Institute of Fundamental Technological Research

The paper presents results of investigation of microstructure and micro-hardness for material of ZnO varistors applied to 110 kV surge arrester and surge arrester counter. The research combined two pairs of varistors, each consisted of one varistor subjected before to operation, while the other one was brand new unit and constituted a reference. All varistors were made of the same material by the reputable manufacture. The tests revealed a different degree of the material degradation for varistors subjected before to operation. This also refers to different degradation mechanism observed for the material of these varistors, if typical effects of degradation of aged ZnO varistors were considered as a reference. Physical state of spinel in the microstructure had a significant impact on the material degradation, however a considerable loosening of the microstructure associated with bismuth oxide was observed too. It was surprising, since the precipitates of the bismuth oxide phase most often showed very good binding to the ZnO matrix and high resistance to associated electrical, thermal and mechanical effects. The degradation effects in the ZnO matrix proved to be limited only.

surge arrester, surge arrester counter, MO varistors, microstructure of ceramics, ceramic material degradation

This paper considers the investigation of photoacoustic transformation in naturally-gyrotropic and magnetoactive crystals, with internal stress under sound excitation in different modes by Bessel light beams (BLB). In the range of high modulation frequencies (Ω > 1 MHz), the dependence of the photoacoustic response amplitude on the radial coordinate ρ exhibits resonant phenomenon, which can be used to increase the resolution of photoacoustic spectroscopy for media with internal stresses. The expressions for amplitudes of photoacoustic signals in strained crystalline samples were obtained under different boundary conditions, taking into account the dependence of the thermoelastic coupling coefficient on the initial strain in the sample. It was showed that a resonant increase in the amplitude signal is related to the dependence on the geometric parameters of the sample-piezoelectric transducer system, the values of Murnagan constants, the mode composition of the Bessel light beam, and its amplitude modulation frequency.

photoacoustic spectroscopy, Bessel light beams, magnetoactive gyrotropic materials

Two-component Langmuir–Blodgett film has been fabricated from equimolar mixture of 5-[[1,3-dioxo-3-[4-(1-oxooctadecyl)phenyl]propyl]amino]-1,3-benzenedicarboxylic acid with cetylamine. Porous one-component derivative of this film has been obtained by removing of cetylamine. Both films have been investigated as sensing layers of the surface acoustic wave sensors for vapors of methanol and ethanol in air. These films react on the alcohol vapors. Time of the sensor reaction is less than 2 s and this reaction is reversible. The response parameters of the sensor depend on the kind of the alcohol and the structure of the layer. An explanation of the observed differences in the behavior of both layers in contact with vapors of the alcohols has been proposed.

Self-assembled monolayer, Langmuir–Blodgett films, Organic films, Surface acoustic wave, Sensors, Alcohols, Methanol, Ethanol

The paper presents the study of frequencies of the acoustic localized modes in metallic Au/V nanolayers. On the basis of Rytov model describing acoustic wave propagation in periodic layered medium and Djafari–Rouhani formula the frequencies of localized modes were numerically calculated. Dependencies of localized modes frequencies were presented graphically as a function of b/L nanolayer parameter (b – thickness of Au sublayer, L – thickness of Au/V bilayer) for first and second phononic stop bands. Obtained experimentally frequencies of localized modes for Au/V nanolayers were compared with calculated values. Accordance between experimental and theoretical results is satisfactory.

metallic nanolayers, localized acoustic modes

The paper presents the results of acoustic wave velocity investigation in metallic Ag/Fe nanolayers deposited on GaAs substrate. Measurements of velocity were performed using femtosecond technique. Ag/Fe samples were characterized by different thickness of bilayers. On the basis of experimental results of velocities, effective elastic constants c11 were evaluated. In the range of bilayers thickness above 80 Å the c11 values are in accordance with those calculated from the elastic constants of bulk materials (Rytov model). For lower values of bilayer thickness elastic constants exhibit large decrease. Grimsditch’s model was applied to interpret changes of elastic constants dependence for low bilayer thickness. This model contains an additional interlayer treated as the parameter. Comparison the values of theoretical elastic constants obtained by applying of Grimsditch model with those calculated from experiment shows qualitative accordance in the range of small bilayer thickness.

metallic nanolayers, effective elastic constants nanolayers

Paper presents the results of study of picosecond acoustic signals generated by femtosecond laser pump pulse in Au/V multilayers. Au/V nanostructures with a period of 36-205Å located on MgO substrate were studied. The dependence of measured changes of the laser light reflectivity from nanostructure surface on different delays of probe beam was examined. Peak frequencies obtained by FFT analysis were interpreted as frequencies of acoustical localized modes. The obtained values of these localized modes are in agreement with numerical results. In the same sample localized modes were excited simultaneously in the first and second frequency forbidden gaps.

picosecond acoustics, metallic nanolayers, FFT analysis

Paper presents the results of theoretical analysis of localized acoustic modes, which can be generated in Au/V nanolayers with “heavy” capping layer. The transfer-matrix method was used to evaluate frequencies of localized acoustic modes in these nanostructures. Up to now the condition of generation of localized modes in nanolayer structure was that the acoustic impedance of capping layer is lower then the acoustic impedance of top (next) layer. This condition was in agreement with experimental results. This paper demonstrates the possibility of generation of localized acoustic modes in case of higher acoustic impedance of capping layer. The frequencies of localized modes for different thickness of capping layer were obtained.

picosecond acoustics, metallic nanolayers, localized acoustics modes

This work presents analysis of localized acoustic modes using theory given by B. Djafari-Rouchani et al. and Rytov model of elastic waves propagation in periodical medium. Localized modes were considered for Au/V nanostructures. Experimentally Au/V nanostructures on MgO substrate with period 120-240 angstrom were studied. Changes of light reflectivity coefficient of these nanostructures caused by femtosecond laser beam excitation were measured. Analysis of experimental results of reflectivity dependence on delay time of probe beam was made over the range up to 150 ps. The dependences of localized modes frequency on thickness of nanostructure bilayers were obtained. Measured frequencies of localized modes remain in agreement to the theoretical values.

metallic nanolayers, picosecond acoustics, localized modes, Rytov model