Igor Avetissov

Thermodynamic features of axial vibrational control technique for crystal growth from the melt

Direct measurements of crystallization heat of NaNO3 and CdTe melts activated by low-frequency vibrations by oscillating an inert baffle submerged into the melt demonstrated up to 30% increase compared to the regular melt. At a stationary state the crystallization heat increase depends on vibrational amplitude and frequency. The study of melt structure by Raman spectroscopy proved the assumption about the changing of component composition followed by its restructure under AVC processing. Kinetics of melt reconstruction depending on temperature and vibrational intensity was examined.

Study of the Kroll-process to produce ultra-pure Ti for the low background experiments

To construct G2 & G3 low background experiments for direct Dark Matter search, a lot of ultra-pure construction materials will be needed. Our study of various Ti samples shows that the levels of contaminations of commercially available industrial Ti can varies from 0.2 to 100 mBq/kg for U/Th. It means that the metal Ti is such a promising material for future experiments if the way of production in bulk quantities with very low level of contaminations (below ∼1 mBq/kg of 238U /232Th) would be developed. Our study of the industrial Kroll-process is focused on the possible sources of U and Th and their migration during the multistage Kroll process. To understand migration of U and Th during the Kroll process the set of other impurities available due to precise ICP-MS analysis have been studied. Preliminary results confirm that the Kroll process could be used for the ultra pure Ti sponge production while the following stages of the metal Ti production of from the Ti sponge with necessary mechanical properties...

Hybrid nanofilms with laser-control luminescence

Nanosize films of organic electroluminophors have offered the challenge to a new generation of light emitting devices - OLED. Tris-(8-oxyquinoline) aluminum (Alq3) was one of the first compounds which demonstrated high efficient green electroluminescence and to the moment it is still used as emission and electron transport material in OLED. Alq3 is known to exist in several polymorphs with photoluminescence (PL) maximum varied from 537 to 481 nm. One of main problem of OLED technology consists in a high cost of organic materials. An attempt to use organic-inorganic hybrid materials for a creation of a novel thin film emission device has not been very successful yet. But the investigation of hybrid material (HM) based on B2O3 glass matrix and Alq3 as phosphor agent showed that there were observed a significant shift of luminescent peak to short waves after bulk HM annealing. The change in the luminescence spectrum can was explained by the polymorph and/or conformation transitions in Alq3 in the crystal field of the matrix.

Spectral properties of CdTe-CdSe powders with controlled nonstoichiometry

Chemical compounds based on A^IIB^VI are widely used as phosphors and photosensitive materials for VIS and IR spectral range. It is of common knowledge that functional properties of A^IIB^VI based materials are strongly depended on a deviation from stoichiometry which could be varied within 10^-2 mol.%. At the same time an influence of nonstoichiometry (native point) defects on structure-sensitive properties is no less than that of dopants. Besides phosphors A^IIB^VI powders are applied as inorganic pigments, which color and tint determined both a (CdTe)_x(CdSe)_1-x solid solution composition and a deviation from stoichiometry.