Optical Constants of Tin Sulphide Single Crystals Measured by the Interference Method

The refractive index, n, of SnS single crystals is measured from reflectance after being normalized to account for the pronounced rise below the energy gap n is also measured by the interference method in the transparency region. An effective thickness smaller than the true one is introduced to account for the photon scattering by the layer structure of the material in this region. The effective thickness hypothesis gives a satisfactory explanation of the pronounced rise in reflectance for E < Eg. The extinetion coefficient, k, is calculated from the measured absorption coefficient. Measurements are performed at room temperature using plane polarized light with the plane of polarization parallel to the a‐ and b‐crystallographic axes which lie in the plane of cleavage. The real and imaginary parts of the complex dielectric constant (εr, εi) are calculated from the values of n and k. It is shown that SnS single crystals exhibit birefringence. Assuming that the SnS binding is partly ionic and partly covalent, the results of the optical constants are satisfactorly fitted to the model of a single effective oscillator.