Dc Bias Electric Field Research Articles

Multipactor susceptibility on a dielectric with a bias dc electric field and a background gas

We use Monte Carlo simulations and analytical calculations to derive the condition for the onset of multipactor discharge on a dielectric surface at various combinations of the bias dc electric field, rf electric field, and background pressures of noble gases, such as Argon. It is found that the presence of a tangential bias dc electric field on the dielectric surface lowers the magnitude of rf electric field threshold to initiate multipactor, therefore plausibly offering robust protection against high power microwaves. The presence of low pressure gases may lead to a lower multipactor saturation level, however. The combined effects of tangential dc electric field and external gases on multipactor susceptibility are presented.

Influence of dc bias electric field on Vogel-Fulcher dynamics in relaxor ferroelectrics

Influence of dc bias electric field on Vogel-Fulcher dynamics in relaxor ferroelectrics

Magnetocapacitance effects of Pb0.7Sr0.3TiO3/La0.7Sr0.3MnO3 thin film on Si substrate

Pb 0.7 Sr 0.3 TiO 3 / La 0.7 Sr 0.3 MnO 3 (PST/LSMO) thin film has been deposited on Si substrate by chemical solution deposition. Obvious changes in dielectric constant and loss as functions of frequency and magnetic field were observed in PST/LSMO thin film. By applying both dc bias electric and magnetic fields, apparent dielectric anomalies were observed in the “butterfly-hysteresis” curves. These effects may be useful for practical application. The mechanism for the magnetocapacitance effects in PST/LSMO is rationalized by combining the Maxwell–Wagner capacitor model and the magnetoresistivity and magnetostriction of the LSMO.

Ultrasonic Investigation of Field-Induced Piezoelectric Properties in Lead Free Materials

Ultrasonic method was applied for evaluation of piezoelectricity in layered crystals of CuInP2S6 family and of La(Mg1/2Ti1/2)O3-BaTiO3 (BT-LMT) electroceramics. Amplitude of electric signal appearing on the plate under ultrasonic excitation is proportional to appropriate piezoelectric constant. In CuInP2S6 family piezosensitivity was observed only in low temperature phase. In BT-LMT ceramics piezosensitivity had anomalies at low temperature phase transitions and had long tails in the high temperature paraelectric phase. Field-induced hysteresis loops of such ultrasonically detected piezoelectric signal amplitude in the ferroelectric phase were observed. In the paraelectric phase field-induced piezosensitivity due to electrostriction appeared in layered crystals and BT-LMT ceramics when DC bias electric field was applied. In centrosymetric AgInP2Se6 crystals comparatively large piezoelectric sensitivity was induced due to electrostriction by DC bias electric field applied along c-axis.

Study of phase transitions in ternary lead indium niobate-lead magnesium niobate-lead titanate relaxor ferroelectric morphotropic single crystals

In this work we report on the elastic hysteretic behavior observed in ferroelectric lead indium niobate-lead magnesium niobate-lead titanate (PIN-PMN-PT) relaxor single crystals under conditions of cooperative stress, temperature, and electric field. Room temperature elastic response displays strong and sharp discontinuity associated with stress induced phase transition. Quasistatic elastic response and ultrasonic wave propagation measurements demonstrated that this strain discontinuity in PIN-PMN-PT single crystal is associated with a ferroelectric rhombohedral (FR)—ferroelectric orthorhombic (FO) phase transition. The temperature dependent elastic response and transition strain were modeled by Devonshire theory. The crystal instability under compression is significantly improved by application of a dc bias electric field.

The giant dielectric tunability effect in bulk [formula omitted] around room temperature

The effect of applied dc bias electric field on dielectric permittivity in bulk La 2NiMnO 6 is investigated in this paper. It is found that a small bias field of 40 V/cm can greatly reduce the dielectric permittivity around the room temperature, compared to the much larger electric field that is required for conventional ferroelectric materials. The observed giant dielectric tunability is retained over a broad range of around room temperature and is most likely related to the charge ordering of Ni 2+ and Mn 4+ ions, further confirming the existence of electronic ferroelectricity in La 2NiMnO 6.

