Initial Stages of FeO Growth on Ru(0001)

TL;DR

This study investigates the growth mechanisms of FeO films on Ru(0001) using real-time microscopy, revealing how oxygen pressure and temperature influence film thickness and nucleation density during molecular beam epitaxy.

Contribution

It provides new insights into how oxygen pressure and temperature control FeO film thickness and nucleation during growth on Ru(0001).

Findings

Bilayer FeO islands form at higher oxygen pressure.

Single-layer FeO islands form at lower oxygen pressure.

Temperature affects nucleation density independently of oxygen pressure.

Abstract

We study how FeO w\"{u}stite films on Ru(0001) grow by oxygen-assisted molecular beam epitaxy at elevated temperatures (800-900 K). The nucleation and growth of FeO islands are observed in real time by low-energy electron microscopy (LEEM). When the growth is performed in an oxygen pressure of 10-6 Torr, the islands are of bilayer thickness (Fe-O-Fe-O). In contrast, under a pressure of 10-8 Torr, the islands are a single FeO layer thick. We propose that the film thickness is controlled by the concentration of oxygen adsorbed on the Ru. More specifically, when monolayer growth increases the adsorbed oxygen concentration above a limiting value, its growth is suppressed. Increasing the temperature at a fixed oxygen pressure decreases the density of FeO islands. However, the nucleation density is not a monotonic function of oxygen pressure.