Twisted bilayer graphene(TBG) has been extensively studied because of its novel physical properties and potential application in electronic devices.Here we report the synthesis and characterization of 300 TBG naturall...Twisted bilayer graphene(TBG) has been extensively studied because of its novel physical properties and potential application in electronic devices.Here we report the synthesis and characterization of 300 TBG naturally grown on Cu_(0.75)Ni_(0.25)(111) film and investigate the electronic structure by angle-resolved photoemission spectroscopy.Compared with other substrates,our TBG with a wafer scale is acquired with a shorter growth time.The Fermi velocity and energy gap of Dirac cones of TBG are comparable with those of a monolayer on Cu_(0.85)Ni_(0.15)(111).The signature of moré lattices has not been observed in either the low-energy electron diffraction patterns or the Fermi surface map within experimental resolution,possibly due to different Cu and Ni contents in the substrates enhancing the different couplings between the substrate and the first/second layers and hindering the formation of a quasiperiodic structure.展开更多
This work shows that despite a lattice mismatch of almost 20%, CdMnTe/CdTe/CdMnTe heterostructures grown directly on Si(111) have surprisingly good optical emission properties. The investigated structures were grown b...This work shows that despite a lattice mismatch of almost 20%, CdMnTe/CdTe/CdMnTe heterostructures grown directly on Si(111) have surprisingly good optical emission properties. The investigated structures were grown by molecular beam epitaxy and characterized by scanning transmission electron microscopy, macro-and micro-photoluminescence. Low temperature macro-photoluminescence experiments indicate three emission bands which depend on the CdTe layer thickness and have different confinement characteristics. Temperature measurements reveal that the lower energy emission band (at 1.48 eV)is associated to defects and bound exciton states, while the main emission at 1.61 eV has a weak 2D character and the higher energy one at 1.71 eV has a well-defined (zero-dimensional, 0D) 0D nature. Micro-photoluminescence measurements show the existence of sharp and strongly circularly polarized (up to 40%) emission lines which can be related to the presence of Mn in the heterostructure. This result opens the possibility of producing photon sources with the typical spin control of the diluted magnetic semiconductors using the low-cost silicon technology.展开更多
Pd-based catalysts are extensively employed to catalyze CO oxidative coupling to generate DMO,while the expensive price and high usage of Pd hinder its massive application in industrial production.Designing Pd-based c...Pd-based catalysts are extensively employed to catalyze CO oxidative coupling to generate DMO,while the expensive price and high usage of Pd hinder its massive application in industrial production.Designing Pd-based catalysts with high efficiency and low Pd usage as well as expounding the catalytic mechanisms are significant for the reaction.In this study,we theoretically predict that Pd stripe doping Co(111)surface exhibits excellent performance than pure Pd(111),Pd monolayer supporting on Co(111)and Pd single atom doping Co(111)surface,and clearly expound the catalytic mechanisms through the density functional theory(DFT)calculation and micro-reaction kinetic model analysis.It is obtained that the favorable reaction pathway is COOCH_(3)-COOCH_(3)coupling pathway over these four catalysts,while the rate-controlling step is COOCH_(3)+CO+OCH_(3)→2COOCH_(3)on Pd stripe doping Co(111)surface,which is different from the case(2COOCH_(3)→DMO)on pure Pd(111),Pd monolayer supporting on Co(111)and Pd single atom doping Co(111)surface.This study can contribute a certain reference value for developing Pd-based catalysts with high efficiency and low Pd usage for CO oxidative coupling to DMO.展开更多
采用密度泛函理论研究了M(M=In,Ir)原子修饰的M-Au(111)合金表面的稳定性,并选其最优模型探讨了合金表面的活性及其对巴豆醛的吸附。合金的几何构型、形成能和结合能等性质表明,In-Au(111)面的稳定性随In原子的间距增大而提高,Ir-Au(111...采用密度泛函理论研究了M(M=In,Ir)原子修饰的M-Au(111)合金表面的稳定性,并选其最优模型探讨了合金表面的活性及其对巴豆醛的吸附。合金的几何构型、形成能和结合能等性质表明,In-Au(111)面的稳定性随In原子的间距增大而提高,Ir-Au(111)面的稳定性随Ir原子的间距增大而降低。对于巴豆醛在MAu(111)面上的吸附,当其通过C=O吸附于合金表面的TopM位时,吸附能最大,吸附构型最稳定。从巴豆醛的结构变化、态密度、差分电荷密度以及Mulliken电荷布居等分析可以看出,稳定吸附构型的巴豆醛分子形变较大,电荷转移明显。其中,位于-7.04 e V至费米能级处的p、d轨道杂化,对体系的吸附具有重要贡献。分析比较In-Au(111)面与Ir-Au(111)面,发现后者的配体效应更佳,不仅具有更高的稳定性和活性,而且对于巴豆醛具有更强的吸附力。此外,相比于改性前的Au(111)面,M原子的修饰明显提升了金属表面的稳定性及吸附能力。展开更多
基金Project supported by the National Key R&D Program of China (Grant Nos. 2022YFB3608000 and 2022YFA1204900)the National Natural Science Foundation of China (Grant Nos. 12222413 and 12074205)+2 种基金the Natural Science Foundation of Shanghai (Grant Nos. 23ZR1482200 and 22ZR1473300)the Natural Science Foundation of Zhejiang Province (Grant No. LQ21A040004)the funding of Ningbo University (Grant No. LJ2024003)。
文摘Twisted bilayer graphene(TBG) has been extensively studied because of its novel physical properties and potential application in electronic devices.Here we report the synthesis and characterization of 300 TBG naturally grown on Cu_(0.75)Ni_(0.25)(111) film and investigate the electronic structure by angle-resolved photoemission spectroscopy.Compared with other substrates,our TBG with a wafer scale is acquired with a shorter growth time.The Fermi velocity and energy gap of Dirac cones of TBG are comparable with those of a monolayer on Cu_(0.85)Ni_(0.15)(111).The signature of moré lattices has not been observed in either the low-energy electron diffraction patterns or the Fermi surface map within experimental resolution,possibly due to different Cu and Ni contents in the substrates enhancing the different couplings between the substrate and the first/second layers and hindering the formation of a quasiperiodic structure.
