A Fractional Drift Diffusion Model for Organic Semiconductor Devices

Because charge carriers of many organic semiconductors(OSCs)exhibit fractional drift diffusion(Fr-DD)transport properties,the need to develop a Fr-DD model solver becomes more apparent.However,the current research on solving the governing equations of the Fr-DD model is practically nonexistent.In this paper,an iterative solver with high precision is developed to solve both the transient and steady-state Fr-DD model for organic semiconductor devices.The Fr-DD model is composed of two fractionalorder carriers(i.e.,electrons and holes)continuity equations coupled with Poisson’s equation.By treating the current density as constants within each pair of consecutive grid nodes,a linear Caputo’s fractional-order ordinary differential equation(FrODE)can be produced,and its analytic solution gives an approximation to the carrier concentration.The convergence of the solver is guaranteed by implementing a successive over-relaxation(SOR)mechanism on each loop of Gummel’s iteration.Based on our derivations,it can be shown that the Scharfetter–Gummel discretization method is essentially a special case of our scheme.In addition,the consistency and convergence of the two core algorithms are proved,with three numerical examples designed to demonstrate the accuracy and computational performance of this solver.Finally,we validate the Fr-DD model for a steady-state organic field effect transistor(OFET)by fitting the simulated transconductance and output curves to the experimental data.

'The Theory of Field-Effect Transistors XII.The Bipolar Drift and Diffusion Currents(1-2-MOS-Gates on Thin-Thick Pure-Impure Base)

The previous report （XI） gave the electrochemical-potential theory of the Bipolar Field-Effect Transistors. This report （XII） gives the drift-diffusion theory. Both treat 1-gate and 2-gate, pure-base and impure-base, and thin and thick base. Both utilize the surface and bulk potentials as the parametric variables to couple the voltage and current equations. In the present drift-diffusion theory, the very many current terms are identified by their mobility multiplier for the components of drift current,and the diffusivity multiplier for the components of the diffusion current. Complete analytical driftdiffusion equations are presented to give the DC current-voltage characteristics of four common MOS transistor structures. The drift current consists of four terms： 1-D （One-Dimensional） bulk charge drift term, 1-D carrier space-charge drift term,l-D Ex^2 （transverse electric field） drift term,2-D drift term. The diffusion current consists of three terms： 1-D bulk charge diffusion term,l-D carrier space-charge diffusion term,and 2-D diffusion term. The 1-D Ex^2 drift term was missed by all the existing transistor theories, and contributes significantly, as much as 25 % of the total current when the base layer is nearly pure. The 2-D terms come from longitudinal gradient of the longitudinal electric field,which scales as the square of the Debye to Channel length ratio, at 25nm channel length with nearly pure base, （LD/L）^2 = 10^6 but with impurity concentration of 10^18cm^-3 , （LD/L）^2 = 10^-2 .

Asymptotic of the Solutions to the Initial Boundary Value Problem for the Diffusion Equations for Semiconductors

In this paper, we study the asymptotic behavior of the solutions to the initial boundary value problem for unipolar drift diffusion equations for semiconductors. Under the proper assumptions on doping profile and initial value, we prove that the smooth solutions to these evolutionary problems tend to the unique stationary solution exponentially as time tends to infinity.

Asymptotic of the Solutions of the Initial Boundary Value Problem for the Diffusion Equations for Semiconductors (Ⅱ)

The paper deal with the asymptotic behavior of the solutions to the initial boundary value problem for unipolar drift diffusion equations for semiconductors. Under the proper assumptions on doping profile and initial value, we prove that the smooth solutions to these evolutionary problems tend to the unique stationary solution exponentially as time tends to infinity.

An improved memristor model for brain-inspired computing

Memristors, as memristive devices, have received a great deal of interest since being fabricated by HP labs. The forgetting effect that has significant influences on memristors＇ performance has to be taken into account when they are employed. It is significant to build a good model that can express the forgetting effect well for application researches due to its promising prospects in brain-inspired computing. Some models are proposed to represent the forgetting effect but do not work well. In this paper, we present a novel window function, which has good performance in a drift model. We analyze the deficiencies of the previous drift diffusion models for the forgetting effect and propose an improved model. Moreover,the improved model is exploited as a synapse model in spiking neural networks to recognize digit images. Simulation results show that the improved model overcomes the defects of the previous models and can be used as a synapse model in brain-inspired computing due to its synaptic characteristics. The results also indicate that the improved model can express the forgetting effect better when it is employed in spiking neural networks, which means that more appropriate evaluations can be obtained in applications.

