Emergence of metallic surface states and negative differential conductance in thin β-FeSi2 films on Si(001)

The electronic properties of the surface of beta-FeSi2 have been debated for a long. We studied the surface states of beta-FeSi2 films grown on Si(001) substrates using scanning tunnelling microscopy (STM) and spectroscopy (STS), with the aid of density functional theory calculations. STM simulations using the surface model proposed by Romanyuk et al (2014 Phys. Rev. B 90 155305) reproduce the detailed features of experimental STM images. The result of STS showed metallic surface states in accordance with theoretical predictions. The Fermi level was pinned by a surface state that appeared in the bulk band gap of the beta-FeSi2 film, irrespective of the polarity of the substrate. We also observed negative differential conductance at similar to 0.45 eV above the Fermi level in STS measurements performed at 4.5 K, reflecting the presence of an energy gap in the unoccupied surface states of beta-FeSi2.

Automated summary

The electronic properties of the surface of beta-FeSi2 were studied using scanning tunnelling microscopy (STM) and spectroscopy (STS) with density functional theory calculations. The STM simulations reproduced the experimental images, while the STS revealed metallic surface states as predicted by theory. The Fermi level was pinned by a surface state within the band gap of beta-FeSi2, regardless of substrate polarity. An energy gap in the unoccupied surface states of beta-FeSi2 was observed, resulting in negative differential conductance at approximately 0.45 eV above the Fermi level in STS measurements at 4.5 K.