Numerical and experimental studies of the sputter yield amplification effect

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Abstract
Recently we have demonstrated the existence of the so-called sputter yield amplification (SYA) effect, based on the preferential sputtering of the lighter species during ion bombardment of composite solids and resulting in enhanced partial sputtering yield of the lighter species as compared to the elemental sputtering yield. In specific cases the enhancement of the sputtering yield could reach one order of magnitude or more. This effect has been both numerically studied and experimentally observed during low energy ion bombardment of i) thin films of low mass on heavy substrates; ii) thin films of high mass on light substrates; iii) simultaneous high mass atom deposition on light substrates; iv) simultaneous low mass atom deposition on heavy substrates. In all cases sputter yield enhancement of the low mass species is observed but in each individual case different specific goals are achieved. For example, in case i) much faster etch rate of the thin film is achieved than what is expected from the elemental sputtering yield. In cases ii) and iii) faster erosion of the target is achieved in view of sputter-deposition processes. In case iv) a nearly complete removal of the deposited species with a partial sputtering yield substantially higher than the elemental sputtering yield is achieved in view of selective ion beam assisted deposition. The SYA effect is also observed in the net growth regime, i.e. during the deposition of composite films with ion co-bombardment. In this case the composition of the growing film differs from that of the deposition flux. This work presents systematic numerical and experimental studies of the SYA effect in all these cases as a function of the ion energy, mass and angle of incidence as well as the target species. The simulations have been performed with the T-DYN program. General rules are given as to when the amplification effect is most pronounced. Potential applications are also discussed.

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