Optical emission from metal targets bombarded by 5–20 keV argon ions

Abstract

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 ...

Ion irradiation-induced decomposition of Al + 4 wt. % Cu supersaturated solid solution

“…A multiple increase in the exposure depth and the rate of solid solution decomposition can be explained by the radiation-dynamic action of accelerated ions [10,11,16]. The essence of this effect is that the nanosized regions of atomic displacement cascades (Thermal Spikes [17,18]) are zones of explosive energy release. The temperature of the cascade regions, which are thermalized within a time of the order of 10 -12 s, may reach, according to Monte Carlo and molecular dynamics calculations, 5000-6000 K and even higher values.…”

“…Experimental proof of the formation of such extremely heated regions [18] has recently been obtained from the analysis of the emission spectra of metal targets (Fe, Zr and W) in the course of ion irradiation. Estimated temperatures are close to the simulated data.…”

“…The pressure at the front of shock waves may exceed not just the real, but also the theoretical yield point of condensed matter [11,18]. For comparison, the characteristic time of explosive energy release in a nuclear and in a chemical explosion is ~10 -8 and 10 -5 s, respectively.…”

Acceleration of volume decomposition of supersaturated Al + 4 wt.% Cu solid solution under irradiation with Ar+ ions

“…A multiple increase in the exposure depth and the rate of solid solution decomposition (especially at low irradiation doses) can be explained by the radiation‐dynamic action of accelerated ions . The essence of this effect is that the nanosized regions of atomic displacement cascades (thermal spikes ) are zones of explosive energy release. The temperature of the cascade regions, which are thermalized within a time of the order of 10 −12 s, may reach, according to Monte Carlo and molecular dynamics calculations, 5000–6000 K and even higher values.…”