- 2355 Bonisteel Blvd.
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- My research focuses on computational materials physics, advanced materials mechanics, especially radiation effects us... moreMy research focuses on computational materials physics, advanced materials mechanics, especially radiation effects using multiscale, first-principles, and MD simulations. (http://qpeng.org)edit
Carbon nanotubes are outstanding reinforcements owing to their unparallel strength, while their effects on the copper nanowire are still not fully understood, hampering their broad applications. Herein, we have investigated the tensile... more
Carbon nanotubes are outstanding reinforcements owing to their unparallel strength, while their effects on the copper nanowire are still not fully understood, hampering their broad applications. Herein, we have investigated the tensile behaviors of the nanocomposite-wire of carbon nanotube-copper using molecular dynamic simulations. For the nanocomposite, both the coated and embedded carbon nanotubes increase the Young's modulus, fracture stress and toughness of the copper nanowire. A reinforcement of over fivefold in both yield strength (5.3 times) and toughness (5.1 times) has been achieved when the carbon nanotubes are coated on the copper nanowires, as well as 1.7 times in the Young's modulus. Higher temperatures and lower loading rates reduce the reinforcement. Supplementary material for this article is available online
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Graphyne was recently facilely synthesized with superior mechanical and electrical performance. We investigate the ballistic protection properties of a-, b-, d-, and g-graphyne sheets using molecular dynamics simulations in conjunction... more
Graphyne was recently facilely synthesized with superior mechanical and electrical performance. We investigate the ballistic protection properties of a-, b-, d-, and g-graphyne sheets using molecular dynamics simulations in conjunction with elastic theory. The velocities of the in-plane elastic wave and out-of-plane cone wave are obtained by both membrane theory and molecular dynamics simulations. The specific penetration energies are approximately 83% that of graphene, indicating high impact resistance. g-Graphyne has high sound wave speeds comparable to those of graphene, and its Young's modulus is approximately 60% that of graphene. d-Graphyne has the highest cone wave speed among the four structures, while a-graphyne possesses the highest penetration energy and impact resistance at most tested projectile speeds. Our results indicate that graphyne is a good protective structural material.
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Hydrogen plays a significant role in the microstructure evolution and macroscopic deformation of materials, causing swelling and surface blistering to reduce service life. In the present work, the atomistic mechanisms of hydrogen bubble... more
Hydrogen plays a significant role in the microstructure evolution and macroscopic deformation of materials, causing swelling and surface blistering to reduce service life. In the present work, the atomistic mechanisms of hydrogen bubble nucleation in vanadium were studied by first-principles calculations. The interstitial hydrogen atoms cannot form significant bound states with other hydrogen atoms in bulk vanadium, which explains the absence of hydrogen self-clustering from the experiments. To find the possible origin of hydrogen bubble in vanadium, we explored the minimum sizes of a vacancy cluster in vanadium for the formation of hydrogen molecule. We show that a freestanding hydrogen molecule can form and remain relatively stable in the center of a 54-hydrogen atom saturated 27-vacancy cluster.
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Chalcopyrite compounds are promising high efficient thermoelectric materials. However, the relatively high lattice thermal conductivity at modest temperatures limits their performance. Here, we investigate the lattice dynamics in a... more
Chalcopyrite compounds are promising high efficient thermoelectric materials. However, the relatively high lattice thermal conductivity at modest temperatures limits their performance. Here, we investigate the lattice dynamics in a polycrystalline CuInTe 2 with a combined experimental and computational approach. The phonon dispersion and density of states are computed using the density functional theory. Raman scattering is performed to investigate the phonon dynamical properties. Together with the bulk modulus from X-ray diffraction, the mode-Grüneisen parameters are determined. The low energy B 1 1 and E 2 modes characterize the weak anharmonicity, thus responsible for the high lattice thermal conductivity. Meanwhile, B 1 1 and E 2 modes display energy redshift under pressure. The softening and enhanced anharmonicity of these modes naturally result in the reduction of the thermal conductivity. Our study suggests that pressure is a routine to reduce the phonon heat conduction at modest temperatures in chalcopyrites.
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Spin polarized density functional theory computations were performed to elucidate electronic effects based on first-row transition metal doped Fe(100) and Fe 5 C 2 IJ100) surfaces for CO dissociation. Both Mn and Cr doped Fe(100) and Fe 5... more
Spin polarized density functional theory computations were performed to elucidate electronic effects based on first-row transition metal doped Fe(100) and Fe 5 C 2 IJ100) surfaces for CO dissociation. Both Mn and Cr doped Fe(100) and Fe 5 C 2 IJ100) surfaces can enhance the dissociation of CO, while the Co, Ni and Cu doped ones are unfavorable for the dissociation of CO. Besides the BEP relationship, a linear relationship between activation energy and the electronegativity of the dopant atom is established. It can be deduced that the metals with lower electronegativity are favorable for the activation of CO. The reason has been analyzed by density of states and crystal orbital Hamilton population. The metals with lower electronegativity relative to Fe could donate electrons to doped sites and then activate CO with a more delocalized O 2p orbital. The electronic effects revealed herein are helpful for the understanding of the CO activation process and for the design of catalysts with desired activity.
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Silicon carbide has excellent properties such as high hardness and decomposition temperature, but its applications are limited by its poor toughness. Here, we investigate the enhancement of SiC's toughness by compositing silicon... more
Silicon carbide has excellent properties such as high hardness and decomposition temperature, but its applications are limited by its poor toughness. Here, we investigate the enhancement of SiC's toughness by compositing silicon carbide-aluminum (SiC-Al) interpenetrating phase composites (IPCs) via molecular dynamics simulations. IPCs are a class of composites consisting of two or more phases that are topologically continuous and three-dimensionally interconnected through the microstructure. The Young's modulus and ultimate strength gradually increases with an increment of the volume fraction of SiC, opposite to the fracture strain. The interface between SiC and Al affects the mechanical properties of SiC-Al IPCs. When the volume fraction of SiC is less than 0.784, the attenuation rate of ultimate strength and fracture strain decreases. The attenuation rate increases when the volume fraction of SiC is more than 0.784. There are a minimum of ultimate strength and fracture strain at the 0.784, 0.7382 and 2.8610, respectively. The hardness of SiC-Al IPCs is about 48% of SiC. The change of SiC-Al IPCs hardness is more stable than that of SiC in the later stage of the nanoindentation test. Supplementary material for this article is available online
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The morphology change is crucial to the catalysis performance of catalyst nanoparticles in heterogeneous cat-alysis. Iron and iron carbide nanoparticles are used as high temperature heterogeneous catalyst, such as Fischer-Tropsch... more
The morphology change is crucial to the catalysis performance of catalyst nanoparticles in heterogeneous cat-alysis. Iron and iron carbide nanoparticles are used as high temperature heterogeneous catalyst, such as Fischer-Tropsch synthesis and carbon nanotube growth. Here we have investigated the effect of temperature and entropy on the surface free energy and morphology of the iron and iron carbide (θ-Fe 3 C, χ-Fe 5 C 2 , and o-Fe 7 C 3) nano-particles using molecular dynamics. The free energies of all the bulk and most of the surface systems drop following a parabolic curve with elevating temperature due to entropic effect. The nanoparticles are covered by low index surfaces at low temperature. At low temperature, the surface free energies of all surfaces usually decrease with a similar slope with increasing temperature. However, a critical temperature exists at which the high-index surfaces starts to dominate the catalyst particles. Fe 7 C 3 shows an unusual minimum surface free energy at 400 K in all the surfaces. This study provides fundamental insights into the modulation of iron-based nanocatalysts morphologies with desired catalytic performance.