Comparative Methodical Assessment of Established MOSFET Threshold Voltage Extraction Methods at 10-nm Technology Node

Threshold voltage (VTH) is the most evocative aspect of MOSFET operation. It is the crucial device constraint to model on-off transition characteristics. Precise VTH value of the device is extracted and evaluated by several estimation techniques. However, these assessed values of VTH diverge from the exact values due to various short channel effects (SCEs) and non-idealities present in the device. Numerous prevalent VTH extraction methods are discussed. All the results are verified by extensive 2-D TCAD simulation and confirmed through analytical results at 10-nm technology node. Aim of this research paper is to explore and present a comparative study of largely applied threshold extraction methods for bulk driven nano-MOSFETs especially at 10-nm technology node along with various sub 45-nm technology nodes. Application of the threshold extraction methods to implement noise analysis is briefly presented to infer the most appropriate extraction method at nanometer technology nodes.

The effects of electric and magnetic fields on the current spin polarization and magnetoresistance in a ferromagnetic/organic semiconductor/ferromagnetic（FM/OSC/FM） system

From experimental results of spin polarized injection and transport in organic semiconductors（OSCs）,we theoretically study the current spin polarization and magnetoresistance under an electric and a magnetic field in a ferromagnetic/organic semiconductor/ferromagnetic（FM/OSC/FM） sandwich structure according to the spin drift-diffusion theory and Ohm＇s law.From the calculations,it is found that the interfacial current spin polarization is enhanced by several orders of magnitude through tuning the magnetic and electric fields by taking into account the specific characteristics of OSC.Furthermore,the effects of the electric and magnetic fields on the magnetoresistance are also discussed in the sandwich structure.

Enhancing betavoltaic nuclear battery performance with 3D P^(+)PNN^(+)multi-groove structure via carrier evolution

Betavoltaic nuclear batteries offer a promising alternative energy source that harnesses the power of beta particles emitted by radioisotopes.To satisfy the power demands of microelectromechanical systems(MEMS),3D structures have been proposed as a potential solution.Accordingly,this paper introduces a novel 3D^(63)Ni–SiC-based P^(+)PNN^(+)structure with a multi-groove design,avoiding the need for PN junctions on the inner surface,and thus reducing leakage current and power losses.Monte Carlo simulations were performed considering the fully coupled physical model to extend the electron–hole pair generation rate to a 3D structure,enabling the efficient design and development of betavoltaic batteries with complex 3D structures.As a result,the proposed model produces the significantly higher maximum output power density of 19.74μW/cm^(2) and corresponding short-circuit current,open-circuit voltage,and conversion efficiency of 8.57μA/cm^(2),2.45 V,and4.58%,respectively,compared with conventional planar batteries.From analysis of the carrier transport and collection characteristics using the COMSOL Multiphysics code,we provide deep insights regarding power increase,and elucidate the discrepancies between the ideal and simulated performances of betavoltaic batteries.Our work offers a promising approach for the design and optimization of high-output betavoltaic nuclear batteries with a unique 3D design,and serves as a valuable reference for future device fabrication.

The effects of electric and magnetic fields on the current spin polarization and magnetoresistance in a ferromagnetic/organic semiconductor/ferromagnetic(FM/OSC/FM) system

From experimental results of spin polarized injection and transport in organic semiconductors(OSCs),we theoretically study the current spin polarization and magnetoresistance under an electric and a magnetic field in a ferromagnetic/organic semiconductor/ferromagnetic(FM/OSC/FM) sandwich structure according to the spin drift-diffusion theory and Ohm’s law.From the calculations,it is found that the interfacial current spin polarization is enhanced by several orders of magnitude through tuning the magnetic and electric fields by taking into account the specific characteristics of OSC.Furthermore,the effects of the electric and magnetic fields on the magnetoresistance are also discussed in the sandwich structure.

