The effect of back-diffusion of Mg dopants on optoelectronic characteristics of InGaN-based green light-emitting diodes (LEDs) is investigated. The LEDs with less Mg back-diffusion show blue shifts of longer wavelen...The effect of back-diffusion of Mg dopants on optoelectronic characteristics of InGaN-based green light-emitting diodes (LEDs) is investigated. The LEDs with less Mg back-diffusion show blue shifts of longer wavelengths and larger wavelengths with the increasing current, which results from the Mg-dopant-related polarization screening. The LEDs show enhanced efficiency with the decreasing Mg back-diffusion in the lower current region. Light outputs follow the power law L α I^m, with smaller parameter m in the LEDs with less Mg back-diffusion, indicating a lower density of trap states. The trap-assisted tunneling current is also suppressed by reducing Mg- defect-related nonradiative centers in the active region. Furthermore, the forward current-voltage characteristics are improved.展开更多
Nanosized ZnO powders were prepared with a two-step precipitation method. The average size of ZnO particles was about 80 nm and their size distribution was narrow. Combining with ultrafine additive powders, ZnO base v...Nanosized ZnO powders were prepared with a two-step precipitation method. The average size of ZnO particles was about 80 nm and their size distribution was narrow. Combining with ultrafine additive powders, ZnO base varistor was produced via an oxide mixing route. ZnO varistor derived from normal reagent grade starting materials was investigated for comparison purpose. Outstanding microstructure of the ZnO varistor derived from nanosize ZnO powders and ultrafine dopants was obtained: uniform distribution of fine ZnO grains (less than 3 microns), grain boundary and the dopant position. Higher varistor voltage (U=492 V/mm) and nonlinear coefficient (α=56.2) as well as lower leakage current (TL=1.5 μuA) were achieved. The better electrical properties were attributed to the uniform microstructure, which in turn led to stable and uniform potential barriers. Also this improved technique is more feasible for producing ZnO nanopowders and resulting varistor in large scales.展开更多
A novel series of chiral dopants synthesized from(S)-1,2-propanediol and mesogenic carboxylic acids were characterized by FT-IR,~1H NMR,elemental analysis and their helical twisting properties were investigated by dop...A novel series of chiral dopants synthesized from(S)-1,2-propanediol and mesogenic carboxylic acids were characterized by FT-IR,~1H NMR,elemental analysis and their helical twisting properties were investigated by doping the chiral dopants into a nematic liquid crystal host(SLC-1717).The results show that,the helical pitch of N~*-LC mixture exhibited a terminal alkyl chain length dependence and the molecular twisting power β also exhibited a temperature dependence(increasing β with increasing temperature).展开更多
A series of white phosphorescent OLED devices with buffer layer and multiple dopant structure is investigated in order to obtain better electro-optic performances and color stability. The color coordinate and color st...A series of white phosphorescent OLED devices with buffer layer and multiple dopant structure is investigated in order to obtain better electro-optic performances and color stability. The color coordinate and color stability are related to the location of multiple dopants layer, and the optimized location can compensate for the change of the blue emission intensity under a high voltage and stabilize the spectrum. The electro-optic performances and color stability can be further improved by changing the composition and thickness of the buffer layer between the emitting layer and the electron transport layer.In device B2, the distance from multiple dopant layer to buffer layer is 2 nm and the thickness of buffer layer is 5 nm,the maximum luminance, current density, and power efficiency can reach 9091 cd/m^2, 364.5 mA/cm^2, and 26.74 lm/W,respectively. The variation of international commission on the illumination(CIE) coordinate of device B2 with voltage increasing from 4 V to 7 V is only(0.006, 0.004).展开更多
Influences of addition of CaO, CoO and V2O5 on the microstructure and magnetic properties of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites were investigated. The powders of (Mg0.476Mn0.448Zn0.007) (Fe1.997...Influences of addition of CaO, CoO and V2O5 on the microstructure and magnetic properties of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites were investigated. The powders of (Mg0.476Mn0.448Zn0.007) (Fe1.997Ti0.002)O4 composition were prepared by using a conventional ceramic powder processing technique. The experimental results showed that the average grain size of the sintered ferrites codoped with 0.03wt% CaO, 0.04wt% CoO and 0.06wt% V2O5 was about 15 μm; the saturation magnetization of ferrites was 68.78 emu/g. The addition of V2O5 in the ferrites can not only increase value of the saturation magnetization, but also decrease the average grain size of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites. Simultaneous incorporation of CoO, CaO and V2O5 dopants into (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites can not only improve the saturation magnetization of the materials, but also inhibit abnormal grain growth.展开更多
We consider intrinsic gate capacitance variations due to random dopants in the nanometer metal oxide semi- conductor field effect transistor (MOSFET) channel. The variations of total gate capacitance and gate transc...We consider intrinsic gate capacitance variations due to random dopants in the nanometer metal oxide semi- conductor field effect transistor (MOSFET) channel. The variations of total gate capacitance and gate transcapacitances are investigated and the strong correlations between the trans-capacitance variations are discovered. A simple statistical model is proposed for accurately capturing total gate capacitance variability based on the correlations. The model fits very well with the Monte Carlo simulations and the average errors are -0.033% for n-type metal-oxide semiconductor and -0.012% for p-type metal-oxide semiconductor, respectively. Our simulation studies also indicate that, owing to these correlations, the total gate capacitance variability will not dominate in gate capacitance variations.展开更多