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Surface feature and its variation along with complex atmosphere are of fundamental significance to understanding the functionality of applied materials especially in heterogeneous catalysis and corrosion prevention. Here we performed a... more
Surface feature and its variation along with complex atmosphere are of fundamental significance to understanding the functionality of applied materials especially in heterogeneous catalysis and corrosion prevention. Here we performed a unified theoretical study on the surface structure and morphology of iron borides and their evolution under dynamic gaseous conditions by combination of density functional theory, ab initio atomic thermodynamics and Wulff construction. In particular, thermodynamic stability of iron borides and corresponding surfaces varied from the boron chemical potential (μ Δ B) of certain atmosphere, which increases with decreasing pressure and increasing temperature and concentration of boron source. The stability of boron-rich surfaces has been improved with increasing μ Δ B , while all the Fe-rich facets of iron borides are favorable at low μ Δ B condition. Accordingly, the crystallite morphology of iron borides undergoes significant evolution upon dynamic condition. Finally, the surface properties of iron borides are carefully tested by CO adsorption which indicated the activation ability of CO is closely connected with boron triggered surface charge transfer between Fe and CO. This work was expected not only to help understand the surface structure and morphology of iron borides under realistic condition, but also provides fundamental insights into rational design of corrosion resistant and catalytic materials.
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Silicon carbide is one of the most important semiconductors with wide bandgaps and various applications including power electronics, nuclear fuel particles, hostile-environment electronics, and blue light emitting diodes. We investigate... more
Silicon carbide is one of the most important semiconductors with wide bandgaps and various applications including power electronics, nuclear fuel particles, hostile-environment electronics, and blue light emitting diodes. We investigate the nonlinear mechanical properties of a proposed graphene-like planar hexagonal silicon carbide (g-SiC) monolayer using first-principles calculations. The strength of g-SiC is about half that of graphene. The ultimate strain of g-SiC is 0.2, 0.25, and 0.19, in the direction of in armchair, zigzag, and biaxial, respectively. The Poisson's ratio is 1.75 times of that of graphene. In the nonlinear elasticity regime, we obtain the high order elastic constants up to fifth order. The stiffness monotonically increases with pressure, has the same trend as that of second order elastic constants but opposes to that of Poisson's ratio. There is a minimum at −4 GPa in the speed-pressure curve of compressive sound wave, different from the monotonic increment of shear waves. These theoretical mechanical properties provide elasticity limits for various applications of g-SiC.
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Despite outstanding and unique properties, the structure-property relationship of high entropy alloys (HEAs) is not well established. The machine learning (ML) is used to scrutinize the effect of nine physical quantities on four phases.... more
Despite outstanding and unique properties, the structure-property relationship of high entropy alloys (HEAs) is not well established. The machine learning (ML) is used to scrutinize the effect of nine physical quantities on four phases. The nine parameters include formation enthalpies determined by the extended Miedema theory, and mixing entropy. They are highly related to the phase formation, common ML methods cannot distinguish accurately. In this paper, feature selection and feature variable transformation based on Kernel Principal Component Analysis (KPCA) are proposed, the feature variables are optimized, the distinction of phases is carried out by Support vector machine (SVM) model. The results indicate that elastic energy and atom-size difference contribute significantly in the formation of different phases. The accuracy of testing set predicted by SVM based on four feature variables and KPCA (4V-KPCA) is 0.9743. The F1-scores predicted detailedly by SVM based on 4V-KPCA for the considered alloy phases are 0.9787, 0.9463, 0.9863 and 0.8103, corresponding to solid solution, amorphous, the mixture of solid solution and intermetallic, and intermetallic respectively. The extended Miedema theory provides accurate thermodynamic properties for the design of HEAs, and ML methods (especially SVM combined KPCA) are powerful in the prediction of alloy phases.
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Dual and triple ion beam irradiations were performed on alpha-Cr using 5 MeV Fe++, 2.9 MeV He++ and/or 270 keV H+ to study the synergy of hydrogen and helium on cavity formation. Results indicate that co-implantation of helium with iron... more
Dual and triple ion beam irradiations were performed on alpha-Cr using 5 MeV Fe++, 2.9 MeV He++ and/or 270 keV H+ to study the synergy of hydrogen and helium on cavity formation. Results indicate that co-implantation of helium with iron enhances cavity nucleation and co-implantation of hydrogen with iron augments cavity growth. Under triple beam irradiation, hydrogen also accelerates cavity nucleation via stabilizing initial embryos. First-principles calculations reveal that the presence of helium increases the maximum number of hydrogen atoms that can be captured by a vacancy from 6 to 9, providing an atomistic explanation to the triple beam synergy.
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High entropy alloy has attracted extensive attention in nuclear energy due to outstanding irradiation resistance, partially due to sluggish diffusion. The mechanism from a defect-generation perspective, however, has received much less... more
High entropy alloy has attracted extensive attention in nuclear energy due to outstanding irradiation resistance, partially due to sluggish diffusion. The mechanism from a defect-generation perspective, however, has received much less attention. In this paper, the formation of dislocation loops, and migration of interstitials and vacancies in CoNiCrFeMn high entropy alloy under consecutive bombardments were studied by molecular dynamics simulations. Compared to pure Ni, less defects were produced in the CoNiCrFeMn. Only a few small dislocation loops were observed, and the length of dislocation was small. The dislocation loops in Ni matrix were obviously longer and so was the length of dislocation. The interstitial clusters had much smaller mean free path during migration in the CoNiCrFeMn. The mean free path of 10-interstitial clusters in CoNiCrFeMn was reduced over 40 times compared to that in pure Ni. In addition, CoNiCrFeMn had a smaller difference of migration energy between interstitial and vacancy, which increased the opportunity of recombination of defects, therefore, led to less defects and much fewer dislocation loops. Our results provide insights into the mechanism of irradiation resistance in the high entropy alloy and could be useful in material design for irradiation tolerance and accident tolerance materials in nuclear energy. Supplementary material for this article is available online
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Elucidating the interactions between hydrogen and catalysts under complex realistic conditions is of great importance in rationally modulating the catalytic performance of hydrogenation processes. Herein, we have investigated the... more
Elucidating the interactions between hydrogen and catalysts under complex realistic conditions is of great importance in rationally modulating the catalytic performance of hydrogenation processes. Herein, we have investigated the interaction between hydrogen and four typical surfaces, (1 0 0), (2 1 0), (2 1 1), and (3 1 1) of pyrite FeS 2 through density functional theory calculations. On (2 1 0) surface, the hydrogen dissociative adsorption on unsaturated-coordination sulfur atoms is favorable both in thermodynamics and kinetics. The hydrogen activation barrier is 0.83 eV with slight exothermic of 0.12 eV on (3 1 1). While on (1 0 0) and (2 1 1) surface, the hydrogen dissociation is unfavorable due to the high activation barriers and remarkable positive reaction energies. For high adsorption coverage, the pure molecule adsorption mode is favorable on (1 0 0) facet, opposed to the other surfaces which have temperature and pressure dependence. The saturated coverage sequence is (1 0 0) > (2 1 0) > (2 1 1) > (3 1 1) for a wide range of temperature and pressure. The remove of sulfur atoms most likely occurs on (2 1 0) surface. Our atomistic insights might be useful in engineering hydrogen-involved processes catalyzed by iron sulfide.
