The research objective of this grant is to elucidate the adhesive interactions between graphene and other materials that might be used in producing large areas of graphene, one of the stiffest and strongest materials known to man. An interfacial force microscope will be used to probe graphene on a variety of substrates with a variety of probe materials. The response will be modeled by a combination of molecular and continuum models to extract traction-separation relations as the continuum representations of these interactions both normal and tangential to the contact surface. The contact radii encountered in IFM experiments are typically 50-100 nm. Scale up issues will then be addressed in fracture experiments where substrate/graphene/substrate laminates are delaminated in a variety of loading conditions, in order to examine the graphene interfaces over larger domains. A special high vacuum fracture facility will allow these interactions to be examined over a range of environmental conditions.
The proposed research will advance our ability to tailor the adhesive characteristics, strength and durability of integrated materials and structures that make use of graphene for novel applications. It also lays the foundation for examining interactions among other types of surfaces such as chemically modified graphene and functionalized carbon nanotubes. Education and outreach activities will be integrated within the proposed project to enhance its societal impacts.
Graphene, which is an allotrope of carbon that is only one atomic layer thick, has attracted much attention since it was discovered in 2004. Its extraordinary optoelectronic and mechanical properties have attracted much attention in a wide range of potential applications. Many of the attractive properties of graphene will only be realized when it can be mass produced. The development of a process known as chemical vapor deposition, where the graphene is grown on a seed metal at high temperature, has allowed graphene to be produced on a massive scale. One current bottleneck in the production of graphene is its efficient transfer between various substrates in nano manufacturing processes such as roll-to-roll and transfer printing. In general graphene will need to be removed from its seed metal and transferred to substrates of interest; both steps require the adhesive behavior between graphene and substrates to be known. The objective of this study was to develop such understanding based on multiscale simulations informed by novel experiments. Intellectual Merit: The intellectual merit of the proposed research stems from the experimental techniques that were developed along with analytical and computational models to understand and characterize the adhesive interactions and the coupling of this understanding to the production of large area graphene. The strength, range and adhesion energy the of the interactions between graphene and its seed layer as well as graphene that had been transferred to silicon, copper and polymer substrates was determined in a series of innovative experiments that allowed the ultra-thin graphene layer to be transferred mechanically while load, displacement, crack length and separations were being measured. The responses were modeled by a combination of atomistic and continuum models to extract traction-separation relations as the continuum representations of these interactions both normal and tangential to the contact surface. A key finding of this work was that, in all cases, the interaction ranges were surprisingly long. This ruled out the commonly held view that the interactions between graphene and substrates are dominated by Van der Waals forces. Particularly for transferred graphene, the presence of moisture was more likely but even then the interaction distances were too long. The modeling component of the work has led to the conclusion that the interactions between both graphene and seed layers and target substrates are dominated by roughness effects. On a very practical level, it has been found that graphene can be selectively transferred by mechanical rather than chemical or electrochemical approaches. This bodes well for mass production schemes such as transfer printing and roll-to-roll transfer. Broader Impacts: This research has advanced our ability to understand and therefore tailor the adhesive characteristics, strength and durability of integrated materials and structures that make use of graphene for novel applications. It has also laid the foundation for developing and implementing nano manufacturing processes for the efficient and effective transfer of large area graphene. The research results have been broadly disseminated through six publications in archival journals and presentations at technical meetings. Education and outreach activities have been integrated within the proposed project to enhance its societal impacts. Four graduate students have been trained with broad knowledge and experience working in interdisciplinary environments. Three undergraduate students, including two Hispanic students, have been provided with research experiences and contributed positively to the overall research goals of the project. Presentations have been made and tours have been provided to students at the Anne Richards School for Girls and Manor Tech, which are both promoting STEM education in Central Texas.
