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MnBi2Te4 can generate a variety of exotic topological quantum states, which are closely related to its special structure. We conduct comprehensive multiple-cycle high-pressure research on MnBi2Te4 by using a diamond anvil cell to study its phase transition behaviors under high pressure. As observed, when the pressure does not exceed 15 GPa, the material undergoes an irreversible metal–semiconductor–metal transition, whereas when the pressure exceeds 17 GPa, the layered structure is damaged and becomes irreversibly amorphous due to the lattice distortion caused by compression, but it is not completely amorphous, which presents some nano-sized grains after decompression. Our investigation vividly reveals the phase transition behaviors of MnBi2Te4 under high pressure cycling and paves the experimental way to find topological phases under high pressure. [ABSTRACT FROM AUTHOR]

Nonlayered palladium sulfide (PdS) is of interest due to its rich physical properties and promising applications in optoelectronic devices. However, the growth of thin nonlayered PdS remains challenging because of its intrinsic 3D lattice structure. Here, the first demonstration of the direct synthesis of thin rectangular PdS ribbons/flakes on SiO2/Si substrates by a facile chemical vapor deposition (CVD) approach is presented. The atomic structure and high crystalline quality of CVD‐derived PdS crystals are shown by scanning transmission electron microscopy. The nonlinear saturable absorption and absorption enhancement are revealed by using ultrafast optical pump‐probe spectroscopy, and the photocarrier dynamics present the hot phonon bottleneck and Auger recombination effects. Additionally, the Raman vibration modes display the polarization‐dependent properties verified by angle‐resolved polarized Raman spectroscopy. Importantly, the photodetector based on PdS ribbon demonstrates a decent photoresponsivity of ≈7.7 × 103 A W−1. These results provide an effective way to form thin nonlayered PdS with potential applications in the field of photodetection. [ABSTRACT FROM AUTHOR]

Topological semimetals have attracted flourishing interest as promising candidates for their unique advantages in achieving highly sensitive, low‐energy photodetection with ultrafast operation. Although various semimetals have been explored recently, new semimetals are still being pursued for high‐responsivity photodetectors with broadband response. Here, a pressure‐induced semiconductor–semimetal transition is observed in two‐dimensional wide‐band semiconducting lead iodide (PbI2). The photocurrent under visible light shows abrupt increases by two orders of magnitude at ≈25 GPa, where the crystalline structure transforms from the Pnma to I4/MMM phase. Meanwhile, the responding band expands from visible light to at least the telecom wavelength 1550 nm. The high‐pressure absorption spectra of PbI2 suggest that the electrical band is closed at the transition point, while the charge transport shows that the sample is still not metallic. Through first‐principles calculations, the photocurrent spurt and infrared band response are attributed to the appearance of a semimetal phase at high pressure, which well explains the nonmetallic transport. The prominent drop in lifetime to a few picoseconds in ultrafast spectroscopy under pressure further confirms the semiconductor–semimetal transition in PbI2. Pressure‐induced semimetallization opens a new strategy for designing a high‐performance photodetector with broadband response. [ABSTRACT FROM AUTHOR]

Understanding the coupling between electrons and phonons in iron chalcogenides FeTe x Se 1 − x has remained a critical but arduous project in recent decades. The direct observation of the electron–phonon coupling effect through electron dynamics and vibrational properties has been lacking. Here, we report the first pressure-dependent ultrafast photocarrier dynamics and Raman scattering studies on an iron chalcogenide FeTe 0.5 Se 0.5 to explore the interaction between electrons and phonons in this unconventional superconductor. The lifetime of the excited electrons evidently decreases as the pressure increases from 0 to 2.2 GPa, and then increases with further compression. The vibrational properties of the A 1 g phonon mode exhibit similar behavior, with a pronounced frequency reduction appearing at approximately 2.3 GPa. The dual evidence reveals the enhanced electron–phonon coupling strength with pressure in FeTe 0.5 Se 0.5 . Our results give an insight into the role of the electron–phonon coupling effect in iron-based superconductors. [ABSTRACT FROM AUTHOR]

Terahertz (THz) time-domain spectroscopy (THz-TDS) of polycrystalline MnCr2O4 was performed at <9 T and low temperatures. A resonance absorption in the sub-THz range with linear blueshifts was observed as the magnetic field was increased from 4 T to 9 T. These magnetism-driven absorptions originated from a ferromagnetic resonance, which agrees with low-field electron spin resonance measurements and ferromagnetic resonance theory. The low-temperature g -factors of MnCr2O4 were also obtained using THz-TDS. This work provides new insights into the spin dynamics of chromite spinel compounds in the THz region. [ABSTRACT FROM AUTHOR]

