Surface Enhancement Raman and Surface Catalysis Reaction in Noble Metal Nanoparticles

Author:Yang Xian Zhong

Supervisor:liang wen jie


Degree Year:2017





Plasmons are elementary excitations of electrons in the solid relative to the background of the ion core.Local surface plasmon resonance can produce strong local electromagnetic field enhancement,so it is widely used in many aspects such as surface enhanced Raman,surface enhanced fluorescence,plasmonic catalytic reaction and so on.In this paper,the self-assembly of Au@Ag core-shell nanocuboids and its surface enhancement effect are discussed systematically.Then,the surface catalytic reaction between silver nanoparticles and molybdenum disulfide hybrid system is introduced.Finally,we discussed the fabrication and characterization of graphene ultrashort channel FET devices.The main research results are as follows:1.The self-assembly of gold nanorods has been extensively studied over the past ten years.At present,single-layer and three-dimensional nanorods assembies have been achieved,but the layer by layer arrangement is not yet achieved.We selected Au@Ag core-shell nanocuboids,and two different arrays were obtained on the same substrate by two-step droplet evaporation method,namely,the horizontal arrangement(the major axis was parallel to the substrate)and the vertical arrangement(the major axis perpendicular to the substrate),and the two arrangements are separated from each other.Horizontal arrangement is equidistant stepped structure,and the width of each step is equal,which is about 768 nm.While the widths of vertical arrangement are inequispaced,they are of several micrometers.And the height of each layer is about 75 nm.The spacing of two nanocuboids can be adjusted by removing the surfactant.The FDTD calculation results show that the reduction of the spacing can greatly improve the electromagnetic field enhancement.We used 4-MBA as a Raman probe molecule to study the enhancement of both arrays.The enhancement factor of monolayer vertical arrays can reach 3.87 × 105,and the Raman intensities increase with the number of array layers,which means the plasmons propagate well in our structure.Our layered structures have great potential applications in the fields of surface-enhanced Raman,plasmonics,solar cells,nanodevices and so on.We have also studied the arrangement of silver nanocubes in a similar way.We found that the types of surfactants had a significant effect on the arrangement of nanocubes.In addition,we also studied the phase separation phenomenon in the nanorod arrangement.2.We transfered MoS2 onto the surface of silver nanoparticles(Ag NPs)to form a MoS2+ Ag NPs hybrid system.By adjusting the size of Ag NPs,we successfully adjusted the absorption peak of the hybrid system from 435 nm to 532 nm,which resulted in resonance absorption of the hybrid system with the incident laser.We measured the enhancement effect of different sizes of Ag NPs on MoS2 fluorescence.The results showed that Ag NPs with average diameter of 6.1,14.5 and 25 nm could enhance the fluorescence of MoS2 by 2.5,13 and 52 times,respectively,which indicated that the plasmon-exciton coupling strength between MoS2 and Ag NPs increases with increasing particle size.The surface catalytic properties of MoS2 + Ag NPs hybrid system were studied by using 4NBT as the probe molecules.The results showed that the catalytic ability of the hybrid system increased with the increase of Ag NPs’ sizes.The catalytic effect comparations between the hybrid system and Ag NPs show that although the MoS2 has an attenuation effect on the electromagnetic field,the catalytic effect of the hybrid system is better.The hybrid system of MoS2 + Ag NPs can be extended to other two-dimensional materials and more metal nanostructures,which has great application in surface-enhanced Raman,fluorescence and surface catalysis.At the end of the paper,we introduced the construction of graphene ultrashort channel devices and measured the transport properties at room and low temperature.This device will have a great application in quantum transport,surface plasmonic photonics and photodetectors.