The Preparation Of VO₂ Spherical Film And Its Study On Sers Temperature Modulation

Surface-Enhanced Raman Scattering（SERS）technology is a highly sensitive and non-destructive detection method that has been widely used in environmental toxicant detection,biochemical assaying,and reaction mechanism research.The SERS substrate plays a vital role in improving test sensitivity and minimum detection concentration.Gold（Au）has become a common SERS substrate material because of its strong stability,good biocompatibility,and optimal SERS activity.However,due to the stable performance of Au,it is difficult to adjust the SERS signal after the substrate structure was fabricated.Vanadium dioxide（VO₂）is a semiconductor material with metal-semiconductor phase transition characteristics.The phase transition will cause a sudden change in the refractive index of VO₂.Combining VO₂nanomaterials and Au nanoparticles not only can tune the local resonance peaks of Au nanoparticles through phase transition-induced refractive index changes,but also,metallic VO₂has the potential to further enhance the SERS performance of the substrates.In this paper,it is proposed to form a composite structure of VO₂thin film and Au nanoparticles on the substrate of SiO₂microsphere array and study the regulation of temperature-regulated Raman signal intensity.This paper first studied the preparation and phase transition properties of ultrathin VO₂spherical film.In order to be compatible with the preparation process of Au nanoparticles,a combination of vacuum thermal annealing and rapid thermal oxidation treatment was proposed to prepare ultra-thin VO₂spherical film on the surface of SiO₂microspheres,and the effect of vacuum thermal annealing temperature on phase transition characteristics was studied.Using an X-ray diffractometer（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,and resistance-temperature measurement system to study the crystalline properties,surface morphology,and electrical properties of the film.The results show that adding vacuum thermal annealing before rapid thermal annealing can increase the phase transition amplitude from 7.58 to 10.23,while the phase transition temperature of the ultra-thin VO₂spherical film decreases from 53.5℃to 52℃,and the width of the thermal hysteresis loop decreases from 19℃to as low as 9℃.Based on the preparation of the above ultrathin VO₂spherical thin films,a three-dimensional periodic AuNPs-VO₂thin film array structure SERS substrate was proposed to be designed and fabricated on the surface of the SiO₂microsphere array.Utilizing the phase transition properties of VO₂to control and enhance the Raman signal intensity of Au nanoparticle SERS substrates.How varying temperature can affect its absorption peak wavelength and Raman signal intensity was studied.The results show that as the test temperature increased from 25℃to 80℃,the absorption peak wavelength of the AuNPs-VO₂thin film array structure blue-shifted from 600nm to 555 nm,and the Raman enhancement factor increased from 8.3×10⁵to 3.9×10⁶.The lowest detection limit reached 10^-9M.FDTD Solutions software was used to simulate the electric field intensity distribution and enhancement factor of the AuNPs-VO₂thin film array structure.After analysis,the tuning and enhancement of SERS performance of AuNPs-VO₂thin film array structure is the combination of the shift of the absorption peak wavelength caused by the VO₂phase transition and the coupling of metal phase VO₂film and Au particles.The three-dimensional periodic AuNPs-VO₂thin film array structure proposed in this paper not only has excellent SERS performance but also can tuning its SERS signal intensity by adjusting the temperature.It has great potential in quantitative detection and sensing of analytes.