Machine learning(ML)integrated with density functional theory(DFT)calculations have recently been used to accelerate the design and discovery of single-atom catalysts(SACs)by establishing deep structure–activity rela...Machine learning(ML)integrated with density functional theory(DFT)calculations have recently been used to accelerate the design and discovery of single-atom catalysts(SACs)by establishing deep structure–activity relationships.The traditional ML models are always difficult to identify the structural differences among the single-atom systems with different modification methods,leading to the limitation of the potential application range.Aiming to the structural properties of several typical two-dimensional MA_(2)Z_(4)-based single-atom systems(bare MA_(2)Z_(4) and metal single-atom doped/supported MA_(2)Z_(4)),an improved crystal graph convolutional neural network(CGCNN)classification model was employed,instead of the traditional machine learning regression model,to address the challenge of incompatibility in the studied systems.The CGCNN model was optimized using crystal graph representation in which the geometric configuration was divided into active layer,surface layer,and bulk layer(ASB-GCNN).Through ML and DFT calculations,five potential single-atom hydrogen evolution reaction(HER)catalysts were screened from chemical space of 600 MA_(2)Z_(4)-based materials,especially V_(1)/HfSn_(2)N_(4)(S)with high stability and activity(Δ_(GH*)is 0.06 eV).Further projected density of states(pDOS)analysis in combination with the wave function analysis of the SAC-H bond revealed that the SAC-dz^(2)orbital coincided with the H-s orbital around the energy level of−2.50 eV,and orbital analysis confirmed the formation ofσbonds.This study provides an efficient multistep screening design framework of metal single-atom catalyst for HER systems with similar two-dimensional supports but different geometric configurations.展开更多
A two-dimensional(2D)MA_(2)Z_(4)family with and phases has been attracting tremendous interest,the MoSi_(2)N_(4)and WSi_(2)N_(4)of which have been successfully fabricated(Science 369,670(2020)).Janus monolayers have b...A two-dimensional(2D)MA_(2)Z_(4)family with and phases has been attracting tremendous interest,the MoSi_(2)N_(4)and WSi_(2)N_(4)of which have been successfully fabricated(Science 369,670(2020)).Janus monolayers have been achieved in many 2D families,so it is interesting to construct a Janus monolayer from the MA_(2)Z_(4)family.In this work,Janus MSiGeN4(M=Zr and Hf)monolayers are predicted from-MA_(2)Z_(4),which exhibit dynamic,mechanical and thermal stabilities.It is found that they are indirect band-gap semiconductors by using generalized gradient approximation(GGA)plus spin-orbit coupling(SOC).With biaxial strain a/a0 from 0.90 to 1.10,the energy band gap shows a nonmonotonic behavior due to a change of conduction band minimum(CBM).A semiconductor to metal transition can be induced by both compressive and tensile strains,and the phase trans-formation point is about 0.96 for compressive strain and 1.10 for tensile strain.The tensile strain can change the positions of CBM and valence band maximum(VBM),and can also induce the weak Rashba-type spin splitting near CBM.For MSiGeN4(M=Zr and Hf)monolayers,both an in-plane and out-of-plane piezoelectric response can be produced,when a uniaxial strain in the basal plane is applied,which reveals the potential as piezoelectric 2D materials.The high absorption coefficients in the visible light region suggest that MSiGeN4(M=Zr and Hf)monolayers have potential photocatalytic applications.Our works provide an idea to achieve a Janus structure from the MA_(2)Z_(4)family,and can hopefully inspire further research exploring Janus MA_(2)Z_(4)monolayers.展开更多
