Onset Of Breakdown Research Articles

Temperature, composition and microstructure variations during pulsed laser irradiation of a deposited film on a substrate

A computer model has been developed to describe melting and resolidification during laser irradiation of elemental and alloy films on a substrate. The computer model predicts the temperature profile, maximum melt depth, maximum solidification rate, onset of cellular breakdown and the final resolidified composition profile. The computer model has been compared with measurements [I. T. H. Chang and B. Cantor, J. Thin Solid Films 230, 167 (1993)] made on cross-section TEM specimens of 1.15 J/cm 2irradiated 400 nm thick Sn and 0.96-1.17 J/cm 2irradiated 120 nm thick Ge-50 at.% Sn films on single crystal Ge substrates. The predicted results give good agreement with the measured data. The maximum melt depth increases with increasing laser energy density. Cellular breakdown takes place at increasing depth with increasing laser energy density.

From Electric Field Dependent Particle Dynamics to Bistability in the Breakdown of the Quantum Hall Effect

Abstract The integer quantum Hall effect (IQHE) and its breakdown (onset of dissipation) reflect general properties of the solutions of the time-dependent Schrödinger equation, where the macroscopic elec­tric field E is properly included. In particular, the dynamics of an electron in a broadened Landau band not only depends on the disorder potential but also on the value of |E|. This leads to an I n ­ dependence of the conductivities σxx and σxy, which implies that the IQHE breaks down if |E| is sufficiently high. We show that the general form of the | El-dependence of σxx and σxy can lead to jumps in the longitudinal resistance at the breakdown of the IQHE, as observed in recent experiments.

Electrostatic Force on a Moist Particle Near a Ground Plane

Abstract The effect of surface moisture on the electrostatic force of attraction between an uncharged particle and a ground plane is investigated. Describing a moist sphere with an effective complex permittivity allows the image force to be calculated using complex linear multipoles. The number of multipoles needed for an accurate image force calculation is determined as a function of particle-plane separation. Adsorbed moisture introduces a relaxation in the electrostatic image force. For particles exposed to a range of relative humidities, the model predicts relaxation times that vary by several orders of magnitude. In addition, at small particle-plane separations adsorbed moisture can increase the image force by several orders of magnitude. Finally, multipolar moments are used to calculate the electric field in the gap separating the particle and ground plane to determine the onset of breakdown or field emission.

Pitch rate and pitch-axis location effects on vortex breakdown onset

Computational results are presented for the onset of vortex breakdown above a 75-deg sweep delta wing subject to a ramp-type pitch maneuver to high angle of attack. The flows are simulated by solving the full threedimensional unsteady NavierStokes equations on a moving grid using the implicit Beam-Warming algorithm. An assessment of the effects of numerical resolution, and comparison with experiment are employed to validate the computational approach. The effects of pitch rate and pitch-axis location are examined. For a range of these parameters, it is found that either increasing pitch rate or moving the axis downstream results in a larger angular delay of vortex bursting. These effects are correlated with the motion-induced effective incidence along the wing. For fixed pitch rate, the change in pivot location is equivalent to a shift in time without significant alteration of the flow structure.

Compressibility effects on vortex breakdown onset above a 75-degree sweep delta wing

The effects of compressibility on the onset of vortex breakdown above a 75-deg sweep delta wing were explored numerically for both static and pitching conditions. The flows were simulated by solving the mass-averaged, three-dimensional, unsteady Navier-Stokes equations using an implicit, time-accurate Beam-Warming algorithm and the algebraic Bald win-Lomax turbulence model. Static computations were performed over the freestream Mach number range 0.2 < M^ < 0.95 and for a chord Reynolds number Rec = 2 x 10 6. Compressibility was found to have a pronounced effect on the flow structure for static conditions. The formation of several shocks and an embedded supersonic region in the vortex core (for M^ as low as 0.4) were encountered prior to the onset of vortex breakdown. Despite these drastic changes in the flow structure, the quasistatic breakdown onset angle varied only slightly. Compressibility effects on the transient onset of vortex breakdown were also investigated for a ramp-type pitch maneuver to high angle of attack with 0.2 < Mx ^ 0.6. Under dynamic conditions increasing Mv, resulted in a larger delay of breakdown and in the formation of a complex, three-dimensional shock structure at Mx = 0.6. Compressibility effects were found to be similar when comparing the results from laminar and turbulent pitching calculations, indicating that these effects are to a great extent in viscid in nature.

Negative resistance characteristics of Zener diode at onset of avalanche breakdown

In a low current region (∼100μA) within a narrow voltage near the onset of primary breakdown, a negative resistance effect has been observed in a 4 kV high-voltage Zener diode. The region is much lower than ihe secondary breakdown region (∼ 100 mA) where negative resistance phenomena have previously been reported for Zener diodes. Measured I—V and oscillation characteristics of high-and low-voltage (<200 V) Zener diodes in the low current region are described, confirming the presence of negative resistance.

