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 similar to2 nm, lengths of 1000 nm, and densities of 10(11)/cm(2). The surface areas of the nanotips are similar to150 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.