Au–Sapphire (0001) solid–solid interfacial energy

This work presents an experimental methodology for the measurement of interfacial energy (γ_SP) and work of adhesion (W _ad) of a metal–ceramic interface. A thin Au film was dewetted on the basal surface of sapphire substrates to form submicron-sized particles, which were analyzed using the Winterbottom method to determine the equilibrated particle–substrate solid–solid interfacial energy. Electron microscopy showed that a large portion of the particles contained grain boundaries, while all of the single crystalline particles had three distinct morphologies and orientations with the substrate. Two orientation relationships were determined from transmission electron microscopy, for which the interfacial energy in air at 1000 °C was determined: Au (111)–sapphire (0001): γ_SP = 2.15 ± 0.04 J/m², W _ad = 0.49 ± 0.04 J/m²; Au (100)–sapphire (0001): 2.18 ± 0.06 J/m², W _ad = 0.55 ± 0.07 J/m².     

The electrical resistivity of liquid carbon under rapid heating of dense isotropic graphite in different media

Experiments are considered which involve pulsed heating of graphite (in several microseconds) and registering of electrical resistance of liquid carbon. Samples of MF-307 dense (2 g/cm³) isotropic graphite with a cross section of ∼0.3 × 0.3 mm and 10–15 mm long are heated in water or in thick-walled (outside diameter D ∼ 10 mm, inside diameter d ∼ 0.5 mm) sapphire capillary tubes. It is confirmed that the heating in water at atmospheric pressure does not enable one to obtain and investigate liquid carbon: at best, only the beginning of the liquid state region is attained. The heating in sapphire tubes causes the emergence of pulsed pressure (up to ten kilobars) after expanding graphite comes against the tube wall. This growing pressure (within several microseconds) enables one to investigate the liquid state of carbon in a confined volume. The isochoric heating provided the possibility of measuring the electrical resistivity of liquid carbon at high specific energies (up to ∼32 kJ/g) and high pressures; such measurements are quite expensive in the case of stationary investigations.     

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.     

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.     

Characteristics of surface states at the insulator-semiconductor interface of ZnS:Mn thin-film electroluminescent emitters

The energy distribution of the density of occupied surface states (N _ss) at the cathode insulatorphosphor interface in ZnS:Mn electroluminescent thin-film (ELTF) emitters has been modeled on the basis of experimental data. Changes in this distribution depending on the parameters of exciting voltage pulses have been studied. It is established that the energy distribution of N _ss shifts toward deeper levels upon a decrease in the frequency of the exciting signal and the resulting increase in the pause between the adjacent switch-on states. This behavior corresponds to a cascade relaxation mechanism of electrons trapped on the surface states. Maximum values of the N _ss (∼2.5 × 10¹³ cm⁻²) and the specific density of surface states per unit energy (2 × 10¹⁴–10¹⁵ cm⁻² eV⁻¹) are determined for the cathode insulator-phosphor interface from which electrons are tunneling. Positions of the equilibrium (∼1.25 eV below the conduction-band bottom) and the quasi-equilibrium (0.6–1.25 eV) Fermi levels during the ELTF emitter operation are estimated.     

Mean Field Superconductivity Approach in Two Dimensions

Within the BCS theory of superconductivity we calculate the superconducting gap at a zero-temperature for metallic hydrogen–graphene system in order to estimate the superconducting critical temperature of quasi-two-dimensional highly oriented pyrolytic graphite. The obtained results are given as a function of the hydrogen-induced density of carriers n and their effective mass m ^⋆ . The obtained gap shows a Maxwell-like distribution with a maximum of ∼60 K at n∼3×10¹⁴ cm⁻² and m ^⋆ /m=1. The theoretical results are discussed taking into account recent experimental evidence for granular superconductivity in graphite.      

