The surface of 6-7 monolayer thick fcc Fe films grown at room temperature on a Cu(100) substrate is characterized by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The STM images show a p4g(2x2) structure at 5 and 80 K, but not at 300 K. LEED, however, indicates an expansion of the interlayer distance and lateral distortions of similar magnitude both at 150 K and at 300 K. No evidence for a significant change of the surface structure is detected by a LEED spot profile analysis between 150 and 300 K. We attribute the apparent absence of the reconstruction in the STM images at 300 K to surface dynamics caused by domain boundary motion. The particular surface structure with bond angles and distances similar to bcc Fe suggests a driving force of the reconstruction which is similar to that operative in the fcc-to-bcc transition of bulk Fe. Dosing less than 5 Langmuirs H2 decorates the p4g(2x2) surface reconstruction, while higher hydrogen doses transform the surface reconstruction to p(2x1).
Corresponding author: A. Biedermann; reprints also available from M. Schmid (schmid).
This paper was featured in Surface Science Perspectives by L. Hammer et al. [Surf. Sci. 569 (2004) 1-3].
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