SELF-ASSEMBLED NANO-PATTERNS BY GAS CLUSTER ION BEAM BOMBARDMENT
Tilakaratne, Buddhi 1979-
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Morphological evolution of surfaces during the course of off-normal cluster ion beam bombardment is investigated. The objective is to realize the Ar cluster ion-induced self-assembled ripple shaped nano-pattern formation process on Si and Au surfaces. During cluster ion beam bombardment, surface atoms undergo three processes: (1) continuous sputtering into the vacuum due to high energy collisions, (2) initial re-deposition of atoms, and (3) surface diffusion of atoms. The first process is an independent of applied dosage, thus carries a minimum impact on nano-ripple pattern formation. In the second process, atoms deposit close to the collision site, which acts as a barrier for the next set of sputtering atoms. Even though this starts to develop ripples, ripples become well-ordered and grow due to surface diffusion and upstream sputtering of atoms. This investigation reveals that cluster ion-induced nano-ripple formation saturates comparatively sooner than that induced by monomer ions. Continuous bombardment creates sand dune-like nano-structures on the Si surfaces at 60o angle of incidence measured from the surface normal. However, at a grazing incidence, surface becomes smooth. Further investigation on Au surfaces conform the above mentioned three-step process of nano-ripple formation. Additionally, it was found that these nano-rippled surfaces show anisotropic properties, which are useful in directional surface wetting and surface plasmonic applications.