Melatonin alleviates endoplasmic reticulum stress to improve ovarian function by regulating the mTOR pathway in aged laying hens.

Granular cell apoptosis is a key factor leading to follicular atresia and decreased laying rate in aged laying hens. Endoplasmic reticulum stress (ERS) induced cell apoptosis is a new type of apoptosis pathway. Previous studies have shown that the ERS pathway is involved in the regulation of follicular development and atresia, and can be regulated by mTOR. Melatonin (MEL) can protect the normal development of follicles, but the precise mechanism by which MEL regulates follicular development is not yet clear. So, we investigated the potential relationship between MEL and ERS and mTOR signaling pathway in vivo through intraperitoneal injection of MEL in aged laying hens. The results show that the laying rate, ovarian follicle number, plasma MEL, E2, LH, FSH concentrations, as well as the mRNA expression of mTOR signaling-associated genes TSC1, TSC2, mTOR, 4E-BP1, and S6K in old later-period chicken control (Old-CN) group was significantly decreased (P < 0.01). In contrast, the ERS-related of plasma and granular cell layer mRNA expression of Grp78, CHOP, and Caspase-3 was significantly increased (P < 0.01). While both of the effects were reversed by MEL. Then, aging granulosa cells were treated with MEL in vitro, followed by RNA seq analysis, and it was found that 259 and 322 genes were upregulated and downregulated. After performing GO enrichment analysis, it was found that DEGs significantly contribute to the biological processes including cell growth and apoptosis. Using pathway enrichment analysis, we found significant overrepresentation of cellular processes related to mTOR signaling and endoplasmic reticulum (ER) stress, involving genes such as GRB10, SGK1, PRKCA, RPS6KA2, RAF1, PIK3R3, FOXO1, DERL3, HMOX1, TLR7, VAMP7 and INSIG2. The obtained results of RT-PCR showed consistency with the RNA-Seq data. In summary, the underlined results revealed that MEL has significantly contributed to follicular development via activating the mTOR signaling pathway-related genes and alleviating ERS-related genes in laying hens. The current study provides a theoretical background for enhancing the egg-laying capability of hens and also providing a basis for elucidating the molecular mechanism of follicular selection.

Melatonin alleviates endoplasmic reticulum stress and follicular granulosa cell apoptosis by regulating ATF4 to activate mTOR signaling pathway in chickens.

Follicular atresia in chickens reduces the number of follicles that can further develop, leading to decrease egg laying. Endoplasmic reticulum stress (ERS) can initiate a unique pathway inducing the apoptosis of follicular granulosa cells, thus reducing egg laying. Melatonin (MEL) is involved in the regulation of follicle development, ovulation, and oocyte maturation, and is closely related to follicle fate. Mammalian target of Rapamycin (mTOR) signaling pathway plays an important role in cell growth regulation, and that there is a possible crosstalk between melatonin and mTOR activity in granular cells maturation and ovulation. This study aimed to investigate whether MEL inhibits ERS and follicular granulosa cell apoptosis by regulating ATF4 to activate mTOR signaling pathway in chickens. Frist, we established an in vitro ERS cell model using tunicamycin (TM). The results showed that different concentrations of TM exhibited dose-dependent inhibition of cell activity and induction of granulosa cells (P<0.01). Therefore, we chose 5 µg/mL of TM and a treatment time for 6 h as the optimal concentration for the following experiments. Then we investigate whether melatonin can inhibit ERS. TM treatment decreased the cell viability and Bcl-2 expression, increasing ROS levels and the mRNA expression of Grp78, ATF4, CHOP, PERK, eIF-2α, and BAX (P<0.01), whereas TM+MEL treatment significantly inhibited these changes (P<0.01). Then we explored whether melatonin protects follicular granulosa cells from ERS-induced apoptosis through the mammalian target of rapamycin (mTOR) signaling pathway by regulating ATF4, we found that ATF4 knockdown inhibited ERS by decreasing the expression of ERS-related genes and proteins and activating mTOR signaling pathway by increasing the protein expression of p4E-BP1 and pT389-S6K (P<0.001), while these changes were promoted by TM+si-ATF4+MEL treatment (P<0.01). These results indicate that MEL could alleviate TM-induced ERS by regulating ATF4 to activate mTOR signaling pathway in follicular granulosa cells, thus providing a new perspective for prolonging the laying cycle in chickens.

