Spectral radiative properties of tungsten thin films in the infrared

Tungsten is an important material for energy harvesting applications due to its high chemical and thermal stability; however, the difficulty in obtaining single-crystal films leads to a large variation in the optical properties. The present work focuses on the radiative and optical properties of thin tungsten films at wavelengths from 1 to 20 μm (wavenumbers from 10,000 to 500 cm−1), considering microstructural variations. Four films of a nominal thickness of 70 nm were deposited on silicon substrates using DC magnetron sputtering, and the effect of pre- and post-deposition treatments was investigated. Several analytical instruments were used to characterize the crystalline phases and microstructures, including X-ray diffraction, Rutherford backscattering, X-ray photoelectron spectroscopy, and scanning electron microscopy. The transmittance and reflectance of the film-substrate composites were measured at room temperature using a Fourier-transform infrared spectrometer. The dielectric function of each sample was obtained by fitting the measured radiative properties using the Drude-Lorentz dispersion model. The difference in the radiative properties between samples was analyzed and related to the crystalline phases and density.