To maximize the catalytic performance of MoS_(2) in the hydrogen evolution reaction,we investigate the electrocatalytic and photocatalytic performance of monolayer MoS_(2) doped with noble metal(Ag,Au,Cu,Pd,and Pt)usi...To maximize the catalytic performance of MoS_(2) in the hydrogen evolution reaction,we investigate the electrocatalytic and photocatalytic performance of monolayer MoS_(2) doped with noble metal(Ag,Au,Cu,Pd,and Pt)using first principles calculation combined with the climbing image nudged elastic band method.We find the band gap of the monolayer MoS_(2) is reduced significantly by the noble metal doping,which is unfavorable to improving its photocatalytic performance.The optical absorption coefficient shows that the doping does not increase the ability of the monolayer MoS_(2) to absorb visible light.The monolayer MoS_(2) doped with the noble metal is not a potential photocatalyst for the hydrogen evolution reaction because the band edge position of the conduction band minimum is lower than-4.44 eV,the reduction potential of H^(+)/H_(2).Fortunately,the band gap reduction increases the electron transport performance of the monolayer MoS_(2),and the activation energy of water splitting is greatly reduced by the noble metal doping,especially the Pt doping.On the whole,noble metal doping can enhance the electrocatalytic performance of the monolayer MoS_(2).展开更多
How to benefit the learners learning English as a foreign language(EFL)from the aspect of instructional design aroused the concerns of many teachers and researchers.The main purpose of this study is to address the que...How to benefit the learners learning English as a foreign language(EFL)from the aspect of instructional design aroused the concerns of many teachers and researchers.The main purpose of this study is to address the question of how teachers can design and implement EFL classroom that benefit the learners.Specifically,the“First Principles of Instruction,”advocated by Merrill(2002),was applied by the English teachers to conduct their day-to-day pedagogical practices.The corresponding effects of this theory in designing EFL classroom activities were reported in this study.Two research questions are formulated as follows:(1)Does the“First Principles of Instruction”benefit the EFL classroom designing in the aspect of student achievement?If yes,what is the effect?(2)How do the English teachers perceive the“First Principles of Instruction”to design EFL classroom?While observing the EFL classroom activities and interviewing the college English teachers,an empirical study was done to perceive how college English teachers could best apply these principles to design EFL classroom activities.展开更多
Boron carbide (B4C) is a rhombic structure composed of icosahedra and atomic chains, which has an important application in armored materials. The application of B4C under super high pressure without failure is a hot s...Boron carbide (B4C) is a rhombic structure composed of icosahedra and atomic chains, which has an important application in armored materials. The application of B4C under super high pressure without failure is a hot spot of research. Previous studies have unmasked the essential cause of B4C failure, i.e., its structure will change subjected to impact, especially under the non-hydrostatic pressure and shear stress. However, the change of structure has not been clearly understood nor accurately determined. Here in this paper, we propose several B4C polymorphs including B4C high pressure phases with non-icosahedra, which are denoted as post-B4C and their structures are formed due to icosahedra broken and may be obtained through high pressure and high temperature (HPHT). The research of their physical properties indicates that these B4C polymorphs have outstanding mechanical and electrical properties. For instance, aP10, mC10, mP20, and oP10-B4C are conductive superhard materials. We hope that our research will enrich the cognition of high pressure structural deformation of B4C and broaden the application scope of B4C.展开更多
In nanomaterials, optical anisotropies reveal a fundamental relationship between structural and optical properties, in which directional optical properties can be exploited to enhance the performance of optoelectronic...In nanomaterials, optical anisotropies reveal a fundamental relationship between structural and optical properties, in which directional optical properties can be exploited to enhance the performance of optoelectronic devices. First principles calculation based on density functional theory(DFT) with the generalized gradient approximation(GGA) are carried out to investigate the energy band gap structure on silicon(Si) and germanium(Ge) nanofilms. Simulation results show that the band gaps in Si(100) and Ge(111) nanofilms become the direct-gap structure in the thickness range less than 7.64 nm and7.25 nm respectively, but the band gaps of Si(111) and Ge(110) nanofilms still keep in an indirect-gap structure and are independent on film thickness, and the band gaps of Si(110) and Ge(100) nanofilms could be transferred into the direct-gap structure in nanofilms with smaller thickness. It is amazing that the band gaps of Si^((1-x)/2)Ge^xSi^((1-x)/2)sandwich structure become the direct-gap structure in a certain area whether(111) or(100) surface. The band structure change of Si and Ge thin films in three orientations is not the same and the physical mechanism is very interesting, where the changes of the band gaps on the Si and Ge nanofilms follow the quantum confinement effects.展开更多
An important challenge facing K-ion batteries lies in exploring earth-abundant and safe cathode materials that can provide high capacity with high migration rate of K ions.Here,we propose a simple and efficient method...An important challenge facing K-ion batteries lies in exploring earth-abundant and safe cathode materials that can provide high capacity with high migration rate of K ions.Here,we propose a simple and efficient method for searching potential K cathode materials with first principles calculations.Our screening is based on combinations of weight capacity,K ion occupation ratio,volume change per K,and valence limit.With this screening method we predicted a series of potential K ions cathodes with favorable electrochemical performance,such as K_(2)VPO_(4)CO_(3)-like structures with 1 D diffusion channels,3 D channel structures K_(2)CoSiO_(4),layered materials KCoO_(2),KCrO_(2),KVF_(4) and K_(5)V_(3)F_(14),and others.These potential cathodes have small volume changes,suitable voltage,and high capacity,with small diffusion barriers.They may be useful in K-ion batteries with high energy density and rate performance.展开更多
