off voltage and based on an intercalation mechanism, the ultrasmall MoS2 nanosheets@nitrogen-doped graphene composite exhibits more preferable cycling and rate performance compared to few-/dozens-layered MoS2 nanosheets@nitrogen-doped graphene, as well as many other reported insertion-type anode materials. Last, detailed kinetics analysis and density functional theory calculation are also employed to explain the Na+ - storage behavior, thus proving the significance in surface-controlled pseudocapacitance contribution at the high rate. Furthermore, this work offers some meaningful preparation and investigation experiences for designing electrode materials for commercial sodium-ion batteries with favorable performance.

Tin (Sn)-based materials are potential alternatives to the commercial graphite anode for next generation Li-ion batteries, but their successful application is always impeded by fast capacity fading upon cycling that stemmed from huge volume variations during lithiation and delithiation. We develop an applicable strategy of encapsulating sub-10-nm-sized Sn-based nanoparticles (i.e., Sn and SnO2) in nitrogen/phosphorus codoped hierarchically porous carbon (NPHPC) or NPHPC-reduced graphene oxide hybrid (NPHPC-G) to effectively solve the issues of Sn-based anodes. Benefiting from the peculiar structure, the composites exhibit unprecedented electrochemical behaviors, for example, NPHPC-G@Sn and NPHPC-G@SnO2 deliver a high reversible capacity of ~1158 and ~1366 mAh g-1 at 200 mA g-1, respectively, and maintain at ~1099 mAh g-1 after 500 cycles and ~1117 mAh g-1 after 300 cycles. In situ transmission electron microscopy and ex situ scanning electron microscopy observations unveil that these composites are able to withstand the volume changes of Sn-based nanoparticles while sustaining the framework of the architectures and hence conferring outstanding electrochemical properties. Our present work provides both in situ and ex situ techniques for understanding the so-called synergistic effect between metals or metal oxides and carbons, which may offer rational guidance to design carbon-based functional materials for energy storage. MOE (Min. of Education, S’pore)

In this work, we demonstrate the wafer-scale heterogeneous integration of III-V MMIC and Silicon complementary metal oxide semiconductor (Si CMOS) on the same Silicon substrate based on epitaxial layer transfer technique, III-V Compound semiconductor devices are vertical stacked at the top of the Si CMOS wafer using wafer bonding technique. Meanwhile, we exhibit a wide band GaAs digital controlled switch circuit and InP HBT quantizing chip with 1:16 demultiplexer as examples, which shows the potential to integrate III-V MMIC and Si CMOS on the same chip to take advance of the two different material systems.

Soil salinity is a stringent abiotic constraint limiting crop growth and productivity. The present study was carried out to appraise the role of xylo-oligosaccharides (XOSs) in improving the salinity tolerance of Chinese cabbage. Salinity stress (0.5% NaCl solution) and four levels (0, 40, 80, 120 mg L(-1)) of XOSs were imposed on 20-day-old plants cultured under controlled conditions. Salinity stress decreased the aboveground fresh biomass, photosynthesis, transpiration rate, stomatal conductance, internal CO2 concentration, water use efficiency, and chlorophyll contents but increased the stomatal limitation value of Chinese cabbage compared with control. Such physiological interferences, disturbances in plant water relations, and visually noticeable growth reductions in Chinese cabbage were significantly alleviated by the addition of XOSs under salinity stress. Under salinity stress, application of XOSs significantly enhanced the activities of enzymatic (superoxide dismutase, peroxidase, catalase) and non-enzymatic (ascorbate, carotene) antioxidants and reduced the malondialdehyde content in the leaves of Chinese cabbage. The XOS-applied plants under salinity stress also recorded higher soluble sugars, proline, and soluble protein content in their leaves. Exposure of salinity stress increased the ratio of Na(+)/K(+), Na(+)/Ca(2+), and Na(+)/Mg(2+) in shoot as well as root of Chinese cabbage, however, XOS application significantly reduced these ratios particularly in shoot. Lower levels of XOSs (40 or 80 mg L(-1)) were more effective for most of the studied attributes. The greater salinity tolerance and better growth in these treatments were related with enhanced antioxidative defense system, reduced lipid peroxidation, increased osmolyte accumulation, and maintenance of ionic balance.

