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Revealing the ultrafast dynamics of three-dimensional (3D) Dirac fermions upon photoexcitation is critical for both fundamental science and device applications. So far, how the cooling of 3D Dirac fermions differs from that of two-dimensional (2D) Dirac fermions and whether there is population inversion are fundamental questions that remain to be answered. Here we reveal the ultrafast dynamics of Dirac fermions in a model 3D Dirac semimetal Cd$_3$As$_2$ by ultrafast time- and angle-resolved photoemission spectroscopy (TrARPES) with a tunable probe photon energy from 5.3 - 6.9 eV. The energy- and momentum-resolved relaxation rate shows a linear dependence on the energy, suggesting Dirac fermion cooling through intraband relaxation. Moreover, a population inversion is reported based on the observation of accumulated photoexcited carriers in the conduction band with a lifetime of $\tau_n$ = 3.0 ps. Our work provides direct experimental evidence for a long-lived population inversion in a 3D Dirac semimetal, which is in contrast to 2D graphene where the interband relaxation occurs on a much faster timescale.

This paper proposes to integrate power fluctuation suppression and active filtering control into the centralized photovoltaic (PV) inverter based on superconducting magnetic energy storage (SMES). The superconducting coil (SC) is interfaced to the DC-link of the PV inverter through a DC/DC converter. The PV-SMES-based system performs the dual demands of transferring maximum power from PV array apart from suppressing power fluctuations and harmonics existing in microgrid. An improved sliding mode controller (SMC) was developed for the DC/DC converter to stabilize the DC-link voltage of PV inverter. The stability of the proposed controller is demonstrated using Lyapunov stability theory. The comprehensive performance of the PV-SMES-based system is verified through a series of simulation comparisons based on a lead-acid battery scheme.

Voltage stability is one of the critical factors for the stable operation of DC microgrids (MG). For the communication free DC MG, the DC voltage is more vulnerable due to the DC voltage deviation caused by the droop characteristics. When facing the transient power fluctuation caused by multiple electric vehicles (EVs) connected to the grid, PV shedding, etc., the DC bus will have a large voltage sag. The voltage quality degradation will bring adverse effects to the DC MG. However, most energy storage systems like battery energy storage systems (BESS) are not suitable for suppressing transient large power fluctuation. In this paper, the SMES is introduced to a DC MG to form a power regulation system. A voltage-based segmented (VBS) control is designed for the SMES-based power regulation system to suppress transient large power fluctuation in the DC MG. The voltage deviation caused by power distribution can be tolerant by VBS controlled SMES. Meanwhile, the dynamic recovery capability of the DC voltage is improved. The control method of SMES is independent of other devices in DC MGs, hence it is not dependent on communication. The control strategy of the SMES is further verified by simulation results.

MnBi$_8$Te$_{13}$ is an intrinsic ferromagnetic (FM) topological insulator with different complex surface terminations. Resolving the electronic structures of different termination surfaces and manipulation of the electronic state are important. Here, by using micrometer spot time- and angle-resolved photoemission spectroscopy ($\mu$-TrARPES), we resolve the electronic structures and reveal the ultrafast dynamics upon photoexcitation. Photoinduced filling of the surface state hybridization gap is observed for the Bi$_2$Te$_3$ quintuple layer directly above MnBi$_2$Te$_4$ accompanied by a nontrivial shift of the surface state, suggesting light-tunable interlayer interaction. Relaxation of photoexcited electrons and holes is observed within 1-2 ps. Our work reveals photoexcitation as a potential control knob for tailoring the interlayer interaction and surface state of MnBi$_8$Te$_{13}$.

Endoscopes are ubiquitous in minimally invasive or keyhole surgeries globally. However, frequent removal of endoscopes from the patient's body due to the lens contaminations results in undesirable consequences. Therefore, a cost-effective process chain to fabricate thermoplastic-based endoscope lenses with superior antifouling and optical properties is proposed in this research. Such multifunctional surface response was achieved by lubricant impregnation of nanostructures. Two types of topographies were produced by femtosecond laser processing of metallic molds, especially to produce single-tier laser-induced periodic surface structures (LIPSS) and two-tier multiscale structures (MS). Then, these two LIPSS and MS masters were used to replicate them onto two thermoplastic substrates, namely polycarbonate and cyclic olefin copolymer, by using hot embossing. Finally, the LIPSS and MS surfaces of the replicas were infiltrated by silicone oils to prepare lubricant-impregnated surfaces (LIS). Droplet sliding tests revealed that the durability of the as-prepared LIS improved with the increase of the lubricant viscosity. Moreover, the single-tier LIPSS replicas exhibited longer-lasting lubricant conservation properties than the MS ones. Also, LIPSS-LIS replicas demonstrated an excellent optical transparency, better than the MS-LIS ones, and almost match the performance of the reference polished ones. Furthermore, the LIPSS-LIS treatment led to superior antifouling characteristics, i.e., regarding fogging, blood adhesion, protein adsorption, and microalgae attachment, and thus demonstrated its high suitability for treating endoscopic lenses. Finally, a proof-of-concept LIPSS-LIS treatment of endoscope lenses was conducted that confirmed their superior multifunctional response.

