Spontaneous extinguishing of a vacuum arc in terms of the ectonmodel

Based on the ecton model, a statistical method for studying the processes in the cathode spot of a vacuum arc has been proposed. It has been demonstrated that the spontaneous extinguishing of a DC arc and the effect of “current chopping” inherent in an AC arc are due to the cellular structure of a cathode spot and by the finite lifetime of an ecton. The principal characteristics that are responsible for the stability of the arc operation are the current per cell and the efficiency of the recovery mechanism. The average operative time of the discharge is longer for the materials showing lower currents per cell. The influence of the conditions of arc operation, such as the parameters of the external electric circuit, the cathode surface condition, the presence (or absence) of an external electric field, etc., is reduced in the main to a change in the efficiency of the recovery mechanism     

Model of collective ion acceleration in a vacuum discharge based on the concept of a deep potential well

An ecton mechanism for the operation of the cathode spot and the concept of a deep nonstationary potential well are used as the basis to propose a model of collective ion acceleration at the spark stage of a vacuum discharge. It is shown that in principle a deep potential well can form in the presence of an external electric field and the conditions for its formation in an explosive-emission diode are clarified. The proposed model can explain the main processes leading to collective ion acceleration and shows good agreement with the experimental results.     

The Ecton Mechanism for the Generation of Ion Flows in a Vacuum Arc

The principal characteristics of the process of generation of the cathode plasma in a vacuum arc (ion erosion, mean charge of ions) are considered in terms of the ecton model of the cathode spot of a vacuum arc. The estimates of the parameters of ions obtained for a unit cell of a cathode spot – an ecton – are in good qualitative and quantitative agreement with experimental data. The following mechanism for the generation of the cathode plasma of a vacuum arc is proposed. When a region of the cathode is destroyed in an explosive manner due to Joule heating, the material of the cathode sequentially goes over a series of states: the condensed state and the states of imperfect and ideal plasma. During this transition the charge state of the plasma is formed and the ions are accelerated under the action of the pressure gradient in the plasma whose density decreases by several orders of magnitude over distances of 10 m from the cathode surface. The increase in current results in an increase in number of cells, and the principal parameters of the ions are formed as a result of the operation of a unit cell of the spot.     

Interaction of plasma jets and droplets in the cathode region of a vacuum arc

The interaction of liquid-metal droplets with plasma jets in the cathode region of a vacuum arc is considered in the context of an ecton model. It is shown that heating of a droplet in the cathode spot region can initiate the droplet transition to the plasma state.     

Erosion of a copper cathode in a negative corona discharge

The pulsed-periodic regime of a negative corona (Trichel pulses) in atmospheric-pressure air, which leads to explosion emission mechanisms (ecton generation) of pointed cathode erosion, is investigated. The jet erosion process at the copper cathode is discovered, and micrometer dendritelike structures formed by erosion products returning to the cathode are detected.     

Mechanism of ion flow generation in vacuum arcs

The ecton model of the cathode spot is used to analyze the main parameters of ion flow in vacuum arcs (ion erosion, mean charge, and velocity). It is shown that the arc plasma is formed as a result of microexplosions at the cathode surface, induced by the Joule heating by the high-density current of explosive electron emission. Ionization processes are localized in a narrow region of the order of a micrometer near the cathode and the ionization composition of the plasma subsequently remains unchanged. Under the action of the electron pressure gradient, ions acquire directional velocities of the order of 10⁶ cm/s even over small distances of the order of several micrometers.     

Peak-type and dip-type metal-clad waveguide sensing

Two types of operation for metal-clad waveguide sensors, peak-type and dip-type operation, are described. The newly discovered peak-type operation [Sens. Actuators B 94, 304 (2003)] can be achieved by use of a few-nanometers-thick cladding of a metal with a large imaginary permittivity, whereas conventional dip-type operation is obtained with a metal cladding with small imaginary permittivity some tens of nanometers thick. Both types of operation are described, and the main differences are illustrated.     

Development and investigation of a metal ion source for accelerators

The design and operation of a new spray-type metal ion source are described. The source is built around a plasma emitter containing metal ions and using a two-step glow discharge with double plasma compression. The necessary temperature of electrons in a discharge chamber is reached by distributing the discharge power without heating. The design of the discharge chamber is optimized. The first set of experimental data for the mass-and-charge composition of a beam generated by this source is presented.     