Conductivity dopants with processing properties suitable for industrial applications are of importance to the organic electronics field. However, the number of commercially available organic molecular dopants is limit...Conductivity dopants with processing properties suitable for industrial applications are of importance to the organic electronics field. However, the number of commercially available organic molecular dopants is limited. The electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyanoquinodimethane (F4-TCNQ) is the most utilized P-dopant;however, it has high volatility and a poor sticking coefficient, which makes it difficult to control doping levels and prevent vacuum system contamination. A design concept for P-type molecular dopants based on the TCNQ core which are substituted to improve processing properties without sacrificing the electronic properties necessary is presented. The correlation between the lowest unoccupied molecular orbital (LUMO) energy and the position of substitution as well as the choice of linker is evaluated. The position of substitution as well as the choice of linker has a significant effect on the electronic properties. However, the geometry of the substituted molecules was not significantly distorted from that of the parent F4-TCNQ, and the electron density was delocalized on the TCNQ core. We also put forward four possible molecular dopants with suitable energy levels.展开更多
Thorium is nearly three times more abundant than uranium in the Earth's crust. Some papers evaluate the thorium resourcesin Brazil over 1,200,000 metric t. These figures mean that the country is probably the biggest ...Thorium is nearly three times more abundant than uranium in the Earth's crust. Some papers evaluate the thorium resourcesin Brazil over 1,200,000 metric t. These figures mean that the country is probably the biggest thorium resource in the world, with onlypart of the territory prospected. Nevertheless, Brazil has not a research program for use of thorium in nuclear reactors, even havingdedicated special attention to the subject in the beginning of its nuclear activities, in the fifties and sixties. From 1985 until 2003 IPENoperated a pilot plant for thorium nitrate production and purification, used by Brazilian industry for production of gas mantles. Thisfacility produced over 170 metric t of thorium nitrate. Despite the non-nuclear application, the pilot plant was unique in the southernhemisphere. On the other hand, Brazil has the biggest world niobium resources. The Brazilian thorium and niobium resources added tothe predictable future importance of alternative fissile materials have motivated this research, since uranium is a finite resource if usedin the present thermal nuclear reactors. Besides this, thorium oxide is an important nuclear reactor material. It is a refractory oxide andits ceramic fabrication process involves a very high temperature sintering treatment considering that thoria melting point is very high(3,650 K). Cations of elements of the group VB (V, Nb and Ta) have a known effect in the reduction of thoria sintering temperature.IPEN has initiated an investigation about the use of niobium as a dopant for thoria sintering temperature reduction. The thoria used inthe research was produced in the IPEN's pilot plant and different amounts of niobium oxide (Nb2Os) will be added to thoria by differentroutes. The powders will be compressed and the compacted pellets will be sintered at different temperatures. The influence of thedifferent parameters in the density of sintered pellets is being investigated. This paper presents the chemical and physicalcharacterization for the thoria used in the investigation.展开更多
X-ray drive asymmetry is one of the main seeds of low-mode implosion asymmetry that blocks further improvement of the nuclear per-formance of“high-foot”experiments on the National Ignition Facility[Miller et al.,Nuc...X-ray drive asymmetry is one of the main seeds of low-mode implosion asymmetry that blocks further improvement of the nuclear per-formance of“high-foot”experiments on the National Ignition Facility[Miller et al.,Nucl.Fusion 44,S228(2004)].More particularly,the P2 asymmetry of Au's M-band flux can also severely influence the implosion performance of ignition capsules[Li et al.,Phys.Plasmas 23,072705(2016)].Here we study the smoothing effect of mid-and/or high-Z dopants in ablator on Au's M-band flux asymmetries,by modeling and comparing the implosion processes of a Ge-doped ignition capsule and a Si-doped one driven by X-ray sources with P2 M-band flux asymmetry.As the results,(1)mid-or high-Z dopants absorb hard X-rays(M-band flux)and re-emit isotropically,which helps to smooth the asymmetric M-band flux arriving at the ablation front,therefore reducing the P2 asymmetries of the imploding shell and hot spot;(2)the smoothing effect of Ge-dopant is more remarkable than Si-dopant because its opacity in Au's M-band is higher than the latter's;and(3)placing the doped layer at a larger radius in ablator is more efficient.Applying this effect may not be a main measure to reduce the low-mode implosion asymmetry,but might be of significance in some critical situations such as inertial confinement fusion(ICF)experiments very near the performance cliffs of asymmetric X-ray drives.展开更多