The intercalation of heteroatoms between graphene and metal substrates is a promising method for integrating epitaxial graphene with functional materials.Various elements and their oxides have been successfully interc...The intercalation of heteroatoms between graphene and metal substrates is a promising method for integrating epitaxial graphene with functional materials.Various elements and their oxides have been successfully intercalated into graphene/metal interfaces to form graphene-based heterostructures,showing potential applications in electronic devices.Here we theoretically investigate the hafnium intercalation between graphene and Ir(111).It is found that the penetration barrier of Hf atom is significantly large due to its large atomic radius,which suggests that hafnium intercalation should be carried out with low deposition doses of Hf atoms and high annealing temperatures.Our results show the different intercalation behaviors of a large-size atom and provide guidance for the integration of graphene and hafnium oxide in device applications.展开更多
Low dimensional materials are suitable candidates applying in next-generation high-performance electronic,optoelectronic,and energy storage devices because of their uniquely physical and chemical properties.In particu...Low dimensional materials are suitable candidates applying in next-generation high-performance electronic,optoelectronic,and energy storage devices because of their uniquely physical and chemical properties.In particular,one-dimensional(1D)atomic wires(AWs)exfoliating from 1D van der Waals(vdW)bulks are more promising in next generation nanometer(nm)even sub-nm device applications owing to their width of few-atoms scale and free dandling bonds states.Although several 1D AWs have been experimentally prepared,few 1D AW candidates could be practically applied in devices owing to lack of enough suitable 1D AWs.Herein,367 kinds of 1D AWs have been screened and the corresponding computational database including structures,electronic structures,magnetic states,and stabilities of these 1D AWs has been organized and established.Among these systems,unary and binary 1D AWs with relatively small exfoliation energy are thermodynamically stable and theoretically feasible to be exfoliated.More significantly,rich quantum states emerge,such as 1D semiconductors,1D metals,1D semimetals,and 1D magnetism.This database will offer an ideal platform to further explore exotic quantum states and exploit practical device applications using 1D materials.The database are openly available at http://www.dx.doi.org/10.11922/sciencedb.j00113.00004.展开更多
Recently,metal-graphene nanocomposite system has aroused much interest due to its radiation tolerance behavior.However,the related atomic mechanism for the metal-graphene interface is still unknown.Further,stainless s...Recently,metal-graphene nanocomposite system has aroused much interest due to its radiation tolerance behavior.However,the related atomic mechanism for the metal-graphene interface is still unknown.Further,stainless steels with Fe as main matrix are widely used in nuclear systems.Therefore,in this study,the atomic behaviors of point defects and helium(He) atoms at the Fe(110)-graphene interface are investigated systematically by first principles calculations.The results indicate that graphene interacts strongly with the Fe(110) substrate.In comparison with those of the original graphene and bulk Fe,the formation energy values of C vacancies and Fe point defects decrease significantly for Fe(110)-graphene.However,as He atoms have a high migration barrier and large binding energy at the interface,they are trapped at the interface once they enter into it.These theoretical results suggest that the Fe(110)-graphene interface acts as a strong sink that traps defects,suggesting the potential usage of steel-graphene with multiply interface structures for tolerating the radiation damage.展开更多
Based on the density functional theory,the energy band and electronic structure ofβ-CuGaO2 are calculated by the modified Becke-Johnson plus an on-site Coulomb U(MBJ+U)approach in this paper.The calculated results sh...Based on the density functional theory,the energy band and electronic structure ofβ-CuGaO2 are calculated by the modified Becke-Johnson plus an on-site Coulomb U(MBJ+U)approach in this paper.The calculated results show that the band gap value ofβ-CuGaO2 obtained by the MBJ+U approach is close to the experimental value.The calculated results of electronic structure indicate that the main properties of the material are determined by the bond between Cu-3 d and O-2p energy levels near the valence band ofβ-CuGaO2,while a weak anti-bond combination is formed mainly by the O-2p energy level and Ga-4 s energy level near the bottom of the conduction band ofβ-CuGaO2.Theβ-CuGaO2 thin film is predicted to hold excellent photovoltaic performance by analysis of the spectroscopic limited maximum efficiency(SLME)method.At the same time,the calculated maximum photoelectric conversion efficiency of the ideal CuGaO2 solar cell is 32.4%.Relevant conclusions can expandβ-CuGaO2 photovoltaic applications.展开更多
Sulfide nanocrystals and their composites have shown great potential in the thermoelectric(TE)field due to their extremely low thermal conductivity.Recently a solid and hollow metastable Au2S nanocrystalline has been ...Sulfide nanocrystals and their composites have shown great potential in the thermoelectric(TE)field due to their extremely low thermal conductivity.Recently a solid and hollow metastable Au2S nanocrystalline has been successfully synthesized.Herein,we study the TE properties of this bulk Au2S by first-principles calculations and semiclassical Boltzmann transport theory,which provides the basis for its further experimental studies.Our results indicate that the highly twofold degeneracy of the bands appears at theΓpoint in the Brillouin zone,resulting in a high Seebeck coefficient.Besides,Au2S exhibits an ultra-low lattice thermal conductivity(~0.88 W·m^-1·K^-1 at 700 K).At 700 K,the thermoelectric figure of merit of the optimal p-type doping is close to 1.76,which is higher than 0.8 of ZrSb at 700 K and 1.4 of PtTe at 750 K.Our work clearly demonstrates the advantages of Au2S as a TE material and would greatly inspire further experimental studies and verifications.展开更多
