  The in-plane optical phonons around 200 meV in few-layer graphene are
investigated utilizing infrared absorption spectroscopy. The phonon spectra
exhibit unusual asymmetric features characteristic of Fano resonances, which
depend critically on the layer thickness and stacking order of the sample. The
phonon intensities in samples with rhombohedral (ABC) stacking are
significantly higher than those with Bernal (AB) stacking. These observations
reflect the strong coupling between phonons and interband electronic
transitions in these systems and the distinctive variation in the joint density
of electronic states in samples of differing thickness and stacking order.