Limitation of CO&lt;inline-formula&gt;&lt;sup&gt;&lt;roman&gt;2&lt;/roman&gt;&lt;/sup&gt;&lt;/inline-formula&gt; laser-induced gas breakdown

To obtain economical extraction of ²³⁵U in the molecular laser isotope separation (MLIS) process, 16-μm laser beams must be generated in a parahydrogen Raman cell with high repetition rates and sufficient intensity. Because the intensities of the 16-μm laser beams are dependent on the intensity of the incoming pump laser beams, the intensity of the CO₂ lasers must be kept as high as possible. The maximum intensity has, however, been found to be controlled by the onset of gas breakdown in the Raman cell at too low a level for efficient Raman conversion. Through tests, the origin of gas breakdown in a 2-kHz-repetition-rate Raman cell is identified as particle contamination. The effect of the degree of contamination is determined and compared with experimental results. Conditions are set and modifications implemented on the Raman cell to ensure efficient Raman conversion.

Avalanche breakdown in (Al x Ga 1- x ) 0.52 In 0.48 P pin junctions

The avalanche breakdown behaviour of (AlxGa1-x)0.52In0.48P has been investigated by growing a series of pin diode structures and by measuring the reverse leakage currents until the onset of avalanche breakdown. Comparing the breakdown voltage (Vbd) with that of GaAs, significant increases are obtained, with AlInP having in excess of twice the Vbd of GaAs.

Circuit-level electrothermal simulation of electrical overstress failures in advanced MOS I/O protection devices

Previous work on electrothermal simulation using network analysis techniques has been of limited use due to the lack of avalanche breakdown modeling capability and the models to efficiently describe the temperature dynamics. Particularly, simulation of electrical overstress (EOS) and electrostatic discharge (ESD), which are important threats to IC reliability, require an accurate description of temperature-dependent device electrical behaviour including breakdown phenomenon. This paper presents electrothermal device models and their implementation in a new circuit-level electrothermal simulator iETSIM. Simulation results for an I/O protection device in an advanced MOS process are presented to demonstrate iETSIM's ability to accurately model device behaviour up to the onset of second breakdown. >

Self-generated and externally driven current oscillations in n-GaAs

Experimental investigations of self-generated and externally driven non-linear current oscillations due to impact ionization of shallow impurities in n-type GaAs at low temperatures are presented. The regular relaxation oscillations which appear at the onset of breakdown are destabilized by a magnetic field normal to the epitaxial layer and multifrequency oscillations and chaotic fluctuations following the Ruelle-Takens-Newhouse scenario can be found. Driving the self-generated oscillations with an external periodic bias voltage quasiperiodicity, mode locking, interaction and overlap of mode locked resonances and period doubling can be observed depending on frequency and amplitude of the external force. The reconstructed return maps, recorded phase diagrams and Devil's staircase agree with theoretical predictions based on the circle map and give new evidence of the universality of the transition from quasiperiodicity to chaos.

Protein phosphatase inhibitors induce the selective breakdown of stable microtubules in fibroblasts and epithelial cells.

In many cell types, a small subset of microtubules (MTs) are unusually long-lived compared with the majority of the MTs. These "stable" MTs may be important mediators of differentiative events since they are usually found aligned with developing asymmetries of cells undergoing morphogenesis. In addition to their longevity, the stable MTs are more resistant to drug depolymerization and are enriched in post-translationally detyrosinated tubulin (Glu-tubulin). To determine the role of protein phosphorylation in the regulation of these stable MTs, we treated NIH 3T3 fibroblasts and TC-7 monkey kidney epithelial cells with okadaic acid (OA) and calyculin A, potent inhibitors of protein phosphatases 1 and 2A (PP1 and PP2A), and then localized dynamic MTs and stable MTs with antibodies specific for tyrosinated tubulin (Tyrtubulin) and Glu-tubulin, respectively. OA at 0.1-10 microM caused a rapid and complete breakdown of Glu-MTs (MTs enriched in Glu-tubulin) in both cell types without substantially affecting the number of Tyr-MTs. While all concentrations of OA over this range resulted in a complete loss of Glu-MTs, the onset of Glu-MT breakdown was proportional to the logarithm of the OA concentration. The inactive analog of OA, 1-norokadaone, had no effect at any concentration. Calyculin A also caused a selective loss of Glu-MTs but was effective at 10 nM, consistent with its more potent inhibition of PP1. That the loss of Glu-MTs reflected the loss of stable MTs from the cells was shown by the absence of nocodazole-resistant MTs in OA-treated cells. OA did not appear to activate a MT-severing activity, since no MT fragments were observed after OA treatment of cells pretreated with taxol. These results suggest that PP1 and perhaps PP2A are involved in the regulation of MT stability in cells and show that the dynamic and stable subsets of MTs are regulated differentially by protein phosphorylation.

