Optical determination of the thickness of 2D flakes of the superconductor β -FeSe

Abstract

We present optical contrast measurements under a controlled atmosphere on samplesof FeSe with thicknesses ranging from 5 to 300 nm. The results are described using optical interference models that allow to obtain the material’s refractive index as a function of wavelength.The calculated optical contrast maps have shown to be sensitive for thinner flakes under smallvariations of the complex refractive index. Also from these kind of maps we show that it is possibleto monitor sample degradation using optical contrast measurements.