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 3 5 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 sp(3)-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. (c) 2006 Elsevier B.V. All rights reserved.