An investigation of the plasmon enhanced/quenched molecular fluorescence based on multi-graded silver nanoparticle array substrates

Combinational Ag nanoparticle assembly substrates with multi-graded nanoparticle densities were fabricated through a dynamic shadow deposition of a collimated cluster beam in oblique incidence. The substrates were used to investigate the interactions between the surface plasmons of the Ag nanoparticle arrays and fluorescent molecules. Rhodamine 6G molecules directly adsorbed on the substrates show obvious fluorescence quenching, which is aggravated with the increase of the surface plasmon resonance strength. On the other hand, with a 15nm silicon nitride spacer on between the Ag nanoparticle layer and the Rhodamine 6G molecules, the fluorescence intensity is significantly enhanced to 4.5 folds by the surface plasmon of the silver nanoparticles. By depositing a silicon nitride spacer with multi-thickness, the enhancement factor was found to decrease exponentially with the increase of spacer thickness.