Semiconductor photocatalysis technology is a promising method to solve the antibiotics pollution in water. Herein, a series of Sn-doped In2.77S4 (Sn-In2.77S4) hybrid photocatalysts for tetracycline degradation have been fabricated via a one-step hydrothermal process. The analytic results exhibit that doping Sn can improve the photocatalytic performance of In2.77S4 nanosheets under the visible light illumination and the doping amount obviously affects the photocatalytic performance of the samples. When the theoretical molar ratio of Sn4+ to In3+ is 0.04:1 (4%), the photocatalytic efficiency of the Sn-In2.77S4 photocatalyst exhibits the highest of 87.4% in comparison with 39.2% of pure In2.77S4 in 20 min. Moreover, its band gap energy has been reduced to 1.56 eV from 1.75 eV and the light absorption range has been broadened. The transfer rate and separation efficiency of photo-generated electron and hole pairs of the samples have also been enhanced. In addition, the holes play a leading role in the photocatalytic degradation process.

The AgBrO3/few-layer g-C3N4 composite photocatalyst has been developed via an in-situ synthetic method. The structure, morphology, light response range, separation and migration efficiency of the photogenerated electron–hole pairs and element valence state of the as-obtained samples have been characterized. The tetracycline was used to discuss the photocatalytic activities of the samples. The photocatalytic degradation mechanism of the as-obtained composites was also researched. The analysis results show that the photocatalytic degradation property of the asobtained composite photocatalyst appears to the tendency of first increasing and then decreasing with increasing the amount of AgBrO3 under visible light illumination. When the mass ratio of AgBrO3 to g-C3N4 is 4:3, in 60 min, the photocatalytic degradation efficiency of the as-obtained composites reaches the maximum of 79%. It is 37% and 45% higher than that of pure AgBrO3 and g-C3N4, respectively. Moreover, the separation and migration efficiency of the photogenerated electron–hole pairs of the as-prepared composites are also enhanced. In addition, superoxide radicals and holes are the dominant active species during the photocatalytic degradation process.

Quantum limit is quite easy to achieve once the band crossing exists exactly at the Fermi level ($E_F$) in topological semimetals. In multilayered Dirac fermion system, the density of Dirac fermions on the zeroth Landau levels (LLs) increases in proportion to the magnetic field, resulting in intriguing angle- and field-dependent interlayer tunneling conductivity near the quantum limit. BaGa$_2$ is an example of multilayered Dirac semimetal with anisotropic Dirac cone close to $E_F$, providing a good platform to study its interlayer transport properties. In this paper, we report the negative interlayer magnetoresistance (NIMR, I//c and B//c) induced by the tunneling of Dirac fermions on the zeroth LLs of neighbouring Ga layers in BaGa$_2$. When the field deviates from the c-axis, the interlayer resistivity $\rho_{zz}(\theta)$ increases and finally results in a peak with the field perpendicular to the c-axis. These unusual interlayer transport properties (NIMR and resistivity peak with B$\perp$c) are observed together for the first time in Dirac semimetal under ambient pressure and are well explained by the model of tunneling between Dirac fermions in the quantum limit., Comment: 12 pages, 8 figures, with supplementary materials

The synergistic anti-tumor effect of a typical chemotherapy drug, 5-fluorouracil, and a natural flavonoid compound, kaempferol, has been reported recently. However, the oral absorption of 5-fluorouracil is incomplete and nonuniform for different individuals due to fast metabolism and an obvious peak-valley phenomenon, while kaempferol has very poor solubility and this consequently leads to low oral bioavailability. The weakness of each drug greatly restricts the potential of anti-tumor drug combination in the clinical application. In this work, a new 1 : 1 drug–drug cocrystal of 5-fluorouracil and kaempferol was successfully prepared by liquid assisted grinding, slurry conversion crystallization and evaporation crystallization. A ternary phase diagram was constructed to gain some insights into the thermodynamics of the cocrystal system. The obtained cocrystal was comprehensively characterized by single crystal and powder X-ray diffraction, differential scanning calorimetry and thermogravimetric analysis, as well as Fourier transform infrared and nuclear magnetic resonance spectroscopy. The drug–drug cocrystal enhances the stability of kaempferol and optimizes the dissolution behavior of each single component as compared to pristine drugs. Therefore, the 5-fluorouracil–kaempferol cocrystal has the potential to be developed as efficient oral formulations for drug combination which will overcome the weaknesses of each parent drug.

The interplay between time-reversal symmetry (TRS) and band topology plays a crucial role in topological states of quantum matter. In time-reversal-invariant (TRI) systems, the inversion of spin-degenerate bands with opposite parity leads to nontrivial topological states, such as topological insulators and Dirac semimetals. When the TRS is broken, the exchange field induces spin splitting of the bands. The inversion of a pair of spin-splitting subbands can generate more exotic topological states, such as quantum anomalous Hall insulators and magnetic Weyl semimetals. So far, such topological phase transitions driven by the TRS breaking have not been visualized. In this work, using angle-resolved photoemission spectroscopy, we have demonstrated that the TRS breaking induces a band inversion of a pair of spin-splitting subbands at the TRI points of Brillouin zone in EuB$_6$, when a long-range ferromagnetic order is developed. The dramatic changes in the electronic structure result in a topological phase transition from a TRI ordinary insulator state to a TRS-broken topological semimetal (TSM) state. Remarkably, the magnetic TSM state has an ideal electronic structure, in which the band crossings are located at the Fermi level without any interference from other bands. Our findings not only reveal the topological phase transition driven by the TRS breaking, but also provide an excellent platform to explore novel physical behavior in the magnetic topological states of quantum matter., Comment: 22 pages, 7 figures, accepted by Phys. Rev. X

A dual-phase Mg-Li-Zn alloy was processed by a severe plastic deformation method which is a method of combination of extrusion and rolling processes and enables production of a very fine grain structure. After this processing, the Mg-Li-Zn alloy exhibited a significantly large fracture elongation of 1400% at 473 K at 0.001 s−1. Moreover, an elongation of more than 600% was observed at 473 K even at high strain rate of 0.01 s−1. Also, at a lower temperature of 423 K, the alloy exhibited a large fracture elongation of 720% at 0.001 s−1. The values of the strain rate sensitivity were approximated to 0.5, which suggested that the superplastic deformation is based on grain boundary sliding. Dislocation glide is identified to be an accommodation mechanism according to the texture evolution during the superplastic deformation. The different trends of the changes of the textures in the α and β phases indicated an inhomogeneity of grain boundary sliding between phases.

