The unique lattice dynamics of nanodiamond - a molecular dynamics and inelastic neutron scattering investigation

Abstract

Nanoparticles exhibit remarkable properties owing to their size-dependent quantum effects and high surface-to-volume ratio. Among such particles, carbon-based nanoparticles stand out for their diverse and extreme properties. In particular, nanodiamond has gained a lot of attention due to its combination of extremely high surface-to-volume ratio (due to confinement in 3 dimensions), unique thermal, optical, and structural properties, and biocompatibility. Most recently, nitrogen-vacancy (NV) centres in nanodiamond have captivated the attention of researchers due to their potential use in quantum sensing, nanoscale imaging, thermometry, and more. Controlling and harnessing the intrinsic lattice vibrations (i.e., phonons) in nanodiamond, including their interaction with NV centres, is essential for advancing the capabilities of nanodiamond-based technologies.

To aid in the advancement of these technologies, we set out to provide a detailed description of the unique lattice dynamics of nanodiamonds through a synergistic approach involving inelastic neutron scattering (INS) and molecular dynamics (MD) simulations. This presentation highlights the observed distinctive vibrational modes available to nanodiamonds, compared with bulk diamond. Specifically, in our MD simulations, we observe the shifting and broadening of phonon modes in energy (acoustic and optical), excess vibrational modes at low energies leading to a deviation from a Debye relationship in the density of states, and excess vibrational modes at energies above the observed optical phonons. Many of these features are confirmed by INS measurements performed on Pelican. Our work underscores the significance of comprehending size-dependent lattice dynamics for harnessing the full potential of nanodiamonds in diverse technological application