Induction of the surface plasmon resonance from C-incorporated Au catalyst in Si1−xCx nanowires

Abstract

Si_1−xC_x nanowires (NWs) were synthesized by varying the ratio of SiH₄ and CH₃SiH₃ gases using a vapor–liquid–solid (VLS) procedure using Au as a catalyst. The growth rate of the Si_1−xC_x NWs and the change in the wire shape from straight to helical near the Au tip were found to be closely related to the ratio of the CH₃SiH₃ content. The large concentration of C in the Si_1−xC_x NWs was proportional to the CH₃SiH₃ content, overcoming the extremely low solubility of C in Si, resulting in an interstitial incorporation of C atoms in the wire. This incorporation can be attributed to the cleavage of Si–C bonds in the CH₃SiH₃ compound through the Au catalyst (an Au–Si liquid-state cluster of about 70–100 nm) during wire growth by the VLS method. Simultaneously supplying CH₃SiH₃ and SiH₄ gases enhanced the diffusion of Au atoms from the tip to the sidewall of the wire, while also deforming the shape of the Au tip. When the CH₃SiH₃ gas was increased to 1.5 sccm, the number of Au nanoparticles (2–3 nm in size) at the lateral surface induced a surface plasmon resonance (SPR) and improved the optical conductivity (σ) of the Si_1−xC_x NWs. For 2 sccm of CH₃SiH₃, a remarkable increase in the number of C atoms incorporated in the Au nanoparticles along the sidewall red shifted the SPR peak, suggesting that the SPR can be modulated by the Au–C interactions in the nanoparticles.