As the homologous compounds of MoSi_(2)N_(4),the MoSi_(2)N_(4)(MoN)n monolay-ers have been synthesized in a recent experiment.These systems consist of homogeneous metal nitride multilayers sandwiched between two SiN s...As the homologous compounds of MoSi_(2)N_(4),the MoSi_(2)N_(4)(MoN)n monolay-ers have been synthesized in a recent experiment.These systems consist of homogeneous metal nitride multilayers sandwiched between two SiN surfaces,which extends the septuple-atomic-layer MSizN4 system to ultra-thick MSi2N4(MN)n forms.In this paper,we perform a first-principles study on the MoSizN4(FeN)monolayer,which is constructed by iron molybdenum nitride intercalated into the SiN layers.As a cousin of MoSi_(2)N_(4)(MoN),this double transition-metal system exhibits robust struc-tural stability from the energetic,mechanical,dynamical and thermal perspectives.Different from the MoSi_(2)N_(4)(MoN)one,the MoSi_(2)N_(4)(FeN)monolayer possesses intrinsic ferromagnetism and presents a bipolar magnetic semiconducting behaviour.The ferromagnetism can be further enhanced by the surface hydrogenation,which raises the Curie tempera-ture to 310 K around room temperature.More interestingly,the hydro-genated MoSi_(2)N_(4)(FeN)monolayer exhibits a quantum anomalous Hall(QAH)insulating behaviour with a sizeable nontrivial band gap of 0.23 eV.The nontrivial topological character can be well described by a two-band k·p model,confirming a non-zero Chern number of C=1.Similar bipolar magnetic semiconducting feature and hydrogenation-induced QAH state are also present in the WSizN4(FeN)monolayer.Our study demonstrates that the double transition-metal MSi2N4(M'N)system will be a fertile plat-form to achieve fascinating spintronic and topological properties.展开更多
The characteristics of 4H-SiC PiN diodes with a carbon-implanted drift layer was investigated and the reason of characteristics improvement was analyzed. The forward voltage drops of the diodes with carbonimplanted dr...The characteristics of 4H-SiC PiN diodes with a carbon-implanted drift layer was investigated and the reason of characteristics improvement was analyzed. The forward voltage drops of the diodes with carbonimplanted drift layer were around 3.3 V, which is lower than that of devices without carbon implantation, the specific-on resistance was decreased from 9.35 to 4.38 mΩcm^2 at 100 A/cm^2, and the reverse leakage current was also decreased. The influence of carbon incorporation in the Si C crystalline grids was studied by using deep-level transient spectroscopy（DLTS）. The DLTS spectra revealed that the Z_（1/2） traps, which were regarded as the main lifetime limiting defects, were dramatically reduced. It is proposed that the reduction of Z_（1/2） traps can achieve longer carrier lifetime in the drift layer, which is beneficial to the performance of bipolar devices.展开更多
基金supported by the National Key R&D Program of China(2021YFA1500900)National Natural Science Foundation of China(U21A20298,22141001).
文摘Machine learning(ML)integrated with density functional theory(DFT)calculations have recently been used to accelerate the design and discovery of single-atom catalysts(SACs)by establishing deep structure–activity relationships.The traditional ML models are always difficult to identify the structural differences among the single-atom systems with different modification methods,leading to the limitation of the potential application range.Aiming to the structural properties of several typical two-dimensional MA_(2)Z_(4)-based single-atom systems(bare MA_(2)Z_(4) and metal single-atom doped/supported MA_(2)Z_(4)),an improved crystal graph convolutional neural network(CGCNN)classification model was employed,instead of the traditional machine learning regression model,to address the challenge of incompatibility in the studied systems.The CGCNN model was optimized using crystal graph representation in which the geometric configuration was divided into active layer,surface layer,and bulk layer(ASB-GCNN).Through ML and DFT calculations,five potential single-atom hydrogen evolution reaction(HER)catalysts were screened from chemical space of 600 MA_(2)Z_(4)-based materials,especially V_(1)/HfSn_(2)N_(4)(S)with high stability and activity(Δ_(GH*)is 0.06 eV).Further projected density of states(pDOS)analysis in combination with the wave function analysis of the SAC-H bond revealed that the SAC-dz^(2)orbital coincided with the H-s orbital around the energy level of−2.50 eV,and orbital analysis confirmed the formation ofσbonds.This study provides an efficient multistep screening design framework of metal single-atom catalyst for HER systems with similar two-dimensional supports but different geometric configurations.
