Fabrication of (TMTSF)2PF6 thin crystals in a confined electrode

In this study of crystal engineering of an organic superconductor, the single crystals of (TMTSF)2PF6 were fabricated in the form of thin crystals by the electrocrystallization method with a confined electrode by applying a low current (10 nA). Almost all of the flattened needle-shape thin crystals grown in the specially designed confined electrode had an enhanced anisotropic morphology with a thickness-to-width (t/wt/w) ratio of about 6%, being about 19 μm thick, which is an order of magnitude smaller than that of the representative bulk crystals (t/w≈57%t/w≈57%) grown in a free environment. The X-ray crystal structure analysis of the (TMTSF)2PF6 thin crystals revealed that they have the same crystal structure and packing mode as the bulk ones. The ν4 and ν3 mode frequencies in the micro-Raman spectra corresponding to the CC in-phase and out-of-phase stretching vibrations were 1457 cm−1 and 1595 cm−1, respectively. These frequencies are in between those of the neutral TMTSF and TMTSF+ cation. The thin crystals also show the same SDW transition at 12.2 K as do the bulk ones. It is concluded that the fabricated thin crystals retain the properties of bulk crystals.