Anisotropic giant dielectric tunability in electronic ferroelectric YbFe 2O 4

We have studied the dielectric properties of YbFe 2O 4 single crystals, which exhibits ferroelectricity due to charge ordering. The dielectric constant of both the c-axis and ab-plane exhibit a large dielectric dispersion, and is greatly suppressed by applying a small DC bias electric field, which leads to a giant dielectric tunability. Due to the layered structure, a strong anisotropy between the c-axis and ab-plane is observed in the dielectric constant, tunability, and loss tangent. The origin of the giant dielectric tunability and dielectric loss is discussed based on the nature of electronic ferroelectricity.

Selective photocurrent generation in the transparent wavelength range of a semiconductor photovoltaic device using a phonon-assisted optical near-field process

In this paper, we propose a novel photovoltaic device using P3HT and ZnO as test materials for the p-type and n-type semiconductors, respectively. To fabricate an electrode of this device, Ag was deposited on a P3HT film by RF-sputtering under light illumination (wavelength λ0=660 nm) while reversely biasing the P3HT/ZnO pn-junction. As a result, a unique granular Ag film was formed, which originated from a phonon-assisted process induced by an optical near-field in a self-organized manner. The fabricated device generated a photocurrent even though the incident light wavelength was as long as 670 nm, which is longer than the long-wavelength cutoff λc (=570 nm) of the P3HT. The photocurrent was generated in a wavelength-selective manner, showing a maximum at the incident light wavelength of 620 nm, which was shorter than λ0 because of the Stark effect brought about by the reverse bias DC electric field applied during the Ag deposition.

Controllable far-infrared electromagnetic radiation from plasmas applied by dc or ac bias electric fields

It is shown theoretically and numerically that a dc/ac bias field applied over tenuous plasma can be converted efficiently into electromagnetic (EM) waves at the plasma frequency ωp, with the amplitude and polarization determined by the bias. The initial phase of the EM waves can be controlled by the triggering time of the bias and therefore circularly/elliptically polarized EM waves can be obtained by applying two bias fields perpendicular to each other. When the bias frequency is near ωp, the resonance appears and the EM waves are generated with the intensity enhanced considerably as compared with the dc-bias case. This approach provides a potential way to produce tunable far-infrared EM waves such as terahertz waves. Limits of this approach by available parameters of plasmas and bias are also discussed.

Electrical properties of PMMA ion-implanted with low-energy Si+ beam

The electrical properties of polymethylmethacrylate (PMMA) after implantation with silicon ions accelerated to an energy of 50 keV are studied under DC electric bias field. The electrical response of the formed material is examined as a function of Si+ fluence in the range 1014 − 1017 cm−2. The carbonaceous subsurface region of the Si+-implanted PMMA displays a significant DC conductivity and a sizable field effect that can be used for electronic applications.

THz Polarization Effects on Detection Responsivity of Glow Discharge Detectors (GDDs)

The detection mechanism of glow discharge plasma in neon indicator lamps has been investigated in the terahertz and microwave spectral regions. The influence of the THz radiation polarization on the responsivity of glow discharge detectors (GDD) is considered here. There are two detection mechanisms in the GDD that exist simultaneously, each at the expense of the other. Experiments with GDD neon indicator lamps in the THz regime prove that the dominant detection mechanism of the GDD is enhanced cascade ionization rather than enhanced diffusion current. Our polarization experiments in the THz regime show that when the electric field of the THz radiation is in the same direction as the DC bias electric field of the lamp, the responsivity is about 50% higher than when the THz electric field is orthogonal to the DC field. This supports the concept that the dominant detection mechanism of the GDD in the THz regime is enhanced cascade ionization.

