Field E0 Research Articles

The tunneling potential for field emission from nanotips

In the quasi-planar approximation of field emission, the potential energy due to an external electrostatic field E0 is expressed as −eγE0Δs, where Δs is the perpendicular distance from the emission site and γ is the local field enhancement factor on the surface of the emitter. We show that for curved emitter tips, the current density can be accurately computed if terms involving (Δs/R2)2 and (Δs/R2)3 are incorporated in the potential where R2 is the second (smaller) principle radius of curvature. The result is established analytically for the hemiellipsoid and hyperboloid emitters, and it is found that for sharply curved emitters, the expansion coefficients are equal and coincide with that of a sphere. The expansion seems to be applicable to generic emitters as demonstrated numerically for an emitter with a conical base and quadratic tip. The correction terms in the potential are adequate for Ra⪆2 nm for local field strengths of 5 V/nm or higher. The result can also be used for nano-tipped emitter arrays or even a randomly placed bunch of sharp emitters.

On the parameters for electrocaloric effect predicted by indirect method**Project supported by the Natural Science Foundation of Shanghai, China (Grant No. 17ZR1447200).

The influences of specific heat capacity CP, temperature step ΔT, electric field step ΔE, and initial electric field E1 on predicted electrocaloric (EC) temperature ΔT of monodomain BaTiO3 are examined by combining the Maxwell equation and phenomenological theory. Since the procedure is similar to indirect measurement of the EC effect, the results can serve as a reference for experiments. The results suggest that (i) it is reasonable to use zero-field CP, (ii) optimized ΔT should be 2 K, (iii) it is better to keep ΔE < EC, and (iv) E1 < EC. Here, EC is the coercive field of material.

Role of oxygen vacancy on the electrical properties of SnO2-Zn2SnO4 ceramic composites with the introduction of Nb2O5 oxide

In this work, the role of oxygen vacancy on the electrical properties of traditionally prepared SnO2-Zn2SnO4 ceramic composites was evaluated by introducing Nb2O5 oxide. With increasing Nb2O5 content, the breakdown electric field E1.0 and the relative permittivity εr measured at low frequencies increased and declined, respectively. In the microstructure photos, the grain size decreased before reaching a saturation point. In addition, Nb was randomly distributed in the grains and along grain boundaries. By doping Nb2O5, the color of the sintered samples darkened, and F-type color centers were generated. In the complex electric modulus spectra, the peak of the imaginary part M″ shifted toward a lower frequency; whereas, the activation energy Ea changed slightly with increasing Nb2O5 content. The results suggest that oxygen vacancy is the origin of the varistor and high permittivity properties of SnO2-Zn2SnO4 ceramic composites. Furthermore, the varistor and dielectric properties can be modulated by changes in the microstructure.

Superheterodyne Amplification for Increase the Working Frequency

The amplification of microwaves in n-GaAs films has been widely studied. On the other hand, using nonlinear parametric effects in microwave, millimeter, and THz ranges has a large potential. In this paper the resonant nonlinear phenomena are investigated in active n-GaAs semiconductor and in films on its base. The phenomena are the nonlinear interactions of space charge waves, including the frequency multiplication and mixing, and the three-wave interaction between two THz electromagnetic waves and a single space charge wave. This three-wave interaction results in the superheterodyne amplification of THz waves. The electron velocity in GaAs is the nonlinear function of an external electric field. If the bias electric field is more E0>Ecrit ≈3KV/cm , it is possible to obtain a negative differential mobility (NDM and space charge waves). The space charge waves have phase velocity of electrons equal to v0=v(E0), E0=V0/Lz , where V0 is the voltage, producing the bias electric field E0 in GaAs film. The superheterodyne amplification and the multiplication of microwaves are very promising for building active sensors in telecommunications system, radiometers, and radio telescopes. The superheterodyne mechanism has an advantage related to decreasing noise because of increasing of frequency in the process of amplification. It is used in the process of amplification of longitudinal space charge waves that in turn causes the transfer of energy from longitudinal wave into transverse one with increasing frequency. This is realized due to parametric coupling of two transverse waves and a single space charge wave in GaAs.

