Electric potential and energy band in ZnO nanofiber tuned by local mechanical loading

Recent success in strain engineering has triggered tremendous interest in its study and potential applications in nanodevice design. In this paper, we establish a coupled piezoelectric/semiconducting model for a wurtzite structure ZnO nanofiber under the local mechanical loading. The energy band structure tuned by the local mechanical loading and local length is calculated via an eight-band k·p method, which includes the coupling of valance and conduction bands. Poisson's effect on the distribution of electric potential inversely depends on the local mechanical loading. Numerical results reveal that both the applied local mechanical loading and the local length exhibit obvious tuning effects on the electric potential and energy band. The band gap at band edges varies linearly with the applied loading. Changing the local length shifts the energy band which is far away from the band edges. This study will be useful in the electronic and optical enhancement of semiconductor devices.

Energy band adjustment of 808 nm GaAs laser power converters via gradient doping

The gradient doping regions were employed in the emitter layer and the base layer of GaAs based laser power converters(LPCs).Silvaco TCAD was used to numerically simulate the linear gradient doping and exponential gradient doping structure,and analyze the transport process of photogenerated carriers.Energy band adjustment via gradient doping improved the separation and transport efficiency of photogenerated carriers and reduced the total recombination rate of GaAs LPCs.Compared with traditional structure of LPCs,the photoelectric conversion efficiency of LPCs with linear and exponential gradient doping structure were improved from 52.7%to 57.2%and 57.7%,respectively,under 808 nm laser light at the power density of 1 W/cm^(2).

Energy band and charge-carrier engineering in skutterudite thermoelectric materials

The binary CoSb_(3) skutterudite thermoelectric material has high thermal conductivity due to the covalent bond between Co and Sb, and the thermoelectric figure of merit, ZT, is very low. The thermal conductivity of CoSb_(3) materials can be significantly reduced through phonon engineering, such as low-dimensional structure, the introduction of nano second phases,nanointerfaces or nanopores, which greatly improves their ZT values. The phonon engineering can optimize significantly the thermal transport properties of CoSb_(3)-based materials. However, the improvement of the electronic transport properties is not obvious, or even worse. Energy band and charge-carrier engineering can significantly improve the electronic transport properties of CoSb_(3)-based materials while optimizing the thermal transport properties. Therefore, the decoupling of thermal and electronic transport properties of CoSb_(3)-based materials can be realized by energy band and charge-carrier engineering. This review summarizes some methods of optimizing synergistically the electronic and thermal transport properties of CoSb_(3) materials through the energy band and charge-carrier engineering strategies. Energy band engineering strategies include band convergence or resonant energy levels caused by doping/filling. The charge-carrier engineering strategy includes the optimization of carrier concentration and mobility caused by doping/filling, forming modulation doped structures or introducing nano second phase. These strategies are effective means to improve performance of thermoelectric materials and provide new research ideas of development of high-efficiency thermoelectric materials.

Studying the variable energy band structure for energy storage materials in charge/discharge process

So far,a clear understanding about the relationship of variable energy band structure with the corresponding charge-discharge process of energy storage materials is still lacking.Here,using optical spectroscopy(red-green-blue(RGB)value,reflectivity,transmittance,UV-vis,XPS,UPS)to studyα-Co(OH)_(2) electrode working in KOH electrolyte as the research object,we provide direct experimental evidence that:(1)The intercalation of OH-ions will reduce the valence/conduction band(VB and CB)and band gap energy(Eg)values;(2)The deintercalation of OH-ions corresponds with the reversion of VB,CB and E_(g) to the initial values;(3)The color of Co(OH)_(2) electrode also exhibit regular variations in RGB value during the charge-discharge process.

Reanalysis of energy band structure in the type-II quantum wells

Band structure analysis holds significant importance for understanding the optoelectronic characteristics of semiconductor structures and exploring their potential applications in practice. For quantum well structures, the energy of carriers in the well splits into discrete energy levels due to the confinement of barriers in the growth direction. However, the discrete energy levels obtained at a fixed wave vector cannot accurately reflect the actual energy band structure. In this work, the band structure of the type-II quantum wells is reanalyzed. When the wave vectors of the entire Brillouin region(corresponding to the growth direction) are taken into account, the quantized energy levels of the carriers in the well are replaced by subbands with certain energy distributions. This new understanding of the energy bands of low-dimensional structures not only helps us to have a deeper cognition of the structure, but also may overturn many viewpoints in traditional band theories and serve as supplementary to the band theory of low-dimensional systems.

