This paper investigates the electron-vibrational（e-V）energy exchange in nitrogencontaining plasma,which is very efficient in the case of gas discharge and high speed flow.Based on Harmonic oscillator approximation a...This paper investigates the electron-vibrational（e-V）energy exchange in nitrogencontaining plasma,which is very efficient in the case of gas discharge and high speed flow.Based on Harmonic oscillator approximation and the assumption of the e-V relaxation through a continuous series of Boltzmann distributions over the vibrational states,an analytic approach is derived from the proposed scaling relation of e-V transition rates.A full kinetic model is then investigated by numerically solving the state-to-state master equation for all vibrational levels.The analytical approach leads to a Landau-Teller（LT）-type equation for relaxation of vibrational energy,and predicts the relaxation time on the right order of magnitude.By comparison with the kinetic model,the LT-type equation is valid in typical electron temperatures in gas discharge.However,the analytical approach is not capable of describing the vibrational distribution function during the e-V process in which a full kinetic model is required.展开更多
MXenes,a new family of two-dimensional(2D)materials,have received extensive interest due to their fascinating physicochemical properties,such as outstandinglight-to-heat conversion efficiency.However,the photothermal ...MXenes,a new family of two-dimensional(2D)materials,have received extensive interest due to their fascinating physicochemical properties,such as outstandinglight-to-heat conversion efficiency.However,the photothermal conversion mechanism of MXenes is still poorly understood.Here,by using femtosecond visible and mid-infrared transient absorption spectroscopy,the electronic energy dissipation dynamics of MXene(Ti_(3)C_(2)T_(x))nanosheets dispersed in various solvents are carefully studied.Our results indicate that the lifetime of photoexcited MXene is strongly dependent on the surrounding environment.Especially,the interfacial electron-vibration coupling between the MXene nanosheets and the adjacent solvent molecules is directly observed following the ultrafast photoexcitation of MXene.It suggests that the interfacial interactions at the MXene-solvent interface play a critical role in the ultrafast energy transport dynamics of MXene,which offers a potentially feasible route for tailoring the light conversion properties of 2D systems.展开更多
Coherent vibrational dynamics can be observed in atomically precise gold nanoclusters using femtosecond time-resolved pump-probe spectroscopy.It can not only reveal the coupling between electrons and vibrations,but al...Coherent vibrational dynamics can be observed in atomically precise gold nanoclusters using femtosecond time-resolved pump-probe spectroscopy.It can not only reveal the coupling between electrons and vibrations,but also reflect the mechanical and electronic properties of metal nanoclusters,which holds potential applications in biological sensing and mass detection.Here,we investigated the coherent vibrational dynamics of[Au_(25)(SR)_(18)]^(-)nanoclusters by ultrafast spectroscopy and revealed the origins of thesecoherent vibrations by analyzing their frequency,phase and probe wavelength distributions.Strong coherent oscillations with frequency of 40 cm^(-1) and 80 cm^(-1) can be reproduced in the excited state dynamics of[Au_(25)(SR)_(18)]^(-),which should originate from acoustic vibrations of the Au13 metal core.Phase analysis on the oscillations indicates that the 80 cm^(-1) mode should arise from the frequency modulation of the electronic states while the 40 cm^(-1) mode should originate from the amplitude modulation of the dynamic spectrum.Moreover,it is found that the vibration frequencies of[Au_(25)(SR)_(18)]^(-)obtained in pump-probe measurements are independent of the surface ligands so that they are intrinsic properties of the metal core.These results are of great value to understand the electron-vibration coupling of metal nanoclusters.展开更多
Electronic excited state inmolecular aggregate or exciton states continue to attract great attention due to the increasing demands for applications of molecular optoelectronics and sensing technology.The working princ...Electronic excited state inmolecular aggregate or exciton states continue to attract great attention due to the increasing demands for applications of molecular optoelectronics and sensing technology.The working principle behind the application is closely related to the excited state structure and dynamic processes inmolecular aggregate.In our previous review article(Aggregate 2021;2:e91),we focused more on the molecular mechanism for aggregation-induced emission process.Here,we are going to summarize our recent progress on theoretical investigations on the effects of excitonic coupling(J)and the intermolecular charge transfer(CT)on the excited state structure and dynamic processes.These are in