We investigate the magnetic transport properties and electronic structures of single crystal CoSi via angle-dependent quantum oscillation measurements. Prominent de Haas--van Alphen oscillations have been observed with the magnetic field tilting from $B\ensuremath{\parallel}[001]$ to $B\ensuremath{\parallel}[110]$, from which three fundamental frequencies are extracted. The low frequency ${F}_{\ensuremath{\alpha}}$, first observed in quantum oscillations, presents the contribution from the hole pocket at the Brillouin zone (BZ) center $\mathrm{\ensuremath{\Gamma}}$ point. Two high frequencies ${F}_{\ensuremath{\beta}}$ and ${F}_{\ensuremath{\gamma}}$, accompanied with asymmetrical peaks in the fast Fourier-transform spectra, are confirmed to stem from the electron pockets with spin-orbit coupling (SOC) at the BZ corner $R$ point. Combined with the analysis of first-principles calculations, the asymmetry of peaks originate from the SOC-induced band splitting when $B\ensuremath{\parallel}[110]$ and the irregular Fermi pockets when $B\ensuremath{\parallel}[001]$, respectively.

${\mathrm{TaAs}}_{2}$ and ${\mathrm{NbAs}}_{2}$ are members of the ${MPn}_{2}$ family with weak topological invariants of ${Z}_{2}$ = [0;111]. Here, we report the tip-induced superconductivity achieved on both materials using the point-contact technique. Although the weak ${Z}_{2}$ number leads to strongly crystal-orientation-dependent surface states, we observed a universal relationship between the zero-temperature upper critical field ${H}_{c2}(0)$ and the critical temperature ${T}_{c}$ for different crystal orientations. Combined with first-principles calculations, the findings here could identify a bulk band, instead of the much speculated surface bands, playing the dominant role in the induced superconductivity. These results predict a great possibility to realize superconductivity in other members of the ${MPn}_{2}$ family possessing similar band structures and provide clues to understand the mechanism of tip-induced superconductivity.

We report the magnetoresistance(MR), de Haas-van Alphen (dHvA) oscillations and the electronic structures of single crystal PtGa. The large unsaturated MR is observed with the magnetic field B//[111]. Evident dHvA oscillations with B//[001] configuration have been observed, from which twelve fundamental frequencies are extracted and the spin-orbit coupling effect (SOC) induced band splitting is revealed. The light cyclotron effective masses are extracted from the fitting by the thermal damping term of the Lifshitz-Kosevich (LK) formula. Combining with the calculated frequencies from the first-principles calculations, the dHvA frequencies F$_1$/F$_3$ and F$_{11}$/F$_{12}$ are confirmed to originate from the electron pockets at $\Gamma$ and R, respectively. The first-principles calculations also reveal the existence of spin-3/2 RSW fermion and time-reversal (TR) doubling of the spin-1 excitation at $\Gamma$ and R with large Chern number $\pm4$ when SOC is included., Comment: 5 pages, 4 figures

In materials chiral fermions such as Weyl fermions are characterized by nonzero chiral charges, which are singular points of Berry curvature in momentum space. Recently, new types of chiral fermions beyond Weyl fermions have been discovered in structurally chiral crystals CoSi, RhSi and PtAl. Here, we have synthesized RhSn single crystals, which have opposite structural chirality to the CoSi crystals we previously studied. Using angle-resolved photoemission spectroscopy, we show that the bulk electronic structures of RhSn are consistent with the band calculations and observe evident surface Fermi arcs and helical surface bands, confirming the existence of chiral fermions in RhSn. It is noteworthy that the helical surface bands of the RhSn and CoSi crystals have opposite handedness, meaning that the chiral fermions are reversed in the crystals of opposite structural chirality. Our discovery establishes a direct connection between chiral fermions in momentum space and chiral lattices in real space., Exotic chiral fermions beyond Weyl fermions have recently been discovered in a series of chiral crystals such as CoSi. Here, the authors report the evidences of chiral fermions in RhSn with opposite handedness compared to those observed in CoSi, where the structural chirality is also opposite.

To ensure the effective design and operation of high-temperature-superconducting (HTS) devices, the electromagnetic properties of HTS materials attract widespread attention. To date, the H-formulation and T-A formulation are two principal formulations applied to the finite element method to analyze the electromagnetic characteristics of HTS materials and devices. It is necessary to verify and to conduct a comparison of different effects of element order, mesh number along the width, and thickness expansion, with regard to calculation efficiency and accuracy under the H model and T-A model respectively. Compared to the H model, the T-A model with linear or quadratic element order can complete the calculation process more efficient having high accuracy and less time. The model with optimal parameters has been verified in a common case of a superconducting pancake coil. The optimal model of this work benefits to design or simulate HTS applications in building practical large-scale devices in terms of calculation efficiency and accuracy.