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Amorphous solids in general exhibit a volume change during plastic deformation due to microstructure change during plastic relaxation. Here the deformation dilatancy of alkane polymer glasses upon shearing is investigated using molecular... more
Amorphous solids in general exhibit a volume change during plastic deformation due to microstructure change during plastic relaxation. Here the deformation dilatancy of alkane polymer glasses upon shearing is investigated using molecular static simulations at zero temperature and pressure. The dilatancy of linear alkane chains has been quantified as a function of strain and chain length. It is found that the system densities decrease linearly with respect to strain after yield point. In addition, dilatability decreases considerably with increasing chain length, suggesting enhanced cooperation of different deformation mechanisms. An analytic model is introduced for dilatability based on the atomistic study. The entanglement chain length is predicted as 43 for alkane polymers from the model, agreeing well with experiments. The study provides insights of correlations of the physical properties and chain length of polymers which might be useful in material design and applications of structural polymers.
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Carbon honeycomb has a nanoporous structure with good mechanical properties including strength. Here we investigate the adsorption and diffusion of hydrogen in carbon honeycomb via grand canonical Monte Carlo simulations and molecular... more
Carbon honeycomb has a nanoporous structure with good mechanical properties including strength. Here we investigate the adsorption and diffusion of hydrogen in carbon honeycomb via grand canonical Monte Carlo simulations and molecular dynamics simulations including strength. Based on the adsorption simulations, molecular dynamics simulations are employed to study the effect of pressure and temperature for the adsorption and diffusion of hydrogen. To study the effect of pressure, we select the 0.1, 1, 5, 10, 15, and 20 bars. Meanwhile, we have studied the hydrogen storage capacities of the carbon honeycomb at 77 K, 153 K, 193 K, 253 K and 298 K. A high hydrogen adsorption of 4.36 wt.% is achieved at 77 K and 20 bars. The excellent mechanical properties of carbon honeycomb and its unique three-dimensional honeycomb microporous structure provide a strong guarantee for its application in practical engineering fields.
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Graphene-reinforced nickel matrix nanocomposites with high-density interfaces are recommended as candidate materials for advanced nuclear reactors because of the potential irradiation tolerance. Nonetheless, the mechanism that graphene... more
Graphene-reinforced nickel matrix nanocomposites with high-density interfaces are recommended as candidate materials for advanced nuclear reactors because of the potential irradiation tolerance. Nonetheless, the mechanism that graphene damage due to irradiation affects the tolerance of the composites remains unclear. Here we report the relationships between irradiation damage behavior of graphene and defect sink efficiency of nickel–graphene interface by using atomistic simulations. With the accumulation of irradiation dose, a nickel–graphene interface exhibits enhanced trapping ability to defects despite the gradually deteriorative damage of graphene. The enhancement originates in that the damaged regions of graphene can provide abundant recombination and/or annihilation sites for irradiation defects and strengthen the energetic and kinetic driving forces of the interface to defects. This study reveals a new possible interface-mediated damage healing mechanism of irradiated materials.
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Due to outstanding electric conductance, copper is widely used as wires in electricity and as interconnects in microchips, where the thermal conductivity could be enhanced by compositing with carbon nanotubes (CNTs). Here, we have... more
Due to outstanding electric conductance, copper is widely used as wires in electricity and as interconnects in microchips, where the thermal conductivity could be enhanced by compositing with carbon nanotubes (CNTs). Here, we have numerically designed a class of sandwich-like CNT/Cu/CNT nanotubes which possess high thermal conductivity revealed by molecular dynamics simulations. The enhancement factor of thermal conductivity of the composite using single-walled CNT is 37.5 times of that of a 5-nm-radius copper nanowire. The enhancement factor is further enlarged to 58.2 using triple-walled CNT in the outer side. The atomic stress analysis manifests that the thermal stresses are concentrated in the region around the CNT/Cu interface. The stabilities and larger enhancement factors at high temperatures imply high temperature applications of these CNT-sandwiched tubular copper nanocomposites in heat management and electronics.
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Ultra-thin and continuous metallic silver films are attracting growing interest due to the applications in flexible transparent conducting electrodes. The surface morphology and structure of silver film are very important for its... more
Ultra-thin and continuous metallic silver films are attracting growing interest due to the applications in flexible transparent conducting electrodes. The surface morphology and structure of silver film are very important for its electrical resistivity and optical loss. Therefore, roughness control is essential for the production of ultra-thin metallic electrode film. We have investigated the effect of aluminum doping on the improvement of surface morphology of ultra-thin silver films using molecular dynamics simulations. Al-doped silver films showed smaller surface roughness than pure silver films at various substrate temperatures. When the temperature of the substrate was 600 K, the roughness of Al-doped silver film first decreased, and then increased with the increase of the incident velocity of silver atoms. Silver atoms were more likely to agglomerate on the surface of the substrate after adding aluminum atoms, as aluminum dopants promoted the immobilization of silver atoms on SiO2 substrate due to the anchoring effect. The smoother surface could be attributable to the reduced mean free path of silver due to the cage effect by the aluminum dopant.
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Various types of topological defects are produced during proton irradiation, which are crucial in functiona-lizing graphene, but the mechanisms of the defect generation process and the structure change are still elusive. Herein, we... more
Various types of topological defects are produced during proton irradiation, which are crucial in functiona-lizing graphene, but the mechanisms of the defect generation process and the structure change are still elusive. Herein, we investigated the graphene defect generation probabilities and defect structures under proton irradiation using both ab initio and classical molecular dynamics simulations. As the proton energy increases from 0.1 keV to 100 keV, defect structures transition from single vacancy and Frenkel pairs to a rich variety of topological defects with the possibility of ejecting multiple atoms. We show that, relatively good agreement on defect generation probabilities can be reached between the two simulation approaches at a proton energy of 1 and 10 keV. However, at 0.1 keV, the single vacancy generation probability differs significantly in two methods due to the difference in the energy required to form single vacancy. Using the classical molecular dynamics simulation, we also studied the evolution of different types of defects and the dependence of their probabilities of occurrence on the proton energy and incident angle. The correlation between the impact positions and defect types allows for the convoluted relationship between the defect probabilities, geometric parameters, and proton energy to be elucidated. We show that the proton energy and incident angle can be used to effectively tune the generation probabilities of different types of defects. Our results provide insights into the controlled defect engineering through ion irradiation, which will be useful for the development of functionalized graphene and graphene electronics.
