Effect of the electronic subsystem excitation on the ionisation probability of atoms sputtered from metals by atomic and molecular projectiles

In the present work an effect of excitation of the metal electronic subsystem on the ionisation probability of atoms sputtered under fast ion bombardment has been studied. Atomic and molecular primary ions with the same velocity were used to produce different degrees of the electronic excitations. Information on the ionisation probability was obtained from the kinetic energy distributions of Nb+ and Ta+ ions sputtered from the respective clean Nb and Ta targets by Au-m(-) projectiles (1 less than or equal tom less than or equal to3) with the energy of E-0 = 6 keV per atom. It was found that, as compared with the atomic ion bombardment (m = 1), the molecular one (m = 2,3) leads to the increase of the ionisation probability P-m(+) (P-1(+) < P-2(+) < P-3(+)). Such an effect depends on the kinetic energy E of the secondary ions, increasing with decreasing E. It was shown that the bombardment of metals by the molecular projectiles produces non-additive sputtering of atomic ions, which is determined by the joint action of such two factors as non-additive sputtering of atoms and non-additive process of their charge state formation. The results obtained are discussed in the framework of the model where the charge state formation occurs in electron exchange between sputtered atoms and a local surface area excited by the impact of the projectile. (C) 2001 Elsevier Science B.V. All rights reserved

"total IBA" - Where are we?

The suite of techniques which are available with the small accelerators used for MeV ion beam analysis (IBA) range from broad beams, microbeams or external beams using the various particle and photon spectrometries (including RBS, EBS, ERD, STIM, PIXE, PIGE, NRA and their variants), to tomography and secondary particle spectrometries like MeV-SIMS. These can potentially yield almost everything there is to know about the 3-D elemental composition of types of samples that have always been hard to analyse, given the sensitivity and the spacial resolution of the techniques used. Molecular and chemical information is available in principle with, respectively, MeV-SIMS and high resolution PIXE. However, these techniques separately give only partial information – the secret of “Total IBA” is to find synergies between techniques used simultaneously which efficiently give extra information. We here review how far “Total IBA” can be considered already a reality, and what further needs to be done to realise its full potential