Surface Modification and Subsequent Fermi Density Enhancement of Bi(111)

Kuanysh Zhussupbekov; Killian Walshe; Brian Walls; Andrei Ionov; Sergei I Bozhko; Andrei Ksenz; Rais N Mozhchil; Ainur Zhussupbekova; Karsten Fleischer; Samuel Berman; Ivan Zhilyaev; David D O'Regan; Igor V Shvets

doi:10.1021/acs.jpcc.0c07345

Surface Modification and Subsequent Fermi Density Enhancement of Bi(111)

J Phys Chem C Nanomater Interfaces. 2021 Mar 18;125(10):5549-5558. doi: 10.1021/acs.jpcc.0c07345. Epub 2021 Mar 5.

Authors

Affiliations

¹ School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Dublin 2, Ireland.
² Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Russia.
³ School of Physical Sciences, Dublin City University, Dublin 9, Ireland.
⁴ Institute of Microelectronics Technology and High Purity Materials, Russian Academy of Sciences, Chernogolovka, Russia.
⁵ AMBER, the SFI Research Centre for Advanced Materials and BioEngineering Research, Dublin 2, Ireland.

Abstract

Defects introduced to the surface of Bi(111) break the translational symmetry and modify the surface states locally. We present a theoretical and experimental study of the 2D defects on the surface of Bi(111) and the states that they induce. Bi crystals cleaved in ultrahigh vacuum (UHV) at low temperature (110 K) and the resulting ion-etched surface are investigated by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), and scanning tunneling microscopy (STM) as well as spectroscopy (STS) techniques in combination with density functional theory (DFT) calculations. STS measurements of cleaved Bi(111) reveal that a commonly observed bilayer step edge has a lower density of states (DOS) around the Fermi level as compared to the atomic-flat terrace. Following ion bombardment, the Bi(111) surface reveals anomalous behavior at both 110 and 300 K: Surface periodicity is observed by LEED, and a significant increase in the number of bilayer step edges and energetically unfavorable monolayer steps is observed by STM. It is suggested that the newly exposed monolayer steps and the type A bilayer step edges result in an increase to the surface Fermi density as evidenced by UPS measurements and the Kohn-Sham DOS. These states appear to be thermodynamically stable under UHV conditions.