Nanosecond electric explosion of thin aluminum films

Pulsed electrodynamic breakage of thin (∼20-nm-thick) aluminum films deposited onto polymer substrates have been experimentally studied. The character of film fracture depends on the level of supplied electric energy W. For 3.5 kJ/g < W < 4.3 kJ/g, discontinuities (striations) are formed in the transverse direction relative to the applied electric field. At high current densities on a level of ∼(1–3) × 10¹² A/m² and explosion times within 50–300 ns, the integral of action to explosion varies within (0.79–1.08) × 10¹⁷ A s/m² depending on the rate of energy supply and differs from published data for relatively massive conductors.     

Some characteristics of electric explosion of zinc wires

Some physical characteristics necessary for calculating the circuit of and selecting the optimum conditions for the electric explosion of zinc wires have been experimentally determined, including the specific action of zinc h _b = (0.70 ± 0.15) × 10⁵ A² s/mm⁴ (for maximum current densities 2.5 × 10⁵ A/mm² < j _M < 4.5 × 10⁵ A/mm²) and the critical length of exploding wire λ_cr = 1.8 × 10³ (ɛν × 10⁻⁶)^0.56.     

Organic impurity preconcentration by a multimembrane inlet system of a mass spectrometer

Using an inlet system comprising a series of membranes sequentially operating in a nonstationary flow regime, it is possible to increase the concentration of an organic impurity in a sample immediately before introduction into a mass spectrometer. The degree of preconcentration calculated in the approximation of a small response time of the membranes is proportional to (k _j /k _m )^N, where k _j and k _m are the membrane permeabilities for the impurity and matrix, respectively, and N is the number of membranes. For a butane admixture in air, the calculated relative effect for an inlet using two membranes instead of one is ∼40, while the experimental verification using 0.1-mm-thick poly(dimethylsiloxane) membranes showed an increase in the degree of preconcentration by a factor of ∼14. It is possible to approach the theoretical value by decreasing the time of impurity diffusion through the membrane at the expense of reduced membrane thickness. It is expected that multimembrane inlet systems will be especially effective in environmental monitoring, where a high sensitivity of the analysis is required with respect to toxic organic substances possessing k _j /k _m ratios much greater as compared to that of butane.     

Studying diffusion in multilayer thin-film structures on silicon by the contact melting technique

Features of the contact melting in thin-film structures comprising an aluminum layer with a thickness of h ₁ = 5 μm and a metal (Ti, Ni, Mo) or semiconductor (Si, Ge) sublayer (h ₂ = 0.1 μm) on a single crystal silicon plate (h ₃ = 500 μm) have been studied. The contact melting was caused by single rectangular electric pulses with a current density of j < 9 × 10¹⁰ A/m² and a duration of τ = 100–1000 μs passing through the Al layer. The duration and rate of melting in the samples were determined using voltage waveforms measured by an oscillograph. A method has been developed based on an analysis of the mechanisms of contact interaction in the Al film—sublayer system (with allowance for experimental data on the time of sublayer dissolution in the Al film) for estimating the coefficients of mutiphase diffusion of the system components during the passage of a current pulse.     

Massless and massive particle-in-a-box states in single- and bi-layer graphene

Electron transport through short, phase-coherent metal-graphene-metal devices occurs via resonant transmission through particle-in-a-box-like states defined by the atomically-sharp metal leads. We study the spectrum of particle-in-a-box states for single- and bi-layer graphene, corresponding to massless and massive two-dimensional (2-D) fermions. The density of states D as a function of particle number n shows the expected relationships D(n) ∼ n ^1/2 for massless 2-D fermions (electrons in single-layer graphene) and D(n) ∼ constant for massive 2-D fermions (electrons in bi-layer graphene). The single parameters of the massless and massive dispersion relations are found, namely Fermi velocity υ _F = 1.1 × 10⁶ m/s and effective mass m* = 0.032 m _e, where m _e is the electron mass, in excellent agreement with theoretical expectations.      

Features of electrostimulated degradation of aluminum metallization on silicon surface in the presence of dielectric steps

Features of thermal degradation of the aluminum metallization layers deposited onto the silicon surface with dielectric steps have been studied during the passage of single rectangular electric pulses with a current density amplitude of j < 8 × 10¹⁰ A/m₂ and a duration of 100–1000 μs. An approach to the diagnostics of metallization in the presence of dielectric sublayers is proposed, which allows the range of safe operation parameters to be determined.     

