Conducting oriented-[(n-C4H9)4N]2[Ni(dcbdt)2]5 and new (BEDT-TTF)[Ni(dcbdt)2] phases as microcrystalline films, electrodeposited on silicon substrates

Abstract

Ni(dcbdt)₂-based molecular materials, namely [(n-C₄H₉)₄N]₂[Ni(dcbdt)₂]₅, and (BEDT-TTF)[Ni(dcbdt)₂] have been processed as microcrystalline films on (001)-oriented silicon substrates using the electrodeposition technique [dcbdt²⁻: 4,5-dicyanobenzene-1,2-dithiolato; BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene]. Electrodeposited [(n-C₄H₉)₄N]₂[Ni(dcbdt)₂]₅ is made of thin platelets. Elemental analysis and X-ray photoelectron spectroscopy data are in agreement with a 2 : 5 stoichiometry. X-Ray powder diffraction measurements indicate that the growth is highly anisotropic, the ab-plane being parallel to the silicon surface. The films exhibit a semiconducting behaviour with a room-temperature conductivity of about 1.2 × 10⁻² S cm⁻¹. Electrodeposition run in the presence of the BEDT-TTF donor molecule leads to faceted microcrystals (size: 5–100 μm) of (BEDT-TTF)[Ni(dcbdt)₂] as evidenced by scanning electron microscopy. Single crystal data show that this new (BEDT-TTF)[Ni(dcbdt)₂] phase is isostructural to the previously described (BEDT-TTF)[Au(dcbdt)₂]. Again, elemental analysis and X-ray photoelectron spectroscopy data are in agreement with a 1 : 1 stoichiometry. The room-temperature conductivity of the film is about 3 × 10⁻⁶ S cm⁻¹. This low value is comparable to that measured on (BEDT-TTF)[Au(dcbdt)₂] single crystals. For both materials the charge transfer is similar, as consistently evaluated from Raman, infrared and photoemission measurements.