Impact of epitaxial strain on crystal field splitting of α-Cr₂O₃(0001) thin films quantified by X-ray photoemission spectroscopy

Figures & data

Figure 1. Evolution of the relative RHEED streak spacing and Cr 2p XPS spectra during the growth of α-Cr₂O₃(0001) under (a) compressive (α-Cr₂O₃ on α-Al₂O₃ substrate) and (b) tensile (α-Cr₂O₃ on α-Fe₂O₃ buffer) in-plane strain. The inset RHEED images were acquired with the 30 keV beam aligned along the $\left[1\overline{1}00\right]$ azimuth. Examples of high-resolution Cr 2p core level spectra are depicted for α-Cr₂O₃ samples under high (c₁) and moderate (c₂) compressive strain as well as for a fully relaxed film (c₃) and under high tensile strain (c₄). A Shirley-type background subtraction was used for all spectra.

Figure 2. Calculated Cr 2p XPS spectra (red line) in comparison with the experimental spectra (black circles) for α-Cr₂O₃(0001) thin films under (a) high and (b) moderate compressive strain as well as (c) fully relaxed and (d) under in-plane tension. Below each spectrum, the calculated stick diagrams (FWHM = 0.1 eV) are shown. At the top right, the relative 3d orbital diagram are plotted for Dq = 0.208 eV, Dσ = 0.600 eV and Dτ = −0.295 ± 0.005 eV (a), −0.280 ± 0.005 eV (b), −0.270 ± 0.005 eV (c) and −0.260 ± 0.005 eV (d). At the top left, a schematic representation of the CrO₆ distortion are depicted.

Figure 3. Evolution of the t_2g level splitting δ with epitaxial strain. The positive or negative sign of the δ parameter indicates that a₁ orbital is above or below e orbital, respectively. In inset, a schema of the 3d energy level for octahedral and trigonal symmetry highlighting the value of the δ parameter.