Mechano-chemical coupling in single-layer graphene


Nov. 2015 – Nov. 2017: Post-doctoral Associate, Fondecyt Fellow (chilean ministry for Science and Technology). Collaboration with Professor Francisco Melo at  SMAT-C, Santiago de Chile.
Title: Influence of fluid adsorption on the mechanical properties of single layer Graphene.
Keywords: 2D materials, nanomechanics, mechano-chemical coupling.

Graphene is a carbon-based honeycomb structure only one atom thick (see figure 1). This unique configuration confers to graphene its exceptional thermal, electrical, optical and mechanical properties, as well as new insight into unconventionnal physics. Those can be shown to the general public using a simple ripple tank. The discovery of graphene has been rewarded the Nobel Prize 2010 to Andre Geim and Konstantin Novoselov. Graphene could soon be used in the future in various fields such as composite materials, electric batteries, quantum computation and even hydrogen storage. Researchers have recently built a graphene sensor that is 1000 times more light sensitive while using 10 times less energy than usual CMOS sensors. Find more about Graphene and its futuristic applications in the great TED talk below.

Figure 1- View of Graphene, a carbon honeycomb lattice only one atom thick. Credit: CRANN/SuperSTEM.

Whereas conventional bulk and thin film materials have been studied extensively, the key mechanical behavior of graphene such as tearing, cracking and folding are just being explored.
This is partly due to its bidimensional nature and ultimate single-atom-layer thickness, which is hard to manipulate and cannot be understood by conventional thin film material models.

Many studies have already looked at some of the interesting transport properties of these structures. A major challenge for nanofluidics lies in building distinct, well controlled but easy-to-make nanochannels and nanocapsules, amenable to the systematic exploration of their properties. In that state of mind, this project proposes to study the complex behavior of graphene under compression and bending in two complimentary configurations (floating on a fluid interface and resting on soft corrugated substrate) and further explore its very specific mechanical properties.

A crucial point is that spontaneous strain localization modes and patterns on “soft” elastic surfaces in compression are highly sensitive and fundamentally different whether a “hard” surface layer is present or not. Folds tend to emerge from post-buckling evolution during a wrinkling process (see Brau2013), where undulations release in-plane compression of the film (as bending is energetically less costly than compression) accompanied by bulk deformation of the foundation material.

With a fluid substrate, the formation of a crease often undergoes a discontinuous transition from a flat surface to a sharp cusp, bypassing the wrinkling state. Creases are thus very different localization processes than folds. We also developed the interesting potential of graphene as a sealing window and achieve encapsulation of biological systems. The mechanical properties of such structures should lead to new interesting physics and prove valuable to develop strategies to study biological samples in real-life conditions with very high-resolution electron microscopy.

Scanning confocal Raman spectroscopy working together with AFM provides a powerful technique to access mechanical and topographic properties of corrugated graphene. Encapsulated micro/nano-droplets can be achieved by mechanical contact of two layers of graphene and be probed by AFM nanoindentation, which should provide clues about the unknown behavior of liquid at the nanoscale. Encapsulation with graphene of biological samples, such as DNA and red blood cells, will be further studied under real-life conditions and at very high-resolution.