2026/03/26 by Alexandra Fălamaş, Alexandra Fălămaș, Ana Maria Mihaela Gherman +5
Materials Science · Engineering · #Metamaterials and Metasurfaces Applications #Plasmonic and Surface Plasmon Research #Thermal Radiation and Cooling Technologies
paper · pdf · doi:10.1021/acsaom.6c00157
High Resolution Image Download MS PowerPoint Slide Hexagonally close-packed polystyrene (PS) microsphere monolayers coated with tantalum pentoxide (Ta 2 O 5 ) form scalable dielectric metasurfaces that support tunable photonic resonances and enhanced local density of optical states (LDOS). Here we combine fabrication, optical and fluorescence spectroscopy, and multiscale electromagnetic simulations to quantify how the thickness of a Ta 2 O 5 shell controls far-field resonances and Rhodamine 6G (Rh6G) emission. Experimentally, Ta 2 O 5 shells of 10 to 70 nm deposited on PS microsphere lattices generate resonances that shift red with the thickness of the shell and systematically enhance the Rh6G fluorescence relative to flat Ta 2 O 5 films. The largest integrated enhancement is obtained for 30 to 50 nm shells, where lattice resonances overlap the Rh6G excitation and emission bands. Finite-cluster finite-difference time-domain simulations reproduce the measured transmittance and reflectance spectra, confirming that the fabricated lattices are well described by the geometry of Ta 2 O 5 shells covering the sphere lattice. Periodic-cell simulations of single electric dipoles yield wavelength-dependent Purcell factors F p (λ) and directional β-factors β top (λ), from which we construct emission-weighted figures of merit that link LDOS modulation to the experimentally accessible top-side fluorescence enhancement. As a complementary test of our emitter–environment model, we compare simulated and measured Purcell factors for PS/Ta 2 O 5 microsphere lattices with the same Ta 2 O 5 thicknesses. A physically motivated averaging scheme that accounts for emitter position, orientation and ensemble spectral smoothing yields very good agreement across all shells. Overall, our results establish Ta 2 O 5 -coated microsphere lattices as robust dielectric substrates for surface-enhanced fluorescence and clarify how shell thickness and emitter placement jointly control photonic resonances, LDOS and fluorescence response.