A microscopic view of secondary ion formation

a b s t r a c t The formation of secondary ions in sputtering is described by combining classical molecular dynamics of the particle kinetics with simple analytical treatments modeling the transfer of kinetic into electronic excitation energy, the transport of excitation away from the point of its generation and the charge transfer between the solid and a sputtered particle. For the simplest case of a metal atom sputtered from a clean metal surface, the predictions of such a model are used to answer a few fundamental questions regarding the ion formation process. The results indicate that the transient local excitation of the bombarded solid plays a dominant role in determining the charge state of a sputtered atom. Moreover, we find that the assumption of a sputtered particle being emitted from an ideal, undisturbed surface with a constant emission velocity -a picture which forms the physical basis of nearly all published secondary ion formation models -is not generally justified

Creation of multiple nanodots by single ions

In the challenging search for tools that are able to modify surfaces on the nanometer scale, heavy ions with energies of several 10 MeV are becoming more and more attractive. In contrast to slow ions where nuclear stopping is important and the energy is dissipated into a large volume in the crystal, in the high energy regime the stopping is due to electronic excitations only. Because of the extremely local (< 1 nm) energy deposition with densities of up to 10E19 W/cm^2, nanoscaled hillocks can be created under normal incidence. Usually, each nanodot is due to the impact of a single ion and the dots are randomly distributed. We demonstrate that multiple periodically spaced dots separated by a few 10 nanometers can be created by a single ion if the sample is irradiated under grazing angles of incidence. By varying this angle the number of dots can be controlled.Comment: 12 pages, 6 figure

Molecular dynamics simulations of non-equilibrium systems

Peer reviewe

Darstellung 2- und 3-dimensionaler Stroemungen

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Computer simulation of internal electron emission in ion-bombarded metals

a b s t r a c t We present a computer simulation study of internal electron emission in ion-bombarded metal-insulator-metal (MIM) junctions. The computational approach consists of (i) a molecular dynamics part describing the particle kinetics upon projectile impact, (ii) the computation of kinetic electronic excitation as well as its transport and (iii) a thermionic model to calculate the flux of electrons from the top electrode to the bottom electrode of the MIM. The results are compared to recent experiments and discussed in terms of different transport models for the description of hot electron propagation in metals

Swift heavy ion irradiation of SrTiO3 under grazing incidence

International audienceThe irradiation of SrTiO3 single crystals with swift heavy ions leads to modifications of the surface. The details of the morphology of these modifications depend strongly on the angle of incidence and can be characterized by atomic force microscopy. At glancing angles, discontinuous chains of nanosized hillocks appear on the surface. From the variation of the length of the chains with the angle of incidence the latent track radius can be determined. This radius is material specific and allows the calculation of the electron– phonon coupling constant for SrTiO3. We show that a theoretical description of the nanodot creation is possible within a two-temperature model if the spatial electron density is taken into account. The appearance of discontinuous features can be explained easily within this model, but it turns out that the electronic excitation dissipates on a femtosecond timescale, too rapidly to feed sufficient energy into the phonon system in order to induce a thermal melting process. We demonstrate that this can be solved if a temperature-dependent diffusion coefficient is introduced into the model

Calculation of electronic stopping power along glancing swift heavy ion tracks in perovskites using ab initio electron density data

In recent experiments the irradiation of insulators of perovskite type with swift (E ~ 100 MeV) heavy ions under glancing incidence has been shown to provide a unique means to generate periodically arranged nanodots at the surface. The physical origin of these patterns has been suggested as stemming from a highly anisotropic electron density distribution within the bulk. In order to show the relevance of the electron density distribution of the target we present a model calculation for the system Xe23+ →SrTiO3 that is known to produce the aforementioned surface modifications. On the basis of the Lindhard model of electronic stopping, we employ highly-resolved ab initio electron density data to describe the conversion of kinetic energy into excitation energy along the ion track. The primary particle dynamics are obtained via integration of the Newtonian equations of motion that are governed by a space- and time-dependent frictional force originating from Lindhard stopping. The analysis of the local electronic stopping power along the ion track reveals a pronounced periodic structure. The periodicity length varies strongly with the particular choice of the polar angle of incidence and is directly correlated to the experimentally observed formation of periodic nanodots at insulator surfaces. (Some figures in this article are in colour only in the electronic version