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The lattice diffusion of silver with various charge states in cubic silicon carbide has been investigated by means of high-fidelity spin-polarized density functional theory calculations. The migration energy barrier of the Ag interstitial... more
The lattice diffusion of silver with various charge states in cubic silicon carbide has been investigated by means of high-fidelity spin-polarized density functional theory calculations. The migration energy barrier of the Ag interstitial diffusion is 1.09 eV and 1.11 eV for neutral and = + q e 1 charge state, respectively, close to the activation energy of Ag diffusion measured in the German HTR fuel program. A general trend is that the migration energy barrier reduces with respect to the increase of charge on Ag, which is much less than the increment in the oxidation energy, suggesting that the lattice diffusion of silver prefers constant neutral state without redox in transition state. Our results indicate a scenario that once Ag is deposited to interstitials via the kickout mechanism , it will highly likely perform lattice diffusion across the SiC layer leading to fast release of Ag in Tristructural-Isotropic fuel induced by irradiation.
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We have investigated the structural, mechanical, electronic, and thermodynamic properties of AlFe 2 B 2 , FeB, AlB 2 and Al 2 Fe using first-principles calculations. The elastic constants imply the elastic stabilities of these structures.... more
We have investigated the structural, mechanical, electronic, and thermodynamic properties of AlFe 2 B 2 , FeB, AlB 2 and Al 2 Fe using first-principles calculations. The elastic constants imply the elastic stabilities of these structures. The elastic anisotropy has been depicted by three-dimensional iso-surface of Young's modulus. The electronic densities of states show that the Fed , Al-p and B-p states are hybridized at Fermi level. The phonon dispersion spectra manifest their dynamical stabilities. Furthermore, the free energy suggests the stabilities of these structures in finite temperature range 0-1500 K. Our results suggest the feasibility of the fabrication approach of AlB 2 + 8FeB + 2Al 2 Fe → 5AlFe 2 B 2. Our study provides insights on structure stabilities and might be helpful in the material design and fabrication of Al-Fe-B compounds.
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The radiation resistance mechanisms of nanoclusters (NCs) in oxide dispersion-strengthened (ODS) steels have been investigated. Molecular dynamics simulation has been used to investigate defect generation during the primary damage state... more
The radiation resistance mechanisms of nanoclusters (NCs) in oxide dispersion-strengthened (ODS) steels have been investigated.
Molecular dynamics simulation has been used to investigate defect generation during the primary damage state of a displacement cascade in
ODS steels for NCs of various radii and a range of primary knock-on atom (PKA) energies. Y2O3 NCs considerably enhance the radiation
resistance of ODS steels by reducing the peak defect generation during the cascade within the Fe matrix. The NC also affects the morphology
of the collision cascades, depending on PKA energy. At lower energies, the NC’s outer circumference act as a cessation point forming a
dampened shockwave compared to a pure Fe system. At higher energies, the PKA energy is able to transfer through the NC, thus causing
two smaller shockwaves in the Fe matrix. Along with the alteration of the cascade morphology, the NC boundary acts as a strong defect
sink to absorb defects and defect clusters, leading to significant recombination of interstitials and vacancies away from the NC. The interfacial
energy of the NCs with the Fe matrix increases with increasing diameter of the oxide NCs. The evolution of the NC is tracked through
the primary damage state of a cascade, and the effects of ballistic dissolution play a key role in this evolution, most evident in the 2 nm NC.
Molecular dynamics simulation has been used to investigate defect generation during the primary damage state of a displacement cascade in
ODS steels for NCs of various radii and a range of primary knock-on atom (PKA) energies. Y2O3 NCs considerably enhance the radiation
resistance of ODS steels by reducing the peak defect generation during the cascade within the Fe matrix. The NC also affects the morphology
of the collision cascades, depending on PKA energy. At lower energies, the NC’s outer circumference act as a cessation point forming a
dampened shockwave compared to a pure Fe system. At higher energies, the PKA energy is able to transfer through the NC, thus causing
two smaller shockwaves in the Fe matrix. Along with the alteration of the cascade morphology, the NC boundary acts as a strong defect
sink to absorb defects and defect clusters, leading to significant recombination of interstitials and vacancies away from the NC. The interfacial
energy of the NCs with the Fe matrix increases with increasing diameter of the oxide NCs. The evolution of the NC is tracked through
the primary damage state of a cascade, and the effects of ballistic dissolution play a key role in this evolution, most evident in the 2 nm NC.
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Medium entropy alloy NiCoCr draws great attention due to its excellent strength-ductility trade-off mechanical behavior. Its irradiation behavior at elevated temperatures has been investigated using ion beam irradiation in a temperature... more
Medium entropy alloy NiCoCr draws great attention due to its excellent strength-ductility trade-off mechanical behavior. Its irradiation behavior at elevated temperatures has been investigated using ion beam irradiation in a temperature range of 420e580 Cand transmission electron microscopy. Irradiation induced stacking fault tetrahedra were only observed at 420 C. With increasing irradiation temperature, all stacking fault tetrahedra vanished, while the size of voids and dislocation loops increased significantly. Nanoindentation-induced structural complexities, including dislocations, stacking faults and twins helped to reduce void swelling. However, at the elevated temperatures, NiCoCr is still much more susceptible to void swelling compared to high entropy alloys such as NiCoFeCrMn and NiCoFeCrPd. Published by Elsevier B.V.
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The structure-activity relationship is crucial in catalytic performance and material design but still largely obscure due to the complexity of heterogeneous catalytic systems. CO activation occurs widely in Fischer-Tropsch reactions and... more
The structure-activity relationship is crucial in catalytic performance and material design but still largely obscure due to the complexity of heterogeneous catalytic systems. CO activation occurs widely in Fischer-Tropsch reactions and pyrometallurgy, and it is a key to understanding carburization. Here, we investigate the structure-activity relationship in Fe nanoparticles by reactive molecular dynamics simulations. We focus on two activities, the adsorption and dissociation of CO, and four structural characteristics , morphologies, sizes, defects, and heteroatoms. The results show that CO adsorption and dissociation varies with the change of nanoparticles. Line dislocation and vacancies can strikingly boost CO dissociation, suggesting an effective way to tune the CO dissociation rate. Further analysis shows that the Eley-Rideal mechanism possibly works in the early periods, followed by the Langmuir-Hinshelwood mechanism in the later periods for CO 2 formation. Our results shed light on the mechanism and possible optimization of the carburization of iron.
