Sputtering of Group-IIIa elements. Properties of the metal cluster formation mechanism

Abstract Neutral and positively charged clusters have been produced by 4 keV argon ion bombardment of liquid gallium and the liquid gallium-indium eutectic alloy. The yields, kinetic energy distributions, and the abundance distributions have been studied by time-of-flight mass spectrometry coupled with single photon post-ionization of the neutrals. The results are compared to experimental data on cluster sputtering from polycrystalline aluminum and indium previously obtained in our laboratory. The abundance distributions of the neutral and ionic mixed gallium-indium clusters with equal number of atoms are found to be statistical. Since the first atomic layer of the gallium-indium system is labeled due to surface segregation, the depth of origin of these clusters becomes experimental assessable. An increasing depth of origin was found for increasing cluster size. While 94% of the sputtered atoms originate from the first atomic layer, only 68% of the atoms comprising clusters containing eight atoms come from this outermost layer. A comparison of the relative yields and kinetic energy distributions for clusters sputtered from the alloy and from the two pure constituents indicates that these parameters are not controlled by the first atomic layer (indium rich) but by the bulk (gallium rich) . The kinetic energies of neutral clusters sputtered from pure aluminum, gallium and indium reveal a correlation between this property and the binding energies of the materials. The mean kinetic energy of the clusters is largest for aluminum followed by gallium and indium. The relative cluster yields decrease with increasing cluster size, the slope of which is least for indium, followed by gallium and aluminum.