Inert Gas Clusters Ejected from Bursting Bubbles during Sputtering

[Formula presented] cluster ions ([Formula presented]) produced during prolonged [Formula presented] 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 [Formula presented] ions in the gas phase up to at least [Formula presented] above the surface. [Formula presented] clusters are similarly produced from [Formula presented]-bombarded solids. The ion intensities of [Formula presented] and [Formula presented] are found to have a characteristic second-order dependence on primary [Formula presented] or [Formula presented] current density.