The two-dimensional (2D) semiconductor lead iodide (PbI2) has recently attracted considerable attention owing to its favorable properties in both applications as photodetectors and as a precursor for lead halide perovskite solar cells. Although earlier experiments have investigated the structural stability of PbI2 below 20 GPa, the electric structures at high pressure remain ambiguous, as does the crystal structure at higher pressures. Herein, a structural phase transition and a semiconductor-metal transition are revealed in PbI2 through high-pressure femtosecond optical pump-probe spectroscopy combined with Raman spectra, synchrotron x-ray diffraction (XRD), and resistance measurements up to 70 GPa. Two discontinuities appear in the pressure-dependent amplitude of the ultrafast spectroscopy at approximately 24.8 and 37.6 GPa. Raman spectra and in situ XRD patterns confirm a structural phase transition from orthorhombic Pnma to tetragonal I4/MMM symmetry at the first discontinuity. The second discontinuity is ascribed to the closure of the bandgap and the enhanced electron-phonon interaction across the semiconductor-metal transition, which is also revealed by the temperature dependencies of resistance for PbI2 under pressure. Our results not only help to design optical devices based on lead iodide but also highlight that ultrafast spectroscopy is an efficient noncontact tool to investigate the crystalline and electric phase transition under pressures simultaneously. [ABSTRACT FROM AUTHOR]

The emerging two-dimensional (2D) platinum disulfide (PtS2) has driven increasing attentions due to its high electron mobility, good air-stability, and strong interlayer interaction which leads to a widely tunable electronic structure. However, a detailed study on its covalent-like layer-dependent properties remains infant. Herein, we demonstrate the successful production of ultrathin 1T-PtS2 ribbons with thickness centralized almost at monolayer 1L–4L and large domain size up to 210 µm on Au foils using chemical vapor deposition (CVD) technique, which enables macro- and microscopic study of its extraordinary layer-dependent features with precise control of the number of layers. Using electron energy loss spectroscopy (EELS) and optical pump-probe spectroscopy (OPPS), we reveal that both the electron and ultrafast optical absorption signals of the as-grown 2D PtS2 show strong nonlinear layer-dependent responses which manifest discriminated transition in 1L–4L PtS2 ribbons. The layer-dependent nonlinear response of 2D PtS2 can be well interpreted in the frame of calculated electron and phonon structures. These achievements offer a platform for successfully fabricating large-sized ultrathin 2D PtS2 and facilitating our knowledge about its electronic and optoelectronic properties. [ABSTRACT FROM AUTHOR]

We employ polarization-resolved femtosecond optical pump–probe spectroscopy to investigate the nonequilibrium photocarrier dynamics in excitonic insulator Ta2NiSe5. The electronic dynamics, including hot carrier cooling, exciton formation, and recombination in the timescale ranging from subpicoseconds to a few tens of picoseconds, have been established from the transient reflectivity spectra, showing strong in-plane anisotropy with respect to the probe polarization. Such anisotropic photocarrier dynamics possibly arise from the crystalline orientation dependence of the excitonic polarizability. Furthermore, we find that the amplitude of coherent phonons with a frequency of 1 THz is subject to the probe polarization, whereas it is not sensitive to the pump polarization. This substantiates that the displacive excitation of coherent phonons plays a decisive role in lattice dynamics. In addition, we find that the photo-induced dielectric screening tends to suppress the amplitude of coherent phonons with increasing pump fluence, manifesting a remarkable polarization dependence. Our work provides valuable insights into the excitonic dynamics and the origin of coherent phonon generation and also may contribute to the development of polarization-sensitive photoelectric devices based on Ta2NiSe5. [ABSTRACT FROM AUTHOR]

A systemic investigation of the terahertz (THz) transmission of La0.67Ca0.33MnO3 film on the (001)-oriented NdGaO3 substrate under external magnetic field and low temperature have been performed. The significant THz absorption difference between the out-of-plane and the in-plane magnetic field direction is observed, which is consistent with the electrical transport measurement using the standard four-probe technique. Furthermore, we find that the complex THz conductivities can be reproduced in terms of the Drude Smith equation as the magnetic field is perpendicular to the film plane, whereas it deviates from this model when the in-plane magnetic field is applied. We suggest that such anisotropies in THz transport dynamics have close correspondences with the phase separation and anisotropic magnetoresistance effects in the perovskite-structured manganites. Our work demonstrates that the THz time-domain spectroscopy (TDS) can be an effective non-contact method for studying the magneto-transport properties of the perovskite-structured manganites. [ABSTRACT FROM AUTHOR]

