High density electronic excitation under heavy ion bombardment

Upon the interaction of heavy ions with a solid, the energy possessed by the impinging ions is imparted to the solid in the form of the kinetic energy of nuclei and the electronic excitation energy. In this paper, the atomic displacement induced by electronic excitation is discussed. Since the energy imparted to electronic excitation by energetic ions is about 103 times as much as that imparted to the kinetic energy of nuclei, the atomic displacement induced by electronic excitation dominates in the materials in which this process is effective. The atomic displacement induced by electronic excitation has been well known, but recently, it has attracted attention anew because the recombination-induced defects in semiconductors arise from the same origin. In this review, the general concept of the atomic displacement induced by electronic excitation is first discussed. Then, the experimental results on its process in the tracks of energetic heavy ions and in laser-irradiated surface layers are presented. Finally, its possible mechanism is surveyed. The present state of the understanding of the phenomena of atomic displacement induced by high density electronic excitation is shown. (Kako, I.)