Collective excitations in an infinite set of aligned spheres

We present here electron energy loss spectra (EELS) calculations for an infinite set of aligned dielectric spheres as a first approximation to calculations in a more complex periodic array with small computer cost. The boundary charge method is analytically developed for such a system with use of local dielectric theory. A convenient distribution of surface charge densities at the spherical interfaces, selfconsistently interacting with each other as well as with the external field created by the incoming electron, can provide a solution of the surface collective modes. Energy loss spectra in the valence range (a few eV) are obtained for trajectories parallel and perpendicular to the axis of the aligned spheres and the nature of the excitations is studied by analysing the charge density distribution induced at the spheres, (C) 1998 Elsevier Science B.V. All rights reserved.