Influence of ion current on plasma electron temperature and density determined by probe methods

It is established that the electron temperature (T _e) of plasma as determined from the slope of the current-voltage (I-U) characteristic or from the second derivative of the probe current (Druyvesteyn method) is overstated. By taking into account the ion current contribution, it is possible to refine the T _e value determined from the slope of the I-U curve. Analysis confirms that the concentration of ions determined from I-U curves for a collisional regime in the near-probe space-charge region is also overstated.     

Effect of electron irradiation attenuated by aluminum screens on the electrical parameters of p-n silicon structures

We have studied the influence of irradiation by 6-MeV electrons via flat aluminum screens with thicknesses d = 2−14 mm (mass thicknesses, 0.5–3.8 g/cm²) on the properties of p ⁺-n-n ⁺ silicon structures, including the nonequilibrium charge carrier lifetime (τ), reverse current (I _R), and forward current-voltage (I-U) characteristics. In the case of a screen with d = 14 mm (3.8 g/cm²), the irradiated structures exhibit significantly smaller changes in I _R values and I-U curves compared to those for d = 2–12 mm, whereas a decrease in τ (from 20 to 1.5 μs) is the same.     

Acoustic wave corrected current-voltage characteristics of GaAs-based structures with Schottky contacts

The effect of ultrasonic treatment (UST) on the current-voltage (I-U) characteristics of Au-TiB_x-n-n ⁺-GaAs diode structures has been studied. Upon acoustic loading with an intensity below 2 W/cm², the character of the UST-induced changes in the reverse branches of I-U curves depends on the predominating mechanism of current transfer. UST at a power density above 2.5 W/cm² increases the reverse current by one or two orders of magnitude. It is shown that UST favors a significant increase in the homogeneity of the characteristics of devices manufactured using integral heat sink technology.     

Ultrafast thin film GaAs photoconductive detectors

The technique of reactive d.c. plasmatron sputtering with elemental targets is characterized by strong interactions of the reactive gas with the target surface and with the condensing target material. These interactions have a marked influence on the current-voltage (I-U) behaviour of the gas discharge which can be used to control the film deposition process in both the single-target mode and in cosputtering. Model calculations of I-U characteristics are carried out for single and multiple targets of silicon and titanium. On the basis of the formula derived it is possible to predict the influence of the process parameters (pressure, deposition rate, target area etc.) on the I-U curves as well as the interactions of various targets. The calculations agree qualitatively with the measured I-U characteristics. Experiments were carried out with silicon and titanium targets in Ar-O₂ mixtures.     

Controlling the Josephson contact parameters in a semiconductor-superconductor eutectic composition

The current-voltage (I–U) curve was studied for the Josephson contact in a GaSb-V₂Ga₅ eutectic composition comprising parallel whiskers of a superconducting V₂Ga₅ phase formed by oriented crystallization in a semiconducting GaSb matrix. It is established that the parameters of the I-U curve can be controlled by varying the angle between the direction of electric current and the axis of whisker orientation. Using the Josephson relation hω=2eV and considering the parallel connection of infinite Josephson clusters in the structure studied, a formula is derived, n ₀ Nhω=2eV, which can be used for estimating the electromagnetic radiation frequency ω of the Josephson weak links, the number N of infinite Josephson clusters, and the number n0N of Josephson weak links in the semiconductor-superconductor eutectic compositions obtained by means of oriented crystallization.     

Current-voltage characteristics of thin-film gas sensor structures based on tin dioxide

The experimental current-voltage (I–U) curves of thin-film structures based on tin dioxide (SnO₂) exhibit nonlinearity in the range of strong applied electric fields. The results of I-U measurements are interpreted within the framework of a model that assumes the drift of adsorbed ions over the film surface. The observed phenomenon can be used both for detecting the impurities in air and for recognizing the types of adsorbed species.     

