Enhanced Raman scattering on lead iodide film.

Surface-enhanced Raman scattering (SERS) on organic-inorganic hybrid perovskites have been proved a promising SERS-active substrate. As its inorganic skeleton, lead iodide (PbI) also represents a novel semiconductor substrate material that serves as either a complement or an alternative to conventional metal-based SERS. Here, for the first time, enhanced Raman scattering (ERS) of 1,2-bis(4-pyridyl)ethylene (BPE) adsorbed on PbI film is observed. To our surprise, we obtained the same ERS spectra on the PbI as SERS spectra obtained on the perovskites, which demonstrates the enhancement of substrate comes from inorganic skeleton rather than organic-inorganic hybrid perovskites. Compared with the normal Raman spectrum of BPE molecules, we find the B mode of the BPE molecule was selectively enhanced. We demonstrate that it involves a charge transfer (CT) resonance mechanism and takes place between the HOMO of BPE and the conduction band edge of PbI. Moreover, the PbI substrate performs good reproducibility, uniformity and good Raman enhancement (EF ≥ 10). It is believed that this unusual discovery not only enables PbI to be an enhanced substrate, which also provides a new advance toward a better understanding of SERS chemical mechanism.