Ultrasonic inspection of stainless steel butt welds using horizontally polarized shear waves

Inspection of austenitic stainless steel weldments by conventional ultrasonic means is fundamentally limited by the textured, columnar grain structure of the weld metal. It is shown that, for selected angles of incidence, shear waves normally polarized with respect to the columnar grains can pass through the weld metal-base metal interface without partial reflection. As a consequence, the inspectability of stainless steel weldments can be improved. The operation of a low frequency, ultrasonic system for stainless steel butt weldments is demonstrated.     

Theoretical model of a planar waveguide refractive index sensor assisted by a corrugated long period metal grating

A theoretical model of a novel planar integrated refractive index sensor based on surface plasmon-polariton (SPP) excitation with a corrugated metal long period grating (LPG) is presented and comprehensively investigated. The main principle of the operation this device is based on co-directional energy transfer by means of a corrugated metal LPG between a p-polarized guided mode propagating in a waveguide layer and the SPP propagating a metal layer separated from the waveguide layer by a buffer. The corrugated LPG is engraved in the metal layer in contact with the sensed medium. The power transmitted through the LPG in the guided mode serves as an input signal for an interrogation unit. This device is free from any moving parts and can be simply integrated into any planar waveguide system. Our sensor simulations are based on the local-normal-mode transfer matrix method and performed in telecom wavelength range.     

Magnetic hysteresis properties of neutron-irradiated VVER440-type nuclear reactor pressure vessel steels

The development of non-destructive evaluation methods for irradiation embrittlement in nuclear reactor pressure vessel steels has a key role for safe and long-term operation of nuclear power plants. In this study, we have investigated the effect of neutron irradiation on base and weld metals of Russian VVER440-type reactor pressure vessel steels by measurements of magnetic minor hysteresis loops. A minor-loop coefficient, which is obtained from a scaling power-law relation of minor-loop parameters and is a sensitive indicator of internal stress, is found to change with neutron fluence for both metals. While the coefficient for base metal exhibits a local maximum at low fluence and a subsequent slow decrease, that for weld metal monotonically decreases with fluence. The observed results are explained by competing mechanisms of nanoscale defect formation and recovery, among which the latter process plays a dominant role for magnetic property changes in weld metal due to its ferritic microstructure.     

Multilayer metal/metal-oxide diffractive structure for photonic temperature sensing

We designed and fabricated multilayer metal/metal-oxide surface relief diffractive grating structures by growing alternating Pt and SnO(x) layers. Optical interrogation at 633 nm reveals the temperature dependence of their reflection and transmission diffractive effects. This function is explored here in the context of a remote, spatially localized, photonic temperature sensing operation, achieving sensitivity of 10% per °C for the zeroth-order in the transmission mode. The experimental demonstration is found to be in good agreement with the results of rigorous coupled wave analysis of the composite metal/metal-oxide element.     

High-speed multibit operation of a dual vacancy-type oxide device with extended bi-polar resistive switching behaviors

We investigated the resistive switching behaviors of the metal–copper oxide–metal devices with the enhanced capability in terms of high speed and multi-bit operation. From the analysis of the normal and extended resistive switching behaviors, the voltage-induced resistive changes were modeled and the resistive switching polarity was explained. Also, we proposed and fabricated a dual vacancy-type device structure with an extended resistive switching behavior and demonstrated a high-speed implemental 2-bit multi-bit operation by controlling specifically switch-on voltage pulses.     

Time-of-flight mass spectrometry studies of an ion beam generated by the titan source

The TITAN source generates wide-aperture beams of gas and metal ions of different materials. This is achieved because of two types of cold-cathode arc discharges, which operate simultaneously in the discharge system of the source. For metal ions to be obtained, use is made of the vacuum arc initiated between an ion-forming cathode and a hollow anode. To produce gas ions, a constricted low-pressure arc discharge is initiated with the same hollow anode. The constitution of ion beams generated by the TITAN source has been investigated using a homemade time-of-flight spectrometer. This paper describes the design of the latter and the principle of its operation, and discusses the physical peculiarities of the spectrometer operation, which affect the ion beam constitution. Institute of High Current Electronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 21–28, February, 2000.     