Vibrational properties and ultrafast photocarrier dynamics of 2H–TaS2 under pressures are studied by the experiments of Raman scattering and femtosecond time resolved spectroscopy. With increasing pressure, the linewidth of two-phonon Raman mode broadens, especially features with a sudden rapid increase above 10 GPa. Meanwhile, the ultrafast dynamics show that the fast decay through optical phonon scattering is significantly suppressed in amplitude and prolonged in lifetime; however, the weight of the slow decay component originating from acoustic phonon scattering is enhanced at high pressures. Furthermore, the electron-phonon (e-ph) coupling constant, λq, and the density of states (DOS) near the Fermi level, N(0), are evaluated qualitatively, which reveals a drastic decrease in e-ph coupling strength and a sudden increase in the DOS beyond 10 GPa. This turning pressure is consistent with the critical point where T c of superconductivity peaks while the charge density wave (CDW) vanishes, indicating the direct correlations between λq, N(0), superconductivity, and the CDW under pressure. The anomaly of the DOS may imply the occurrence of a topological transition of the electronic structure. Our work not only provides valuable information for the understanding of competition between the CDW and superconductivity in 2H–TaS2 but also may open up a routine to unveil the pressure-induced electronic topological transition. [ABSTRACT FROM AUTHOR]

Temperature and pressure dependent measurements have been performed on 3.5 nm ZnS:Mn[sup 2+] nanoparticles. As temperature increases, the donor-acceptor (DA) emission of ZnS:Mn[sup 2+] nanoparticles at 440 nm shifts to longer wavelengths while the Mn[sup 2+] emission ([sup 4]T[sub 1] - [sup 6]A[sub 1]) shifts to shorter wavelengths. Both the DA and Mn[sup 2+] emission intensities decrease with temperature with the intensity decrease of the DA emission being much more pronounced. The intensity decreases are fit well with the theory of thermal quenching. As pressure increases, the Mn[sup 2+] emission shifts to longer wavelengths while the DA emission wavelength remains almost constant. The pressure coefficient of the DA emission in ZnS:Mn[sup 2+] nanoparticles is approximately -3.2meV/GPa, which is significantly smaller than that measured for bulk materials. The relatively weak pressure dependence of the DA emission is attributed to the increase of the binding energies and the localization of the defect wave functions in nanoparticles. The pressure coefficient of Mn[sup 2+] emission in ZnS:Mn[sup 2+] nanoparticles is roughly -34.3 meV/GPa, consistent with crystal field theory. The results indicate that the energy transfer from the ZnS host to Mn[sup 2+] ions is mainly from the recombination of carriers localized at Mn[sup 2+] ions. [ABSTRACT FROM AUTHOR]

Polycrystalline bulk samples of BaSn1−xCrxO3 with different Cr concentrations were prepared by standard solid state reaction method. The effects of Cr concentration on crystal structure of BaSn1−xCrxO3, as well as optical and magnetic properties were investigated. Powder X-ray diffraction (XRD) shows that each of these samples possess a perovskite structure with P m 3 ¯ m space group. The Cr ions are located at the substitution Sn sites as revealed by the XRD, Diffuse reflectance spectra and Raman spectra. Moreover, it is found that room-temperature ferromagnetism (FM) can be reversed by annealing in the nitrogen atmosphere. This can be well explained by a modified model of F-center mediated FM. [ABSTRACT FROM AUTHOR]

Abstract: The 2D terahertz (THz) modulator, enabling efficient manipulation of such versatile band in nanoscale, is crucial for THz microdevices and systems, but its implementation is difficult and remains challenging in practice. Here, a novel 2D THz modulator based on single‐layered graphene under mechanical strain is demonstrated. Bidirectional, i.e., both positive and negative, THz modulation effect is realized by utilizing unconventionally distributed strains on graphene. Such mechanical modulation is found to be stable and reversible, and its modulation depth can exceed 26% at 1 THz under 10–2 GPa strain. Observations of both the strain and frequency dependent modulation behavior evidence the mechanical strain‐induced change of the Dirac‐like energy dispersion in graphene, which is distinctive from that of the electrical and optical approaches. Due to the reliability and wide applicability of mechanical forces, these results provide an alternative route for chip‐scale THz modulation devices based on 2D materials. [ABSTRACT FROM AUTHOR]