general missing for molecular quantum chemistry studies.We will first present a novel definition of exciton coherence length which can present a bijective relation with the radiative decay rate and obviously we have clarified the confusion appeared in literature.Then,we will look at the CT effect for aggregate starting from a simple three-state model coupled with quantum chemical calculation for molecular dimer and we focus on the intensity borrowing,which can turn H-aggregate into emissive when the electron transfer and hole transfer integrals possessing the same sign and being large enough.We are able to propose amolecular descriptor to designmolecularmaterials possibly possessing both high photoluminescence quantum yield and carrier mobility.Finally,we introduce our work on the modified energy gap law for non-radiative decay rate in aggregates.We found there exist optimal J to minimize the non-radiative decay loss.展开更多
Scanning tunneling microscopy/spectroscopy is applied herein to study the pristine and potassium(K)-doped single-layer pquaterphenyl(P4P) films grown on the Au(111) substrate at the molecular level. Abundant complex s...Scanning tunneling microscopy/spectroscopy is applied herein to study the pristine and potassium(K)-doped single-layer pquaterphenyl(P4P) films grown on the Au(111) substrate at the molecular level. Abundant complex structural and electronic phases are induced by various K doping. The Fermi-level pinning effect is observed at a low doping level. On the contrary,K3P4P exhibits intriguing versatile phases and properties because charge carriers are effectively doped in. For example, two kinds of molecular vibration modes with energies below 100 meV are observed, indicating a possible strong electron-phonon coupling. The splitting of the lowest unoccupied molecular orbital state in K3P4P illustrates an electronic correlation effect, and its strength varies for four different K3P4P phases with different structures. In addition, the appearance of a Kondo resonance on the molecular vacancy/impurity implies a local molecular magnetic moment. Our results demonstrate that the complex electronic properties of an alkali metal-doped P4P/Au film stem from the existence of many competing interactions, such as electronelectron correlations and electron-vibration coupling, which can be effectively tuned via variable carrier doping and molecular structure. Our work also opens new routes toward engineering novel molecular devices and creating new electronic phases in strongly correlated molecular materials.展开更多
基金supported by National Natural Science Foundation of China(No.11505015)the National High-Tech Research and Development Program of China(863 Program)
文摘This paper investigates the electron-vibrational（e-V）energy exchange in nitrogencontaining plasma,which is very efficient in the case of gas discharge and high speed flow.Based on Harmonic oscillator approximation and the assumption of the e-V relaxation through a continuous series of Boltzmann distributions over the vibrational states,an analytic approach is derived from the proposed scaling relation of e-V transition rates.A full kinetic model is then investigated by numerically solving the state-to-state master equation for all vibrational levels.The analytical approach leads to a Landau-Teller（LT）-type equation for relaxation of vibrational energy,and predicts the relaxation time on the right order of magnitude.By comparison with the kinetic model,the LT-type equation is valid in typical electron temperatures in gas discharge.However,the analytical approach is not capable of describing the vibrational distribution function during the e-V process in which a full kinetic model is required.
基金supported by the National Key Research and Development Program of China(No.2018YFA0208700)the National Natural Science Foundation of China (No.21773302)the Strategic Priority Research Program of Chinese Academy of Sciences (No.XDB30000000)
文摘MXenes,a new family of two-dimensional(2D)materials,have received extensive interest due to their fascinating physicochemical properties,such as outstandinglight-to-heat conversion efficiency.However,the photothermal conversion mechanism of MXenes is still poorly understood.Here,by using femtosecond visible and mid-infrared transient absorption spectroscopy,the electronic energy dissipation dynamics of MXene(Ti_(3)C_(2)T_(x))nanosheets dispersed in various solvents are carefully studied.Our results indicate that the lifetime of photoexcited MXene is strongly dependent on the surrounding environment.Especially,the interfacial electron-vibration coupling between the MXene nanosheets and the adjacent solvent molecules is directly observed following the ultrafast photoexcitation of MXene.It suggests that the interfacial interactions at the MXene-solvent interface play a critical role in the ultrafast energy transport dynamics of MXene,which offers a potentially feasible route for tailoring the light conversion properties of 2D systems.