Electric current and heat induced acoustic emission in cadmium sulfide

Acoustic emission (AE) induced by the electric current passing through a cadmium sulfide (CdS) single crystal was studied. In the temperature range T=300–450 K, the intensity of the AE signals excited in the CdS crystal exposed to a constant electric field increases with the current density. It is suggested that AE in CdS is due to the dislocations breaking off and moving under the action of direct electric current and thermoelastic stresses. The activation energy for this process (E _a=0.35±0.5 eV) was estimated for a current density in the range of j=(1−7)×10⁵ A/m².     

Subnanosecond breakage of current in high-power semiconductor switches

The process of high-density current breakage in an SOS diode structure was studied using a corresponding theoretical model. For a p-n junction depth of ∼200 μm, a forward pumping time shorter than 60 ns, and a reverse pumping time of ∼10–15 ns, the structure studied exhibits a subnanosecond breakage of a current with a density of up to 10³–10⁴ A/cm². The mechanism of current breakage involves the formation of two spatially separated domains featuring strong electric field build-up on the p side of the diode structure, which expand during the current breakage at a velocity close to the carrier velocity saturation level.     

Degradation processes in the aluminum-silicon system induced by pulsed electric signals

Thermal conditions in a metallization layer deposited onto a single crystal silicon substrate were studied during the passage of single electric pulses with a current density of j=(1–8)×10¹⁰ A/m² and a duration of τ=50–800 μs. Mechanisms of the irreversible degradation in the aluminum-silicon contact under the pulsed current action are established. The degradation is manifested by the contact melting and the metallization layer fusion. Methods for the identification of these phenomena and determination of the critical current densities j _k are proposed. The critical current density depends on the current pulse duration as described by the relationship $j_k \sim 1/\sqrt[4]{\tau }$ . It is established that the passage of single current pulses with j≥5×10¹⁰ A/m² and τ≥200 μs leads to the formation of linear defects in the region of maximum temperature gradient in the test structure.     

Electrical properties of Sb2O3–CaO–V2O5 glasses and glass-ceramics

The d.c. conductivity (σ) of (a) glasses prepared by the press-quenching method and (b) glass-ceramics (crystallized glass) produced by post-heat treatment was investigated in the system Sb₂O₃–CaO–V₂O₅ and their conduction mechanism was studied. The glasses were n-type semiconductors with σ = 2.6 × 10^-6 ∼ 2.8 × 10^-5 S cm^-1 at 333 K for varying glass compositions. The conduction was attributed to small polaron hopping in the adiabatic regime. The estimated carrier density was 1.7 ∼ 3.8 × 10²¹ cm^-3 for V₂O₅ = 70 ∼ 80 mol% and the mobility was 3.5 × 10^-9 to 6.9 × 10^-8 cm² V^-1 s^-1. Crystallization raised the conductivity by a factor of 10³. The crystalline product in the glass-ceramics was Ca_0.17V₂O₅. The glass-ceramics were n-type semiconductors, and the conduction was interpreted by a superposition of the small polaron hopping in the crystalline and glassy phases. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesis of B-Sb by rapid thermal annealing of B/Sb multilayer films

Group III-V compound B-Sb films were synthesized from B/Sb/…/B multilayer films deposited by electron gun evaporation onto silicon substrate and subjecting the above multilayer to rapid thermal annealing at 773 K for 3 min. The films were characterized by XRD, TEM, XPS and optical studies. XPS studies indicated the ratio of B: Sb ∼ 1. XRD and electron diffraction patterns indicated the reflections from (100), (111), (102) and (112) planes of zinc blende BSb. Band gap evaluated from optical studies was ∼ 0·51 eV. Refractive index of the films varied between 1·65 and 2·18 with increasing energy of incident photon and plasma frequency (ω_p) was estimated to be ∼2·378×10⁻¹⁴ s⁻¹. The effective mass was computed to be ∼ 0·0845 m_e.     

