MXenes have wide applications in energy storage devices because of their compositional diversity.Electronic and optical properties,Bader charge and quantum capacitance of Janus ScHfCO_(2)MXene under biaxial strain are...MXenes have wide applications in energy storage devices because of their compositional diversity.Electronic and optical properties,Bader charge and quantum capacitance of Janus ScHfCO_(2)MXene under biaxial strain are studied by density functional theory(DFT).The substitution of Hf atoms induces the decrease of the band gap of ScHfCO_(2),which changes from direct semiconductor into indirect semiconductor.Band gap generally increases with the increase of the tensile strain because of the blueshift of Sc-d and Hf-d orbits,and ScHfCO_(2)changes to M→K indirect semiconductor at 5%strain.ScHfCO_(2)under strains from-5%to 4%maintains the indirect bandgap characteristics.The appearance of built-in electric field in ScHfCO_(2)under strain improves the charge redistribution across Janus layer.ScHfCO_(2)under compressive strain has better conductivity than ScHfCO_(2)under tensile strain.ScHfCO_(2)under strains are all promising cathode materials.Larger voltage improves the character of cathode materials because of their much larger|Qc|when compared with those at aqueous system.展开更多
This study presents an analysis of the structural,electronic,and surface properties of NiO using first-principles density func-tional theory(DFT)calculations.The investigation focuses on three lattice parameters(a=4.2...This study presents an analysis of the structural,electronic,and surface properties of NiO using first-principles density func-tional theory(DFT)calculations.The investigation focuses on three lattice parameters(a=4.23Å,4.187Å,and 4.183Å)to explore how lattice strain influences the electronic band structure,density of states(DOS),quantum capacitance(QC),and adsorption energies of alkali metals(Li,Na,K)on the NiO[001]and[111]planes.The study reveals that a decrease in the lattice parameter leads to a reduction in the band gap(from 2.28 to 2.19 eV).The adsorption energies demonstrate a strong surface reactivity,with Li showing the highest affinity for the NiO[001]surface and Na exhibiting the highest adsorption energy on the more reactive NiO[111]surface.The QC analysis demonstrated notable enhancements following alkali metal adsorption,with Li on the NiO[001]surface exhibiting a QC of 38.9μF/cm^(2)at a=4.23Å,whereas Na on the NiO[111]surface achieved a QC of 32.7μF/cm^(2)at a=4.187Å.These findings underscore the critical role of lattice strain and surface orientation in modulating the electrochemical performance of NiO,with potential applications in catalysis,energy storage,and electronic devices.展开更多
This paper proposes a compact model for carbon nanotube field effect transistor（CNTFET） based on surface potential and conduction band minima. The proposed model relates the I–V characteristics to chirality under q...This paper proposes a compact model for carbon nanotube field effect transistor（CNTFET） based on surface potential and conduction band minima. The proposed model relates the I–V characteristics to chirality under quantum capacitance limit. C–V characteristics have been efficiently modelled for different capacitance models which are used to find the relationship between CNT surface potential and gate voltage. The role of different capacitances is discussed and it has been found that the proposed circuit compact model strictly follows quantum capacitance limit. The proposed model is efficiently designed for circuit simulations as it denies self-consistent numerical simulation. Furthermore, this compact model is compared with experimental results. The model has been used to simulate an inverter using HSPICE.展开更多
Transistor size is constantly being reduced to improve performance as well as power consumption. For the channel length to be reduced, the corresponding gate dielectric thickness should also be reduced. Unfortunately,...Transistor size is constantly being reduced to improve performance as well as power consumption. For the channel length to be reduced, the corresponding gate dielectric thickness should also be reduced. Unfortunately, graphene devices are more complicated due to an extra capacitance called quantum capacitance （CQ） which limits the effective gate dielectric reduction. In this work, we analyzed the effect of CQ on device-scaling issues by extracting it from scaling of the channel length of devices. In contrast to previous reports for metal-insulator- metal structures, a practical device structure was used in conjunction with direct radio-frequency field-effect transistor measurements to describe the graphene channels. In order to precisely extract device parameters, we reassessed the equivalent circuit, and concluded that the on-state model should in fact be used. By careful consideration of the underlap region, our device modeling was shown to be in good agreement with the experimental data. CQ contributions to equivalent oxide thickness were analyzed in detail for varying impurity concentrations in graphene. Finally, we were able to demonstrate that despite contributions from CQ, graphene＇s high mobility and low-voltage operation allows for ~raphene channels suitable for next generation transistors.展开更多
