Chemical ordering and composition fluctuations at the (001) surface of the Fe64Ni36 Invar alloy

M. Ondráček, F. Máca, J. Kudrnovský, J. Redinger, A. Biedermann, C. Fritscher, M. Schmid, and P. Varga
Phys. Rev. B 74, 235437 – Published 22 December 2006

Abstract

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 Fe64Ni36(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.

  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
  • Received 15 September 2006

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

©2006 American Physical Society

Authors & Affiliations

M. Ondráček, F. Máca*, and J. Kudrnovský

  • Institute of Physics ASCR, Na Slovance 2, CZ-182 21 Praha 8, Czech Republic

J. Redinger

  • Center for Computational Materials Science, Getreidemarkt 9/134, A-1060 Vienna, Austria

A. Biedermann

  • Institut für Materialphysik, University of Vienna, Strudlhofgasse 4, A-1090 Vienna, Austria

C. Fritscher, M. Schmid, and P. Varga

  • Institut für Allgemeine Physik, Vienna University of Technology, Wiedner Hauptstrasse 8-10, A-1040 Vienna, Austria

  • *Electronic address: maca@fzu.cz
  • Present address: Institute of Materials Science and Technology, Vienna University of Technology, Favoritenstrasse 9-11, 1040 Vienna, Austria.

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand
Issue

Vol. 74, Iss. 23 — 15 December 2006

Reuse & Permissions
Access Options
Author publication services for translation and copyediting assistance advertisement

Authorization Required


×
×

Images

×

Sign up to receive regular email alerts from Physical Review B

Log In

Cancel
×

Search


Article Lookup

Paste a citation or DOI

Enter a citation
×