Near-Edge X-Ray Absorption Fine-Structure Investigation of Graphene

We report the near-edge x-ray absorption fine-structure (NEXAFS) spectrum of a single layer of graphite (graphene) obtained by micromechanical cleavage of highly ordered pyrolytic graphite on a ${\mathrm{SiO}}_2$ substrate. We utilized a photoemission electron microscope to separately study single-, double-, and few-layers graphene samples. In single-layer graphene we observe a splitting of the ${\pi }^{*}$ resonance and a clear signature of the predicted interlayer state. The NEXAFS data illustrate the rapid evolution of the electronic structure with the increased number of layers.

Figure 1

OM images [(a), (c), and (e)] and PEEM ones [(b), (d), and (f)] of some selected samples (S1, S2, and S3). Scale bars are: $5\mu \mathrm{m}$ in (a) and (e); $10\mu \mathrm{m}$ in (c).

Figure 2

C $K$-edge photoabsorption spectra of (from the bottom): graphene, bilayer graphene, and FLG samples. The dashed lines show the C $1s$ ${\pi }^{*}$ and C $1s$ ${\sigma }^{*}$ transitions.

Figure 3

Expanded C $K$-edge photoabsorption spectra extracted from Fig. 2. The inset shows DOS calculations of single- and double-layer graphene [8], in the energy region (0.0–5.0) eV above $E_F$. The Fermi level, as extracted from Ref. 8, is also reported in the graph. Arrows show the double structure of the ${\pi }^{*}$ resonance in graphene. The separation between the two features in the theoretical DOS of single-layer graphene is about 0.8 eV, while the experimental separation is between 1.2 and 1.8 eV for our samples.

Figure 4

C $K$-edge photoabsorption spectra of graphene taken from sample S2. Upper inset: the Raman spectrum of graphene at 514 nm showing the single component of the 2D peak. Lower inset: close-up of photoabsorption spectra extracted from sample S2.