基金the financial support by the Brazilian funding agencies CAPES, CNPq (306201/2022-4)FAPEMIG (APQ-00371-17, APQ-02500-22, APQ-00388-22, and RED00223-23)FAPESP (2021/06803-4)。
文摘This work shows that despite a lattice mismatch of almost 20%, CdMnTe/CdTe/CdMnTe heterostructures grown directly on Si(111) have surprisingly good optical emission properties. The investigated structures were grown by molecular beam epitaxy and characterized by scanning transmission electron microscopy, macro-and micro-photoluminescence. Low temperature macro-photoluminescence experiments indicate three emission bands which depend on the CdTe layer thickness and have different confinement characteristics. Temperature measurements reveal that the lower energy emission band (at 1.48 eV)is associated to defects and bound exciton states, while the main emission at 1.61 eV has a weak 2D character and the higher energy one at 1.71 eV has a well-defined (zero-dimensional, 0D) 0D nature. Micro-photoluminescence measurements show the existence of sharp and strongly circularly polarized (up to 40%) emission lines which can be related to the presence of Mn in the heterostructure. This result opens the possibility of producing photon sources with the typical spin control of the diluted magnetic semiconductors using the low-cost silicon technology.
基金financially supported by the National Key Research and Development Program of China(2021YFA1502804)the Regional Innovation and Development Joint Fund of the National Natural Science Foundation of China(U22A20430)+3 种基金the Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering(2022SX-FR001)the Natural Science Foundation of Shanxi Province(202203021212201)the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxithe Foundation of Taiyuan University of Technology(2022QN138)
文摘Pd-based catalysts are extensively employed to catalyze CO oxidative coupling to generate DMO,while the expensive price and high usage of Pd hinder its massive application in industrial production.Designing Pd-based catalysts with high efficiency and low Pd usage as well as expounding the catalytic mechanisms are significant for the reaction.In this study,we theoretically predict that Pd stripe doping Co(111)surface exhibits excellent performance than pure Pd(111),Pd monolayer supporting on Co(111)and Pd single atom doping Co(111)surface,and clearly expound the catalytic mechanisms through the density functional theory(DFT)calculation and micro-reaction kinetic model analysis.It is obtained that the favorable reaction pathway is COOCH_(3)-COOCH_(3)coupling pathway over these four catalysts,while the rate-controlling step is COOCH_(3)+CO+OCH_(3)→2COOCH_(3)on Pd stripe doping Co(111)surface,which is different from the case(2COOCH_(3)→DMO)on pure Pd(111),Pd monolayer supporting on Co(111)and Pd single atom doping Co(111)surface.This study can contribute a certain reference value for developing Pd-based catalysts with high efficiency and low Pd usage for CO oxidative coupling to DMO.
文摘采用密度泛函理论研究了M(M=In,Ir)原子修饰的M-Au(111)合金表面的稳定性,并选其最优模型探讨了合金表面的活性及其对巴豆醛的吸附。合金的几何构型、形成能和结合能等性质表明,In-Au(111)面的稳定性随In原子的间距增大而提高,Ir-Au(111)面的稳定性随Ir原子的间距增大而降低。对于巴豆醛在MAu(111)面上的吸附,当其通过C=O吸附于合金表面的TopM位时,吸附能最大,吸附构型最稳定。从巴豆醛的结构变化、态密度、差分电荷密度以及Mulliken电荷布居等分析可以看出,稳定吸附构型的巴豆醛分子形变较大,电荷转移明显。其中,位于-7.04 e V至费米能级处的p、d轨道杂化,对体系的吸附具有重要贡献。分析比较In-Au(111)面与Ir-Au(111)面,发现后者的配体效应更佳,不仅具有更高的稳定性和活性,而且对于巴豆醛具有更强的吸附力。此外,相比于改性前的Au(111)面,M原子的修饰明显提升了金属表面的稳定性及吸附能力。