Modified Solution for Finding the Optimal Angle of Spacecraft Walls Under Orbital Debris Impacts

stream of the onset of breakdown, are apparent by comparing images acquired at successive times. The concept of a switch in sign of the azimuthal vorticity at the onset of vortex breakdown is shown to be an essential feature of the vortex breakdown process. This criterion, first proposed in the theoretical model of Brown and Lopez, persists during transient development of vortex breakdown following cessation of pitching motion of the wing.

Temperature dependence of base-current reversals and breakdown characteristics of n- p- n transistors

Base current reversal phenomena due to the avalanche breakdown have been the focus of the study of advanced Si n- p- n BJTs in the past. The base-current reversals in transistors can happen before the onset of junction breakdown and at the condition of junction breakdown. However, the distinction of these has not been presented yet. We define the collector-emitter voltage V CE-IBr as the voltage at which the base current reversal occurs. For a fixed base-emitter voltage V be, we define the collector-emitter breakdown voltage BV CE-BE at which the collector current rises steeply with increasing V cb. We vary the temperature of the device, and compare both quantities. Physical mechanisms have been proposed to interpret the temperature-dependent current reversals and breakdown phenomena.

Synthesis, processing, and third‐order nonlinear optical properties of benzobisthiazole polymers containing thiophene moieties

AbstractBenzobisthiazole polymers containing mono‐, bi‐, and terthiophene moieties were synthesized through polycondensation in polyphosphoric acid of 2,5‐diamino‐1,4‐benzenedithiol dihydrochloride with thiophene‐2,5‐dicarboxylic acid, 2,2′‐bithiophene‐5,5′‐dicarboxylic acid, and 2,2′:5′,2″‐terthlophene‐5,5″‐dicarboxylic acid, or their corresponding diacid chlorides, respectively. Intrinsic viscosities of up to 8.1 dL/g (methanesulfonic acid, 30°C) were recorded. Polymer structures were verified by elemental analysis and spectroscopic comparison of the polymers with appropriate model compounds. Onset of breakdown under thermogravimetric analysis in air occurred in the 460–590°C range with the benzobisthiazole polymers containing a monothiophene linkage being the most stable. Films suitable for third‐order optical susceptibility measurements could be prepared by extrusion techniques from the benzobisthiazole polymer containing a monothiophene linkage. Degenerate four wave mixing measurements on this film yielded a third order optical susceptibility χ(3) of approximately 4.5 × 10−10 esu. © 1993 John Wiley &amp; Sons, Inc.

Kinetics and mechanism of thermal decomposition of lithium oxalate catalysed by Cd 1− xCo xFe 2O 4( x =0.0, 0.5 and 1.0) ferrospinel additives

The thermal decomposition of lithium oxalate (Li 2C 2O 4) in air was investigated by means of TG, DTA, X-ray and scanning electron microscopic (SEM) techniques. The non-isothermal study reveals that lithium oxalate decomposes in one step to the carbonate. The kinetics of the isothermal decompositon of the pure salt were studied in the temperature range 556–585°C. The fraction decomposed (α) against time ( t) curves were sigmoid in shape with relatively long induction periods of the onset of salt breakdown. The kinetic parameters of the decomposition reaction were deduced employing a computeroriented kinetic analysis of the α'- t' data. This indicates that the decomposition process is governed by the random nucleation Erofe'ev equation over the entire temperature range. The kinetic evidence was supported by SEM observations. In order to evaluate the effect of Cd 1− x Co x Fe 2O 4 ( x=0.0, 0.5 and 1.0) ferrospinels on the thermal decomposition reaction, the decomposition of Li 2O 2O 4 was followed in the presence of 10wt.% of the additive. The results show that these ferrites promote the thermal decomposition rates of the oxalate with increasing x in the order 0.0 < 0.5 < 1.0. In the presence of these additives also the decomposition reaction obeys the Erofe'ev equation and proceeds by the nucleation-and-growth mechanism. The promotional effect of these catalysts is described. Their activity in promoting salt breakdown is a consequence of their appreciable solubility in the host oxalate crystals.