TiO2/reduced graphene oxide (rGO) nanocomposites were prepared via a facile one-step hydrothermal method using TiCl3 as the TiO2 precursor. Cetyltrimethyl ammonium bromide (CTAB) was introduced as a stabilizer for GO in solution. The effects of GO content, Ti3+ concentration and urea additive on phase constituent and morphology of the TiO2 crystallites in the nanocomposites were systematically investigated. UV–vis absorption ability of the as-made composites was further tested and discussed. Ag nanocrystals (NCs) were photocatalytically grown on the surfaces of biphasic (anatase + brookite) and triphasic (anatase + brookite + rutile) TiO2/rGO nanocomposites to evaluate their surface-enhanced Raman scattering (SERS) performances. Morphology evolution of the Ag NCs in response to different photocatalytic ability of the TiO2/rGO nanocomposite was also investigated in detail. The nanocomposite with triphasic TiO2 of proper phase constituents was confirmed to favor the growth of Ag particles of two distinctly different sizes and to produce SERS substrates of substantially better performance.

Extremely large magnetoresistance (XMR) has been explored in many nonmagnetic topologically nontrivial/trivial semimetals, while it is experimentally ambiguous which mechanism should be responsible in a specific material due to the complex electronic structures. In this paper, the magnetoresistance origin of single crystal CaAl4 with C2/m structure at low temperature is investigated, exhibiting unsaturated magnetoresistance of ∼ 3000% at 2.5 K and 14 T as the fingerprints of XMR materials. By the combination of ARPES and the first-principles calculations, we elaborate multiband features and anisotropic Fermi surfaces, which can explain the mismatch of isotropic two-band model. Although the structural phase transition from I4/mmm to C2/m has been recognized, the subtle impact on electronic structure is revealed by our ARPES measurements. Considering that both charge compensation and potential topologically nontrivial band structure exist in CaAl4, our findings report CaAl4 as a new reference material for exploring the XMR phenomena.

Dirac materials exhibit intriguing low-energy carrier dynamics that offer a fertile ground for novel physics discovery. Of particular interest is the interplay of Dirac carriers with other quantum phenomena such as magnetism. Here we report on a two-magnon Raman scattering study of AMnBi2 (A=Ca, Sr), a prototypical magnetic Dirac system comprising alternating Dirac carrier and magnetic layers. We present the first accurate determination of the exchange energies in these compounds and, by comparison with the reference compound BaMn2Bi2, we show that the Dirac carrier layers in AMnBi2 significantly enhance the exchange coupling between the magnetic layers, which in turn drives a charge-gap opening along the Dirac locus. Our findings break new grounds in unveiling the fundamental physics of magnetic Dirac materials, which offer a novel platform for probing a distinct type of spin–Fermion interaction. The results also hold great promise for applications in magnetic Dirac devices., The interplay between the low-energy carriers in Dirac materials and magnetism is likely to reveal many novel physical phenomena. Here, the authors use two-magnon Raman scattering to determine the exchange energies of two prototypical magnetic Dirac systems, CaMnBi2 and SrMnBi2.

We report the effects of cobalt doping on the magnetic properties of two-dimensional van der Waals ferromagnet Fe3GeTe2. Single crystals of (Fe{1-x}Cox)3GeTe2 with x=0-0.78 were successfully synthesized and characterized with x-ray diffraction, energy dispersive x-ray spectroscopy and magnetization measurements. Both the Curie-Weiss temperature and ferromagnetic (FM) ordered moment of Fe3GeTe2 are gradually suppressed upon Co doping. A kink in zero-field-cooling low field M(T) curve which is previously explained as an antiferromagnetic transition is observed for samples with x=0-0.58. Our detailed magnetization measurements and theoretical calculations strongly suggest that this kink is originated from the pinning of magnetic domain walls. The domain pinning effects are suddenly enhanced when the doping concentration of cobalt is around 50%, both the coercive field Hc and the magnetic remanence to saturated magnetization ratio MR/MS are largely improved and a hard magnetic phase emerges in bulk single crystal samples. The strong doping dependent magnetic properties suggest more spintronic applications of Fe3GeTe2., 6 pages, 4 figures, accepted by PRB

Van der Waals (vdW) layered materials have rather weaker interlayer bonding than the intra-layer bonding, therefore the exfoliation along the stacking direction enables the achievement of monolayer or few layers vdW materials with emerging novel physical properties and functionalities. The ferroelectricity in vdW materials recently attracts renewed interest for the potential use in high-density storage devices. As the thickness going thinner, the competition between the surface energy, depolarization field and interfacial chemical bonds may give rise to the modification of ferroelectricity and crystalline structure, which has limited investigations. In this work, combining the piezoresponse force microscope scanning, contact resonance imaging, we report the existence of the intrinsic in-plane polarization in vdW ferroelectrics CuInP2S6 (CIPS) single crystals, whereas below a critical thickness between 90-100 nm, the in-plane polarization disappears. The Young's modulus also shows an abrupt stiffness at the critical thickness. Based on the density functional theory calculations, we ascribe these behaviors to a structural phase transition from monoclinic to trigonal structure, which is further verified by transmission electron microscope technique. Taken together, these findings demonstrate the foundational importance of structural phase transition for enhancing the rich functionality and broad utility of vdW ferroelectrics.