In order to have a better understanding of the electronic structures and physical properties of Cu<sub>2-<span style="white-space:nowrap;"><em>δ</em></span></sub>X (X = S...In order to have a better understanding of the electronic structures and physical properties of Cu<sub>2-<span style="white-space:nowrap;"><em>δ</em></span></sub>X (X = Se, S, Te) copper chalcogenides. First principles were performed to calculate the chemical shift, band structure, and electron density of states of Cu<span style="white-space:nowrap;"><sub>2-<em>δ</em></sub></span>X (X = Se, S, Te). By comparing our calculation results with previous experimental works, we found that the predicted electronic structures of Cu<sub>2</sub>Se, Cu<sub>2</sub>Te and Cu<sub>2</sub>S transform from semimetal to semiconductor after adding on-site Coulomb U, which reflects the real properties of the materials. By using (Density Functional Theory) DFT + U method, the calculation result is close to the real electronic structure. The calculation result of chemical shift of adding U does not reach the ideal expectation, and the reason is not clear at present. In this paper, the theoretical electronic structures of Cu<sub>2</sub>Se, Cu<sub>2</sub>Te and Cu<sub>2</sub>S are better calculated by DFT + U method and compared with the actual properties. The effect of Cu-s electron on the chemical shift is understood, and a theoretical result of the chemical shift is calculated, which provides a powerful reference for the subsequent research and understanding of the electronic structure and physical properties of the compounds with S groups of Cu.展开更多
Polymer composites as thermal interface materials have been widely used in modern electronic equipment.In this work,we report a novel method to prepare highly through-plane thermally conductive silicone rubber(SR)comp...Polymer composites as thermal interface materials have been widely used in modern electronic equipment.In this work,we report a novel method to prepare highly through-plane thermally conductive silicone rubber(SR)composites with vertically aligned silicon carbide fibers(VA-SiCFs)entangled by SiC nanowires(SiCNWs)networks.First,a series of carbon fibers(CFs)skeletons were fabricated in sequence of coating poor thermally conductive polyacrylonitrile-based CFs with polydopamine,icetemplated assembly,and freeze-drying processes.Furthermore,VA-SiCFs networks,i.e.,long-range continuous SiCFs-SiCNWs networks,based on the prepared CFs skeletons,were in-situ obtained via template-assisted chemical vapor deposition method.The thermal conductivity enhancement mechanism of VA-SiCFs networks on its SR composites was also intensively studied by finite element simulation,based on the first principles investigation of SiC,and Foygel’s theory.The in-situ grown VA-SiCFs networks possess high intrinsic thermal conductivity without the thermal interface between fillers,acting as the high-efficiency through-plane long-range continuous thermal conduction path,in which the SiCNWs were the in-plane“thermal spreader”.The VA-SiCFs/SR composites reached a high through-plane thermal conductivity,2.13 W/(m·K),at the filler loading of 15 vol.%,which is 868.2%,and 249.2%higher than that of pure SR sample,and random-CFs@polydopamine(PDA)/SR composites at the same content,respectively.The VA-SiCFs/SR composites also exhibited good electrical insulation performance and excellent dimensional stability,which guaranteed the stable interfacial heat transfer of high-power density electronic devices.展开更多
Carbon-doped titanium oxide(C/Ti-O)films were prepared on Si(100)wafer,stainless steel(type 304)and glass by reactive magnetron sputtering(RMS)using CO2 gas as carbon and oxygen source under room temperature(RT).X-ray...Carbon-doped titanium oxide(C/Ti-O)films were prepared on Si(100)wafer,stainless steel(type 304)and glass by reactive magnetron sputtering(RMS)using CO2 gas as carbon and oxygen source under room temperature(RT).X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)were used to analyze structure and composition of the as-prepared C/Ti-O film.It could be observed from XRD that the as-prepared C/Ti-O film contained TiO crystal phase structure.Ti2p XPS spectrum of the as-prepared C/Ti-O film showed that the valences of titanium were made up of Ti^(2+),Ti^(3+)and Ti^(4+).C1s XPS spectrum revealed that carbon was doped into titanium oxide based on the existence of the typical Ti-C bond.The optical absorption curve by ultraviolet-visible(UV-Vis)spectrophotometer showed that the C/Ti-O film appeared the remarkable red shift of absorption edge,which contributed to C substitution in O sites in amorphous TiO_(2).Photocatalysis test using methyl orange(MO)as indicator confirmed that the as-prepared C/Ti-O film had photocatalytic activity.Combined with the results of the tests and first-principles calculations,a potential photocatalysis mechanism was proposed.展开更多
We study the electronic properties of CuAlO2 doped with S by the first principles calculations and find that the band gap of CuAlO2 is reduced after the doping.At the same time,the effective masses are also reduced an...We study the electronic properties of CuAlO2 doped with S by the first principles calculations and find that the band gap of CuAlO2 is reduced after the doping.At the same time,the effective masses are also reduced and the density of states could cross the Fermi level.These results show that the conductivity of CuAlO2 could be enhanced by doping the impurities of S,which needs to be further studied.展开更多
The mechanical properties,thermodynamic properties and electronic structure of Mo1-xTax(Mo-Ta)alloys(x=0,0.0625,0.125,0.25,0.3125,0.5 and 1)were calculated by using firstprinciples.The electronic structure of Mo-Ta al...The mechanical properties,thermodynamic properties and electronic structure of Mo1-xTax(Mo-Ta)alloys(x=0,0.0625,0.125,0.25,0.3125,0.5 and 1)were calculated by using firstprinciples.The electronic structure of Mo-Ta alloys was analysed by the projected density of states(PDOS).The low temperature heat capacity was estimated by Fermi energy and Debye temperature.It is shown that the formation enthalpy will decrease with the increase of Ta content,and the cohesive energy will increase with the increase of the Ta content.On the other hand,the addition of Ta atoms will reduce the strength and improve the ductility of Mo-Ta alloys,the Debye temperature will decrease and the low temperature heat capacity will be improved with the increase of the Ta content.All these results will be useful for the research of new plasma grid(PG)materials,which is mainly used in neutral beam injection(NBI)systems to produce negative hydrogen ions.展开更多
