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 μA/cm², with a total dose of 3.0 × 10¹⁶ ions/cm². Nanoparticle morphology and surface morphology by AFM were significantly dependent not only on dose rate but also on the boundary conditions. With increasing dose rate, 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.