Embedded Core-shell Nanostructure For High Temperature In Situ Surface Enhanced Raman Spectroscopy

High temperature heterogeneous reactions constitute the foundation of modern chemical and energy industry as one of the most widely applied reactions.It is of great significance to perform in-situ analysis of high temperature reaction,which can provide critical information for reaction mechanism,material design,and efficiency improvement.Surface-enhanced Raman Spectroscopy(SERS)utilizes plasma resonance excitons from gold,silver and other metal nanostructures to enhance Raman signals significantly.SERS not only possesses the advantages of conventional Raman spectroscopy,including non-destructive,non-vacuum operating,no heating radiation and water interference,but also has the capability of trace analysis and dynamic response,which are crucial for in situ tracking of trace key species and microstructure evolution at the reaction interface.However,the harsh environment of high temperature reactions imposes strict requirements on the stability of SERS nanostructures.The previously reported nanostructures suffer from the problems of thermal-induced activity degradation and limited substrate universality,only applicable for a few material systems with specialized substrate design.These problems greatly hinder the wide application of SERS in high temperature reactions.Hence,there is an urgent demand to develop a SERS nanostructure with high stability,high activity and substrate universality for in situ characterization of the high temperature reactions.This work reports a novel embedded core-shell nanostructure(noted as ECSN)with high SERS sensitivity,strong thermal-robustness and good substrate universality.Si O2 is chosen as the core and shell materials.Ag nanoparticles are embedded into the framework of Si O2 to use the nano-limiting effect of Si O2 core-shell layer providing a thermal stable framework for Ag embedding and maximizing the plasma resonance effect of embedded nanoparticles.Moreover,combined microstructure characterization with three dimensional finite difference time domain simulation,it is found that the embedded Ag nanoparticles form plasma"hot spots",contributing a strong SERS effect on individual ECSN.Combined the experimental tests with the theoretical calculations,it is proved that the ECSN particles provide excellent SERS enhancement and high thermal stability.The Raman enhancement factor is larger than 10~4 and maintains stable under reducing and oxidative atmospheres.After heating at 400?for 2h,the Raman enhancement factor still reaches approximately 80%compared to the initial value.With the ECSNs,high sensibility has been achieved on trace analysis of carbon and in situ monitoring of ceria species at elevated temperatures.Direct spectroscopic evidence of lattice dynamics on ceria has been obtained under operative conditions.These measurements illustrate that the hybrid nanospheres effectively increase the sensibility and flexibility for high temperature SERS,which should find utility in operando analysis of various metal oxides and surface species for high temperature heterogeneous processes.