Helicity-resolved Raman scattering of MoS2 bulk crystal.

Helicity-resolved Raman spectroscopy (HRRS) can effectively distinguish the Raman modes of two-dimensional (2D) layered materials by phonon symmetry. In this paper, we systematically investigated the phonon helicity selection of basal and edge planes of MoS2 bulk by HRRS. We find that the symmetry of the crystal structure changes the helicity selection of the E1g, E1 2g, and A1g modes in the edge plane. The theoretical calculation results confirm that the E1 2g and A1g modes of the basal plane exhibit a perfect helicity exchange, and the helicity selections of the E1 2g and A1g modes of the edge plane are eliminated or weakened. Our study provides references for phonon helicity selection of 2D layered materials represented by MoS2.

Intralayer Phonons in Multilayer Graphene Moiré Superlattices.

Moiré pattern in twisted multilayers (tMLs) induces many emergent phenomena by subtle variation of atomic registry to modulate quasiparticles and their interactions, such as superconductivity, moiré excitons, and moiré phonons. The periodic superlattice potential introduced by moiré pattern also underlies patterned interlayer coupling at the interface of tMLs. Although this arising patterned interfacial coupling is much weaker than in-plane atomic interactions, it is crucial in moiré systems, as captured by the renormalized interlayer phonons in twisted bilayer transitional metal dichalcogenides. Here, we determine the quantitative relationship between the lattice dynamics of intralayer out-of-plane optical (ZO) phonons and patterned interfacial coupling in multilayer graphene moiré superlattices (MLG-MS) by the proposed perturbation model, which is previously challenging for MLGs due to their out-of-phase displacements of adjacent atoms in one atomic plane. We unveil that patterned interfacial coupling introduces profound modulations on Davydov components of nonfolded ZO phonon that are localized within the AB-stacked constituents, while the coupling results in layer-extended vibrations with symmetry of moiré pattern for moiré ZO phonons. Our work brings further degrees of freedom to engineer moiré physics according to the modulations imprinted on the phonon frequency and wavefunction.

Phonon and Exciton Properties between WS2 and MoS2 Layers via Inversion Heterostructure Engineering.

Recently, two-dimensional (2D) van der Waals heterostructures (vdWHs) have exhibited emergent electronic and optical properties due to their peculiar phonons and excitons, which lay the foundation for the development of photoelectronic devices. The dielectric environment plays an important role in the interlayer coupling of vdWHs. Here, we studied the interlayer and extra-layer dielectric effects on phonon and exciton properties in WS2/MoS2 and MoS2/WS2 vdWHs by Raman and photoluminescence (PL) spectroscopy. The ultralow frequency (ULF) Raman modes are insensitive to atomic arrangement at the interface between 1LW and 1LM and dielectric environments of neighboring materials, and the layer breathing mode (LBM) frequency follows that of WS2. The shift of high-frequency (HF) Raman modes is attributable to interlayer dielectric screening and charge transfer effects. Furthermore, the energy of interlayer coupling exciton peak I is insensitive to atomic arrangement at the interface between 1LW and 1LM and its energy follows that of MoS2, but the slight intensity difference in inversion vdWHs means that the substrate's dielectric properties may induce doping on the bottom layer. This paper provides fundamental understanding of phonon and exciton properties of such artificially formed vdWHs structures, which is important for new insights into manipulating the performances of potential devices.

Magneto-Raman Study of Magnon-Phonon Coupling in Two-Dimensional Ising Antiferromagnetic FePS3.

