High Local Electric Field Research Articles

Impact of corona on the long-term performance of nonceramic insulators

A majority of nonceramic insulator (NCI) application is under relatively clean conditions where leakage current may be nonexistent. Occurrence of corona for long periods of time on NCI operating under relatively clean conditions is possible due to localized high electric field (E-field) brought about by design and manufacturing deficiencies. Therefore, resistance to corona-induced degradation of NCI housing materials is an important factor that impacts NCI long-term reliability, and is the focal point of this paper. Two sources of corona have been investigated: corona from a metal electrode, and corona from water droplets. Field inspections were performed on 230 and 500 kV insulators to demonstrate the existence of corona even under relatively clean and dry conditions. Three commonly used NCI housing materials, namely high temperature vulcanized (HTV) silicone rubber (SIR), ethylene propylene diene monomer (EPDM) and a blend of EPDM and silicone polymer were evaluated in the laboratory. In addition, housing materials from several insulators removed from the field were analyzed. Data gathered from electrical and physicochemical analyses show that corona induced degradation is dominantly due to a combination of electro-chemical reactions rather than thermal effects.

A scanning tunneling microscopy tip with a stable atomic structure

A single stable adatom on a {110}-type plane of a tungsten tip is created via field-evaporation in a field-ion microscope (FIM) operating at room temperature. This single adatom has sufficient surface mobility at room temperature and migrates, in one-dimension, along a -type direction toward an edge of a {110}-type plane, due to the existence of an electric field gradient. The plane edge has a higher local electric field than its center, since it has a higher local geometric curvature. This result implies that the stable position of a single adatom during a scan of a scanning tunneling microscope (STM) tip on a surface is at the edge and not at the center of a {110}-type plane at room temperature. Therefore, the electron wave function of a tip is not symmetric and this fact should be taken into account in a careful analysis of STM images. Also a tip with a dislocation emerging at a {110}-type plane is suggested as an improved STM tip configuration, as the step at the surface, created by the intersection of the dislocation with it, is a perpetual source of single adatoms.

Polymer Based Photodetectors

AbstractRecent developments in our laboratory related to polymer-based light sensors are reviewed. The inherent processibility of the active polymer medium is utilized in the implementation of different designs for the opto-electronic applications. The utility of these devices as sensitive photodetectors, image sensors and position sensitive detectors is demonstrated. The schottky-type layer formation at interfaces of polymers such as polyalkylthiophenes and aluminum accompanied by the enhanced photo-induced charge separation due to high local electric field is tapped for some of these device structures. The sensitivity of polymer-based field effect transistors to light also provides a convenient lateral geometry for efficient optical-coupling and control of the transistor state. The range of these polymer-detectors available with the option of operating in the diode and transistor modes should be an attractive feature for many potential applications.

ワイヤ放電加工における放電位置制御性の向上

In this study, it was clarified that discharge locations can be controlled by locally superimposing high electric fields. On the basis of this principle, two methods for improving the controllability of discharge locations in wire electrical discharge machining (WEDM) were proposed: 1) increasing the local high electric field by increasing the superimposing voltage, and 2) increasing the discharge probability by successive superimposition in each discharge cycle. The experimental results showed that discharge locations in conventional dry WEDM can be dispersed uniformly over the workpiece surface, and the discharge can be successfully moved to the vicinity of the point where high voltage is applied.

Trends in the ultimate breakdown strength of high dielectric-constant materials

The ultimate breakdown strength E/sub bd/ of a dielectric material is found to decrease as the dielectric-constant k increases. A thermochemical description of the ultimate breakdown strength of high-k dielectrics suggests that E/sub bd/ should reduce approximately as (k)/sup -1/2/ over a wide range of dielectric materials while the field-acceleration parameter /spl gamma/ should increase in similar but inverse manner. New time-dependent dielectric breakdown (TDDB) data are presented over a wide range of dielectric materials and E/sub bd/ was found to decrease as (k)/sup -0.65/ while /spl gamma/ increases as (k)/sup 0.66/. The good agreement between thermochemical theory and high-k TDDB observations suggests that the very high local electric field (Lorentz-relation/Mossotti-field) in high-k dielectrics tends to distort/weaken the polar molecular bonds making them more susceptible to bond breakage by standard Boltzmann processes and/or by hole-capture and thus lowers the breakdown strength.

