ИСТИНА

The radiation-chemical transformations induced by electrons or photons with different energies in condensed matter are basically similar at molecular level since they result mainly from the interactions with secondary electrons of low energy. On the other hand, it is well known that the macroscopic distribution of radiation effects (damage or modification) may be significantly different, depending on the energy of primary particles (e. g., for relatively soft X-rays, γ-rays and fast electrons) due to different penetration depth. At low energies the distribution is shifted to microscopic level, with a number of implications (from surface modification to physical imaging). Meanwhile, this consideration is generally valid under an assumption that the primary absorption of radiation is uniform. In the case of X-rays with E < 50 keV, this is true only for the systems with uniform chemical composition, because the absorption cross-section reveals drastic dependence upon the atomic number of absorber (this is actually a basis for a common effect of X-ray contrast). The situation becomes particularly specific for organized systems, where strong absorbers are distributed in the form of clusters or nanostructures, which may strongly affect the local spectra of secondary electrons and, thus, change the radiation-induced chemistry at nanoscale level. This effect may be denoted as the radiation-chemical contrast. This lecture will present an overview of related specific features of the X-ray induced effects (in comparison with those produced by γ-rays and fast electrons), illustrated with examples obtained in our laboratory for a wide range of systems (from thin atomic layers doped with molecular impurities to polymers and metal-polymer nanocomposites). A particular impact will be made to recent results on formation and evolution of metal nanostructures in the interpolyelectrolyte films, which clearly demonstrate the variety of “images” originating from the radiation-chemical contrast. The basic mechanisms will be discussed and possible implications for selective sensitization of materials, modification of interface and lithography will be outlined.