Graphene surface tuning could enable wearable, stretchable technologies

10/28/2019

Veronica Holloway

Postdoctoral researcher Jangyup Son and his advisor, Assistant Professor Arend van der Zande, have opened a world of possibilities by discovering a method of using chemical functionalization to tune and pattern graphene’s surface properties.

They have published the resulting paper, “Tailoring Surface Properties via Functionalized Hydrofluorinated Graphene Compounds,” in the leading journal Advanced Materials

Postdoctoral researcher Jangyup Son.
Postdoctoral researcher Jangyup Son.
As a single layer of carbon atoms, graphene is the ultimate limit of both a mechanical atomic membrane and an electronic material, with many potential applications. However, the same property that stabilizes it as a monolayer, called the van der Waals interface, makes it such that graphene does not interact very strongly with its environment. Several years ago, researchers found that graphene can be covalently functionalized with fluorine or hydrogen to form fluorinated or hydrogenated graphene. These new materials significantly change how the graphene interacts with its environment – such as the electronic conductivity or the surface wettability – and the fluorinated and hydrogenated graphene affect the surface in opposite ways. The challenge was to achieve the desired level of interaction from the functionalized surfaces, because different applications and devices require different levels of interaction.

The innovation by the van der Zande lab was to perform the functionalization with both fluorine and hydrogen consecutively to create hydrofluorinated graphene, a substance for which they can actually tune the surface characteristics between two extremes of fluorinated and hydrogenated graphene. This concept is a nanoscale equivalent to the use of compounding or alloying in bulk materials to tailor properties like corrosion resistance, mechanical strength or optical bandgap. Depending on the ratio of functionalization between the two elements, the wettability and surface friction of the graphene could be tailored to the desired level. Moreover, using standard lithographic patterning techniques from microelectronics, the team showed that it is possible to imprint patterns such as gradients or patches of different functionalization onto the surface of the graphene, making it useful for devices. 

Assistant Professor Arend van der Zande.
Assistant Professor Arend van der Zande.
The hope among researchers is to create 2D integrated systems such as atomically thin electronic circuits, lab­on­a­chip (LOC), and chemically patterned nanotemplates for future transparent, wearable, flexible, and stretchable technologies, and the discoveries from this work may be the key to enabling those technologies. One current barrier includes the inability to attract the desired molecules to interact with the surface of the graphene, but the MechSE team’s newfound ability to tune and pattern those surfaces may enable such interactions. The lab has successfully shown the tuning capabilities of hydrofluorinated graphene and their next steps are seeing how well molecules take to these different surface characteristics and patterns.

The publication’s significance is in the introduction of a new, foundational approach to patterning a surface. Son credits van der Zande for the guidance he gives in foundational research and noted the importance of his advisor’s ability to find the most compelling research path and follow it. 

“Actually, in this work, we began with a different hypothesis, that one functionalization would prevent the other gas from reacting with the graphene surface, thereby creating an atomically thin mask. However, when we started the research, we found the compounding process instead, which turned out to be just as interesting and potentially more useful.” said Son. “I feel Arend is an expert who finds hidden scientific meanings and lets the data lead him to the most interesting questions.”