Monte Carlo simulation of the implantation profile of e+ in nanochanneled silicon

The process of implantation and diffusion of positron in nanochanneled silicon crystals has been simulated in detail through the Monte Carlo technique. Our implantation simulations evidenced the fraction of empty volume inside the sample to be the decisive factor in the determination of the shape of the implantation profile, with the specific shape of the nanoscopic structure playing a marginal role for implantation processes with an energy above 3 keV. Moreover we observed that, due to the high density of surfaces inside of the silicon sample, the subsequent diffusion process is highly suppressed and that thermalized positrons reach the surface of a nanoscopic channel close to their implantation depth. Due to this suppression of the diffusion process, 60-80% of the positrons implanted at an energy comprised between 4 and 13 keV will reach, at thermal energy, the surface of a channel without escaping the sample or undergoing annihilation.