Electric field enhancement in guided-mode resonance filters

Electric fields inside guided-mode resonance filters (GMRFs) may be intensified by resonance effects. The electric field enhancement is investigated in two GMRFs: one is resonant at normal incidence, the other at oblique incidence. It is shown that the two GMRFs exhibit different behaviors in their electric enhancement. Differences between the electric field distributions of the two GMRFs arise because coupling between counterpropagating modes occurs in the first case. It is also shown that the order of the electric field of maximum amplitude can be controlled by modulation of the dielectric constant of the grating.     

Electrical properties and Pockels effect in BaTiO_{3}/SrTiO_{3} superlattices

The electrical and linear electro-optical properties of BaTiO $_{3}$ (BT)/SrTiO $_{3}$ (ST) superlattices epitaxially grown on ST substrate are theoretically investigated using a microscopic quantum mechanical model based on the orbital approximation in correlation with the dipole–dipole interaction. Both the first-, second-, and third-order electronic polarizabilities were considered in this calculation in order to obtain accurate results for both the spontaneous local electric field, spontaneous polarization, relative dielectric constant, and linear electro-optic coefficients (Pockels constants) of BT/ST superlattices. The calculations show that the spontaneous local electric field, spontaneous polarization and linear electro-optic coefficients of BT/ST superlattices increase with their content in BT while the relative dielectric constant increases with their content in ST. Moreover, we have shown that significant enhancement of the linear electro-optic coefficients can be achieved in BT/ST superlattices. This enhancement, which concerns the ST as well as the BT layers, arises from the combined effects of strain, induced in the BT layers by the epitaxial growth, and internal polarizing electric field originating in the BT layers and acting on the electronic clouds of the polarizable constituent ions of the system.     

Critical (burst) electron emission from dielectrics, induced by injection of a dense electron beam

A dense pulsed electron beam and nanosecond pulse length has been used to inject negative electric charge into various dielectric materials (single crystals, glasses, composites, plastics) for initiation of electron field emission from the dielectric into a vacuum. It has been shown that upon reaching a critical electric field in the bulk and at the dielectric surface there is intense critical electron emission. The local current density from the emission centers reaches a record value (for dielectrics) of the order of 10⁶ A/cm². The emission occurs in the form of a single gigantic pulse. The measured amplitude of the emission current averaged over the emitting surface is the same order of magnitude as the injected electron current: 10–1000 A. the emission current pulse lages behind the current pulse of the primary electron beam injected into the sample. The delay time is in the range 1–20 nsec and decreases with increasing current density of the injected beam. Direct experimental evidence is found for intense generation of carriers (band or quasifree electrons) in the near-surface layer of the dielectric in a strong electric field due to the Frenkel-Poole effect and collisional ionization of traps, usually various donor levels. This process greatly strengthens the field emission from the dielectric. It has been shown experimentally that the emission is nonuniform and is accompanied by “point bursts” at the surface of the dielectric and ionized plasma spikes in the vacuum interval. These spikes are the main reason that the transition of the field emission into “bursts” is critical, similar to the current which has been previously observed in metals and semiconductors. However there are a number of substantial differences. For example the critical field emission current density needed for the transition into “bursts” is three orders of magnitude less than for metals. If we provide sufficient electron current at the surface or from the bulk of the dielectric to the emission centers, then the critical emission is always accompanied by a vacuum discharge between the surface of the dielectric and a metallic collector. A detailed computer model of the processes in the dielectric during injection of a high-density electron beam has been developed which allows one to understand the complex physical pattern of the phenomenon. Tomsk Polytechnic University. Institute of High-Current Electronics, Siberian Section, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 45–67, November, 1997.     

Observation of non-linear relaxational polarization effects at high electric field strengths

High field dielectric relaxational effects have been studied in Al₂O₃. It is found that the relaxational polarization increases steeper than linear versus the electric field for field strengths E ≳ 1 MVcm⁻¹.     

