Get started
Work

Characterization of the normal and shear interactions between bilayer graphene and sapphire following a novel CVD growth process

Year: 2024
Type: dissertation
Abstract: Being the pioneer 2D material, graphene has been extensively researched owing to its excellent electronic, mechanical, thermal, and optical properties. Copper foil, which is one of the most common substrates employed in graphene CVD (chemical vapor deposition), provides a catalytic surface for the large-area growth of graphene. However, graphene cannot be directly used on copper and needs to be transferred to suitable substrates. Wet transfer methods, which use polymeric support, pose serious challenges such as long processing times, residual organic contamination, and doping from copper etchants. Dry transfer methods that rely on mechanical delamination, on the other hand, allow for recyclability of the growth substrate, eliminate the use of etchants, and provide interfacial mechanical properties between graphene and substrates. Using dry transfer for Cu/graphene has been challenging due to the high adhesion between graphene and copper, and the lack of mechanical rigidity of the foils. To circumvent these challenges, this study focuses on the use of sapphire for the direct, metal-free growth of graphene. An atmospheric pressure CVD process was optimized for obtaining uniform bilayer graphene on sapphire. It was found that thermally annealing the sapphire prior to growth is a key factor in obtaining a suitable surface reconstruction required for growing high quality graphene at conventional metal CVD temperatures. The growth and annealing parameters were optimized, and the graphene was characterized using Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Additionally, the number of layers of synthesized graphene was determined using Raman mapping and high-resolution transmission electron microscopy. Following growth, dry transfer was carried out on laminated beam specimens using a dual actuator loading device. The transfer was carried out under both nominally mode I and mixed mode loading conditions, and the quality and yield of transfer were determined using Raman, SEM and AFM. Using a beam-on-elastic foundation analysis, the adhesion energy and strength of the graphene-sapphire interface was determined experimentally, and it was found that the overall toughness decreased in going from Mode I to Mode II loading. This is the first-time dry transfer of graphene has been carried out under such a range of mixed-mode conditions, and while the current studies have been carried out on strips, these results have significant implications in employing other loading configurations for the transfer which may be easier to employ at wafer-scales. To explore other loading configurations, normal and shear interactions were first experimentally determined at the transferred graphene-silicon interface. A cohesive surface based finite element model was developed on Abaqus to obtain a Mode I transfer map that showed that with competing interfaces, the crack grew along the interface with lower strength rather than lower fracture energy. Finally, using the mixed-mode results of graphene-sapphire and graphene-silicon interfaces, a three-point bending model was proposed on Abaqus to explore the feasibility of a direct, polymer-free, one-step dry transfer of graphene from sapphire to silicon.
DOI: 10.26153/tsw/63025
Language: English
Open Access status: gold
OpenAlex ID: W7136380814
Cites:
Cited by:
Related to: