We report the observation of an intense anomalous peak at 1608 cm−1 in the Raman spectrum of graphene associated to the presence of chromium nanoparticles in contact with graphene. Bombardment with an electron beam demonstrates that this peak is distinct from the well studied D′ peak appearing as defects are created in graphene; the new peak is found non dispersive. We argue that the bonding of chromium atoms with carbon atoms softens the out-of-plane optical (ZO) phonon mode, in such a way that the frequency of its overtone decreases to 2ωZO∼ωG, where ωG=1585~cm−1 is the frequency of the Raman-active E2g mode. Thus, the observed new peak is attributed to the 2ZO mode which becomes Raman-active following a mechanism known as Fermi resonance. First-principles calculations on vibrational and anharmonic properties of the graphene/Cr interface support this scenario.
@article{arxiv.2011.09166,
title = {Fermi resonance in the Raman spectrum of graphene},
author = {Dipankar Kalita and Michele Amato and Alexandre Artaud and Laëtitia Marty and Vincent Bouchiat and Johann Coraux and Christian Brouder and Michele Lazzeri and Nedjma Bendiab},
journal= {arXiv preprint arXiv:2011.09166},
year = {2020}
}