Low energy phonon dynamics of graphene-like monolayers

There is emerging interest in the deformation dynamics of graphene and 2D graphene-like materials that couple to the electronic, optical, mechanical and thermal properties. Most of these studies have relied on molecular dynamics simulations to predict the occurrence of rippling and buckling deformations developed in relation to low energy and long wavelength phonons involving out- of-plane motions of the 2D structures. In the course of a series of QENS (quasi- elastic neutron scattering) measurements designed to investigate the dynamics of the polytriazine imide (PTI) carbon layers and H2O molecules intercalated within them, we discovered the existence of a low energy dispersive phonon. We associate it with buckling of the C6N9H3 nanosheets, that is predicted by ab initio density functional theoretical (DFT) and quantum molecular dynamics (QMD) calculations. This would represent the first observation of the low energy phonon dynamics in graphene-related nanomaterials using QENS to probe the intralayer excitations via the H atoms bound to them within the intercalant free PTI (IF-PTI) structure.