Scanning tunneling microscopy and spectroscopy study on the submonolayer growth of Mn on Fe( [formula omitted

Abstract

The submonolayer growth of Mn on Fe(0 0 1) in the temperature range between 50 and 200 °C is studied by scanning tunneling microscopy and scanning tunneling spectroscopy. For growth temperatures above 100 °C, atomically resolved STM images with chemical contrast clearly reveal the incorporation of Mn atoms in the Fe(0 0 1) substrate. The fraction of place exchanged Mn atoms is observed to increase with growth temperature. Although on islands a c(2×2) structure forms locally which is attributed to an ordered MnFe surface alloy, long range order could not be obtained for the growth temperatures and coverages studied. Spectroscopy results are presented for clean Fe(0 0 1), pure Mn ad-islands, single incorporated Mn atoms and c(2×2)-ordered MnFe areas. In contrast to embedded Cr atoms in the Fe(0 0 1) surface [Phys. Rev. Lett. 76 (1996) 4175], isolated embedded Mn atoms do not lead to double peak structures in d I/d V curves. Nevertheless, on the ordered c(2×2) MnFe structure and the pure Mn monoatomic islands surface states are detected as peaks in the d I/d V and (d I/d V)/( I/ V) curves. However, due to the strong influence of a tip-dependent background on these peaks, the corresponding surface state energies cannot be found directly from those curves. The real surface state energies were recovered by normalizing the measured d I/d V curves by fitted quadratic backgrounds. Thus, surface state energies of about +0.35 and +0.25 eV are estimated for pure Mn islands and alloyed MnFe areas, respectively.