Letter to the editor

Classical theory of dynamical image interactions

The phenomenon of bulk and surface plasmons in solids of different geometries is analyzed in detail, giving special consideration to Ritchie's pioneering works and his relevant contributions to the advance of the knowledge in the field. A review of plasmon processes is made, illustrating the characteristics of surface and bulk modes and showing alternative formulations based on the dielectric function formalism, the hydrodynamical model, and the Hamiltonian method. The main characteristics of plasmons in infinite media, planar interfaces, cylindrical, and spherical nanostructures are discussed.

We present a theoretical study of the energy loss due to distant collisions with the surface of a highly charged ion passing through a microcapillary. Our results indicate that the correlation between the angular distribution and the energy loss of transmitted ions that do not experience charge exchange with the walls can be used to probe the dielectric properties of the capillary material at large distances.

Transmission of highly charged ions through microcapillaries is studied theoretically by a classical trajectory Monte Carlo method. The interaction of highly charged ions with the internal surface of the capillary is treated within the framework of dielectric response theory. We analyze the distance of closest approach and the angular distribution of the highly charged ions. As a projectile we consider N${}^{\mathrm{6+}}$ with an energy of 2.1 keV/amu. We find the resulting charge-state distribution of transmitted projectiles in good agreement with first measurements. Moreover, our calculations indicate that grazing collisions with the microcapillary surface hold the promise of direct observation of charge transfer and hollow-atom formation at large distance from the surface.

We analyze the transmission of highly charged ions (HCI) through microcapillaries. The interaction of an HCI with the internal surface of the capillary is treated within the framework of linear response. In the limiting case of an ideal conducting cylindrical surface, the interaction reduces to a classical image potential. For Ne^q+ projectiles transmitting through a Ni capillary calculations for the impact parameter distribution and angular distribution of hollow atoms are presented. We find the fraction of transmitted projectiles which are partially neutralized in good agreement with recent experiments.

The present report deals with the main aspects of the interaction of slow (impact velocity typically below 1 a.u.) multicharged ions (MCI) with atomically clean solid surfaces of metals, semiconductors and insulators. It is based to a large extent on the results obtained by the authors and their affiliates within the Human Capital and Mobility Network of the European Union on “Interaction of Slow Highly Charged Ions with Solid Surfaces”, which has been carried out during the last three years.

After briefly reviewing the pertinent historical developments, the experimental and theoretical techniques applied nowadays in the field of MCI-surface interaction studies are explained in detail, discussing especially the transient formation and relaxation of “hollow atoms” formed in such collisions. Further on, the status of the field is exemplified by numerous results from recent studies on MCI-induced emission of slow and fast electrons (yields and energy distributions), projectile soft X-ray spectroscopy, charge-changing and energy loss of scattered and surface-channelled projectiles, MCI-induced sputtering and secondary ion emission, and coincidence measurements involving different signatures from the above processes. The presented theoretical and experimental work has greatly contributed to an improved understanding of the strongly inter-related electronic transitions taking place for MCI above, at and below a solid surface.

The dynamic screening charge and potential induced by a charged particle moving through or nearby condensed matter are central quantities required for an understanding of various phenomena; the pioneering ideas of Ritchie on dynamic screening have led the way to a great deal of theoretical and experimental work on this topic. The asymmetry of the induced charge leads to a retarding force acting on the particle, i.e., stopping power. At high velocities, the collective response of the medium manifests itself in an oscillatory trailing wake. The energy levels of the incoming ion, modified by the presence of the induced charge are important in the understanding of the resonant-coherent excitation effect at bulk and surfaces, charge states, and X-ray emission of intra-atomic Auger transitions between levels of moving ions in solids. Recent results related to the above for different velocity regimes, both in linear and nonlinear theories, in bulk and surfaces, are discussed.