Surface-Enhanced Raman Spectroscopy Using Self-Assembled Silver Nanoparticles on Silicon Nanotips

A new substrate for surface-enhanced Raman spectroscopy has been developed in the form of silicon nanotips, by electron cyclotron resonance plasma chemical vapor deposition, with apex diameters of ∼2 nm, lengths of 1000 nm, and densities of 10 11 /cm 2 . The surface areas of the nanotips are ∼150 m 2 cm - 3, comparable with the best-quality porous silicon. Ion-beam-sputtered silver self-assembles on these substrates as nanoparticles of 4−10 nm diameter and these metallic nanoparticles act as surface enhancement centers for Raman spectroscopy. Standard molecules such as Rhodamine 6G and trans -1,2-bis(4-pyridyl)ethylene (BPE) of concentrations in the range of 10 - 6 to 10 - 10 M have been studied on these substrates and enhancements in the range of 10 6 to 10 8 were observed. These dry etched substrates, unlike those conventionally prepared by wet chemistry, are compatible with silicon device technology and are remarkably stable and reproducible.