High-pressure laser-heating induced formation and equation of state of benzene-derived carbon nanothreads

We formed two-dimensional pseudo-hexagonally ordered diamond-like carbon nano-threads by laser heating dense molecular benzene, the archetypal aromatic compound, to temperatures exceeding 1000 K at about 40 GPa in diamond anvil cells. The heated samples were then rapidly (<1 s) temperature quenched. Instead, in previous studies, carbon nano-threads were obtained by subjecting benzene to slow compression-decompression cycles (<2-3 GPa/h) at room temperature, reaching maximum pressures of 23-24 GPa. Our pressure-temperature-time reaction path for this kinetically driven transformation differs substantially from previous studies, as it is significantly more extreme and faster. Synchrotron x-ray diffraction measurements of temperature-quenched products were performed during a compression-decompression cycle from 40 to 54 to 0 GPa, allowing the determination of a one-dimensional equation of state for the characteristic interlayer spacing. This spacing reflects the van der Waals distance between neighboring threads. Comparison with previously reported ab initio equations of state constrains the local internal structure of the threads, which is otherwise elusive at high pressures due to disorder along the chain axis.