Selenium and zinc are used as anionic and cationic dopant elements to dope PbS nanostructures. The undoped and doped PbS nanostructures are grown using a thermal evaporation method. Scanning electron microscopy (SEM...Selenium and zinc are used as anionic and cationic dopant elements to dope PbS nanostructures. The undoped and doped PbS nanostructures are grown using a thermal evaporation method. Scanning electron microscopy (SEM) results show similar morphologies for the undoped and doped PbS nanostructures. X-ray diffraction (XRD) patterns of three sets of the nanostructures indicate that these nanostructures each have a PbS structure with a cubic phase. Evidence of dopant incorporation is demonstrated by X-ray photoelectron spectroscopy (XPS). Raman spectra of the synthesized samples con- firm the XRD results and indicate five Raman active modes, which relate to the PbS cubic phase for all the nanostructures. Room temperature photoluminescence (PL) and UV-Vis spectrometers are used to study optical properties of the undoped and doped PbS nanostructures. Optical characterization shows that emission and absorption peaks are in the infrared (IR) region of the electromagnetic spectrum for all PbS nanostructures. In addition, the optical studies of the doped PbS nanos- tructures reveal that the band gap of the Se-doped PbS is smaller, and the band gap of the Zn-doped PbS is bigger than the band gap of the undoped PbS nanostructures.展开更多
A new method to increase the luminance and quantum efficiency of polymer light emitting diodes with a lower threshold voltage has been reported.The threshold voltagef luminajice and quantum efficiency have been signif...A new method to increase the luminance and quantum efficiency of polymer light emitting diodes with a lower threshold voltage has been reported.The threshold voltagef luminajice and quantum efficiency have been significantly improved by doping certain dopants with a lower highest occupied molecular orbital(HOMO)level into the hole transporting layer.A high performance device has been achieved by addition of the perylene and tri ph enylamin e as a dopant into poly(N-vinylcarbazole).The luminance and quantum efficiency increase by 2-3 times in comparison with the undoped device,reaching 10000cd/m^(2) in luminance and 0.58%in quantum efficiency,while threshold voltage is reduced to one half va/ue.The energy diagram has been obtained by measuring the HOMO levels and band gap values.Based on this,the carriers injection and balance between electrons and holes as well as the action of dopant are discussed.展开更多
The Ni(OH) 2 film electrodes doped respectively with alkali-earth metal aluminum, lead, partial transition metal and some rare-earth metal(altogether 17 kinds of metals) ions were prepared by cathode electrodeposition...The Ni(OH) 2 film electrodes doped respectively with alkali-earth metal aluminum, lead, partial transition metal and some rare-earth metal(altogether 17 kinds of metals) ions were prepared by cathode electrodeposition. The electrode reaction reversibility, the difficult extent of oxygen evolution, the proton diffusion coefficient, the discharge potential of middle value and the active material utilization of the Ni(OH) 2 film electrode were compared with those of the ones doped with the metal ions by means of cyclic voltammetry, potential step and constant current charge-discharge experiments. It was found that Ca 2+ , Co 2+ , Cd 2+ , Al 3+ etc. have obviously positive effect.展开更多
The effects of various dopants on solitons in polyacetylene were studied by using CNDO/2 level semiempirical quantum chemical method. The width of solitons is reduced when dopant is present, and the charge density wav...The effects of various dopants on solitons in polyacetylene were studied by using CNDO/2 level semiempirical quantum chemical method. The width of solitons is reduced when dopant is present, and the charge density wave(CDW) is further gathered on the carbon atom in soliton center. The effects of p-type of dopants are greater than those of n-type of ones. The charge transfer in doped polyacetylene can be achieved by the propagation of CDW along the chain. The conductivity of doped polyacetylene is proportional to the quantity of charge transfer between dopant and polyacetylene chain.展开更多
We adopt a self-consistent real space Kerker method to prevent the divergence from charge sloshing in the simulating transistors with realistic discrete dopants in the source and drain regions. The method achieves eff...We adopt a self-consistent real space Kerker method to prevent the divergence from charge sloshing in the simulating transistors with realistic discrete dopants in the source and drain regions. The method achieves efficient convergence by avoiding unrealistic long range charge sloshing but keeping effects from short range charge sloshing. Numerical results show that discrete dopants in the source and drain regions could have a bigger influence on the electrical variability than the usual continuous doping without considering charge sloshing. Few discrete dopants and the narrow geometry create a situation with short range Coulomb screening and oscillations of charge density in real space. The dopants induced quasilocalized defect modes in the source region experience short range oscillations in order to reach the drain end of the device.The charging of the defect modes and the oscillations of the charge density are identified by the simulation of the electron density.展开更多
Molecular doping is one of the most important tools to manipulate the electrical properties of conjugated polymers for application in organic optoelectronics.The polymer crystallinity and distribution position of the ...Molecular doping is one of the most important tools to manipulate the electrical properties of conjugated polymers for application in organic optoelectronics.The polymer crystallinity and distribution position of the dopant crucially determine electrical conductivity of the doped polymer.However,in solution-mixed doping,the interplay between polymer and dopant leads to highly structural disorder of polymer and random arrangement of dopant.Here,we propose a strategy to ensure the dopant induced polarons have high charge dissociation and transport by letting the conjugated polymers aggregate in the marginal solvent solution by cooling it from higher temperature to room temperature.We select poly(3-hexylthiophene-2,5-diyl)(P3HT)solution doped by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4TCNQ)as a model system.P3HT crystallizes in the marginal solvent,such as 1,1,2-trichloroethane(TCE)driven by the favorπ-πinteraction between planar polymer backbone.The dopant F4TCNQ enters the alkyl side chain region not theπ-πstacking region and thus guarantees high crystallinity and theπ-πinteraction of P3HT.This distribution of F4TCNQ which away from the polymer backbone to ensure higher charge dissociation and transport.Finally,we obtained a high conductivity value of 23 S/cm by doping P3HT with 20%F4TCNQ by using the marginal solvent,which is higher than doping P3HT with a disordered coil conformation in chlorobenzene(CB)of 7 S/cm,which the dopants enter both the alkyl side chain region and theπ-πstacking region.展开更多