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Boron nitride honeycomb structure is a new three-dimensional material similar to carbon honeycomb, which has attracted a great deal of attention due to its special structure and properties. In this paper, the tensile mechanical properties... more
Boron nitride honeycomb structure is a new three-dimensional material similar to carbon honeycomb, which has attracted a great deal of attention due to its special structure and properties. In this paper, the tensile mechanical properties of boron nitride honeycomb structures in the zigzag, armchair and axial directions are studied at room temperature by using molecular dynamics simulations. Effects of temperature and strain rate on mechanical properties are also discussed. According to the observed tensile mechanical properties, the piezoelectric effect in the zigzag direction was analyzed for boron nitride honeycomb structures. The obtained results showed that the failure strains of boron nitride honeycomb structures under tensile loading were up to 0.83, 0.78 and 0.55 in the armchair, zigzag and axial directions, respectively, at room temperature. These findings indicated that boron nitride honeycomb structures have excellent ductility at room temperature. Moreover, temperature had a significant effect on the mechanical and tensile mechanical properties of boron nitride honeycomb structures, which can be improved by lowering the temperature within a certain range. In addition, strain rate affected the maximum tensile strength and failure strain of boron nitride honeycomb structures. Furthermore, due to the unique polarization of boron nitride honeycomb structures, they possessed an excellent piezoelectric effect. The piezoelectric coefficient e obtained from molecular dynamics was 0.702 C/m 2 , which was lower than that of the monolayer boron nitride honeycomb structures, e = 0.79 C/m 2. Such excellent piezoelectric properties and failure strain detected in boron nitride honeycomb structures suggest a broad prospect for the application of these new materials in novel nanodevices with ultrahigh tensile mechanical properties and ultralight-weight materials.
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Highly efficient thermoelectric materials always have low thermal conductivities. Their phonon spectrum information is essential for understanding the procedure of thermal transport on thermoelectrics. Recently, palladium sulfide was... more
Highly efficient thermoelectric materials always have low thermal conductivities. Their phonon spectrum information is essential for understanding the procedure of thermal transport on thermoelectrics. Recently, palladium sulfide was found to be a potential thermoelectric material. However, the high thermal conductivity limits its thermoelectric performance and technological applications. Here, the phonon dispersion and phonon density of state in PdS are presented by using the first-principles theory. The phonon modes are assigned and compared with experiments. The evolution of optical modes with pressure is studied by using Raman spectroscopy. The low-energy and high-energy phonon bands are related to the vibrations of the heavy atom and the light atom, respectively. By combining Raman scattering and X-ray diffraction measurements, we obtain the mode-Grüneisen parameters for the detected phonon modes. The small mode-Grüneisen parameters indicate a weak anharmonicity in this material. This offers an explanation for its high thermal conductivity. The evolution of linewidths with pressure accounts for the decrease of the thermal conductivity upon compression.
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Nickel-graphene nanolayers with high-density interfaces are expected to have excellent resistance to helium (He) embrittlement and proposed as candidate materials for molten salt reactor systems. However, He irradiation effects on... more
Nickel-graphene nanolayers with high-density interfaces are expected to have excellent resistance to helium (He) embrittlement and proposed as candidate materials for molten salt reactor systems. However, He irradiation effects on nickel-graphene nanolayers remains poorly understood at present. In this work, the influence of a nickel-graphene interface (NGI) on the nucleation and growth of He-related clusters was studied by using atomistic simulations. The NGI reduces formation energies and diffusion energy barriers for He-related clusters. The reduction makes He-related clusters easily be trapped by the interface, thus leading to significant segregation. Consequently, He concentration in the bulk is considerably reduced, and the nucleation and growth rates of He-related clusters in the bulk are delayed. Owing to the high mobility of He-related clusters at the NGI, these clusters easily coalesce to form larger clusters than those in the bulk. A reasonable design of nanolayers may promote He releasing from materials. Results of the current study can provide fundamental support for the service life assessment of nickel-graphene nanolayers in extreme environments.
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Functional groups and grain boundaries of polycrystalline graphenes play important roles in their tribological behaviors but the mechanism is still elusive. Here, we have investigated the influences of hydroxyl groups, coverage, and grain... more
Functional groups and grain boundaries of polycrystalline graphenes play important roles in their tribological behaviors but the mechanism is still elusive. Here, we have investigated the influences of hydroxyl groups, coverage, and grain size on the surface corrugation, friction, and motion behavior of polycrystalline graphene using molecular dynamics simulations. The results show that the corrugation of polycrystalline graphene increases with respect to an increase in grain size. The introduction of hydroxyl groups suppresses the corrugation. The friction between carbon nanotube (CNT) and polycrystalline graphene increases the formation of hydrogen bonds when the interfaces are grafted with hydroxyl groups. The highest amount of friction appears when the ratio of hydroxyl groups on CNT, and polycrystalline graphene, is about 15%-5%. This is due to the balance between the interface space and the formed hydrogen bonds. Furthermore, polycrystalline slides following the movement of CNT owing to high friction. In addition, the energy dissipation as a result of the vibration of the hydroxyl groups plays a more important role as the ratio of hydroxyl groups increases.
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We have examined the effects of temperature, stress, and grain size on the creep process including creep strain, crystal structure, dislocations and diffusions of nanocrystalline NiAl alloy through molecular dynamics simulations. A... more
We have examined the effects of temperature, stress, and grain size on the creep process including creep strain, crystal structure, dislocations and diffusions of nanocrystalline NiAl alloy through molecular dynamics simulations. A smaller grain size accelerates the creep process due to the large volume fraction of grain boundaries. Higher temperatures and stress levels also speed up this process in terms of dislocation changes and atom diffusion. In both primary creep and steady-state creep stages, atomic diffusion at the grain boundary could be seen and the dislocation density increased gradually, indicating that the creep mechanism at these stages is Coble creep controlled by grain boundary diffusion while accompanied by dislocation nucleation. When the model enters the tertiary creep stage, it can be observed that the diffusion of atoms in the grain boundary and in the crystal and the dislocation density gradually decreases, implying that the creep mechanisms at this stage are Coble creep, controlled by grain boundary diffusion, and Nabarro-Herring creep, controlled by lattice diffusion.
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The nanofriction of graphene is critical for its broad applications as a lubricant and in flexible electronics. Herein, using a Au substrate as an example, we have investigated the effect of the grain boundary on the nanofriction of... more
The nanofriction of graphene is critical for its broad applications as a lubricant and in flexible electronics. Herein, using a Au substrate as an example, we have investigated the effect of the grain boundary on the nanofriction of graphene by means of molecular dynamics simulations. We have systematically examined the coupling effects of the grain boundary with different mechanical pressures, velocities, temperatures, contact areas, and relative rotation angles on nanofriction. It is revealed that grain boundaries could reduce the friction between graphene and the gold substrate with a small deformation of the latter. Large lateral forces were observed under severe deformation around the grain boundary. The fluctuation of lateral forces was bigger on surfaces with grain boundaries than that on single-crystal surfaces. Friction forces induced by the armchair grain boundaries was smaller than those by the zigzag grain boundaries.
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We report that carbon honeycomb, a new three-dimension carbon allotrope, exhibits large negative Poisson's ratio, as large as −0.32, in tensile revealed via molecular dynamics simulations. The Poisson's ratio of carbon honeycomb is... more
We report that carbon honeycomb, a new three-dimension carbon allotrope, exhibits large negative Poisson's ratio, as large as −0.32, in tensile revealed via molecular dynamics simulations. The Poisson's ratio of carbon honeycomb is anisotropic, and sensitive to temperature. The carbon honeycomb has phase transformation from normal to auxetic by tensile, along both zigzag and armchair directions. The critical strain for the normal-auxetic transition along the cell-axis direction reduces with respect to an increase in temperature. Combined with high strength of 50 GPa, such a unique and adjustable negative Poisson ratio suggests broad engineering applications of carbon honeycomb.
