Modeling of Focused-Ion-Beam-based Synthesis of Nanowire Structures

Reaction pathways of a novel method to fabricate nanowires (NWs) using focused ion beams (FIBs) are presented. This investigation is based on an extension of TRIM simulations to realistic FIB profiles and on kinetic Monte Carlo simulations by which post-implantation phase separation is described. A focused ion implantation along a straight line leads to local supersaturation of the implanted species in the substrate. During post-implantation annealing, NWs embedded in the substrate form along the implantation trace if the ion fluence was sufficiently high. The dominating driving force of NW formation is a free energy gain by phase separation and by reduction of high interface curvatures. During long-term thermal annealing, NWs disintegrate into regular chains of nanoparticles (Rayleigh instability). Thus, regular chains of metallic nanoparticles can be fabricated which are applicable as surface-plasmon-polariton (SPP) waveguides. Even complex structures involving several NWs, e.g. T- or X-junctions, may be obtained. Crossing points, corners and ends of NWs are subject to a preferential disintegration. Thus, structures suitable for single-electron-transistors may be realized where an isolated nanocluster is located in a tunnel distance from several NW contacts. Moreover, multi-gate NW field effect transistors are predicted to form by crossing FIB traces of different ion fluences.