Electrically manipulating magnetization reversal via energy band engineering

Realization of a magnetization reversal by an external electric field is vital for developing ultra-low-power spintronic devices.In this report,starting from energy band engineering,a general design principle is proposed for achieving electrical manipulation of a nonvolatile 180°magnetization reversal.A half semiconductor(HSC)and a bipolar magnetic semiconductor(BMS)are selected as the model of magnetic layers,whose conduction-band minimum and valence-band maximum are in the same and opposite spin states,respectively.Based on the analysis of virtual hopping and tight-binding models,the interlayer coupling of HSC/insulator/BMS devices is successfully tuned between ferromagnetic and antiferromagnetic interactions by varying electric field directions.Moreover,the interlayer coupling nearly disappears after removing the electric field,proving the nonvolatile magnetization reversal.Using first-principles calculations,the feasibility of present design strategy is further confirmed by a representative device with the structure of CrBr3/h-BN/2H-VSe_(2).This design guideline and physical phenomena may open an avenue to explore magnetoelectric coupling mechanisms and develop next-generation spintronic devices.

Electronic band energy of a bent ZnO piezoelectric semiconductor nanowire

The electric band energy variation in a bent piezoelectric semiconductor(PSC) nanowire of circular cross-section induced by the mechanical force is analyzed based on a six-band k · p method. The electric-mechanical fields are first obtained analytically in a cantilever bent PSC nanowire by solving the fully-coupled electro-mechanical equations. Then, the band energy is acquired numerically via the six-band Hamiltonian.By considering further the nonlinear coupling between the piezoelectric and semiconducting quantities, the contribution of the redistribution carriers to the electric field is analyzed from the Gauss’ s law. Numerical examples are carried out for an n-type Zn O nanowire in different locations induced by an applied concentrated end force. They include the electric potential, heavy hole(HH), light hole(LH), spin-orbit split-off(SO),and conduction band(CB) edges along the axial and thickness directions. Our results show that the applied force has a significant effect on the band energies. For instance, on the bottom surface along the axial direction, the bandgaps near the fixed end are greater than those near the loading end, and this trend is reversed on the top surface. Moreover,at a fixed axial location, the energy level of the lower side can be enhanced by applying a bending force at the end. The present results could be of significant guidance to the electronic devices and piezotronics.

Energy band engineering via“Bite”defect located on N=8 armchair graphene nanoribbons

Graphene nanoribbons(GNRs)not only share many superlative properties of graphene but also display an exceptional degree of tunability of their electronic properties.The bandgaps of GNRs depend greatly on their widths,edges,etc.Herein,we report the synthesis path and the physical properties of atomic accuracy staggered narrow N=8 armchair graphene nanoribbons(sn-8AGNR)with alternating"Bite"defects on the opposite side.The intermediate structures in the surface physicochemical reactions from the precursors to the sn-8AGNR are characterized by scanning tunneling microscopy.The electronic properties of the sn-8AGNR are characterized by scanning tunneling spectroscopies and 6//6V mappings.Compared with the perfect N=8 armchair graphene nanoribbons(8AGNR),the sn-8AGNR has a larger bandgap,indicating that the liB\Xen edges can effectively regulate the electronic structures of GNRs.

Regulation of excitation energy transfer in Sb-alloyed Cs_(4)MnBi_(2)Cl_(12) perovskites for efficient CO_(2) photoreduction to CO and water oxidation toward H_(2)O_(2)

Lead(Pb)-free halide perovskites have recently attracted increasing attention as potential catalysts for CO_(2) photoreduction to CO due to their potential to capture solar energy and drive catalytic reaction.However,issues of the poor charge transfer still remain one of the main obstacles limiting their performance due to the overwhelming radiative and nonradiative charge-carrier recombination losses.Herein,Pb-free Sb-alloyed all-inorganic quadruple perovskite Cs_(4)Mn(Bi_(1-x)Sb_(x))_(2)Cl_(12)(0≤x≤1)is synthesized as efficient photocatalyst.By Sb alloying,the undesired relaxation of photogenerated electrons from conduction band to emission centers of[MnCl6]^(4-)is greatly suppressed,resulting in a weakened PL emission and enhanced charge transfer for photocatalyst.The ensuing Cs_(4)Mn(Bi_(1-x)Sb_(x))_(2)Cl_(12) photocatalyst accomplishes efficient conversion of CO_(2)into CO,accompanied by a surprising production of H_(2)O_(2),a high valueadded product associated with water oxidation.By optimizing Sb^(3+) concentration,a high CO evolution rate of 35.1μmol g^(-1)h^(-1)is achieved,superior to most other Pb and Pb-free halide perovskites.Our findings provide new insights into the mixed-cation alloying strategies for improved photocatalytic performance of Pb-free perovskites and shed light on the rational design of robust band structure toward efficient energy transfer.

