Phonon confinement effect of silicon nanowires synthesized by laser ablation

Abstract

A gradual downshift and asymmetric broadening of the Si optical phonon peak were observed by Raman scattering measurements of continuously thermally oxidized silicon nanowires ͑SiNWs͒ synthesized by laser ablation. This downshift and broadening can be interpreted by the phonon confinement effect. Further thermal oxidation produced a reverse change; namely, an upshift of the optical phonon peak. This is considered to be due to compressive stress since this stress was relieved by removing the oxide layers formed around the SiNW cores, resulting in a downshift of the optical phonon peak.

Codoping of boron and phosphorus in silicon nanowires synthesized by laser ablation

“…The details of these laser ablation procedures are reported in Ref. 11. SiNWs were directly deposited on a SiO 2 substrate for micro-Raman scattering measurements.…”

Phonon confinement and self-limiting oxidation effect of silicon nanowires synthesized by laser ablation

“…This can be explained by the increase in the compressive stress toward the center of the SiNWs, arising from the expansion of the surrounding surface oxide layer. 10 The upshift of the Si optical phonon peak of the 1000°C SiNWs was observed from lower oxidation temperatures than that seen in 1200°C SiNWs, as shown in Fig. 5.…”

“…The downshift is due to phonon confinement, while the upshift is caused by the increased compressive stress due to the progress of surface oxidation. 10,21 The optical phonon peak of the 1000°C SiNWs before and after thermal oxidation at 700°C showed a lower shift than that seen in 1200°C SiNWs. Furthermore, the upshift of the Si optical phonon peak of the 1000°C SiNWs was observed from lower oxidation temperatures than 1200°C SiNWs.…”

“…20 More recently, we have also investigated the phonon confinement effect of continuously thermally oxidized SiNWs. 10,21 Thermal oxidation of the SiNWs clearly resulted in a gradual downshift and broadening of the Si optical phonon peak as a result of a stepwise decrease in the diameter of the SiNWs. Furthermore, excess oxidation produced an opposite change to the phonon confinement effect; namely, an upshift of the Si optical phonon peak due to compressive stress.…”

“…6 In order to realize the above-mentioned applications, it is important to investigate size control and the quantum size effects that vary with their diameters. Generally, SiNWs are synthesized by laser ablation [7][8][9][10] or chemical vapor deposition ͑CVD͒. 11,12 In the latter case, the diameter can be controlled by the size of the metal catalyst particles which are placed in advance.…”