Phase H(MgSiO_4H_2), one of the dense hydrous magnesium silicates(DHMSs), is supposed to be vital to transporting water into the lower mantle. Here the crystal structure, elasticity and Raman vibrational properties of...Phase H(MgSiO_4H_2), one of the dense hydrous magnesium silicates(DHMSs), is supposed to be vital to transporting water into the lower mantle. Here the crystal structure, elasticity and Raman vibrational properties of the two possible structures of phase H with Pm and P2/m symmetry under high pressures are evaluated by first-principles simulations. The cell parameters, elastic and Raman vibrational properties of the Pm symmetry become the same as the P2/m symmetry at～ 30 GPa. The symmetrization of hydrogen bonds of the Pm symmetry at ～ 30 GPa results in this structural transformation from Pm to P2/m. Seismic wave velocities of phase H are calculated in a range from 0 GPa to 100 GPa and the results testify the existence and stability of phase H in the lower mantle. The azimuthal anisotropies for phase H are A_(P0)= 14.7%,A_(S0)= 21.2%(P2/m symmetry) and A_(P0)= 16.4%, A_(S0)= 27.1%(Pm symmetry) at 0 GPa, and increase to A_(P30)= 17.9%,A_(S30)= 40.0%(P2/m symmetry) and A_(P30)= 19.2%, A_(S30)= 37.8%(Pm symmetry) at 30 GPa. The maximum V P direction for phase H is [101] and the minimum direction is [110]. The anisotropic results of seismic wave velocities imply that phase H might be a source of seismic anisotropy in the lower mantle. Furthermore, Raman vibrational modes are analyzed to figure out the effect of symmetrization of hydrogen bonds on Raman vibrational pattern and the dependence of Raman spectrum on pressure. Our results may lead to an in-depth understanding of the stability of phase H in the mantle.展开更多
Tin(Sn)isotope geochemistry has great potential in tracing geological processes.However,lack of equilibrium Sn isotope fractionation factors of various Sn species limits the development of Sn isotope geochemistry.Equi...Tin(Sn)isotope geochemistry has great potential in tracing geological processes.However,lack of equilibrium Sn isotope fractionation factors of various Sn species limits the development of Sn isotope geochemistry.Equilibrium Sn isotope fractionation factors(124Sn/116Sn and 122Sn/116Sn)among various Sn(II,IV)complexes in aqueous solution were calculated using first-principles calculations.The results show that the oxidation states and the change of Sn(II,IV)species in hydrothermal fluids are the main factors leading to tin isotope fractionation in hydrothermal systems.For the Sn(IV)complexes,Sn isotope fractionation factors depend on the number of H2O molecules.For the Sn(II)complexes,the Sn isotope fractionation between Sn(II)−F,Sn(II)−Cl and Sn(II)−OH complexes is mainly affected by the bond length and the coordination number of anion,whereas the difference in 1000lnβvalues of Sn(II)−SO4 and Sn(II)−CO_(3) complexes is insignificant with the change of anion coordination number.By comparing the 1000lnβvalues of all Sn(II,IV)complexes,the enrichment trend in heavy Sn isotopes is Sn(IV)complexes>Sn(II)complexes.The equilibrium Sn isotopic fractionation factors enhance our understanding of the tin transportation and enrichment processes in hydrothermal systems.展开更多
We review our efforts to develop and implement robust computational approaches for exploring phase stability to facilitate the prediction-to-synthesis process of novel functional oxides.These efforts focus on a synerg...We review our efforts to develop and implement robust computational approaches for exploring phase stability to facilitate the prediction-to-synthesis process of novel functional oxides.These efforts focus on a synergy between(i)electronic structure calculations for properties predictions,(ii)phenomenological/empirical methods for examining phase stability as related to both phase segregation and temperature-dependent transitions and(iii)experimental validation through synthesis and characterization.We illustrate this philosophy by examining an inaugural study that seeks to discover novel functional oxides with high piezoelectric responses.Our results show progress towards developing a framework through which solid solutions can be studied to predict materials with enhanced properties that can be synthesized and remain active under device relevant conditions.展开更多
Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coatin...Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coating materials.In this paper,we present a first-principles calculations of the phonon transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers.Both materials possess low lattice thermal conductivity,at least two orders of magnitude lower than graphene and h-BN.The room temperature thermal conductivity of Pb_(2)SbAs(0.91 W/m K)is only a quarter of that of Pb_(2)PAs(3.88 W/m K).We analyze in depth the bonding,lattice dynamics,and phonon mode level information of these materials.Ultimately,it is determined that the synergistic effect of low group velocity due to weak bonding and strong phonon anharmonicity is the fundamental cause of the intrinsic low thermal conductivity in these Janus structures.Relative regular residual analysis further indicates that the four-phonon processes are limited in Pb_(2)PAs and Pb_(2)SbAs,and the three-phonon scattering is sufficient to describe their anharmonicity.In this study,the thermal transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers are illuminated based on fundamental physical mechanisms,and the low lattice thermal conductivity endows them with the potential applications in the field of thermal barriers and thermoelectrics.展开更多
The electronic transport properties of armchair-edged boron nitride nanoribbons(ABNNRs) devices were investigated by the first principle calculations. The calculated results show that the ABNNR device doped with carbo...The electronic transport properties of armchair-edged boron nitride nanoribbons(ABNNRs) devices were investigated by the first principle calculations. The calculated results show that the ABNNR device doped with carbon atoms in one of the electrodes acts as a high performance nanoribbon rectifier. It is interesting to find that there exists a particular bias-polarity-dependent matching band between two electrodes,leading to a similar current-voltage(I-V) behavior as conventional P-N diodes. The I-V behavior presents a linear positive-bias I-V characteristic,an absolutely negligible leakage current,and a stable rectifying property under a large bias region. The results suggest that C doping might be an effective way to raise ABNNRs devices' rectifying performance.展开更多
基金the Joint Funds of the National Natural Science Foundation of China(Grant No.U1967212)the National Science and Technology Major Project of China(Grant No.2019XS06004009)the Fundamental Research Funds for the Central Universities(Grant No.2018ZD10).