Discrimination of Motor Imagery Patterns by Electroencephalogram Phase Synchronization Combined With Frequency Band Energy

Central nerve signal evoked by thoughts can be directly used to control a robot or prosthetic devices without the involvement of the peripheral nerve and muscles.This is a new strategy of human-computer interaction.A method of electroencephalogram(EEG) phase synchronization combined with band energy was proposed to construct a feature vector for pattern recognition of brain-computer interaction based on EEG induced by motor imagery in this paper,rhythm and beta rhythm were first extracted from EEG by band pass filter and then the frequency band energy was calculated by the sliding time window;the instantaneous phase values were obtained using Hilbert transform and then the phase synchronization feature was calculated by the phase locking value(PLV) and the best time interval for extracting the phase synchronization feature was searched by the distribution of the PLV value in the time domain.Finally,discrimination of motor imagery patterns was performed by the support vector machine(SVM).The results showed that the phase synchronization feature more effective in4s-7s and the correct classification rate was 91.4%.Compared with the results achieved by a single EEG feature related to motor imagery,the correct classification rate was improved by 3.5 and4.3 percentage points by combining phase synchronization with band energy.These indicate that the proposed method is effective and it is expected that the study provides a way to improve the performance of the online real-time brain-computer interaction control system based on EEG related to motor imagery.

Speech Resampling Detection Based on Inconsistency of Band Energy

Speech resampling is a typical tempering behavior,which is often integrated into various speech forgeries,such as splicing,electronic disguising,quality faking and so on.By analyzing the principle of resampling,we found that,compared with natural speech,the inconsistency between the bandwidth of the resampled speech and its sampling ratio will be caused because the interpolation process in resampling is imperfect.Based on our observation,a new resampling detection algorithm based on the inconsistency of band energy is proposed.First,according to the sampling ratio of the suspected speech,a band-pass Butterworth filter is designed to filter out the residual signal.Then,the logarithmic ratio of band energy is calculated by the suspected speech and the filtered speech.Finally,with the logarithmic ratio,the resampled and original speech can be discriminated.The experimental results show that the proposed algorithm can effectively detect the resampling behavior under various conditions and is robust to MP3 compression.

An advanced theoretical approach to study super-multiperiod superlattices:theory vs experiments

A new theoretical method to study super-multiperiod superlattices has been developed.The method combines the precision of the 8-band kp-method with the flexibility of the shooting method and the Monte Carlo approach.This method was applied to examine the finest quality samples of super-multiperiod Al_(0.3)Ga_(0.7)As/GaAs superlattices grown by molecular beam epitaxy.The express photoreflectance spectroscopy method was utilized to validate the proposed theoretical method.For the first time,the accurate theoretical analysis of the energy band diagram of super-multiperiod superlattices with experimental verification has been conducted.The proposed approach highly accurately determines transition peak positions and enables the calculation of the energy band diagram,transition energies,relaxation rates,and gain estimation.It has achieved a remarkably low 5%error compared to the commonly used method,which typically results in a 25%error,and allowed to recover the superlattice parameters.The retrieved intrinsic parameters of the samples aligned with XRD data and growth parameters.The proposed method also accurately predicted the escape of the second energy level for quantum well thicknesses less than 5 nm,as was observed in photoreflectance experiments.The new designs of THz light-emitting devices operating at room temperature were suggested by the developed method.

Determination of Band Structure of Gallium-Arsenide and Aluminium-Arsenide Using Density Functional Theory

This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical atomic-centered orbital basis sets. The electronic band structure, total density of state (DOS) and band gap energy were calculated for Gallium-Arsenide and Aluminium-Arsenide in diamond structures. The result of minimum total energy and computational time obtained from the experimental lattice constant 5.63 A for both Gallium Arsenide and Aluminium Arsenide is -114,915.7903 eV and 64.989 s, respectively. The electronic band structure analysis shows that Aluminium-Arsenide is an indirect band gap semiconductor while Gallium-Arsenide is a direct band gap semiconductor. The energy gap results obtained for GaAs is 0.37 eV and AlAs is 1.42 eV. The band gap in GaAs observed is very small when compared to AlAs. This indicates that GaAs can exhibit high transport property of the electron in the semiconductor which makes it suitable for optoelectronics devices while the wider band gap of AlAs indicates their potentials can be used in high temperature and strong electric fields device applications. The results reveal a good agreement within reasonable acceptable errors when compared with the theoretical and experimental values obtained in the work of Federico and Yin wang [1] [2].

