Sputtering and surface topography modification of bismuth thin films under swift 84Kr15+ ion irradiation

Thermal spike model interpretation of sputtering yield data for Bi thin films irradiated by MeV 84Kr15+ ions

“…Relative to existing sputtering yield experimental data, notice, first, that the only one Y(E) value measured previously within the nuclear stopping power energy regime for 45 keV [34] Kr ions in Bi is found to be in good agreement with our calculated sputtering yield. The previously measured sputtering yields in the electronic stopping power high energy regime, notably our recently reported [17] data for Bi thin films irradiated by 27.5 MeV 84 Kr 15+ ions are quite consistent with our calculated sputtering yields using Eqs. (7a) and (7b).…”

“…(7a) and (7b)), over time and radial distance in the computer program generating the atomic temperature, we have calculated the total sputtering yields from a Bi thin film and a bulk Bi target for two different values of the electronic stopping power derived by the CasP code [31] for two charge states (equilibrium, q e:c:s: ¼ 13:84, and fixed, q f :c:s: ¼ þ15, charge states) of incident 27.5 MeV Kr ions. The obtained results are reported in Table 1 where they are compared to our sputtering yield experimental data [17] for Bi. For the fixed ion charge state, these calculations give Y(E) results lower than our experimental data by $47% and $52%, respectively, for the Bi thin film and the bulk Bi target.…”

“…Therefore, our sputtering yield experimental data are better described by the thermal spike model with considering a Bi thin film as target bombarded by 27.5 MeV krypton ions of fixed +15 charge state. The energy of the highly charged Kr ions used as well as target properties like its thickness, grain size, specific heat and thermal conductivities play an important role in the enhancement of experimental sputtering yields and in ion irradiation-induced surface effects previously observed [17] in Bi thin films. Let us now consider the variation of sputtering yields versus the Bi electronic stopping power.…”

“…They can be solved numerically by using an explicit finite difference method with the condition of convergence, 2D e Dt=ðDrÞ 2 < 1, where the time and radial steps (Dt, Dr) are assumed to amount, respectively, to 2 Â 10 À17 s and 0.2 nm. The specific heats (C e , C a ) and thermal conductivities (K e , K a ) are taken as those corresponding to experimental values in the case of Bi thin films [25,26] within a thickness of $300 nm corresponding to that used in our recent experiment (see Reference [17]). These values of thermo-physical quantities (e.g., for thermal conductivities) are lower by $16% up to $43% than those for a bulk Bi target [27][28][29].…”

“…Therefore, materials of different natures are expected to be differently effected under the same SHI irradiation conditions. Recently, we have carried out an experimental investigation of the sputtering of Bi/Si thin films irradiated by MeV 84 Kr 15+ ions [17] using XRD, AFM and RBS techniques to evaluate, respectively, the induced surface structure changes, surface topography evolution and corresponding sputtering yields. The obtained experimental data have been discussed in the framework of Sigmund's collision cascade transport theory [18,19] and related semi-empirical sputtering models [20,21].…”