By means of oxide molecular beam epitaxy with shutter-growth mode, we fabricate a series of electron-doped (Sr1-xLax)2IrO4 (001) (x=0, 0.05, 0.1 and 0.15) single crystalline thin films and then investigate the d...By means of oxide molecular beam epitaxy with shutter-growth mode, we fabricate a series of electron-doped (Sr1-xLax)2IrO4 (001) (x=0, 0.05, 0.1 and 0.15) single crystalline thin films and then investigate the doping dependence of the electronic structure utilizing in-situ angle-resolved photoemission spectroscopy. It is found that with the increasing doping content, the Fermi levels of samples progressively shift upward. Prominently, an extra electron pocket crossing the Fermi level around the M point is evidently observed in the 15% nominal doping sample. Moreover, bulk-sensitive transport measurements confirm that the doping effectively suppresses the insulating state with respect to the as-grown Sr2IrO4, though the doped samples still remain insulating at low temperatures due to the localization effect possibly stemming from disorders including oxygen deficiencies. Our work provides another feasible doping method to tune electronic structure of Sr2 IrO4.展开更多
Silicene, a silicon analogue of graphene, has attracted increasing research attention in recent years because of its unique electrical and thermal conductivities. In this study, phonon thermal conductivity and its iso...Silicene, a silicon analogue of graphene, has attracted increasing research attention in recent years because of its unique electrical and thermal conductivities. In this study, phonon thermal conductivity and its isotopic doping effect in silicene nanoribbons(SNRs) are investigated by using molecular dynamics simulations. The calculated thermal conductivities are approximately 32 W/mK and 35 W/mK for armchair-edged SNRs and zigzag-edged SNRs, respectively, which show anisotropic behaviors. Isotope doping induces mass disorder in the lattice, which results in increased phonon scattering, thus reducing the thermal conductivity. The phonon thermal conductivity of isotopic doped SNR is dependent on the concentration and arrangement pattern of dopants. A maximum reduction of about 15% is obtained at 50% randomly isotopic doping with ^(30)Si. In addition, ordered doping(i.e., isotope superlattice) leads to a much larger reduction in thermal conductivity than random doping for the same doping concentration. Particularly, the periodicity of the doping superlattice structure has a significant influence on the thermal conductivity of SNR. Phonon spectrum analysis is also used to qualitatively explain the mechanism of thermal conductivity change induced by isotopic doping. This study highlights the importance of isotopic doping in tuning the thermal properties of silicene, thus guiding defect engineering of the thermal properties of two-dimensional silicon materials.展开更多
Molecular doping has become a widely used method to modulate the electric performance of organic semiconductors(OSC).Highly effective charge transfer during molecular doping is desired to achieve ideal electrical cond...Molecular doping has become a widely used method to modulate the electric performance of organic semiconductors(OSC).Highly effective charge transfer during molecular doping is desired to achieve ideal electrical conductivity.Two types of charge transfer mechanisms are widely accepted in molecular doping process:integer charge transfer(ICT)and charge transfer complex(CTC).In this review,fundamental principles of two mechanisms are revisited and the characterization methods are depicted.The key points for the formation of two mechanisms are highlighted from aspects of molecular structure and process engineering.Then,the strategies to improve the proportion of ICT are discussed.Finally,the challenges and perspectives for future developments in the molecular doping of polymer semiconductors are provided.展开更多
Many studies in metal-organic frameworks(MOFs)aiming for high photocatalytic activity resort to self-assembling both energy donor and acceptor building units in skeleton to achieve effective energy transfer,which,howe...Many studies in metal-organic frameworks(MOFs)aiming for high photocatalytic activity resort to self-assembling both energy donor and acceptor building units in skeleton to achieve effective energy transfer,which,however,usually needs tedious synthetic procedure and design of a new MOF.In this work,we demonstrated that building a Förster resonance energy transfer(FRET)pathway can be realized through suitable molecular doping in a given MOF structure without altering the original porous structure,presenting an alternative strategy to design efficient photocatalysts for CO_(2)reduction.In situ electron spin resonance,ultrafast transient absorption spectroscopy,and computational studies reveal that the FRET-induced excitation has dramatically altered the exciton transfer pathway in structure and facilitated electron-hole separation.As a result,the molecular doped MOFs synthesized through one-pot reaction show outstanding selectivity(96%)and activity(1314μmol⋅g^(−1)⋅h^(−1))for CO production versus almost no activity for the pristine MOFs,and this result stands out from existing competitors.Furthermore,the reaction mechanism was proposed and the intermediate signals were detected by in situ diffuse reflectance infrared Fourier transform spectroscopies.This study presents a clear picture of building FRET process in MOFs through molecular doping and provides a new design strategy for MOF-based photocatalysts.展开更多
