Subsurface imaging of two-dimensional materials at the nanoscale.

Scanning probe microscopy (SPM) represents a powerful tool that, in the past 30 years, has allowed for the investigation of material surfaces in unprecedented ways at the nanoscale level. However, SPM has shown very little capability for depth penetration, which several nanotechnology applications require. Subsurface imaging has been achieved only in a few cases, when subsurface features influence the physical properties of the surface, such as the electronic states or the heat transfer.

Electromechanical sensing of substrate charge hidden under atomic 2D crystals.

The functionality of graphene and other two-dimensional materials in electronic devices is highly influenced by the film-substrate charge transfer affecting local carrier density. We demonstrate that charges buried under the few layer graphene on/in the insulating substrate can be detected using electromechanical actuation of the conductive atomically thin layers, allowing measurements of areal density of film-substrate transferred charges under few layer graphene and MoS2 suspended films.

Nanoscale interfacial interactions of graphene with polar and nonpolar liquids.

While mechanical and frictional properties of graphene in air have been extensively studied, graphene's nanomechanical behavior in liquids, vital for its operation in rechargeable batteries, supercapacitors, and sensors, is still largely unexplored. In this paper, we investigate the nanomechanics of normal (adhesive and elastic) and tangential (friction) forces between a stationary, moving, and ultrasonically excited nanoscale atomic force microscope (AFM) tip and exfoliated few layer graphene (FLG) on SiO2 substrate as a function of surrounding media-air, polar (water), and nonpolar (dodecane) liquids. We find that, while the friction coefficient is significantly reduced in liquids, and is always lower for FLG than SiO2, it is higher for graphene in nonpolar dodecane than highly polar water.