Fig. 2: The scattering-type scanning near-field optical microscopy (s-SNOM) nano-infrared images of phonon polaritons in hBN isotopic heterostructures.

s-SNOM amplitude images of ¹⁰B−¹¹B isotopic heterostructures at representative infrared (IR) frequency ω = 1440 cm⁻¹ (a), 1420 cm⁻¹ (b), 1380 cm⁻¹ (e), and 1385 cm⁻¹ (f). c, d s-SNOM profiles cut along dashed lines in (a) and (b) reveal short-period beats in ¹⁰B−¹¹B isotopic heterostructures (black, red, blue, cyan, and pink) and long-period fringes in single slab ¹⁰B and ¹¹B hBN (gray and green). L is the distance from the slab or heterostructure edge. Scale bar: 2 µm. The compositions of ¹⁰B and ¹¹B building blocks in each region are denoted by the stacking from top to bottom.