We present experimental evidence of an intriguing phase transition between distinct topological states in the type-II Weyl semimetal MoTe2. We observe anomalies in the Raman phonon frequencies and linewidths as well as electronic quasielastic peaks around 70 K, which, together with structural, thermodynamic measurements, and electron-phonon coupling calculations, demonstrate a temperature-induced transition between two topological phases previously identified by contrasting spectroscopic measurements. An analysis of experimental data suggests electron-phonon coupling as the main driving mechanism for the change of key topological characters in the electronic structure of MoTe2.We also find the phase transition to be sensitive to sample conditions distinguished by synthesis methods. These discoveries of temperature and material condition-dependent topological phase evolutions and transitions in MoTe2 advance the fundamental understanding of the underlying physics and enable an effective approach to tuning Weyl semimetal states for technological applications., Comment: 6 pages, 4 figures

Adhesion of viscous liquids on packaging surfaces could lead to wastage, an increase of recycling costs, and even customers' dissatisfaction in applications related to food, cosmetics and agrochemical industries. Lubricant-impregnated surfaces (LIS) gained much attention recently over other surface functionalisation technologies due to their non-sticking response to highly viscous liquids. This work reports an investigation into anti-adhesive properties of LIS, with an emphasis on their durability. It provides an insight into the rationale design of LIS topographies in order to maximise their lubricant retention in potential food packaging applications. Femtosecond laser processing and hot embossing were employed to produce two types of topographies for LIS on stainless steel, polypropylene and polystyrene surfaces. The first type was single-scale sub-micron laser induced periodic surface structures (LIPSS), while the second one was multi-scale (MS) structures with both micron and sub-micron features. Droplet shedding characteristics of such LIPSS-LIS and MS-LIS substrates with water, milk and honey were examined under vibration and shear. The critical sliding angles at which liquid droplets attained motion on LIS were observed to be less than 32° for all investigated liquids. However, the LIPSS-LIS substrates retained their functionality even after subjecting them to severe vibration, while the MS-LIS substrates partially lost their anti-adhesive characteristics. At the same time, the MS-LIS substrates exhibited premature pinning of droplets as compared to LIPSS-LIS substrates, under shear forces. Both vibration- and shear-induced loss of lubricant impacted the MS-LIS functionality.

Conventionally, effective mechanical vibration energy harvesting is based on (Pb,Zr)TiO3 (PZT) ceramics, poly(vinylidene fluoride) (PVDF) polymers or PVDF/PZT or other piezoelectric composite materials, and their working temperature is normally limited to room temperature (R-T) or below 150 °C. Here, bismuth scandium lead titanate (BiScO3-PbTiO3, abbreviated as BSPT) ceramic is reported which has a high Curie temperature point around 450 °C and its application for high-temperature (H-T) vibration energy harvesting. Experimental results show that it exhibits an excellent H-T piezoelectricity, converting mechanical vibration energy into electric power effectively in a wide temperature range from R-T till 250 °C. This research shows the BSPT piezoelectric energy harvester having the potential application for self-power source of wireless sensor network system in high temperature circumstance.

The optical, thermal and electrical properties of ultra-thin two-dimensional (2D) crystal materials are highly related to their thickness. Therefore, identifying the atomic planes of few-layer crystal materials rapidly is crucial to fundamental study. Here, a simple technique was demonstrated based on optical contrast for counting atomic planes (n) of few-layer MoSe2 on SiO2/Si substrates. It is found that the optical contrast of single-layer MoSe2 depends on light wavelength and thickness of SiO2 on Si substrate. The data calculated based on a Fresnel law-based model as well as atomic force microscopy (AFM) measurements fit well with the values measured by spectroscopic ellipsometer. Furthermore, the calculated and measured contrasts were integral and plotted, which can be used to determine the MoSe2 atomic planes (1 ≤ n ≤ 4) accurately and rapidly. The optical contrast of thin-layer (1 ≤ n ≤ 4) MoSe2 sample was calculated by Fresnel’s law, and the contrast was measured by OM image. By combining these two group data, a function of layer numbers and contrast was developed: C (contrast) = 0.07N + 0.177. This proves that contrast is linear to layer numbers of MoSe2 when layer number is less than 4.

Iron-based superconductors have the second-highest superconducting transition temperature next to cuprate superconductors. There are many electronic phases such as superconducting, antiferromagnetic and nematic phases, coexisting in the family of iron pnictides. The charge/spin orders are the key factors for understanding the mechanism of high-temperature superconductivity. In this paper we have performed a Raman scattering study of parent compound BaFe2As2. A relatively strong electron–phonon coupling is observed for B1g phonon mode and is weakened after the structural transition at ∼140 K. Through a careful symmetry analysis, we revealed the possibility that B1g mode can be effectively coupled with dxz and dyz orbits. The coupling can remove the degeneracy of the two orbits and further cause the fluctuations of electronic nematic phases. The study suggests that electron–phonon coupling can be a possible origin of nematic phase.

This paper presents a study of the influence of gradient doping on solar cell performance. The gradient doping of the emitter layer of a a-Si:H(n)/a-Si:H(i)/c-Si(P) solar cell was simulated using the AFORS-Het software simulation package. Band structure adjustment due to gradient doping was studied. The adjustment manifests itself in two separate ways: the gradient quasi-Fermi level splitting (ΔeF) and the gradient band slope. The relationship between ΔeF and doping concentrations has been theoretically deduced and simulated using the AFORS-Het software package. The study shows that the ΔeF caused by gradient doping can improve the spectral response of the cell at long wavelengths and enhance the open circuit voltage. The steeper energy band caused by the higher doping gradient, G, promotes the effective separation of the carriers and reduces their recombination by 2–3 orders of magnitude compared to that of the uniform band. The photovoltaic conversion efficiency of the silicon heterojunction solar cell increases from 13.65% (uniform doping) to 20.86% for the gradient doping cell with the highest G and steepest energy band. This numerical simulation shows that the band structure adjustment caused by gradient doping can achieve higher utilization of solar energy and suppress the recombination of the carriers at the heterojunction interface. The study will guide practical preparation of future solar cells.