Thermally activated conductivity and current-voltage characteristic of dielectric phase in granular metals

Models of thermally activated linear and high-field nonlinear conductivity of a dielectric phase in granular metals (nanocomposites), i.e., aggregates of small metallic grains in a dielectric matrix, have been suggested. Given a sufficiently large spread of grain sizes, the temperature dependence of the nanocomposite conductivity should be described by a universal “power-1/2” law: G∝exp[−(T ₀/T)^1/2]. An analytical expression for T ₀ has been obtained. It is found that there are two regimes of nonlinear conductivity in a high electric field, namely, a low-field regime, when both the number and mobility of carriers change with the field strength, and a high-field regime, when only the mobility of carriers is variable. Analytical expressions for the nonlinear conductance in both regimes have been obtained. Zh. éksp. Teor. Fiz. 115, 1484–1496 (April 1999)     

Dielectric properties of pyridine N-oxide aqueous solution under the static electric field and microwave field

Molecular dynamics simulations of the pyridine N-oxide aqueous solution have been performed in the canonical ensemble macroscopic canonical ensemble (NVT) both in the absence and presence of an external electromagnetic field. It extracts the radial distribution function for each concentration solution, dielectric constant and other information on dielectric properties. Analysing the microscopic dielectric information of the aqueous solution under the static electric field (0–3×10⁹ V/m) and microwave frequencies (2.45G, 0–3×10⁹ V/m), and comparing the dielectric information between the different concentrations and different field strengths, we can get the dielectric properties of two kinds of polar aqueous solution under microwave irradiation. Thus, this project can provide the data of the sample to other correlation studies.     

Effect of dopant Cr ions on the dielectric properties of melt-grown ZnSe crystals

The frequency and temperature dependences of the real and imaginary parts of the permittivity of Cr-doped (n _Cr ? 10¹⁸ cm^?3) melt-grown ZnSe crystals have been measured in the low-frequency region. It has been established that such doping reduces the heterogeneity of the dielectric properties and the level of energy losses of ac electric field in a crystalline ingot. The effect of dopant atoms on the dielectric properties has been explained as being caused by formation of defect associates with participation of these atoms and intrinsic crystal defects.     

Enhancing surface plasmon polariton propagation by two-layer dielectric-loaded waveguides on silver surface

We report a study of a two-layer dielectric-loaded surface plasmon polariton waveguide (TDLSPPW) which consisted of two dielectric layers (high-index/low-index) on a silver film. The discontinuity of the electric field at the interfaces resulted in a concentrated field in the low-index region. It efficiently reduced the propagation loss of the surface plasmon polariton mode. The mode fields and corresponding complex propagation constants were calculated by a vector finite-difference method. The propagation properties were measured by a modified near-field optical microscope. It is confirmed that the propagation length of the proposed TDLSPPW was about 1.6 times longer than conventional single-layer SPP waveguides. In addition, a 90^° waveguide turn with 3 μm radius showed that the bending loss was smaller than 2 dB.     

Antiferroelectric and ferroelectric phase transitions of the displacive and order-disorder type in PbZrO3 and PbZr1-xTi x O3 single crystals

For PbZrO₃ and PbZr_0.99Ti_0.01O₃ single crystals the first order Raman light scattering spectra in the paraelectric phase have been analysed. In lead zirconate two kinds of crystals, with and without a transient phase, were investigated. It was found that temperature dependence of the defect-induced soft mode frequency in the paraelectric phase has a negligible contribution to the low-frequency dielectric response. From the point of view of strong dielectric relaxation in the range of 10⁶–10⁹ Hz, which originates in a disorder of the lead sites, crossover of the order-disorder and displacive type of antiferroelectric phase transition in lead zirconate is considered: the phase transition mechanism is neither purely displacive nor order-disorder. Contribution of physical phenomena responsible for the ε(ω,T) dielectric response at low frequencies of an external electric field are described.     

The response of the dielectric susceptibility to an external electric field around the phase transition temperature in Li:KTaO3

Experimental results of measurements of dielectric susceptibility vs applied electric field at various temperatures on 3.5 and 8% Li: KTaO₃ are presented. It is found that there is an enhancement of the dielectric susceptibility as a function of increasing applied electric field at temperatures below ～ 90 K for the 8% Li crystal and at temperatures below ～ 60 K for the 3.5% Li crystal. The results are consistent with a slightly first-order phase transition.     

