J. Filipecki

Dynamic radiation-induced effects in chalcogenide vitreous compounds

The experimental results on time degradation of radiation-induced darkening effects in vitreous chalcogenide semiconductors of ternary stoichiometric (As 2 S 3 ) y (GeS 2 ) 1 (y 0.1, 0.2, 0.4, 0.6) and non-stoichiometric (As 2 S 3 ) x (Ge 2 S 3 ) 1 (x: 0.1, 0.2, 0.4, 0.8) systems with a variation of the average co-ordination number, Z, are discussed. It is established that adequate model for the quantitative description of these effects can be developed at the basis of bimolecular relaxation function (RF) proper to annihilation of specific structural defects in the form of oppositively charged atoms with various co-ordinations. The observed features of the investigated dynamic radiation-optical changes in these glasses are explained by compositional dependences of their atomic compactness, as well as covalent bond statistics.

Radiation-induced defect formation in chalcogenide glasses

Abstract The modified model of native and radiation-induced microvoid-type positron traps in vitreous chalcogenide semiconductors is developed to explain compositional features of positron annihilation lifetime measurements in stoichiometric As2S3–GeS2 and non-stoichiometric As2S3–Ge2S3 chalcogenide glasses before and after γ-irradiation.

Radiation-induced defects in vitreous chalcogenide semiconductors studied by positron annihilation method

Abstract The defect formation process in vitreous chalcogenide semiconductors (VChS) of the ternary As–Ge–S system, induced by 60 Co γ-irradiation with 2.82 MGy absorbed dose, is studied using positron annihilation lifetime method. The measured results are explained in terms of a modified model of coordination topological defects (CTD) with associated open volume microvoids, described by radiation-structural transformations at the level of both short-, and medium-range ordering.

Positron annihilation and diffraction studies of the photopolymers based on the acrylate oligomers

Abstract Positron annihilation lifetime and X-ray diffraction measurements were made on photopolymers based on acrylate oligomers. Polymerization was caused by exposure to ultra violet light. The measurements were made on photopolymer specimens with different ultra violet light exposure times. The longest positron lifetime, τ 3 , was associated with the pick-off annihilation of orthopositronium (o-Ps) trapped in voids. Interatomic distances and coordination numbers for the investigated samples have been determined from X-ray data. Ultra violet light exposure time affects mainly the sizes of the voids. The nearest neighbour distances and coordination numbers are independent of the ultra violet exposure time.

Free volumes in UV-cured polymers based on acrylate oligomers

Abstract Polymerization in polymers based on acrylate oligomers was caused by exposure to ultraviolet light. Polymer specimens with different ultraviolet light exposure times have been investigated by positron annihilation lifetime spectroscopy (PALS). The longest lifetime, τ 3 , in observed lifetime spectra for positrons was associated with the pick-off annihilation of ortho -positronium ( o -Ps) trapped by free volume in the structure. The aim of this paper was to investigate the influence of the time of UV exposure on free volume sizes in two different polymers based on acrylate oligomers. UV exposure time influences the free volume size: longer time reduces it. The concentration of the free volumes is independent of UV exposure time.

Positron lifetime study of native vacancy-like defects in chalcogenide glasses

Abstract Modified model for positron annihilation in vitreous chalcogenide semiconductors is developed to explain a number of previously obtained results on positron lifetime measurements in glassy As–Ge–S of stoichiometric As2S3–GeS2 and non-stoichiometric As2S3–Ge2S3 cut-sections.

Application of Positron Annihilation Lifetime Technique for γ-Irradiation Stresses Study in Chalcogenide Vitreous Semiconductors

The influence of γ-irradiation on the positron annihilation lifetime spectra in chalcogenide vitreous semiconductors of As-Ge-S system has been analysed. The correlations between lifetime data, structural features and chemical compositions of glasses have been discussed. The observed lifetime components are connected with bulk positron annihilation and positron annihilation on various native and γ-induced open volume defects. It is concluded that after γ-irradiation of investigated materials the γ-induced microvoids based on S - 1 , As2, and Ge - 3 coordination defects play the major role in positron annihilation processes.

Acousto-optical investigations of the phase transitions in the oligoethermetacrylates

We investigated the changes of acousto-optical quality coefficients in olygoethermethacrylate photopolymers of the different chemical contents from temperature. It was revealed that increasing of the aromatics rings leads to increasing of the acousto-optical quality coefficients M, and only after we have observed the influence of the distances between the C equals O chemical bonds. We also found an increasing of M with the decrease of the temperature below the 80...100 K. The maximal value of the M reaches its value at 4.2 K. The data obtained are in good agreement with previous investigations of the optical second harmonic generation. An essential influence of external electric field on the acousto-optical properties of the mentioned photopolymers was revealed. In our opinion it reflects an essential role of the acentrical quasicrystallines, which give contributions into the piezo-optical constants.