A collaboration with Institut Néel (Grenoble) 

In the development of graphene based electronic devices a lot of care is usually taken in order to preserve its outstanding electronic properties. The quality of the graphene itself and the absence of defects or contamination are at the heart of most of the researches. A lot of efforts are also focused on the choice of the substrate which is known to play an important role. However, these devices require the presence of metallic electrodes to connect it to the outside world. Very little is known about the impact of these metallic contacts on the properties of graphene. In particular, the mechanical stress that is induced in graphene during the metal thin film deposition can greatly influence the graphene properties near the contact and further limit the electronic mobility of the global device.

STM imaging and tunneling spectroscopy of graphene performed in the vicinity of a metallic film deposited on top of it, reveal intense shear stress. They lead to a series of mechanical instabilities which take different morphologies as one comes closer to the metal contact edges. In particular, for positions less than a micron away from the contact, we show a bias dependent rippling of graphene which is enhanced by increasing the transverse electric field induced under the tip of the STM. (Fig. 1A & 1B) These ripples are suspended areas of graphene which can be easily pulled by the STM electric field and therefore manipulated at will. In extreme situations, we observed a strong buckling of graphene nearby the metallic electrode. (Fig. 1C) In this case tunneling spectroscopy reveals a gap of a few hundred millivolts in the local electronic density of states in graphene. This gap can be explained by the interplay of quantum confinement and Coulomb blockade.