Predictions on ion-assisted synthesis of functional 1D-nanostructures using atomistic computer simulations

Nanowires (NWs) and chains of nanocrystals (NCs) embedded in dielectrics or semiconductors are intensively studied for applications in photonics and nanoelectronics. CoSi2 NWs and NC chains are of particular interest for photonic functionalities of system-on-a-chip architectures because of their full CMOS compatibility, the low damping of surface plasmons at the CoSi2-Si interface, and the transparency of Si at the plasmon frequency. Here, we present predictions of atomistic computer simulations which describe the ion beam synthesis of CoSi2 NWs in Si and their thermally activated decay into chains of CoSi2 NCs. The simulations on focused ion beam (FIB) Co implantation is based on the binary collision codes TRIDYN and TRIM incorporating a convolution over the few tens of nanometer beam profile. The resulting 3D implantation profile serves as input for kinetic lattice Monte-Carlo simulations by means of which nucleation and growth of CoSi2 precipitates and their coalescence into a CoSi2 NW are predicted. From an evolutionary viewpoint, NW synthesis proceeds on a shorter time scale than its decay. The NW decay into a NC chain (“Rayleigh instability”) is driven by the minimization of interfacial free energy. Moreover, we demonstrate that the orientation of the Co implantation profile to the single crystalline Si matrix strongly influences the stability of the synthesized CoSi2 NW. Since the system energetically favors the coherent CoSi2(111)/Si(111) interface, driving faceting forces may occur which accelerate the NW decay into a NC chain for FIB implantation not aligned with the Si-[110] orientation. Thus, intentional misalignment between the focused Co ion beam and the Si substrate is suggested as way to a controlled decay of the ion beam synthesized CoSi2 NW into a chain of monodisperse and equidistant CoSi2 NCs.