Cluster and Velocity Effects on Yields and Kinetic Energy Distributions of Li+ Desorbed from LiF

MeV $\mathrm{N}{}^{+}$ and $\mathrm{N}{}_{2}{}^{+}$ ions were used to induce $\mathrm{Li}{}^{+}$ desorption from LiF. The contributions due to elastic atomic collisions and electronic excitation processes to the sputtering yield could be unambiguously separated. In the case of $\mathrm{N}{}_{2}{}^{+}$ ions, a $\mathrm{Li}{}^{+}$ yield enhancement, i.e., $Y(\mathrm{N}{}_{2}{}^{+})>2Y(\mathrm{N}{}^{+})$, was found only for the electronic process. The maximum sputtering yield was observed in a projectile velocity range where the projectile electronic energy loss still increases. These results are simultaneously explained using the radial distribution of the deposited energy rather than the electronic energy loss.