Nonlinear optical properties of nanometer-size silver coated polydiacetylene composite vesicles and resulting Langmuir–Blodgett films

Noble metal-coated PDA composite vesicles were expected to increase the effective third-order nonlinear optical susceptibility χ ⁽³⁾(ω), due to the enhancement of the optical electric field induced by localized surface plasmon resonance. Different size (20, 50 and 80 nm) Ag colloidal nanoparticles were coated on the outer surface of polydiacetylene (PDA) vesicles to form PDA/Ag nanocomposite vesicles and the size-dependent effect of Ag colloidal nanoparticles on NLO properties enhancement has been explored. The explanation based on the competition of a size-dependent light-confinement effect and a size-dependent dielectric constant of Ag particles had been presented. Furthermore, these PDA/Ag composite vesicles were successfully immobilized onto the solid substrate by the Langmuir–Blodgett (LB) method and their linear and nonlinear optical properties were characterized, respectively. Obviously, PDA/Ag composite vesicles Langmuir–Blodgett (LB) films promoted the enhancement of the third-order NLO properties.     

The giant dielectric tunability effect in bulk La2NiMnO6 around room temperature

The effect of applied dc bias electric field on dielectric permittivity in bulk La₂NiMnO₆ 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 Ni²⁺ and Mn⁴⁺ ions, further confirming the existence of electronic ferroelectricity in La₂NiMnO₆.     

Effects of PVA organic binder on electric properties of CaCu3Ti4O12 ceramics

CaCu₃Ti₄O₁₂ ceramics with incorporation of polyvinyl alcohol (PVA) are prepared from the powder synthesized by a solid state reaction. Their electric and dielectric properties are investigated in this study. It is found that adding PVA can dramatically reduce the dielectric loss of CCTO in the low frequency region, and stabilize the dependence of dielectric constant on the measuring frequency. The minimum dielectric loss of 0.045 is obtained from the sample with 8 wt% PVA. The nonlinear coefficient (α) and breakdown electric field (E_b) increase with an increase of PVA binder.     

The giant dielectric tunability effect in bulk Y<Subscript>2</Subscript>NiMnO<Subscript>6</Subscript> around room temperature

The effect of applied dc bias electric field on dielectric permittivity in bulk Y₂NiMnO₆ 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 Ni²⁺ and Mn⁴⁺ ions. This may further confirm the existence of electronic ferroelectricity in Y₂NiMnO₆.     

Novel Ag–BaTiO3/PVDF three-component nanocomposites with high energy density and the influence of nano-Ag on the dielectric properties

Novel Ag–BaTiO₃/PVDF (polyvinylidene fluoride) three-component nanocomposites and traditional BaTiO₃/PVDF two-component nanocomposites were prepared by the same procedures. The dielectric properties of these two kinds of composites were compared. The results showed that the kind of three-component nanocomposites had better dielectric properties. The energy density of such kind of composites could reach nearly 10 J/cm³, which indicated that these nanocomposites could be used as the dielectric layers of pulse-power capacitors. The Coulomb blockade effect was used to explain the dielectric breakdown properties and the resistivities under high electric field of such new kind of nanocomposites.     

Corrugated-enhanced second harmonic generation in metal–insulator–metal plasmonic waveguides

Nonlinear effects such as second-harmonic generation (SHG) are important for applications such as switching and wavelength conversion. In this study, the generation of second harmonic in metal–insulator–metal (MIM) plasmonic waveguides was investigated for both symmetric and asymmetric structures. Symmetric means that the metals at the top and bottom of the dielectric layer are the same and asymmetric means that the metals at the top and bottom of the dielectric layer are different. Two different structures are considered here as plasmonic waveguide for generation of second harmonic and analyzed using finite-difference time domain method. Besides the structure has grating on both sides for more coupling between photons and plasmons. The wavelength duration of grating per length unit (number of grooves) will be optimized to reach the highest second harmonic generation. To perform this optimization, the wavelength of operation λ = 458 nm is considered. It was shown that field enhancement in symmetric MIM waveguides can result in enhancement of SHG magnitude compared to the literature values and asymmetric device results in more than two orders of magnitude enhancement in SHG compared to symmetric structure. It is also shown that the electric field of second harmonic depends on the thickness of crystal (insulator). So, its thickness is optimized to achieve the highest electric field.     