文摘To maximize the catalytic performance of MoS_(2) in the hydrogen evolution reaction,we investigate the electrocatalytic and photocatalytic performance of monolayer MoS_(2) doped with noble metal(Ag,Au,Cu,Pd,and Pt)using first principles calculation combined with the climbing image nudged elastic band method.We find the band gap of the monolayer MoS_(2) is reduced significantly by the noble metal doping,which is unfavorable to improving its photocatalytic performance.The optical absorption coefficient shows that the doping does not increase the ability of the monolayer MoS_(2) to absorb visible light.The monolayer MoS_(2) doped with the noble metal is not a potential photocatalyst for the hydrogen evolution reaction because the band edge position of the conduction band minimum is lower than-4.44 eV,the reduction potential of H^(+)/H_(2).Fortunately,the band gap reduction increases the electron transport performance of the monolayer MoS_(2),and the activation energy of water splitting is greatly reduced by the noble metal doping,especially the Pt doping.On the whole,noble metal doping can enhance the electrocatalytic performance of the monolayer MoS_(2).
基金supported by two grants from Nanning University Teaching Research Foundation:The learner autonomy towards college English learning based on the flipped class teaching philosophy(2019XJJG05)Task-based college English teaching mode based on the flipped class teaching philosophy(2020XJJG06).
文摘How to benefit the learners learning English as a foreign language(EFL)from the aspect of instructional design aroused the concerns of many teachers and researchers.The main purpose of this study is to address the question of how teachers can design and implement EFL classroom that benefit the learners.Specifically,the“First Principles of Instruction,”advocated by Merrill(2002),was applied by the English teachers to conduct their day-to-day pedagogical practices.The corresponding effects of this theory in designing EFL classroom activities were reported in this study.Two research questions are formulated as follows:(1)Does the“First Principles of Instruction”benefit the EFL classroom designing in the aspect of student achievement?If yes,what is the effect?(2)How do the English teachers perceive the“First Principles of Instruction”to design EFL classroom?While observing the EFL classroom activities and interviewing the college English teachers,an empirical study was done to perceive how college English teachers could best apply these principles to design EFL classroom activities.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 51871114 and 12064013)the Natural Science Foundation of Jiangxi Province, China (Grant No. 20202BAB214010)+3 种基金the Research Foundation of the Education Department of Jiangxi Province, China (Grant Nos. GJJ180433 and GJJ180477)the Open Funds of the State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, China (Grant No. 201906)the Ganzhou Science and Technology Innovation Project, China (Grant No. 201960)the Jiangxi University of Science and Technology Scientific Research Starting Foundation, China (Grant No. jxxjbs17053).
文摘Boron carbide (B4C) is a rhombic structure composed of icosahedra and atomic chains, which has an important application in armored materials. The application of B4C under super high pressure without failure is a hot spot of research. Previous studies have unmasked the essential cause of B4C failure, i.e., its structure will change subjected to impact, especially under the non-hydrostatic pressure and shear stress. However, the change of structure has not been clearly understood nor accurately determined. Here in this paper, we propose several B4C polymorphs including B4C high pressure phases with non-icosahedra, which are denoted as post-B4C and their structures are formed due to icosahedra broken and may be obtained through high pressure and high temperature (HPHT). The research of their physical properties indicates that these B4C polymorphs have outstanding mechanical and electrical properties. For instance, aP10, mC10, mP20, and oP10-B4C are conductive superhard materials. We hope that our research will enrich the cognition of high pressure structural deformation of B4C and broaden the application scope of B4C.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11264007 and 61465003)
文摘In nanomaterials, optical anisotropies reveal a fundamental relationship between structural and optical properties, in which directional optical properties can be exploited to enhance the performance of optoelectronic devices. First principles calculation based on density functional theory(DFT) with the generalized gradient approximation(GGA) are carried out to investigate the energy band gap structure on silicon(Si) and germanium(Ge) nanofilms. Simulation results show that the band gaps in Si(100) and Ge(111) nanofilms become the direct-gap structure in the thickness range less than 7.64 nm and7.25 nm respectively, but the band gaps of Si(111) and Ge(110) nanofilms still keep in an indirect-gap structure and are independent on film thickness, and the band gaps of Si(110) and Ge(100) nanofilms could be transferred into the direct-gap structure in nanofilms with smaller thickness. It is amazing that the band gaps of Si^((1-x)/2)Ge^xSi^((1-x)/2)sandwich structure become the direct-gap structure in a certain area whether(111) or(100) surface. The band structure change of Si and Ge thin films in three orientations is not the same and the physical mechanism is very interesting, where the changes of the band gaps on the Si and Ge nanofilms follow the quantum confinement effects.
基金supported by the National Key R&D Program of China(Grant No.2016YFA0200400)the National Natural Science Foundation of China(Grant No.11504123 and No.51627805)。
文摘An important challenge facing K-ion batteries lies in exploring earth-abundant and safe cathode materials that can provide high capacity with high migration rate of K ions.Here,we propose a simple and efficient method for searching potential K cathode materials with first principles calculations.Our screening is based on combinations of weight capacity,K ion occupation ratio,volume change per K,and valence limit.With this screening method we predicted a series of potential K ions cathodes with favorable electrochemical performance,such as K_(2)VPO_(4)CO_(3)-like structures with 1 D diffusion channels,3 D channel structures K_(2)CoSiO_(4),layered materials KCoO_(2),KCrO_(2),KVF_(4) and K_(5)V_(3)F_(14),and others.These potential cathodes have small volume changes,suitable voltage,and high capacity,with small diffusion barriers.They may be useful in K-ion batteries with high energy density and rate performance.
基金Project supported by the National Natural Science Foundation of China(Grant No.61888102)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB30000000)the Fundamental Research Funds for the Central Universities,China。
文摘The intercalation of heteroatoms between graphene and metal substrates is a promising method for integrating epitaxial graphene with functional materials.Various elements and their oxides have been successfully intercalated into graphene/metal interfaces to form graphene-based heterostructures,showing potential applications in electronic devices.Here we theoretically investigate the hafnium intercalation between graphene and Ir(111).It is found that the penetration barrier of Hf atom is significantly large due to its large atomic radius,which suggests that hafnium intercalation should be carried out with low deposition doses of Hf atoms and high annealing temperatures.Our results show the different intercalation behaviors of a large-size atom and provide guidance for the integration of graphene and hafnium oxide in device applications.
