Chemical ordering and composition fluctuations at the (001) surface of the Fe64 Ni36 Invar alloy

Autor(en)

M Ondracek, Frantisek Maca, Josef Kudrnovsky, Josef Redinger, Albert Biedermann, C Fritscher, Michael A. Schmid, Peter Varga

Abstrakt

We report on a study of (001) oriented fcc Fe-Ni alloy surfaces which combines first-principles calculations and low-temperature scanning tunneling microscopy (STM) experiments. Density functional theory calculations show that Fe-Ni alloy surfaces are buckled with the Fe atoms slightly shifted outwards and the Ni atoms inwards. This is consistent with the observation that the atoms in the surface layer can be chemically distinguished in the STM image: brighter spots (corrugation maxima with increased apparent height) indicate iron atoms, darker ones nickel atoms. This chemical contrast reveals a c (2×2) chemical order (50% Fe) with frequent Fe-rich defects on the Fe₆₄ Ni₃₆ (001) surface. The calculations also indicate that subsurface composition fluctuations may additionally modulate the apparent height of the surface atoms. The STM images show that this effect is pronounced compared to the surfaces of other disordered alloys, which suggests that some chemical order and corresponding concentration fluctuations exist also in the subsurface layers of Invar alloy. In addition, detailed electronic structure calculations allow us to identify the nature of a distinct peak below the Fermi level observed in the tunneling spectra. This peak corresponds to a surface resonance band which is particularly pronounced in iron-rich surface regions and provides a second type of chemical contrast with less spatial resolution but one that is essentially independent of the subsurface composition. © 2006 The American Physical Society.

Organisation(en)

Physik Nanostrukturierter Materialien

Externe Organisation(en)

Czech Academy of Sciences, Center for Computational Materials Science, CMS, Technische Universität Wien

Journal

Physical Review B

Band

74

ISSN

1098-0121

DOI

https://doi.org/10.1103/PhysRevB.74.235437

Publikationsdatum

2006

Peer-reviewed

Ja

ÖFOS 2012

103020 Oberflächenphysik

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/02ea618f-af58-497d-8e66-15a813e7e553