Tin diselenide van der Waals materials as new candidates for mid-infrared waveguide chips

Mid-infrared is a spectral region of molecular vibration and rotation modes and thus, it has been widely used in chem/bio analysis. On-chip MIR waveguides combining attenuated total reflection spectroscopy provide an efficient way to minimize equipment size and benefit chemical trace analysis. But, inevitable surface roughness-induced scattering is harmful for waveguide mode propagation in traditional sensors. Two-dimensional materials are natural thin slabs with atomic-scale smooth surfaces and thus could be excellent for building weak surface scattering waveguides. Here, we used near-field microscopy to investigate a waveguide mode of 1T tin diselenide slabs at nanoscale resolution in 5.13-6.57 mu m and manipulate the mode strengths and wavelengths by controlling the slab thickness. This work extends two-dimensional materials as building blocks for integrated MIR chips.