ИСТИНА

In this paper, we consider the effect of the argon-oxygen and oxygen-argon irradiation sequences on changes in the chemical composition, type of chemical bond and local atomic structure of ultrathin (~ 20 nm) Armco iron surface layers. A series of experiments was carried out on the irradiation of the Armco iron surface in a pulse-periodic mode with Ar+ ions with an energy of 30 keV, a fluence of 5*1016 ion/cm2 and O+ with an energy of 30 keV, a fluence of 1017 ion/cm2 in various sequences. Investigation of the chemical compound and chemical bonds and local atomic structure of the ion-modified surface was carried out by the XPS (X-ray photoelectron spectroscopy) and Auger electron spectroscopy. Comparison with changes caused by the modification with only one type of ions has been carried out. The totality of the obtained results shows that combined irradiation with ions of different chemical activity leads to significant changes both in the chemical state of iron and in the local atomic structure of the thin surface layer. Study of changes in the local atomic structure was carried out by an XAFS-like method - EELFS spectroscopy (EELFS - Electron Energy Loss Fine Structure). Experimental EELFS spectra were obtained beyond the M2,3 edge of iron excitation and the K edge of oxygen excitation. The analysis of experimental data was carried out by the method of solving the inverse problem; atomic pair correlation functions were obtained. The parameters of the local atomic structure of ion-modified surfaces — partial interatomic distances, dispersion parameters, and coordination numbers — were obtained. The obtained results are show the irradiation O+→Ar+ iron retains its metallic state for a long period of time (30 days). At the same time, argon was found in this ionized layer. It can be assumed that argon penetrates deep into the iron by defects and fills the formed pores, preventing further oxidation. At the Ar+→O+ sequence irradiation, a superposition of nonstoichiometric oxides based on Fe2+ и Fe3+ is formed on the iron surface.