A Theoretical and Experimental Investigation of the Electronic Structure of Alpha-Fe2O3 Thin Films

Ground and excited states of alpha -Fe2O3 have been investigated by determining the spin-polarized wavefunctions and eigenvalues of an embedded Fe2O912- cluster using the discrete variational Xalpha method. The computed transition energies compare reasonably well with the recorded experimental spectrum of high-purity alpha -Fe2O3 thin films obtained by the sol-gel technique. The theoretical data herein reported predict a very high valence-conduction band gap incompatible with the experimental outcomes, which were routinely interpreted as originated by an interband transition. In contrast to this, the lowest-energy optical transitions have a charge transfer nature, involving excitation of electrons from the occupied O 2p-based spin down levels to the empty Fe atom-like spin down orbitals.