The elastic component of anisotropic strain dominates the observed shift in the F_2g Raman mode of anelastic ceria thin films

Raman spectroscopy is applied for non-destructive characterization of strain in crystalline thin films. The analysis makes use of the numerical value of the mode Gr & uuml;neisen parameter gamma, which relates the fractional change in the frequency of a Raman-active vibrational mode and the strain-induced fractional change in the unit cell volume. When in-plane, compressive biaxial strain in aliovalent doped CeO2-films is relieved by partial substrate removal, the films exhibit values of gamma for the F-2g vibrational mode which are similar to 30% of the literature values for bulk ceramics under isostatic stress. This discrepancy has been attributed to a negative contribution from the anelastic (time-dependent) mechanical properties of aliovalent-doped ceria. Here we propose a way to "separate" anelastic and elastic contributions to the F-2g mode Gr & uuml;neisen parameter. Mechanically elastic yttria (Y2O3) films on Ti/SiO2/Si substrate serve as "control". The values of gamma calculated from the change in frequency of the similar to 375 cm(-1) F-2g Raman-active mode are close to the literature values for bulk yttria under isostatic stress. This work should serve to provide a protocol for characterization of selective sensitivity to different strain components of doped ceria thin films.