Density and refractive index measurements in hexaheptyloxytriphenylene, a discotic liquid crystal

Density and refractive index measurements in the discotic liquid crystal hexaheptyloxytriphenylene were performed in the hexagonal columnar Colho and isotropic I phases. The temperature dependence of the density ρ(T) for this compound was obtained by combining small angle X-ray data and capillary methods. The ordinary n o extraordinary n e and isotropic liquid n i refractive indices were measured using a modified Abbe refractometer to an accuracy of about 10−3. To check the consistency of the density and the refractometry experiments we used the Lorentz–Lorenz relation. An anomaly in the empirical relationship at the Colho–I phase transition, which holds for many uniaxial liquid crystals, was detected. A discrepancy between low birefringence Δn∼0.109 and a relatively high local electric field anisotropy for hexaheptyloxytriphenylene is discussed.

Correlated topographic and spectroscopic imaging beyond diffraction limit by atomic force microscopy metallic tip-enhanced near-field fluorescence lifetime microscopy

A near-field optical imaging approach is demonstrated for simultaneous topographic and spectroscopic imaging with spatial resolution beyond the optical diffraction limit. The method combines metallic-tip-based tapping-mode atomic force microscopy (AFM) with fluorescence lifetime imaging microscopy (FLIM). The AFM metallic tip was formed by sputter coating a Si tapping mode tip with Au, in a way that forms a globular tip apex. Such tip apex generates high local electric field enhancement under laser illumination, which provides a strong electric-field interaction between the AFM tip and the fluorescent molecules under the tip. The tip perturbation of fluorescence gives the fluorescence lifetime changes that provide the AFM–FLIM imaging contrast. A finite element method simulation was used to further evaluate the electric near-field enhancement and electric field distribution originating from the metallic Au-coated AFM tapping-mode tip. We have demonstrated that spatially mapping the change in fluorescence lifetime and intensity is a promising approach to spectroscopic imaging at an AFM spatial resolution typically defined by the apex diameter of the AFM tips. The globular Au-coated AFM tip not only gives adequate spatial AFM tapping-mode imaging spatial resolution but also is “environmentally friendly” to soft samples, such as polymeric dye-labeled nanospheres and even biological specimens such as POPO-3 labeled DNA.

Thermochemical description of dielectric breakdown in high dielectric constant materials

A thermochemical/molecular model is developed for breakdown in high dielectric constant materials and the model suggests that a fundamental relationship exists between dielectric breakdown strength (Ebd) and dielectric constant (k). The model indicates that Ebd should show an approximate (k)−1/2 dependence over a wide range of high dielectric constant materials. The model also predicts that the field-acceleration parameter (γ), from time-dependent dielectric breakdown (TDDB) testing, should increase with dielectric constant. TDDB and Ebd data are presented for model support. The thermochemical model suggests that the very high local electric field (Lorentz-relation/Mossotti-field) in high-k dielectrics tends to distort/weaken the polar molecular bonds making them more susceptible to bond breakage by standard Boltzmann processes and/or by hole capture and thus lowers the breakdown strength.

Carbon-nanotube-based nonvolatile memory with oxide–nitride–oxide film and nanoscale channel

We have fabricated a single-wall carbon-nanotube (CNT)-based nonvolatile memory device using SiO2–Si3N4–SiO2 (ONO) layers as a storage node. The memory device is composed of a top gate structure with a channel width of a few nanometers and the ONO layer embedded between CNT and gate electrode. When the bias voltage between the CNT and gate electrode increases to 4 V, charges are tunneled out from CNT surfaces and captured to the traps in the ONO layers. Stored charges on the trap sites make the threshold voltage shift of 60 mV and is independent of charging time, suggesting that the ONO has traps with a quasiquantized energy state. The quantized state is related to the localized high electric field associated with CNT channel. The CNT-field-effect transistor with an ONO storage node could be used for an ultrahigh-density nonvolatile memory.