Generally,long wavelength absorbed near-infrared II(NIR-II)dyes have a low fluorescence efficiency in aggregate states for aggregate-caused quenching effect,simultaneously enhancing efficiency and extending absorption...Generally,long wavelength absorbed near-infrared II(NIR-II)dyes have a low fluorescence efficiency in aggregate states for aggregate-caused quenching effect,simultaneously enhancing efficiency and extending absorption is a challenging issue for NIR-II dyes.Here,three benzo[1,2-c:4,5-c’]bis[1,2,5]thiadiazole(BBT)derivatives(TPA-BBT,FT-BBT,and BTBT-BBT)are used to clarify fluorescence quenching mechanisms.When the BBT derivatives are doped into a small molecule matrix,they show quite different fluorescence behaviors.Structuredistorted TPA-BBT displays fluorescence quenching originating from short-range exchange interaction,while FT-BBT and BTBT-BBT with a co-planar-conjugated backbone exhibit concentration-dependent quenching processes,namely changing from long-range dipole-dipole interaction to exchange interaction,which could be majorly ascribed to large spectral overlap between absorption and emission.By precisely tuning doping concentration,both FT-BBT and BTBT-BBT nanoparticles(NPs)present the optimal NIR-II fluorescence brightness at∼2.5 wt%doping concentration.The doped NPs have good biocompatibility and could be served as fluorescence contrast agents for vascular imaging with a high resolution under 980-nm laser excitation.Those paradigms evidence that molecular doping can promote fluorescence efficiency of long wavelength-absorbed NIR-II fluorophores via suppressing long-range energy migration.展开更多
基金Supported by the National Basic Research Program of China(973 Program)under Grant Nos 2011CBA00106 and2012CB927400the National Natural Science Foundation of China under Grant Nos 11274332 and 11227902Helmholtz Association through the Virtual Institute for Topological Insulators(VITI).M.Y.Li and D.W.Shen are also supported by the Strategic Priority Research Program(B)of the Chinese Academy of Sciences under Grant No XDB04040300
文摘By means of oxide molecular beam epitaxy with shutter-growth mode, we fabricate a series of electron-doped (Sr1-xLax)2IrO4 (001) (x=0, 0.05, 0.1 and 0.15) single crystalline thin films and then investigate the doping dependence of the electronic structure utilizing in-situ angle-resolved photoemission spectroscopy. It is found that with the increasing doping content, the Fermi levels of samples progressively shift upward. Prominently, an extra electron pocket crossing the Fermi level around the M point is evidently observed in the 15% nominal doping sample. Moreover, bulk-sensitive transport measurements confirm that the doping effectively suppresses the insulating state with respect to the as-grown Sr2IrO4, though the doped samples still remain insulating at low temperatures due to the localization effect possibly stemming from disorders including oxygen deficiencies. Our work provides another feasible doping method to tune electronic structure of Sr2 IrO4.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11504418 and 11447033)the Natural Science Fund for Colleges and Universities in Jiangsu Province,China(Grant No.16KJB460022)the Fundamental Research Funds for the Central Universities of CUMT,China(Grant No.2015XKMS075)
文摘Silicene, a silicon analogue of graphene, has attracted increasing research attention in recent years because of its unique electrical and thermal conductivities. In this study, phonon thermal conductivity and its isotopic doping effect in silicene nanoribbons(SNRs) are investigated by using molecular dynamics simulations. The calculated thermal conductivities are approximately 32 W/mK and 35 W/mK for armchair-edged SNRs and zigzag-edged SNRs, respectively, which show anisotropic behaviors. Isotope doping induces mass disorder in the lattice, which results in increased phonon scattering, thus reducing the thermal conductivity. The phonon thermal conductivity of isotopic doped SNR is dependent on the concentration and arrangement pattern of dopants. A maximum reduction of about 15% is obtained at 50% randomly isotopic doping with ^(30)Si. In addition, ordered doping(i.e., isotope superlattice) leads to a much larger reduction in thermal conductivity than random doping for the same doping concentration. Particularly, the periodicity of the doping superlattice structure has a significant influence on the thermal conductivity of SNR. Phonon spectrum analysis is also used to qualitatively explain the mechanism of thermal conductivity change induced by isotopic doping. This study highlights the importance of isotopic doping in tuning the thermal properties of silicene, thus guiding defect engineering of the thermal properties of two-dimensional silicon materials.