Graphene-based frameworks suffer from a low quantum capacitance due to graphene’s Dirac point at the Fermi level.This theoretical study investigated the effect structural defects,nitrogen and boron doping,and surface...Graphene-based frameworks suffer from a low quantum capacitance due to graphene’s Dirac point at the Fermi level.This theoretical study investigated the effect structural defects,nitrogen and boron doping,and surface epoxy/hydroxy groups have on the electronic structure and capacitance of graphene.Density functional theory calculations reveal that the lowest energy configurations for nitrogen or boron substitutional doping occur when the dopant atoms are segregated.This elucidates why the magnetic transition for nitrogen doping is experimentally only observed at higher doping levels.We also highlight that the lowest energy configuration for a single vacancy defect is magnetic.Joint density functional theory calculations show that the fixed band approximation becomes increasingly inaccurate for electrolytes with lower dielectric constants.The introduction of structural defects rather than nitrogen or boron substitutional doping,or the introduction of adatoms leads to the largest increase in density of states and capacitance around graphene’s Dirac point.However,the presence of adatoms or substitutional doping leads to a larger shift of the potential of zero charge away from graphene’s Dirac point.展开更多
A mathematical model is developed predicting the behavior of gate capacitance with the nanoscale variation of barrier thickness in AlN/GaN MOSHEMT and its effect on gate capacitances of AIInN/GaN and AlGaN/GaN MOSHEMT...A mathematical model is developed predicting the behavior of gate capacitance with the nanoscale variation of barrier thickness in AlN/GaN MOSHEMT and its effect on gate capacitances of AIInN/GaN and AlGaN/GaN MOSHEMTs through TCAD simulations is compared analytically. AlN/GaN and AIInN/GaN MOSHEMTs have an advantage of a significant decrease in gate capacitance up to 108 fF/μm^2 with an increase in barrier thickness up to 10 nm as compared to conventional AlGaN/GaN MOSHEMT. This decrease in gate capacitance leads to improved RF performance and hence reduced propagation delay.展开更多
We demonstrate the effects of electron-electron （e-e） interactions in monolayer graphene quantum capacitors. Ultrathin yttrium oxide showed excellent per-formance as the dielectric layer in top-gate device geometry....We demonstrate the effects of electron-electron （e-e） interactions in monolayer graphene quantum capacitors. Ultrathin yttrium oxide showed excellent per-formance as the dielectric layer in top-gate device geometry. The structure and dielectric constant of the yttrium oxide layers have been carefully studied. The inverse compressibility retrieved from the quantum capacitance agreed fairly well with the theoretical predictions for the e--e interactions in monolayer graphene at different temperatures. We found that electron-hole puddles played a significant role in the low-density carrier region in graphene. By considering the temperature-dependent charge fluctuation, we established a model to explain the round-off effect originating from the e-e interactions in monolayer graphene near the Dirac point.展开更多
Tetralayer graphene has shown several interesting properties such as tunable Lifshitz transitions,helical edge states,and high-temperature anomalous Hall effects.The band structure,which directly relates to these phen...Tetralayer graphene has shown several interesting properties such as tunable Lifshitz transitions,helical edge states,and high-temperature anomalous Hall effects.The band structure,which directly relates to these phenomena,has so far been predominantly determined by fitting Landau-level spectra.Here,by characterizing the electronic capacitance,we reveal unprecedented details of its band structure:the energy shift between the heavy-and light-mass band edges in the conduction band is much larger than that in the valence band.Their responses to displacement fields are also distinct:while the former increases monotonically and significantly,the latter first decreases and then increases slightly.Our results suggest that the interlayer interactions and hopping parameters are more complex than previously expected,calling for precise measurements of band structures in various multilayer van der Waals systems.展开更多
The most attractive merit of tunneling carbon nanotube field effect transistors（T-CNFETs） is the ultra-small inverse sub-threshold slope.In order to obtain as small an average sub-threshold slope as possible,several...The most attractive merit of tunneling carbon nanotube field effect transistors（T-CNFETs） is the ultra-small inverse sub-threshold slope.In order to obtain as small an average sub-threshold slope as possible,several effective approaches have been proposed based on a numerical insight into the working mechanism of T-CNFETs：tuning the doping level of source/drain leads,minimizing the quantum capacitance value via tuning the bias condition or increasing the insulator capacitance,and adopting a staircase doping strategy in the drain lead.Non-equilibrium Green＇s function based simulation results show that all these approaches can contribute to a smaller average inverse sub-threshold slope, which is quite desirable in high-frequency or low-power applications.展开更多
文摘MXenes have wide applications in energy storage devices because of their compositional diversity.Electronic and optical properties,Bader charge and quantum capacitance of Janus ScHfCO_(2)MXene under biaxial strain are studied by density functional theory(DFT).The substitution of Hf atoms induces the decrease of the band gap of ScHfCO_(2),which changes from direct semiconductor into indirect semiconductor.Band gap generally increases with the increase of the tensile strain because of the blueshift of Sc-d and Hf-d orbits,and ScHfCO_(2)changes to M→K indirect semiconductor at 5%strain.ScHfCO_(2)under strains from-5%to 4%maintains the indirect bandgap characteristics.The appearance of built-in electric field in ScHfCO_(2)under strain improves the charge redistribution across Janus layer.ScHfCO_(2)under compressive strain has better conductivity than ScHfCO_(2)under tensile strain.ScHfCO_(2)under strains are all promising cathode materials.Larger voltage improves the character of cathode materials because of their much larger|Qc|when compared with those at aqueous system.