Photosensitive silicon bipolar negative-differential-resistance device with controlled <Emphasis Type="Italic">I-U</Emphasis> characteristic

A photosensitive negative-differential-resistance (NDR) device has been developed based on two low-power bipolar silicon transistors on a common substrate, with the emitter junction of one transistor shunted by the conducting channel of the other transistor. As the intensity of IR radiation incident on the shunting transistor increases, the peak current in the N-shaped I-U characteristic decreases until it vanishes completely. An increase in the intensity of IR radiation incident on the shunted transistor leads to a significant increase in the peak current.     

Endohedral metallo [80] fullerene interactions with small polar molecules

The interaction of M@C₈₀ (M = Li, K and Na) with small polar molecules (H₂O, CH₃OH, HF and NH₃) is described by density functional theory (DFT) calculations. Our theoretical studies show that in several computed cases the binding energies of M@C₈₀ complexes with small polar molecules increases upon encapsulation. The observed behavior can be accounted for by charge transfer effects between the encapsulated metal and the surface of the C₈₀ cage. These assertions have been solidified by a corresponding analysis of the thermochemistry, vibrational frequencies and HOMO molecular orbital plots of the optimized species.     

<Emphasis Type="Italic">N-S</Emphasis> transition in nonisothermal characteristics of silicon diodes and thyristors

The results of numerical modeling of the stationary nonisothermal current-voltage (I-U) characteristics of forward-biased high-voltage diodes and thyristors in the interval of current densities J ～ 200–500 A/cm² revealed an N-S transition in the shape of these curves and a hysteresis in the constant current source regimes. It is established that the mechanism of these phenomena is related to a temperature-induced decrease in the coefficient of ambipolar diffusion under the conditions of enhanced recombination. Devices with such I-U characteristics can be irreversibly switched by short current pulses from stable states on the working branch to the states with high heat evolution, which leads to a risk of thermal breakdown.     

Specific heat at the spin-peierls transition in CuGeO3 under magnetic fields up to 22 tesla

We report on heat capacity measurements of the spin-Peierls compound CuGeO₃ under magnetic fields between 0 and 22 teslas. We have determined the magnetic phase diagram between the three different phases (U=uniform,I=incommensurate,D=dimerised) of this system, unknown up to now forH>14 T, and which can be well interpreted within the Hartree-Fock approximation. We have studied the 2nd order phase transition forH=const. at the crossing ofD-U andI-U phases. The spin-Peierls transition gives rise to a well pronounced specific heat jump. The phase diagram and the specific heat results are discussed in the framework of a B.C.S.-like theoretical model.     

2.28 Current noise in W2O5−x films due to surface adsorption of water

Films of W₂O_5?x, obtained by vacuum evaporation of W₂O₅ on a heated insulating substrate, are electrically conducting, transparent to visible light, and have a conductivity which can be reversibly changed by single heating in an oxygen atmosphere or in vacuum. An interesting feature of these films represented by the rather low current noise, is strongly enhanced when exposed to vapours of polar molecules, like H₂O, in a suitable range of temperatures, the excess noise being generated by the dynamical adsorption-desorption processes of the vapour.The power spectrum of the excess noise can be measured and used to get information about this process.     

Electric-field-controlled memory effect in heterostructures for gas sensors

A capacitive gas sensor has been created on the basis of an n-SnO₂/SiO₂/p-Si heterostructure with two successive oxide layers. The presence of polar C₂H₅OH, NH₃, and H₂O gas molecules in air leads to a significant increase in the capacitance of the structure at room temperature. An important feature of the adsorption process is a memory effect, which is confined to the possibility of maintaining the capacitance value after removal of the active component from the gas mixture. The possibility of quenching the accumulated useful signal by electric-field pulses has been realized for the first time as applied to gas sensors. Pis’ma Zh. Tekh. Fiz. 25, 22–29 (June 26, 1999)     