Layer-type LiNi0.9Mn0.1O2is promising to be the primary cathode material for lithium-ion batteries(LIBs)due to its excellent electrochemical performance.Unfortunately,the cathode with high nickel content suffers from ...Layer-type LiNi0.9Mn0.1O2is promising to be the primary cathode material for lithium-ion batteries(LIBs)due to its excellent electrochemical performance.Unfortunately,the cathode with high nickel content suffers from severely detrimental structural transformation that causes rapid capacity attenuation.Herein,site-specific dual-doping with Fe and Mg ions is proposed to enhance the structural stability of LiNi0.9Mn0.1O2.The Fe3+dopants are inserted into transition metal sites(3b)and can favorably provide additional redox potential to compensate for charge and enhance the reversibility of anionic redox.The Mg ions are doped into the Li sites(3a)and serve as O_(2)^(-)-Mg^(2+)-O_(2)^(-)pillar to reinforce the electrostatic cohesion between the two adjacent transition-metal layers,which further suppress the cracking and the generation of harmful phase transitions,ultimately improving the cyclability.The theoretical calculations,including Bader charge and crystal orbital Hamilton populations(COHP)analyses,confirm that the doped Fe and Mg can form stable bonds with oxygen and the electrostatic repulsion of O_(2)^(-)-O_(2)^(-)can be effectively suppressed,which effectively mitigates oxygen anion loss at the high delithiation state.This dual-site doping strategy offers new avenues for understanding and regulating the crystalline oxygen redox and demonstrates significant potential for designing high-performance cobalt-free nickel-rich cathodes.展开更多
In this work,Eu^(3+)doped SrTiO_(3)powders were synthesized by sol-gel method and the influences of Eu^(3+)dopants on the crystalline structure,micro structure mo rphology,electronic band-gap and photocatalytic perfor...In this work,Eu^(3+)doped SrTiO_(3)powders were synthesized by sol-gel method and the influences of Eu^(3+)dopants on the crystalline structure,micro structure mo rphology,electronic band-gap and photocatalytic performance for degradation of o rganic pollutant were investigated in detail.Research results reveal that the incorporated Eu^(3+)ions in SrTiO_(3)lattice are preferable to substitute the Sr^(2+)-Ti^(4+)ions pair by two Eu^(3+)ions.The presence of Eu^(3+)ions plays a significant role for the microstructure morphology of the S rTiO_(3)powders,leading to the formation of smaller size nanoparticles with a higher specific surface area.The light absorption capability of the resulting materials is improved owing to the narrowing of the band-gap induced by Eu^(3+)dopants.As a result,the enhanced photocatalytic activity application for photodegradation of Rhodamine B solution is demonstrated for the SrTiO_(3)powders doped with Eu^(3+)ions.展开更多
Tuning of the magnetic interaction plays the vital role in reducing the clustering of magnetic dopant in diluted magnetic semiconductors(DMS).Due to the not well understood magnetic mechanism and the interplay between...Tuning of the magnetic interaction plays the vital role in reducing the clustering of magnetic dopant in diluted magnetic semiconductors(DMS).Due to the not well understood magnetic mechanism and the interplay between different magnetic mechanisms,no efficient and universal tuning strategy is proposed at present.Here,the magnetic interactions and formation energies of isovalent-doped(Mn) and aliovalent(Cr)-doped LiZnAs are studied based on density functional theory(DFT).It is found that the dopant–dopant distance-dependent magnetic interaction is highly sensitive to the carrier concentration and carrier type and can only be explained by the interplay between two magnetic mechanisms,i.e.,superexchange and Zener’s p–d exchange model.Thus,the magnetic behavior and clustering of magnetic dopant can be tuned by the interplay between two magnetic mechanisms.The insensitivity of the tuning effect to U parameter suggests that our strategy could be universal to other DMS.展开更多
We fabricate white phosphorescent organic light-emitting diodes (PHOLEDs) with three dopants and double emissive layer (EML) to achieve color stability. The white PHOLEDs use FIrpic dopant for blue EML (B- EML),...We fabricate white phosphorescent organic light-emitting diodes (PHOLEDs) with three dopants and double emissive layer (EML) to achieve color stability. The white PHOLEDs use FIrpic dopant for blue EML (B- EML), and Ir(ppy)3:Ir(piq)3 dopants for green:red EML (GR-EML) with N,N'-dicarbazolyl-3, 5-benzene (mCP) as host material. Thicknesses of B-EML and GR-EML are adjusted to form a narrow recombination zone at two EML's interface and charge trapping happens in EML according to wide highest occupied molecular orbital and/or lowest unoccupied molecular orbital energy band gap of mCP and smaller energy band gap of dopants. The total thickness of both EMLs is fixed at 30 nm in the device structure of ITO (150 nm)/MoO3 (2 nm)/N,N'-diphenyl-N,N'-bis(1-naphthyl-phenyl)-(1,1″-biphenyl)-4, 4'-diamine (70 nm)/ meP:Firpic-8.0% (12 nm)/mCP:Ir(ppy)3-3.0%:Ir(piq)3-1.5% (18 nm)/2″,2',2"'-(1,3,5-benzinetriyl)-tris(1- phenyl-l-H-benzimidazole) (30 nm)/8-hydroxyquinolinolato-lithium (2 nm)/A1 (120 nm). White PHOLED shows 18.25 cd/A of luminous efficiency and white color coordinates of (0.358 and 0.378) at 5000 cd/m2 and color stability with slight CIExy change of (0.028 and 0.002) as increasing luminance from 1000 to 5000 cd/m^2.展开更多
