On the temperature dependence of sputtered cluster yields

The yields of both ionic and neutral clusters sputtered from ion bombarded metal surfaces were determined as a function of the target temperature. For the case of secondary ions emitted from a polycrystalline silver surface u nder 12-keV Xe+ bombardment, a drastic yield enhancement is observed with i ncreasing target temperature. The magnitude of this effect is different for atomic and cluster ions in such a way that the emission of larger cluster ions is favored at higher temperature. In order to elucidate the physical r eason for this behavior, a second set of experiments was per formed in whic h the yields of sputtered neutral clusters and secondary cluster ions have been determined in situ under otherwise identical experimental conditions, the neutral species being post-ionized using pulsed laser photoionization. It is seen that the yields of sputtered neutrals are essentially independen t of the target temperature. The yield enhancement observed for the seconda ry ions must therefore be due to a temperature dependence of the ionization probability characterizing the secondary ion formation process. Possible c auses for this finding are discussed. (C) 2000 Elsevier Science B.V. All ri ghts reserved.