Nanowire synthesis with focused ion beams: predictive atomistic simulations on the fabrication of functional nanowire structures

Nanowires (NWs) play an important role as basic components of electronic and photonic devices, such as interconnects or surface-plasmon propagators. Here, theoretical studies are presented on reaction pathways of the CMOS-compatible fabrication of metal silicide or semiconductor nanowires (NWs) by focused ion beam (FIB) implantation and subsequent thermal annealing. On realistic time and length scales, the simulation of the whole process is divided into two steps: (i) The spatio-temporal evolution of FIB implantation profiles is calculated by a new computer code including dynamical target changes, local ion erosion etc. The FIB implantation along a straight trace leads to a local and surface-near supersaturation in the substrate. (ii) Post-implantation annealing causes NW formation by self-organization, which is described theoretically by kinetic Monte Carlo simulations. It is demonstrated that the evolution of the FIB implantation profile proceeds in three well-separated stages: (1) Phase separation by nucleation and growth, (2) NW formation by coalescence of nanoclusters, (3) NW surface smoothening. After this evolution, a NW diameter which is several times smaller than the width of the FIB implantation trace (some tens of nanometers) is found. Likewise, components for functional devices involving several NWs, like T- or X-junctions, can be obtained by crossing different FIB traces.