1 Introduction A particularly efficient and elegant route to chiral mesophases is based on the addition of small amounts of an enantiomerically pure dopant to a nematic phase so that the latter is converted into a cho...1 Introduction A particularly efficient and elegant route to chiral mesophases is based on the addition of small amounts of an enantiomerically pure dopant to a nematic phase so that the latter is converted into a cholesteric phase(See Fig.1).Fig.1 A nematic phase is converted into a cholesteric phase Fig.2 Bis-chelated imine-alkoxy-titanium complexes2 ExperimetalBis-chelated imine-alkoxy-titanium complexes like 1 and 2 (Fig.2) have been synthesizedstarting from triphenyl-substituted aminoethanols, T...展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 61505197 and 61334009the National High-Technology Research and Development Program of China under Grant No 2014AA032604
文摘The effect of back-diffusion of Mg dopants on optoelectronic characteristics of InGaN-based green light-emitting diodes (LEDs) is investigated. The LEDs with less Mg back-diffusion show blue shifts of longer wavelengths and larger wavelengths with the increasing current, which results from the Mg-dopant-related polarization screening. The LEDs show enhanced efficiency with the decreasing Mg back-diffusion in the lower current region. Light outputs follow the power law L α I^m, with smaller parameter m in the LEDs with less Mg back-diffusion, indicating a lower density of trap states. The trap-assisted tunneling current is also suppressed by reducing Mg- defect-related nonradiative centers in the active region. Furthermore, the forward current-voltage characteristics are improved.
文摘Nanosized ZnO powders were prepared with a two-step precipitation method. The average size of ZnO particles was about 80 nm and their size distribution was narrow. Combining with ultrafine additive powders, ZnO base varistor was produced via an oxide mixing route. ZnO varistor derived from normal reagent grade starting materials was investigated for comparison purpose. Outstanding microstructure of the ZnO varistor derived from nanosize ZnO powders and ultrafine dopants was obtained: uniform distribution of fine ZnO grains (less than 3 microns), grain boundary and the dopant position. Higher varistor voltage (U=492 V/mm) and nonlinear coefficient (α=56.2) as well as lower leakage current (TL=1.5 μuA) were achieved. The better electrical properties were attributed to the uniform microstructure, which in turn led to stable and uniform potential barriers. Also this improved technique is more feasible for producing ZnO nanopowders and resulting varistor in large scales.
基金the National Science Foundation(No.20674005)the Flat-Panel Display Special Project of China 863 Plan(No.2008AA03A318)Projects of Chinese National Science and Technology Tackling Key Problems(No.2007BAE31B02)
文摘A novel series of chiral dopants synthesized from(S)-1,2-propanediol and mesogenic carboxylic acids were characterized by FT-IR,~1H NMR,elemental analysis and their helical twisting properties were investigated by doping the chiral dopants into a nematic liquid crystal host(SLC-1717).The results show that,the helical pitch of N~*-LC mixture exhibited a terminal alkyl chain length dependence and the molecular twisting power β also exhibited a temperature dependence(increasing β with increasing temperature).
文摘A series of white phosphorescent OLED devices with buffer layer and multiple dopant structure is investigated in order to obtain better electro-optic performances and color stability. The color coordinate and color stability are related to the location of multiple dopants layer, and the optimized location can compensate for the change of the blue emission intensity under a high voltage and stabilize the spectrum. The electro-optic performances and color stability can be further improved by changing the composition and thickness of the buffer layer between the emitting layer and the electron transport layer.In device B2, the distance from multiple dopant layer to buffer layer is 2 nm and the thickness of buffer layer is 5 nm,the maximum luminance, current density, and power efficiency can reach 9091 cd/m^2, 364.5 mA/cm^2, and 26.74 lm/W,respectively. The variation of international commission on the illumination(CIE) coordinate of device B2 with voltage increasing from 4 V to 7 V is only(0.006, 0.004).
文摘Influences of addition of CaO, CoO and V2O5 on the microstructure and magnetic properties of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites were investigated. The powders of (Mg0.476Mn0.448Zn0.007) (Fe1.997Ti0.002)O4 composition were prepared by using a conventional ceramic powder processing technique. The experimental results showed that the average grain size of the sintered ferrites codoped with 0.03wt% CaO, 0.04wt% CoO and 0.06wt% V2O5 was about 15 μm; the saturation magnetization of ferrites was 68.78 emu/g. The addition of V2O5 in the ferrites can not only increase value of the saturation magnetization, but also decrease the average grain size of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites. Simultaneous incorporation of CoO, CaO and V2O5 dopants into (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 ferrites can not only improve the saturation magnetization of the materials, but also inhibit abnormal grain growth.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61271064,61571171 and 61302009the Zhejiang Provincial Natural Science Foundation of China under Grant No LZ12F01001
文摘We consider intrinsic gate capacitance variations due to random dopants in the nanometer metal oxide semi- conductor field effect transistor (MOSFET) channel. The variations of total gate capacitance and gate transcapacitances are investigated and the strong correlations between the trans-capacitance variations are discovered. A simple statistical model is proposed for accurately capturing total gate capacitance variability based on the correlations. The model fits very well with the Monte Carlo simulations and the average errors are -0.033% for n-type metal-oxide semiconductor and -0.012% for p-type metal-oxide semiconductor, respectively. Our simulation studies also indicate that, owing to these correlations, the total gate capacitance variability will not dominate in gate capacitance variations.
