Topology-optimized distributed 3d anisotropic Raman emission.

Area of Science:

• Nanotechnology
• Computational Physics
• Materials Science

Background:

• Topology optimization (TO) for 3D surface-enhanced Raman scattering (SERS) substrates is challenging due to field singularities and anisotropic molecule modeling.
• Existing methods struggle with orientation-averaged signals from randomly oriented, anisotropic molecules.

Purpose of the Study:

• To develop 3D TO for manufacturable SERS substrates that maximize spatially averaged signals from randomly oriented, anisotropic molecules.
• To address challenges in managing field singularities and modeling molecular orientation in SERS substrate design.

Main Methods:

• Introduced a new trace formulation for closed-form rotational averaging of anisotropic Raman tensors, accounting for tensor nonlinearity.
• Applied 3D TO with lengthscale constraints to suppress unphysical field divergences in designs.
• Optimized silver (Ag) and silicon nitride (Si3N4) SERS devices.

Main Results:

• Optimized Ag and Si3N4 devices demonstrated manufacturability by suppressing designs reliant on sharp-corner field divergences.
• Metallic SERS designs provided broadband enhancement and robustness to Raman shifts.
• Dielectric designs showed narrower, Q-limited gains, performing worse than metallic designs for Q≲500.

Conclusions:

• The developed 3D TO approach offers a practical method for designing improved, manufacturable SERS substrates.
• The methodology successfully maximizes signals from randomly oriented, anisotropic molecules for both elastic and inelastic scattering.
• The approach is extensible to other distributed-emitter design problems and can incorporate additional physics like nonlinear damage models.