Fig. 3. Edge-tailored PhPs in rectangle α-MoO₃ nanocavities with different aspect ratios and rotation angles.

Nano-infrared imaging of near-field amplitude s(ω) in rectangle α-MoO₃ nanocavities with different aspect ratios (L/W, on the left) and angle θ (on the top). The length L and width W are defined in the panel a. The width W of each rectangle is 2 μm and the thickness is 155 nm. The length L of each rectangle are 1 μm (a–e), 2 μm (f–j), 3 μm (k–o), and 4 μm (p–t), respectively. All the images were measured at frequency ω = 896.9 cm⁻¹. The white dotted parallelogram in panel s indicates the forbidden zone of PhPs waves.