Inert gas clusters ejected from bursting bubbles during sputtering.

Ar(+)(n) cluster ions (n<or=6) produced during prolonged Ar+ ion surface bombardment of various sample materials at room temperature are shown to result from the ejection of neutral argon clusters following the rupture of high-pressure subsurface gas bubbles. Subsequent ion formation is shown to take place by resonant charge exchange with incident primary Ar+ ions in the gas phase up to at least 175 microm above the surface. Xe+2 clusters are similarly produced from Xe+-bombarded solids. The ion intensities of Ar+2 and Xe+2 are found to have a characteristic second-order dependence on primary Ar+ or Xe+ current density.