**8. Conclusions and outlook**

spectra of graphene and functionalized MWNTs is a further proof of evidence of the formation of tetrahedrally coordinated bonds between carbon atoms and molecular groups.

We acquired SERS spectra for each point of a selected area of pristine graphene films with a high-resolution micro-Raman spectrometer (Horiba Xplora) (see **Figure 11**). The areas were scanned with an acquisition grid of 0.6 and 0.8 μm in x and y, respectively. We selected the wavenumber region 500–1280 cm−1 to represent the functional groups concentration and we constructed the SERS images, illustrated in **Figure 11(b)** and **(d)**, plotting the intensity of the

Optical images show significant variation in the dried film thickness along the scanned area, due to a poor dispersibility of pristine graphene in the distilled water. However, the SERS signal is always detectable with good spectral reproducibility and an intensity variation much smaller than that expected, considering that the SERS signal from the second monolayer and beyond is strongly reduced. This finding further confirms that the functional groups are distributed at the edges of graphene structure: the larger thickness and hence the weaker enhancement experienced by the molecular groups, can be compensated by a higher

**Figure 11.** (a) Image of pristine graphene dried film, acquired with the optical microscope coupled with the Raman spectrometer; the green rectangle indicates the region selected to acquire the map (b). (c) and (d) represent the same for another region of the substrate. The visualization of Raman maps is obtained by using as contrast parameters the

peaks located in this region.

intensity of functional group peaks.

concentration.

216 Raman Spectroscopy

In summary, we performed SERS measurements on graphene pristine and functionalized MWNTS and graphene nano-structured film deposited on gold-coated Si nano-pillar substrates. The strong surface enhancement effect allowed us to record the Raman signal from functional molecules that are not recorded in conventional Raman spectra proving experimentally their linkages to the CNT walls and graphene edges. By using the relative intensities of specific SERS features as contrast parameters to obtain SERS maps, it is possible to study the distribution of functional groups across the scanned area.

The obtained results encourage us to consider SERS as a powerful method to obtain a rapid monitor either of the procedures used to interface graphene and nanotubes with functionalizing groups either of synthesis process of graphene as chemical exfoliation.