Magnetic Anisotropy and Magneto-Transport Properties of Co–Ni–N Granular Alloys Thin Films

The effect of nitrogen addition on the morphology, magnetic anisotropy, and magnetoresistance properties of Co–Ni–N granular thin films were investigated. The films were grown by electrodeposition onto aluminum substrates at room temperature. By a complex process of cationic catalysis occurring at the cathode/electrolyte interface, nitrogen is adsorbed in the Co–Ni film. Finally, a granular film grows by a tridimensional progressive nucleation mechanism. The nature of the grains and of the interface between them influences exchange interactions between grains, which play an important role in determining the magnetic anisotropy. From the magnetic measurements, we found that the magnetic anisotropy constant varied in the range K _eff=(−21.5÷36.6)×10⁴ J⋅m⁻³ and the coercivity varied between H _c=(13÷67) kA⋅m⁻¹ depending on the sodium nitrate content in the plating bath. The Co–Ni–N granular thin films display large values (∼160%) of magnetoresistance. These large values of magnetoresistance make such structures attractive for applications as sensitive magnetic field sensors.     

Creep behavior of AZ31 magnesium alloy in low temperature range between 423 K and 473 K

The deformation behavior of coarse-grained AZ31 magnesium alloy was examined in creep at low temperatures below 0.5 T _m and low strain rates below 5 × 10⁻⁴ s⁻¹. The creep test was conducted in the temperature range between 423 and 473 K (0.46–0.51 T _m) under various constant stresses covering the strain rate range 5 × 10⁻⁸ s⁻¹–5 × 10⁻⁴ s⁻¹. All of the creep curves exhibited two types depending on stress level. At low stress (σ/G < 4 × 10³), the creep curve was typical of class I behavior. However, at high stresses (σ/G > 4 × 10³), the creep curve was typical of class II. At the low stress level, deformation could be well described by solute drag creep whereas at the high stress level, deformation could be well described by dislocation climb creep associated with pipe diffusion or lattice diffusion. The transition of deformation mechanism from solute drag creep to dislocation climb creep, on the other hand, could be explained in terms of solute-atmosphere-breakaway concept.     

Acoustic emission in dislocation-containing silicon exposed to current and thermal influences

An investigation was made of acoustic emission in silicon single crystals during passage of an electric current. It was observed that in the temperature range studied (T=300−450K) acoustic emission signals whose intensity increases with increasing dislocation density are excited in a static electric field. The acoustic emission of silicon single crystals with and without dislocations is compared. It is assumed that the acoustic emission in silicon is caused by the unpinning and migration of dislocations under the influence of the direct electric current and thermoelastic stresses. The activation energy of this process is estimated as E=0.53±0.05 eV during passage of a direct current of density j=2.8×10⁵ A/m². Pis’ma Zh. Tekh. Fiz. 25, 28–32 (February 12, 1999)     

Diffusion of promethium in silicon

The first investigations have been made on the diffusion of promethium in silicon. In the temperature range from 1100 to 1250 °C the diffusion constant of promethium increases from ∼1×10⁻¹³ cm²/s to ∼1.5×10⁻¹² cm²/s. The temperature dependence of the diffusion coefficient can be described by D = 5 x 10⁻¹ exp[-(3.3 eV/kT]cm²/s. Pis’ma Zh. Tekh. Fiz. 23, 46–50 (January 26, 1997)     

Method for microwave radiation enhancement using elongated nanotubes dispersed in a gaseous medium

A new method is proposed to enhance microwave radiation with a wavelength of λ ∼ 1 cm in an active medium comprising elongated conducting nanotubes dispersed in air, which is energy pumped by a nonstationary electric field. For a volume fraction of nanoparticles c ₀ ≈ 10⁻³ in air at atmospheric pressure, the necessary value of the nonstationary pumping electric field (generated by a high-power nanosecond pulsed voltage source) is estimated at ∼ 200 J/m³ and the weak signal gain is estimated at Γ₀ = 0.055 m⁻¹. One possible mechanism of microwave radiation enhancement in a spatial resonator is considered.     

