Raman scattering of individual silicon nanowires made by metal-assisted chemical etching

D. Ratchford, J. Yeom, J.P. Long, P.E. Pehrsson
Naval Research Laboratory, US

Keywords: Raman spectroscopy, silicon nanowires

Summary:

The combination of nanosphere lithography with metal-assisted chemical etching (MACE) allows for cheap and scalable production of vast arrays of vertically aligned silicon nanowires (SiNWs). The large-scale surface coverage, large surface-to-volume ratio, and ability to functionalize the vertically aligned arrays of SiNWs makes them well suited to optical, chemical, and biological sensing applications. Utilizing confocal Raman spectroscopy, we characterize MACE-SiNWs of various diameters, heights, and pitch. We examine the Raman enhancement and investigate the role of surface roughness, localized porosity induced by the MACE process, and ensemble effects on heating in individual SiNWs and in SiNW arrays. The Raman enhancement is measured along the length of vertical SiNWs of varying lengths while they are still attached at one end to the starting wafer substrate. These results are compared to other nanowires which have been harvested from the original wafer substrate and deposited horizontally onto other materials with varying thermal conductivities. Finite element calculations are used to model heat flow in the nanowires and the predictions are compared to the experimental results. These results will provide insight into heat flow in nanowires of different diameters, as needed for example, in a SiNW sensor regenerated by Joule heating.