Scanning tunneling spectroscopy on Co(0001):Spectroscopic signature of stacking faults and dislocation lines

The growth morphology and electronic structure of Co(0001) grown on W(110) are studied using scanning tunneling microscopy and scanning tunneling spectroscopy (STS) at T=6 K. Depending on growth conditions, continuous Co films or Co islands on top of a wetting layer are formed. Within the continuous films, dislocation lines appear and increase in density after annealing. Co islands and films exhibit dI/dV curves with a pronounced peak at -0.3 eV below the Fermi energy. The intensity of this peak is changing in different areas of the surface. Using monolayer high islands with a different shape deposited on the same Co layer we attribute the different intensity to a different stacking of the Co surface. The change in intensity is reproduced by first-principles electronic structure calculations, which reveal that the peak is caused by a d(3z)(2)-r(2)-like surface resonance of a minority-spin character more strongly coupled to the bulk states in the case of hcp (ABA) stacking than in the case of fcc (ABC) stacking. An increased STS intensity of the surface resonance was also found above dislocation lines located at the Co/W interface