文摘Conductivity dopants with processing properties suitable for industrial applications are of importance to the organic electronics field. However, the number of commercially available organic molecular dopants is limited. The electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyanoquinodimethane (F4-TCNQ) is the most utilized P-dopant;however, it has high volatility and a poor sticking coefficient, which makes it difficult to control doping levels and prevent vacuum system contamination. A design concept for P-type molecular dopants based on the TCNQ core which are substituted to improve processing properties without sacrificing the electronic properties necessary is presented. The correlation between the lowest unoccupied molecular orbital (LUMO) energy and the position of substitution as well as the choice of linker is evaluated. The position of substitution as well as the choice of linker has a significant effect on the electronic properties. However, the geometry of the substituted molecules was not significantly distorted from that of the parent F4-TCNQ, and the electron density was delocalized on the TCNQ core. We also put forward four possible molecular dopants with suitable energy levels.
文摘Thorium is nearly three times more abundant than uranium in the Earth's crust. Some papers evaluate the thorium resourcesin Brazil over 1,200,000 metric t. These figures mean that the country is probably the biggest thorium resource in the world, with onlypart of the territory prospected. Nevertheless, Brazil has not a research program for use of thorium in nuclear reactors, even havingdedicated special attention to the subject in the beginning of its nuclear activities, in the fifties and sixties. From 1985 until 2003 IPENoperated a pilot plant for thorium nitrate production and purification, used by Brazilian industry for production of gas mantles. Thisfacility produced over 170 metric t of thorium nitrate. Despite the non-nuclear application, the pilot plant was unique in the southernhemisphere. On the other hand, Brazil has the biggest world niobium resources. The Brazilian thorium and niobium resources added tothe predictable future importance of alternative fissile materials have motivated this research, since uranium is a finite resource if usedin the present thermal nuclear reactors. Besides this, thorium oxide is an important nuclear reactor material. It is a refractory oxide andits ceramic fabrication process involves a very high temperature sintering treatment considering that thoria melting point is very high(3,650 K). Cations of elements of the group VB (V, Nb and Ta) have a known effect in the reduction of thoria sintering temperature.IPEN has initiated an investigation about the use of niobium as a dopant for thoria sintering temperature reduction. The thoria used inthe research was produced in the IPEN's pilot plant and different amounts of niobium oxide (Nb2Os) will be added to thoria by differentroutes. The powders will be compressed and the compacted pellets will be sintered at different temperatures. The influence of thedifferent parameters in the density of sintered pellets is being investigated. This paper presents the chemical and physicalcharacterization for the thoria used in the investigation.
基金This work is partly supported by the National Natural Science Foundation of China under Grant Nos.11575034,11275031,11475033the Fundamental Research Program of CAEP(Contract No.2013A0102002).
文摘X-ray drive asymmetry is one of the main seeds of low-mode implosion asymmetry that blocks further improvement of the nuclear per-formance of“high-foot”experiments on the National Ignition Facility[Miller et al.,Nucl.Fusion 44,S228(2004)].More particularly,the P2 asymmetry of Au's M-band flux can also severely influence the implosion performance of ignition capsules[Li et al.,Phys.Plasmas 23,072705(2016)].Here we study the smoothing effect of mid-and/or high-Z dopants in ablator on Au's M-band flux asymmetries,by modeling and comparing the implosion processes of a Ge-doped ignition capsule and a Si-doped one driven by X-ray sources with P2 M-band flux asymmetry.As the results,(1)mid-or high-Z dopants absorb hard X-rays(M-band flux)and re-emit isotropically,which helps to smooth the asymmetric M-band flux arriving at the ablation front,therefore reducing the P2 asymmetries of the imploding shell and hot spot;(2)the smoothing effect of Ge-dopant is more remarkable than Si-dopant because its opacity in Au's M-band is higher than the latter's;and(3)placing the doped layer at a larger radius in ablator is more efficient.Applying this effect may not be a main measure to reduce the low-mode implosion asymmetry,but might be of significance in some critical situations such as inertial confinement fusion(ICF)experiments very near the performance cliffs of asymmetric X-ray drives.
基金the Iranian National Science Foundation (INSF) for a research grant support the Islamic Azad University(I.A.U.), Masjed-Soleiman and Ahwaz Branches, respectively, for their financial support of this research workthe financial support from the Ministry of Higher Education of Malaysia for the High Impact Research Grant (UM.C/1/HIR/MOHE/SC/21)
文摘Selenium and zinc are used as anionic and cationic dopant elements to dope PbS nanostructures. The undoped and doped PbS nanostructures are grown using a thermal evaporation method. Scanning electron microscopy (SEM) results show similar morphologies for the undoped and doped PbS nanostructures. X-ray diffraction (XRD) patterns of three sets of the nanostructures indicate that these nanostructures each have a PbS structure with a cubic phase. Evidence of dopant incorporation is demonstrated by X-ray photoelectron spectroscopy (XPS). Raman spectra of the synthesized samples con- firm the XRD results and indicate five Raman active modes, which relate to the PbS cubic phase for all the nanostructures. Room temperature photoluminescence (PL) and UV-Vis spectrometers are used to study optical properties of the undoped and doped PbS nanostructures. Optical characterization shows that emission and absorption peaks are in the infrared (IR) region of the electromagnetic spectrum for all PbS nanostructures. In addition, the optical studies of the doped PbS nanos- tructures reveal that the band gap of the Se-doped PbS is smaller, and the band gap of the Zn-doped PbS is bigger than the band gap of the undoped PbS nanostructures.
