Effect of gamma irradiation on photoconversion characteristics of metal/gallium arsenide barrier structures with textured interface

The effect of ⁶⁰Co gamma irradiation at doses of 10³-2×10⁵ Gy on the photoconversion and dark I-V characteristics of Au/GaAs surface-barrier solar cells (SCs) is studied. The morphology of the interface microrelief is varied to reach the highest photoconversion efficiency. Of the two types of microrelief morphology (dendritic and quasi-grating) obtained by the chemical anisotropic etching of n-(100)GaAs, the latter is more promising, particularly for SCs designed for space application, since the associated SCs offer higher efficiency and radiation resistance.     

Effect of γ radiation from <Superscript>60</Superscript>Co on the formation of metal contacts to GaAs (Al<Subscript>x</Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>As) structures

The properties of nonrectifying AuGe/GaAs (Al_0.4Ga_0.6As) contacts exposed to heat treatment, ⁶⁰Co γ radiation, and γ radiation combined with the application of an electrical bias are studied. A correlation between the type of interfacial interaction in the contacts and their resistance is found. Results obtained are explained in terms of a diffusion model with a movable boundary of the metal layer.     

Form of the dihedral angle dependence of the spin-spin coupling constant JHNNH

Cyclic hydrazides (derivatives of phtalhydrazide,pyrozolidone-3, indazolone, cyclic hydrazide camphoric acid) are studied by the NMR¹H method. The size of the dihedral HNNH angle of several model compounds (pyrozolidone-3, cyclic hydrazide norcamphoric acid) are calculated by the MINDO/3 SSF MO LCAO method. It is shown that in the hydrazides with HNNH dihedral angle 0–70° the magnitude of the HNNH spin-spin interaction constant does not exceed 1 Hz. The form of its dependence on the dihedral angle is determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 363–366, 1989.     

Comparative characterisation by atomic force microscopy and ellipsometry of soft and solid thin films

Ellipsometry and atomic force microscopy (AFM) were used to study the film thickness and the surface roughness of both ‘soft’ and solid thin films. ‘Soft’ polymer thin films of polystyrene and poly(styrene–ethylene/butylene–styrene) block copolymer were prepared by spin‐coating onto planar silicon wafers. Ellipsometric parameters were fitted by the Cauchy approach using a two‐layer model with planar boundaries between the layers. The smooth surfaces of the prepared polymer films were confirmed by AFM. There is good agreement between AFM and ellipsometry in the 80–130 nm thickness range. Semiconductor surfaces (Si) obtained by anisotropic chemical etching were investigated as an example of a randomly rough surface. To define roughness parameters by ellipsometry, the top rough layers were treated as thin films according to the Bruggeman effective medium approximation (BEMA). Surface roughness values measured by AFM and ellipsometry show the same tendency of increasing roughness with increased etching time, although AFM results depend on the used window size. The combined use of both methods appears to offer the most comprehensive route to quantitative surface roughness characterisation of solid films. Copyright © 2007 John Wiley & Sons, Ltd.     

Local plasmon excitations in one-dimensional array of metal nanowires for sensor applications

Optical properties of a one-dimensional periodic array of subwavelength metal nanowires in the regime of local plasmon excitation are investigated experimentally and theoretically. Both gas and liquid sensing by one-dimensional gold nanowires on a glass substrate produced by holographic lithography are demonstrated experimentally. The obtained spectral sensitivity of a local plasmon sensor to the refractive index of the environment is found comparable to that of a surface plasmon polariton sensor based on the grating coupler effect. The influence of nanowire shape on spectral sensitivity is studied theoretically in a differential formalism framework using a curvilinear coordinate transformation for triangular, trapezoidal, and rectangular cross sections of the nanowires. For nanowires with trapezoidal cross section, theoretical calculations for the spectral sensitivity to variation of the refractive index of the environment agree well with experimental data.     

Characterization of H3PO4/HNO3–NANO2 oxidized bacterial cellulose and its usage as a carrier for the controlled release of cephalexin

Biocompatibility, biodegradation, good sorption characteristics, and unique structure of highly oxidized bacterial cellulose (OBC) are of great interest for the development of new drug delivery systems. In this study, OBC with 9.6, 13.0 and 19.5% carboxyl groups for 5, 20, and 48 h of synthesis, respectively, was successfully obtained using the HNO₃/H₃PO₄–NaNO₂. The results of morphological analysis showed that with an increase in the number of carboxyl groups, OBC fibers become thicker and rougher. Fourier-transform infrared spectroscopy showed the formation of carboxyl groups in the OBC after the oxidation reaction. The crystallinity of the samples according to X-Ray diffraction analysis decreased with increasing reaction time. The immobilization of cephalexin in the polymer matrix was studied in detail, it took 120 min to achieve balance in the solution with a concentration of 1 mg/ml, and the maximum amount of a sorbed antibiotic reached 43 mg/g. The drug release in vitro at 37 °C in PBS with pH 7.4 and 2.0 was prolonged. Various models were used to describe the release mechanism, the best of which was Ritger-Peppas with a diffusion exponent value ranging from 0.743 to 0.830, which explains the drug release mainly through non-Fickian diffusional release. The cephalexin-loaded OBC showed high antimicrobial activity against Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus. The structure and properties of the resulting highly oxidized cellulose make it an excellent candidate as a drug delivery carrier with prolonged antimicrobial drug release characteristics.

     

Relaxation in polycrystalline ferroelectric ceramics upon the simultaneous impact of mechanical stresses and electric field

The motions of domain walls at low stresses are known to result in the relaxation of structural over-stresses and their balancing, while at high stresses we observe overstress increases and microcrack formation, i.e., the changing of resonance frequencies and emerging of spurious resonances of piezoelectric elements [1, 2]. In view of the above, the influence of electromechanical impacts on ceramics of compositions PZT-19 and PZT-35 are investigated in order to estimate the resonance curve changes.     

Optimal observation of multistage systems

The problem of optimal observation of a nonlinear step system is considered. The task is to obtain guaranteed estimates of the initial state from given incomplete and inaccurate measurements of the current states. The cases of fixed and unfixed transition times in a step system are examined. Algorithms for solving a posteriori and positional observation problems are proposed. The results are illustrated by examples.     

Role of the conformations of tetraoxides in the mechanism of the recombination of peroxide radicals

The MINDO/3 method was used to calculate the equilibrium three-dimensional structure of the simplest representatives of the series of tetraoxides (TO) — H₂O₄ and CH₃O₄H. In the harmonic approximation their force field, and the frequencies and forms of the normal vibrations were calculated. Satisfactory agreement between the theoretically calculated and experimentally measured frequencies was obtained for a peroxide condensate. It was shown that the recombination of tertiary peroxide radicals proceeds through a transoid configuration of the TO, while recombination of primary and secondary peroxide radicals is associated with the formation of a cisoid configuration.Translated from Teoreticheskaya i ksperimental'naya Khimiya, Vol. 22, No. 3, pp. 363–366, May–June, 1986.     

Reactivity of the C-H bond of organic molecules with various structures in hydrogen abstraction by peroxyl radicals

A model of an early transition state with charge transfer is proposed for calculation of the activation parameters of the abstraction of a hydrogen atom by peroxyl radicals from the molecules of organic compounds. It was shown that the compensation effect in this reaction is due to the fact that the change in the preexponential factor is determined by change in the vibrational component of the entropy of activation. L. M. Litvinenko Institute of Physical Chemistry and Coal Chemistry, Academy of Sciences of Ukraine, Donetsk. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 1, pp. 6–11, January–February, 1997.