Atomic-Scale Structure of the Hematite ?-Fe₂O₃(1102) "R-Cut" Surface.

ABSTRACT: The ?-Fe₂O₃(11?02) surface (also known as the hematite r-cut or (012) surface) was studied using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling microscopy (STM), noncontact atomic force microscopy (nc-AFM), and ab initio density functional theory (DFT)+U calculations. Two surface structures are stable under ultrahigh vacuum (UHV) conditions; a stoichiometric (1 × 1) surface can be prepared by annealing at 450 °C in ?10^-6 mbar O₂, and a reduced (2 × 1) reconstruction is formed by UHV annealing at 540 °C. The (1 × 1) surface is close to an ideal bulk termination, and the undercoordinated surface Fe atoms reduce the surface bandgap by ?0.2 eV with respect to the bulk. The work function is measured to be 5.7 ± 0.2 eV, and the VBM is located 1.5 ± 0.1 eV below E_F. The images obtained from the (2 × 1) reconstruction cannot be reconciled with previously proposed models, and a new "alternating trench" structure is proposed based on an ordered removal of lattice oxygen atoms. DFT+U calculations show that this surface is favored in reducing conditions and that 4-fold-coordinated Fe²⁺ cations at the surface introduce gap states approximately 1 eV below E_F. The work function on the (2 × 1) termination is 5.4 ± 0.2 eV.

SUBMITTER: Kraushofer F 

PROVIDER: S-EPMC5823487 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature