title: The effect of Fe-coverage on the structure, morphology and magnetic properties of α-FeSi2 nanoislands.
abstract: Self-assembled α-FeSi(2) nanoislands were formed using solid-phase epitaxy of low (~1.2 ML) and high (~21 ML) Fe coverages onto vicinal Si(111) surfaces followed by thermal annealing. At a resulting low Fe-covered Si(111) surface, we observed in situ, by real-time scanning tunneling microscopy and surface electron diffraction, the entire sequence of Fe-silicide formation and transformation from the initially two-dimensional (2 × 2)-reconstructed layer at 300 °C into (2 × 2)-reconstructed nanoislands decorating the vicinal step-bunch edges in a self-ordered fashion at higher temperatures. In contrast, the silicide nanoislands at a high Fe-covered surface were noticeably larger, more three-dimensional, and randomly distributed all over the surface. Ex situ x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy indicated the formation of an α-FeSi(2) island phase, in an α-FeSi(2){112} // Si{111} orientation. Superconducting quantum interference device magnetometry showed considerable superparamagnetism, with ~1.9 μ(B)/Fe atom at 4 K for the low Fe-coverage, indicating stronger ferromagnetic coupling of individual magnetic moments, as compared to high Fe-coverage, where the calculated moments were only ~0.8 μ(B)/Fe atom. Such anomalous magnetic behavior, particularly for the low Fe-coverage case, is radically different from the non-magnetic bulk α-FeSi(2) phase, and may open new pathways to high-density magnetic memory storage devices.
authors.affiliation: School of Mechanical Engineering and Materials and Nanotechnologies Program, Faculty of Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
authors.forename: J K
authors.initials: JK
authors.lastname: Tripathi
authors.forename: M
authors.initials: M
authors.lastname: Garbrecht
authors.forename: W D
authors.initials: WD
authors.lastname: Kaplan
authors.forename: G
authors.initials: G
authors.lastname: Markovich
authors.forename: I
authors.initials: I
authors.lastname: Goldfarb
mesh_terms: D003460:Crystallization / Q000379:methods*; D007501:Iron / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D060526:Magnetic Fields; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D012825:Silicon / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D046911:Macromolecular Substances; D007501:Iron; D012825:Silicon