Preparation Of Gold Nanoparticles/Boron Doped Diamond Substrates And Studies On Surface-enhanced Raman Scattering

Surface enhanced Raman scattering?SERS?as an efficient and sensitive spectral analysis tool has been widely used in physical,chemical,biological,and medical analysis sensitive specific detection.The SERS principle was mainly to stimulate the free electrons of the base by incident light to form local surface plasmon resonance?LSPR?to enhance the surface local electromagnetic field,so as to amplify the Raman signal of probe molecules.Since the discovery of SERS phenomenon in the 1970s,the substrate materials studied have been extended from precious metals?Au,Ag and Cu,etc.?,some alkali metals?Na,K and Li,etc.?and transition metals?Al,Pd and Pt,etc.?discovered at the beginning to semiconductor materials?TiO₂,SiO₂ and ZnO,etc.?.Metal nanostructures have been developed as substrates,but their poor biocompatibility and unstable chemical properties still need to be solved.Although the shortcomings of metal nanostructure were overcome,the enhanced effect of semiconductor SERS substrate was not satisfactory.As a semiconductor SERS substrate,Boron doped diamond has the advantages of adjustable band gap,stable chemical properties and fewer Raman scattering peaks.It has been proved to be a new type of single-element semiconductor SERS substrate.In this paper,we study mainly by microwave plasma chemical vapor deposition?MPCVD?of boron doped diamond,prepared as a base,on its surface by vacuum plasma sputtering deposition and high temperature annealing method modified gold nanoparticles,the formation of gold nanoparticles/boron doped diamond?AuNPs/BDD?composite base,used to achieve good SERS effect.The morphology and structure of AuNPs/BDD composite substrate,SERS performance and enhancement mechanism were characterized,tested and discussed in detail.The specific contents are as follows:1.Microwave plasma chemical vapor deposition?MPCVD?was used to deposit boron-doped diamond films on the surface of the treated silicon wafers,and then the surface was gilded by vacuum plasma coating equipment,and then the gold films were changed into gold nanoparticles by high temperature annealing.Gold nanoparticles of different sizes?10 nm,20 nm and 30 nm?can be obtained by controlling the coating time?10 s,20 s and 40 s?.The obtained composite substrate with three sizes of nanoparticles was stimulated by 633 nm laser respectively,and methylene blue was used as probe molecule to detect SERS performance.It was found that when the size of gold nanoparticles was 20 nm,the SERS enhanced effect was the best,the enhancement factor was 10⁵,and the detection limit reached 10^-88 M2.The enhancement mechanism of AuNPs/BDD composite substrate was studied.We believed that the good SERS enhanced effect of the composite substrate was attributed to the composite effect of semiconductor enhancement of BDD and electromagnetic enhancement of gold nanoparticles..Because the size of gold nanoparticles is different,the enhancement effect of each sample is different.Finite difference time domain method?FDTD?was used to simulate and calculate the electromagnetic field enhancement distribution of AuNPs/BDD composite structure with different sizes of gold nanoparticles.3.The properties of AuNPs/BDD composite substrate were systematically characterized by using methylene blue as probe molecule under 633 nm excitation light.Fifteen points were randomly selected on the composite structure for SERS test,and it was found that the difference of SERS enhanced factor in different locations was less than 10,showing good consistency,which proved that the substrate had good homogeneity.The prepared composite substrate was placed in an air atmosphere for120 days before SERS test,and compared with the newly prepared samples,it was found that there was no significant difference in the enhancement effect between the two,which proved that the substrate had excellent stability.Samples tested by SERS were cleaned by ultrasonic in deionized water to remove probe molecules attached to the surface,and then tested again.After four repeated tests,it was found that the test data had good consistency,which proved that the composite substrate structure was stable and could be tested repeatedly.4.R6G was used as probe molecule to further study the performance of AuNPs/BDD composite substrate and excellent SERS performance was found.The enhanced effect of composite substrate may be attributed to the electromagnetic field enhancement effect of gold nanoparticles on the surface of BDD on the one hand,and on the other hand,the introduction of gold provides a new channel for charge transfer.In summary,a kind of precious metal/semiconductor composite structure SERS substrate was prepared by combining gold nanoparticles with boron-doped diamond film in this paper,and its enhancement mechanism was analyzed.At the same time,the substrate has good homogeneity,stability and repeatability,and has an important application prospect.