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The experimental data regarding to vacancy clustering obtained earlier by positron annihilation method in irradiated Sic are analyzed on the basis of a positron trapping model. The size and concentration of clusters forming in the process of isochronous annealing of neutron irradiated n-SiC crystals are estimated as a function of annealing temperature. A possible mechanism of vacancy clustering is concisely considered which allows to understand qualitatively the observed distinctions of clusterization depending on irradiation dose and as well on type and doping level of the Sic crystals. K J I~C T~P H~~U H U BaKaHmfi B 06nyYeHHOM Sic n p o a~a n u 3 n p o~a~b i na ocHoBe Mon,enH s a x~a~a nOJIy WHHbIe PaHee MeTOAOM aHHHTHJIRUHH n03HTPOHOB 9KCIIePHMeHTanbHbIe AaHHbIe OTHOCHTenbHO II03HTPOHOB. OqeHeHbI pa3MepbI H KOHIfeHTPaIfHR KJIaCTepOB B 3aBHCHMOCTH OT TeMIIepaTypbI H30XpOHHOrO OTXHK3 B 06JIyWHHbIX HetTPOHaMH KpHCTaJlJIaX n-SiC .KpaTKO PaCCMOTpeH B03MOX-HbIg MeXaHH3M KJIaCTepH3aIfHH BaKaHCHt, Il03BOJIXIoWHfi KaYeCTBeHHO IlOHRTb OCO6eHHOCTH KJIBC-TepH3aUHH B 3aBHCHMOCTH OT ,40361 O~J I~Y~H H X , a TaKXe OT THIIa H CTeIleHH JIerHpOBaHHX o6pa3qo~ sic.

Measurements of the angular correlation of annihilation radiation and infrared absorption spectra were conducted with porous silicon samples, containing capillary macropores with a diameter of about 1 µm. The set of data shows that a high proportion of Si -O bonds contribute to positron annihilation and IR absorption for porous silicon. Annihilation parameters and estimated values of the specific surface area point to the availability of a nanoporous system in the macroporous silicon. Most likely the macropore surface is covered by the nanoporous material to a thickness of 100 -200 nm. The characteristic size of the nanopores is estimated at 1 -2 nm. Si -O bonds are located at the nanopore surface and do not exceed one monolayer.1 Introduction The positron diagnostics of structural defects in solids is based on the phenomenon of positron capture by vacancy type voids, which are defined as energy wells [1]. As a consequence of the reduced electron density, the lifetime of captured positrons is longer in comparison with bulk annihilation. Other annihilation characteristics also vary: the angular and energy distributions of annihilation quanta become narrower for localized positrons. Positronium atoms (Ps) are generated in many substances. They have two spin states: singlet p-Ps (S = 0, statistical weight 2S + 1 = 1) and triplet o-Ps (S = 1, 2S + 1 = 3). A p-Ps self-annihilation has lifetime τ p = 0.125 ns and gives the so-called narrow component in angular correlation of annihilahion radiation (ACAR). If p-Ps atoms are free, the full width at half-maximum (FWHM) of this component is determined by apparatus resolution and, as a rule, is not more than 1 mrad. For captured p-Ps atoms, broadening of the narrow component takes place, and in this case the FWHM is determined by void size. Bulk annihilation of o-Ps atoms produces a lifetime component of 1-2 ns and, as well as positrons, a broad component (FWHM = 10 -15 mrad) in ACAR. However, the lifetime of o-Ps atoms captured in voids depends on the void size and may be as much as several tens of nanoseconds.The first measurements of positron lifetime in porous silicon [2] displayed the intermediate component of ~0.5 ns, while there is a single one of τ = 0.22 ns in defectless silicon crystals. The subsequent investigations [3 -6] revealed the presence of very long positron lifetime components (up to ~50 ns [5]). This indicates that a major fraction of positrons are localized before annihilation in nanopores, partially forming positronium atoms. It was found that the average nanopore radius is on the order of 1 nm [3] and