A spectroscopic ellipsometry study of cerium dioxide thin films grown on sapphire by rf magnetron sputtering

Abstract

Variable angle spectroscopic ellipsometry (VASE) has been used in the photon energy range 1.25–5.0 eV to study the structure and optical properties of cerium dioxide (CeO2) films. Both amorphous and highly oriented crystalline films were grown on sapphire by rf magnetron sputtering. The crystallinity, chemical structure, and surface morphology of the films were studied by x-ray diffraction, x-ray photoelectron spectroscopy, and atomic force microscopy, respectively. The measured VASE spectra on a series of films with different thicknesses were analyzed by using multiple optical models. In this way, the complex refractive index N=n+ik of CeO2, the film thicknesses, and the surface roughness of the different films could be determined. The ellipsometrically deduced refractive index spectrum was observed to be strongly dependent on the film structure. Highly oriented crystalline CeO2 films exhibited a higher refractive index and a higher band gap energy than the amorphous film. The surface roughness of the crystalline films increased with film thickness. The optical dispersion relations have also been analyzed by line-shape fitting with a modified Lorentz oscillator model.

Determination of optical and microstructural parameters of ceria films

“…The resulting fits are shown in red in the plots in Figure 3 ("dispersion fit"), and the corresponding parameter values are provided in Table II. The dispersion behavior implied for undoped and 20% Sm doped ceria is summarized in Figure 4, where Fig. 4(a) compares the present results for undoped ceria with literature values, [14][15][16][17][18][19] and Fig. 4(b) compares the three films studied here to one another.…”

“…The parameters obtained from the fitting are in good agreement with the independently measured values, providing a validation of the procedures. [14][15][16][17][18][19] (b) substrate and dopant effects. Deposition on MgO(100) (Film #3) leads to a slight decrease in n relative to deposition on YSZ(100) (Film #1), likely due to poorer crystallographic registry between film and substrate creating a slightly lower density.…”

“…Specifically, the optical band gap, E g , is related to the absorption coefficient (Eq. (1)) according to the expression, 14,19,23 …”

Effect of Fe2+(Fe3+) Doping on Structural Properties οf CeO2Nanocrystals

“…Nanostructured CeO 2 based materials have reached significant impact in practical applications due to general improvement of catalytic [1], electrical [2], optical [3] and electrooptical [4] properties. Technology of solid oxide fuel cells is currently the most relevant field where CeO 2 found applications [5].…”

“…Various methods of preparation, such as sol-gel [4], spray pyrolysis [6], sputtering [3], have been used to obtain nanosized CeO 2 . One of the major challenges for the preparation of these nanostructured oxides is precise control of particle size.…”