Interface effects on titanium growth on graphene

TL;DR

This study investigates the atomic-scale interface between titanium and graphene, revealing epitaxial growth, lattice strain, and charge transfer, which are crucial for improving graphene-based electronic devices.

Contribution

It provides detailed atomic-level insights into Ti growth on graphene, including epitaxial relationships, strain effects, and growth modes, using advanced microscopy and spectroscopy techniques.

Findings

Ti forms a 30° epitaxial relationship with graphene.

Ti lattice is strained by approximately 3.7% at monolayer thickness.

Ti initially grows in clusters rather than fully wetting the graphene surface.

Abstract

Poor quality interfaces between metal and graphene cause non-linearity and impair the carrier mobility in graphene devices. Here, we use aberration corrected scanning transmission electron microscopy to observe hexagonally close-packed Ti nano-islands grown on atomically clean graphene, and establish a 30{\deg} epitaxial relationship between the lattices. Due to the strong binding of Ti on graphene, at the limit of a monolayer, the Ti lattice constant is mediated by the graphene epitaxy, and compared to bulk Ti, is strained by ca. 3.7% to a value of 0.306(3) nm. The resulting interfacial strain is slightly greater than what has been predicted by density functional theory calculations. Our early growth stage investigations also reveal that, in contrast to widespread assumptions, Ti does not fully wet graphene but grows initially in clusters with a thickness of 1-2 layers. Raman spectroscopy implies charge transfer between the Ti islands and graphene substrate.