Wrinkles in graphene on iridium (29th of July 2015)

>> Graphene is a layer of carbon atoms arranged like a honeycomb - carbon atoms form hexagons.

Yesterday, >> a paper was published in Carbon journal with me as a coauthor (impact factor of Carbon is 6.2) entitled Wrinkles of graphene on Ir(111): Macroscopic network ordering and internal multi-lobed structure.

I have worked with one layer of carbon atoms for at least 13 years - those who may be interested can get a detailed insight by inspecting my >> publication list. It all started >> in year 2002 with the adsorption of gases in carbon nanotubes - carbon nanotubes can be thought of as pieces of graphene "folder" into a cylinder / tube. In year 2006 I got interested in the energetics of "folded" graphene which I >> investigated in the framework of theory of elasticity of sheets. This is a classical approach based on a quantum-mechanical calculation of the elastic parameters of graphene, but the same theoretical methods can be applied to a piece of paper or a plastic foil - that is exactly what I did >> in year 2011, in an experimental-theoretical work dealing with pressing of cylinders made of foil for overhead projectors. A recent "experiment" on that track is shown in the photo below (in preparation) - this is a circular paper strip confined within a screw cap of a bottle.

paper strip in a screw cap of a bottle

I also investigated carbon nanotubes in the context of >> van der Waals interactions (in year 2009), and I was applying theory of elasticity of sheets and shells to different systems, >> especially viruses.

>> The paper published yesterday reports observation of wrinkle formation in a graphene layer on iridium substrate. On iridium surface, graphene is made from ethylene heated to high temperatures. When the temperature is lowered, the iridium substrate shrinks (metals expand on high temperatures), significantly more than the graphene layer whose thermal expansion coefficient is negligible. That is why the graphene wrinkles, following in that way the shrinking of the substrate (iridium).

All that was known for some time, but in our work the process of wrinkle formation was experimentally investigated in details. We observed wide wrinkles, having several maxima (lobes) and "woven" into a two-dimensional network which was approximately described as (non-Poissonian) Voronoi tiling of the surface (... huh ...). Formation of multi-lobed wrinkles was explained as a consequence of competition of energies - one (elastic) required to wrinkle the graphene and the other (van der Waals) resulting from the interaction of graphene with the substrate.

Concerning visualization, the image below made by the first author of the paper, Marin Petrović (with his permission), shows triple wrinkles meeting in a 120 degrees crossing. Exactly such crossings (120 degrees) were observed experimentally.

Last updated on 29th of July 2015.