Circularly polarized harmonic generation by intense bicircular laser pulses: electron recollision dynamics and frequency dependent helicity

Numerical solutions of time-dependent Schrödinger equations for one and two electron cyclic molecules exposed to intense bichromatic circularly polarized laser pulses of frequencies and , such that (integer) produce circularly polarized high order harmonics with a cut-off recollision maximum energy at and greater than the linear polarization law (in atomic units) , where Ip is the ionization potential and is the ponderomotive energy defined by the field E0 (intensity ) from each pulse and mean frequency . An electron recollision model in a rotating frame at rotating frequency predicts this simple result as a result of recollision dynamics in a combination of bichromatic circularly polarized pulses. The harmonic helicities and their intensities are shown to depend on compatible symmetries of the net pulse electric fields with that of the molecules.

Effect of SiO2 on the Varistor and Dielectric Properties of SnO2-Zn2SnO4 Ceramic Composites

ABSTRACTSnO2-Zn2SnO4 ceramic composites are prepared by traditional ceramics processing and the effect of SiO2 on the varistor, dielectric properties has been investigated. With increasing SiO2 content to 0.2 mol%, the nonlinear coefficient α and the breakdown electrical field E1.0 gets to the maximum of 7.7 and minimum of 12V.mm–1, respectively. Meanwhile, the dielectric spectra show that the sample doped with 0.2 mol% SiO2 has the highest relative permittivity εr of ∼7×103 at 40 Hz, 40°C. The dielectric temperature spectra show that the temperature stability of the dielectric properties can be improved by doping 0.2 mol% SiO2. The good properties indicate that SiO2 doped SnO2-Zn2SnO4 ceramic composites are viable candidate for capacitor-varistor functional devices to protect electrical micro-machines. Further studies show that the density and grain uniformity of the composites are improved by doping proper content of SiO2. The compact and uniform microstructure may be responsible for the excellent varistor and dielectric properties.

Piezocaloric and multicaloric effect in the KH2PO4 type ferroelectrics

ABSTRACTUsing the proton ordering model modified by taking into account the dependence of the dipole moments on the order parameter, we explore the piezocaloric and multicaloric effects in the KH2PO4 type ferroelectrics, caused by the shear stress σ6 and longitudinal electric field E3. The multicaloric effect is shown to be stronger than either electrocaloric or piezocaloric effects, especially at temperatures far from the phase transition.

An explicit open image theorem for products of elliptic curves

Let K be a number field and let E1,…,En be elliptic curves over K, pairwise non-isogenous over K‾ and without complex multiplication over K‾. We study the image G∞ of the adelic representation of Gal(K‾/K) naturally attached to E1×⋯×En. The main result is an explicit bound for the index of G∞ in {(x1,…,xn)∈GL2(Zˆ)n|det⁡xi=det⁡xj∀i,j}.

Electrical Parameters of SnO2 Based Varistor Ceramics with CaO and BaO Additions

In the tested SnO2-Co3O4-Nb2O5-Cr2O3-CuO varistor ceramics the adding of CaO or BaO oxides leads to the decrease of the electric conductivity in the low electric field and correlated increase of the potential barrier height at the SnO2 grain boundaries (from 0.7 to 1.0 eV). The coordinated changes of electrical parameters with the increase of the burning temperature from 1520 to 1620 К (the increase of the linear shrinkage, a grain size, an electric conductivity, a nonlinear coefficient , a normalized nonlinear coefficient , a dielectric permittivity and the decrease of the qualifying electric field E1, an activation energy of electric conduction and a grain specific resistance) prove the barrier mechanism of electric conductivity in the SnO2 based ceramics. The highest data and = 0.02 cm·V-1 has ceramics with CaO addition baked at 1620 K. According to the impulse experimental data in the high electric field the increase of burning temperature causes the increase of SnO2 grain average size and the decrease of their grain specific resistance . The obtained value = 1.1 Ohm·cm for SnO2-Co3O4-Nb2O5-Cr2O3-CuO ceramics is the lowest among those found in SnO2 based ceramics.&#x0D;

