Abstract

Titanium (Ti) is an adhesion and contact metal commonly used in nanoelectronics and two-dimensional (2D) materials research. However, we find that dramatically different film morphology can result when Ti is deposited on graphene (Gr), depending on the experimental conditions. Through a combination of transmission electron microscopy, atomic force microscopy, and Raman spectroscopy, we show that the most critical parameters are the number of Gr layers, the nature of the Gr support, and the deposition temperature. Monolayer Gr is particularly distinctive in both its island morphology and its high defect density in Gr, compared to bilayer or thicker Gr. We attribute these results to the 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. This is supported by ab initio density functional theory calculations which suggest that differences in the Ti interaction between monolayer and thicker Gr are due to extrinsic factors such as surface roughness. 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.

Abstract

Titanium (Ti) is an adhesion and contact metal commonly used in nanoelectronics and two-dimensional (2D) materials research. However, we find that dramatically different film morphology can result when Ti is deposited on graphene (Gr), depending on the experimental conditions. Through a combination of transmission electron microscopy, atomic force microscopy, and Raman spectroscopy, we show that the most critical parameters are the number of Gr layers, the nature of the Gr support, and the deposition temperature. Monolayer Gr is particularly distinctive in both its island morphology and its high defect density in Gr, compared to bilayer or thicker Gr. We attribute these results to the 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. This is supported by ab initio density functional theory calculations which suggest that differences in the Ti interaction between monolayer and thicker Gr are due to extrinsic factors such as surface roughness. 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.

Abstract

Titanium (Ti) is an adhesion and contact metal commonly used in nanoelectronics and two-dimensional (2D) materials research. However, we find that dramatically different film morphology can result when Ti is deposited on graphene (Gr), depending on the experimental conditions. Through a combination of transmission electron microscopy, atomic force microscopy, and Raman spectroscopy, we show that the most critical parameters are the number of Gr layers, the nature of the Gr support, and the deposition temperature. Monolayer Gr is particularly distinctive in both its island morphology and its high defect density in Gr, compared to bilayer or thicker Gr. We attribute these results to the 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. This is supported by ab initio density functional theory calculations which suggest that differences in the Ti interaction between monolayer and thicker Gr are due to extrinsic factors such as surface roughness. 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.

Abstract

Titanium (Ti) is an adhesion and contact metal commonly used in nanoelectronics and two-dimensional (2D) materials research. However, we find that dramatically different film morphology can result when Ti is deposited on graphene (Gr), depending on the experimental conditions. Through a combination of transmission electron microscopy, atomic force microscopy, and Raman spectroscopy, we show that the most critical parameters are the number of Gr layers, the nature of the Gr support, and the deposition temperature. Monolayer Gr is particularly distinctive in both its island morphology and its high defect density in Gr, compared to bilayer or thicker Gr. We attribute these results to the 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. This is supported by ab initio density functional theory calculations which suggest that differences in the Ti interaction between monolayer and thicker Gr are due to extrinsic factors such as surface roughness. 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.