Onset of breakdown and formation of cathode spots

When an increasing diode voltage is applied, enhanced field emission of electrons begins from a growing number of small spots or whiskers on the cathode surface. This stimulates desorption of weakly bound adsorbates from the surface of a whisker. As the diode voltage increases, the 100-V equipotential surface moving toward the cathode is met by the desorbed neutrals moving away from the cathode, resulting in sharp risetime for the onset of ionization of desorbed neutrals by field-emitted electrons. Positive ions produced in the ionization region a few microns from the electron emitting spot are accelerated back to it. This bombardment leads to surface heating of the spot. The onset of breakdown by this mechanism requires much less current than the Joule heating mechanism. The localized buildup of plasma above the electron emitting spot leads to pressure and electric field distributions that ignite unipolar arcs. The high current density of the unipolar arc and the associated surface heating by ions result in the explosive formation of cathode spot plasma. >

Glycogen breakdown in cleaving xenopus embryos is limited by ADP

Xenopus eggs contain large stores of glycogen, but this glycogen is not glycolytically processed during cleavage. The Embden-Meyerhof pathway is inhibited by the absence of pyruvate kinase activity in vivo, and lactate and pyruvate are present at relatively low levels. In the late blastula, just preceding gastrulation, lactate levels increase, indicating the onset of glycogen breakdown and glycolytic flux. Glycolysis from microinjected [14C]glucose-6-phosphate could be transiently activated, however, by the coinjection of ADP into fertilized eggs, and constitutively activated by the injection of the ATPase potato apyrase, indicating the presence of all enzymes necessary for glycolytic activity. The isozyme profiles of pyruvate kinase and malic enzyme, two enzymes involved in carbon metabolism during cleavage or in the subsequent activation of glycogen breakdown, do not change between the egg and gastrula stages. These data suggest that the activation of glycogen breakdown and glycolysis in the late blastula is probably not a result of new gene activity but may be the metabolic consequence of increased free ADP that is then able to support the pyruvate kinase reaction.

Regular and chaotic current oscillations in n-type GaAs in transverse and longitudinal magnetic fields.

Self-sustained current oscillations due to impurity breakdown in n-type GaAs epitaxial layers are reported for various magnetic-field strengths and orientations of the field with respect to the direction of current. In all cases relaxation oscillations at the onset of breakdown and formation of a current filament in the postbreakdown regime are observed. A magnetic field normal to the epitaxial layer destabilizes the filament and causes multifrequency oscillations and chaotic fluctuations. On the other hand, if the magnetic field lies in the plane of the layer the filamentary current flow is stable up to field strengths of 2 T.

Design considerations for p-i-n thyristor structures

An analysis of a high-voltage gate turn-off (GTO) thyristor structure with a double-layered n base (p-i-n structure) is presented. From integration of Poisson's equation, an expression for the forward-blocking voltage at the onset of avalanche breakdown is obtained. Simple design criteria are developed to calculate the optimal thickness and doping density of the n base of a conventional pnpn structure designed for a specific voltage-blocking capability. The same principle is applied to design for the doping densities and thicknesses of the high-resistivity region and the buffer layer of the p-i-n GTO structure. The forward-blocking voltage, as well as the on-state voltage (at a current density of 300 A cm/sup -2/) is predicted for a wide range of base layer thicknesses and doping densities to illustrate the available tradeoff options. Lowest on-state power dissipation for high blocking voltages (>6000 V) is predicted for a doping level of 5*10/sup 12/ cm/sup -3/ in the high-resistivity layer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ion formation on the surfaces of electrodes

The initial phase of the onset of electrical breakdown in a vacuum discharge is characterized by very rapid ionization of surface material which leads to a kind of “explosive” plasma formation on the electrodes. As an increasing electric field is applied between the two electrodes of a vacuum diode the ionization process is initiated by the field emission of electrons from highly localized spots on the cathode surface. Despite the fundamental importance of cathode spots for the breakdown process, the structure of cathode spots and the fast ionization rates of surface layers were not fully understood. Besides the Joule heating of the field emitting spot, the electrons also desorb contaminants and ionize some of the released neutrals. Ions produced a short distance (∼1 μm) from the spot are accelerated back towards the cathode. This ion bombardment leads to surface heating of the spot and calculations of the power deposition show that ion surface heating is initially orders of magnitude larger than Joule heating. Ion bombardment is especially important at low initial current densities since it is efficient in producing desorption and sputtering of neutrals from the surface and hence increases the neutral density which in turn increases the ionization rate. As more ions are produced, a positive space charge layer forms which enhances the electric field and thus strongly enhances the field emitted electron current. Surface heating and the buildup of positive space charge rapidly lead to further enhanced field emission and finally thermionic electron emission. The localized buildup of an ion sheath above the electron emitting spot naturally leads to pressure and electric field distributions which provide such a large electron flow and ion sputtering rates that the spot explodes into a dense plasma within a few nanoseconds.