# Confined step-flow growth of Cu intercalated between graphene and a Ru(0001) surface

## TL;DR

This study demonstrates that graphene acts as a surfactant enabling step-flow growth of Cu films on Ru(0001), contrasting with island growth on bare Ru, and offers new insights into controlling thin film morphology.

## Contribution

It reveals that Cu can intercalate and grow in a step-flow manner beneath graphene on Ru(0001), a novel growth mode induced by graphene's presence.

## Key findings

- Cu intercalates below graphene and grows via step-flow.
- On bare Ru, Cu exhibits Stranski-Krastanov growth.
- Graphene enables flat, controlled Cu film formation.

## Abstract

By comparing the growth of Cu thin films on bare and graphene-covered Ru(0001) surfaces, we demonstrate the role of graphene as a surfactant allowing the formation of flat Cu films. Low-energy electron microscopy, X-ray photoemission electron microscopy and X-ray absorption spectroscopy reveal that depositing Cu at 580 K leads to distinct behaviors on both types of surfaces. On bare Ru, a Stranski-Krastanov growth is observed, with first the formation of an atomically flat and monolayer-thick wetting layer, followed by the nucleation of three-dimensional islands. In sharp contrast, when Cu is deposited on a graphene-covered Ru surface under the very same conditions, Cu intercalates below graphene and grows in a step-flow manner: atomically-high growth fronts of intercalated Cu form at the graphene edges, and extend towards the center of the flakes. Our findings suggest potential routes in metal heteroepitaxy for the control of thin film morphology.