基金the National Natural Science Foundation of China (No. 92263109)the Shanghai Rising-Star Program (No. 22QA1410400)Natural Science Foundation of Shanghai (No. 23ZR1472200).
文摘Molecular doping has become a widely used method to modulate the electric performance of organic semiconductors(OSC).Highly effective charge transfer during molecular doping is desired to achieve ideal electrical conductivity.Two types of charge transfer mechanisms are widely accepted in molecular doping process:integer charge transfer(ICT)and charge transfer complex(CTC).In this review,fundamental principles of two mechanisms are revisited and the characterization methods are depicted.The key points for the formation of two mechanisms are highlighted from aspects of molecular structure and process engineering.Then,the strategies to improve the proportion of ICT are discussed.Finally,the challenges and perspectives for future developments in the molecular doping of polymer semiconductors are provided.
基金National Key Research and Development Program of China,Grant/Award Number:2018YFA0208600National Natural Science Foundation of China,Grant/Award Numbers:21871267,22071246,22272178CAS-Iranian Vice Presidency for Science and Technology Joint Research Project,Grant/Award Number:121835KYSB20200034。
文摘Many studies in metal-organic frameworks(MOFs)aiming for high photocatalytic activity resort to self-assembling both energy donor and acceptor building units in skeleton to achieve effective energy transfer,which,however,usually needs tedious synthetic procedure and design of a new MOF.In this work,we demonstrated that building a Förster resonance energy transfer(FRET)pathway can be realized through suitable molecular doping in a given MOF structure without altering the original porous structure,presenting an alternative strategy to design efficient photocatalysts for CO_(2)reduction.In situ electron spin resonance,ultrafast transient absorption spectroscopy,and computational studies reveal that the FRET-induced excitation has dramatically altered the exciton transfer pathway in structure and facilitated electron-hole separation.As a result,the molecular doped MOFs synthesized through one-pot reaction show outstanding selectivity(96%)and activity(1314μmol⋅g^(−1)⋅h^(−1))for CO production versus almost no activity for the pristine MOFs,and this result stands out from existing competitors.Furthermore,the reaction mechanism was proposed and the intermediate signals were detected by in situ diffuse reflectance infrared Fourier transform spectroscopies.This study presents a clear picture of building FRET process in MOFs through molecular doping and provides a new design strategy for MOF-based photocatalysts.
基金NNSF,Grant/Award Numbers:62120106002,22175089Jiangsu Provincial Policy Key Research and Development Plan,Grant/Award Numbers:BE2021711,BE2022812+1 种基金open research fund of State Key Laboratory of Organic Electronics and Information DisplaysStartup Foundation for Introducing Talent of NUIST,Grant/Award Number:2021r089。
文摘Generally,long wavelength absorbed near-infrared II(NIR-II)dyes have a low fluorescence efficiency in aggregate states for aggregate-caused quenching effect,simultaneously enhancing efficiency and extending absorption is a challenging issue for NIR-II dyes.Here,three benzo[1,2-c:4,5-c’]bis[1,2,5]thiadiazole(BBT)derivatives(TPA-BBT,FT-BBT,and BTBT-BBT)are used to clarify fluorescence quenching mechanisms.When the BBT derivatives are doped into a small molecule matrix,they show quite different fluorescence behaviors.Structuredistorted TPA-BBT displays fluorescence quenching originating from short-range exchange interaction,while FT-BBT and BTBT-BBT with a co-planar-conjugated backbone exhibit concentration-dependent quenching processes,namely changing from long-range dipole-dipole interaction to exchange interaction,which could be majorly ascribed to large spectral overlap between absorption and emission.By precisely tuning doping concentration,both FT-BBT and BTBT-BBT nanoparticles(NPs)present the optimal NIR-II fluorescence brightness at∼2.5 wt%doping concentration.The doped NPs have good biocompatibility and could be served as fluorescence contrast agents for vascular imaging with a high resolution under 980-nm laser excitation.Those paradigms evidence that molecular doping can promote fluorescence efficiency of long wavelength-absorbed NIR-II fluorophores via suppressing long-range energy migration.