Formation of large clusters during sputtering of silver

Abstract

We have studied the formation of polyatomic clusters during sputtering of metal surfaces by keV ion bombardment. Both positively charged (secondary cluster ions) and neutral clusters have been detected in a time-of-¯ight mass spectrometer under otherwise identical experimental conditions, the sputtered neutrals being post-ionized by single photon absorption using a pulsed 157 nm VUV laser beam. Due to the high achievable laser intensity, the photoionization of all clusters could be saturated, thus enabling a quantitative determination of the respective partial sputtering yields. We ®nd that the relative yield distributions of sputtered clusters are strongly correlated with the total sputtering yield in a way that higher yields lead to higher abundances of large clusters. By using heavy projectile ions (Xe ) in connection with bombarding energies up to 15 keV, we have been able to detect sputtered neutral silver clusters containing up to about 60 atoms. For cluster sizes above 40 atoms, doubly charged species are shown to be produced in the photoionization process with non-negligible eciency. From a direct comparison of secondary neutral and ion yields, the ionization probability of sputtered clusters is determined as a function of the cluster size. It is demonstrated that even the largest silver clusters are still predominantly sputtered as neutrals. Ó

Cluster formation under bombardment with polyatomic projectiles

“…5. Interestingly, an almost linear increase of Y tot with increasing bombarding cluster size is found, which means that ± at a total bombarding energy of 8 keV ± the self-sputtering yield In our previous work on sputtering of silver with monatomic rare gas ions, we have always found a monotonic correlation between the total sputtering yield and the relative abundances of sputtered clusters in such a way that, whenever the sputtering conditions were changed such as to increase the sputtering yield, the relative yields of sputtered clusters were enhanced [15]. From the results presented in Fig.…”

Soft landing of size-selected clusters in rare gas matrices

“…1. These iron clusters were generated by sputtering [17] of a high purity iron target with a 28 keV Xe + beam [6,7,18]. As can be seen in Fig.…”

Bimetallic silver-gold clusters by matrix-assisted laser desorption/ionization

“…However, to achieve these specific goals much information on the physical and chemical properties of the clusters as the function of their composition and size should be gained. Mass spectrometric methods provide a unique experimental tool for the investigation of the electronic and geometric properties of small-size metal clusters [6].In the past decades several methods were explored to induce gas-phase generation of metal clusters, and most of these techniques were based on the evaporation of metals by heating [7,8], or using laser ablation [9 -11] and ion-bombardment [12][13][14][15]. The production and investigation of binary silver-gold [2,16,17] and those of the pure silver [12][13][14]18] and gold clusters [12,13] has been reported by several research groups.…”