Energy distributions of sputtered particles

Abstract

A study was made of the ionised and neutral particles sputtered from a range of mono- and poly-crystalline targets by an argon ion beam of energy 10 keV under high vacuum conditions. A novel energy-mass analysis system with high angular resolution for ions of energy up to 500 eV, together with the ancillary mechanical and electrical equipment was designed. This was used to measure the angular and energy distributions of ions sputtered from mono- and poly-crystalline specimens in directions at right angles to the incident beam. For polycrystalline targets a near cosine distribution was established for this geometry. The energy spectrum for most materials in the high energy regime was a function of (energy) n , with 1.2 < n < 1.5. The previously reported cusp structure in the spectra was verified and shown to depend upon the target structure and orientation. By comparison with a randomly chosen direction some energy dependent processes apply to the Cu⁺ ions from the <110> and <100> directions in copper targets. A characteristic energy of 56 ± 2 eV and 200 ± 20 eV can be associated with these two directions and which compares favourably with the simple and assisted focusing values of 50 ± 10 eV and 300 ± 50 eV for copper previously measured for the sputtered neutral particles. The molecular ions Cu₂⁺ and Cu₃⁺ do not show such energy dependencies. Similar angular and energy measurements have been made for gold and germanium targets. An electron bombardment ioniser was adapted to the apparatus and preliminary measurements on sputtered neutral atoms have been made. A novel method of suppressing most of the ions formed in the ambient gas was developed. A numerical fast Fourier transform method was used to deconvolute the measured spectrum. The near-head-on collision theory of sputter spot formation was extended to include those atoms from the next-to-surface atomic layer and it was shown that these particles make a substantial contribution to the total sputtered. Show more