On a current mechanism in Ta2O5 thin films

Electrical conduction in the temperature range of 120–370 K has been studied in sandwiched structures of Al/Ta₂O₅/Si. The tantalum oxide films were prepared by evaporation of tantalum on a p-Si crystal substrate, followed by oxidation at a temperature of 600°C. The temperature-dependent current-voltage (I–V) characteristics are explained on the basis of a phonon-assisted tunnelling model. The same explanation is given for I–V data measured on Ta₂O₅ films by other investigators. From the comparison of experimental data with theory the density of states in the interface layer is derived and the electron-phonon interaction constant is assessed.      

Analysis and modification of nonhyperbolic kinetic models

A nonhyperbolic model of Rabin (Biochem J 1967, 102, 22C–23C) in which four conformational states are considered has been simplified to the three‐state one. Only multistate models (if the concentration of enzyme or receptor is assumed to be low) can yield nonhyperbolic kinetics. The simplified model has been shown to retain all the essential properties of the original four‐state model. The model yields a diversity of nonhyperbolic dose–response curves both with higher and lower steepness than that of Henri‐type ones. The three‐state model can be further reduced to the hyperbolic one by making identical the different (unliganded) states. The bistate model in which protein concentration is assumed to be high yields nonhyperbolic kinetics as well; the model is reduced to the hyperbolic one if the protein concentration is assumed to be low. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 253–258, 2008     

Phonon-assisted tunneling in Schottky barriers

Experimental current-voltage characteristics and their temperature dependencies for AlGaAs Schottky barrier structures are shown to be in agreement with the recent theory of phonon-assisted tunneling.     

The explosive divergence in iterative maps of matrices

The effect of explosive divergence in generalized iterative maps of matrices is defined and described using formal algebraic techniques. It is shown that the effect of explosive divergence can be observed in an iterative map of square matrices of order 2 if and only if the matrix of initial conditions is a nilpotent matrix and the Lyapunov exponent of the corresponding scalar iterative map is greater than zero. Computational experiments with the logistic map and the circle map are used to illustrate the effect of explosive divergence occurring in iterative maps of matrices.     

Control of light polarization by acousto-optic diffraction from leaky acoustic wave in LiNbO₃

The acousto-optic control of light polarization due to diffraction by leaky acoustic waves in ZX-LiNbO? has been demonstrated. The randomly polarized light of 633 nm wavelength is converted by the anisotropic diffraction into two beams with mutually orthogonal polarizations, the relative intensities of which depend on the light incidence angle and acoustic frequency. Variation in acoustic frequency from 108 to 112 MHz rotates the polarization of the output optical beam by 90°. The acousto-optic control is accomplished entirely by electronic means and can be applied for implementation of fast polarization converters.     

Influence of Ar/C2H2 ratio on the structure of hydrogenated carbon films

The amorphous hydrogenated carbon films (a-C:H) were obtained on Si (1 1 1) wafers by plasma jet chemical vapor deposition (PJCVD). a-C:H coatings have been prepared at 1000 Pa in argon/acetylene mixture. The Ar/C₂H₂ gas volume ratio varied from 1:1 to 8:1. It was demonstrated that by varying the Ar/C₂H₂ ratio the composition, growth rate of the coatings, and consequently the structure of the film, can be controlled. The growth rate and surface porosity of coatings deposited at Ar/C₂H₂ = 8:1 ratio decrease slightly with an increase in the distance between the plasma torch nozzle and substrate from 0.04 to 0.095 m. The transmittance of the coatings in the IR region of 2.5–25 μm slightly increases, while the absorption peaks at 2850–2960 cm^?1 related with sp³ CH_2–3 modes remain unchanged with an increase in the distance. The Raman spectroscopy indicated that the a-C:H coating formed at the Ar/C₂H₂ = 8:1 and 0.06 m has the highest sp³ C–C fraction. The proposed PJCVD technique allows to achieve the growth rates up to 300 nm/s.     

Acousto-optic interaction with leaky surface acoustic waves in Y-cut LiTaO3 crystals

The acousto-optic interaction with leaky surface acoustic wave radiation into the bulk of YX-cut LiTaO₃ crystals has been investigated. The light incidence and diffraction angles corresponding to the strongest acousto-optic interaction were calculated and measured as functions of the acoustic wave frequency. The dependencies of the diffracted light intensity on the amplitude of radio-frequency voltage applied to the interdigital transducer (IDT) were studied. Our acousto-optic measurements revealed generation, by the IDTs, of slow shear bulk acoustic waves propagating at different angles depending on their frequency. A secondary acousto-optic interaction from the bulk waves radiated by the receiving IDT has been studied.     

Temperature-dependent attenuation of surface acoustic waves in proton-exchanged 128°-rotated Y-cut LiNbO3

3 has been experimentally studied in the frequency range 100 to 460 MHz and in the temperature range 90 to 300 K. At room temperature, the proton exchange leads to the considerable enhancement of acoustic attenuation as compared to the pure samples. Annealing in air, in general, reduces the attenuation. However, an anomalous enhancement of the attenuation at several frequencies for particular conditions of annealing is observed. When the temperature is reduced, the attenuation decreases practically to zero in as-exchanged samples. In the annealed ones, the attenuation attains a minimum in the vicinity of 160 K, and begins to grow at lower temperatures. A sharp peak in the attenuation is observed at 210 K. Several different physical mechanisms including acousto-protonic interaction and structural phase transition seem to be responsible for the observed acoustic attenuation behaviour. Received: 17 July 1996/Accepted: 2 December 1996     

Modification of the amorphous carbon films by the ns-laser irradiation

The effect of a nanosecond laser irradiation of thin (60 and 145 nm) amorphous, diamond-like carbon films deposited on Si substrate by an ion beam deposition (IBD) from pure acetylene and acetylene/hydrogen (1:2) gas mixture was analyzed in this work. The films were irradiated with the infrared (IR) and ultraviolet (UV) radiation of the nanosecond Nd:YAG lasers working at the first (1.16 eV) and the third (3.48 eV) harmonics, using a multi-shot regime. The IR laser irradiation stimulated a minor increase in the fraction of sp² bonds, causing a slight decrease in the hardness of the films and initiated SiC formation. Irradiation with the UV laser caused the formation of carbides and increased hydrogenization of the Si substrate and the fraction of sp² sites. Spalliation and ablation were observed at a higher energy density and with a large number of laser pulses per spot.