The Science
Researchers used a special robotic system to assemble very large pieces of atomically clean two-dimensional materials into stacks. The study involved materials called graphene heterostructures. These are sheets just atoms thick made up of tiny hexagonal crystals that change the properties of the electrons in the graphene. This gives the material special properties useful for batteries and other electronics. The assembled materials in this study have record-setting dimensions--as large as 7.5 square millimeters, huge in the world of microelectronics. The robotic assembly tool aided in the discovery of a new interface cleaning mechanism that combines mechanical and thermal forces. This process results in atomically clean 2D heterostructures, a key characteristic in how well these structures perform.
The Impact
Layered assembly of 2D materials such as graphene has potential roles in the development of new electronic devices. Manufacturing these materials at a large scale while making them atomically clean is a major challenge. This new cleaning mechanism is an important tool. It will help nanoscience researchers develop manufacturing protocols for large area, high-quality devices. It will also streamline the production of these materials by removing the need for additional processes after they are cleaned.
Summary
Researchers from New York University and the Center for Functional Nanomaterials (CFN), a Department of Energy Office of Science user facility at Brookhaven National Laboratory, used the CFN Quantum Material Press (QPress) to assemble 2D graphene heterostructures materials. This study showed that the interface cleaning process of layered heterostructures made from contaminated 2D layers involves more complex mechanisms than a simple thermal actuation that is typically used to make clean interfaces. The combination of non-bonding interactions of the polymer with graphene, thermally activated mobilization of polymer residues, and mechanical actuation is essential for fabricating heterostructures with atomically clean interfaces from polyvinyl acetate-contaminated graphene. This study opened a new opportunity to develop a more effective process to make large and clean layered heterostructure devices.
This study used multiple resources at the CFN. The researchers conducted the systematic experiments on the effects of thermal activation and mechanical actuation on the cleaning process using the CFN Quantum Material Press, which is a new, integrated facility for robotic assembly of heterostructures from 2D layered materials. The team also performed density functional theory calculations to understand the interactions between the polymer residues and 2D layers (i.e., graphene). The team examined the heterostructure interfaces using cross-sectional transmission electron microscopy and energy dispersive spectroscopy analysis.
Funding
This research used resources of the Center for Functional Nanomaterials, a Department of Energy Office of Science user facility, at Brookhaven National Laboratory. The research was funded by the National Science Foundation; the Elemental Strategy Initiative conducted by the Ministry of Education, Culture, Sports, Science, and Technology of Japan; and the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research. This work was performed in part at the Advanced Science Research Center Nano Fabrication Facility of the City University of New York.