基金supported by the startup funding from University of Science and Technology of China(KY2340000137)the startup funding from Chinese Academy of Sciences
文摘Coherent vibrational dynamics can be observed in atomically precise gold nanoclusters using femtosecond time-resolved pump-probe spectroscopy.It can not only reveal the coupling between electrons and vibrations,but also reflect the mechanical and electronic properties of metal nanoclusters,which holds potential applications in biological sensing and mass detection.Here,we investigated the coherent vibrational dynamics of[Au_(25)(SR)_(18)]^(-)nanoclusters by ultrafast spectroscopy and revealed the origins of thesecoherent vibrations by analyzing their frequency,phase and probe wavelength distributions.Strong coherent oscillations with frequency of 40 cm^(-1) and 80 cm^(-1) can be reproduced in the excited state dynamics of[Au_(25)(SR)_(18)]^(-),which should originate from acoustic vibrations of the Au13 metal core.Phase analysis on the oscillations indicates that the 80 cm^(-1) mode should arise from the frequency modulation of the electronic states while the 40 cm^(-1) mode should originate from the amplitude modulation of the dynamic spectrum.Moreover,it is found that the vibration frequencies of[Au_(25)(SR)_(18)]^(-)obtained in pump-probe measurements are independent of the surface ligands so that they are intrinsic properties of the metal core.These results are of great value to understand the electron-vibration coupling of metal nanoclusters.
基金supported by the National Natural Science Foundation of China(grant nos.T2350009 and 22433007)the Guangdong Provincial Natural Science Foundation(grant no.2024A1515011185)+1 种基金the Shenzhen City Pengcheng Peacock Talent Program,and Shenzhen Science and Technology Program(no.KQTD20240729102028011)supported by the National Natural Science Foundation of China(grant nos.22273005 and 22422301).
文摘Electronic excited state inmolecular aggregate or exciton states continue to attract great attention due to the increasing demands for applications of molecular optoelectronics and sensing technology.The working principle behind the application is closely related to the excited state structure and dynamic processes inmolecular aggregate.In our previous review article(Aggregate 2021;2:e91),we focused more on the molecular mechanism for aggregation-induced emission process.Here,we are going to summarize our recent progress on theoretical investigations on the effects of excitonic coupling(J)and the intermolecular charge transfer(CT)on the excited state structure and dynamic processes.These are in general missing for molecular quantum chemistry studies.We will first present a novel definition of exciton coherence length which can present a bijective relation with the radiative decay rate and obviously we have clarified the confusion appeared in literature.Then,we will look at the CT effect for aggregate starting from a simple three-state model coupled with quantum chemical calculation for molecular dimer and we focus on the intensity borrowing,which can turn H-aggregate into emissive when the electron transfer and hole transfer integrals possessing the same sign and being large enough.We are able to propose amolecular descriptor to designmolecularmaterials possibly possessing both high photoluminescence quantum yield and carrier mobility.Finally,we introduce our work on the modified energy gap law for non-radiative decay rate in aggregates.We found there exist optimal J to minimize the non-radiative decay loss.
基金supported by the National Natural Science Foundation of China(Grant No.11774060)the National Key R&D Program of the MOST of China(Grant Nos.2016YFA0300200,2017YFA0303004,2017YFA0303104,2016YFA0302300,and 2017YFA0303003)+2 种基金the National Basic Research Program of China(Grant No.2015CB921700)the Science Challenge Project(Grant No.TZ2016004)the Shanghai Education Development Foundation and Shanghai Municipal Education Commission(Chenguang Program)。
文摘Scanning tunneling microscopy/spectroscopy is applied herein to study the pristine and potassium(K)-doped single-layer pquaterphenyl(P4P) films grown on the Au(111) substrate at the molecular level. Abundant complex structural and electronic phases are induced by various K doping. The Fermi-level pinning effect is observed at a low doping level. On the contrary,K3P4P exhibits intriguing versatile phases and properties because charge carriers are effectively doped in. For example, two kinds of molecular vibration modes with energies below 100 meV are observed, indicating a possible strong electron-phonon coupling. The splitting of the lowest unoccupied molecular orbital state in K3P4P illustrates an electronic correlation effect, and its strength varies for four different K3P4P phases with different structures. In addition, the appearance of a Kondo resonance on the molecular vacancy/impurity implies a local molecular magnetic moment. Our results demonstrate that the complex electronic properties of an alkali metal-doped P4P/Au film stem from the existence of many competing interactions, such as electronelectron correlations and electron-vibration coupling, which can be effectively tuned via variable carrier doping and molecular structure. Our work also opens new routes toward engineering novel molecular devices and creating new electronic phases in strongly correlated molecular materials.
