42Optical emission from the surface of various sub stances under the action of low and medium energy ion beams has been observed in many investigations. The emission spectra displayed both discrete lines and continuous bands. The discrete line emission can be generated by a fraction of atoms, ions, and molecules sputtered in excited states from the surface layers of solid targets.The hypotheses that have been formulated in order to explain the nature of broad bands of continuous emission mostly refer to various kinds of luminescence accompanying related to the decay of excitons, recombination of electron-hole pairs on intrinsic and induced radiation defects, and radiative reactions between radicals created by the ion bombardment. However, some researchers have pointed out [1][2][3] that the radiation that forms continuous bands in the spectra of emission from solids bombarded by acceler ated ions does not exhibits some characteristic features of luminescence. No one of the theoretical models proposed so far, which can be conditionally subdivided into thermodynamic, molecular, detachment, and collisional ones [2, 3], can exhaustively explain the spectra of optical emission from ion irradiated targets. It should be noted that the models of these types are based on the consideration of mechanisms that lead to the formation of ensembles of sputtered atoms in excited states.Evidently, any non equilibrium emission from out side a solid must be discrete in view of the absence of quasi continuous energy bands. In connection with this, an alternative hypothesis can assume that we are dealing with some equilibrium (in other words, ther mal) or at least quasi equilibrium emission. This can be, e.g., the emission from so called thermal spikes that are formed in the immediate vicinity of the surfaces of solids [4][5][6][7] bombarded by ions of low and medium energy (1-100 keV). These spikes appear as a result of the evolution of dense (non branched) atomic colli sion cascades.According to the results of Monte Carlo simula tions [8] these regions are heated to several thousand degrees and occur at depths not exceeding (for the indicated energy range) several hundred nanometers. Since the depth of visible radiation penetration into metals is on the order of λ/2 (where λ is the wave length) the emission from thermal spikes can be observed and its features can be experimentally studied as dependent on the parameters of ion irradiation.In order to verify the aforementioned alternative hypothesis, we have analyzed the spectral composition of optical emission from high purity iron, zirconium, and tungsten bombarded by Ar + ions with energies E = 5-20 keV.The samples of high purity iron (99.99% Fe), zir conium (99.98% Zr), and tungsten (99.96% W) in the form of 3 mm thick plates suspended on thin fila ments possessing low thermal conductivity (so as to ensure only radiative heat exchange) were bombarded in vacuum (at a residual pressure of ~5 × 10 -5 Torr) by continuous beams of Ar + ions with an energy that could be controlled from ...

No abstract

No abstract

No abstract

Using electron microscopy it was found that irradiation of clad cold-worked specimens made of commercial aluminium-lithium alloy 1441 by the Ar + ions of energy 40 keV at low doses of irradiation (10 15 cm -2 , irradiation time 1 s, Т < 70°C) and ion-current density of about 100 µA/cm 2 results in the transformation of the cellular structure formed in the alloy under deformation. As the dose of irradiation is increased up to 10 16 cm -2 , a transition from a cellular to a subgrain structure close to a polygonal one is observed. The efficiency of the process is increased with ion-current density. Furthermore, under ion irradiation at increased ion-current densities, the β'(Al 3 Zr) and Al 8 Fe 2 Si particles present in the deformed alloy dissolve, and disperse particles of a new Al 2 LiMg phase of platelet shape are formed. The changes in the dislocation structure and phase composition in alloy 1441 are observed several seconds after irradiation not only in the surface layer adjacent to the ion incorporation band but also through the thickness of the specimen tens of thousands times greater than ion projective ranges.Ural Branch of the Russian Academy of Sciences,