Metamaterials have emerged as a promising platform for their various optical properties including wavefront control, optical cloaking, and their application for meta-lenses.  These phenomena emerge from the confinement of light into modular nanoscale geometries, and manipulation of electromagnetic fields. On the sub-diffraction scales, resonance interactions with incident light occur as an effect of the refractive index, geometry, and dielectric environment leading to enhanced electromagnetic field[DFS1] s. Interestingly, enhancements in electromagnetic fields can lead to the lowering of activation barriers for chemical reactions. By engineering and fabricating metasurfaces with high field enhancements throughout the visible region, we can drive chemical reactions using light. Here, recent work will be presented on Si-based dielectric metasurfaces. Finite Difference Time Domain (FDTD) simulations were performed on Lumerical software by systematically varying the height, radius, periodicity of the metasurface. We targeted structures with magnetic and electric dipoles with overlapping resonance frequencies to target anapole excitations within individual meta-atoms and to maximize local electromagnetic field enhancement. Si-metasurfaces were fabricated using standard nanofabrication techniques. Briefly a Si on sapphire wafer was coated with a low and high-density polymethylmethacrylate resistor and employing a chromium mask. Next, the desired structure was written on the wafer using electron beam lithography and followed by reactive ion etching. To verify the height, radius, and periodicity of our fabricated structures, profilometry and scanning electron microscopy were employed. To test our hypothesis that electric fields of dielectric metasurfaces can enhance chemical reactions we developed a home-built reactor capable of monitoring chemical transformations under optical illumination and studied the reduction of <i>p</i>-nitrothiophenol to <i>p-</i>aminothiophenol as a well-known model reaction. In conclusion, Si metasurface were engineered to exhibit large electromagnetic field enhancements and demonstrated the use of metasurface platforms for photochemistry.

Field enhancements in metamaterials for surface chemistry

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.