Effect of a weak DC electric field on the grain size distribution in isothermally-annealed yttria-stabilized zirconia (3Y-TZP)

The grain size distributions (GSDs) in 3mol% yttria-stabilized zirconia (3 Y-TZP) which had been isothermally annealed for various times at 1300°C and 1400°C without and with a weak DC electric field E0*=18V/cm were determined. The GSDs for all test conditions fit a single curve whose form is in accord with the Bitti–Di Nunzio model, and moreover is in accord with the GSDs for sintering and plastic deformation. The results for all three processes suggest the GSD to be a unique function of the mean linear intercept grain size.

Flash sintering incubation in Al2O3/TZP composites

The flash sintering incubation process was characterized with Al2O3/TZP composites in isothermal furnace experiments. The compositions in tetragonal zirconia, TZP and Al2O3 were 0, 20, 40 and 60vol.% of Al2O3. AC electrical field E0 (1000Hz) of 100 or 200V/cm was used. The current density was limited at 10 or 20A/cm2, and the pre-heating temperatures were 900, 1000 and 1100°C. The flash phenomenon depends on the overall conductivity of the sample. For a constant electrical field, the incubation time only depends on the sample overall conductivity whatever its temperature or composition. The power density supplied to the sample is the key parameter. The incubation time is affected by the heat losses, which mainly occur by thermal conduction through the electrode contacts, as evidenced by the marked influence of the sample geometry. A simple energy balance equation accounts for the observed current variations.

Size dependence of the polarizability and Haynes rule for an exciton bound to an ionized donor in a single spherical quantum dot

We study the effect of an external electric field on an exciton bound to an ionized donor (D+, X) confined in a spherical quantum dot using a perturbative-variational method where the wave function and energy are developed in series of powers of the electric field strength. After testing this new approach in the determination of the band gap for some semiconductor materials, we generalize it to the case of (D+, X) in the presence of the electric field and for several materials ZnO, PbSe, and InAs, with significant values of the mass ratio. Three interesting results can be deduced: First, we show that the present method allows to determine the ground state energy in the presence of a weak electric field in a simple way (E = E0 − αf2) using the energy without electric field E0 and the polarizability α. The second point is that our theoretical predictions show that the polarizability of (D+, X) varies proportionally to R3.5 and follows an ordering αD0&amp;lt;αX&amp;lt;α(D+,X). The last point to highlight is that the Haynes rule remains valid even in the presence of a weak electric field.

Temperature dependences of dynamic hysteresis in Pb(Zr,Sn,Ti)O3 ceramics extending over Curie temperature

Dynamic hysteresis of Nb-doped Pb(Zr,Sn,Ti)O3 ferroelectric ceramics with the first-order phase transition was investigated in a wide temperature (T) range from 293 K to 433 K, which extended over its Curie temperature (Tc = 422 K) and another transition temperature (T0 = 413 K). Three linear scaling relations were obtained when the working fields E0 were over 1.5 times of coercive field Ec, where the well-saturated loops occurred. The highest applicable temperature of these scaling relations was T0 (not Tc) because of the coexistence of stable ferroelectric phase and metastable paraelectric phase in the range between T0 and Tc. As E0 decreased, the lowest applicable temperature shifted to the higher and the temperature range became narrow.