Potassium (K) is an essential macronutrient for plant growth and development. Plant growth and development can be seriously affected by K deficiency. However, plants with different K efficiencies behave differently. It is still not fully understood how plants with higher K efficiency could maintain better growth in a low K environment and what is the relationship between K recycling and photosynthesis metabolism. The aim of this study was to investigate whether the difference in K re-translocation and photosynthesis transportation can explain genotype differences in K efficiency between K-efficient genotype 103 and K-inefficient genotype 122. Results of this study showed that the dry matter accumulation of genotype 122 decreased much more than that of genotype 103 affected by K deficiency environment. Root growth of the two genotypes was inhibited by K deficiency, but genotype 122 was affected more than genotype 103. Using the K utilization index as an evaluation factor for K efficiency, it was found that...

The study aimed to determine if the variability of the effect of boron (B) deficiency on Newhall navel orange grafted on trifoliate orange (deficient-B-sensitive) and on citrange (deficient-B-tolerant) can be explained on the basis of changes in cell-wall content and in cell-wall B and calcium (Ca) concentrations. The plants were cultured in the nutrient solution (with or without B) for 65 days. Boron deficiency increased the cell-wall content in old leaves (leaves from last season) of trifoliate orange but had no impact on citrange. Boron deficiency did not reduce B concentration in cell walls of old leaves of citrange-grafted plants but increased their Ca concentration. For trifoliate-orange-grafted plants, however, B deficiency decreased the B concentration in cell walls of old leaves and did not increase their Ca concentration. The changes of B and Ca concentrations between with and without B supply in pectin were in good agreement with the changes of those in cell walls. The relatively greater abilit...

Ammonia (NH3) volatilization and greenhouse gas (GHG) emission from rice (Oryza sativa L.) fields contaminate the atmospheric environment and lead to global warming. Field trials (2013-2015) were conducted to estimate the influences of different types of fertilization practices on grain yield, NH3 volatilization, and methane (CH4) and nitrous oxide (N2O) emissions in a double rice cropping system in Central China. Results showed that grain yields of rice were improved significantly by using slow/controlled-release urea (S/C-RU). Compared with farmers' fertilizer practice (FFP) treatment, average annual grain yield with application of polymer-coated urea (CRU), nitrapyrin-treated urea (CP), and urea with effective microorganism (EM) treatments was increased by 18.0%, 16.2%, and 15.4%, respectively. However, the effects on NH3 volatilization and CH4 and N2O emissions differed in diverse S/C-RU. Compared with that of the FFP treatment, the annual NH3 volatilization, CH4 emission, and N2O emissions of the CRU treatment were decreased by 64.8%, 19.7%, and 35.2%, respectively; the annual CH4 and N2O emissions of the CP treatment were reduced by 33.7% and 40.3%, respectively, while the NH3 volatilization was increased by 18.5%; the annual NH3 and N2O emissions of the EM treatment were reduced by 6.3% and 28.7%, while the CH4 emission was improved by 4.3%. Overall, CP showed the best emission reduction with a decrement of 34.3% in global warming potential (GWP) and 44.4% in the greenhouse gas intensity (GHGI), followed by CRU treatment with a decrement of 21.1% in GWP and 31.7% in GHGI, compared with that of the FFP treatment. Hence, it is suggested that polymer-coated urea can be a feasible way of mitigating NH3 volatilization and CH4 and N2O emission from rice fields while maintaining or increasing the grain yield in Chinese, the double rice cropping system.

Two-dimensional (2D) semiconductors are opening a new platform for revitalizing widely spread optoelectronic applications. The realisation of room-temperature vertical 2D lasing from monolayer semiconductors is fundamentally interesting and highly desired for appealing on-chip laser applications such as optical interconnects and supercomputing. Here, we present room-temperature low-threshold lasing from 2D semiconductor activated vertical-cavity surface-emitting lasers (VCSELs) under continuous-wave pumping. 2D lasing is achieved from a 2D semiconductor. Structurally, dielectric oxides were used to construct the half-wavelength-thick cavity and distributed Bragg reflectors, in favour of single-mode operation and ultralow optical loss; in the cavity centre, the direct-bandgap monolayer WS2 was embedded as the gain medium, compatible with the planar VCSEL configuration and the monolithic integration technology. This work demonstrates 2D semiconductor activated VCSELs with desirable emission characteristics, which represents a major step towards practical optoelectronic applications of 2D semiconductor lasers., Two-dimensional materials have recently emerged as interesting materials for optoelectronic applications. Here, Shang et al. demonstrate two-dimensional semiconductor activated vertical-cavity surface-emitting lasers where both the gain material and the lasing characteristics are two-dimensional.