Ions in the bulk of solvent-free ionic liquids bind into ion pairs and clusters.The competition between the propensity of ions to stay in a bound state,and the reduction of the energy when unbinding in electric field,...Ions in the bulk of solvent-free ionic liquids bind into ion pairs and clusters.The competition between the propensity of ions to stay in a bound state,and the reduction of the energy when unbinding in electric field,determines the portion of free ions in the electrical double layer.We present the simplest possible mean-field theory to study this effect."Cracking"of ion pairs into free ions in electric field is accompanied by the change of the dielectric response of the ionic liquid.The predictions from the theory are verified and further explored by molecular dynamics simulations.A particular finding of the theory is that the differential capacitance vs potential curve displays a bell shape,despite the low concentration of free charge carriers,because the dielectric response reduces the threshold concentration for the bell-to camelshape transition.The presented theory does not take into account overscreening and oscillating charge distributions in the electrical double layer.But in spite of the simplicity of the model,its findings demonstrate a clear physical effect:a preference to be a charged monopole rather than a dipole(or higher order multipole)in strong electric field.展开更多
Based on a developed theory,we show that introducing a meta-grid of sub-wavelength-sized plasmonic nanoparticles(NPs)into existing semiconductor light-emitting-devices(LEDs)can lead to enhanced transmission of light a...Based on a developed theory,we show that introducing a meta-grid of sub-wavelength-sized plasmonic nanoparticles(NPs)into existing semiconductor light-emitting-devices(LEDs)can lead to enhanced transmission of light across the LED-chip/encapsulant interface.This results from destructive interference between light reflected from the chip/encapsulant interface and light reflected by the NP meta-grid,which conspicuously increase the efficiency of light extraction from LEDs.The“meta-grid”,should be inserted on top of a conventional LED chip within its usual encapsulating packaging.As described by the theory,the nanoparticle composition,size,interparticle spacing,and distance from the LED-chip surface can be tailored to facilitate maximal transmission of light emitted from the chip into its encapsulating layer by reducing the Fresnel loss.The analysis shows that transmission across a typical LEDchip/encapsulant interface at the peak emission wavelength can be boosted up to ~99%,which is otherwise mere~84% at normal incidence.The scheme could provide improved transmission within the photon escape cone over the entire emission spectrum of an LED.This would benefit energy saving,in addition to increasing the lifetime of LEDs by reducing heating.Potentially,the scheme will be easy to implement and adopt into existing semiconductor-device technologies,and it can be used separately or in conjunction with other methods for mitigating the critical angle loss in LEDs.展开更多
基金funding support from the National Natural Science Foundation of China(51876072)financial support from National Natural Science Foundation of China(21802170)+2 种基金supported through a studentship of the Centre for Doctoral Training on Theory and Simulation of Materials at Imperial College London,funded by the EPSRC(EP/L015579/1)the funding from the Thomas Young Centre under grant number TYC-101funding from the Leverhulme Trust(Grant No.RPG2016-223)
文摘Ions in the bulk of solvent-free ionic liquids bind into ion pairs and clusters.The competition between the propensity of ions to stay in a bound state,and the reduction of the energy when unbinding in electric field,determines the portion of free ions in the electrical double layer.We present the simplest possible mean-field theory to study this effect."Cracking"of ion pairs into free ions in electric field is accompanied by the change of the dielectric response of the ionic liquid.The predictions from the theory are verified and further explored by molecular dynamics simulations.A particular finding of the theory is that the differential capacitance vs potential curve displays a bell shape,despite the low concentration of free charge carriers,because the dielectric response reduces the threshold concentration for the bell-to camelshape transition.The presented theory does not take into account overscreening and oscillating charge distributions in the electrical double layer.But in spite of the simplicity of the model,its findings demonstrate a clear physical effect:a preference to be a charged monopole rather than a dipole(or higher order multipole)in strong electric field.
基金the support of the Marie Skodowska-Curie individual fellowship(S-OMMs)from the European Commissiona grant from the Engineering and Physical Sciences Research Council UK,“Electrotuneable Molecular Alarm”,EP/L02098X/1.
文摘Based on a developed theory,we show that introducing a meta-grid of sub-wavelength-sized plasmonic nanoparticles(NPs)into existing semiconductor light-emitting-devices(LEDs)can lead to enhanced transmission of light across the LED-chip/encapsulant interface.This results from destructive interference between light reflected from the chip/encapsulant interface and light reflected by the NP meta-grid,which conspicuously increase the efficiency of light extraction from LEDs.The“meta-grid”,should be inserted on top of a conventional LED chip within its usual encapsulating packaging.As described by the theory,the nanoparticle composition,size,interparticle spacing,and distance from the LED-chip surface can be tailored to facilitate maximal transmission of light emitted from the chip into its encapsulating layer by reducing the Fresnel loss.The analysis shows that transmission across a typical LEDchip/encapsulant interface at the peak emission wavelength can be boosted up to ~99%,which is otherwise mere~84% at normal incidence.The scheme could provide improved transmission within the photon escape cone over the entire emission spectrum of an LED.This would benefit energy saving,in addition to increasing the lifetime of LEDs by reducing heating.Potentially,the scheme will be easy to implement and adopt into existing semiconductor-device technologies,and it can be used separately or in conjunction with other methods for mitigating the critical angle loss in LEDs.