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
Piezoelectric transmission spectroelectrochemistry (PTSEC), i.e., the combination of electrochemistry and spectroelectrochemistry (SEC) with electrochemical quartz crystal microbalance (EQCM) technique is reported by ...Piezoelectric transmission spectroelectrochemistry (PTSEC), i.e., the combination of electrochemistry and spectroelectrochemistry (SEC) with electrochemical quartz crystal microbalance (EQCM) technique is reported by using a normal piezoelectric quartz crystal (PQC) as an optically-transparent electrode (OTE). A theoretical relationship between the PQC response and the spectroelectrochemical response is derived and used to estimate the apparent molar absorptivity of the absorbing species deposited on the OTE on the PQC surface. The complex of copper with aspartic acid is used to test this new PQC-SEC technique. Results show that the combination of three such diverse techniques provides a very useful methodology for studying electrode processes and electrode surface characteristics in situ.展开更多
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Project supported by the National Natural Science Foundation of China and the Education commission Foundation of China.
文摘Piezoelectric transmission spectroelectrochemistry (PTSEC), i.e., the combination of electrochemistry and spectroelectrochemistry (SEC) with electrochemical quartz crystal microbalance (EQCM) technique is reported by using a normal piezoelectric quartz crystal (PQC) as an optically-transparent electrode (OTE). A theoretical relationship between the PQC response and the spectroelectrochemical response is derived and used to estimate the apparent molar absorptivity of the absorbing species deposited on the OTE on the PQC surface. The complex of copper with aspartic acid is used to test this new PQC-SEC technique. Results show that the combination of three such diverse techniques provides a very useful methodology for studying electrode processes and electrode surface characteristics in situ.
