Single-Walled Carbon Nanotubes Shock-Compressed to 0.5 Mbar

Following our dynamic (shock wave) compression experiments on single-walled (SW) HiPCO carbon nanotubes (CNTs) [ M. Nol et al., Phys. Status Solidi RRL 2014, 8, 935], we extended the range of shock compression to 0.5 Mbar in quest of new forms of nanostructured carbon derived from crushed SWCNTs. The material recovered after shock is characterised by multi-wavelength Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM). Two distinct types of material are identified: (i) multi-layer graphene (MLG) and (ii) a mixture of disordered nanometer-sized graphene clusters and amorphous carbon. No diamond-like carbon or carbon nano-onions are found in the sample. The coherent scattering size of MLG clusters (L-a) is estimated at 30nm from the D- to G-band intensity ratio dependence on the photon excitation energy. We demonstrate the capabilities of Raman spectroscopy for characterisation and analysis of the multi-phase spectra of disordered carbon. Particulars of CNT transformation to other structural forms of carbon at high pressure/temperature are discussed.