基金supported by Natural Science Basis Research Plan in Shaanxi Province of China(2021JM-456)。
文摘A two-dimensional(2D)MA_(2)Z_(4)family with and phases has been attracting tremendous interest,the MoSi_(2)N_(4)and WSi_(2)N_(4)of which have been successfully fabricated(Science 369,670(2020)).Janus monolayers have been achieved in many 2D families,so it is interesting to construct a Janus monolayer from the MA_(2)Z_(4)family.In this work,Janus MSiGeN4(M=Zr and Hf)monolayers are predicted from-MA_(2)Z_(4),which exhibit dynamic,mechanical and thermal stabilities.It is found that they are indirect band-gap semiconductors by using generalized gradient approximation(GGA)plus spin-orbit coupling(SOC).With biaxial strain a/a0 from 0.90 to 1.10,the energy band gap shows a nonmonotonic behavior due to a change of conduction band minimum(CBM).A semiconductor to metal transition can be induced by both compressive and tensile strains,and the phase trans-formation point is about 0.96 for compressive strain and 1.10 for tensile strain.The tensile strain can change the positions of CBM and valence band maximum(VBM),and can also induce the weak Rashba-type spin splitting near CBM.For MSiGeN4(M=Zr and Hf)monolayers,both an in-plane and out-of-plane piezoelectric response can be produced,when a uniaxial strain in the basal plane is applied,which reveals the potential as piezoelectric 2D materials.The high absorption coefficients in the visible light region suggest that MSiGeN4(M=Zr and Hf)monolayers have potential photocatalytic applications.Our works provide an idea to achieve a Janus structure from the MA_(2)Z_(4)family,and can hopefully inspire further research exploring Janus MA_(2)Z_(4)monolayers.
基金support from the National Natural Science Foundation of China(No.11774312).
文摘As the homologous compounds of MoSi_(2)N_(4),the MoSi_(2)N_(4)(MoN)n monolay-ers have been synthesized in a recent experiment.These systems consist of homogeneous metal nitride multilayers sandwiched between two SiN surfaces,which extends the septuple-atomic-layer MSizN4 system to ultra-thick MSi2N4(MN)n forms.In this paper,we perform a first-principles study on the MoSizN4(FeN)monolayer,which is constructed by iron molybdenum nitride intercalated into the SiN layers.As a cousin of MoSi_(2)N_(4)(MoN),this double transition-metal system exhibits robust struc-tural stability from the energetic,mechanical,dynamical and thermal perspectives.Different from the MoSi_(2)N_(4)(MoN)one,the MoSi_(2)N_(4)(FeN)monolayer possesses intrinsic ferromagnetism and presents a bipolar magnetic semiconducting behaviour.The ferromagnetism can be further enhanced by the surface hydrogenation,which raises the Curie tempera-ture to 310 K around room temperature.More interestingly,the hydro-genated MoSi_(2)N_(4)(FeN)monolayer exhibits a quantum anomalous Hall(QAH)insulating behaviour with a sizeable nontrivial band gap of 0.23 eV.The nontrivial topological character can be well described by a two-band k·p model,confirming a non-zero Chern number of C=1.Similar bipolar magnetic semiconducting feature and hydrogenation-induced QAH state are also present in the WSizN4(FeN)monolayer.Our study demonstrates that the double transition-metal MSi2N4(M'N)system will be a fertile plat-form to achieve fascinating spintronic and topological properties.
基金Project supported by the Opening Project of Key Laboratory of Microelectronics Devices & Integrated Technology,Institute of Microelectronics,Chinese Academy of Sciences
文摘The characteristics of 4H-SiC PiN diodes with a carbon-implanted drift layer was investigated and the reason of characteristics improvement was analyzed. The forward voltage drops of the diodes with carbonimplanted drift layer were around 3.3 V, which is lower than that of devices without carbon implantation, the specific-on resistance was decreased from 9.35 to 4.38 mΩcm^2 at 100 A/cm^2, and the reverse leakage current was also decreased. The influence of carbon incorporation in the Si C crystalline grids was studied by using deep-level transient spectroscopy（DLTS）. The DLTS spectra revealed that the Z_（1/2） traps, which were regarded as the main lifetime limiting defects, were dramatically reduced. It is proposed that the reduction of Z_（1/2） traps can achieve longer carrier lifetime in the drift layer, which is beneficial to the performance of bipolar devices.
