First Principles Study of Bismuth Films on the Nickel(111) Surface

TL;DR

This study uses density functional theory to investigate the stability of bismuth films on Ni(111), revealing that covalent bonding and bulk-like structures are more favorable than free-electron-based models.

Contribution

It challenges previous free-electron models by demonstrating the stability of rhombohedral Bi films due to covalent bonding, not quantum size effects.

Findings

HCP film stability does not match experimental odd-layer preference.

Rhombohedral Bi structures are energetically more favorable.

Covalent bonding explains the stability of Bi films better than free-electron models.

Abstract

A recent experiment(Bollmann11) suggested that bismuth forms hexagonal close packed (HCP) films on the Ni(111) surface, of heights 3, 5 and 7 layers. A quantum size effect based on free electrons was proposed in explanation. To test this idea, we calculate the total energies of Bi on the Ni(111) surface using density functional theory. We find that HCP film stabilities disagree with the observed odd layer preferences, and the structures are mechanically destabilized by adding capping atoms which pucker the HCP layers. Furthermore, we find that rhombohedral films based on the bulk Bi structure are energetically more favorable than the proposed HCP films. These structures also favor odd numbers of layers, but owing to covalent chemical bonding rather than confinement of free electrons. Specifically, a strongly bound adsorbed surface monolayer forms, followed by bulk-like rhombohedral bilayers.