Interfacial reaction-dominated full oxidation of 5 nm diameter silicon nanowires

Abstract

Silver catalyzed ultrathin silicon nanowires grown by low-temperature chemical-vapor-deposition J. Appl. Phys. 107, 096105 (2010); 10.1063/1.3393601Study of the effect of gas pressure and catalyst droplets number density on silicon nanowires growth, tapering, and gold coverage While almost all Si nanostructures, including Si nanowires (SiNWs), Si nanocrystals, and Si nanotrench-like structures on a supra-or sub-10 nm scale exhibit self-limiting oxidative behavior, herein we report full oxidation of SiNWs 5 nm in diameter. We investigated the oxidative behavior of SiNWs with diameters of 5 nm and compared our findings with those for SiNWs with diameters of 30 nm. Single-crystalline SiNWs 5 and 30 nm in diameter were grown by a chemical vapor deposition (CVD) process using Ti as a catalyst. The SiNWs were then oxidized at 600-1000 C for 30 min to 240 min in O 2 . The thicknesses of the resulting oxide layers were determined by transmission electron microscopy (TEM). As expected, the SiNWs 30 nm in underwent self-limiting oxidation that was parabolic in nature. However, under the same conditions, the SiNWs 5 nm in diameter underwent full oxidation that was linear in nature. Atomic-scale molecular dynamic simulations revealed that the compressive stress in the oxide layer, which is generated owing to the increase in the volume of the oxide formed, decreased in the case of the SiNWs 5 nm in diameter. It is likely that this decrease in the compressive stress results in a lowering of the energy barrier for the diffusion of oxygen into the oxide layer, leading to the full oxidation of the SiNWs 5 nm in diameter. It is also responsible for the oxidation in the case of SiNWs 5 nm in diameter being interfacial reaction-dominated as opposed to the diffusion dominated-oxidation typical for SiNWs. V C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4764004] 094308-2 Kim et al.

Stress evolution during the oxidation of silicon nanowires in the sub-10 nm diameter regime

“…Consequently, the thinner Si-NWs will be readily oxidized under the same driving force of oxidation, leading to full oxidation, as observed in the sub-10 nm Si-NWs. [10][11][12]14 In summary, the present MD simulation showed that the residual stress decreased with increasing curvature in the sub-10 nm regime of the diameter. In this regime, the unoxidized Si core of the thinner Si-NWs deformed more to compensate for the volume expansion of the surface oxide layer, resulting in the smaller compressive stress.…”

“…[2][3][4][5][6][7][8][9][10][11][12][13] However, recent experimental work with Si-NWs with diameters of approximately 10 nm reported full oxidation of the NWs. [10][11][12][13][14] These experimental observations are puzzling from the viewpoint of the previous theoretical model that the self-limiting oxidation is caused by the interfacial compressive stress which is proportional to the curvature of NWs. [7][8][9] The theoretical analysis would imply that the oxidation is extremely limited or totally suppressed in very thin Si-NWs.…”