Ion Implantation and Synthesis of Materials - Studium

82 7 Displacements and Radiation Damage7.4 Primary Knock-on-Atom Damage EnergyA PKA loses energy in both electronic and nuclear collisions as it slows down andcomes to rest in a crystal. Only the latter process creates lattice disorder around theion track and is responsible for radiation-damage effects. Therefore, in consideringthe disorder created by a PKA, one must first determine the partition of energybetween electronic and nuclear processes. A similar procedure was used in determiningthe range distribution of implanted atoms in Chap. 6. The differencebetween range and disorder calculations is that, in the latter case, the energy partitionof the displaced atoms must be considered as well. As in the case of ion-rangedistributions, the crystal structure can influence the amount of energy lost in nuclearcollisions. For example, a well-channeled particle loses more of its energy in electronicprocesses, and so creates less disorder, than a particle whose initial directiondirection of motion is not aligned with any low-order lattice axis or plane. However,for the moment, we will exclude consideration of the influence of channeling effects.As a theoretical treatment for the distribution of energy between electronic andnuclear processes for both the primary and the secondary knocked-on particles,consider η as the sum total of the energy given to electrons, ν as the total energyending up in atomic motion, and η + ν = E ≡ the energy of the incoming particle.Figure 7.3 shows ν/E, the fraction of PKA energy deposited in the solid in theform of atomic collision, as a function of PKA energy for several monatomicmaterials for the case M 1 = M 2 .1.0Damage Efficiency (ν(E)/E)0.80.60.40.2BeCAlUNbCuAu0.010 1 10 2 10 3 10 4 10 5 10 6PKA Energy (E), eVFig. 7.3. The fraction of the PKA energy deposited in atomic collisions (damage efficiency,v(E)/E) as a function of PKA energy and self-ion type. Here we define the PKA energy as E(after Robinson 1965)