基金supported by Prof.C.D.Lokhande Endowment Charitable Trust and Science and Engineering Research Board(ECR/2017/002099).
文摘This study presents an analysis of the structural,electronic,and surface properties of NiO using first-principles density func-tional theory(DFT)calculations.The investigation focuses on three lattice parameters(a=4.23Å,4.187Å,and 4.183Å)to explore how lattice strain influences the electronic band structure,density of states(DOS),quantum capacitance(QC),and adsorption energies of alkali metals(Li,Na,K)on the NiO[001]and[111]planes.The study reveals that a decrease in the lattice parameter leads to a reduction in the band gap(from 2.28 to 2.19 eV).The adsorption energies demonstrate a strong surface reactivity,with Li showing the highest affinity for the NiO[001]surface and Na exhibiting the highest adsorption energy on the more reactive NiO[111]surface.The QC analysis demonstrated notable enhancements following alkali metal adsorption,with Li on the NiO[001]surface exhibiting a QC of 38.9μF/cm^(2)at a=4.23Å,whereas Na on the NiO[111]surface achieved a QC of 32.7μF/cm^(2)at a=4.187Å.These findings underscore the critical role of lattice strain and surface orientation in modulating the electrochemical performance of NiO,with potential applications in catalysis,energy storage,and electronic devices.
文摘This paper proposes a compact model for carbon nanotube field effect transistor（CNTFET） based on surface potential and conduction band minima. The proposed model relates the I–V characteristics to chirality under quantum capacitance limit. C–V characteristics have been efficiently modelled for different capacitance models which are used to find the relationship between CNT surface potential and gate voltage. The role of different capacitances is discussed and it has been found that the proposed circuit compact model strictly follows quantum capacitance limit. The proposed model is efficiently designed for circuit simulations as it denies self-consistent numerical simulation. Furthermore, this compact model is compared with experimental results. The model has been used to simulate an inverter using HSPICE.
文摘Transistor size is constantly being reduced to improve performance as well as power consumption. For the channel length to be reduced, the corresponding gate dielectric thickness should also be reduced. Unfortunately, graphene devices are more complicated due to an extra capacitance called quantum capacitance （CQ） which limits the effective gate dielectric reduction. In this work, we analyzed the effect of CQ on device-scaling issues by extracting it from scaling of the channel length of devices. In contrast to previous reports for metal-insulator- metal structures, a practical device structure was used in conjunction with direct radio-frequency field-effect transistor measurements to describe the graphene channels. In order to precisely extract device parameters, we reassessed the equivalent circuit, and concluded that the on-state model should in fact be used. By careful consideration of the underlap region, our device modeling was shown to be in good agreement with the experimental data. CQ contributions to equivalent oxide thickness were analyzed in detail for varying impurity concentrations in graphene. Finally, we were able to demonstrate that despite contributions from CQ, graphene＇s high mobility and low-voltage operation allows for ~raphene channels suitable for next generation transistors.
