Chemical analysis of ligand-free silicon nanocrystal surfaces by surface enhanced Raman spectroscopy (original) (raw)

Surface enhanced Raman spectroscopy (SERS) was used to probe the surface chemistry of chlorine-terminated silicon nanocrystal (Si-NC) surfaces in an air-free environment. SERS effect was observed from the thin films of AgxO using 514 nm laser wavelength. When a monolayer of Si-NCs were spin-coated on AgxO SERS substrates, a very clear signal of surface states, including Si-Clx, and Si-Hx were observed. Upon air-exposure, we observed the temporal reduction of Si-Clx peak intensity, and a development of oxidation-related peak intensities, like Si-Ox and Si-O-Hx. In addition, first, second and third order transverse optical (TO) modes of Si-NCs were also observed at 519, 1000 and 1600 cm−1, respectively. As a comparison, Raman analysis of a thick film (> 200 nm) of Si-NCs deposited on ordinary glass substrates were performed. This analysis only demonstrated the first TO mode of Si-NCs, and the all the other features originated from SERS enhancement did not appear in the spectrum. These results conclude that, SERS is not only capable of single-molecule detection, but also a powerful technique for monitoring the surface chemistry of nanoparticles.