基金Supported by the National Natural Science Foundation of China.
文摘A new method to increase the luminance and quantum efficiency of polymer light emitting diodes with a lower threshold voltage has been reported.The threshold voltagef luminajice and quantum efficiency have been significantly improved by doping certain dopants with a lower highest occupied molecular orbital(HOMO)level into the hole transporting layer.A high performance device has been achieved by addition of the perylene and tri ph enylamin e as a dopant into poly(N-vinylcarbazole).The luminance and quantum efficiency increase by 2-3 times in comparison with the undoped device,reaching 10000cd/m^(2) in luminance and 0.58%in quantum efficiency,while threshold voltage is reduced to one half va/ue.The energy diagram has been obtained by measuring the HOMO levels and band gap values.Based on this,the carriers injection and balance between electrons and holes as well as the action of dopant are discussed.
基金Supported by the Science Foundation of Jilin Province( No.980 5 6 2
文摘The Ni(OH) 2 film electrodes doped respectively with alkali-earth metal aluminum, lead, partial transition metal and some rare-earth metal(altogether 17 kinds of metals) ions were prepared by cathode electrodeposition. The electrode reaction reversibility, the difficult extent of oxygen evolution, the proton diffusion coefficient, the discharge potential of middle value and the active material utilization of the Ni(OH) 2 film electrode were compared with those of the ones doped with the metal ions by means of cyclic voltammetry, potential step and constant current charge-discharge experiments. It was found that Ca 2+ , Co 2+ , Cd 2+ , Al 3+ etc. have obviously positive effect.
文摘The effects of various dopants on solitons in polyacetylene were studied by using CNDO/2 level semiempirical quantum chemical method. The width of solitons is reduced when dopant is present, and the charge density wave(CDW) is further gathered on the carbon atom in soliton center. The effects of p-type of dopants are greater than those of n-type of ones. The charge transfer in doped polyacetylene can be achieved by the propagation of CDW along the chain. The conductivity of doped polyacetylene is proportional to the quantity of charge transfer between dopant and polyacetylene chain.
基金Project supported by the National Natural Science Foundation of China(Grant No.11104069)
文摘We adopt a self-consistent real space Kerker method to prevent the divergence from charge sloshing in the simulating transistors with realistic discrete dopants in the source and drain regions. The method achieves efficient convergence by avoiding unrealistic long range charge sloshing but keeping effects from short range charge sloshing. Numerical results show that discrete dopants in the source and drain regions could have a bigger influence on the electrical variability than the usual continuous doping without considering charge sloshing. Few discrete dopants and the narrow geometry create a situation with short range Coulomb screening and oscillations of charge density in real space. The dopants induced quasilocalized defect modes in the source region experience short range oscillations in order to reach the drain end of the device.The charging of the defect modes and the oscillations of the charge density are identified by the simulation of the electron density.
基金financially supported by the National Natural Science Foundation of China(No.51933010)。
文摘Molecular doping is one of the most important tools to manipulate the electrical properties of conjugated polymers for application in organic optoelectronics.The polymer crystallinity and distribution position of the dopant crucially determine electrical conductivity of the doped polymer.However,in solution-mixed doping,the interplay between polymer and dopant leads to highly structural disorder of polymer and random arrangement of dopant.Here,we propose a strategy to ensure the dopant induced polarons have high charge dissociation and transport by letting the conjugated polymers aggregate in the marginal solvent solution by cooling it from higher temperature to room temperature.We select poly(3-hexylthiophene-2,5-diyl)(P3HT)solution doped by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4TCNQ)as a model system.P3HT crystallizes in the marginal solvent,such as 1,1,2-trichloroethane(TCE)driven by the favorπ-πinteraction between planar polymer backbone.The dopant F4TCNQ enters the alkyl side chain region not theπ-πstacking region and thus guarantees high crystallinity and theπ-πinteraction of P3HT.This distribution of F4TCNQ which away from the polymer backbone to ensure higher charge dissociation and transport.Finally,we obtained a high conductivity value of 23 S/cm by doping P3HT with 20%F4TCNQ by using the marginal solvent,which is higher than doping P3HT with a disordered coil conformation in chlorobenzene(CB)of 7 S/cm,which the dopants enter both the alkyl side chain region and theπ-πstacking region.
