Reorganization of Langmuir-Blodgett layers of silica nanoparticles induced by the low energy, high fluence ion irradiation

The Langmuir-Blodgett (LB) layers with different selforganization of small, medium, and large size silica nanoparticles, when exposed to the low energy, high fluence ion beam, show reorganization. The reorganization appears as the net effect between the forces caused by charging and by heating of particles, whereas the Coulomb repulsive force between the particles overcomes their adhesion to the Si substrate. The threshold force was estimated for the case of small thermal effects (solid particle on the solid substrate), of higher thermal effects (soft particle on the solid substrate), and of the strong thermal effects (soft particle on the soft substrate), as function of the ion fluence. The increase of fluence causes simultaneous decrease of the Coulomb repulsion and increase of adhesion, so that the mobility of particles decreases affecting the reorganization process. The reorganization depends on the ion fluence, but also on the initial selforganization of the LB layer, being different for the small, medium, and the large size particles. The hydroclusters of small particles become reorganized into "infinite" complex irregular chain-cluster: the small crystal-grains of medium size particles become rhombic and hexagonal clusters, while the 2D hexagonal crystals of large size particles become only slightly disturbed. The reorganization occurs until the increasing ion fluence reaches the reorganization-breakdown-threshold, and overwhelming thermal effects turn the process into particle destruction. (C) 2012 Elsevier B.V. All rights reserved.