Modeling of the impurity-induced silicon nanocone growth by low energy helium plasma irradiation

Abstract

The formation mechanism of nanocone structure on silicon (Si) surface irradiated by helium plasma has been investigated by experiments and simulations. Impurity (molybdenum) aggregated as shields on Si was found to be a key factor to form a high density of nanocone in our previous study. Here to concrete this theory, a simulation work has been developed with SURO code based on the impurity concentration measurement of the nanocones by using electron dispersive x-ray spectroscopy. The formation process of the nanocone from a flat surface was presented. The modeling structure under an inclining ion incident direction was in good agreement with the experimental result. Moreover, the redeposition effect was proposed as another important process of nanocone formation based on results from the comparison of the cone diameter and sputtering yield between cases with and without the redeposition effect.

The dependence of Mo ratio on the formation of uniform black silicon by helium plasma irradiation

“…The high density of Mo observed at the tip of the cone (figure 7) was considered as the shield formed initially and caused the formation of nanocone due to the preferential sputtering. Moreover, a numerical study demonstrated the formation of nanocones based on this shielding effect [30].…”

“…Considering that the He ion energy (40 eV) on Si sample was too small to sputter Mo, the redeposition of Mo can be ignored. A Monte-Carlo simulation of Si nanocone formation based on the shielding effect model has been conducted in our recent work [30]. Sputtered Si atoms could be traced after they were sputtered by He ions until the Si atoms are redeposited on the surface or leave the simulation region.…”

Germanium nanostructures by helium plasma irradiation

“…30) It was revealed from the energy dispersive X-ray (EDX) mapping of the nanocones of chromium and Si that small amounts of deposition of metal such as molybdenum (Mo) are the seed (tip) and sputtering led to the nanocones. 4,34) It should be noted that sputtering plays a major role rather than deposition in this process; the process is completely different from chemical vapor deposition, where metal catalysts are the seed for nanowires. Although the sputtering yield of the sample holder (tantalum and molybdenum) is much lower than that of Ge, we cannot neglect that the small amounts of sputtering from the sample holder deposit and lead to the formation of nanocones.…”

“…Rather, in addition to adatom diffusion, 30) a small amount of impurity deposition formed clusters on the surface and started to form protrusion, leading to the nanocones. 34) Thompson et al performed He plasma irradiation on Ge, which has a bandgap of ∼0.7 eV, at low incident ion energies (<36 eV). 30) Pyramidal structures and nanocones were grown on the surface exposed to He plasma.…”