Fowler-Nordheim Tunneling, Photovoltaic Applications and New Band Structure Models of Electroconductive a-CNx:H Films Formed by Supermagnetron Plasma CVD

Hydrogenated amorphous carbon nitride (a-CNx:H) films were formed on Al films deposited on Si or glass (SiO2) substrates, using pulsed radio frequency (PRF) supermagnetron plasma (SMP) chemical vapor deposition (CVD) with N2/i-C4H10 mixed gases. a-CNx:H films were grown under the upper and lower electrode RF powers (13.56 MHz) of continuous and pulsed conditions, respectively, which showed low band gap of about 0.7 eV. a-CNx:H films deposited on the Al/Si or Al/SiO2 substrates showed same low threshold emission electric field (ETH) of 12 V/μm. Multiple layer of Al or ITO (anode)/50nm-SiO2/a-CNx:H/Al (cathode)/Si structures showed Fowler-Nordheim (FN) electron tunneling effect in both forward and reverse current directions. 12.5 nm a-CNx:H film on p-Si substrate showed a photoelectric conversion. Energy band structure and electron conduction models were proposed for the active states of both the field emission and FN tunneling devices and photovoltaic cells.

Superior energy storage efficiency through tailoring relaxor behavior and band energy gap in KNN-based ferroelectric ceramic capacitors

With the increasing demand of high-power and pulsed power electronic devices,environmental-friendly potassium sodium niobate((Na_(0.5)K_(0.5))NbO_(3),KNN)ceramic-based capacitors have attracted much attention in recent years owning to the boosted energy storage density(W_(rec)).Nevertheless,the dielectric loss also increases as the external electric field increases,which will generate much dissipated energy and raise the temperature of ceramic capacitors.Thus,an effective strategy is proposed to enhance the energy storage efficiency(η)via tailoring relaxor behavior and bad gap energy in the ferroelectric 0.9(Na_(0.5)K_(0.5))-NbO_(3)-0.1Bi(Zn_(2/3)(Nb_(x)Ta_(1−x))1/3)O_(3) ceramics.On the one hand,the more diverse ions in the B-sites owing to introducing the Ta could further disturb the long-range ferroelectric polar order to form the short−range polar nanoregions(PNRs),resulting in the highη.On the other hand,the introduction of Ta ions could boost the intrinsic band energy gap and thus improve the Eb.As a result,high Wrec of 3.29 J/cm^(3) and ultrahighηof 90.1%at the high external electric field of 310 kV/cm are achieved in x=0.5 sample.These results reveal that the KNN-based ceramics are promising lead-free candidate for high-power electronic devices.

Highly Enhanced Visible-Light-Driven Photoelectrochemical Performance of ZnO-Modified In_2S_3 Nanosheet Arrays by Atomic Layer Deposition

Photoanodes based on In_2S_3/ZnO heterojunction nanosheet arrays(NSAs) have been fabricated by atomic layer deposition of ZnO over In_2S_3 NSAs, which were in situ grown on fluorine-doped tin oxide glasses via a facile solvothermal process. The as-prepared photoanodes show dramatically enhanced performance for photoelectrochemical(PEC) water splitting, compared to single semiconductor counterparts. The optical and PEC properties of In_2S_3/ZnO NSAs have been optimized by modulating the thickness of the Zn O overlayer. After pairing with ZnO, the NSAs exhibit a broadened absorption range and an increased light absorptance over a wide wavelength region of 250–850 nm. The optimized sample of In_2S_3/ZnO-50 NSAs shows a photocurrent density of 1.642 m A cm^(-2)(1.5 V vs. RHE) and an incident photonto-current efficiency of 27.64% at 380 nm(1.23 V vs.RHE), which are 70 and 116 times higher than those of the pristine In_2S_3 NSAs, respectively. A detailed energy band edge analysis reveals the type-II band alignment of the In_2S_3/ZnO heterojunction, which enables efficient separation and collection of photogenerated carriers,especially with the assistance of positive bias potential, and then results in the significantly increased PEC activity.