In this study, we prepared gold nanoparticles by electrochemical synthesis and inlaid in the photo-electrode of dye-sensitized solar cells (DSSCs) to study the surface plasma resonant (SPR) and light-scattering effects on the properties of dye-sensitized solar cells. The analyses of field emission scanning electron microscopy (FE-SEM) show that the average diameter of gold nanoparticles is 50nm. The results of ultraviolet-visible absorption spectra show that the absorption wavelength is about 533nm for gold nanoparticles. The conversion efficiency with different amounts of gold nanoparticles in TiO2 photo-electrodes is 5.42%, 5.92%, 6.06%, and 5.51% with the amounts of 0µL, 300µL, 400µL, and 500µL, respectively. The best conversion efficiency of the dye-sensitized solar cells with gold nanoparticles added is 6.06%, and is higher than that the cells without gold nanoparticles, which is 5.42%. In addition, in order to study light-scattering effects on the photo-electrode, different thicknesses of large particle size TiO2 (~250nm) coated onto photo-electrode to form double layer structure. The best conversion efficiency of the dye-sensitized solar cells with gold nanoparticles added and with the thickness of 3.3µm light scattering layer is 7.10%, which is higher than that of the cell without light-scattering layer, which is 6.06%. This result indicates that the effect of gold nanoparticles on the photo-electrode can increase the conductivity and reduce the recombination of charges in the photo-electrode, and the light-scattering structure can enhance light transmission path in TiO2 films and the absorption of photons in the photo-electrode, resulting in the increase of the photoelectric conversion efficiency for DSSCs. The addition of gold nanoparticles leads to a linear increase in conversion efficiency of the DSSC. When the volume of added gold nanoparticles is 500µL, the Jsc begins to decrease.Display Omitted The effect of gold nanoparticles can increase the conductivity and reduce the recombination of charges in the photo-electrode.The light-scattering structure can enhance light transmission path in TiO2 films and the absorption of photons.Gold nanoparticles result in the increase of the photoelectric conversion efficiency for DSSCs.

Bismuth layer-structured ferroelectric (BLSF) calcium bismuth titanate (CaBi 4 Ti 4 O 15 , CBT) piezoelectric ceramics with 0.0–1.0 wt.% cobalt oxide (Co 2 O 3 ) have been prepared via a conventional solid-state reaction method. Microstructural morphology and electrical properties of cobalt oxide-modified CBT ceramics were investigated in detail. X-ray powder diffraction (XRPD) analysis revealed that the cobalt oxide-modified CBT ceramics have a pure four-layer Aurivillius-type structure. The piezoelectric properties of CBT ceramics were significantly enhanced by cobalt oxide modifications. The piezoelectric coefficient d 33 and Curie temperature T c of 0.2 wt. % cobalt oxide-modified CBT ceramics (CBT-Co4) are 14 pC/N and 782 °C, respectively. The DC resistivity and thermal depoling behavior at elevated temperature indicated that the CBT-Co4 ceramics exhibit good thermal stability, demonstrating that the CBT-Co4 ceramics are potential materials for high temperature piezoelectric applications.

(0.98 − x)Bi(Sc3/4In1/4)O3–xPbTiO3–0.02Pb(Mg1/3Nb2/3)O3 (BSI–xPT–PMN, x = 0.56–0.60) ternary solid solutions near the morphotropic phase boundary (MPB) have been designed and prepared using the two-step columbite precursor method. Microstructural morphology, phase transition, and electrical properties of the BSI–xPT–PMN ceramics were investigated in detail. X-ray powder diffraction analysis indicated that the BSI–xPT–PMN ceramics were of pure perovskite phase, and the MPB between the rhombohedral and tetragonal phases located at x = 0.58, which are also confirmed by their compositional dependence piezoelectric and electromechanical properties. The piezoelectric properties were enhanced significantly by the introduction of a small amount of PMN, and the piezoelectric constant d 33 is doubled that of the binary Bi(Sc3/4In1/4)O3–PbTiO3 system. The optimal piezoelectric properties were obtained for the MPB composition 0.40BSI–0.58PT–0.02PMN, which exhibits a piezoelectric constant d 33 of 403 pC/N, planar electromechanical coupling factor k p of 47.2 %, remnant polarization P r of 36.4 µC/cm2, and Curie temperature T c of 421 °C. Additionally, the BSI–xPT–PMN systems reduce the content of Sc2O3 in comparison with the BS–PT systems. The enhanced piezoelectric performance, together with the good thermal stabilities, makes the BSI–xPT–PMN ceramics promising candidates for high temperature piezoelectric applications.

