Here, we demonstrate that contact resonance atomic force microscopy (CR-AFM) can yield a quantitative, subsurface-structure sensitive, mechanical fingerprint of 2D layered materials. First, we show a new method that combines ab initio and continuum modeling approaches to deconvolute the experimentally measured, aggregate contact stiffness and to quantify the nano-mechanical stiffness contributions from each material layer. We demonstrate the power of our method on epitaxially monolayer (MLG), bilayer (BLG), trilayer graphene (TLG), grown on silicon carbide, i.e., a system for which well-defined structure models exist. The experimental method can clearly distinguish, nanometer-sized, subsurface domains of oxygen-intercalated graphene grown on SiC(0001). Next, we apply CR-AFM to study how the head-group chemistry of self-assembled monolayers (SAMs) affects the interfacial mechanical properties of graphene on SAMs. Variations in these properties affect the stress transfer between substrate and the supported graphene and thus the performance of the graphene-based devices. We show that the changes in interfacial mechanical properties can be characterized through out-of-plane elastic properties measurements. Combining CR-AFM experiments with Molecular Dynamics (MD) simulations we show that the head group chemistry of the SAMs can have a significant effect on the out-of-plane elastic modulus of graphene on SAMs through the interfacial interactions. The MD simulations clearly show that water molecules located at the FLG-SAM interfaces mediate the interaction between graphene and the SAM and are the key factor for the observed stiffness difference between graphene on hydrophobic and hydrophilic SAMs. Our approaches are able to extract, in addition to topographic information, also chemical information from burried interfaces in 2D layered materials by unravelling the origin of mechanical subsurface-structure “fingerprints" with high lateral resolution.

Subsurface structure fingerprint of 2D materials and heterostructures by their nanomechanical response

253rd National Meeting (2017)

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