Raman study of ultrathin Fe 3 O 4 films on GaAs(001) substrate: stoichiometry, epitaxial orientation and strain

The growth and characterization of high‐quality ultrathin Fe 3 O 4 films on semiconductor substrates is a key step for spintronic devices. A stable, single‐crystalline ultrathin Fe 3 O 4 film on GaAs(001) substrate is obtained by post‐growth annealing of epitaxial Fe film with thicknesses of 5 and 12 nm in air. Raman spectroscopy shows a high ability to convincingly characterize the stoichiometry, epitaxial orientation and strain of such ultrathin Fe 3 O 4 films. Polarized Raman spectroscopy confirms the unit cell of Fe 3 O 4 films is rotated by 45° to match that of the Fe (001) layer on GaAs, which results in a built‐in strain of − 3.5% in Fe 3 O 4 films. The phonon strain‐shift coefficient(−126 cm −1 ) of the A 1 g mode is proposed to probe strain effect and strain relaxation of thin Fe 3 O 4 films on substrates. It can be used to identify whether the Fe layer is fully oxidized to Fe 3 O 4 or not. Copyright © 2011 John Wiley & Sons, Ltd.