Figure 8.

FDTD simulations (Lumerical ANSYS). Reflection from a structure of 100-nm-wide (30-nm-thick) Cr or Au ring of 900 nm diameter on an etched inverted pyramid on Si $\langle 001\rangle$ plane at different wavelengths; top-row is reference with no metal ring. Color map shows light enhancement; incident light is $E=1$. Calculations were carried out with periodic boundary conditions (in surface plane of Si wafer). Material properties are taken from Lumerical database. Note the different dimensions in horizontal and vertical directions.