Electron Microscopy Characterization And Single Particle Sers Performance Of Self-assembly Hexagonal Ag@SiOx

Self-assembly materials have attracted wide interest of researchers because of its application in fields such as biological medicine,batteries,catalysis,surface modification and optical devices.In this paper,self-assembly microspheres different in morphology were synthesized by co-evaporation method.The microstructure and SERS property of these spheres were studied.The main findings are as follows:?1?Surface topography of microspheres were studied by SEM and classified into three types which are named sparse sphere,closely packed sphere and smooth sphere,respectively.Smooth spheres are spheres with smooth surface.Sparse spheres and closely packed spheres are related to spheres with particles distributed in hexagon on the top surface of spheres,whose corresponding neighbouring particles are separated by a certain distance and adjacent closely,respectively.?2?Ordered columnar arrays were achieved by FIB surface irradiation.The arrays are believed to form under different etching rate related with material species on the surface.SiOx with slower etching rate act as a mask so that the columns arrange regularly just as the hemi-spherical SiOx particles and the columnar direction is in accordance with the incident direction of ion beam.?3?The microstructure of self-assembly Ag@SiOx was investigated by FIB cross-section lift-out.It is revealed that the latter two types are a kind of particle coated core-shell structure.In detail,separated hemi-spherical SiOx particles distributed in hexagon are coated on top surface of ellipsoidal silver.Smooth spheres are just ellipsoidal silver.The SiOx particles are amorphous and ellipsoidal silver is crystal by SAED technique with TEM.?4?SERS performance was tested by laser Raman spectrometer when a single Ag@SiOx sphere was served as SERS substrate.The result shows that the closely packed spheres has the best sensitivity with the limit of detection for crystal violet was 10^-8 mol/L,which is followed by sparse spheres.SERS effect was not affected by the size of spheres and testing position so that the Ag@SiOx spherical SERS substrate is with good reproducibility.It is believed that three enhanced mechanism are possible to function for the Ag@SiOx spherical SERS substrate.Therefore,the self-assembled Ag@SiOx is ideal SERS substrate for mechanism research.