Cd-free Ⅰ-Ⅲ-Ⅵ group semiconductor quantum dots (QDs) like Ag-ln-S and Cu-ln-S show unstructured absorption spectra with a pronounced Urbach tail,rendering the determination of their band gap energy (Eg) and the ene...Cd-free Ⅰ-Ⅲ-Ⅵ group semiconductor quantum dots (QDs) like Ag-ln-S and Cu-ln-S show unstructured absorption spectra with a pronounced Urbach tail,rendering the determination of their band gap energy (Eg) and the energy structure of the exciton difficult.Additionally,the origin of the broad photoluminescence (PL) band with lifetimes of several hundred nanoseconds is still debated.This encouraged us to study the excitation energy dependence (EED) of the PL maxima,PL spectral band widths,quantum yields (QYs),and decay kinetics of AlS/ZnS QDs of j different size,composition,and surface capping ligands.These results were then correlated with the second derivatives of the corresponding absorption spectra.The excellent match between the onset of changes in PL band position and spectral width with the minima found for the second derivatives of the absorption spectra underlines the potential of the EED approach for deriving Eg values of these ternary QDs from PL data.The PL QY is,however,independent of excitation energy in the energy range studied.From the EED of the PL features of the AlS/ZnS QDs we could also derive a mechanism of the formation of the low-energy electronic structure.This was additionally confirmed by a comparison of the EED of PL data of as-synthesized and size-selected QD ensembles and the comparison of these PL data with PL spectra of single QDs.These results indicate a strong contribution of intrinsic inhomogeneous PL broadening to the overall emission features of AlS/ZnS QDs originating from radiative transitions from a set of energy states of defects localized at different positions within the quantum dot volume,in addition to contributions from dimensional and chemical broadening.This mechanism was confirmed by numerically modelling the absorption and PL energies with a simple mass approximation for spherical QDs and a modified donor-acceptor model,thereby utilizing the advantages of previously proposed PL mechanisms of ternary QDs.These findings will pave the road to a deeper understanding of the nature of PL in quantum confined Ⅰ-Ⅲ-Ⅵ group semiconductor nanomaterials.展开更多
Nanomeasuring machines developed at the Technische Universitat Ilmenau enable three-dimensional measurements and manufacturing processes with the lowest uncertainties.Due to the requirements for these processes,a high...Nanomeasuring machines developed at the Technische Universitat Ilmenau enable three-dimensional measurements and manufacturing processes with the lowest uncertainties.Due to the requirements for these processes,a highly reproducible and long-term stable tool changing system is needed.For this purpose,kinematically determined couplings are widely used.The state-of-the-art investigations on those are not sufficient for the highest demands on the reproducibility required for this application.A theoretical determination of the reproducibility based on analytical or numerical methods is possible,however not in the desired nanometer range.Due to this,a measurement setup for the determination of the reproducibility in five degrees of freedom with nanometer uncertainty was developed.First,potential measuring devices are systematically examined and measurement principles were developed out of this.A three-dimensional vector-based uncertainty analysis is performed to prove the feasibility of the measurement principle and provides a basis for further design.As a result,a transla-tory measurement uncertainty of 10 nm and a rotatory uncertainty of 11 nrad can be reached.Afterwards,the measurement setup is designed,focusing on the metrological frame and the lift-off device.The developed setup exceeds the uncertainties of the measurement setups presented in the state-of-the-art by an order of magnitude,allowing new in-depth investigations of the reproducibility of kinematic couplings.展开更多
文摘Cd-free Ⅰ-Ⅲ-Ⅵ group semiconductor quantum dots (QDs) like Ag-ln-S and Cu-ln-S show unstructured absorption spectra with a pronounced Urbach tail,rendering the determination of their band gap energy (Eg) and the energy structure of the exciton difficult.Additionally,the origin of the broad photoluminescence (PL) band with lifetimes of several hundred nanoseconds is still debated.This encouraged us to study the excitation energy dependence (EED) of the PL maxima,PL spectral band widths,quantum yields (QYs),and decay kinetics of AlS/ZnS QDs of j different size,composition,and surface capping ligands.These results were then correlated with the second derivatives of the corresponding absorption spectra.The excellent match between the onset of changes in PL band position and spectral width with the minima found for the second derivatives of the absorption spectra underlines the potential of the EED approach for deriving Eg values of these ternary QDs from PL data.The PL QY is,however,independent of excitation energy in the energy range studied.From the EED of the PL features of the AlS/ZnS QDs we could also derive a mechanism of the formation of the low-energy electronic structure.This was additionally confirmed by a comparison of the EED of PL data of as-synthesized and size-selected QD ensembles and the comparison of these PL data with PL spectra of single QDs.These results indicate a strong contribution of intrinsic inhomogeneous PL broadening to the overall emission features of AlS/ZnS QDs originating from radiative transitions from a set of energy states of defects localized at different positions within the quantum dot volume,in addition to contributions from dimensional and chemical broadening.This mechanism was confirmed by numerically modelling the absorption and PL energies with a simple mass approximation for spherical QDs and a modified donor-acceptor model,thereby utilizing the advantages of previously proposed PL mechanisms of ternary QDs.These findings will pave the road to a deeper understanding of the nature of PL in quantum confined Ⅰ-Ⅲ-Ⅵ group semiconductor nanomaterials.
基金the support by the Deutsche Forschungsgemeinschaft(DFG)in the framework of Research Training Group"Tip-and laser-based 3D-Nanofabrication inextended macroscopic working areas"(GRK 2182)at the Technische Universiat Ilmenau,Germany.
文摘Nanomeasuring machines developed at the Technische Universitat Ilmenau enable three-dimensional measurements and manufacturing processes with the lowest uncertainties.Due to the requirements for these processes,a highly reproducible and long-term stable tool changing system is needed.For this purpose,kinematically determined couplings are widely used.The state-of-the-art investigations on those are not sufficient for the highest demands on the reproducibility required for this application.A theoretical determination of the reproducibility based on analytical or numerical methods is possible,however not in the desired nanometer range.Due to this,a measurement setup for the determination of the reproducibility in five degrees of freedom with nanometer uncertainty was developed.First,potential measuring devices are systematically examined and measurement principles were developed out of this.A three-dimensional vector-based uncertainty analysis is performed to prove the feasibility of the measurement principle and provides a basis for further design.As a result,a transla-tory measurement uncertainty of 10 nm and a rotatory uncertainty of 11 nrad can be reached.Afterwards,the measurement setup is designed,focusing on the metrological frame and the lift-off device.The developed setup exceeds the uncertainties of the measurement setups presented in the state-of-the-art by an order of magnitude,allowing new in-depth investigations of the reproducibility of kinematic couplings.
