Study On Optical And Electrical Control Of SERS Effect Of Composite Materials

Since the surface-enhanced Raman scattering(SERS)was discovered in 1974,SERS spectroscopy technology has been widely used in physical,chemical,materials and even life sciences.The core of SERS is to design and construct high-performance SERS substrates to meet the requirements of different use environments.However,it is difficult to actively control the enhancement of SERS signals after the substrate has been fabricated.In this dissertation,three types of SERS substrates with adjustable performance are designed and constructed.And the SERS performance of the substrates are actively controlled by light irradiation or applying gate voltage,so that it can be used in food safety or monitoring chemical reaction.The main content is summarized as follows:1.The modulation of SERS signal for molecule/metal-semiconductor hybrid system by near-infrared light have been realized.Firstly,the molecule-linked silver and silver-doped titanium dioxide hybrid system was successfully designed and prepared.We observed that the SERS signal of the hybrid system shows an irreversible accumulation exponential change under near-infrared light irradiation.By analyzing the microstructure of the hybrid system and the molecular dynamics,three factors were found to contribute this effect:(1)higher crystallinity of silver/silver-doped titanium dioxide substrate;(2)photo-induced charge transfer;(3)charge-induced molecular reorientation.2.We proposed and demonstrate a new strategy to actively control the SERS effect by ultraviolet light.A dual-enhanced SERS substrate were developed,which is composed of a silver-coated polystyrene nanosphere array covered by a self-assembled reduced graphene oxide film.The reversible modulation of the SERS signal is achieved by actively manipulated ultraviolet-induced adsorption and desorption of gas molecules.And the first-principles calculations have confirmed that the modulation of the SERS signal is due to the adsorption and desorption of gas molecules on graphene can tune the Fermi level of graphene,which in turn regulates the charge transfer between the substrate and analyte.Finally,the proposed SERS platform was successfully applied to the trance detection of pesticides on fruits peels.3.An electrically tunable device was constructed using graphene/ion-gel hybrid structure to realize a low-voltage modulation of graphene-based SERS effect.The SERS signals of molecules adsorbed on graphene/ion-gel hybrid structure can be continuously tunable through an external small bias voltage.As such a tuning process is highly related with the charge transfer between the adsorbed molecules and graphene.4.We systematically study the thermal and photoinduced isomerization of paminoazobenzene(p AAB)directly anchored on molybdenum disulfide/graphene oxide nanocomposites by employing in-situ and real-time SERS spectroscopy.The introduction of molybdenum disulfide/graphene oxide nanocomposites provide the enhancements for the thermal isomerization efficiency of p AAB of more than 3-fold compared with that of the bare p AAB.The effect of molybdenum disulfide/graphene oxide nanocomposites on photoinduced isomerization of p AAB depends on the irradiation wavelength,which can be attributed to the competing interplay of charge transfer and structural relaxation.