Microwave radiation enhancement and self-focusing using quasi-stationary electric field in a medium with elongated nanoparticles

It is shown that a mechanism of microwave radiation enhancement and self-focusing can be operative in a wave channel and spatial cavity filled with air containing elongated (dumbbell-shaped) nanoparticles at a volume fraction of c ₀ ∼ 10⁻³. This nonlinear medium can be pumped using a quasi-stationary electric field. At an oscillation frequency of Ω ∼ 10¹⁰−10¹¹s⁻¹, the radiation enhancement and self-focusing in a wave channel is possible over a length of Δz ∼ 50−200 m, while that in a spatial cavity can take place within a period of time Δt ∼ (2−7) × 10⁻⁷ s.     

Measurements of thermophysical properties of molten silicon by a high-temperature electrostatic levitator

Several thermophysical properties of molten silicon measured by the high-temperature electrostatic levitator at JPL are presented. They are density, constant-pressure specific heat capacity, hemispherical total emissivity, and surface tension. Over the temperature range investigated (1350<T _m<1825 K), the measured liquid density (in g·cm⁻³) can be expressed by a quadratic function,p(T)=p _m−1.69×10⁻⁴(T−T _m)−1.75×10⁻⁷(T−T _m)² withT _m andp _m being 1687 K and 2.56 g·cm⁻³, respectively. The hemispherical total emissivity of molten silicon at the melting temperature was determined to be 0.18, and the constant-pressure specific heat was evaluated as a function of temperature. The surface tension (in 10⁻³ N·m⁻¹) of molten silicon over a similar temperature range can be expressed by σ(T)=875–0.22(T−T _m). Invited paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

Parabolic Flights @ Home

We developed an unmanned air vehicle (UAV) suitable for small parabolic-flight experiments. The flight speed of 100 m s^− 1 is sufficient for zero-gravity parabolas of 16 s duration. The flight path’s length of slightly more than 1 km and 400 m difference in altitude is suitable for ground controlled or supervised flights. Since this fits within the limits set for model aircraft, no additional clearance is required for operation. Our UAV provides a cost-effective platform readily available for low-g experiments, which can be performed locally without major preparation. A payload with a size of up to 0.9 ×0.3 ×0.3 m³ and a mass of ∼5 kg can be exposed to 0 g ₀–5 g ₀, with g ₀ being the gravitational acceleration of the Earth. Flight-duration depends on the desired acceleration level, e.g. 17 s at 0.17 g ₀ (lunar surface level) or 21 s at 0.38 g ₀ (Martian surface level). The aircraft has a mass of 25 kg (including payload) and a wingspan of 2 m. It is powered by a jet engine with an exhaust speed of 450 m s^− 1 providing a thrust of 180 N. The parabolic-flight curves are automated by exploiting the advantages of sophisticated micro-electronics to minimize acceleration errors.     

High thermal conductivity composites consisting of diamond filler with tungsten coating and copper (silver) matrix

Tungsten coatings with thickness of 5–500 nm are applied onto plane-faced synthetic diamonds with particle sizes of about 430 and 180 μm. The composition and structure of the coatings are investigated using scanning electron microscopy, X-ray spectral analysis, X-ray diffraction, and atomic force microscopy. The composition of the coatings varies within the range W–W₂C–WC. The average roughness, R _a, of the coatings’ surfaces (20–100 nm) increases with the weight–average thickness of the coating. Composites with a thermal conductivity (TC) as high as 900 W m⁻¹ K⁻¹ are obtained by spontaneous infiltration, without the aid of pressure, using the coated diamond grains as a filler, and copper or silver as a binder. The optimal coating thickness for producing a composite with maximal TC is 100–250 nm. For this thickness the heat conductance of coatings as a filler/matrix interface is calculated as G = (2–10) × 10⁷ W m⁻² K⁻¹. The effects of coating composition, thickness and roughness, as well as of impurities, on wettability during the metal impregnation process and on the TC of the composites are considered.     

