E Evgeniy Tkalya

Tip-Enhanced Raman Spectroscopy and Mapping of Graphene Sheets

Abstract: Single graphene sheets, a few graphene layers, and bulk graphite, obtained via both micromechanical cleavage of highly oriented pyrolytic graphite and carbon vapor deposition methods, were deposited on a thin glass substrate without the use of any chemical treatment. Micro-Raman spectroscopy, tip-enhanced Raman spectroscopy (TERS), and tip-enhanced Raman spectroscopy mapping (TERM) were used for characterization of the graphene layers. In particular, TERM allows for the investigation of individual graphene sheets with high Raman signal enhancement factors and allows for imaging of local defects with nanometer resolution. Enhancement up to 560% of the graphene Raman band intensity was obtained using TERS. TERM (with resolution better than 100 nm) showed an increase in the number of structural defects (D band) on the edges of both graphene and graphite regions.

Experimental and theoretical study of the influence of the state of dispersion of graphene on the percolation threshold of conductive graphene/polystyrene nanocomposites

The effect of the dispersed state of graphene is studied as a factor influencing the electrical percolation threshold of graphene/polystyrene nanocomposites. We find the percolation threshold of our nanocomposites, prepared with graphene dispersions with different thermodynamic stabilities, degrees of exfoliation, and size polydispersities, to range from 2 to 4.5 wt %. Connectedness percolation theory is applied to calculate percolation thresholds of the corresponding nanocomposites, based on the premise that size polydispersity of graphene platelets in the corresponding solutions must have a strong influence on it. Theory and experimental results agree qualitatively.