P.L. Grande

Improved charge-state formulas

Abstract A large set of experimental charge-state distributions is analyzed in this work. Two fit formulas are presented for mean equilibrium charge states of projectiles ranging from protons to uranium. One formula is given for all ions in gas targets and another one for solid targets. The deviation from the experimental data is reduced by roughly a factor of two in comparison with the widely used formula by Nikolaev and Dmitriev as well as with the Bohr stripping criterion as revised by Northcliffe. Finally, the influence of the projectile charge state on the prediction of stopping powers for fast projectiles in carbon is shown and comparison is made with experimental energy-loss data.

Range parameters study of medium-heavy ions implanted into light substrates

Abstract Carbon films were implanted with Cs, Xe, Sn, Rb, Kr, Ga and Cu and boron films with Bi, Pb, Au, Yb, Cs and Rb ions in an energy range of 10 to 300 keV. Range parameters were determined using the Rutherford backscattering technique. The experimental results are 20–40% higher than the theoretical predictions by Ziegler, Biersack and Littmark. Good agreement is achieved only when inelastic effects are included in the nuclear stopping regime. These features are also observed when previously published range parameter data for medium-heavy ions implanted into Be films are analyzed.

A unitary convolution approximation for the impact-parameter dependent electronic energy loss

Abstract In this work, we propose a simple method to calculate the impact-parameter dependence of the electronic energy loss of bare ions for all impact parameters. This perturbative convolution approximation (PCA) is based on first-order perturbation theory, and thus, it is only valid for fast particles with low projectile charges. Using Blochs stopping-power result and a simple scaling, we get rid of the restriction to low charge states and derive the unitary convolution approximation (UCA). Results of the UCA are then compared with full quantum-mechanical coupled-channel calculations for the impact-parameter dependent electronic energy loss.

Femtosecond dynamics: snapshots of the early ion-track evolution

The energy dissipation and femtosecond dynamics due to fast heavy ions in matter is critically reviewed with emphasis on possible mechanisms that lead to materials modifications. Starting from a discussion of the initial electronic energy-deposition processes, three basic mechanisms for the conversion of electronic into atomic energy are investigated by means of Auger-electron spectroscopy. Results for amorphous Si, amorphous C and polypropylene are presented and discussed. Experimental evidence for a highly charged track region as well as for hot electrons inside tracks is shown. As follows mainly from Auger-electron spectroscopy, there are strong indications for different track-production mechanisms in different

Energy dissipation of fast heavy ions in matter

Abstract The energy dissipation due to fast heavy ions in matter is critically reviewed with emphasis on possible mechanisms that lead to material modifications. Starting from a discussion of the initial electronic energy-deposition processes, three basic mechanisms for the conversion of electronic into atomic energy are investigated. Experimental evidence for a highly charged track region as well as for hot electrons inside tracks is presented. As follows mainly from Auger-electron spectroscopy, there are strong indications for different track-production mechanisms in different materials.

Electronic stopping power of 〈100〉 axial-channelled He ions in Si crystals

Abstract Measurements of the electronic stopping power of He2+ ions along the 〈100〉 direction in Si crystal with energies ranging between 200 keV and 4.5 MeV are presented. The Rutherford backscattering technique has been used with SIMOX samples consisting of a Si single-crystal layer on top of a buried layer of 500 nm SiO2 built into a Si 〈100〉 wafer.

The unitary convolution approximation for heavy ions

The convolution approximation for the impact-parameter dependent energy loss is reviewed with emphasis on the determination of the stopping force for heavy projectiles. In this method, the energy loss in different impact-parameter regions is well determined and interpolated smoothly. The physical inputs of the model are the projectile-screening function (in the case of dressed ions), the electron density and oscillators strengths of the target atoms. Moreover, the convolution approximation, in the perturbative mode (called PCA), yields remarkable agreement with full semi-classical-approximation (SCA) results for bare as well as for screened ions at all impact parameters. In the unitary mode (called UCA), the method contains some higher-order effects (yielding in some cases rather good agreement with full coupled-channel calculations) and approaches the classical regime similar as the Bohr model for large perturbations (Z/v≫1). The results are then used to compare with experimental values of the non-equilibrium stopping force as a function of the projectile charge as well as with the equilibrium energy loss under non-aligned and channeling conditions.

Auger electrons from ion tracks

Abstract The target KVV Auger electron emission has been investigated experimentally and theoretically for heavy-ion irradiation of amorphous carbon at an ion velocity of 14.1 a.u. (5 MeV/u). We extend previous investigations of multiple ionization and electronic nuclear-track temperatures to a large variety of charged projectiles, covering electrons to uranium ions. Experimental data are compared with non-pertubative calculations of multiple ionization and with results of two thermal-spike models.

Impact-parameter dependent energy loss of screened ions

Abstract We describe a simple model for the electronic energy loss as a function of the impact parameter for screened projectiles at high velocities. The physical inputs are the projectile screening potential, the electronic density and the oscillators strengths for the target electrons. An excellent agreement with full first-order Born calculations is obtained. The results are then used to compute the angular dependence of the electronic energy loss under channeling conditions.

Characterization of nanoparticles through medium-energy ion scattering

In this work we review the use of the medium-energy ion scattering (MEIS) technique to characterize nanostructures at the surface of a substrate. We discuss here how the determination of shape and size distribution of the nanoparticles is influenced by the energy loss at the backscattering collision, which leads to an asymmetrical energy-loss line shape. We show that the use of a Gaussian line shape may lead to important misinterpretations of a MEIS spectrum for nanoparticles smaller than 5 nm. The results are compared to measurements of gold nanoparticles adsorbed on a multilayered film of weak polyelectrolyte.