Electrical studies on sputtered CuCl thin films

CuCl is a wide-direct band gap semiconductor, lattice matched to Si and it possesses excellent ultra violet (UV) emission properties. It is thus a promising candidate for the next generation Si based UV optoelectronics. CuCl films were deposited using RF magnetron sputtering technique. X-ray diffraction analysis reveals that the grains are strongly <111> oriented. Triangular crystallites of CuCl were observed in the AFM surface topograph. Au–CuCl–Si–Au structures were fabricated and field dependent electrical studies were carried out in the electric field range of 1.25 × 10⁶ to 2.5 × 10⁷ V/m. I–V characteristics show that ohmic conduction prevails in low electric fields up to 2.5 × 10⁶ V/m. In the higher field range, from 2.5 × 10⁶ to 2.5 × 10⁷ V/m, the conduction mechanism was Schottky emission controlled. There was no trap related charge transport observed at higher electric fields. Preliminary electrical studies are reported in this article.     

Experimental determination of solid–liquid interfacial energy for succinonitrile solid solution in equilibrium with the succinonitrile–(D) camphor eutectic liquid

The equilibrated grain boundary groove shapes for Succinonitrile (SCN) solid solution in equilibrium with the Succinonitrile (SCN)–D Camphor (DC) eutectic liquid were directly observed. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient and solid–liquid interface energy for SCN solid solution in equilibrium with the SCN–DC eutectic liquid has been determined to be (5.39 ± 0.27) × 10⁻⁸ K m and (7.88 ± 0.79) × 10⁻³ J m⁻² with present numerical method and Gibbs–Thomson equation, respectively. The grain boundary energy of SCN rich phase of the SCN–DC eutectic system has been determined to be (14.95 ± 1.79) × 10⁻³ J m⁻² from the observed grain boundary groove shapes. Thermal conductivity ratio of the liquid phase to the solid phase for SCN–0.16 mole % DC alloy has also been measured.     

Size quantization effects in optical and electrical properties of II–VI semiconductor films in nanocrystalline form

The electrical properties of CdTe and optical properties of ZnS in nanocrystalline thin film form are studied with a view to have a clearer understanding of the optical processes and the carrier transport mechanisms in nanocrystalline II–VI semiconductors, in general. Nanocrystalline ZnS and CdTe films were deposited by magnetron sputtering of respective targets in argon plasma. The optical absorption data of nanocrystalline ZnS films (thickness 10–40 nm) could be explained by the combined effects of phonon and inhomogeneity broadening along with optical loss due to light scattering at the nanocrystallites. The conductivity of CdTe (grain size within 4–4·7 nm) showed (T ₀/T) ^p dependence withp ∼ 0·5 indicating the presence of a Coulomb gap near the Fermi level. The width of the Coulomb gap varied within 0·02–0·04 eV depending on the deposition condition. The existing theoretical models were used for estimating hopping energy (0·02–0·04 eV) and hopping distance (2·8–5·1 nm) in nano CdTe films.     

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.     

Density and Thermal Conductivity Measurements for Silicon Melt by Electromagnetic Levitation under a Static Magnetic Field

The density and thermal conductivity of a high-purity silicon melt were measured over a wide temperature range including the undercooled regime by non-contact techniques accompanied with electromagnetic levitation (EML) under a homogeneous and static magnetic field. The maximum undercooling of 320 K for silicon was controlled by the residual impurity in the specimen, not by the melt motion or by contamination of the material. The temperature dependence of the measured density showed a linear relation for temperature as: ρ(T) = 2.51 × 10³−0.271(T−T _m) kg · m⁻³ for 1367 K < T < 1767 K, where T _m is the melting point of silicon. A periodic heating method with a CO₂ laser was adopted for the thermal conductivity measurement of the silicon melt. The measured thermal conductivity of the melt agreed roughly with values estimated by a Wiedemann–Franz law.