Scamming has never been so easy. While a refractive index is not decently defined for a material that is thinner that optical penetration depth, new sites have appeared proposing some refractive index for 2D materials. Those are unfortunately completely unphysical for the reason mentioned above. At that scale, non-local effects emerge and lead to the weakening of the definition of optical refractive index. Still they are sufficient to define the compression of the wave-function.

A collaborator sent us an ellipsometric measurement of MXene sample. Not only ellipsometry usually mistreat the imaginary parts, but they also provide erroneous data when they are used with samples that are too thin, and too narrow for the measurement spot.