The Application Of Two-dimensional GaTe In Surface Enhanced Raman Scattering

Surface enhanced Raman scattering is an intrinsic phenomenon of molecules with Raman-enhanced effect on surfaces of solid or liquid materials.With high surface sensitivity and fingerprint recognition,SERS has been widely employed in medical,environment monitoring,food safety,and security.The preparation of SERS substrates is one of the key issues in SERS technology.An ideal SERS substrate should meet the following requirements,i.e.high SERS activity,surface uniformity,stability,reproducibility,and cost-effectiveness;however,these requirements have not been fulfilled yet.The two-dimensional(2D)materials based SERS substrates developed in recent years are usually uniform,stable,and reproducible,and they present higher detection capability than traditional substrates for some molecules,such as non-thiol aromatic molecules.In this thesis work,2D GaTe has been employed to prepare the AuNPs/GaTe,AuNPs/GaTe/Au-film and AuNPs/GaTe/Au-hole array SERS substrates.The main results are as follows:1.2D GaTe layers were firstly prepared via mechanically exfoliation and characterized byoptical microscopy,Raman scattering,photoluminescence and atomic force microscope.Then AuNPs/GaTe nano structure was prepared through immersion of GaTe in HAuCL4 solution.The immersion-time dependent morphology of AuNPs was observed by a scanning electron microscope.The maximum coverage rate reaches 98%.The formation mechanism of AuNPs is that the Au-Te compounds are produced by metathesis reaction of GaTe and Au3+,which subsequently decompose to Au and Te.The achieved AuNPs/GaTe nano structure demonstrates outstanding properties as a superior SERS substrate for ultrasensitive detection of aromatic molecules.Remarkably,the enhancement factor reaches up to 1.6 × 104,and the minmum detectable molecule concentration is 10-11 M.For R101 and MB molecules,the minimum detectable concentration is 10"10 M.Moreover,AuNPs/GaTe nano structure has good uniformity,repeatability,stability and low cost.2.The AuNPs/GaTe/Au-film nano structure was prepared by transferring the 2D GaTe onto the gold film and then modifying the gold particles on GaTe.FDTD numerical simulations demonstrate that the plasmonic coupling in the hybrid structure,particularly the LSPs coupling of AuNPs and Au-film,promotes an enhanced electric field,consequently,greatly enhances the Raman activity.The increase of GaTe thickness remarkably reduces Raman signal enhancement.Thus,single or few-layer GaTe should be utilized.It is found that few-layer GaTe could be susceptible to oxidation in the atmosphere.To slow down the oxidation of GaTe film,an immediate AuNPs decoration should be employed.The Raman enhancement is influenced by the length of decoration time.Decoration time of 960 s suits the detection of molecules with high concentration,while the decoration time of 240 s suits the detection of trace molecules.Impressively,the enha1cement factor of 3 × 105 and the limiting detection concentration of 10-14M have been achieved for the rhodamine 6G molecules,which are almost the same as the best result achieved from the patterned graphene substrates.Moreover,AuNPs/GaTe/Au-film nano structure also has good uniformity,reproducibility and stability.3.The AuNPs/GaTe/Au-hole array structure was prepared by transferring the 2D GaTe onto the Au-hole array and then modifying the gold particles on GaTe.FDTD simulation of ordered gold arrays with different parameters was employed,and the results indicated that the circle hole array with period of 4-12/im and depth of 100nm is the most suitable choice.Then Au-hole array with optimized parameters was fabricated by photolithography.With R6G the probe molecule,the strongest Raman signal on AuNPs/GaTe/Au-hole structure was observed at the edge of Au holes,which was 6 times of that on AuNPs/GaTe/Au-film structure.The enhancement factor of 1.8×l06 and the limiting detection concentration of 10-16 M have been achieved,which enables the single-molecule detection.Moreover,AuNPs/GaTe/Au-hole structure also displays good reproducibility and stability.