基金supported partially by JST SICORP(Grant No.JPMJSC2112)JST Adaptable and Seamless Technology Transfer Program through Target-driven R&D(A-STEP)(Grant No.JPMJTR22T6),and JSPS KAKENHI(Grant No.22K14757)+1 种基金Calculations were performed using the U.K.National Supercomputing Facility ARCHER2(http://www.archer2.ac.uk)via our membership of the U.K.’s HEC Materials Chemistry Consortium,which is funded by the EPSRC(Grant Nos.EP/L000202 and EP/R029431)the Molecular Modelling Hub for computational resources,MMM Hub,which is partially funded by EPSRC(Grant No.EP/P020194/1).This research has also utilized Queen Mary’s Apocrita HPC facility,supported by QMUL Research-IT.
文摘Graphene-based frameworks suffer from a low quantum capacitance due to graphene’s Dirac point at the Fermi level.This theoretical study investigated the effect structural defects,nitrogen and boron doping,and surface epoxy/hydroxy groups have on the electronic structure and capacitance of graphene.Density functional theory calculations reveal that the lowest energy configurations for nitrogen or boron substitutional doping occur when the dopant atoms are segregated.This elucidates why the magnetic transition for nitrogen doping is experimentally only observed at higher doping levels.We also highlight that the lowest energy configuration for a single vacancy defect is magnetic.Joint density functional theory calculations show that the fixed band approximation becomes increasingly inaccurate for electrolytes with lower dielectric constants.The introduction of structural defects rather than nitrogen or boron substitutional doping,or the introduction of adatoms leads to the largest increase in density of states and capacitance around graphene’s Dirac point.However,the presence of adatoms or substitutional doping leads to a larger shift of the potential of zero charge away from graphene’s Dirac point.
文摘A mathematical model is developed predicting the behavior of gate capacitance with the nanoscale variation of barrier thickness in AlN/GaN MOSHEMT and its effect on gate capacitances of AIInN/GaN and AlGaN/GaN MOSHEMTs through TCAD simulations is compared analytically. AlN/GaN and AIInN/GaN MOSHEMTs have an advantage of a significant decrease in gate capacitance up to 108 fF/μm^2 with an increase in barrier thickness up to 10 nm as compared to conventional AlGaN/GaN MOSHEMT. This decrease in gate capacitance leads to improved RF performance and hence reduced propagation delay.
文摘We demonstrate the effects of electron-electron （e-e） interactions in monolayer graphene quantum capacitors. Ultrathin yttrium oxide showed excellent per-formance as the dielectric layer in top-gate device geometry. The structure and dielectric constant of the yttrium oxide layers have been carefully studied. The inverse compressibility retrieved from the quantum capacitance agreed fairly well with the theoretical predictions for the e--e interactions in monolayer graphene at different temperatures. We found that electron-hole puddles played a significant role in the low-density carrier region in graphene. By considering the temperature-dependent charge fluctuation, we established a model to explain the round-off effect originating from the e-e interactions in monolayer graphene near the Dirac point.
基金supported by the National Natural Science Foundation of China(Grant Nos.123B1037 and 12274402)the National Key Research and Development Program of China(Grant No.2024YFA1409700).
文摘Tetralayer graphene has shown several interesting properties such as tunable Lifshitz transitions,helical edge states,and high-temperature anomalous Hall effects.The band structure,which directly relates to these phenomena,has so far been predominantly determined by fitting Landau-level spectra.Here,by characterizing the electronic capacitance,we reveal unprecedented details of its band structure:the energy shift between the heavy-and light-mass band edges in the conduction band is much larger than that in the valence band.Their responses to displacement fields are also distinct:while the former increases monotonically and significantly,the latter first decreases and then increases slightly.Our results suggest that the interlayer interactions and hopping parameters are more complex than previously expected,calling for precise measurements of band structures in various multilayer van der Waals systems.
基金supported by the Hi-Tech Research and Development Program of China(No.2009AA01Z114)
文摘The most attractive merit of tunneling carbon nanotube field effect transistors（T-CNFETs） is the ultra-small inverse sub-threshold slope.In order to obtain as small an average sub-threshold slope as possible,several effective approaches have been proposed based on a numerical insight into the working mechanism of T-CNFETs：tuning the doping level of source/drain leads,minimizing the quantum capacitance value via tuning the bias condition or increasing the insulator capacitance,and adopting a staircase doping strategy in the drain lead.Non-equilibrium Green＇s function based simulation results show that all these approaches can contribute to a smaller average inverse sub-threshold slope, which is quite desirable in high-frequency or low-power applications.
