On Fano effect in IR spectra of hydrogenated nanodiamonds

TL;DR

This paper investigates the Fano resonance phenomenon in IR spectra of hydrogenated nanodiamonds, analyzing how surface structures influence the transmission window and related conductivity.

Contribution

It provides a detailed spectral analysis across various nanodiamond sizes and proposes a coupling mechanism involving monohydride termination and diamond phonons.

Findings

C-H stretch vibrations are not responsible for Fano resonance.

Bending mode of monohydride on (111) face may couple with optical phonon.

Morphology and size distribution influence the resonance and conductivity.

Abstract

Hydrogenated nanodiamonds may show a "transmission window" in infra-red spectra in the vicinity of diamond Raman frequency. This phenomenon is a manifestation of resonance coupling of incident photons with continuum states (Fano resonance). Hpwever, precise mechanism of appearence of the resonance and of related conductivity - surface hydrogenation or specific type of surface reconstruction - remains debatable. We present detailed analysis of infra-red spectra of nanodiamonds of different sizes (2.6-30 nm) possessing the "transmission window" and show that the C-H stretch vibrations of adsorbed functional groups cannot be responsible the the Fano resonance. At the same time, it is suggested that a bending mode of monohydride termination on nanodiamond (111) face may couple with diamond optical phonon, explaining the Fano resonance in some cases. The relative importance of the monohydride contribution and of the graphitic islets to the appearence of the "transmission window" and conductivity is likely dependent on dominating morphology and size distribution of nanodiamond grains.