Ion Implantation and Synthesis of Materials - Studium

13.2 Ballistic Mixing 18513.2.2 Cascade MixingIn addition to recoil mixing, other ballistic phenomena are possible during ionirradiation and implantation. For example, enhanced atomic mixing can occurwhen multiple displacements of target atoms result from a single incident ion. Inthe multiple displacement process, an initially displaced target atom (primaryrecoil) continues the knock-on-atom processes, producing secondary recoil atomdisplacements which in turn displace additional atoms. The multiple displacementsequence of collision events is commonly referred to as a collision cascade.Unlike the highly directed recoil implantation process, in which one atomreceives a large amount of kinetic energy in a single displacement, atoms in acollision cascade undergo many multiple uncorrelated low-energy displacementand relocation events. Atomic mixing resulting from a series of uncorrelated lowenergyatomic displacements is referred to as cascade mixing.The ballistic interactions of an energetic ion with a solid are shownschematically in Fig. 13.6. The figure shows sputtering events at the surface,single-ion/single-atom recoil events, and the development of a collision cascadethat involves many low-energy displaced atoms. The cascade is shown in the earlydisplacement stage of development, where the displaced atoms occupy interstitialpositions surrounding a core of vacant lattice sites.Ballistic ProcessesSputteringRecoilImplantationDisplacementSolidCascadeNormal atomInterstitial atomIncident ionFig. 13.6. The ballistic interactions of an energetic ion with a solid. Graphically displayedare sputtering events at the surface, single-ion/single-atom recoil events, the developmentof a collision cascade that involves a large number of low-energy displaced atoms, and theion implantation of the incident ion