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Iron sulfides have emerged as a fascinating class of materials in electromagnetics and catalysis areas, which however are challenging in first-principles modeling because of the strongly-correlated interactions between Fe 3d and S 3p... more
Iron sulfides have emerged as a fascinating class of materials in electromagnetics and catalysis areas, which however are challenging in first-principles modeling because of the strongly-correlated interactions between Fe 3d and S 3p electrons. Here, we assess the performances of 14 density functionals on the structural, electronic, and magnetic properties of five iron sulfides. The PBE + U with U eff = 2.0 eV has the overall best performance. After evaluating functionals and obtaining reliable properties, our final goal is from predicting to correlating in order to do high throughput screening for the systems since the complex structures and phases of iron sulfides, to put it in another way, to hunting a reliable descriptor for predicting their properties. In the work, we demonstrate that the crystal orbital Hamilton population (COHP) and Bader charge of Fe atoms presents a good correlation with the empirical bond valence. Our results open a new avenue to effectively investigate phases and properties for various structures of iron sulfides. Indeed, the correlations between COHP/Bader charge and bond valence can be extended to other systems.
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Carbon honeycomb is a newly synthesized carbon allotropy with promising applications in many fields of science and engineering. In this work, we investigate the mechanical properties of carbon honeycomb with focus on the anisotropicity in... more
Carbon honeycomb is a newly synthesized carbon allotropy with promising applications in many fields of science and engineering. In this work, we investigate the mechanical properties of carbon honeycomb with focus on the anisotropicity in terms of the tilt angle θ in zigzag-armchair (x-y) plane using molecular dynamics simulations. Results show that the tensile strength of carbon honeycomb ranges from 15.0 to 23.7 GPa at room temperature, which is lower than that of graphene due to the weakness on the junction. Meanwhile, except in armchair direction, the strength of carbon honeycomb reduces as stretching direction away from zigzag direction, similar to that of graphene. While, the Young's moduli decrease with respect to tilt angle, opposite to that of graphene. Increasing temperature will weaken carbon honeycomb by reducing the strength, and there is only a 16% reduction of the minimum strength in x-y plane as temperature increases from 100 to 900 K. In addition, the crack occurs first in cell axis direction then in the x-y plane, different from graphene which appears to along zigzag direction only.
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Hexagonal binary intermetallics A 5 B 3 has a unique A 6 octahedra chain structure , providing space for interstitial chemical engineering the physical, mechanical, electrical, and chemical properties without change in the basic structure... more
Hexagonal binary intermetallics A 5 B 3 has a unique A 6 octahedra chain structure , providing space for interstitial chemical engineering the physical, mechanical, electrical, and chemical properties without change in the basic structure of crystal. Because of the engineering importance of Zr-Sn alloy, here, we investigate the influence of 24 interstitial alloying elements X (X = B, and Sn) on stability and properties of hexagonal Zr 5 Sn 3 via first-principles calculations. A general trend is that the additional element with small atom size and high electronegativity is favorable as interstitials in Zr 5 Sn 3. The calculated formation enthalpy and the elastic constants suggest that these Zr 5 Sn 3 X structures are thermodynamically and mechanically stable. The calculated phonon spectra indicate that Zr 5 Sn 3 X structures are dynamically stable except X = V, Cr, Mn, Zn, and Nb. We show that their electronic structures including bonding characters have strong correlation with the stability and mechanical properties. With strong covalent bonds, Zr 5 Sn 3 B has the highest Young's modulus, bulk modulus, shear modulus, Debye temperature, and microhard-ness. The addition of alloying elements decreases the anisotropy except X = O, Sc, Ti, V and Nb. All the additive elements increase the specific heat capacity of Zr 5 Sn 3. Our results could be helpful in designing and improve the performance of Zr-Sn alloy on demand.
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We use first-principles calculations to reveal the effects of divalent Pb, Ca, and Sn doping of Bi 2 Te 3 on the band structure and transport properties, including the Seebeck coefficient, α, and the reduced power factor, α 2 σ/τ, where σ... more
We use first-principles calculations to reveal the effects of divalent Pb, Ca, and Sn doping of Bi 2 Te 3 on the band structure and transport properties, including the Seebeck coefficient, α, and the reduced power factor, α 2 σ/τ, where σ is the electrical conductivity and τ is the effective relaxation time. Pb and Ca additions exhibit up to 60%-75% higher peak α 2 σ/τ than that of intrinsic Bi 2 Te 3 with Bi antisite defects. Pb occupancy and Ca occupancy of Bi sites increase σ/τ by activating high-degeneracy low-effective-mass bands near the valence band edge, unlike Bi antisite occupancy of Te sites that eliminates near-edge valence states in intrinsic Bi 2 Te 3. Neither Pb doping nor subatomic-percent Ca doping increases α significantly, due to band averaging. Higher Ca levels increase α and diminish σ, due to the emergence of a corrugated band structure underpinned by high-effective-mass bands, attributable to Ca-Te bond ionicity. Sn doping results in a distortion of the bands with a higher density of states that may be characterized as a resonant state but decreases α 2 σ by up to 30% due to increases in the charge carrier effective mass and decreases in both spin-orbit coupling and valence band quasidegeneracy. These results, and thermal conductivity calculations for nanostructured Bi 2 Te 3 , suggest that Pb or Ca doping can enhance the thermoelectric figure of merit ZT to values up to ZT ∼ 1.7, based on an experimentally determined τ. Our findings suggest that divalent doping can be attractive for realizing large ZT enhancements in pnictogen chalcogenides. Published under license by AIP Publishing. https://doi.
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Solids exhibit transverse shrinkage when they are stretched, except auxetics that abnormally demonstrate lateral expansion instead. Graphene possesses the unique normal-auxeticity (NA) transition when it is stretched along the armchair... more
Solids exhibit transverse shrinkage when they are stretched, except auxetics that abnormally demonstrate lateral expansion instead. Graphene possesses the unique normal-auxeticity (NA) transition when it is stretched along the armchair direction but not along the zigzag direction. Here we report on the anisotropic temperature-dependent NA transitions in strained graphene using molecular dynamics simulations. The critical strain where the NA transition occurs increases with respect to an increase in the tilt angle deviating from armchair direction upon uniaxial loading. The magic angle for the NA transition is 10.9 , beyond which the critical strain is close to fracture strain. In addition, the critical strain decreases with an increasing temperature when the tilt angle is smaller than the NA magic angle. Our results shed lights on the unprecedented nonlinear dimensional response of graphene to the large mechanical loading at various temperatures.