Generation Of High Energy Ion Beams from a Plasma Focus Modified for Low Pressure Operation

This paper reports on the modification of a small plasma focus device (UNU/ICTP PFF) to operate at low pressure for enhanced ion beam generation. For the present operation, the electrode geometry of the plasma focus device is modified to redirect the plasma motion at the end of the axial rundown phase so that normal plasma focus action will not occur. The redirection of the plasma leads to a rapid increase in the plasma resistivity and hence a high localized electric field will be established and as a result, high energy ion beam will be generated. With air as the working gas, pressure as low as 10-3 mbar has been tested. At such a low pressure, breakdown of the discharge must be initiated with the use of a set of twelve plasma injection cable guns. The modified plasma focus has been shown to be able to produce high energy ion beams of nitrogen, argon and hydrogen consistently.

Electron field emission from diamond-like carbon films and a patterned array by using a Ti interfacial layer

Electron field emission from diamond-like carbon (DLC) films deposited on Si, Ti/Si, and Au/Si substrates by a filtered arc deposition technique was studied. As compared to DLC/Si and DLC/Au/Si, electron field emission from DLC/Ti/Si was enhanced, showing an increased emission current density and emission site density (∼1.2×103/cm2). An emission site density up to 2.2∼2.2×103/cm2 was obtained after the DLC/Ti/Si had been annealed at 430 °C for 0.5 h. A patterned DLC/Ti/Si array fabricated by the oxygen reactive ion beam etching technique showed further field emission enhancement. An emission site density up to 3.2∼3.5×103/cm2 and a threshold field as low as 2.1 V/μm were achieved. It was shown that the low potential barrier at the interface and high local geometric electric field enhancement around the edges produced by reactive ion beam etching were possible causes of the enhancing effects. It could also be explained by Geis’ metal-diamond-vacuum triple junction emission mechanism.

A phase transition in H 2O due to a high electric field close to an electrode

In this study a phase transition in H 2O due to an applied very high local electric field E at ambient conditions is predicted. We analyse the equation of state and behaviour of entropy. For E=10 9 V m −1 some characteristic features of local electrostriction pressure Π and of entropy change ΔS as a function of the field strength E are noted. These features are interpreted as testifying to a phase transition: water in low field → H 2O in high field (or, in other words, H 2O compressed by the field). A consistency of the present results with recent off-specular surface X-ray scattering studies is discussed.

Carbon nano-/micro-structures in field emission: environmental stability and field enhancement distribution

The field emission (FE) properties of carbon films can be understood in terms of local field enhancement β(x,y), which can be determined with x,y-scanning FE. β(x,y)⇒ the spatial distribution of emitting sites, which can be counted as f(β)∝exp(−kβ). f(β) is connected with the presence of sharp protruding objects, whiskers or nanotubes on the surface. Investigations of the current–time (I–t) characteristics of field emission from single-walled carbon nanotubes (SWNT) do not show any significant dependence on ambient partial pressures of hydrogen or water up to 10−5 mbar. Oxygen however, causes a substantial reduction of the FE current. Field emission microscopy (FEM) during short-time nanotube annealing (∼1000 K) reveals dim five-fold as well as six-fold feinstructures, which are believed to be nanotube cap states. The nanotube cap states have a short lifetime due to impinging atoms/ions that are adsorbed due to the high local electric field at the cap (∼3000 V/μm) and create resonant tunnelling states. The anode material is believed to be the main source of adsorbed species and not the ambient gas phase.

