Investigation of the (100) and (001) surfaces of the Al5Fe2 intermetallic compound

The bulk structure of the eta-Al5Fe2 intermetallic compound consists in an ordered framework of pentagonal antiprims with composition Al2Fe inside which nearly continuous chains of fractionally occupied Al sites exist. At low temperature, ordering of these Al channel atoms can occur, leading to various superstructures. Although the Al5Fe2 intermetallic phase is of technological importance being present in protective coating for steel parts, a detailed surface investigation of this compound has not been reported yet. Here we describe the growth of a single crystal of the Al5Fe2 compound by the Czochralski method. Its bulk structure is identified as the low temperature polymorph eta ''. Density Functional Theory calculations were performed to determine its formation enthalpy and its electronic structure. A deep pseudogap is noticeable at the Fermi energy, and this compound is found to be magnetic. Two samples have been extracted, presenting a surface oriented either perpendicular to the channel's direction ((0 0 1) surface) or parallel to them ((1 0 0) surface). The two surfaces have been investigated by X-ray photoemission spectroscopy, low-energy electron diffraction and scanning tunneling microscopy. Both surfaces exhibit some superstructures of various complexities, whose origin can be explained in the light of density functional theory calculations performed on model surfaces.