MnBi2Te4 can generate a variety of exotic topological quantum states, which are closely related to its special structure. We conduct comprehensive multiple-cycle high-pressure research on MnBi2Te4 by using a diamond anvil cell to study its phase transition behaviors under high pressure. As observed, when the pressure does not exceed 15 GPa, the material undergoes an irreversible metal–semiconductor–metal transition, whereas when the pressure exceeds 17 GPa, the layered structure is damaged and becomes irreversibly amorphous due to the lattice distortion caused by compression, but it is not completely amorphous, which presents some nano-sized grains after decompression. Our investigation vividly reveals the phase transition behaviors of MnBi2Te4 under high pressure cycling and paves the experimental way to find topological phases under high pressure. [ABSTRACT FROM AUTHOR]

A highly accurate method for measuring pentachlorophenol (PCP) concentrations in textile samples was developed. This highly accurate method for the analysis of textile samples is valuable, given the inherent challenges associated with the complexity of the sample matrix. This method can be applied to certify the concentration of pentachlorophenol in textile CRMs. A measurement procedure based on isotope dilution liquid chromatography-isotope dilution mass spectrometry (LC-IDMS) was developed. Samples were pretreated with acid and then with n-hexane. Excellent precision was obtained. The validated concentration ranges for the method were 1.0-50 ng/g, the LOD was 1.0 ng/g, and the LOQ was 5.0 ng/g. The precision of this method is in the range of 0.80-1.40%. The method can trace to mass. [ABSTRACT FROM AUTHOR]

Abstract: Zn2SiO4:Mn2+, Zn2SiO4:Eu3+ and Zn2SiO4:Mn2+,Eu3+ phosphors were prepared by a sol-gel process and their luminescence spectra were investigated. The emission bands from intra-ion transitions of Mn2+ and Eu3+ samples were studied as a function of pressure. The pressure coefficient of Mn2+ emission was found to be –25.3±0.5 and –28.5±0.9meV/GPa for Zn2SiO4:Mn2+ and Zn2SiO4:Mn2+,Eu3+, respectively. The Eu3+ emission shows only weak pressure dependence. The pressure dependences of the Mn2+ and Eu3+ emissions in Zn2SiO4:Mn2+,Eu3+ are slightly different from that in Zn2SiO4:Mn2+ and Zn2SiO4:Eu3+ samples, which can be attributed to the co-doping of Mn2+ and Eu3+ ions. The Mn2+ emission in the two samples, however, exhibits analogous temperature dependence and similar luminescence lifetimes, indicating no energy transfer from Mn2+ to Eu3+ occurs. [Copyright &y& Elsevier]

Low temperature (10 K) strong anti-Stokes photoluminescence (ASPL) of ZnO microcrystal excited by low power cw 532 nm laser is reported here. Energy upconversion of 1.1 eV is obtained in our experiment with no conventional nonlinear effect. Through the study of the normal photoluminescence and temperature dependence of ASPL we conclude that the green band luminescence in ZnO is related to deep donor to valance band transition. Using the two-step two-photon absorption model, we provide a plausible mechanism leading to the ASPL phenomenon in our experiment. [ABSTRACT FROM AUTHOR]

Photoluminescence measurements for pure BaSnO3 are carried out at low temperatures and high magnetic fields, down to 4 K and up to 8 T, respectively. Multiple phonon replicas are observed in the near-infrared region, which allows for a quantitative estimation of the Huang-Rhys factor, . Due to the extremely narrow linewidth, a magnetic-field–induced nonlinear blueshift of the zero phonon line (ZPL) and a small increase of the phonon energy are clearly distinguishable. The magnetic-field dependence of the ZPL energies can be interpreted in terms of diamagnetic effects of the s-like local electronic state. The electron effective mass value of 0.14m0 is extracted from the best fitting. [ABSTRACT FROM AUTHOR]

• High-spatial-frequency LIPSS were constructed on carbon fibers by FLDW technology. • LIPSS dramatically change the surface wetting behavior of carbon fibers. • LIPSS make the carbon fiber support Pt nanoparticles in a hydrophilic environment. In this work, carbon fiber cloth is proposed by femtosecond laser direct writing technology (FLDWT) with different conditions. As consequence, series of laser-induced periodic surface structures (LIPSS) are constructed on the surface of carbon fiber cloth, and the hydrophobic property of carbon fiber cloth is changed dramatically, the contact angle of pristine carbon fiber cloth sharply decreases from 150.8° to 20.4°, which makes carbon fiber cloth successfully support platinum nanoparticles in a hydrophilic reaction environment. [ABSTRACT FROM AUTHOR]