Recently, the coupling between magnons (quanta of spin waves) and phonons (quanta of lattice vibrations) in two-dimensional (2D) antiferromagnet FePS3 offers a myriad of applications ranging from spintronic devices to quantum information technologies. However, the reported magnon-phonon coupling in the FePS3 flake using Raman measurements requires an ultrahigh magnetic field up to 30 T. Here, we investigate the magnon-phonon coupling in FePS3 by near-resonant magneto-Raman spectroscopy under a relatively small magnetic field (|H0| ≤ 9 T). Under near-resonant excitation, we find more pronounced coupling effects that are absent in non-resonant excitation: three optical phonons sensitive to the applied magnetic field are resolved, two of which show a frequency anti-crossing coupling with magnon, while the other coupled phonon exhibits only a polarization-coupled character without frequency anti-crossing. Besides, our polarized Raman results also show the polarization transferring between coupled magnon-phonon modes. On the basis of a modified theoretical model, we can well explain the measured Raman spectra.

Donor-Acceptor Pair Quantum Emitters in Hexagonal Boron Nitride.

Quantum emitters are needed for a myriad of applications ranging from quantum sensing to quantum computing. Hexagonal boron nitride (hBN) quantum emitters are one of the most promising solid-state platforms to date due to their high brightness and stability and the possibility of a spin-photon interface. However, the understanding of the physical origins of the single-photon emitters (SPEs) is still limited. Here we report dense SPEs in hBN across the entire visible spectrum and present evidence that most of these SPEs can be well explained by donor-acceptor pairs (DAPs). On the basis of the DAP transition generation mechanism, we calculated their wavelength fingerprint, matching well with the experimentally observed photoluminescence spectrum. Our work serves as a step forward for the physical understanding of SPEs in hBN and their applications in quantum technologies.

A tunable Raman system based on ultrafast laser for Raman excitation profile measurement.

The measurement of the Raman excitation profile (REP) is of great importance to obtain the energies of van Hove singularities and the lifetime of the excited state involved in the Raman process of semiconductors. In this Note, we develop a simple tunable Raman system based on an ultrafast laser and tunable Raman filters for REP measurement. The system is testified by measuring REP of twisted bilayer graphene, and the corresponding energy of van Hove singularity is determined.

Observation of nonreciprocal magnetophonon effect in nonencapsulated few-layered CrI3.

"Magneto-optical" effect refers to a rotation of polarization plane, which has been widely studied in traditional ferromagnetic metal and insulator films and scarcely in two-dimensional layered materials. Here, we uncover a new nonreciprocal magnetophonon Raman scattering effect in ferromagnetic few-layer CrI3 We observed a rotation of the polarization plane of inelastically scattered light between -20o and +60o that are tunable by an out-of-plane magnetic field from -2.5 to 2.5 T. It is experimentally observed that the degree of polarization can be magnetically manipulated between -20 and 85%. This work raises a new magneto-optical phenomenon and could create opportunities of applying two-dimensional ferromagnetic materials in Raman lasing, topological photonics, and magneto-optical modulator for information transport and storage.

Understanding angle-resolved polarized Raman scattering from black phosphorus at normal and oblique laser incidences.

The selection rule for angle-resolved polarized Raman (ARPR) intensity of phonons from standard group-theoretical method in isotropic materials would break down in anisotropic layered materials (ALMs) due to birefringence and linear dichroism effects. The two effects result in depth-dependent polarization and intensity of incident laser and scattered signal inside ALMs and thus make a challenge to predict ARPR intensity at any laser incidence direction. Herein, taking in-plane anisotropic black phosphorus as a prototype, we developed a so-called birefringence-linear-dichroism (BLD) model to quantitatively understand its ARPR intensity at both normal and oblique laser incidences by the same set of real Raman tensors for certain laser excitation. No fitting parameter is needed, once the birefringence and linear dichroism effects are considered with the complex refractive indexes. An approach was proposed to experimentally determine real Raman tensor and complex refractive indexes, respectively, from the relative Raman intensity along its principle axes and incident-angle resolved reflectivity by Fresnel's law. The results suggest that the previously reported ARPR intensity of ultrathin ALM flakes deposited on a multilayered substrate at normal laser incidence can be also understood based on the BLD model by considering the depth-dependent polarization and intensity of incident laser and scattered Raman signal induced by both birefringence and linear dichroism effects within ALM flakes and the interference effects in the multilayered structures, which are dependent on the excitation wavelength, thickness of ALM flakes and dielectric layers of the substrate. This work can be generally applicable to any opaque anisotropic crystals, offering a promising route to predict and manipulate the polarized behaviors of related phonons.

