Towards a better understanding of the structure of diamano\"ids and diamano\"id/graphene hybrids

TL;DR

This study investigates the structural changes in diamanoids and diamanoid/graphene hybrids induced by a hot-filament process, revealing partial sp2 to sp3 carbon conversion, twisted domain formation, and specific Raman signatures supported by experimental and theoretical evidence.

Contribution

It provides new experimental and theoretical insights into the structure of diamanoids and hybrids, especially the formation of twisted domains and the origin of the Raman T peak.

Findings

Partial sp2 to sp3 conversion confirmed by electron diffraction, Raman, and DFT.

Formation of twisted coherent domains due to stress relaxation.

Identification of the Raman T peak origin from a sp2-sp3 mixed layer.

Abstract

Hot-filament process was recently employed to convert, totally or partially, few-layer graphene (FLG) with Bernal stacking into crystalline sp$^3$-C sheets at low pressure. Those materials constitute new synthetic carbon nanoforms. The result reported earlier relies on Raman spectroscopy and Fourier transform infrared microscopy. As soon as the number of graphene layers in the starting FLG is higher than 2-3, the sp$^2$-C to sp$^3$-C conversion tends to be partial only. We hereby report new evidences confirming the sp$^2$-C to sp$^3$-C conversion from electron diffraction at low energy,Raman spectroscopy and Density Functional Theory (DFT) calculations. Partial sp$^2$-C to sp$^3$-C conversion generates couples of twisted, superimposed coherent domains (TCD), supposedly because of stress relaxation, which are evidenced by electron diffraction and Raman spectroscopy. TCDs come with the occurrence of a twisted bilayer graphene feature located at the interface between the upper diamano\"id domain and the non-converted graphenic domain underneath, as evidenced by a specific Raman signature consistent with the literature. DFT calculations show that the up-to-now poorly understood Raman T peak originates from a sp$^2$-C-sp$^3$-C mixt layer located between a highly hydrogenated sp$^3$-C surface layer and an underneath graphene layer.