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The PSI-graphene, a two-dimensional structure, was a novel carbon allotrope. In this paper, based on molecular dynamics simulation, the effects of stretching direction, temperature and vacancy defects on the mechanical properties of... more
The PSI-graphene, a two-dimensional structure, was a novel carbon allotrope. In this paper, based on molecular dynamics simulation, the effects of stretching direction, temperature and vacancy defects on the mechanical properties of PSI-graphene were studied. We found that when PSI-graphene was stretched along 0 • and 90 • at 300 K, the ultimate strength reached a maximum of about 65 GPa. And when stretched along 54.2 • and 155.2 • at 300 K, the Young's modulus had peaks, which were 1105 GPa and 2082 GPa, respectively. In addition, when the temperature was raised from 300 K to 900 K, the ultimate strength in all directions was reduced. The fracture morphology of PSI-graphene stretched at different angles was also shown in the text. In addition, the number of points removed from PSI-graphene sheet also seriously affected the tensile properties of the material. It was found that, compared with graphene, PSI-graphene didn't have the negative Poisson's ratio phenomenon when it was stretched along the direction of 0 • , 11.2 • , 24.8 • and 34.7 •. Our results provided a reference for studying the multi-angle stretching of other carbon structures at various temperatures.
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There are a large number of materials with mild stiffness, which are not as soft as tissues and not as strong as metals. These semihard materials include energetic materials, molecular crystals, layered materials, and van der Waals... more
There are a large number of materials with mild stiffness, which are not as soft as tissues and not as strong as metals. These semihard materials include energetic materials, molecular crystals, layered materials, and van der Waals crystals. The integrity and mechanical stability are mainly determined by the interactions between instantaneously induced dipoles, the so called London dispersion force or van der Waals force. It is challenging to accurately model the structural and mechanical properties of these semihard materials in the frame of density functional theory where the non-local correlation functionals are not well known. Here, we propose a van der Waals density functional named vdW-DFq to accurately model the density and geometry of semihard materials. Using β-cyclotetramethylene tetranitramine as a prototype, we adjust the enhancement factor of the exchange energy functional with generalized gradient approximations. We find this method to be simple and robust over a wide tuning range when calibrating the functional on-demand with experimental data. With a calibrated value q = 1.05, the proposed vdW-DFq method shows good performance in predicting the geometries of 11 common energetic material molecular crystals and three typical layered van der Waals crystals. This success could be attributed to the similar electronic charge density gradients, suggesting a wide use in modeling semihard materials. This method could be useful in developing non-empirical density functional theories for semihard and soft materials.
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To tune CH 4 selectivity of Fe-based Fischer-Tropsch synthesis (FTS) in the initial stage is of prime scientific and industrial importance to further improve the catalyst performance. Herein, distribution of CH 4 selectivity on the... more
To tune CH 4 selectivity of Fe-based Fischer-Tropsch synthesis (FTS) in the initial stage is of prime scientific and industrial importance to further improve the catalyst performance. Herein, distribution of CH 4 selectivity on the metallic Fe nanoparticle is predicted by DFT calculations and micro-kinetics analysis about the competition between C 1 hydrogenations and C 1 + C 1 couplings on abundant Fe surfaces including Fe(1 0 0), Fe(1 1 0), Fe(1 1 1), Fe(2 1 1), and Fe(3 1 0). The results show that HCO mechanism (HCO ? CH + O) is an available source of C 1 species apart from CO direct dissociation. These Fe surfaces exhibit high effective barriers for CH 4 formation, which is linearly correlated to the thermal stability of CH 2 species. However, carbon chain prolongation on the more stable surfaces greatly depends on the coupling of C and CH species. On the less stable Fe(1 1 1) surface, the CO + C coupling is the main route for chain pro-longation. Utilizing the effective barrier difference between the CH 4 formation and the most feasible C 1 + C 1 coupling as a descriptor of CH 4 selectivity, it is quantified that CH 4 selectivity decreases in sequence of Fe(1 0 0) > Fe(2 1 1) > Fe(1 1 0) > Fe(3 1 0) > Fe(1 1 1). It is revealed that thermal stability of the CH 2 species and exposition of the Fe facets could play essential roles in tuning CH 4 selectivity. Trying to expand the area of Fe(2 1 1), Fe(3 1 0) and especially Fe(1 1 1) surfaces would greatly suppress CH 4 selectivity without a decrease of activity. This work provides new insights and design principles for the Fe-based FTS catalysts.
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We report that carbon honeycomb, a new three-dimension carbon allotrope, exhibits large negative Poisson's ratio, as large as −0.32, in tensile revealed via molecular dynamics simulations. The Poisson's ratio of carbon honeycomb is... more
We report that carbon honeycomb, a new three-dimension carbon allotrope, exhibits large negative Poisson's ratio, as large as −0.32, in tensile revealed via molecular dynamics simulations. The Poisson's ratio of carbon honeycomb is anisotropic, and sensitive to temperature. The carbon honeycomb has phase transformation from normal to auxetic by tensile, along both zigzag and armchair directions. The critical strain for the normal-auxetic transition along the cell-axis direction reduces with respect to an increase in temperature. Combined with high strength of 50 GPa, such a unique and adjustable negative Poisson ratio suggests broad engineering applications of carbon honeycomb.
Research Interests:
Atom-thick two-dimensional materials usually possess unique properties compared to their bulk counterparts. Their properties are significantly affected by defects, which could be uncontrollably introduced by irradiation. The effects of... more
Atom-thick two-dimensional materials usually possess unique properties compared to their bulk counterparts. Their properties are significantly affected by defects, which could be uncontrollably introduced by irradiation. The effects of electromagnetic irradiation and particle irradiation on 2H MoS2 two-dimensional nanolayers are reviewed in this paper, covering heavy ions, protons, electrons, gamma rays, X-rays, ultraviolet light, terahertz, and infrared irradiation. Various defects in MoS2 layers were created by the defect engineering. Here we focus on their influence on the structural, electronic, catalytic, and magnetic performance of the 2D materials. Additionally, irradiation-induced doping is discussed and involved.
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Stable p‐type doping of zinc oxide (ZnO) is an unsolved but critical issue for ultraviolet optoelectronic applications despite extensive investigations. Here, an Er‐N codoping strategy for defect engineering of ZnO to suppress the... more
Stable p‐type doping of zinc oxide (ZnO) is an unsolved but critical issue for ultraviolet optoelectronic applications despite extensive investigations. Here, an Er‐N codoping strategy for defect engineering of ZnO to suppress the self‐compensation of the donor‐type intrinsic point defects (IPDs) over the acceptor‐type ones is proposed. Via first‐principles calculations, the influence of nitrogen and erbium concentration on the stability of ZnO is investigated. The complex (ErZn‐mNO) consisting of multiple substitutional N on O sites and one substitutional Er on Zn site is a crucial stabilizer. With an increase of the concentration of N, the absorption edges redshift to lower energy due to the impurity band broadening in the bandgap. The results suggest that codoping Er‐N into the ZnO matrix is a feasible way to manufacture stable p‐type ZnO.
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With ultrahigh carrier mobility and large band gap, blue phosphorene (bP) is a promising photoelectronics surpassing black phosphorene and can be further improved by heterostacking. Herein, strain‐engineering of the electronic band gaps... more
With ultrahigh carrier mobility and large band gap, blue phosphorene (bP) is a promising photoelectronics surpassing black phosphorene and can be further improved by heterostacking. Herein, strain‐engineering of the electronic band gaps and light absorption of two van der Waals heterostructures bP/MoS2 and bP/MoSe2 via first‐principles calculations has been reported. Their electronic band structures are sensitive to in‐plane strains. It is interesting and beneficial that biaxial compressive strain range of −0.02 to −0.055 induces the direct band gap in bP/MoSe2. There are two critical strains for bP/MoS(Se)2 heterostructures, where the semiconductor–metal transition can be observed. The bP/MoS(Se)2 heterostructures exhibit strong visible–ultraviolet light absorption, which can be further enhanced via biaxial strain. Our results suggest that bP/MoS(Se)2 heterostructures have promising electronics and visible–ultraviolet optoelectronic applications.
