Low-frequency modes in the Raman spectrum of sp-sp2 nanostructured carbon

TL;DR

This study investigates low-frequency vibrational modes in a novel amorphous carbon with mixed sp-sp2 hybridization, revealing two characteristic peaks linked to specific structural features through Raman spectroscopy and DFT simulations.

Contribution

It provides the first in situ Raman analysis of low-frequency modes in sp-sp2 amorphous carbon, identifying their origins and relation to structural disorder.

Findings

Two Raman peaks at 450 cm-1 and 720 cm-1 identified

450 cm-1 peak linked to bending modes of sp structures

720 cm-1 peak associated with disorder in sp2 phase

Abstract

A novel form of amorphous carbon with sp-sp2 hybridization has been recently produced by supersonic cluster beam deposition showing the presence in the film of both polyynic and cumulenic species [L. Ravagnan et al. Phys. Rev. Lett. 98, 216103 (2007)]. Here we present a in situ Raman characterization of the low frequency vibrational region (400-800 cm-1) of sp-sp2 films at different temperatures. We report the presence of two peaks at 450 cm-1 and 720 cm-1. The lower frequency peak shows an evolution with the variation of the sp content and it can be attributed, with the support of density functional theory (DFT) simulations, to bending modes of sp linear structures. The peak at 720 cm-1 does not vary with the sp content and it can be attributed to a feature in the vibrational density of states activated by the disorder of the sp2 phase.