Nanotomy of Graphite to Produce Graphene Nanostructures of Controlled Structure and Transport Properties; and Graphene-Based Sensors for Molecular-Mechanics

Vikas Berry, Kansas State University

This presentation will consist of two parts: (A) carrier transport properties of graphene nanostructures, and (B) graphene sensors for molecular mechanics. (A) Due to electronic edge states and quantum confinement, graphene nano-ribbons (GNRs) and graphene quantum dots (GQDs) – single-atom-thick nanostructures of sp2 hybridized carbon atoms – exhibit shape and size dependent electrical, magnetic, optical and chemical properties. These properties can be tuned over a wide range by controlling the nanostructure of GNRs and GQDs. However, large-scale synthesis of these graphene nanostructures (GNs) with predetermined shape/size has remained a challenge. This talk will demonstrate a route to produce GNs with predetermined shapes (square, rectangle, triangle and ribbon) and controlled dimensions. This is achieved by diamond-edge-induced nanotomy (nanoscale-cutting) of graphite into graphite nanoblocks, which are then exfoliated. The overall yield of the process is ~ 80 %. Our results show that the edges of the produced graphene nanostructures are straight and relatively smooth with a Raman ID/IG ratio of 0.22–0.28 and roughness < 1 nm. Further, the talk will also show the first direct proof that thin films of GNRs exhibit a bandgap evolution with width reduction (0, 10 and ~35 meV for 50, 25 and 15 nm, respectively). The high throughput method to synthesize GN of high-quality is a quantum leap in graphene research. We envision that this versatile proc¬ess can provide access to a wide variety of GNs at large densities (on substrates or as dispersions) for development of fundamental optical/electrical/structural correlations and novel applications. Further, the nanotomy process may be applied to other 2D nano-materials (BN, MoS2 and NbSe2) to produce unique 2D nanostruc¬tures, which can significantly expand the scope of their applications and fundamental studies. (B) The second part of the talk will demonstrate that the lateral charge confinement and the quantum capacitance of ultrathin graphenic sheets can enable detection of molecular mechanics on its surface. Here, graphenic sheets functionalized with azo-benzene-molecules are externally isomerized from their trans state (benzene head faces away from graphene) to cis state (benzene head is closer to graphene). We show that the 12 picometer displacement of the azo’s benzene head changes the dipolar interaction with graphene to generate 7.5 X 103 holes/m2. This phenomena is similar to electrical gating and corresponds to the 5 nA increase in current for 100 mV source-drain voltage in the p-type device. Unfunctionalized graphene oxide devices do not show this response. We envision that graphene’s sensitivity to mechanically-active molecules can make it an important component of next-generation molecular machines.