Cross-dimensional electron-phonon coupling in van der Waals heterostructures.

The electron-phonon coupling (EPC) in a material is at the frontier of the fundamental research, underlying many quantum behaviors. van der Waals heterostructures (vdWHs) provide an ideal platform to reveal the intrinsic interaction between their electrons and phonons. In particular, the flexible van der Waals stacking of different atomic crystals leads to multiple opportunities to engineer the interlayer phonon modes for EPC. Here, in hBN/WS2 vdWH, we report the strong cross-dimensional coupling between the layer-breathing phonons well extended over tens to hundreds of layer thick vdWH and the electrons localized within the few-layer WS2 constituent. The strength of such cross-dimensional EPC can be well reproduced by a microscopic picture through the mediation by the interfacial coupling and also the interlayer bond polarizability model in vdWHs. The study on cross-dimensional EPC paves the way to manipulate the interaction between electrons and phonons in various vdWHs by interfacial engineering for possible interesting physical phenomena.

Probing the Magnetic Ordering of Antiferromagnetic MnPS3 by Raman Spectroscopy.

Ferromagnetic/antiferromagnetic materials are of crucial importance in information storage and spintronics devices. Herein we present a comprehensive study of 2D Heisenberg-like antiferromagnetic material MnPS3 by optical contrast and Raman spectroscopy. We propose a criterion of 0.1 × ( N - 1) < (Δ R/ R)max < 0.1 × N ( N ≤ 7) to quickly identify the layer number N by using maximum optical contrast (Δ R/ R)max of few-layer MnPS3 on a SiO2/Si substrate (90 nm thick SiO2). The Raman modes are also identified by polarization Raman spectroscopy. Furthermore, by temperature-dependent Raman measurements, we obtain three phase transition temperatures of MnPS3. The transition temperature at around 80 K corresponds to the transition from the antiferromagnetic to paramagnetic phase; the one at around 120 K is related to its second magnetic phase transition temperature due to two-dimensional spin critical fluctuations; the one at around 55 K is associated with unbinding of spin vortices. Our studies provide more evidence to advance knowledge of the magnetic critical dynamics of 2D ferromagnetic/antiferromagnetic systems.

Research progress on international studies on applied ecology based on Web of Science.

Applied ecology is one of the most important scientific and technological tools for natural resources management and environment protection. Under the current situation of natural resource shortage, serious environmental pollution, and ecosystem degradation, understanding the theoretical basis, research methods and research hotspots of international studies on applied ecology is of great significance for consolidating the knowledge base, indicating the research direction, defining the strategic position of China's studies on applied ecology. Based on the principle of bibliometrics and information visualization software (CiteSpace and Carrot2), we took two document datasets as research objects which were searched from Web of Science based on different search strategies in the field of international studies on applied ecology from 1980 to 2018. We analyzed the spatial and temporal distribution of the literature, the core research forces, the evolution and frontier trend of research hotspots from three dimensions, i.e. research carrier, research strength, and research content. Our results could reveal its evolutionary trajectory, research status and development trend and provide reference for future studies on applied ecology in China.

Highly Conductive Graphene Paper with Vertically Aligned Reduced Graphene Oxide Sheets Fabricated by Improved Electrospray Deposition Technique.