Critical thicknesses of electrostatic powder coatings from inside

A simple electrostatic model is applied to the charge powder coating of a grounded conductor eventually covered by insulating layers. The electric field inside the powder coating and its evolution during the process are established with also the corresponding evolution in the dielectric layer and some practical consequences are also discussed. The thickness of the charged powder layer is limited by two types of process: a self-limiting process related to the vanishing field in the air gap and a field strength process occurring on one of the two sides of the coating–dielectric interface. Inside the powder coating, the electric field induces an increased electrostatic pressure on the powder grains at the substrate–coating interface and a vanishing pressure on the grains at the coating–air interface. This internal field is amplified into air bubbles and it may be responsible for the back ionisation process and of the formation of moon craters via the ionisation of the air molecules followed by the pressure exerted by the ions pushed in the direction of the free surface. For each of these limits, analytical expressions are established and they permit to identify the role of physical properties of the deposited powder (particle size and dielectric constant) as well as the role of thickness, structure, and dielectric constant of the insulating substrate. The present approach explains the difficulty in obtaining thick coatings on thick insulating substrates or thick coatings from the use of too fine powder grains. Finally, different behaviours as a function of the size of the deposited powder grains are deduced from the contribution of the electric field to the velocity of the particles sticking to the surface. Then and for the first time, the present contribution underlines the important role of the subsurface composition and the need to characterize the structure, dimension and dielectric constant of this subsurface for various applications concerning electrostatic spraying and powder painting of plastics and of insulating coatings on metallic work pieces.     

The effect of an external electric field on the optical properties of a quantum molecule with a resonance D(-)-state

The average binding energy and the level width for the resonant D^(-)-state in a quantum molecule have been calculated in the presence of an external electric field. The calculations were performed in the zeroradius potential model with allowance for the tunneling decay of the resonant state. The external electric field is shown to stimulate the decay of resonant D^(-)-states under conditions of dissipative tunneling. It was found that the curve of the probability of photoionization of the D^(-)-center as a function of the external electric field strength has two peaks that are connected with a change in the symmetry of the double-well oscillator potential of the quantum molecule and with the transformation (caused by the electric field) of envelope wave functions, respectively.     

Electric quadrupole interaction of 100Rh in antimony, hafnium and rhenium

The effects of the Mg(II)/Fe(III) ratio on the structure and Fe microenvironments in MgFe LDH substances were investigated. The LDHs were prepared by the co-precipitation method with Mg(II)/Fe(III) ratios from 2:1 to 6:1. The materials were characterized by ⁵⁷Fe Mössbauer spectroscopy and powder X-ray diffractometry. The ⁵⁷Fe Mössbauer spectra exhibited asymmetric doublet corresponding to high-spin Fe(III) microenvironments in all LDH structure. It was found that the quadrupole splitting decreased with increasing Mg(II)/Fe(III)ratio reflecting change in the electric field gradient due to the incorporation of different amounts of iron into the Mg-containing layers.     

Formation of aligned ZnO nanorods on self-grown ZnO template and its enhanced field emission characteristics

We report a novel method for producing aligned ZnO nanorods (ANR) on self-grown ZnO template in a single step process involving growth of ZnO by vapor transport, followed by quenching of growing ZnO flux in liquid nitrogen. In the present study Zn powder turns into ZnO sheet under oxygen flow at ∼900 °C and bottom surface of the sheet acts as template for the growth of ANR. It is revealed from XRD and EDAX analysis that the bottom of the sheet is Zn rich region and acts as self catalyst for the growth of ANR. The grown nanorods have length up to several tens of micrometers with diameters ranging from ∼100 to 150 nm. Microstructural analysis of ANR indicates the fractal like configuration. The field emission properties have been investigated for ANR with fractal geometry using the ANR on self-grown ZnO template as a cathode directly. The turn-on electric field required to draw current density of ∼1.0 μA/cm² has been found to be ∼0.98 V/μm. The field enhancement factor based on Fowler-Nordheim (F-N) plot was found to be ∼7815 for ANR. The fractal geometry of ANR has been shown to be advantageous for achieving improved field emission features. The present investigations of synthesis involving formation of ANR over self-grown ZnO template, together with fractal configuration of the as-synthesized ANR, are first of their type.