Insights into the efficient charge separation over Nb_(2)O_(5)/2D-C_(3)N_(4) heterostructure for exceptional visible-light driven H_(2) evolution

Two-dimensional carbon nitride(2 D-C_(3) N_(4))nanosheets are promising materials in photocatalytic water splitting,but still suffer from easy agglomeration and fast photogene rated electron-hole pairs recombination.To tackle this issue,herein,a hierarchical Nb_(2) O_(5)/2 D-C_(3) N_(4) heterostructure is precisely constructed and the built-in electric field between Nb_(2)O_(5) and 2 D-C_(3) N_(4) can provide the driving force to separate/transfer the charge carriers efficiently.Moreover,the strongly Lewis acidic Nb_(2)O_(5) can adsorb TEOA molecules on its surface at locally high concentrations to facilitate the oxidation reaction kinetics under irradiation,resulting in efficient photogene rated electrons-holes separation and exceptional photocatalytic hydrogen evolution.As expected,the champion Nb_(2)O_(5)/2 D-C_(3)N_(4) heterostructure achieves an exceptional H2 evolution rate of 31.6 mmol g^(-1) h^(-1),which is 213.6 times and 4.3 times higher than that of pristine Nb_(2)O_(5) and2 D-C_(3)N_(4),respectively.Moreover,the champion heterostructure possesses a high apparent quantum efficiency(AQE)of 45.08%atλ=405 nm and superior cycling stability.Furthermore,a possible photocatalytic mechanism of the energy band alignment at the hetero-interface is proposed based on the systematical characterizations accompanied by density functional theory(DFT)calculations.This work paves the way for the precise construction of a high-quality heterostructured photocatalyst with efficient charge separation to boost hydrogen production.

Simultaneous passivation of bulk and interface defects through synergistic effect of anion and cation toward efficient and stable planar perovskite solar cells

Bulk and interface carrier nonradiative recombination losses impede the further improvement of power conversion efficiency(PCE)and stability of perovskite solar cells(PSCs).It is highly necessary to develop multifunctional strategy to minimize surface and interface nonradiative recombination losses.Herein,we report a bulk and interface defect passivation strategy via the synergistic effect of anions and cations,where multifunctional potassium sulphate(K_(2)SO_(4))is incorporated at SnO_(2)/perovskite interface.We find that K^(+)ions in K_(2)SO_(4)diffuse into perovskite layer and suppress the formation of bulk defects in perovskite films,and the SO_(4)^(2-)ions remain located at interface via the strong chemical interaction with SnO_(2)layer and perovskite layer,respectively.Through this synergistic modification strategy,effective defect passivation and improved energy band alignment are achieved simultaneously.These beneficial effects are translated into an efficiency increase from 19.45%to 21.18%with a low voltage deficit of0.53 V mainly as a result of boosted open-circuit voltage(V_(oc))after K_(2)SO_(4)modification.In addition,the K_(2)SO_(4)modification contributes to ameliorated stability.The present work provides a route to minimize bulk and interface nonradiative recombination losses for the simultaneous realization of PCE and stability enhancement by rational anion and cation synergistic engineering.

Superionic Conductivity in Ceria‑Based Heterostructure Composites for Low‑Temperature Solid Oxide Fuel Cells

Ceria-based heterostructure composite(CHC)has become a new stream to develop advanced low-temperature(300–600°C)solid oxide fuel cells(LTSOFCs)with excellent power outputs at 1000 mW cm−2 level.The state-ofthe-art ceria–carbonate or ceria–semiconductor heterostructure composites have made the CHC systems significantly contribute to both fundamental and applied science researches of LTSOFCs;however,a deep scientific understanding to achieve excellent fuel cell performance and high superionic conduction is still missing,which may hinder its wide application and commercialization.This review aims to establish a new fundamental strategy for superionic conduction of the CHC materials and relevant LTSOFCs.This involves energy band and built-in-field assisting superionic conduction,highlighting coupling effect among the ionic transfer,band structure and alignment impact.Furthermore,theories of ceria–carbonate,e.g.,space charge and multi-ion conduction,as well as new scientific understanding are discussed and presented for functional CHC materials.

One-dimensional method of investigating the localized states in armchair graphene-like nanoribbons with defects

In this paper we propose a type of new analytical method to investigate the localized states in the armchair graphenelike nanoribbons. The method is based on the tight-binding model and with a standing wave assumption. The system of armchair graphene-like nanoribbons includes the armchair supercells with arbitrary elongation-type line defects and the semi-infinite nanoribbons. With this method, we analyze many interesting localized states near the line defects in the graphene and boron-nitride nanoribbons. We also derive the analytical expressions and the criteria for the localized states in the semi-infinite nanoribbons.