Large anisotropic negative thermal expansion in Cu-TDPAT metalorganic framework:A combined in situ X-ray diffraction and DRIFTS study

Cu-TDPAT(H_(6)TDPAT=2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine),a stable nanoporous metal-organic framework with rht topology,has sparked broad interest as an adsorbent for several chemical separation processes.In this work,in situ synchrotron diffraction experiments followed by sequential LeBail refinements reveal that Cu-TDPAT shows unusually large anisotropic negative thermal expansion(NTE).The PASCal crystallography tool,used to analyze the magnitude of the NTE,reveals an average volumetric thermal expansion coefficientαv=-20.3 MK^(-1).This value is significantly higher than the one reported for Cu-BTC(also known as HKUST-1),which contains the same Cu-paddlewheel building unit,αv=-12 MK^(-1).In situ synchrotron single crystal X-ray diffraction and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)were employed to shed light on the NTE mechanism.Using these two methods,we were able to elucidate the three main structural motions that are responsible for the NTE effect.The more pronounced NTE behavior of Cu-TDPAT is attributed to the lower symmetry combined with the more complex ligand structure when compared to Cu-BTC.The knowledge obtained in this work is important for understanding the behavior of the adsorbent under transient variable temperature conditions in fixed adsorption beds.

Highly efficient photo-thermal synergistic catalysis of CO_(2)methanation over La_(1-x)Ce_(x)NiO_(3)perovskite-catalyst

Solar-driven photo-thermal catalytic CO_(2)methanation reaction is a promising technology to alleviate the problems posed by greenhouse gases emissions.However,designing advanced photo-thermal catalysts remains a research challenge for CO_(2)methanation reaction.In this work,a series of ABO3(A=lanthanide,B=transition metal)perovskite catalysts with Ce-substituted LaNiO3(La_(1-x)Ce_(x)NiO_(3),x=0,0.2,0.5,0.8,1)were synthesized for CO_(2)methanation.The La_(0.2)Ce_(0.8)NiO_(3) exhibited the highest CH_(4) formation rate of 258.9 mmol·g^(-1)·hcat-1,CO_(2)conversion of 55.4%and 97.2%CH_(4) selectivity at 300℃with the light intensity of 2.9 W·cm^(-2).Then the catalysts were thoroughly analyzed by physicochemical structure and optical properties characterizations.The partial substitution of the A-site provided more active sites for the adsorption and activation of CO_(2)/H_(2).The sources of the active sites were considered to be the oxygen vacancies(O_(v))created by lattice distortions due to different species of ions(La^(3+),Ce^(4+),Ce^(3+))and exsolved Ni0 by H_(2)reduction.The catalysts have excellent light absorption absorbance and low electron-hole(e^(-)/h^(+))recombination rate,which greatly contribute to the excellent performance in photo-thermal synergistic catalysis(PTC)CO_(2)methanation.The results of in situ irradiated electron paramagnetic resonance spectrometer(ISI-EPR)and ISI-X-ray photoelectron spectroscopy(XPS)indicated that the aggregation of unpaired electrons near the defects and Ni metal(from La and Ce ions to Ov and Ni0)accelerated adsorption and activation of CO_(2)/H_(2).At last,the catalyst properties and structure were correlated with the proposed reaction mechanism from the in situ diffuse reflection infrared Fourier transform spectrum(DRIFTS)measurements.The in situ precipitation of the B-site enhanced the dispersion of Ni,while its enriched photoelectrons upon illumination further promote hydrogen dissociation.More H^(*)spillover accelerated the rate-determining step(RDS)of HCOO*hydrogenation.This work provides the theoretical basis for the development of catalysts and industrial application.

Enhancement of toluene oxidation performance over La_(1-x)CoO_(3-δ) perovskite by lanthanum non-stoichiometry

La_(1-x)CoO_(3-δ)catalysts with different non-stoichiometry of lanthanum ions were synthesized by using the sol-gel method,and their catalytic performance in toluene combustion was investigated.The results showed that the catalytic activity and stability of A-site nonstoichiometric La_(1-x)CoO_(3-δ)were improved to a certain extent compared with pure LaCoO_(3)perovskite.Among them,the La_(0.9)CoO_(3-δ)catalyst gave the best catalytic performance for toluene oxidation.It achieved 90%toluene conversion at 205℃under the conditions of a WHSV(weight hourly space velocity)of 22,500 mL/(g·hr)and a 500 ppmV-toluene concentration.Various characterization techniques were used to investigate the relationship between the structure of these catalysts and their catalytic performance.It was found that the non-stoichiometric modification of the lanthanum ion at position A in LaCoO_(3)changed the surface element state of the catalyst and increased the oxygen vacancy content,thus,combined with improved reducibility,improving toluene degradation on the catalyst.