A Multicomponent Approach for Strongly Collisional Plasmas in the Solar Atmosphere

A simple collisional three-component plasma model consisting of electrons, ions, and neutrals with arbitrary collision frequencies and dynamic time scales is considered. For the partially ionized plasma with a strong collisional coupling of neutrals with ions, magnetosonic and Alfven waves modified by neutrals are obtained. It is shown that the magnetic diffusivity appears for magnetosonic waves as a result of the ion transverse collision current connected with the field E1⊥ and for Alfven waves because both the ion transverse collision current and the electron longitudinal collision current are connected with E1z at the angular propagation of perturbations relative to the background magnetic field.

New developed cylindrical TM010 mode EPR cavity for X-band in vivo tooth dosimetry.

EPR tooth in vivo dosimetry is an attractive approach for initial triage after unexpected nuclear events. An X-band cylindrical TM010 mode resonant cavity was developed for in vivo tooth dosimetry and used in EPR applications for the first time. The cavity had a trapezoidal measuring aperture at the exact position of the cavity’s cylindrical wall where strong microwave magnetic field H1 concentrated and weak microwave electric field E1 distributed. Theoretical calculations and simulations were used to design and optimize the cavity parameters. The cavity features were evaluated by measuring DPPH sample, intact incisor samples embed in a gum model and the rhesus monkey teeth. The results showed that the cavity worked at designed frequency and had the ability to make EPR spectroscopy in relative high sensitivity. Sufficient modulation amplitude and microwave power could be applied into the aperture. Radiation induced EPR signal could be observed remarkably from 1 Gy irradiated intact incisor within only 30 seconds, which was among the best in scan time and detection limit. The in vivo spectroscopy was also realized by acquiring the radiation induced EPR signal from teeth of rhesus monkey whose teeth was irradiated by dose of 2 Gy. The results suggested that the cavity was sensitive to meet the demand to assess doses of significant level in short time. This cavity provided a very potential option for the development of X-band in vivo dosimetry.

Study of field-induced phase transitions in 0.68PbMg1/3Nb2/3O3–0.32PbTiO3 relaxor single crystal by polarized micro-Raman spectroscopy

Polarized Raman spectroscopy has been performed to investigate the effects of the electric field on 0.68PbMg1/3Nb2/3O3–0.32PbTiO3 (PMN–32PT) relaxor single crystal. Based on the group theory analysis, the Raman modes of PMN–32PT single crystal at zero-field are assigned to the monoclinic structure. The electric-field-evolution of Raman spectra reveal that a structural transition to tetragonal phase is initiated at a threshold electric field E1 and completed at higher field E2. In the intermediate field range from E1 to E2, the structure of the crystal is determined to be a coexistence of monoclinic and tetragonal phases. These results of the Raman spectra allow us to better understand the field-induced ultrahigh macroscopic strain in the relaxor ferroelectrics.

Piezoelectric response of a PZT thin film to magnetic fields from permanent magnet and coil combination

In this study, we report the magnetically induced electric field E3 in Pb(Zr0.57Ti0.43)O3 (PZT) thin films, when they are subjected to both dynamic magnetic induction (magnitude Bac at 45 kHz) and static magnetic induction (Bdc) generated by a coil and a single permanent magnet, respectively. It is found that highest sensitivity to Bdc—\( {{\Delta \left| {E_{3} } \right|} \mathord{\left/ {\vphantom {{\Delta \left| {E_{3} } \right|} {\Delta B_{\text{dc}} }}} \right. \kern-0pt} {\Delta B_{\text{dc}} }} \)—is achieved for the thin film with largest effective electrode. This magnetoelectric (ME) effect is interpreted in terms of coupling between eddy current-induced Lorentz forces (stress) in the electrodes of PZT and piezoelectricity. Such coupling was evidenced by convenient modelling of experimental variations of electric field magnitude with both Bac and Bdc induction magnitudes, providing imperfect open circuit condition was considered. Phase angle of E3 versus Bdc could also be modelled. At last, the results show that similar to multilayered piezoelectric-magnetostrictive composite film, a PZT thin film made with a simple manufacturing process can behave as a static or dynamic magnetic field sensor. In this latter case, a large ME voltage coefficient of \( \alpha = {{\left| {E_{3} } \right|} \mathord{\left/ {\vphantom {{\left| {E_{3} } \right|} {B_{\text{ac}} }}} \right. \kern-0pt} {B_{\text{ac}} }} = 3.55\,{\text{V}}/{\text{cm}}\,{\text{Oe}} \) under Bdc = 0.3 T was found. All these results may provide promising low-cost magnetic energy harvesting applications with microsized systems.

