Thermal effects in the Raman scattering of vertically-aligned silicon nanowire arrays as investigated by fluence-dependent measurements
We report on the thermal effects on the Raman scattering of vertically-aligned silicon nanowires (Si NWs) as investigated by fluence-dependent micro-Raman spectroscopy. The Si NWs were grown on p-type Si(100) substrates through electroless metal-assisted chemical etching using an electrolyte composed of hydrofluoric acid and silver nitrate. The Si NWs have a nominal length of 10 μm and nominal width of 100 nm. Fluence-dependent measurements showed that at low laser fluence, the Si NWs exhibit bulk-like features as shown by the 519 cm-1 peak associated with the degenerate longitudinal/transverse optical phonon (LTO) mode. A second broad and downshifted peak at 488-510 cm-1 emerged at high fluences due to the Raman scattering from the array of laser-heated Si NWs. The presence of the two peaks indicated the formation of a thermal gradient across the NWs. The temperature of the Si NWs at the beam spot was also measured through fluence-dependent measurements. The results suggest that Raman spectroscopy is a viable technique to analyze the thermal properties of a material.