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With extra space, a carbon nanotube (CNT) could serve as an absorber of point defects, including helium interstitials, and outgas the accumulate helium via “nano-chimneys”. The radiation resistance of CNT/Fe has still not been fully... more
With extra space, a carbon nanotube (CNT) could serve as an absorber of point defects, including helium interstitials, and outgas the accumulate helium via “nano-chimneys”. The radiation resistance of CNT/Fe has still not been fully understood. Herein, we investigated the influence of CNTs on low-energy helium irradiation resistance in CNT/Fe composites by molecular dynamic simulations. CNTs reduced the small and medium He clusters in the Fe matrix. When the incident energy of the He atoms was 300 eV, the He atoms aggregated at the outer surface of CNTs. CNTs postponed the formation of He bubbles. When the irradiation energy was higher than 600 eV, He atoms could penetrate the walls of CNTs and form clusters inside the single-walled CNTs or the space in double-walled CNTs—the latter presented better performance. The reduction of Frenkel pair point defects suggested the enhancement of radiation resistance by the presentation of CNTs. Our results might be useful for the material design of advanced steels for radiation resistance.
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With an ultralarge surface-to-volume ratio, a recently synthesized three-dimensional graphene structure, namely, carbon honeycomb, promises important engineering applications. Herein, we have investigated, via molecular dynamics... more
With an ultralarge surface-to-volume ratio, a recently synthesized three-dimensional graphene structure, namely, carbon honeycomb, promises important engineering applications. Herein, we have investigated, via molecular dynamics simulations, its mechanical properties, which are inevitable for its integrity and desirable for any feasible implementations. The uniaxial tension and nanoindentation behaviors are numerically examined. Stress–strain curves manifest a transformation of covalent bonds of hinge atoms when they are stretched in the channel direction. The load–displacement curve in nanoindentation simulation implies the hardness and Young’s modulus to be 50.9 GPa and 461±9 GPa, respectively. Our results might be useful for material and device design for carbon honeycomb-based systems.
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Graphene is an ideal material in the reinforcement of metal-matrix composites owing to its outstanding mechanical and physical properties. Herein, we have investigated the surface enhancement of iron via a computational nanoindentation... more
Graphene is an ideal material in the reinforcement of metal-matrix composites owing to its outstanding mechanical and physical properties. Herein, we have investigated the surface enhancement of iron via a computational nanoindentation process using molecular dynamics simulations. The findings of our study show that graphene can enhance the critical yield strength, hardness and elastic modulus of the composite to different degrees with the change of the number of graphene layers. In the six tested models, the composite with trilayer graphene on the surface produces the strongest reinforcement, with an increased magnitude of 432.1% and 169.5% in the hardness and elastic modulus, respectively, compared with pure iron. Furthermore, it is revealed that high temperature could weaken the elastic bearing capacity of the graphene, resulting in a decrease on the elastic mechanical properties of the graphene/Fe composite.
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Point defects are inevitable, at least due to thermodynamics, and essential for engineering semiconductors. Herein, we investigate the formation and electronic structures of fifteen different kinds of intrinsic point defects of zinc... more
Point defects are inevitable, at least due to thermodynamics, and essential for engineering semiconductors. Herein, we investigate the formation and electronic structures of fifteen different kinds of intrinsic point defects of zinc blende indium arsenide (zb-InAs ) using first-principles calculations. For As-rich environment, substitutional point defects are the primary intrinsic point defects in zb-InAs until the n-type doping region with Fermi level above 0.32 eV is reached, where the dominant intrinsic point defects are changed to In vacancies. For In-rich environment, In tetrahedral interstitial has the lowest formation energy till n-type doped region with Fermi level 0.24 eV where substitutional point defects InAs take over. The dumbbell interstitials prefer <110> configurations. For tetrahedral interstitials, In atoms prefer 4-As tetrahedral site for both As-rich and In-rich environments until the Fermi level goes above 0.26 eV in n-type doped region, where In atoms acquire the same formation energy at both tetrahedral sites and the same charge state. This implies a fast diffusion along the t−T−t path among the tetrahedral sites for In atoms. The In vacancies VIn decrease quickly and monotonically with increasing Fermi level and has a q=−3e charge state at the same time. The most popular vacancy-type defect is VIn in an As-rich environment, but switches to VAs in an In-rich environment at light p-doped region when Fermi level below 0.2 eV. This study sheds light on the relative stabilities of these intrinsic point defects, their concentrations and possible diffusions, which is expected useful in defect-engineering zb-InAs based semiconductors, as well as the material design for radiation-tolerant electronics.
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Carbon honeycomb (CHC) has great application potential in many aspects for the outstanding mechanical properties. However, the effect of both defects and temperature on the mechanical properties are far from reasonable understanding,... more
Carbon honeycomb (CHC) has great application potential in many aspects for the outstanding mechanical properties. However, the effect of both defects and temperature on the mechanical properties are far from reasonable understanding, which might be a huge obstacle for its promising applications as engineering materials. In this work, we investigate the effect of vacancy-type defect, which is inevitably exists in material, on the mechanical properties of CHC via reactive molecular dynamics simulations. The mechanical strength is anisotropic and decreases with the increasing temperature. CHC yield in cell axis direction since the break of C–C bonds on the junction. Vacancies weaken CHC by reducing the strength and failure strain. The effect of single vacancy on strength of CHC becomes more obvious with reducing temperature and is sensitive to the location and bonding of the vacancies. The maximum reduction of strength in cell axis direction is with vacancy on the middle of the wall of CHC where sp2 bonds are removed. The strength is reduced by 8.1% at 500 K, 11.5% at 300 K and 12.8% at 100 K. With 0.77% defect concentration, the strength reduces 40.3% in cell axis direction but only 18.7% in zigzag direction and 24.4% in armchair direction.
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The structural, electronic, dipole-induced internal electric field, optical and photocatalytic properties of monolayer GeS and GeSe under external biaxial strain were investigated by using first-principles calculations. The monolayer GeS... more
The structural, electronic, dipole-induced internal electric field, optical and photocatalytic properties of monolayer GeS and GeSe under external biaxial strain were investigated by using first-principles calculations. The monolayer GeS and GeSe are indirect semiconductors with the band gaps of 3.265 eV and 2.993 eV, respectively. The band alignment of the monolayer GeS and GeSe manifests the photocatalytic activity for water splitting. Especially, it is effective to tune the properties including structures, band gaps, surface potential difference, dipole moment P, dipole-induced internal electric field, absorption and photocatalytic activity of the monolayer GeS and GeSe via biaxial strain. Our results suggest that monolayer GeS and GeSe possess photocatalytic properties for water splitting, and strain engineering, especially tensile strain, can enhance the photocatalytic activity under ultraviolet and visible light.