Interaction of streamers and stationary corrugated ionization waves in semiconductors.

A numerical simulation of evolution of an identical interacting streamers array in semiconductors has been performed using the diffusion-drift approximation and taking into account the impact and tunnel ionization. It has been assumed that the external electric field E0 is static and uniform, the background electrons and holes are absent, the initial avalanches start simultaneously from the nodes of the plane hexagonal lattice, which is perpendicular to the external field, but the avalanches and streamers are axially symmetric within a cylinder of radius R. It has been shown that under certain conditions, the interaction between the streamers leads finally either to the formation of two types of stationary ionization waves with corrugated front or to a stationary plane ionization wave. A diagram of different steady states of this type of waves in the plane of parameter E0,R has been presented, and a qualitative explanation of the plane partition into four different regions has been given. Characteristics of corrugated waves have been studied in detail and discussed in the region of R and E0 large values, in which the maximum field strength at the front is large enough for the tunnel ionization implementation. It has been shown that corrugated waves ionize semiconductors more efficiently than flat ones, especially in relatively weak external fields.

Dynamics of dipole-type discharge formation studied by the method of microwave scattering

Microwave scattering (MWS) measurements have been used to study the evolution of a plasma structure comprising a linear chain of thin dipoles (with thicknesses small compared to wavelength) formed in air at pressures within (1–1.4) × 104 Pa (slightly above the breakdown threshold). An analysis of the MWS dynamics reveals the main stages in development of both a single plasma dipole and the entire structure. The average speed of elongation of a plasma structure (microwave streamer) in the direction of applied electric field E0 and the average velocity of propagation of the discharge front toward the microwave source are determined.

汤森系数与涂硼正比计数管中气体放大的关系研究

基于正比计数管的气体放大，提出四个约化量：约化汤森系数αre、约化倍增因子Mre、临界约化电场e0、临界约化汤森系数Σ，并得出对应于线性、幂指数和自然指数αre-e关系的约化倍增因子表达式。以P10气体充入特定涂硼正比管为例，做出了三类关系的约化倍增因子Mre-ea曲线。分析表明描述约化汤森系数、约化倍增因子和约化电场之间的三类关系具有良好的统一性。正比管中存在临界约化电场和临界约化汤森系数，其取值因αre-e关系而异。正比管中约化倍增因子随阳极丝表面电场递增，其增速受αre-e关系的影响，但倍增因子取值变化很小。Based on the gas amplification in proportional counters, four reduced quantities: reduced Town-send coefficient αre, reduced multiplication factor Mre, reduced critical electric field e0, and reduced critical Townsend coefficient Σ are proposed. Expressions of Mre, which are corresponding to linear, exponential and natural exponential relationship of αre vs. e, are deduced. By taking example for a special boron-lined proportional counter (BLPC) filled with P10 gas, Mre-ea curves based on three kinds of mentioned relationships are plotted. Analysis shows that reduced Townsend coefficient αre , reduced multiplication factor Mre , and reduced electric field e have good uniformities. Critical reduced electric field and critical reduced Townsend efficiency exist in the operation of PCs, but their values varies with the relationship of αre-e. Reduced multiplication factors of PCs increase with the electric field on the surface of the anode wire, and the increase rate would be affected by the relationship of αre-e while the value of Mre changes little.