We study the average charge and the electronic energy loss of the swift (but not relativistic) clusters in a solid A self-consistent average-charge theory for clusters in foils is presented on the basis of the fluid-mechanical model Here the electron stripping rate is evaluated not only for an isolated ion, but also for cluster ions under the same background by taking into account the binding effect of the surrounding ions This theory can elucidate very well not only the reduction of the cluster average charge per ion, but also its cluster-size and foil-thickness dependences of the recent data for the MeV/atom carbon clusters $({\mathrm{C}}_{n})$ in carbon foils The structure dependence is also proposed theoretically In spite of the average-charge reduction, we can reconcile the enhancement of the energy losses of the corresponding clusters The cluster energy losses with the inclusion of the Coulomb explosion by the wave-packet model is in much better agreement with the data at energies of 1--565 MeV/atom Consistent agreement both in the diminution of average charge and in the enhancement of energy loss supports that the charge-state bulk effect is dominant in the cluster average charge

Theory of average charge and energy loss of cluster ions in foils

In this paper is presented for the first time an accurate, physically based simulator for boron, arsenic, and phosphorus ion implantation covering a very wide range of energies from a few keV to several MeV. This wide range of energies, as well as on-axis and off-axis implantations, is covered by a single, comprehensive model. Combined with previously developed models for damage accumulation, this model allows physically-based simulation of 3-D profiles over an extremely wide range of implant conditions.

Modeling of boron, phosphorus, and arsenic implants into single-crystal silicon over a wide energy range (few keV to several MeV)

We calculate the wave-vector and frequency-dependent dielectric matrix of bulk crystals by use of first-principles, all-electron Kohn–Sham states in the integral of the irreducible polarizability in the random phase approximation. From this we determine the macroscopic “head” element, the ( 0 , 0 ) -element, of the inverse matrix (the energy loss function), and integrate over energy and momentum transfers to obtain the electronic energy loss of protons at low velocities. Numerical results are given for hexagonal close packed lithium.

/pdf/electronic-stopping-of-protons-for-lithium-in-the-dielectric-4gb2fl0y44.pdf

Electronic stopping of protons for lithium in the dielectric formulation obtained from first-principles calculations

Based on the three-step model, we theoretically studied the energy distribution of low-energy (less than 50 eV) secondary electrons emitted from highly-oriented pyrolytic graphite (HOPG), induced by the 0.24 MeV/atom carbon-cluster C n + ( n =1,2,4,8) ions. Here we treated the kinetic excitation process of an electron gas, described by the dynamical dielectric function. In the projectile system, we took into account the charge state, the spatial structure of the cluster and the size of the electron cloud on the constituent atoms. The numerical results show that the intensity of energy spectra per carbon ion is less than that induced by a single carbon ion at the equivalent speed. This sub-linear effect was supported by a recent experimental result. We concluded that this effect could be explained to a considerable extent by the screening effect and the vicinage effect of the incident cluster.

Secondary Electron Emission from Graphite Induced by MeV/atom Carbon Cluster Impacts

Impact-parameter-dependent energy loss and straggling at low-energy light-ion scattering

Partial and total electronic stopping cross sections of solids and atoms for protons are estimated by the recently developed wave packet theory and the Lindhard theory. The wavepacket theory presents the one-shell dielectric function for the bound electrons (BE's) in the framework of RPA by adopting the momentum space representation, where the BE's are treated as an interacting electron gas. Numerical estimation of the stoppings are performed over a wide specific energy range, i.e., 1 to 104 keV/amu, on the basis of the independent shell model. The oscillatory behavior of the stopping cross sections are also shown with respect to target atomic number. The calculated results are in good agreement with the data.



Es werden die partiellen und totalen elektronischen Bremsquerschnitte von Festkorpern und Atomen fur Protonen mittels der kurzlich entwickelten Wellenpakettheorie und der Theorie von Lindhard berechnet. Durch Benutzung der Impulsraumdarstellung im Rahmen der RPA liefert die Wellenpunkttheorie die Ein-Schalen-Dielektrische Funktion fur gebundene Elektronen (BE), wobei die BE als wechselwirkendes Elektronengas behandelt werden. Eine numerische Berechnung der Bremsquerschnitte wird uber einen breiten spezifischen Energiebereich, d. h. 1 bis 104 keV/amu auf der Grundlage des unabhangigen Schalenmodells durchgefuhrt. Das oszillatorische Verhalten der Bremsquerschnitte wird auch bezuglich der Atomzahl des Targets gezeigt. Die berechneten Ergebnisse sind in guter Ubereinstimmung mit den Werten.

T. Kaneko

Papers

Partial and Total Electronic Stoppings of Solids and Atoms for Energetic Ions