基金the National Key Research and Development Program of China(Grant No.2017YFE0129000)the National Natural Science Foundation of China(Grant Nos.51871121,11874223,and 11404172).
文摘Low dimensional materials are suitable candidates applying in next-generation high-performance electronic,optoelectronic,and energy storage devices because of their uniquely physical and chemical properties.In particular,one-dimensional(1D)atomic wires(AWs)exfoliating from 1D van der Waals(vdW)bulks are more promising in next generation nanometer(nm)even sub-nm device applications owing to their width of few-atoms scale and free dandling bonds states.Although several 1D AWs have been experimentally prepared,few 1D AW candidates could be practically applied in devices owing to lack of enough suitable 1D AWs.Herein,367 kinds of 1D AWs have been screened and the corresponding computational database including structures,electronic structures,magnetic states,and stabilities of these 1D AWs has been organized and established.Among these systems,unary and binary 1D AWs with relatively small exfoliation energy are thermodynamically stable and theoretically feasible to be exfoliated.More significantly,rich quantum states emerge,such as 1D semiconductors,1D metals,1D semimetals,and 1D magnetism.This database will offer an ideal platform to further explore exotic quantum states and exploit practical device applications using 1D materials.The database are openly available at http://www.dx.doi.org/10.11922/sciencedb.j00113.00004.
基金Project supported by the Nuclear Power Technology Innovation Center ProgramNational Defense Science&Technology Industry,China(Grant No.HDLCXZX-2019-ZH-028)。
文摘Recently,metal-graphene nanocomposite system has aroused much interest due to its radiation tolerance behavior.However,the related atomic mechanism for the metal-graphene interface is still unknown.Further,stainless steels with Fe as main matrix are widely used in nuclear systems.Therefore,in this study,the atomic behaviors of point defects and helium(He) atoms at the Fe(110)-graphene interface are investigated systematically by first principles calculations.The results indicate that graphene interacts strongly with the Fe(110) substrate.In comparison with those of the original graphene and bulk Fe,the formation energy values of C vacancies and Fe point defects decrease significantly for Fe(110)-graphene.However,as He atoms have a high migration barrier and large binding energy at the interface,they are trapped at the interface once they enter into it.These theoretical results suggest that the Fe(110)-graphene interface acts as a strong sink that traps defects,suggesting the potential usage of steel-graphene with multiply interface structures for tolerating the radiation damage.
基金supported by the NSFC(Grant No.11547201)Natural Science Foundation of Guangdong Province,China(Grant No.2017A030307008)+1 种基金Natural Science Basic Research Program of Shaanxi(Program No.2019JQ-380)Natural Science Foundation of Guangdong Petrochemical University of Technology,China(Grant No.2017rc20)。
文摘Based on the density functional theory,the energy band and electronic structure ofβ-CuGaO2 are calculated by the modified Becke-Johnson plus an on-site Coulomb U(MBJ+U)approach in this paper.The calculated results show that the band gap value ofβ-CuGaO2 obtained by the MBJ+U approach is close to the experimental value.The calculated results of electronic structure indicate that the main properties of the material are determined by the bond between Cu-3 d and O-2p energy levels near the valence band ofβ-CuGaO2,while a weak anti-bond combination is formed mainly by the O-2p energy level and Ga-4 s energy level near the bottom of the conduction band ofβ-CuGaO2.Theβ-CuGaO2 thin film is predicted to hold excellent photovoltaic performance by analysis of the spectroscopic limited maximum efficiency(SLME)method.At the same time,the calculated maximum photoelectric conversion efficiency of the ideal CuGaO2 solar cell is 32.4%.Relevant conclusions can expandβ-CuGaO2 photovoltaic applications.
基金the National Natural Science Foundation of China(Grant Nos.11504312,11775102,and 11805088)the National Basic Research Program of China(Grant No.2015CB921103)+2 种基金China Postdoctoral Science Foundation(Grant No.2018M641477)Guangdong Provincial Department of Science and Technology,China(Grant No.2018A0303100013)the Fundamental Research Funds for the Central Universities,China(Lanzhou University,Grant No.lzujbky-2018-19).
文摘Sulfide nanocrystals and their composites have shown great potential in the thermoelectric(TE)field due to their extremely low thermal conductivity.Recently a solid and hollow metastable Au2S nanocrystalline has been successfully synthesized.Herein,we study the TE properties of this bulk Au2S by first-principles calculations and semiclassical Boltzmann transport theory,which provides the basis for its further experimental studies.Our results indicate that the highly twofold degeneracy of the bands appears at theΓpoint in the Brillouin zone,resulting in a high Seebeck coefficient.Besides,Au2S exhibits an ultra-low lattice thermal conductivity(~0.88 W·m^-1·K^-1 at 700 K).At 700 K,the thermoelectric figure of merit of the optimal p-type doping is close to 1.76,which is higher than 0.8 of ZrSb at 700 K and 1.4 of PtTe at 750 K.Our work clearly demonstrates the advantages of Au2S as a TE material and would greatly inspire further experimental studies and verifications.
文摘In order to have a better understanding of the electronic structures and physical properties of Cu<sub>2-<span style="white-space:nowrap;"><em>δ</em></span></sub>X (X = Se, S, Te) copper chalcogenides. First principles were performed to calculate the chemical shift, band structure, and electron density of states of Cu<span style="white-space:nowrap;"><sub>2-<em>δ</em></sub></span>X (X = Se, S, Te). By comparing our calculation results with previous experimental works, we found that the predicted electronic structures of Cu<sub>2</sub>Se, Cu<sub>2</sub>Te and Cu<sub>2</sub>S transform from semimetal to semiconductor after adding on-site Coulomb U, which reflects the real properties of the materials. By using (Density Functional Theory) DFT + U method, the calculation result is close to the real electronic structure. The calculation result of chemical shift of adding U does not reach the ideal expectation, and the reason is not clear at present. In this paper, the theoretical electronic structures of Cu<sub>2</sub>Se, Cu<sub>2</sub>Te and Cu<sub>2</sub>S are better calculated by DFT + U method and compared with the actual properties. The effect of Cu-s electron on the chemical shift is understood, and a theoretical result of the chemical shift is calculated, which provides a powerful reference for the subsequent research and understanding of the electronic structure and physical properties of the compounds with S groups of Cu.