Because of its notable electrical and mechanical properties, the highly conductive graphene paper has great potential applications in future flexible electronics. In this study, we report a simple and effective method to prepare vertically aligned graphene oxide papers from graphene oxide suspensions by an improved electrospray deposition technique with a moving stage, which is controlled by computer. Then, the flexible reduced graphene oxide papers are successfully synthesized after reduction by using hydroiodic acid. The obtained reduced graphene oxide paper has an electrical conductivity as high as 6180 S/m, which is more than one and a half times of the reduced graphene oxide paper film, which was fabricated by using the electrospray deposition technique without the moving stage. The experimental results approved for the first time that the degree of alignment of reduced graphene oxide sheets can affect the conductivity of the reduced graphene oxide papers. Further electrochemical measurements for a symmetrical supercapacitor device based on the prepared reduced graphene oxide paper indicate that it has great capacitive performance and electrochemical stability. It exhibited relatively high specific capacitance (174 F·g-1) at a current density of 1 A·g-1 in 6 M KOH aqueous solution, and its capacitance can retain approximately 86% after 1000 cycles. In addition, patterned freestanding reduced graphene oxide papers, which have potential applications in many fields such as stretchable electronics and wearable devices, also can be fabricated by using this method.

Phonon-Assisted Photoluminescence Up-Conversion of Silicon-Vacancy Centers in Diamond.

Phonon-assisted anti-Stokes photoluminescence (ASPL) up-conversion lies at the heart of optical refrigeration in solids. The thermal energy contained in the lattice vibrations is taken away by the emitted anti-Stokes photons' ASPL process, resulting in laser cooling of solids. To date, net laser cooling of solids is limited in rare-earth (RE)-doped crystals, glasses, and direct band gap semiconductors. Searching more solid materials with efficient phonon-assisted photoluminescence up-conversion is important to enrich optical refrigeration research. Here, we demonstrate the phonon-assisted PL up-conversion process from the silicon vacancy (SiV) center in diamond for the first time by studying ASPL spectra for the dependence of temperature, laser power, and excitation energy. Although net cooling has not been observed, our results show that net laser cooling might be eventually achieved in diamond by improving the external quantum efficiency to higher than 95%. Our work provides a promising route to investigate the laser cooling effect in diamond.

Stokes and anti-Stokes Raman scattering in mono- and bilayer graphene.

Stokes and anti-Stokes Raman spectroscopy associated with the intervalley double resonance process in carbon materials is a unique technique to reveal the relationship between their characteristic electronic band structures and phonon dispersion. In graphene, the dominant resonant behavior for its 2D mode is an intervalley triple resonance Raman process. In this paper, we report the Stokes and anti-Stokes Raman scattering of the 2D mode in pristine graphene. The excitation energy (Eex)-dependent frequency discrepancy between anti-Stokes and Stokes components of the 2D mode (Δω(2D)) is observed, which is in good agreement with the theoretical results. This is attributed to the nonlinear dispersion of the in-plane transverse optical (iTO) phonon branch near the K point, confirmed by the nonlinear Eex-dependent frequency of the 2D mode (ω(2D)) in the range of 1.58-3.81 eV. The wavevector-dependent phonon group velocity of the iTO phonon branch is directly derived from Δω(2D). The Stokes and anti-Stokes Raman scattering of the D mode in defected graphene and the 2D mode in bilayer graphene associated with intervalley double resonance Raman processes is also reported.

The phonon confinement effect in two-dimensional nanocrystals of black phosphorus with anisotropic phonon dispersions.

The RWL model for the phonon confinement effect in nanocrystals (NCs) had been found to result in deviations and limitations for crystals exhibiting obvious anisotropic phonon dispersions and modified models have been proposed to overcome these deficiencies. Here, we examine this issue in black phosphorus (BP), a typical anisotropic two-dimensional crystal exhibiting pronounced anisotropy in phonon dispersions. A detailed study is performed on the Raman spectra of BP NCs prepared by the ion implantation technique. With decreasing NC size, the peak positions of the three characteristic Raman modes, Ag1, B2g and Ag2 modes, remain almost unchanged, while the Ag1 and Ag2 modes show significant asymmetrical broadening tails towards higher- and lower-frequency sides, respectively. It is found that the RWL model based on one-dimensional phonon dispersion along Γ-Y and Γ-X axes in the Brillouin zone (BZ) cannot interpret the unusual frequency invariance and inhomogeneous line shape broadening of these three modes. However, after considering the contribution of two-dimensional anisotropic phonon dispersions from the whole BZ, the frequency and asymmetrical broadening of the Ag1 and Ag2 modes can be well reproduced. This study demonstrates that the RWL model can be applicable for crystals with anisotropic phonon dispersions once the phonons in the whole two-dimensional or three-dimensional BZ are properly taken into account, and provides a physically sound route into understanding the phonon confinement effect for anisotropic systems.

