Preparation,Characterization And Applications Of Ag-Oxide Composite Structures As SERS Substrates

In this dissertation,the nanocomposite substrates with Ag nanorods?AgNRs?and various oxides were prepared by glancing angle deposition?GLAD?and atomic layer deposition?ALD?techniques to satisfy the practical demands of surface-enhanced Raman scattering?SERS?substrates.The SERS sensitivity,stability,shelf life,reusability,adsorption activity,interfacial adhesion et al.were controlled and optimized,so as to create a practical substrate system with superior comprehensive properties.The main research results and conclusions are as follows:Firstly,AgNRs@Al₂O₃ core-shell composites were prepared as sensitive and stable SERS substrates.The thickness of Al₂O₃ layers can be precisely controlled during ALD process.The oxide layers effectively protected the Ag surface and thus improved the temporal stability,thermal stability and chemical stability of the composite substrates.Meanwhile,the AgNRs@Al₂O₃ substrates possessed outstanding SERS sensitivity and signal uniformity,exhibiting ultralow detection limit and quantitative analysis capability during SERS measurements.Secondly,when the oxide layer of AgNRs@Al₂O₃ was less than 1 nm,there were a few pinholes on the Al₂O₃ shell,which caused the exposed Ag surface.Through adjusting the pinhole ratio of Al₂O₃,pinholes'influence on the substrates was quantitatively analyzed.AgNRs@Al₂O₃ with proper pinhole rate was finally selected as the optimal substrate under some harsh detection conditions such as high temperature and corrosive environment.In addition,the pinhole-containing substrate utilized both Ag and Al₂O₃surfaces to specifically adsorb a variety of molecules and hence achieved sensitive SERS detections,and the quantitative models were accurate.Thirdly,in order to reduce the costs of SERS measurements,the reusability of composite substrates were developed.Based on the photocatalytic ability of TiO₂ and the high melting point characteristic of HfO₂,the AgNRs@TiO₂ substrate with self-cleaning ability under ultraviolet light irradiation was prepared,and the AgNRs@HfO₂ substrate that could desorb surface organics after heating was developed.The process of photocatalytic degradation and high-temperature desorption of organic molecules from SERS substrates was easy and efficient,therefore the reusability could greatly reduce the expenses of SERS sensing.The composite substrates also realized in situ detection of trace gas molecules,which is of great significance for practical applications.Fourthly,the methods of adding transition layers and subsequent thermal annealing were adopted to enhance the interfacial adhesion of SERS substrates.Ti transition layers could alleviate the property mismatch between Ag and Si films,so the stress distribution of the entire structure was adjusted.Thermal annealing contributed to strengthening the diffusion and interaction between atoms and reducing the interfacial porosity.In this way,the interfacial adhesion of SERS substrates was dramatically improved,which ensured the reliability during substrate transportation,storage and employment.Finally,AgNRs-Al₂O₃ substrates with Al₂O₃ capping were designed and synthesized,which were recognized as ideal substrates with both thermal stability and SERS activity.Al₂O₃ capping suppressed the diffusion of Ag atoms from nanorod tips to sides at high temperatures,thus enhancing the thermal stability of SERS substrates.Meanwhile,the uncovered side surface of AgNRs could directly adsorb probing molecules,so the electromagnetic enhancement was outstanding.Besides,the preparation of AgNRs-Al₂O₃structures only required the electron beam deposition equipment,which was very simple and efficient.