Nanostructured superhard carbon phase obtained under high pressure with shear deformation from single-wall nanotubes HiPco

Raman spectra of single-wall nanotubes under high pressure combined with shear deformation are investigated in situ in a diamond cell. Shear deformation applied under 35 GPa led to pressure multiplication up to 60 GPa, and increased the intensity of Raman bands more than ten times without essential change of G-mode position while causing its essential broadening. The G-mode remained broad after pressure unloading and shifted to 1534 cm−1. The hardness of the superhard material was 58±6 GPa, comparable to the hardness of carbo-boro-nitride. A broad band appeared in the photoluminescence spectrum with a maximum at about 2 eV, which allowed to assume a high content of sp3-bonds in the sample. The large dispersion of the G-mode almost vanished after pressure unloading. However, a noticeable dispersion of the D-mode was found, which is a sign of certain ordering in the superhard phase. TEM study of the superhard phase detected clusters with graphene sheets with a size about 1 nm.