Damage-free and rapid transfer of CVD-grown two-dimensional transition metal dichalcogenides by dissolving sacrificial water-soluble layers.

As one of the most important family members of two-dimensional (2D) materials, the growth and damage-free transfer of transition metal dichalcogenides (TMDs) play crucial roles in their future applications. Here, we report a damage-free and highly efficient approach to transfer single and few-layer 2D TMDs to arbitrary substrates by dissolving a sacrificial water-soluble layer, which is formed underneath 2D TMD flakes simultaneously during the growth process. It is demonstrated, for monolayer MoS2, that no quality degradation is found after the transfer by performing transmission electron microscopy, Raman spectroscopy, photoluminescence and electrical transport studies. The field effect mobility of the post-transfer MoS2 flakes was found to be improved by 2-3 orders compared with that of the as-grown ones. This approach was also demonstrated to be applicable to other TMDs, other halide salts as precursors, or other growth substrates, indicating its universality for other 2D materials. Our work may pave the way for material synthesis of future integrated electronic and optoelectronic devices based on 2D TMD materials.

Interfacial Interactions in van der Waals Heterostructures of MoS2 and Graphene.

Interfacial coupling between neighboring layers of van der Waals heterostructures (vdWHs), formed by vertically stacking more than two types of two-dimensional materials (2DMs), greatly affects their physical properties and device performance. Although high-resolution cross-sectional scanning tunneling electron microscopy can directly image the atomically sharp interfaces in the vdWHs, the interfacial coupling and lattice dynamics of vdWHs formed by two different types of 2DMs, such as semimetal and semiconductor, are not clear so far. Here, we report the ultralow-frequency Raman spectroscopy investigation on interfacial couplings in the vdWHs formed by graphene and MoS2 flakes. Because of the significant interfacial layer-breathing couplings between MoS2 and graphene flakes, a series of layer-breathing modes with frequencies dependent on their layer numbers are observed in the vdWHs, which can be described by the linear chain model. It is found that the interfacial layer-breathing force constant between MoS2 and graphene, α0⊥(I) = 60 × 1018 N/m3, is comparable with the layer-breathing force constant of multilayer MoS2 and graphene. The results suggest that the interfacial layer-breathing couplings in the vdWHs formed by MoS2 and graphene flakes are not sensitive to their stacking order and twist angle between the two constituents. Our results demonstrate that the interfacial interlayer coupling in vdWHs formed by two-dimensional semimetals and semiconductors can lead to new lattice vibration modes, which not only can be used to measure the interfacial interactions in vdWHs but also is beneficial to fundamentally understand the properties of vdWHs for further engineering the vdWHs-based electronic and photonic devices.

Filter-based ultralow-frequency Raman measurement down to 2 cm-1 for fast Brillouin spectroscopy measurement.

Simultaneous Stokes and anti-Stokes ultralow-frequency (ULF) Raman measurement down to ∼2 cm-1 or 60 GHz is realized by a single-stage spectrometer in combination with volume-Bragg-grating-based notch filters. This system reveals its excellent performance by probing Brillouin signal of acoustic phonons in silicon, germanium, gallium arsenide, and gallium nitride. The deduced sound velocity and elastic constants are in good accordance with previous results determined by various methods. This system can shorten the integration time of the Brillouin signal with a good signal-to-noise ratio by more than 2000-fold compared to a Fabry-Perot interferometer (FPI). This study shows how a filter-based ULF Raman system can be used to reliably achieve Brillouin spectroscopy for condensed materials with high sensitivity and high signal-to-noise ratio, stimulating fast Brillouin spectrum measurements to probe acoustic phonons in semiconductors.