Nano-scale analysis of graphene layers by tip-enhanced near-field Raman spectroscopy

We demonstrate nano-scale optical analysis of graphene layers by tip-enhanced near-field Raman spectroscopy (TERS). In this technique, the spatial resolution similar to 30 nm is realized by the near-field probe which acts as a nano-light source. From the intensity change of the Raman band of silicon generated from the near-field probe, we can conveniently estimate the edge boundaries and the number of stacking layers. TIERS measurement across the layer edges reveals the nano-scale properties of the material as well as the existence of local defects and edge boundaries. The intensity change of the G-band shows the step-like behavior that follows the layer boundary, whereas the two components in 2D peak show more complex behaviors even inside layers. The peak fluctuation in the 2D band also suggests the local stress distribution due to interlayer interactions. An excess charge effect is observed through the correlation between the peak position and the width of the G-band and their nano-scale distribution within a layer is revealed. Besides the vibrational analysis, we successfully performed the estimation of the number of layers in two-dimensional imaging by the same experimental platform, which allows us high-throughput nondestructive identification of graphene layers critical for the evaluation of this material especially in future device applications. Copyright (C) 2009 John Wiley & Sons, Ltd.