Plasmon decay mechanisms in proton-metal collisions

G.A. BOCAN; J.E. MIRAGLIA

San Sebastián, España

Workshop; Workshop in honor of Antoine Salin: Recent advances on the dynamics of atomic and molecular particles interacting with gas and solid targets; 2005

Donostia International Physics Center

Abstract A projectile travelling inside a metal can excite collective oscillations in the electron gas, also known as bulk plasmons. These oscillations have a finite lifetime and eventually decay. The two main mechanisms for plasmon decay are the excitation of a Bloch electron that performs an interband transition (inspected by Rösler and collaborators) and the excitation of two interacting electrons (mentioned by DuBois, Sturm&Oliveira and others). In this work, we introduce a model to describe these processeswithin the frame of collision theory. Electronic wave functions and the transition matrix are approximated to first perturbative order in the projectile charge. The electronic response to the projectile is condensed in the dielectric function of Mermin-Lindhard which is a modified version of that of Lindhard's so as to include a finite plasmon linewidth in a preserving f-sum-rule way.Four targets, Al, Mg, K and Na, will be studied as they cover a reasonable variety of characteristics such as quantity of valence electrons, Fermi momentum and lattice structure. Also, two different projectiles, protons and electrons, will be considered for the case of Al.We present total electron production, total excitation energy, and single differential probability in terms of energy and angle of the excited electrons. They are compared with total plasmon production and the energy deposited by the projectile. For Al targets the spectra are compared with those corresponding to binary electron excitation and inner shell ionization. Some comments are made regarding the relative importance of the two mechanisms for each element and the role that parameters like the electron density, the crystal structure and the plasmon linewidth play in this.Also an approximate scaling rule is found for the plasmon creation probability as well as for the 2e contribution to the plasmon decay probability.