The relaxor enigma — charge disorder and random fields in ferroelectrics

Substitutional charge disorder giving rise to quenched electric random-fields (RF s) is probably at the origin of the peculiar behavior of relaxor ferroelectrics, which are primarily characterized by their strong frequency dispersion of the dielectric response and by an apparent lack of macroscopic symmetry breaking at the phase transition. Spatial fluctuations of the RF s correlate the dipolar fluctuations and give rise to polar nanoregions in the paraelectric regime as has been evidenced by piezoresponse force microscopy (PFM) at the nanoscale. The dimension of the order parameter decides upon whether the ferroelectric phase transition is destroyed (e.g. in cubic PbMg_1/3Nb_2/3O₃, PMN) or modified towards RF Ising model behavior (e.g. in tetragonal Sr_{1− x} Ba _x Nb₂O_6, SBN, x ≈ 0.4). Frustrated interaction between the polar nanoregions in cubic relaxors gives rise to cluster glass states as evidenced by strong pressure dependence, typical dipolar slowing-down and theoretically treated within a spherical random bond-RF model. On the other hand, freezing into a domain state takes place in uniaxial relaxors. While at T _c non-classical critical behavior with critical exponents γ ≈ 1.8, β ≈ 0.1 and α ≈ 0 is encountered in accordance with the RF Ising model, below T _c ≈ 350 K RF pinning of the walls of frozen-in nanodomains gives rise to non-Debye dielectric response. It is relaxation- and creep-like at radio and very low frequencies, respectively.     

Semiconductive Single Molecular Bilayers Realized Using Geometrical Frustration

A unique solution‐based technology to manufacture self‐assembled ultrathin organic‐semiconductor layers with ultrauniform single‐molecular‐bilayer thickness over an area as large as wafer scale is developed. A novel concept is adopted in this technique, based upon the idea of geometrical frustration, which can effectively suppress the interlayer stacking (or multilayer crystallization) while maintaining the assembly of the intralayer, which originates from the strong intermolecular interactions between π‐conjugated molecules. For this purpose, a mixed solution of extended π‐conjugated frameworks substituted asymmetrically by alkyl chains of variable lengths (i.e., (πCore)‐C_n's) is utilized for the solution process. A simple blade‐coating with a solution containing two (πCore)‐C_n's with different alkyl chain lengths is effective to provide single molecular bilayers (SMBs) composed of a pair of polar monomolecular layers, which is analogical to the cell membranes of living organisms. It is demonstrated that the chain‐length disorder does not perturb the in‐plane crystalline order, but acts effectively as a geometrical frustration to inhibit multilayer crystallization. The uniformity, stability, and size scale are unprecedented, as produced by other conventional self‐assembly processes. The obtained SMBs also exhibit efficient 2D carrier transport as organic thin‐film transistors. This finding should open a new route to SMB‐based ultrathin superflexible electronics.     

Switchable Polar Nanotexture in Nanolaminates HfO2-ZrO2 for Ultrafast Logic-in-Memory Operations

Nontrivial topological polar textures in ferroelectric materials, including vortices, skyrmions, and others, have the potential to develop ultrafast, high-density, reliable multilevel memory storage and conceptually innovative processing units, even beyond the limit of binary storage of 180° aligned polar materials. However, the realization of switchable polar textures at room temperature in ferroelectric materials integrated directly into silicon using a straightforward large area fabrication technique and effectively utilizing it to design multilevel programable memory and processing units has not yet been demonstrated. Here, utilizing vector piezoresponse force and conductive atomic force microscopy, microscopic evidence of the electric field switchable polar nanotexture is provided at room temperature in HfO₂-ZrO₂ nanolaminates grown directly onto silicon using an atomic layer deposition technique. Additionally, a two-terminal Au/nanolaminates/Si ferroelectric tunnel junction is designed, which shows ultrafast (≈83 ns) nonvolatile multilevel current switching with high on/off ratio (>10⁶), long-term durability (>4000 s), and giant tunnel electroresistance (10⁸%). Furthermore, 14 Boolean logic operations are tested utilizing a single device as a proof-of-concept for reconfigurable logic-in-memory processing. The results offer a potential approach to “processing with polar textures” and addressing the challenges of developing high-performance multilevel in-memory processing technology by virtue of its fundamentally distinct mechanism of operation.     

