Formation of sputtered silver clusters under bombardment with SF5+ ions

The formation of Agn clusters and Agn+ cluster ions under bombardment of a silver surface with SF5+ and Xe+ projectile ions was investigated experimentally. In order to obtain information about the relative abundance of clusters among the flux of sputtered particles independent of their charge state, mass spectra of both secondary ions and sputtered neutral particles were recorded. The neutral species were post-ionized prior to mass analysis by means of photo-ionization using an intense UV laser at a wavelength of 193 nm. It is found that measured Agn+ signals increase significantly if SF5+ projectiles are used instead of rare gas (Ar+ or Xe+) ions of the same kinetic impact energy. The signals of neutral Ag atoms and Agn clusters, on the other hand, exhibit only a relatively small increase, thus indicating that the enhancement observed for the secondary ions is predominantly caused by an increased ionization probability of sputtered particles under SF5+ bombardment rather than by enhanced partial sputtering yields. While the transition from Ar+ to Xe+ projectiles leads to a drastic increase of the relative abundance of larger clusters in the spectrum, practically no such effect can be detected for the transition from Ar+ to SF5+. This finding shows that the use of polyatomic SF5 projectiles does not lead to a higher efficiency in producing sputtered clusters