In-beam growth and rearrangement of nanoparticles in insulators induced by high-current negative copper ions

In fabricating metal nanoparticles in insulators, high-current negative ions have been shown to cause efficient and spontaneous growth of nanospheres. The in-beam growth is inevitably subjected to rearrangement of implanted atoms, departing from initially deposited positions. For high-current techniques for insulators, we discuss important experimental factors and explore possible mechanisms of the in-beam growth and atomic rearrangement of nanoparticles, Experimental data of interest are for negative Cu ion implantation at 60 keV into insulators, amorphous(a-), crystalline (c-) SiO2 and a spinel oxide, MgAl2O4. Dose rates ranged up to 260 mu A/cm(2), with a total dose of 3.0 x 10(16) ions/cm(2). Nanoparticle morphology and surface morphology by AFM were significantly dependent not only on dose rate but also on the boundary conditions. With increasing close ratel the in-beam growth of nanoparticles became pronounced and the atomic profile shifted toward the surface. Since beam heating, especially in vacuum, is of concern, thermal analysis was carried out with a one-dimensional simulation code. Candidate mechanisms are depth-oriented gradients of deposited nuclear/electronic energy, chemical/elastic potentials and thermal effects. The relevant mechanisms are explored among these candidates. (C) 2000 Elsevier Science Ltd, All rights reserved.