Fast chemistry in ion wakes

Abstract

The energy loss of an MeV/amu ion to the electrons of a substance can be as great as keV/Å. With such an enormous amount of energy available, it is not surprising that a wide variety of phenomena can occur. Among them are track formation and induced desorption of molecular ions. A common ingredient in models of such processes is the requirement that the electronic excitation has a sufficiently long lifetime (∼ picoseconds) that energy can be transferred to atomic motion. Recently, several new phenomena have been observed that indicate that atomic motion/chemical rearrangement can occur even when the electronic excitation is shorter lived (∼ femtoseconds). Two of these processes, which are also induced by MeV ion bombardment, are track damage in heavily doped compound semiconductors and greatly enhanced adhesion of metal films to metallic and semiconducting substrates. Neither of these effects can be easily accomodated within the existing theoretical models; thus, it is possible that an even richer variety of ion induced effects will be discovered. Speculations on the form of a new theoretical approach are presented.