Effects of annealing of (Ba,Sr)RuO3 bottom electrodes on the electrical properties of (Ba,Sr)TiO3 thin films

The annealing of (Ba,Sr)RuO3 films which are structurally and chemically matched with (Ba,Sr)TiO3 films was performed in oxygen and nitrogen atmospheres in the temperature range of 600–750 °C for 30 min. The effects of annealing the (Ba,Sr)RuO3 on the physical and electrical properties of the (Ba,Sr)TiO3 films were investigated. The x-ray diffraction peak of the annealed (Ba,Sr)RuO3 film at high temperatures revealed that the (Ba,Sr)TiO3 film is thermally more stable than RuO2. The (Ba,Sr)RuO3 film under N2 annealed showed lower electrical resistivity and larger surface roughness compared with those under O2. In addition, from the sequential two-step annealing process using O2 and N2, and by reversing the annealing sequence, the electrical resistivity and the surface roughness of the (Ba,Sr)RuO3 film turned out to be reversible. The (Ba,Sr)TiO3 film on the N2 annealed (Ba,Sr)RuO3 showed a higher leakage current than that on the O2 annealed bottom electrode because rough surface can cause a high local electric field. The dielectric constant of the (Ba,Sr)TiO3 thin film increased with the annealing temperature of the (Ba,Sr)RuO3 bottom electrode regardless of the annealing atmosphere.

The Case For 0.1eV EELS in a 1Å STEM

Abstract Semiconductor devices are rapidly heading towards nanometer sizes, with dielectric gate oxides already in the 2-3nm thickness range and transistor channel lengths of order 10-20nm. There is good reason to believe, therefore, that physical limits imposed by atomic level granularity will dominate operation of semiconductor devices in the future. Thus, recent work has identified a physical limit for the thickness of SiO2 in order to maintain its insulating character. [1] On the other hand, new opportunities are created, based on new behavior at the atomic level. In the presence of very high local electric fields, for instance, the local electronic structure can change from insulating to conductive, forming a very small, very fast “Mott” transistor. [2] In a single molecule having a localized electronic level which is positioned well with respect to a conducting environment, single electron transistor operation may be possible at room temperature. [3]

Electron field emission from a patterned diamond-like carbon flat thin film using a Ti interfacial layer

A 200-nm-thick diamond-like carbon film was prepared on Ti-deposited Si (ρ<0.01 Ω cm) using a filtered arc deposition technique. Field-emission properties of it are enhanced as compared to films deposited on Si, showing an increased current and emission site density (∼1.2×103/cm2). A patterned diamond-like carbon flat thin film on Ti-deposited Si fabricated by the oxygen reactive ion-beam etching technique shows further enhanced field-emission properties. An emission site density of 3×103/cm2 was obtained. Field emission could be observed at a field value as low as 2.1 V/μm. It is shown that the low potential barrier at the interface and high local geometric electric field enhancement around the edges produced by reactive ion-beam etching are possible causes for the enhanced effects. It can also be explained by the Geis’ metal–diamond–vacuum triple junction emission mechanism.

EHD/EMHD Transport Processes and Electric Reconnection in Dusty and Dirty Plasmas

ABSTRACT: For dusty and dirty plasmas, fully or partially ionized, collisionless or collisional, containing dust grains or aerosols, charged and/or uncharged, an electrohydrodynamics (EHD)/electromagnetohydrodynamics (EMHD) is presented on the basis of a new equation of electric field transport in a charged fluid, supplemented by the equations of fluid vorticity, magnetic field, energy transport, and heat transfer extended for this new regime. The ‘electric Reynolds number’, RE=ɛμvL/T (ɛ: dielectric constant; μ: permeability; v: fluid velocity; L: characteristic length; T: characteristic time) plays an important role in the EHD/EMHD regime as a criterion of relative importance of convection, diffusion, dissipation, propagation, and radiation. The equation of electric field transport recovers the Kelvin‐Helmholtz theorem for high electric Reynolds numbers with a space‐charge related frozen‐in field concept. Tenuous cosmic plasmas where dust particles can be highly charged, need to be considered a multi‐component fluid, composed of electrons, ions, charged and/ or uncharged dust, and specifications are given briefly to a multi‐ component fluid model. By analogy with fluid vortex merging in the HD regime and magnetic reconnection in the MHD regime, electric reconnection is newly introduced in the EHD/EMHD regime. Following dust‐related electric reconnection, subsequent processes are divided into two cases, depending on whether the local electric fields on the grain surface are below or beyond the breakdown threshold of the background gas. For the former case, some of the electrostatic energy tends to be converted into the kinetic energy of the particle, leading to its rapid acceleration. For the latter case, a local surface discharge will take place due to sufficiently high local electric fields, forming a corona around the dust or object and leading to critical ionization flow in the form of streamer and leader followed by an eventual main discharge, or rarely by a plasma layer formation around the dust grain. Applications of EHD/EMHD and electric reconnection to a number of examples are indicated, including the formation of diffuse dust layers or dust distributions between the clouds and the ionosphere with reference to pre‐earthquake effects, natural and triggered lightning, tornadic thunderstorms, cloud‐to‐ionosphere discharges, ball lightning, nebular lightning, Chondrule production in meteorites, and a new universal electric‐cusp type plasma reactor.