Ultrasonic and Piezoelectric Studies of Phase Transitions in Two-Dimensional CuInP2S6 Type Crystals

In this contribution, we present results of piezoelectric and ultrasonic investigations of CuInP2S6 family solid solutions where various Cu was substituted with Ag and S to Se. The ultrasonic attenuation, velocity and piezoelectric sensitivity anomalies were recorded at phase transitions in these new compounds. It was shown that with increasing Ag and Se content in the solid solutions, the phase transition temperature decreases. The phase transition type changes to the second order in Ag0.1Cu0.9InP2S6crystal. Pure AgInP2S6 and AgInP2Se6 crystals did not reveal the phase transition in the temperature range 100–300 K. The piezoelectric sensitivity in these pure crystals was observed only when DC bias electric field was applied along direction normal to layers. In this case the piezoelectric sensitivity appeared due to electrostriction.

Characteristics of photoconductivity oscillation in semi-insulating GaAs photoconductive semiconductor switches

The 4 mm gap and 5 ns pulse width semi-insulating GaAs photoconductive switches were triggered by 532 nm laser pulse with gradual increase of bias voltage from 500 V in steps of 50 V until the emergence of nonlinear electrical pulse. The expermental results showed that the linear and nonlinear electrical pulse waveforms had smaller amplitude and varying degrees of oscillation reduction after going through a main pulse. Then the microscopic state and transport process of carriers （hot-electron） in the switch material were studied in detail using the quantum theory. It was found that in the DC bias electric field, when the relaxation time of the hot-electrons in the electron-electron and electron-phonon interaction process is longer than the carrier life, the photoconductivity oscillation can be caused by the change of mobility in the process of optoelectronic transport, which is the main cause for the output electrical pulse to show oscillations.

Study of the dipole rotation path of BaTiO3 single crystal based on dielectric properties in structure phase transition

The temperature-dependence of dielectric-constant of BaTiO3 single crystals in 〈001〉 direction is measured under different voltages and frequencies. The crystal experiences rhombohedral-orthorhombic-tetragonal phase transition with the increase of temperature. Base on the assumption of dipoles rotation and the experimental results of dielectric constant, a model is proposed, which holds that the dipoles rotation path can be inferred by the dielectric properties of the adjacent structure phase of BaTiO3. The dipoles rotation paths of rhombohedral, orthorhombic and tetragonal phases are given. The influences of bias dc electric field on the dipoles rotation path are discussed.

Dielectric Character Modified by Perpendicular Electric Field in Triglycine Sulfate

The dielectric dispersion of a triglycine sulfate single crystal has been measured after a prolonged application of the electric field perpendicular to the ferroelectric b axis. As the perpendicular electric field dwarfs the dielectric dispersion, the influence on the dielectric permittivity by the perpendicular electric field looks like the influence by the DC bias electric field parallel to the ferroelectric axis. It is concluded that the perpendicular electric field robustly immobilizes motion of the domain walls which contribute to the dielectric permittivity.

Nonlinear harmonic components in dielectric relaxation of polyelectrolytes

The problem of the nonlinear ac dielectric response in polyelectrolytes is carried out by considering these electrically charged systems acted on by a strong dc bias electric field superimposed on a weak ac field. An infinite set of coupled (translation-rotation) kinetic equations is derived, and by using a perturbation procedure, we establish a new expression for the complex dielectric increment of an assembly of nonpolar rodlike macroions surrounded by small counterions. By considering the stationary regime, we show that the electric polarization of the nonpolar macroion is given by calculating the expectation value of P(1)(cos theta)H(1)(x), where P(1) and H(1) stand for the first Legendre and Hermite polynomials, respectively. The results so obtained provide new relaxation features, which are presented in the form of analytic expressions and illustrated by Cole-Cole-like diagrams and three-dimensional dispersion and absorption plots in order to show the influence of the coupling parameter a measuring the importance of the rotational motion over the translational one.