The virial coefficients of five binary mixtures of fluorinated methanes and ethanes

We have made new measurements of the gas-phasePVT surface of five binary mixtures of hydrofluorocarbons (HFCs) in a Burnett/isochoric apparatus. The components chosen all have moderate to large reduced dipole moments. We presentPVT data, derived mixture virial coefficients, cross second virial coefficients, and binary interaction parameters for these systems, and we compare the results with a recently published model for calculating second and third viral coefficients of polar gases and their mixtures. That model accounts for the polar nature of the molecules with a term containing the reduced dipole moment, _R, and it contains mixing rules for the substance-specific parameters needed to calculate the second and third cross virial coefficients. The model and data are in satisfactory agreement. and the model can be used to greatly extend the useful range of the limited set of data.     

Studies on the relaxor behavior of sol-gel derived Ba(Zr x Ti1− x )O3 (0.30≤x≤0.70) thin films

We have studied the relaxor behavior of sol-gel derived Ba(Zr _x Ti_{1− x} )O₃ (0.30≤ x≤0.70) thin films. The plausible mechanism of the relaxor behavior has been analyzed from the dielectric data and micro-Raman spectra. Substitution of Zr⁺⁴ for Ti⁺⁴ in BaTiO₃ lattice reduces its long-range polarization order yielding a diffused paraelectric to ferroelectric phase transition. The solid solution system is visualized as a mixture of Ti⁺⁴ rich polar region and Zr⁺⁴ rich regions and with the increase in Zr contents the volume fraction of the polar regions are progressively reduced. At about 25.0 at% Zr contents the polar regions exhibit typical relaxor behavior. The degree of relaxation increases with Zr content and maximizes at 40.0 at% Zr doped film. The frequency dependence of the polar regions follows Vogel-Fulcher relation with a characteristic cooperative freezing at freezing temperature (T _f). Below T_f, a long range polarization ordering was ascertained from the polarization hysteresis measurement.     

Protonic conduction in Al2(SO4)3·16H2O: coulometry,transient ionic current,infrared and electrical conductivity studies

Proton transport in Al₂(SO₄)₃·16H₂O has been established using different techniques namely coulometry, transient ionic current, i.r., DTA/TGA and electrical conductivity. The possible charge carriers are H⁺ and OH⁻ generated as a result of possible electrolysis of hydrate water molecules. The mobilities of the two charge carriers are approximately 4×10⁻⁵ and 2.4×10⁻⁵cm²V⁻¹s⁻¹. The electrical conductivity shows strong dependence upon humidity and also shows a against 1/T behaviour closely related with its thermal dehydration reaction.     

Studies of the Vortex Related Phase Transition in YBCO Thin Films with Strong In-Plane Anisotropy

We have studied the vortex-related phase transition in a number of YBCO thin films that have in-plane anisotropy due to the c-axis lying at an angle to the substrate normal. The critical parameters T _t , z, and have been extracted from the scaling of dc I-V measurements made along the two principal transport directions in magnetic fields up to 1 tesla. The dependence of T _t upon the direction of the transport current in some classes of film and the very high z values cast doubt upon the established interpretation based simply upon a vortex liquid–vortex glass phase transition.     

Effect of bronze on the compression of Nb3Sn in multifilamentary conductors

Nb₃Sn in multifilamentary conductors is subject to compressive strain as a result of the relatively small thermal contraction of the filaments as compared to bronze. The critical current l_c is consequently degraded. The critical current increases, when an external tensile stress is applied, and passes through a maximum. The ratio of the maximum critical current to the initial critical current increases with the flux density and reaches a value of two at a flux density of 16 T for technical conductors. The strain _m, at which the l_c maximum is reached, lies between 0.4% and 0.7% for the conductors investigated and depends on the material parameters. For a constant ratio of bronze to filament cross section this strain _m is reduced as the Nb₃Sn layer thickness is increased and can be determined approximately by a graphical method from the stress-strain diagram. _m is to a large extent dependent on the metallurgical properties of bronze, which vary to a considerable extent depending upon the heat treatment.