基金the financial supports from the Key Research and Development Project in Shaanxi Province(2023-YBGY-446)the Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering(2022SX-TD003)。
文摘Layer-type LiNi0.9Mn0.1O2is promising to be the primary cathode material for lithium-ion batteries(LIBs)due to its excellent electrochemical performance.Unfortunately,the cathode with high nickel content suffers from severely detrimental structural transformation that causes rapid capacity attenuation.Herein,site-specific dual-doping with Fe and Mg ions is proposed to enhance the structural stability of LiNi0.9Mn0.1O2.The Fe3+dopants are inserted into transition metal sites(3b)and can favorably provide additional redox potential to compensate for charge and enhance the reversibility of anionic redox.The Mg ions are doped into the Li sites(3a)and serve as O_(2)^(-)-Mg^(2+)-O_(2)^(-)pillar to reinforce the electrostatic cohesion between the two adjacent transition-metal layers,which further suppress the cracking and the generation of harmful phase transitions,ultimately improving the cyclability.The theoretical calculations,including Bader charge and crystal orbital Hamilton populations(COHP)analyses,confirm that the doped Fe and Mg can form stable bonds with oxygen and the electrostatic repulsion of O_(2)^(-)-O_(2)^(-)can be effectively suppressed,which effectively mitigates oxygen anion loss at the high delithiation state.This dual-site doping strategy offers new avenues for understanding and regulating the crystalline oxygen redox and demonstrates significant potential for designing high-performance cobalt-free nickel-rich cathodes.
基金Project supported by the National Natural Science Foundation of China(51777138)Natural Science Foundation of Tianjin City(18JCZDJC99700,18JCYBJC87400,18JCQNJC73900)Scientific Developing Foundation of Tianjin Education Commission(2018KJ130)。
文摘In this work,Eu^(3+)doped SrTiO_(3)powders were synthesized by sol-gel method and the influences of Eu^(3+)dopants on the crystalline structure,micro structure mo rphology,electronic band-gap and photocatalytic performance for degradation of o rganic pollutant were investigated in detail.Research results reveal that the incorporated Eu^(3+)ions in SrTiO_(3)lattice are preferable to substitute the Sr^(2+)-Ti^(4+)ions pair by two Eu^(3+)ions.The presence of Eu^(3+)ions plays a significant role for the microstructure morphology of the S rTiO_(3)powders,leading to the formation of smaller size nanoparticles with a higher specific surface area.The light absorption capability of the resulting materials is improved owing to the narrowing of the band-gap induced by Eu^(3+)dopants.As a result,the enhanced photocatalytic activity application for photodegradation of Rhodamine B solution is demonstrated for the SrTiO_(3)powders doped with Eu^(3+)ions.
基金Project supported by the Natural Science Foundation of Shaanxi Province of China(Grant No.2013JQ1018)the Natural Science Foundation of Department of Education of Shaanxi Province of China(Grant No.15JK1759)+3 种基金the Double First-class University Construction Project of Northwest Universitythe financial support of Chinese University of Hong Kong(CUHK)(Grant No.4053084)University Grants Committee of Hong Kong,China(Grant No.24300814)start-up funding of CUHK。
文摘Tuning of the magnetic interaction plays the vital role in reducing the clustering of magnetic dopant in diluted magnetic semiconductors(DMS).Due to the not well understood magnetic mechanism and the interplay between different magnetic mechanisms,no efficient and universal tuning strategy is proposed at present.Here,the magnetic interactions and formation energies of isovalent-doped(Mn) and aliovalent(Cr)-doped LiZnAs are studied based on density functional theory(DFT).It is found that the dopant–dopant distance-dependent magnetic interaction is highly sensitive to the carrier concentration and carrier type and can only be explained by the interplay between two magnetic mechanisms,i.e.,superexchange and Zener’s p–d exchange model.Thus,the magnetic behavior and clustering of magnetic dopant can be tuned by the interplay between two magnetic mechanisms.The insensitivity of the tuning effect to U parameter suggests that our strategy could be universal to other DMS.
文摘We fabricate white phosphorescent organic light-emitting diodes (PHOLEDs) with three dopants and double emissive layer (EML) to achieve color stability. The white PHOLEDs use FIrpic dopant for blue EML (B- EML), and Ir(ppy)3:Ir(piq)3 dopants for green:red EML (GR-EML) with N,N'-dicarbazolyl-3, 5-benzene (mCP) as host material. Thicknesses of B-EML and GR-EML are adjusted to form a narrow recombination zone at two EML's interface and charge trapping happens in EML according to wide highest occupied molecular orbital and/or lowest unoccupied molecular orbital energy band gap of mCP and smaller energy band gap of dopants. The total thickness of both EMLs is fixed at 30 nm in the device structure of ITO (150 nm)/MoO3 (2 nm)/N,N'-diphenyl-N,N'-bis(1-naphthyl-phenyl)-(1,1″-biphenyl)-4, 4'-diamine (70 nm)/ meP:Firpic-8.0% (12 nm)/mCP:Ir(ppy)3-3.0%:Ir(piq)3-1.5% (18 nm)/2″,2',2"'-(1,3,5-benzinetriyl)-tris(1- phenyl-l-H-benzimidazole) (30 nm)/8-hydroxyquinolinolato-lithium (2 nm)/A1 (120 nm). White PHOLED shows 18.25 cd/A of luminous efficiency and white color coordinates of (0.358 and 0.378) at 5000 cd/m2 and color stability with slight CIExy change of (0.028 and 0.002) as increasing luminance from 1000 to 5000 cd/m^2.
文摘1 Introduction A particularly efficient and elegant route to chiral mesophases is based on the addition of small amounts of an enantiomerically pure dopant to a nematic phase so that the latter is converted into a cholesteric phase(See Fig.1).Fig.1 A nematic phase is converted into a cholesteric phase Fig.2 Bis-chelated imine-alkoxy-titanium complexes2 ExperimetalBis-chelated imine-alkoxy-titanium complexes like 1 and 2 (Fig.2) have been synthesizedstarting from triphenyl-substituted aminoethanols, T...