Thin single crystals of organic insulators, metals, and superconductors by confined electrocrystallization

The confined electrocrystallization technique, first described by Thakur et al., involves forcing electrocrystallization to occur within the interface of two opposite substrates. This technique is further demonstrated and extended herein to the synthesis of a variety of thin crystalline films of conducting and insulating molecular materials alike, regardless of their structural dimensionality and shape, form, or habit of the corresponding bulk phases grown independently by standard electrocrystallization in solution. Given that in a confined environment the molecular species will progress much more slowly, or barely at all, to the vicinity of the active electrode, the deposition of neutral π-donor molecules in the form of a 1 μm thick layer on the surface of a glass slide, by sublimation under vacuum, proved to be a major experimental improvement, and also yielded better crystal quality in more reasonable amounts of time. The effect of temperature and the typically high current densities commonly achieved under these conditions, are discussed along with the experimental conditions used to grow thin crystals of (TMTTF)2ReO4 and (TMTSF)2ReO4, κ-(BEDT-TTF)2Cu(NCS)2 (25°C), (BEDT-TTF)Cu2(NCS)3 (60°C), (EDT-TTF)3[PW12O40]· (CH3CN)·(CH2Cl-CHCl2), β″-(BEDT-TTF)4·(guest)·[Re6 Se6Cl8] and β″-(BEDT-TTF)4· (guest)·[Mo6Cl14]. It is concluded that the confined electrocrystallization technique appears to be suitable for growing thin crystals of radical ion salts of essentially all the phases previously obtained in bulk crystal form by classical electrocrystallization in solution.