  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.