基金The authors gratefully acknowledge the financial support of this work by the National Natural Science Foundation of China(Nos.21978240,52003219,and 52006057)Youth project of basic research program of Natural Science in Shaanxi Province(No.2020JQ-179)+5 种基金the Fundamental Research Funds for the Central Universities(Nos.3102018AX004,3102017jc01001,and 531119200237)Shenzhen Xuni University Lab Construction Funding(No.YFJGJS1.0,20191024213117281)Guangdong Province Key Field R&D Project(No.2020B010178001)the student innovation fund of Northwestern Polytechnical University(No.202110699234)the Open Testing Foundation of the Analytical&Testing Center of Northwestern Polytechnical University(No.2020T020)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX2022072).
文摘Polymer composites as thermal interface materials have been widely used in modern electronic equipment.In this work,we report a novel method to prepare highly through-plane thermally conductive silicone rubber(SR)composites with vertically aligned silicon carbide fibers(VA-SiCFs)entangled by SiC nanowires(SiCNWs)networks.First,a series of carbon fibers(CFs)skeletons were fabricated in sequence of coating poor thermally conductive polyacrylonitrile-based CFs with polydopamine,icetemplated assembly,and freeze-drying processes.Furthermore,VA-SiCFs networks,i.e.,long-range continuous SiCFs-SiCNWs networks,based on the prepared CFs skeletons,were in-situ obtained via template-assisted chemical vapor deposition method.The thermal conductivity enhancement mechanism of VA-SiCFs networks on its SR composites was also intensively studied by finite element simulation,based on the first principles investigation of SiC,and Foygel’s theory.The in-situ grown VA-SiCFs networks possess high intrinsic thermal conductivity without the thermal interface between fillers,acting as the high-efficiency through-plane long-range continuous thermal conduction path,in which the SiCNWs were the in-plane“thermal spreader”.The VA-SiCFs/SR composites reached a high through-plane thermal conductivity,2.13 W/(m·K),at the filler loading of 15 vol.%,which is 868.2%,and 249.2%higher than that of pure SR sample,and random-CFs@polydopamine(PDA)/SR composites at the same content,respectively.The VA-SiCFs/SR composites also exhibited good electrical insulation performance and excellent dimensional stability,which guaranteed the stable interfacial heat transfer of high-power density electronic devices.
基金supported by the National Natural Science Foundation of China(Nos.51062002 and 81171462)National Science Fund of Hainan Province(No.511113)Key Project of Science and Technology Planning of Hainan Province(No.ZDXM20110051).
文摘Carbon-doped titanium oxide(C/Ti-O)films were prepared on Si(100)wafer,stainless steel(type 304)and glass by reactive magnetron sputtering(RMS)using CO2 gas as carbon and oxygen source under room temperature(RT).X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)were used to analyze structure and composition of the as-prepared C/Ti-O film.It could be observed from XRD that the as-prepared C/Ti-O film contained TiO crystal phase structure.Ti2p XPS spectrum of the as-prepared C/Ti-O film showed that the valences of titanium were made up of Ti^(2+),Ti^(3+)and Ti^(4+).C1s XPS spectrum revealed that carbon was doped into titanium oxide based on the existence of the typical Ti-C bond.The optical absorption curve by ultraviolet-visible(UV-Vis)spectrophotometer showed that the C/Ti-O film appeared the remarkable red shift of absorption edge,which contributed to C substitution in O sites in amorphous TiO_(2).Photocatalysis test using methyl orange(MO)as indicator confirmed that the as-prepared C/Ti-O film had photocatalytic activity.Combined with the results of the tests and first-principles calculations,a potential photocatalysis mechanism was proposed.
基金supported by the National Laboratory of Solid State Microstructures (Grant No. 2010YJ07)
文摘We study the electronic properties of CuAlO2 doped with S by the first principles calculations and find that the band gap of CuAlO2 is reduced after the doping.At the same time,the effective masses are also reduced and the density of states could cross the Fermi level.These results show that the conductivity of CuAlO2 could be enhanced by doping the impurities of S,which needs to be further studied.
基金supported by National Natural Science Foundation of China(No.11820101004)the National Key R&D Program of China(2017YFE0300100,2017YFE0301100)。
文摘The mechanical properties,thermodynamic properties and electronic structure of Mo1-xTax(Mo-Ta)alloys(x=0,0.0625,0.125,0.25,0.3125,0.5 and 1)were calculated by using firstprinciples.The electronic structure of Mo-Ta alloys was analysed by the projected density of states(PDOS).The low temperature heat capacity was estimated by Fermi energy and Debye temperature.It is shown that the formation enthalpy will decrease with the increase of Ta content,and the cohesive energy will increase with the increase of the Ta content.On the other hand,the addition of Ta atoms will reduce the strength and improve the ductility of Mo-Ta alloys,the Debye temperature will decrease and the low temperature heat capacity will be improved with the increase of the Ta content.All these results will be useful for the research of new plasma grid(PG)materials,which is mainly used in neutral beam injection(NBI)systems to produce negative hydrogen ions.