Kinetic Theory of the Langevin Saturation in Dilute Solution of Dipolar Symmetric-Top Molecules in Spherical Solvents

Assuming the low molecular reorientation approximation, the formulae for the third-order electric polarization induced in liquids composed of rigid noninteracting dipolar, symmetric-top molecules in spherical solvents were derived. Our medium is acted on by a strong external dc bias electric field superimposed on a weak ac electric field, and the classical Smoluchowski– Debye equation for rotational diffusion of the symmetric-top molecules is applied. In order to highlight the influence of the anisotropy of rotational diffusion tensor components and the orientation of permanent dipole moment of the molecule on the complex linear and nonlinear electric susceptibilities, we present three-dimensional plots of the linear and nonlinear dispersion and absorption spectra, for different values of the frequency of ac electric field.

Quasistatic dielectric and strain characterization of transparent relaxor ferroelectric lead lanthanum zirconate titanate ceramics

The relative permittivity and dielectric loss tangent of transparent lead lanthanum zirconate titanate (PLZT) (9.5/65/35) and (9.0/65/35) ceramics were measured as a function of temperature, ranging from −60 to 100 °C, and as a function of frequency, ranging from 0.12 to 5000 kHz. Diffuse maxima were observed in the complex permittivity plots of both PLZT compositions. These maxima correspond to phase transitions from ferroelectric to paraelectric and finally to cubic in the PLZT crystal structure. Second, a Sawyer–Tower circuit was used to determine the electric displacement of each ceramic composition as a function of a dc bias field, ranging from −1.7 to 1.7 MV/m. Third, a Polytech vibrometer was used to measure the longitudinal ac strain response of (9.5/65/35) and (9.0/65/35) PLZT ceramics under various dc bias and ac electric fields with a 120 Hz driving frequency. A maximum piezoelectric strain of 0.8×10−3 m/m occurred for a 0.64 mm thick (9.5/65/35) PLZT at 1.1 MV/m dc and 1.09 MV/m ac peak to peak, and 1.3×10−3 m/m for a 0.54 mm thick (9.0/65/35) PLZT at 1.4 MV/m dc and 0.68 MV/m ac peak-to-peak. Fourier analysis was performed on the raw vibrometer data and the strain response at the second, third, and fourth harmonics were obtained as a function of dc and ac fields. Finally, the measured data were fitted to a theoretical model and the material coefficients for these PLZT compositions were obtained.

Field emission from strained carbon nanotubes on cathode substrate

Experimental studies on the collective field emission from carbon nanotubes (CNTs) on metallic cathode substrate show wide variability. In this paper, we investigate several related effects, such as the relationship between the electron–phonon transport and the mechanical deformation in the CNTs. A systematically coupled model of randomly oriented CNTs in a thin film is developed. Numerical simulations are reported, which are able to reproduce several experimentally observed phenomena, such as a fluctuating field emission current, deflected CNT tips and the heating process. Examples are shown, where the electrodynamic stretching of the initially deflected CNTs can produce transients in the collective field emission current as large as 1 0 3 times the usual field emission current. Correspondingly, the tip temperature rises from 303 to 520 K within a time interval of 40 s. A 10 K variability in the maximum temperature is observed over the 0.0144–0.0202 V/nm range of the DC bias electric field. The maximum tensile stress is found to be 1.2 GPa, which is much smaller than the fracture stress.

The model of electric field dependent dielectric properties for porous ceramics

The electric field dependence on the dielectric properties of the porous ceramics was studied theoretically. The dielectric constant of the porous ceramics under certain direct current (dc) bias field and the real strength electric field in the porous ceramics were given quantitatively. As the pore can share the electric field, the tunability of the porous ceramics will be decreased when the porosity increases. The dielectric constant evolution of Ba0.6Sr0.4TiO3-based porous ceramics with the dc bias electric field can be successfully explained by our theoretical results. Taking Ba0.6Sr0.4TiO3-based porous ceramic samples, for example, there is good correspondence between the theoretical and the experimental results.