Surface-Enhanced Raman Scattering Of Ultra-Thin Ta-C Films Coated Al And Suspended Au Nanostructures

Surface plasmon is an electromagnetic mode that propagates along the metal surface due to the mutual coupling of light and free electrons on the conduction band near the Fermi level of the metal,resulting in collective coherent fluctuations of free electrons on the metal surface.When the plasmon resonance mode is excited,the metal micro / nano structure selectively absorbs and scatters incident photons of a certain frequency,and at the same time,it focuses the energy of the incident light field in the sub-wavelength space and forms near the metal surface.Locally enhanced electromagnetic fields.The use of this enhanced electromagnetic field can improve the efficiency of optical processes in its vicinity,as exemplified by Surface-Enhanced Raman Scattering(SERS).The enhancement substrates currently used by SERS are based on Au and Ag,and their operating bands are excited in visible and near infrared.The metal aluminum(Al)plasmon resonance can support the ultraviolet band,but Al is relatively easy to oxidize in the air,especially the Al film deposited under low vacuum conditions.Although the Al film prepared by high vacuum will form a dense oxide protective film on the surface,its thickness is a few nanometers,so it will still cause the loss of the plasmon electromagnetic field.Therefore,how to improve the chemical stability of Al in air and maintain the activity of Al plasmon has important value for the application of ultraviolet surface plasmon.In addition,metal micro / nano structures with ultra-small gaps and suspended structures have important application value in the field of SERS detection due to strong coupling and enhanced electromagnetic fields.Therefore,it is particularly important to study their application in biomolecule detection.In this thesis,the ultra-thin Tetrahedral-Amorphous carbon film(ta-C)wascoated on the Al nanostructures obtained by conventional coating.Since the ta-C film has a high level even at 1nm Therefore,by simultaneously etching away the oxidized Al layer and the deposition of the ta-C thin film in the vacuum chamber,an Al / ta-C micro-nano structure can be obtained,and a high-purity aluminum nanostructure can be obtained and maintained at the same time.Its plasmon performance in the ultraviolet band.Secondly,we used suspended Au / ta-C / Au micro-nano structures obtained by combining nano-imprint technology and etching technology to study the harmful plasticizers(phthalates,etc.)in children's urine.Detection has promoted the application of SERS in health diagnosis.details as follows.First,the Al nanostructure is first prepared by a stencil method combined with thermal evaporation(or sputtering)deposition,and then in-situ sputtering etching(mainly to remove the oxidized Al film)and subsequent 1-nm ta-C film was deposited,and finally the Al / ta-C composite micro / nano structure was obtained.The surface plasmon response of Al / ta-C in the ultraviolet band was studied by spectral measurement,XPS characterization and Comsol simulation calculation.In addition,UV-Raman was used to study the application of Al / ta-C in ultraviolet SERS.The results show that the 1nm-ta-C thin film can maintain the chemical stability of Al and has a good UV surface plasmon response.It provides a good research basis for the practical application of Al surface plasmons.Second,the application of suspended Au nano-finger structure as a SERS substrate in the detection of plasticizers in children's urine was studied.Children inevitably come into contact with plastic products in daily life,including plastic file bags,plastic bottles,and plastic tablecloths.In the plastic production process,organic compounds such as plasticizers are usually used.After entering the human body,they undergo complex metabolic processes to form phthalates(MBP).It is a class of endocrine disruptors that can disrupt the normal endocrine function of the human body and is particularly dangerous for children under 12 years of age.The suspended Au / nano-array structure was used as a SERS substrate to detect MBP in urine of children that had been confirmed by gas chromatography-spectroscopy.The SERS spectrum of urine showed that compared with the pure MBP,it was found that the urine did contain MBP.In this case,GC-MS confirmed that the content of MBP in the urine of children was 100 ng / ml,which is the limit for medical determination ofplasticizer poisoning.The above results indicate that SERS can be suggested as a rapid and pre-diagnostic judgment for child health monitoring.