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

Abstract

The phonon confinement and self-limiting oxidation effects of silicon nanowires ͑SiNWs͒ synthesized by laser ablation were investigated. The size of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs' surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement, while excess oxidation causes an upshift due to compressive stress. The compressive stress retarded the oxidation of the SiNWs by self-limiting oxidation effect. This result shows that the Si core diameter can be controlled by compressive stress.

Impurity Doping in Silicon Nanowires

“…They were carried out at 4.2 K using an X-band ESR spectrometer with a magnetic-field modulation of 100 kHz. Figure 3b shows typical results of ESR measurements for P-doped and undoped SiNWs synthesized using Si 90 (Ni 2 P) 10 and Si 99 Ni 1 targets, respectively. The ESR signal observed for P-doped SiNWs is deconvoluted to at least two components, with g-values of 1.998 and 2.005-2.006, while no component with a g-value of 1.998 was observed for undoped SiNWs.…”

“…This can be explained by the phonon confinement effect. [8][9][10] Finite-size effects or disorder can partially relax momentum conservation, and as a result the Raman selection rule is relaxed. This gives a downshift and an asymmetric broadening of the Si optical phonon peak.…”

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

“…The excitation power was set at about 0.02 mW to avoid local heating effects from the excitation laser. 13,14 ESR measurements were carried out at 4.2 K using an X-band ESR spectrometer with a magnetic field modulation of 100 kHz to investigate the state of P donors and defects in the SiNWs. Scanning transmission electron microscopy ͑STEM͒ ͑Hita-chi, S-5500, 30 kV͒ and transmission electron microscopy ͑TEM͒ ͑JEOL, JEM3100FEF: 300 kV͒ were used to observe the SiNWs and to investigate the details of their structures.…”

Raman Spectroscopy on Semiconductor Nanowires

“…For nanoscale object such as nanocrystals or nanowires, the exact shape of the Raman peak becomes a convolution of the dispersion relation of phonons in the material (Richter et al, 1981;Campbell et al, 1986). Such effect was initially observed in nanocrystals and more recently in nanowires (Fauchet et al, 1988;Adu et al, 2006a;Jalilian et al, 2006;Fukata et al, 2006). In the particular case of nanowires, the confinement occurs in the diameter direction.…”