Stopping Cross Sections For Ions Research Articles

Electronic energy-loss mechanisms for H, He, and Ne in TiN

The specific energy loss of medium-energy hydrogen, helium, and neon ions in titanium nitride is studied. Electronic stopping cross sections of ions in the energy range of 3--140 keV/amu were measured in backscattering geometry using time-of-flight medium-energy ion scattering, from the energy loss experienced in TiN thin films on Si. For the lowest energies, data for H show a strong deviation from Bragg's rule. For hydrogen and Ne ions, electronic stopping exhibits velocity proportionality at ion velocities below 1 a.u. Comparison to density functional theory calculations of the stopping power yields very good agreement for H, while for He and Ne, the experimentally observed electronic stopping power is considerably higher than predicted. For He the extrapolation of the stopping power at low energies points to a nonvanishing energy loss at vanishing ion velocity. The present data can thus be taken as an indication of additional energy-loss processes different from direct electron-hole pair excitation. Furthermore, the results provide reference values for ion-beam-based analysis of TiN, a material with huge technological relevance.

Coupled-channel calculations of the electronic energy loss

A review is given on the use of the coupled-channel method to calculate the electronic energy loss of ions penetrating matter. This first principle calculation, based on an expansion of the time-dependent electronic wave function in terms of atomic orbitals, has been applied to evaluate the impact parameter and angular dependence of the electronic energy loss and the stopping cross-section of ions (antiprotons, H and He) colliding with H and He atoms at energies of 1–500 keV/amu. The results are compared to experimental data as well as to others current energy-loss models.

Four-parameter formulae for the electronic stopping cross section of low energy ions in solids

A set of four parameter formulae of the electronic stopping cross section is provided for use in the prediction of electronic stopping cross sections of ions in various solids in the low energy range, 0.25 keV/amu < E/ m 1, ≤ 200 keV/amu. The parameters, a, b, a and E 0 in the formulae are determined. The formulae can be used not only to describe the experimental Z 1 and Z 2 oscillations of electronic stopping powers but also to satisfactorily describe the dependence of the electronic stopping cross section, S e, on ion energy E.

Non-evidence forZ1oscillations of the nuclear ion-atom interaction in an amorphous target

Abstract Periodic variations in the Z 1 dependence of the interatomic potential has recently bevlen revealed by a channeling technique. To search for oscillations of similar kind in a target of randomly arranged atoms we have made systematic measurements on the scattering distributions of energetic (32–56 keV) ions in amorphous carbon. Our technique was to transmit light mass ions through carbon foils with a thickness of 2–4 μg/cm2. The atomic number of the ions, Z, ranged from 3 to 18. The scattering distribution of the transmitted particles was recorded. From these curves the angular halfwidth,ψ 1/2, and the relative intensity at a scattering angle 2.5 times ψ 1/2 was determined. The experimental values are in good agreement with theoretical calculations based on the Thomas-Fermi and Lenz- Jensen potentials. Furthermore, the saturation value of the mean nuclear stopping cross sections for ions scattered in the straight forward direction with a mean energy of 50 keV are given. No evidence for a Z 1 oscil...

Structure effects in low-energy electronic stopping

Recent experiments have shown electronic stopping cross-sections to have an oscillatory dependence on ionic atomic numbers with minima in the region of Li, Na and Cu. The amplitudes of the oscillations are enhanced when the ions are channelled. To explain these effects we have modified the Firsov theory of electronic stopping by replacing the Thomas-Fermi atom with simple Hartree-Fock wave functions, thus allowing for the different ionic sizes. Theoretical predictions are made for the stopping cross-sections of ions in amorphous carbon and of channelled ions in silicon.