Catalytic Combustion of Lean Methane Assisted by Electric Field over Pd/Co_3O_4 Catalysts at Low Temperature

A series of Pd/Co_3O_4 catalysts were prepared by Self-Propagating High-Temperature Synthesis(SHS)method in this study, and electric field was applied for catalytic combustion of lean methane over Pd/Co_3O_4 catalysts at low temperature. When electric field was applied, the catalytic combustion performance of Pd/Co_3O_4 catalysts was greatly improved, and the application of electric field could reduce the load of active element Pd to some extent while maintaining the same efficiency. Based on experimental tests and the analysis results of X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), H2-temperature-programmed reduction(H2-TPR) and in-situ diffuse reflectance infrared Fourier transform spectroscopy(in-situ DRIFTS), the mechanism of catalytic oxidation of CH_4 over Pd/Co_3O_4 catalysts in electric field was proposed. The catalytic combustion of CH_4 occurs only when the temperature is higher than 250?C normally, but when electric field was applied, the whole process of CH_4 oxidation was promoted significantly and the reaction temperature was reduced. Electric field could promote the reduction of the support Co_3O_4 to release the lattice oxygen, resulting in the increase of PdOxand the surface chemisorbed oxygen, which could provide more active sites for the low-temperature oxidation of CH_4. Furthermore, electric field could accelerate the dehydroxylation of CoOOH to further enhance the activity of the catalysts.

Effect of ceria surface facet on stability and reactivity of isolated platinum atoms

Well-defined surface structures and uniformity are key factors in exploring structure–activity relationships in heterogeneous catalysts.A modified atomic layer deposition method and three well-defined CeO_(2) nanoshapes,octahedra with(111)surfaces,cubes exposing(100)facets,and rods with(100)and(110)surface facet terminations,were utilized to synthesize ultra-low loading Pt/CeO_(2) catalysts and allow investigations on the influence of ceria surface facet on isolated Pt species under reducing conditions.A mild reduction temperature(150℃)reduces the initial platinum ions present on the surfaces of the ceria support but preserves the isolated Pt atoms on all ceria surface facets.In contrast,a reduction temperature of 350°C,reveals very different interactions between the initial single Pt atoms and the various ceria surface facets,leading to dissimilar and nonuniform Pt ensembles on the three ceria shapes.To isolate facet dependent Pt–CeO_(2) interactions and avoid variations between Pt species,the Pt1/CeO_(2) catalysts after reduction at 150°C were subjected to CO oxidation conditions.The isolated Pt atoms on the CeO_(2) octahedra and cubes are less active in the CO oxidation reaction,compared with Pt on CeO_(2) rods.In the case of Pt on the CeO_(2) octahedra this is due to strongly bound CO blocking active sites together with a stable CeO_(2)(111)surface limiting the oxygen supply from the support.On the CeO_(2) cubes,some Pt is not available for reaction and CO is bound strongly on the available Pt species.In addition,the Pt catalysts supported on the CeO_(2) cubes are not stable with time on stream.The isolated Pt atoms on the CeO_(2) rods are considerably more active under these conditions and this is due to a weaker Pt–CO bond strength and more facile reverse oxygen spillover from the defect-rich(110)surfaces of the rods due to the lower energy of oxygen vacancy formation on this CeO_(2) surface.The Pt supported on the CeO_(2) rods is also remarkably stable with time on stream.This work demonstrates the importance of using ultra-low loadings of active metal and well-defined oxide supports to isolate interactions between single metal atoms and oxide supports and determine the effects of the oxide support surface facet on the active metal at the atomic level.

Study on Oxidation Activity of CuCeZrO_x Doped with K for Diesel Engine Particles in NO/O_2

CuCeZrO_x and KCuCeZrO_x catalysts were synthesized and coated on the blank diesel particulate filter(DPF)substrate and a particulate matter(PM)loading apparatus was used for soot loading.The catalytic performances of soot oxidation were evaluated by temperature programmed combustion(TPC)test and characterization tests were conducted to investigate the physicochemical properties of the catalysts.The reaction mechanism in the oxidation process was analyzed with diffuse reflectance infrared Fourier transform spectroscopy.The results demonstrated that CuCeZrO_x catalyst exhibited high activities of soot oxidation at low temperature and the best results have been attained with Cu_(0.9)Ce_(0.05)Zr_(0.05)O_x over which the maximum soot oxidation rate decreased to 410~?C.Characterization tests have shown that catalysts containing 90%Cu have uniformly distributed grains and small particle sizes,which provide excellent oxidation activity by providing more active sites and forming a good bond between the catalyst and the soot.The low-temperature oxidation activity of soot could be further optimized due to the excellent elevated NO’s conversion rate by partially substituting Cu with K.The maximum particle oxidation rate can be easily realized at such a low temperature as 347~?C.