We report the doping effects of cobalt on van der Waals (vdW) magnet Fe$_5$GeTe$_2$. A series of (Fe$_{1-x}$Co$_x$)$_5$GeTe$_2$ (0$\leq$x$\leq$0.44) single crystals have been successfully grown, their structural, magnetic and transport properties are investigated. For x=0.20, The Curie temperature $T_C$ increases from 276~K to 337~K. Moreover, the magnetic easy-axis is reoriented to the $ab$-plane from the $c$-axis in undoped Fe$_5$GeTe$_2$ with largely enhanced magnetic anisotropy. These magnetic properties would make (Fe$_{0.8}$Co$_{0.2}$)$_5$GeTe$_2$ more effective in stabilizing magnetic order in the two-dimensional limit. A complex magnetic phase diagram is identified on the higher doping side. The x=0.44 crystal first orders ferromagnetically at $T_C$=363~K then undergoes an antiferromagnetic transition at $T_N$=335~K. Furthermore magnetic-field-induced spin-flop transitions are observed for the AFM ground state. Our work reveals (Fe$_{1-x}$Co$_x$)$_5$GeTe$_2$ as promising candidates for developing new spin-related applications and proposes a method to engineer the magnetic properties of vdW magnet., Comment: 5 pages, 5 figures

BaAgAs and its family materials MRPn (M = Ca, Sr, Ba, R = Ag, Au, Pn = As, Bi) were theoretically predicted to hold various topological phases. In this paper, the growth method of MRPn family materials was investigated and single crystals were successfully obtained by flux method. The crystal composition was confirmed by the energy dispersive X-ray spectroscopy (EDS). Crystal structure and surface planes were examined by X-ray diffraction (XRD). Temperature-dependent resistivity measurements from 2.5 K to 300 K reveal that all the samples are metallic.

We report the magnetotransport properties of HoSb, a semimetal with antiferromagnetic ground state. HoSb shows extremely large magnetoresistance (XMR) and Shubnikov-de Haas (SdH) oscillation at low temperature and high magnetic field. Different from previous reports in other rare earth monopnictides, kinks in $\rho(B)$ and $\rho_{xy}(B)$ curves and the field dependent resistivity plateau are observed in HoSb, which result from the magnetic phase transitions. The fast Fourier transform analysis of the SdH oscillation reveals the split of Fermi surfaces induced by the nonsymmetric spin-orbit interaction. The Berry phase extracted from SdH oscillation indicates the possible nontrivial electronic structure of HoSb in the presence of magnetic field. The Hall measurements suggest that the XMR originates from the electron-hole compensation and high mobility., Comment: 7 pages, 5 figures

We report the magneto-transport properties and the electronic structure of TmSb. TmSb exhibits extremely large transverse magnetoresistance and Shubnikov-de Haas (SdH) oscillation at low temperature and high magnetic field. Interestingly, the split of Fermi surfaces induced by the nonsymmetric spin-orbit interaction has been observed from SdH oscillation. The analysis of the angle-dependent SdH oscillation illustrates the contribution of each Fermi surface to the conductivity. The electronic structure revealed by angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations demonstrates a gap at $X$ point and the absence of band inversion. Combined with the trivial Berry phase extracted from SdH oscillation and the nearly equal concentrations of electron and hole from Hall measurements, it is suggested that TmSb is a topologically trivial semimetal and the observed XMR originates from the electron-hole compensation and high mobility., Comment: 6 pages, 5 figures

We report the magneto-transport properties and electronic structures of BaZnBi$_2$. BaZnBi$_2$ is a quasi-two-dimensional (2D) material with metallic behavior. The transverse magnetoresistance (MR) depends on magnetic field linearly and exhibits Shubnikov-de Haas (SdH) oscillation at low temperature and high field. The observed linear MR may originate from the disorder in samples or the edge conductivity in compensated two-component systems. The first-principles calculations reveal the absence of stable gapless Dirac fermion. Combining with the trivial Berry phase extracted from SdH oscillation, BaZnBi$_2$ is suggested to be a topologically trivial semimetal. Nearly compensated electron-like Fermi surfaces (FSs) and hole-like FSs coexist in BaZnBi$_2$., Comment: 6 pages, 6 figures

The cobalt-modified potassium bismuth titanate (K0.5Bi4.5Ti4O15, KBT) piezoelectric ceramics have been prepared using conventional solid–state reaction. X-ray diffraction analysis revealed that the cobalt-modified KBT ceramics have a pure four-layer (m = 4) Aurivillius-type structure. The dielectric, ferroelectric, and piezoelectric properties of cobalt-modified KBT ceramics were investigated in detail. The piezoelectric activities of KBT ceramics were significantly improved by the cobalt modification. The reasons for piezoelectric activities enhancement with cobalt modification were given. The piezoelectric coefficient d33 and Curie temperature Tc for the 5 mol% cobalt-modified KBT ceramics (KBT-Co5) were found to be 28 pC/N and 575 °C, respectively. The DC resistivity, frequency constants (Np and Nt), and electromechanical properties at elevated temperature were investigated, indicating the cobalt-modified KBT piezoelectric ceramics possess stable piezoelectric properties up to 500 °C. The results show the cobalt-modified KBT ceramics are potential materials for high temperature piezoelectric applications.

A graphene-based magnetic hybrid porous material was fabricated through a one-step solvothermal approach using graphene oxide and iron precursors, in which the reduction of the graphene oxide and the formation of the magnetic iron oxide nanoparticles proceeded simultaneously. Owing to the driving force of the chemisorption interaction, the graphene sheets and magnetic nanoparticles assembled into three-dimensional structures. The materials exhibit superparamagnetism (saturation magnetization: 0.1–20.3 emu g −1 ), and were characterized by X-ray diffraction, thermal gravimetric analysis, transmission electron microscopy, infrared spectra and Raman spectroscopy. Gas sorption analysis shows the as-prepared hybrid material has high porosity (BET specific surface area: 418–901 m 2 g −1 ), and the hydrogen uptake value ranges from 0.88 to 1.44 wt.%.

