Fig. 4

a SEM micrograph of the ALD layers on an oxidized silicon wafer. Thicknesses measured by ellipsometry are t _s = 76 nm, t _b = 185 nm, and t _t = 197 nm. The large flake-like structures are due to cleaving. b Effective indices of the fundamental and the first order TM slab modes of the horizontal slot waveguide for different cladding thicknesses. The curves are the simulated effective indices and the blue dots (TM₀) and the red squares (TM₁) are the measured values