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 / 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 %) 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 C{double bond, long}C 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.