A new study reports on the tendency of stacks of graphene to form saw-tooth crinkles with intense electrical charges when compressed. Source: Kim Lab/Brown University.Another peculiar and potentially useful property of wonder-material graphene has been reported in a study from Brown University. The researchers call it “quantum flexoelectric crinkles.”

The study demonstrates mathematically what happens to stacks of graphene — one atom-thick sheets of carbon — under slight lateral compression. Rather than forming smooth, gently-sloping warps and wrinkles across their surface, the layered graphene forms sharp, saw-tooth kinks. Each produces a thin line of intense electrical charge, a flexoelectric phenomenon that could be useful in a variety of applications including guiding nanoscale self-assembly and analyzing DNA or other biomolecules.

The charge, according to study senior author Kyung-Suk Kim, is generated by the quantum behavior of electrons surrounding the carbon atoms in the graphene lattice. When the atomic layer is bent, the electron cloud becomes concentrated either above or below the layer plane. That electron concentration causes the bend to localize into a sharp point, producing a line of electrical charge roughly one nanometer wide and running the length of the crinkle.

Moreover, across the tip of an upraised ridge, the charge is negative; it’s positive along the bottom of a valley. The charged crinkles attract particles with an opposite charge, causing them to assemble along crinkle ridges or valleys.

According to Kim, particle assembly along crinkles has already been observed in previous experiments, but at the time it was unclear what was happening.

For instance, an experiment that involved graphene sheets and buckyballs — soccer-ball-shaped molecules formed by 60 carbon atoms — showed that, in one particular type of multilayer graphene, the balls spontaneously assembled themselves into straight chains stretching across the surface.

Biomolecules like DNA and RNA, most of which possess an inherent negative charge, have also been seen to arrange themselves in peculiar patterns. Kim envisions engineering a crinkled surface that causes DNA molecules to stretch out in straight lines, making them easier to sequence.

"Now that we understand why these molecules line up the way they do, we can think about making graphene surfaces with particular crinkle patterns to manipulate molecules in specific ways," he added.

The research appears in Proceedings of the Royal Society.