The progressive stacking of chalcogenide single layers gives rise to two- dimensional semiconducting materials with tunable properties that can be exploited for new field-effect transistors and photonic devices. Yet t...The progressive stacking of chalcogenide single layers gives rise to two- dimensional semiconducting materials with tunable properties that can be exploited for new field-effect transistors and photonic devices. Yet the properties of some members of the chalcogenide family remain unexplored. Indium selenide （InSe） is attractive for applications due to its direct bandgap in the near infrared, controllable p- and n-type doping and high chemical stability. Here, we reveal the lattice dynamics, optical and electronic properties of atomically thin InSe flakes prepared by micromechanical cleavage. Raman active modes stiffen or soften in the flakes depending on which electronic bonds are excited. A progressive blue-shift of the photoluminescence peaks is observed for decreasing flake thickness （as large as 0.2 eV for three single layers）. First-principles calculations predict an even larger increase in the bandgap, 0.40 eV, for three single layers, and as much as 1.1 eV for a single layer. These results are promising from the point of view of the versatility of this material for optoelectronic applications at the nanometer scale and compatible with Si and III-V technologies.展开更多
Pure ZnO hexagonal microwires and Fe(Ⅲ)-doped ZnO microwires(MWs)with a novel rectangular cross section were synthesized in a confined chamber by a convenient one-step thermal evaporation method.An oriented attachmen...Pure ZnO hexagonal microwires and Fe(Ⅲ)-doped ZnO microwires(MWs)with a novel rectangular cross section were synthesized in a confined chamber by a convenient one-step thermal evaporation method.An oriented attachment mechanism is consistent with a vapor-solid growth process.Photoluminescence(PL)and Raman spectroscopy of the Fe(Ⅲ)-doped ZnO MWs and in situ spectral mappings indicate a quasi-periodic distribution of Fe(Ⅲ)along a one-dimensional(1-D)superlattice ZnO:ZnFe_(2)O_(4) wire,while PL mapping shows the presence of optical multicavities and related multimodes.The PL spectra at room temperature show weak near-edge doublets(376 nm and 383 nm)and a broad band(450-650 nm)composed of strong discrete lines,due to a 1-D photonic crystal structure.Such a 1-D coupled optical cavity material may find many applications in future photonic and spintronic devices.展开更多
Increasing temperature is known to quench the excitonic emission of bulk silicon,which is due to thermally induced dissociation of excitons.Here,we demonstrate that the effect of temperature on the excitonic emission ...Increasing temperature is known to quench the excitonic emission of bulk silicon,which is due to thermally induced dissociation of excitons.Here,we demonstrate that the effect of temperature on the excitonic emission is reversed for quantumconfined silicon nanocrystals.Using laser-induced heating of silicon nanocrystals embedded in SiO2,we achieved a more than threefold(4300%)increase in the radiative(photon)emission rate.We theoretically modeled the observed enhancement in terms of the thermally stimulated effect,taking into account the massive phonon production under intense illumination.These results elucidate one more important advantage of silicon nanostructures,illustrating that their optical properties can be influenced by temperature.They also provide an important insight into the mechanisms of energy conversion and dissipation in ensembles of silicon nanocrystals in solid matrices.In practice,the radiative rate enhancement under strong continuous wave optical pumping is relevant for the possible application of silicon nanocrystals for spectral conversion layers in concentrator photovoltaics.展开更多
文摘The progressive stacking of chalcogenide single layers gives rise to two- dimensional semiconducting materials with tunable properties that can be exploited for new field-effect transistors and photonic devices. Yet the properties of some members of the chalcogenide family remain unexplored. Indium selenide （InSe） is attractive for applications due to its direct bandgap in the near infrared, controllable p- and n-type doping and high chemical stability. Here, we reveal the lattice dynamics, optical and electronic properties of atomically thin InSe flakes prepared by micromechanical cleavage. Raman active modes stiffen or soften in the flakes depending on which electronic bonds are excited. A progressive blue-shift of the photoluminescence peaks is observed for decreasing flake thickness （as large as 0.2 eV for three single layers）. First-principles calculations predict an even larger increase in the bandgap, 0.40 eV, for three single layers, and as much as 1.1 eV for a single layer. These results are promising from the point of view of the versatility of this material for optoelectronic applications at the nanometer scale and compatible with Si and III-V technologies.
基金The authors thank the National Natural Science Foundation of China(NSFC)of China(Nos.90606001,20873039,and 90406024)for financial support.
文摘Pure ZnO hexagonal microwires and Fe(Ⅲ)-doped ZnO microwires(MWs)with a novel rectangular cross section were synthesized in a confined chamber by a convenient one-step thermal evaporation method.An oriented attachment mechanism is consistent with a vapor-solid growth process.Photoluminescence(PL)and Raman spectroscopy of the Fe(Ⅲ)-doped ZnO MWs and in situ spectral mappings indicate a quasi-periodic distribution of Fe(Ⅲ)along a one-dimensional(1-D)superlattice ZnO:ZnFe_(2)O_(4) wire,while PL mapping shows the presence of optical multicavities and related multimodes.The PL spectra at room temperature show weak near-edge doublets(376 nm and 383 nm)and a broad band(450-650 nm)composed of strong discrete lines,due to a 1-D photonic crystal structure.Such a 1-D coupled optical cavity material may find many applications in future photonic and spintronic devices.
基金supported by the Dutch Technology Foundation STW,which is part of the Netherlands Organisation for Scientific Research(NWO)funded by the Ministry of Economic Affairs+1 种基金support within the framework of the Czech-German collaborative project,16-09745J(DFT-GACR)supported by the Russian Science Foundation,Grant No.14-12-01067。
文摘Increasing temperature is known to quench the excitonic emission of bulk silicon,which is due to thermally induced dissociation of excitons.Here,we demonstrate that the effect of temperature on the excitonic emission is reversed for quantumconfined silicon nanocrystals.Using laser-induced heating of silicon nanocrystals embedded in SiO2,we achieved a more than threefold(4300%)increase in the radiative(photon)emission rate.We theoretically modeled the observed enhancement in terms of the thermally stimulated effect,taking into account the massive phonon production under intense illumination.These results elucidate one more important advantage of silicon nanostructures,illustrating that their optical properties can be influenced by temperature.They also provide an important insight into the mechanisms of energy conversion and dissipation in ensembles of silicon nanocrystals in solid matrices.In practice,the radiative rate enhancement under strong continuous wave optical pumping is relevant for the possible application of silicon nanocrystals for spectral conversion layers in concentrator photovoltaics.
