Reconstructed bcc Co films on the Cr(110)/W(110) surface

Ultrathin epitaxial Co films on Cr(110) are examined by scanning tunneling microscopy and spectroscopy (STM and STS). At room temperature Co grows as pseudomorphic bcc layers for the first two monolayers and forms close-packed Co layers with stacking faults for thicker coverages. A periodic lattice distortion appears in two equivalent (3 × 1) reconstruction domains in combination with a regular lattice of dislocation lines oriented along the in-plane close-packed row directions bcc[11¯1] and bcc[1¯11]. The reconstruction and the occurrence of dislocation lines are caused by the epitaxial strain. The local density-of-states function is mapped by scanning tunneling spectroscopy. The bcc Co layers show pronounced differences in comparison to close-packed layers in agreement with theoretical predictions.