基金supported by the Key Laboratory of Earthquake Prediction,Institute of Earthquake Science,China Earthquake Administration(CEA)(Grant Nos.2016IES010104 and 2012ES0408)the National Natural Science Foundation of China(Grant Nos.41174071,41273073,41373060,and 41573121)
文摘Phase H(MgSiO_4H_2), one of the dense hydrous magnesium silicates(DHMSs), is supposed to be vital to transporting water into the lower mantle. Here the crystal structure, elasticity and Raman vibrational properties of the two possible structures of phase H with Pm and P2/m symmetry under high pressures are evaluated by first-principles simulations. The cell parameters, elastic and Raman vibrational properties of the Pm symmetry become the same as the P2/m symmetry at～ 30 GPa. The symmetrization of hydrogen bonds of the Pm symmetry at ～ 30 GPa results in this structural transformation from Pm to P2/m. Seismic wave velocities of phase H are calculated in a range from 0 GPa to 100 GPa and the results testify the existence and stability of phase H in the lower mantle. The azimuthal anisotropies for phase H are A_(P0)= 14.7%,A_(S0)= 21.2%(P2/m symmetry) and A_(P0)= 16.4%, A_(S0)= 27.1%(Pm symmetry) at 0 GPa, and increase to A_(P30)= 17.9%,A_(S30)= 40.0%(P2/m symmetry) and A_(P30)= 19.2%, A_(S30)= 37.8%(Pm symmetry) at 30 GPa. The maximum V P direction for phase H is [101] and the minimum direction is [110]. The anisotropic results of seismic wave velocities imply that phase H might be a source of seismic anisotropy in the lower mantle. Furthermore, Raman vibrational modes are analyzed to figure out the effect of symmetrization of hydrogen bonds on Raman vibrational pattern and the dependence of Raman spectrum on pressure. Our results may lead to an in-depth understanding of the stability of phase H in the mantle.
基金supported financially by the National Natural Science Foundation of China(92062218,41822304).
文摘Tin(Sn)isotope geochemistry has great potential in tracing geological processes.However,lack of equilibrium Sn isotope fractionation factors of various Sn species limits the development of Sn isotope geochemistry.Equilibrium Sn isotope fractionation factors(124Sn/116Sn and 122Sn/116Sn)among various Sn(II,IV)complexes in aqueous solution were calculated using first-principles calculations.The results show that the oxidation states and the change of Sn(II,IV)species in hydrothermal fluids are the main factors leading to tin isotope fractionation in hydrothermal systems.For the Sn(IV)complexes,Sn isotope fractionation factors depend on the number of H2O molecules.For the Sn(II)complexes,the Sn isotope fractionation between Sn(II)−F,Sn(II)−Cl and Sn(II)−OH complexes is mainly affected by the bond length and the coordination number of anion,whereas the difference in 1000lnβvalues of Sn(II)−SO4 and Sn(II)−CO_(3) complexes is insignificant with the change of anion coordination number.By comparing the 1000lnβvalues of all Sn(II,IV)complexes,the enrichment trend in heavy Sn isotopes is Sn(IV)complexes>Sn(II)complexes.The equilibrium Sn isotopic fractionation factors enhance our understanding of the tin transportation and enrichment processes in hydrothermal systems.
基金the US Department of Energy(DOE),Office of Science,Basic Energy Sciences(BES),Materials Sciences and Engineering Division(VRC,JRM),and the Office of Science Early Career Research Program(VRC).SPB acknowledges support from the US National Science Foundation under Grant No.DMR-1037898CAB acknowledges support from the Laboratory Directed Research and Development program of Oak Ridge National Laboratory,managed by UT-Battelle,LLC,for the U.S.Department of Energy.This research used resources of the National Energy Research Scientific Computing Center,which is supported by the Office of Science of the US Department of Energy under Contract No.DE-AC02-05CH11231.
文摘We review our efforts to develop and implement robust computational approaches for exploring phase stability to facilitate the prediction-to-synthesis process of novel functional oxides.These efforts focus on a synergy between(i)electronic structure calculations for properties predictions,(ii)phenomenological/empirical methods for examining phase stability as related to both phase segregation and temperature-dependent transitions and(iii)experimental validation through synthesis and characterization.We illustrate this philosophy by examining an inaugural study that seeks to discover novel functional oxides with high piezoelectric responses.Our results show progress towards developing a framework through which solid solutions can be studied to predict materials with enhanced properties that can be synthesized and remain active under device relevant conditions.
基金Project supported by the Youth Science and Technology Talent Project of Hunan Province of China (Grant No.2022RC1197)the National Natural Science Foundation of China (Grant No.52372260)。
文摘Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coating materials.In this paper,we present a first-principles calculations of the phonon transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers.Both materials possess low lattice thermal conductivity,at least two orders of magnitude lower than graphene and h-BN.The room temperature thermal conductivity of Pb_(2)SbAs(0.91 W/m K)is only a quarter of that of Pb_(2)PAs(3.88 W/m K).We analyze in depth the bonding,lattice dynamics,and phonon mode level information of these materials.Ultimately,it is determined that the synergistic effect of low group velocity due to weak bonding and strong phonon anharmonicity is the fundamental cause of the intrinsic low thermal conductivity in these Janus structures.Relative regular residual analysis further indicates that the four-phonon processes are limited in Pb_(2)PAs and Pb_(2)SbAs,and the three-phonon scattering is sufficient to describe their anharmonicity.In this study,the thermal transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers are illuminated based on fundamental physical mechanisms,and the low lattice thermal conductivity endows them with the potential applications in the field of thermal barriers and thermoelectrics.
基金supported by the National Natural Science Foundation of China(21401023 and 21374017)Cultivating Fund for Excellent Young Scholar of Fujian Normal University(FJSDJK2012063)Program for Innovative Research Team in Science and Technology in Fujian Province University(IRTSTFJ)
文摘The electronic transport properties of armchair-edged boron nitride nanoribbons(ABNNRs) devices were investigated by the first principle calculations. The calculated results show that the ABNNR device doped with carbon atoms in one of the electrodes acts as a high performance nanoribbon rectifier. It is interesting to find that there exists a particular bias-polarity-dependent matching band between two electrodes,leading to a similar current-voltage(I-V) behavior as conventional P-N diodes. The I-V behavior presents a linear positive-bias I-V characteristic,an absolutely negligible leakage current,and a stable rectifying property under a large bias region. The results suggest that C doping might be an effective way to raise ABNNRs devices' rectifying performance.
