Metasurface Engineering with Tantalum Pentoxide-Coated Microspheres: Tailoring Optical Resonances and Enhancing Local Density of States
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2026
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| author | Fălamaş, Alexandra Gherman, Ana Maria M. Vallée, Renaud Farcău, Cosmin |
| author_facet | Fălamaş, Alexandra Gherman, Ana Maria M. Vallée, Renaud Farcău, Cosmin |
| contents | Hexagonally-packed polystyrene (PS) microsphere lattices coated with tantalum pentoxide (Ta$_2$O$_5$) form scalable dielectric metasurfaces supporting tunable photonic resonances and enhanced local density of optical states (LDOS). Here we combine fabrication, optical and fluorescence spectroscopy, and multi-scale electromagnetic simulations to quantify how the thickness of Ta$_2$O$_5$ shells control far-field resonances and Rhodamine 6G (Rh6G) emission. Experimentally, Ta$_2$O$_5$ shells of 10 - 70 nm deposited on 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 enhancement is obtained for 30 - 50 nm shells, when lattice resonances overlap the Rh6G excitation and emission bands. Finite-cluster finite-difference time-domain simulations reproduce the measured transmittance and reflectance spectra, confirming the assumed geometry of the Ta$_2$O$_5$ shells covering the sphere lattice. Periodic-cell simulations of single electric dipoles yield wavelength-dependent Purcell factors $Fp(λ)$ 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. A physically motivated averaging 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. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2603_25828 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Metasurface Engineering with Tantalum Pentoxide-Coated Microspheres: Tailoring Optical Resonances and Enhancing Local Density of States Fălamaş, Alexandra Gherman, Ana Maria M. Vallée, Renaud Farcău, Cosmin Optics Mesoscale and Nanoscale Physics Hexagonally-packed polystyrene (PS) microsphere lattices coated with tantalum pentoxide (Ta$_2$O$_5$) form scalable dielectric metasurfaces supporting tunable photonic resonances and enhanced local density of optical states (LDOS). Here we combine fabrication, optical and fluorescence spectroscopy, and multi-scale electromagnetic simulations to quantify how the thickness of Ta$_2$O$_5$ shells control far-field resonances and Rhodamine 6G (Rh6G) emission. Experimentally, Ta$_2$O$_5$ shells of 10 - 70 nm deposited on 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 enhancement is obtained for 30 - 50 nm shells, when lattice resonances overlap the Rh6G excitation and emission bands. Finite-cluster finite-difference time-domain simulations reproduce the measured transmittance and reflectance spectra, confirming the assumed geometry of the Ta$_2$O$_5$ shells covering the sphere lattice. Periodic-cell simulations of single electric dipoles yield wavelength-dependent Purcell factors $Fp(λ)$ 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. A physically motivated averaging 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. |
| title | Metasurface Engineering with Tantalum Pentoxide-Coated Microspheres: Tailoring Optical Resonances and Enhancing Local Density of States |
| topic | Optics Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2603.25828 |