Effect of electron heating and radiation pressure on tunneling across Schottky barrier due to giant near field of FIR laser radiation

The conductance of tunnel junctions formed by n-GaAs and a semitransparent metal electrode on its surface was shown to be changed by normally incident radiation with frequency below the plasma edge of n-GaAs. A spatial redistribution of the electrons due to the radiation pressure and the corresponding change in the shape of the self-consistent Schottky barrier are observed as a photoconductivity response. The comparison of the measured intensity dependence of the response to the theory has revealed an effective enhancement of the radiation field close to the n-GaAs/Me interface. The ratio K e of the effective radiation intensity to the incident plain-wave intensity has turned out to be as large as 10 5. The high local electric field results in strong heating of the degenerate electron gas in the Schottky-barrier region that is mostly apparent as a photo-e.m.f. An analysis of the intensity dependence of the photo-e.m.f. is carried out involving the modification of the Schottky barrier by the ponderomotive force, the electron gas heating in Γ- and L-valleys, as well as the heating of LO phonons. The results confirm the value of K e and allow to estimate the hot-electron temperature in Γ- and L-valleys.

Modelling of the initiation and development of a filamentary discharge in XeCl excimer lasers

The dynamics of a filamentary discharge in discharge-excited XeCl excimer laser has been examined using a two dimensional fluid model. The entire process of the filamentary discharge, from its initiation and development, is presented and the role of protrusions on a cathode surface to induce a filamentary discharge is discussed. The filament develops in the direction of the anode, assisted by a space-charge induced local high electric field. The features of the spatio-temporal evolution of the filament, including the gas temperature rise are discussed comparing the ArF discharge case and experimental observation.

Preparation of SrBi2Ta2O9 Thin Films by Liquid-Delivery Metalorganic Chemical Vapor Deposition using a Double Alcoholate Source

A liquid-delivery metalorganic chemical vapor deposition (MOCVD) apparatus for preparing SrBi2Ta2O9 (SBT) thin films was designed and set up. For the preparation of SBT thin films, a double alcoholate source, Sr[Ta(OC2H5)6]2, was used for supplying Sr and Ta atoms with a stoichiometric composition, while Bi(C6H5)3 was used for supplying Bi atoms. In the experiment, variation of the film composition with the deposition temperature and source-supply mol ratio was primarily investigated. It was found that the Bi/Ta mol ratio in the films varied with the deposition temperature and became smaller at lower deposition temperatures. It was also found that the Sr/Ta mol ratio was considerably smaller than stoichiometry above 500°C, probably because of the dissociation of Sr[Ta(OC2H5)6]2. It was ascertained that a 200-nm-thick SBT thin film with the Sr/Ta mol ratio of about 0.4, which was deposited at 350°C and subsequently annealed in O2 atmosphere at 750°C for 30 min, exhibited ferroelectricity. The dielectric constant of the film was about 120. Remanent polarization and coercive field at 10 V were 3.8 µC/cm2 and 73 kV/cm, respectively. However, the leakage current density was found to be as high as the order of 10-4 A/cm2 at 3 V. It is speculated from atomic force microscope (AFM) observation of the surface roughness of the film that the origin of the high leakage current density is the existence of local high electric field spots in the film.