Growth and vibrational properties of ultra-thin Cr2O3 films grown on Cr(110) studied by RAIRS

Ultra-thin films of Cr2O3(0 0 0 1) grown on Cr(1 1 0) were investigated by reflection absorption infrared spectroscopy (RAIRS). An absorption band at 720 cm−1 is assigned to a longitudinal optical phonon of Cr2O3. With increasing O2 exposure, this absorption band shifts to higher frequency, which is qualitatively explained by a simple spring model. After successive oxidation with 18O2 and 16O2, two absorption bands corresponding to Cr 2 18 O 3 and Cr 2 16 O 3 were distinctly observed suggesting that oxygen diffusion hardly occurs during the oxide growth. Temperature dependence of the RAIRS spectrum taken from the Cr2O3 film revealed that the absorption band position shifts to lower frequency along with broadening of the band width. Anharmonic coupling with low-frequency phonons and effects of the antiferromagnetic to paramagnetic phase transition are discussed.