Emergence of metallic surface states and negative differential conductance in thin β-FeSi2films on Si(001)

Keisuke Sagisaka; Tomoko Kusawake; David Bowler; Shinya Ohno

doi:10.1088/1361-648X/acb628

Emergence of metallic surface states and negative differential conductance in thin β-FeSi₂films on Si(001)

J Phys Condens Matter. 2023 Feb 10;35(13). doi: 10.1088/1361-648X/acb628.

Authors

Keisuke Sagisaka¹, Tomoko Kusawake¹, David Bowler^{2

3

4}, Shinya Ohno⁵

Affiliations

¹ Research Center for Advanced Measurement and Characterization, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
² London Centre for Nanotechnology, University College London, 17-19 Gordon St., London WC1H 0AH, United Kingdom.
³ Department of Physics & Astronomy, University College London, Gower St, London WC1E 6BT, United Kingdom.
⁴ International Centre for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
⁵ Yokohama National University, 79-5 Tokiwadai Hodogaya-ku, Yokohama, Kanagawa 240-8501, Japan.

PMID: 36696697
DOI: 10.1088/1361-648X/acb628

Abstract

The electronic properties of the surface ofβ-FeSi₂have been debated for a long. We studied the surface states ofβ-FeSi₂films 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 Romanyuket al(2014Phys. Rev.B90155305) 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 theβ-FeSi₂film, irrespective of the polarity of the substrate. We also observed negative differential conductance at ∼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 ofβ-FeSi₂.

Keywords: density functional theory calculations; local density of states; scanning tunneling microscopy; scanning tunneling spectroscopy; silicide thin films.