We have performed polarized and temperature-dependent Raman scattering measurements on extremely large magnetoresistance compounds ${\mathrm{TaAs}}_{2}$ and ${\mathrm{NbAs}}_{2}$. In both crystals, all the Raman active modes, including six ${A}_{g}$ modes and three ${B}_{g}$ modes, are clearly observed and well assigned with the combination of symmetry analysis and first-principles calculations. The well-resolved periodic intensity modulations of the observed modes with rotating crystal orientations verify the symmetry of each assigned mode and are fitted to experimentally determine the elements of Raman tensor matrices. The broadening of two ${A}_{g}$ modes seen in both compounds allows us to estimate the electron-phonon coupling constant, which suggests a relatively small electron-phonon coupling in the semimetals ${\mathrm{TaAs}}_{2}$ and ${\mathrm{NbAs}}_{2}$. The present study provides the fundamental lattice dynamics information on ${\mathrm{TaAs}}_{2}$ and ${\mathrm{NbAs}}_{2}$ and may shed light on the understanding of their extraordinary large magnetoresistance.

In topological insulators (TIs), metallic surface conductance saturates the insulating bulk resistance with de- creasing temperature, resulting in resistivity plateau at low temperatures as a transport signature originating from metallic surface modes protected by time reversal symmetry (TRS). Such characteristic has been found in several materials including Bi2Te2Se, SmB6 etc. Recently, similar behavior has been observed in metallic com- pound LaSb, accompanying an extremely large magetoresistance (XMR). Shubnikov-de Hass (SdH) oscillation at low temperatures further confirms the metallic behavior of plateau region under magnetic fields. LaSb[1] has been proposed by the authors as a possible topological semimetal (TSM), while negative magnetoresistance is absent at this moment. Here, high quality single crystals of NbAs2/TaAs2 with inversion symmetry have been grown and the resistivity under magnetic field is systematically investigated. Both of them exhibit metallic behavior under zero magnetic field, and a metal-to-insulator transition occurs when a nonzero magnetic field is applied, resulting in XMR (1.0*105% for NbAs2 and 7.3*105% for TaAs2 at 2.5 K & 14 T). With tempera- ture decreased, a resistivity plateau emerges after the insulator-like regime and SdH oscillation has also been observed in NbAs2 and TaAs2.

This paper presents an investigation on the ablation characteristics of excimer laser (λ = 248 nm, τ = 15 ns) and femtosecond laser (λ = 800 nm, τ = 100 fs) on ABS polymer sheets. The laser-material interaction parameters (ablation threshold, optical penetration depth and incubation factor) and the changes in material chemical properties were evaluated and compared between the two lasers. The work shows that the ablation threshold and effective optical penetration depth values are dependent on the wavelength of laser beam (photon energy) and the pulse width. The ablation threshold value is lower for the excimer laser ablation of ABS (Fth = 0.087 J/cm2) than that for the femtosecond laser ablation of ABS (Fth = 1.576 J/cm2), demonstrating a more dominating role of laser wavelength than the pulse width in influencing the ablation threshold. The ablation depth versus the logarithmic scale of laser fluence shows two linear regions for the fs laser ablation, not previously known for polymers. The effective optical penetration depth value is lower for excimer laser ablation (α-1 = 223 nm) than that for femtosecond laser ablation (α-1 = 2917 nm). The ablation threshold decreases with increasing number of pulses (NOP) due to the chain scission process that shortens the polymeric chains, resulting in a weaker polymeric configuration and the dependency is governed by the incubation factor. Excimer laser treatment of ABS eliminates the C=C bond completely through the chain scission process whereas C=C bond is partially eliminated through the femtosecond laser treatment due to the difference in photon energy of the two laser beams. A reduction in the C=C bond through the chain scission process creates free radical carbons which then form crosslinks with each other or react with oxygen, nitrogen and water in air producing oxygen-rich (C-O and C=O bond) and nitrogen-rich (C-N) functional groups.

YSb crystals are grown and the transport properties under magnetic field are measured. The resistivity exhibits metallic behavior under zero magnetic field and the low temperature resistivity shows a clear upturn once a moderate magnetic field is applied. The upturn is greatly enhanced by increasing magnetic field, finally resulting in a metal-to-insulator-like transition. With temperature further decreased, a resistivity plateau emerges after the insulator-like regime. At low temperature (2.5 K) and high field (14 T), the transverse magnetoresistance (MR) is quite large (3.47 $\times 10^4\%$ ). In addition, Shubnikov-de Haas (SdH) oscillation has also been observed in YSb. Periodic behavior of the oscillation amplitude reveals the related information about Fermi surface and two major oscillation frequencies can be obtained from the FFT spectra of the oscillations. The trivial Berry phase extracted from SdH oscillation, band structure revealed by angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations demonstrate that YSb is a topologically trivial material., Comment: 6 pages, 7 figures

Thermal conductivity of a model nanowire, composed of Zr–Ti–Cu–Ni–Be amorphous alloy, has been studied by computer simulations and theoretical calculations. The results from the molecular dynamics simulations are compared to predictions from Fourier continuum mechanics theory, and with published experimental data. Analysis of the theoretical phonon thermal conductivity follows the previously published incoherent particle model. The novelty of this study is in the employment of amorphous structure, lacking any order or superlattice. The simulated thermal conductivity is significantly lower than that measured by experiments on bulk alloy. It appears that amorphous structure and side-wall scattering reduce thermal diffusivity significantly. Velocity auto correlation time constant increases during heating cycle in proportion to the ratio of atomic weight divided by atomic scattering cross-sectional area.