Measurements of the Dielectric Properties of Zns in the Far Infrared Using THz- TDS

Abstract

The purpose of this study was to characterize the frequency dependent optical and dielectric properties of ZnS in the far infrared region by using the highly precise method of THz time domain spectroscopy. Single crystal, polycrystalline and nanoparticles of ZnS were characterized. The experimentally determined, frequency- dependent power absorption coefficients and refractive indices of the crystalline ZnS samples were fit using the damped harmonic oscillator model while the simple mixing model was used to determine the corresponding values for nanoparticles of ZnS. The experimental results for the absorption coefficient and refractive index of crystalline ZnS fit well with the published results. It is observed that the absorption in both the single- and poly-crystalline ZnS is characterized by prominent acoustic phonons which account for the increased absorption as indicated by the resonance lines in the spectra. At a low frequency, superposition of difference phonons was also observed. The measured index of refraction of the crystalline samples is found to be dominated by the TO-phonon resonance which is verified by a theoretical fit using the relation for the dielectric response of the damped harmonic oscillator. The frequency dependent optical properties of the nanoparticles of ZnS were found using the simple mixing model which revealed that the large absorption by nanoparticles is attributed to confinement effects and the refractive index is related to the density of nanoparticles.