Enhanced Raman Scattering On Lead Iodide Film

The selection of active substrates is important for the Surface-enhanced Raman scattering spectroscopy?SERS?.Traditional SERS substrates include the noble metals Au,Ag,and some transition metals.However,due to the disadvantages of less varieties,poor biocompatibility,easy agglomeration,secondary pollution,and non-recyclability,the further application of SERS in production and life is limited to a large extent.Therefore,it is very important to find a more suitable SERS active base.As a new type of solar cell material,Organic-inorganic hybrid perovskite,has been found to have good SERS activity and high enhancement performance.As its inorganic skeleton,lead iodide?PbI₂?also represents a novel semiconductor substrate material that serves as either a complement or an alternative for conventional metal-based SERS.This thesis compares it with the perovskite SERS substrate,and explores the source of SERS enhancement,the mechanism of the enhancement,and the specific adsorption capacity of lead iodide.The main research contents are as follows:?1?Enhanced Raman spectroscopy of lead iodide filmFor the first time,enhanced Raman scattering?ERS?of1,2-bis?4-pyridyl?ethylene?BPE?adsorbed on PbI₂ film is observed.To our surprise,we obtained the same ERS spectra on the PbI₂ 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_u 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 PbI₂.Moreover,the PbI₂ substrate performs good reproducibility,uniformity and good Raman enhancement?EF?10⁵?.It is believed that this unusual discovery not only enables PbI₂ to be an enhanced substrate,which also provides a new advance toward a better understanding of SERS chemical mechanism.?2?Raman studies on the specific adsorption of BPE with PbI₂Intercalation,the insertion of guest atomic and molecular entities into the architecture of a crystal,is an efficient route for generating new materials with novel properties.The detailed analysis of their new structure and properties is of great importance.Here,1,2-bis?4-pyridyl?ethylene?BPE?intercalated PbI2?BIP?was studied by Raman spectroscopy,and new spectral lines were generated and some Raman peaks were shifted.This indicates that the formation of new crystals and the chemical interaction between the host material PbI₂ and the nitrogen atom of the guest molecule.Through Step Profiler test,the thickness of the PbI₂ film is significantly increased by the insertion of the BPE molecules into the PbI₂.X-ray diffraction also confirmed the intercalation of guest molecules into a host matrix through the appearance of diffraction lines at lower angles that are corresponding to the enlarged unit cell in c-axis.Furthermore,we also found that the PbI₂ can specifically adsorb of BPE molecules,which was confirmed by an adsorption experiment revealed by adsorption capacity toward BPE is higher than2,2-bipyridine and 4,4-bipyridine,suggesting the good adsorptive selectivity toward BPE by PbI₂ film.This work further demonstrated our mechanism on enhanced Raman spectroscopy on PbI₂.It is believed that this unusual discovery not only enables PbI₂ to be a specific adsorbent,which also provides a new advance toward a better understanding of structure about PbI₂.The main contents of this paper are as follows:?1?We demonstrate the enhancement of substrate comes from inorganic skeleton rather than organic–inorganic hybrid perovskites.And a molecule-to-semiconductor charge transfer mechanism is proposed,which enriches chemical enhancement theory of Raman.?2?We evaluate the PbI₂ as a Raman enhanced substrate,which indicates a promising substrate with good reproducibility,uniformity and good Raman enhancement ?EF?10⁵?.?3?Due to the special layered structure of lead iodide,BPE molecules can enter the lead iodide crystal lattice,and can specifically adsorb BPE molecules,making it a special adsorbent.