Metallic Thin Films of TTF[Ni(dmit)₂]₂ by Electrodeposition on (001)‐Oriented Silicon Substrates

Abstract

Dedicated to Patrick Cassoux to let him know that the dream of a TTF[Ni(dmit) 2 ] 2 -based device may come true!The preparation of thin films of crystalline molecular organic materials with specific physical properties (magnetic order, metallic behavior, superconductivity, etc.) is an active field boosted by the ever-increasing availability of remarkable new materials and their potential applications.[ , due to the high conduction activation barriers induced by grain boundaries.[2]Here, we present results on the preparation of metallic thin films of the molecular metal TTF[Ni(dmit) 2 ] 2 , where dmit 2± = 1,3-dithiole-2-thione-4,5-dithiolato, by electrocrystallization, using silicon wafers as electrodes. TTF[Ni(dmit) 2 ] 2 single crystals (obtained by a diffusion process) exhibit metallic behavior down to 3 K, with r RT~3 00 S cm ±1 and superconductivity is observed at T c = 1.6 K under application of a hydrostatic pressure of 7 kbar.[6] Our films exhibit metallic character down to ca. 12 K in spite of their polycrystalline morphology. Electrocrystallization is the most suitable technique to obtain charge transfer (CT) compounds. [7] The advantages of this technique over, e.g., vapor-phase deposition methods [8] include precise control of the concentration of solute at the interface, the ability to fabricate thin films on substrates with unusual geometries, and the fact that vapor-phase deposition is limited to sublimation/evaporation of neutral species. Although the electrocrystallization technique has been extensively used, the utilization of substrates as electrodes is rare. [9] On the other hand, there is great interest in characterizing hybrid organic±silicon structures. Molecular materials have been shown to be complementary to inorganic-based materials (organic light-emitting diodes, organic thinfilm transistors, etc.), and certain applications are receptive to their substitution because they can be processed as thin films at lower cost.[10]Electrodeposition of TTF[Ni(dmit) 2 ] 2 was carried out with intrinsic Si(001) as the anode and a platinum wire as the cathode. We have selected silicon single crystals as substrates in order to eliminate spurious effects associated with grain boundaries, avoiding, e.g., non-homogeneous current densities. The anodic oxidation of the TTF is performed at constant current density (1.5 lA cm ±2 ) at room temperature. Within 5 days, a black air-stable thin film is formed on the polished face of the (001) Si(001) wafers as anodes in an electrocrystallization process. Scanning electron microscopy (SEM) micrographs of a covered area show a dense film made of roughly spherical grains with sizes ranging from 0.6 to 1 lm (Fig. 1). The estimated thickness of the films is ca. 1 lm. Other works have reported quite different morphologies. Applying a low current density (< 5 lA cm ±2 ), Wang et al. reported electrodeposited films of (BEDT-TTF) 2 PF 6 as 100 lm long needles.[9] When the current density values were increased (> 10 lA cm ±2 ), they ob-

Four Molecular Superconductors Isolated as Nanoparticles

“…[14] The phase diagram of this compound was additionally investigated recently. [15] The preparation of thin films, nanowires, and nanoparticles of TTF[Ni(dmit) 2 ] 2 was investigated, [16] and superconductivity was evidenced in electrodeposited films. [4] Previously synthesized NPs of TTF[Ni(dmit) 2 ] 2 were prepared using a chemical procedure that involved the reaction of (TTF) 3 (BF 4 ) 2 with nBu 4 N[Ni(dmit) 2 ].…”

Molecular conductors as nanoparticles in the presence of long-chain alkyl imidazolium salts or amphiphilic molecules

“…Transmission electron micrographs exclusively evidenced sticks (Fig. 3) were obviously lower than those on single crystals [23] due to resistive boundaries between the particles. powder XRD studies.…”

TTF[Ni(dmit)2]2: From single-crystals to thin layers, nanowires, and nanoparticles

“…9a) show that the film comprises roughly spherical grains ranging from 0. temperature region values for cooling (black dots) and heating (grey dots). These figures have been reproduced from [87] with the permission of the copyright holders.…”

“…A c c e p t e d M a n u s c r i p t [87]. TTF was oxidized at room temperature at a constant current density of 1.5 Acm -1 in the presence of (n-Bu 4 N)[Ni(dmit) 2 ], which was used as both the reactive species and the supporting electrolyte.…”