Prof. Vikas Berry, Kansas State University
May 2, 2013
11:00 AM - 12:00 PM
Properties and Applications of Graphene Quantum materials and Graphene-Encased Biological Cells
Abstract:
This presentation will outline the extraordinary properties of graphene and will then discuss the results of two recently completed projects: (A) graphene nanostructures for energy and semiconducting applications, and (B) graphene encasement for liquid-phase imaging under electron microscopy conditions. (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 (published in Nature Communications). This is achieved by diamond-edge-induced nanotomy (nanoscale-cutting) of graphite into graphite nanoblocks, which are then exfoliated (overall yield ~ 80 %). The edges of these graphene nanostructures are straight and relatively smooth with a Raman ID/IG ratio of 0.22–0.28 (roughness < 1 nm). Further, thin films of GNRs exhibit a bandgap evolution with width reduction (0, 10 and ~35 meV for 50, 25 and 15 nm, respectively). 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. The presentation will also demonstrate a humidity sensor based on electron-tunneling modulation between GQDs. (B) Imaging of hygroscopic, permeable, and electron-absorbing biological cells under transmission electron microscopy (TEM) at high vacuum and fixed electron beam has been a challenge due to the resultant volumetric-shrinkage, electrostatic charging, and structural degradation of cells. The second part of the seminar will demonstrate that bacterial cells can be encased within graphenic chambers to preserve their dimensional and topological characteristics under high vacuum (10-5 Torr) and beam current (150 A/cm2) (published in Nano Letters). The strongly-repelling clouds in the interstitial sites of graphene’s lattice reduces the graphene-encased-cell’s permeability from 7.6 – 20 nm/s to 0 nm/s. The C-C bond flexibility enables conformal encasement of cells. Additionally, graphene’s high Young’s modulus retains cell’s structural integrity under TEM conditions, while its high electrical and thermal conductivity significantly abates electrostatic-charging. Further, a novel process to wrap liposomes with liquid samples will be shown. We envision that the graphenic encasement approach will facilitate real-time TEM imaging of fluidic samples and potentially obtain snapshots of live biochemical activities.
Date posted
Jun 17, 2019
Date updated
Jun 17, 2019