Comprehensive determination of potential-dependent heat- and mass-transfer characteristics of disperse materials

A method is proposed for parametric identification of a mathematical model of coupled heat and mass transfer (HMT) in a disperse medium.Notation T temperature of the medium, K - U concentration of substances distributed in the medium, kg/kg - a _m diffusion, m₂/sec - a _m ^T thermodiffusion, m²/(sec·K) - C, C₀, C_q specific heat capacity of the medium, the medium at U=0, and the substance distributed in the medium, J/(kg·K) - y₀ density of the dry material, kg/m³ - thermal conductivity, W/(m·K) - a diffusivity, m²/sec - j_m ^u, j_m ^T, j_m density of the diffusion, thermodiffusion, and total fluxes of the substances, kg/(m²·sec) - q heat flux, W/m² - x space coordinate - time Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 5, pp. 773–779, May, 1989.     

A two species trap for chromium and rubidium atoms

Abstract

We realize a combined trap for bosonic chromium (⁵²Cr) and rubidium (⁸⁷Rb) atoms. Initial experiments focus on exploring a suitable loading scheme for the combined trap and on studies of new trap loss mechanisms originating from simultaneous trapping of two species. By comparing the trap loss from the ⁸⁷Rb magneto-optical trap (MOT) in the absence and presence of magnetically trapped ground state ⁵²Cr atoms we determine the scattering cross-section of σ _inel,RbCr = 5.0 ± 4.0 × 10^?18 m² for light-induced inelastic collisions between the two species. Studying the trap loss from the Rb magneto-optical trap induced by the Cr cooling-laser light, the photoionization cross-section of the excited 5P_3/1 state at an ionizing wavelength of 426 nm is measured to be σ _P = 1.1 ± 0.3 × 10^?21 m².     

Frequency-dependent dielectric properties and electrical conductivity of CdIn<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

The real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity and ac conductivity (σ_ac) of CdIn₂S₄ single crystals (cubic structure) have been measured in the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. In the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz, the ac conductivity of single-crystal CdIn₂S₄ follows the relation σ_ac ∼ f ^0.8, characteristic of hopping conduction through localized states near the Fermi level.     

Photoluminescence and Raman studies in swift heavy ion irradiated polycrystalline aluminum oxide

Polycrystalline aluminum oxide is synthesized by combustion technique and XRD studies of the sample revealed the α-phase. The synthesized sample is irradiated with 120 MeV swift Au⁹⁺ ions for the fluence in the range from 1 × 10¹¹ to 1 × 10¹³ ions cm⁻². A broad photoluminescence (PL) emission with peak at ∼ 447 nm and two sharp emissions with peak at ∼ 679 and ∼ 695 nm are observed in pristine when sample was excited with 326 nm. However, in the irradiated samples the PL intensity at ∼ 447, 679 and 695 nm decreases with increase in ion fluence. The α-Al₂O₃ gives rise to seven Raman modes with Raman intensity with peaks at ∼ 253, 396, 417, 546, 630, 842, 867 cm⁻¹ observed in pristine. The intensity of these modes decreases with increase in ion fluence. However, the Raman modes observed at lower fluences are found to disappear at higher fluence.     

Space charge limited conduction and determination of density of localised states in semiconductor cobalt doped TiO2

Abstract

The space charge limited conduction (SCLC) mechanism in Co doped TiO₂ has been investigated at different temperatures. At lower electric fields, ohmic behaviour is observed while at higher electric fields nonohmic behaviour is observed. The results obtained confirm the presence of SCLC in Co doped TiO₂. The electronic parameters such as the position of the Fermi level above the valence band edge E _F, the density of states in valence band N _V and effective mass of holes m _h were found as 12·32 meV, 1·26 × 10¹⁵ m^?3 and 1·33 × 10^?7 m_e, respectively. The distribution of localised states in the forbidden band gap of the Co doped TiO₂ was characterised by current–voltage measurements and the density of localised states near the Fermi level N(E_F) was found to be 2·11 × 10¹⁷ eV^?1 m^?3.     