We employ polarization-resolved femtosecond optical pump–probe spectroscopy to investigate the nonequilibrium photocarrier dynamics in excitonic insulator Ta2NiSe5. The electronic dynamics, including hot carrier cooling, exciton formation, and recombination in the timescale ranging from subpicoseconds to a few tens of picoseconds, have been established from the transient reflectivity spectra, showing strong in-plane anisotropy with respect to the probe polarization. Such anisotropic photocarrier dynamics possibly arise from the crystalline orientation dependence of the excitonic polarizability. Furthermore, we find that the amplitude of coherent phonons with a frequency of 1 THz is subject to the probe polarization, whereas it is not sensitive to the pump polarization. This substantiates that the displacive excitation of coherent phonons plays a decisive role in lattice dynamics. In addition, we find that the photo-induced dielectric screening tends to suppress the amplitude of coherent phonons with increasing pump fluence, manifesting a remarkable polarization dependence. Our work provides valuable insights into the excitonic dynamics and the origin of coherent phonon generation and also may contribute to the development of polarization-sensitive photoelectric devices based on Ta2NiSe5. [ABSTRACT FROM AUTHOR]

Abstract: A high order method for measuring urea concentrations in milk and milk powder was developed. The method can be applied to certify the concentration of urea in some new milk and milk powder CRMs. This high accurate method for analysis of milk is valuable given the inherent challenges associated with the complexity of the sample matrix. A measurement procedure based on gas chromatography/isotope dilution mass spectrometry (GC/IDMS) was developed. Samples were pre-treated with acetonitrile to remove proteins and the method was applied to determine urea concentrations in milk and milk powder. Excellent precision was obtained, with within- and between-set coefficients of variation of 0.15–0.46 and 0.18–0.65%, respectively. The measurement uncertainty is evaluated. The method can trace to mass. [Copyright &y& Elsevier]

The structure and photoluminscence (PL) properties of Pr-implanted GaN thin films have been studied. RBS/channeling technique was used to explore the damage recovery at high annealing temperature and study the dependence of the radiation damage with ion implantation direction. A complete recovery of the ion implantation damage cannot be achieved at annealing temperatures up to 1050°C. It is found that the channeling implantation results in the decrease of the damage. The PL experimental results indicate that the PL efficiency increases exponentially with annealing temperature up to the maximum temperature of 1050°C. Moreover, the PL intensity is also seriously affected by ion implantation geometries. The PL intensity for the sample implanted along channeled direction is nearly 2 times more intense than that observed from the sample implanted along random direction. The thermal quenching of PL intensity from 10 to 300 K for sample annealed at 1050°C is only 30%. [Copyright &y& Elsevier]

Two-dimensional layered bi-transition metal chalcogenides with exotic physical and optoelectronic properties are becoming attractive and promising candidates for next-generation electronics and optoelectronics. Herein, we report a representative of bi-transition metal sulfide, the strip-shaped CuTaS 3 crystal, analyzing its intrinsic electrical transport properties and potential optoelectronic applications by fabricating CuTaS 3 -based devices. The time-resolved Terahertz (THz) spectroscopy (TRTS) results indicate a rapid quenching of photoconductivity in CuTaS 3 bulk within 4.1 ps photoexcitation. PL measurement and CuTaS 3 -based field effect transistors (FETs) show a typical n-type semiconducting behavior with a small, direct bandgap of 1.24 eV. Density functional theory (DFT) calculations reveal charge transfers between different atoms and phonon dispersion relations to help understand the structural and vibrational properties of CuTaS 3. A CuTaS 3 -based-phototransistor was demonstrated with a responsivity of 7.6 mA W−1 and fast photoresponse time of 0.3–0.4 s, as well as excellent photoswitching stability. Our results may pave the way for developing other layered bi-transition metal chalcogenides and implementations in electronic and optoelectronic applications. • A representative bi-transition metal sulfide, strip-shaped CuTaS 3 crystal was presented and characterized. • DFT calculations were performed for electronic properties and phonon dispersion relations of CuTaS 3. • Investigation of intrinsic electrical transport properties and optoelectronic applications for first time • Finally, we got a responsivity of 7.6 mA W−1 and a fast photoresponse time of 0.3–0.4 s. [ABSTRACT FROM AUTHOR]