Time dependencies of photoluminescence decay of the powder luminophore consisting of ZnS nanoparticles doped with Mn in micro- and millisecond range were registered experimentally. It was shown that the experimental decay curves could not be correctly described in the framework of the existing models. A simple model was suggested describing the kinetics of photoluminescence decay kinetics with participation of Mn centers that included the possibility of electron transfer between ZnS nanoparticles.

A study of sonochemically synthesized ZnS:Mn nanoparticles is presented. The particles prepared at low rf power (about 20 W) and room temperature coalesce to form morphologically amorphous large species (30-100 nm in diameter). As the power is increased in the range from 20 to 70 W, and the solution temperature is raised to 60 to 80 degrees C, finer particles are produced with the size ranging from 2 to 20 nm and improved crystallinity. The results indicate the dispersion of the Mn2+ ions at near-surface sites in the particles. It is shown that the sonochemically fabricated particles approach the quality of the ones obtained by a standard chemical route and show a reasonable luminescence performance.

We report on an extremely narrow linewidth of a two-dimensional electron-gas photoluminescence in GaAs/AlGaAs quantum wells pumped by ultrasonic vibrations. Below the threshold pumping amplitude, the observed emission line is weak, broad, and undergoes a redshift consistent with the evolution of an electron-hole plasma recombination in the oscillating piezoelectric fields accompanying the sample vibrations. Above the threshold, a narrow emission line arises, which sharpens up to similar to0.1-meV full width at half maximum, and gains intensity with increasing pumping amplitude. Weighing different alternatives, it is suggested that the data are best explained within the framework of stimulated emission originating from the acoustically pumped injection of enhanced electron and hole densities. (Less)

The variations of the electroacoustic parameters (Q factor, electromechanical coupling coefficient, and capacitance) of lithium niobate piezoelectric transducers with increasing high-frequency excitation voltage are studied experimentally. The relative acoustic strain is found to reach a maximum of about 10−4 in the frequency range from 2 to 3 MHz. The Q factor of the transducers may increase by 100% in the range of acoustic strains studied. This increase is accompanied with acoustic emission. The reason for this effect is the block structure of the lithium niobate crystal.

We report on a novel method of charge particle transport. It is based on the application of a moving electrostatic potential and an oscillating friction force to the particle which occur due to acoustic waves travelling in a piezoelectric medium. ZnS grains placed onto the surface of a Y-cut, Z-propagating LiNbO3 plate experience a sequence of jumps in the forward and in the backward directions with respect to the phase velocity of the plate wave. The jump probability appears to change with the Lamb mode supported by the plate and the sign of the grain charge. We present computed spatial profiles of the piezoelectric potential and the displacement components on the surface of the plate for the two lowest resonant modes of Lamb waves. The occurrence of the grain motions is then explained by the presence of the electrical and friction forces, and good qualitative correspondence of the theory and experiment is found.

A reorientation of the ferroelectric domains under an action of ultrasound in LiNbO3 is observed for the first time. The involvement of the ferroelectric domain boundaries is experimentally identified by the analysis of X-ray reflection and crystal etching. The reorientation of the domains takes place under acoustic deformation of the order of 1E-5 in megahertz frequency range.

The effect of an ultrasonic treatment on the content of metal impurities in Si surface layers was studied by using secondary-ion mass spectrometry and the photoconductivity relaxation method. It is shown that ultrasound treatment increases the content of K and Na in Si surface layers at room temperature.

The effect of ultrasonic treatment on the mobility of short surface dislocations in Si crystals is investigated. It is found that ultrasonic treatment of Si crystals changes the velocity of dislocations under a permanent mechanical load. The nature of variation of dislocation velocity is determined by the sign of external stresses acting on the sample: compressive forces decrease while tensile forces increase the velocity of dislocations. After ultrasonic treatment of the samples, a decrease in the activation energy for dislocation motion and the enhancement of the electroplastic effect are observed. A possible mechanism of the observed effects is considered.

Ultrasound (US) influence on dislocation free (DF) silicon is investigated. Ultrasonic waves attenuation (alpha), mobility of intentionally induced superficial dislocations, and minority carriers diffusion length (L) are measured from a dislocation free Cz-Si as a function of US amplitude. The general results consist of some changes in the properties under study that takes place in a threshold way. Under US deformation S > 10(-5) attenuation alpha becomes nonlinear, dislocation mobility and so microplasticity vary significantly, and L increases up to 2 times.US in DF Cz-Si can effectively interact with a system of point defects. The acoustostimulated changes in DF Cz-Si properties under study are connected to ultrasonically activated transformations in a system of crystal point defects and their complexes.. We find there are two thresholds of US deformation: S(1)similar to 10(-6) and S(2)similar to 10(-5). Under deformation S S-2 the process of defects redistribution takes place.

The effect of ultrasonic treatment on the microplastic properties of a near-surface layer in dislocation-free silicon single crystals was studied using [111]-oriented p-Si samples with artificial dislocation rosettes. The ultrasonic processing resulted in the formation of an approximately 100-µm-thick hardened near-surface layer and the emergence of point-defect pileups of the vacancy and/or vacancy-impurity cluster type on the sample surface. Possible mechanisms of the observed phenomena are discussed.

In case of low dislocation density, an intensive ultrasound (US) wave call cause a motion of jogs in screw dislocations which is accompanied by formation of point defects. A detailed theoretical study and computer simulation of the motion is given. Defect modification takes place only above the critical amplitude of US. Under certain threshold US intensities the jog starts oscillating and both types of point defects (vacancies and interstitials) are continuously generated. The theoretical results are compared with the experimental data on US attenuation in Si and other materials. Acoustic emission and photoconductivity prove the acousto-dislocation interaction which leads to the defect modification. The experimental results turned out to prove the results of computer simulation.

We have investigated the influence of ultrasound treatment on dislocation mobility in silicon crystals. Our research was based on dislocations in silicon crystals induced by scratches. We have found that the ultrasound treatment (UST) of silicon crystals results in changes in the dislocation displacement speed under the constant mechanical load. When applying compressing stress, UST makes the dislocation speed slower, while stretching stress accelerates it. The UST has decreased the energy of thermo-activated dislocation movements. Before the treatment the energy is equal to 2.03 eV, and after the UST the energy is 1.61 eV. Below, we describe the experiments and a possible mechanism which causes the phenomena we have observed.

The sonoluminescence of ionic semiconductors were studied. The main attention is paid to threshold phenomena which accompany the light irradiation, namely --- point defect creation and nonlinear ultrasound wave attenuation. The model for description of processes under investigation which connects the sonoluminescence excitation with the onset of point defects (vacancies and intersticials) generation by moving under ultrasound action screw dislocation with a jog. The attempt is made to estimate the parameters of crystals which define the jog motion in its cristal relief.