Physical Properties of AZ91D Measured Using the Draining Crucible Method: Effect of SF<Subscript>6</Subscript>

The draining crucible (DC) technique was used for measurements on AZ91D under Ar and SF₆. The DC technique is a new method developed to simultaneously measure the physical properties of fluids, the density, surface tension, and viscosity. Based on the relationship between the height of a metal in a crucible and the outgoing flow rate, a multi-variable regression is used to calculate the values of these fluid properties. Experiments performed with AZ91D at temperatures from 923 K to 1173 K indicate that under argon, the surface tension (N · m⁻¹) and density (kg · m⁻³) are [0.63 − 2.13 × 10⁻⁴ (T − T _L)] and [1656 − 0.158 (T − T _L)], respectively. The viscosity (Pa · s) has been determined to be [1.455 × 10⁻³ − 1.209 × 10⁻⁵ (T − T _L)] over the temperature range from 921 K to 967 K superheat. Above 967 K, the viscosity of the alloy under argon seems to be constant at (2.66 × 10⁻⁴ ± 8.67 × 10⁻⁵) Pa · s. SF₆ reduces the surface tension of AZ91D.     

Modeling of the emission rates of methyl ethyl ketone and effects of additives on the emission rate

Abstract

VOC(Volatile organic compound) emission rate was modelled in this study. The effects of the different environmental factors and the additives upon the emission rates were also determined. The study was conducted in a test chamber and in the field for determination of the emission rate of methyl ethyl ketone (MEK). Additionally, the theory of mass transfer was used to derive an MEK emission model with three variables (temperature, humidity, ventilation rate) and five coefficients (T ₁, R ₁, K_B , ACH_std and C_std ); these were determined by the results of emission rate in a test chamber. The emission rate of MEK ranged from 16.1 × 10³ to 101.0 × 10³ mg/m²/hr/(g‐MEK) for those cases which used solvents and plasticizer, and from 5.6×10³ to 58.1×10³ mg/m²/hr/(g‐MEK) when PVC powder was added. Additionally, the MEK emission rates increased with an increase in temperature, humidity, and ventilation rate. The mass transfer coefficients of MEK determined from the VOC emission model were approximately 0.00246 m/sec for those cases which used solvents and plasticizer, and decreased by a factor of 0.67 to 0.00164 m/sec for those cases which used solvents, plasticizer and PVC powder.     

Asymmetrically Encapsulated Vertical ITO/MoS2/Cu2O Photodetector with Ultrahigh Sensitivity

Strong light absorption, coupled with moderate carrier transport properties, makes 2D layered transition metal dichalcogenide semiconductors promising candidates for low intensity photodetection applications. However, the performance of these devices is severely bottlenecked by slow response with persistent photocurrent due to long lived charge trapping, and nonreliable characteristics due to undesirable ambience and substrate effects. Here ultrahigh specific detectivity (D*) of 3.2 × 10¹⁴ Jones and responsivity (R) of 5.77 × 10⁴ A W^?1 are demonstrated at an optical power density (P_op) of 0.26 W m^?2 and external bias (V_ext) of ?0.5 V in an indium tin oxide/MoS₂/copper oxide/Au vertical multi‐heterojunction photodetector exhibiting small carrier transit time. The active MoS₂ layer being encapsulated by carrier collection layers allows us to achieve repeatable characteristics over large number of cycles with negligible trap assisted persistent photocurrent. A large D* > 10¹⁴ Jones at zero external bias is also achieved due to the built‐in field of the asymmetric photodetector. Benchmarking the performance against existing reports in literature shows a viable pathway for achieving reliable and highly sensitive photodetectors for ultralow intensity photodetection applications.     

La0.9Sr0.1Ga0.8M0.2O3-δ (M = Mn, Co, Ni, Cu or Zn): Transition metal-substituted derivatives of lanthanum-strontium-galliummagnesium (LSGM) perovskite oxide ion conductor

Perovskite oxides of the general formula, La_0.9Sr_0.1Ga_0.8M_0.2O_3-δ for M = Mn, Co, Ni, Cu and Zn, have been prepared and investigated. All the oxides exhibit high electrical conductivities (σ R∼ 10⁻² S/cm at 800°C) comparable to that of the best perovskite oxide ion conductor, La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) (σ ∼ 8 × 10⁻² S/cm at 800°C). While M = Mn, Co, Ni, Cu members appear to be mixed conductors with a variable electronic contribution to the conductivity, especially at high oxygen partial pressures (pO₂ ≥1 atm), arising from mixed-valency of the transition metals, the M = Zn(II) phase is a pure oxide ion conductor exhibiting a conductivity (σ ∼ 1.5 × 10⁻² S/cm at 800°C) that is slightly lower than that of LSGM. The lower conductivity of the M = Zn(II) derivative could be due to the preference of Zn(II) for a tetrahedral oxygen coordination.