化学镀金在GaN基发光二极管电极制备上的应用

采用真空蒸镀与化学镀两种方法制备GaN基发光二极管（LED）金电极,分析比较了两种工艺所得芯片成本、外观色差、打线拉力。结果表明,化学镀金可选择性还原欲沉积的金属于电极上,较之蒸镀整面金属,可大幅度节省金属成本,且操作简单易行。化学镀金法所制得金属层,较蒸镀法所制得金属层表面粗糙,可有效减少电极间的色差,且能提高打线或焊线的附着力。     

Evaluation of the morphology of particles produced by plasma-chemical synthesis of ceramic powders

A physicomathematical model of thermal and diffusion processes in a drop of a dilute metal salt solution during its heating in a plasma-chemical reactor for synthesizing metal oxide powders is presented. The results of numerical calculations are analyzed to assess the possible influence of the operation parameters of the reactor and the characteristics of the initial solution (precursor) on the morphology of the particles formed.     

Controllable switching ratio in quantum dot/metal–metal oxide nanostructure based non-volatile memory device

In this paper, we report a facile quantum dot/In?CInOx(nanostructure)/quantum dot/In based non-volatile resistive memory device. The solution processed tri-layer structure exhibited bipolar resistive switching with a ratio of 100 between the high-resistance state and low-resistance state. The memory device was stable and functional even after 100,000 cycles of operation and it exhibited good retention characteristics. The ON/OFF switching ratio could be controlled by choosing appropriate metal in the structure. Memory operating mechanism is discussed based on charge trapping in quantum dots with InOx acting as barrier. A comparative study of memory devices consisting of aluminum and titanium in place of indium is presented. The possible reason for the variation in ON/OFF ratio is discussed on the size of the nano-sized grains of the middle metal layer.     

Surface plasmon resonance biosensing by electro-optically modulated attenuated total reflection

This study presents a surface plasmon resonance biosensing technique based on electro-optically modulated attenuated total reflection. The initial wavevector of the light for exciting surface plasmons is specified by setting the incident angle and is then modulated by electro-optic effect. The light power which is attenuated-total-reflected from the metal/dielectric interface is correspondingly electro-optically modulated. Its variation with the applied voltage is utilized to determine the analyte concentration. In the biosensing process, the incident angle determines the initial position of the operation point and thus the detection sensitivity. The presented technique has the features of resolution tunability and sensitivity tunability under various base indices of sensing layer or analyte solution for optimal operation. In this work, the effects of the incident angle, the Au-film thickness, and the ridge width on the detection sensitivity are also discussed.     

金属板疲劳损伤非线性兰姆波混频检测

针对金属板结构安全运行需要,开展了金属板结构疲劳损伤非线性兰姆波混频检测方法研究.通过数值仿真,研究了两列A0兰姆波与材料损伤间的非线性相互作用.结果 表明,两列共线A0兰姆波在结构材料损伤处产生单向传播的和频S0波,且和频波幅值随传播距离具有积累增长效应.对不同疲劳程度金属板试件进行了共线混频兰姆波检测实验,结果表明...     

Simulation on effect of metal/graphene hybrid transparent electrode on characteristics of GaN light emitting diodes

In order to decrease the Schottky barrier height and sheet resistance between graphene(Gr) and the p-GaN layers in GaN-based light-emitting diodes(LEDs), some transparent thin films with good conductivity and large work function are essential to insert into Gr and p-GaN layers. In this work, the ultra-thin films of four metals(silver(Ag), golden(Au), nickel(Ni), platinum(Pt)) are explored to introduce as a bridge layer into Gr and p-GaN, respectively. The effect of a different combination of Gr/metal transparent conductive layers(TCLs) on the electrical, optical, and thermal characteristics of LED was investigated by the finite element methods. It is found that both the TCLs transmittance and the surface temperature of the LED chip reduces with the increase of the metal thickness, and the transmittance decreases to about 80% with the metal thickness increasing to 2 nm. The surface temperature distribution, operation voltage, and optical output power of the LED chips with different metal/Gr combination were calculated and analyzed. Based on the electrical, optical, and thermal performance of LEDs, it is found that 1.5-nm Ag or Ni or Pt, but 1-nm Au combined with 3 layered(L) Gr is the optimal Gr/metal hybrid transparent and current spreading electrode for ultra-violet(UV) or near-UV LEDs.