ABSTRACT
260A group of atoms bound together by interatomic forces is called an atomic cluster. Clusters are formed of matter intermediation between atoms (or molecules) and the solids. The novelty of atomic cluster physics arises mostly from the fact that cluster properties explain the transition from single atoms or molecules to the solid state. Modern experimental techniques have made it possible to study this transition. Cluster emission phenomena are of scientific and technological interest because of the potential of clusters to form materials with new chemical and physical properties. Consequently, it is important to get high intensity of different cluster flux for their investigations and interactions with matters. The most widely used method of clusters production is the adiabatic expansion of a gas or a vapor through a small nozzle into vacuum. The method of laser evaporation is used very often as well. Clusters from solids can be easily obtained by sputtering surfaces using depositing energy through ions, electrons, or photons onto a surface. In the present work, emission of clusters during ion bombardment of surfaces is investigated. Now the volume of researches on studying the mechanism of formation of clusters is significant and continues to grow, but for a while, an overview of the processes resulting in emission clusters at ion sputtering of surfaces is absent. Especially, it is complicated to determinate the mechanism of emission of positive and negative clusters and their excited states, and despite the multitude of works that are represented in this direction, till now there is no certain view toward process of formation of a charge and exited states of cluster. Investigation of dissociation processes of atomic clusters in different states during production and emission is also very important. With this purpose in the present work, sputtering of various surfaces in a wide range of energy bombardment by various primary ions under different bombarding conditions is presented in experimental investigations of cluster ions emission due to the experimental difficulties encountered in the analysis of sputtered neutral particles.
In the present work, measurements of the negative and positive cluster ions yields from C, NaCl, Mg, Al, Si, S, Ti, and GaAs surfaces under 0.5-50 keV N+, O+, N2 +, O2 +, Ar+ bombardment at different experimental conditions are reported. Cluster ions yields are investigated depending on number of atoms in cluster at different conditions of experimental researches. The emission of small (n < 10), “light” clusters occurs by a collective motion during the development of the collision cascade after impact. Energy transferred to the surface is strongly directional and can lead to the simultaneous emission of a group of neighboring surface atoms, which in some cases will remain bounded and form a cluster after emission.
