Fabrication And Spectra Of Two-dimensional Ordered SiO₂Cavities On Electrode Surfaces

In this paper, we prepared a well-designed silver/silica cavity array usingpolystyrene （PS） sphere monolayer as template. For preparation, we first immobilizedsilver nanoparticles on the surface of indium-doped tin oxide （ITO） glass byelectrostatic interaction, and then PS monolayer spread on the surface of air/waterinterface was transferred onto the silver modified ITO, finally, silica array was built byspin-coating the silica sol into the interstice of the PS particles. We have carried out alarge number of spectral studies using silver/silica cavity array as SERS substrate andp-aminothiophenol （PATP） as a probe molecule, and the result showed that: Ramanintensities of b₂modes of PATP molecules on silver/silica cavity array, as compared tothe intensities got from silver nanoparticles （AgNPs） monolayer, were selectivelyenhanced. we believe that it is the negative charged surface of silica cavities cause theredistribution of the charges in the silver nanoparticles, making it be favorable to theoverall charge transfer from the metal nanoparticles to the adsorbed PATP molecules,resulting in the improvement of the chemical enhancement and the selectivelyenhancement of b₂modes. Furthermore, the Raman spectra of methylviolegen cation(MV²⁺) on this AgNPs/silica cavity array suggested that the negatively charged silicacavity can enrich this kind of cationic phytocide. Due to the deprotonation of hydroxy,the selective enrichment effect increased with the increasing of the pH value of thesolution.When using the silica cavity modified ITO as working electrode, goldnanoparticles can be electrochemically deposited into the cavities. SEM shows that thenanosized Au particles are deposited onto the bottom of cavities, even the irregular ones,and no Au particle grows in the internal wall or outer fringe of the cavities owing to thepoor conductivity of the SiO2cavities structure. Based on the relative low melting pointof gold nanoparticles, we managed to change the morphology of gold nanoparticles by calcination melting. The gold particles began to melt and aggregate as the temperaturerise, when the temperature reaches700℃, there is only a single gold nanoparticle in thecavity of each ball. XRD characterization shows that the growth gold particle is alongwith the Au （111） of crystal. Through the cyclic voltammogram researches, we foundthat single crystal gold modified electrode exhibit a good electrochemical catalyticeffect on the oxidation of glucose, and we attributed this catalytic behavior to the role ofthe crystal surface due to Au （111）.