The morphology and interface structure of titanium on graphene

TL;DR

This study investigates how titanium's film morphology on graphene varies with experimental conditions, revealing critical factors like layer number and temperature that influence interface properties and defect formation.

Contribution

The paper combines microscopy, spectroscopy, and theoretical calculations to identify key parameters affecting Ti on graphene morphology and proposes design rules for interface control.

Findings

Ti forms island structures on monolayer graphene with high defect density.

Morphology depends on graphene layer number, support type, and deposition temperature.

Monolayer graphene's flexibility and roughness influence Ti diffusivity and damage.

Abstract

Titanium (Ti) is an adhesion and contact metal commonly used in nanoelectronics and two-dimensional (2D) materials research. However, when Ti is deposited on graphene (Gr), we obtain dramatically different film morphology depending on the experimental conditions. Through a combination of transmission electron microscopy, Raman spectroscopy, and ab initio density functional theory calculations, we show that the most critical parameters are the number of Gr layers, the nature of the Gr support, and the deposition temperature. Particularly distinctive is the island morphology and large defect density of Ti on monolayer Gr, compared to bilayer or thicker Gr. We propose that this results from structural and mechanical differences between monolayer and thicker Gr flakes, where monolayer Gr is more flexible, exhibits larger surface roughness and therefore lower Ti diffusivity, and is more easily damaged. Our results highlight the extreme sensitivity of Ti morphology on Gr to processing and substrate conditions, allowing us to propose design rules for controlling Ti-Gr interface properties and morphology and to discuss the implications for other technologically relevant metal deposition processes.