Dominique de Caro

A facile route for the preparation of nanoparticles of the spin-crossover complex [Fe(Htrz)2(trz)](BF4) in xerogel transparent composite films

Films and monoliths containing the spin crossover complex [Fe(Htrz)(2)(trz)](BF(4)) (trz = 1,2,4-triazole) as nanoparticles have been obtained. The dispersion and consecutive inclusion of the Fe complex in a silica matrix prepared from tetramethoxysilane or tetraethoxysilane afford monoliths or films with a violet colour at room temperature, which turns white above 380 K. This change of colour is reversible. This thermochromic behaviour has been characterized by measuring the magnetic properties together with thermogravimetric studies and Raman spectroscopy, the result of which all demonstrate that both films and monoliths undergo a spin crossover. Microscopy studies confirm the occurrence of the Fe complex as nanoparticles, in both the monoliths and the films. The facile synthesis of these materials as nanoparticles in transparent films should open the possibility of the synthesis of high quality films.

Nanowires of molecule-based charge-transfer salts

Nanowires of molecule-based charge-transfer salts are prepared using two different processing techniques. Isolated [TTF][TCNQ] nanowires are grown by a simple adsorption in organic solution method on stainless steel conversion coatings, used as substrates. They are characterized by Raman spectroscopy and current–voltage measurements. Nanowire films of Per2[Au(mnt)2] and (EDT-TTFVO)4(FeCl4)2 are electrodeposited on (001)-oriented silicon wafers, used as anodes. In the second case, growth as nanowires occurs after functionalizing the Si electrode with a phospholipidic membrane. Electrodeposited nanowire films are studied by various techniques, including electron microscopy, vibrational spectroscopies, X-ray photoelectron spectroscopy and conductivity measurements.

H2-induced structural evolution in non-crystalline rhodium nanoparticles

A THF solution of [Rh(μ-Cl)(C2H4)2]2 reacts in the presence of poly(vinylpyrrolidone) (PVP) with the 15-electron complex vanadocene, [V(C5H5)2], to give PVP-protected native rhodium particles. High resolution electron microscopy (HREM) and wide angle X-ray scattering (WAXS) experiments confirm the presence of a non-periodic structure (polytetrahedral atomic organization); when exposed to hydrogen, the rhodium particles exhibit a pattern consistent with the signature of a fcc lattice.

Suspensions of Organic Microcrystals Produced in the Presence of Polymers : Diversity of UV/Vis Absorption and Fluorescence Properties According to the Preparation Conditions

Free-standing microcrystals of an organic fluorescent dye, specifically, 4-n-octylamino-7-nitrobenz-2-oxa-1,3-diazole, were prepared using a solvent-exchange process at room temperature, in the presence of polymers used as additives. Parameters such as the dye concentration, the nature and concentration of the polymer, and the pH of the solution were varied. Six samples of microcrystals were therefore obtained and characterized by fluorescence microscopy and by electron microscopy (TEM and SEM). They differed by their content in microcrystals, the shape and size of which depends strongly on experimental conditions. Curiously, the UV/vis absorption spectra of the microcrystal suspensions were very different from one sample to another. As a result the emission spectra were also varied. The diversity of the optical response obtained was attributed to the presence of several dye populations in the microcrystal suspensions. A distinction was made between the intrinsic spectral properties of the microcrystals and artifacts due to the presence of the additives.

Nanoparticles of organic conductors: synthesis and application as electrode material in organic field effect transistors

Stabilization of TTF·TCNQ nanoparticles is studied by varying the ionic liquid nature and solvent medium. The best dispersion is obtained in an acetonitrile/acetone mixture and the smaller size by using [BMIM][BF4], as a stabilizing ionic liquid. Applications of well-dispersed TTF·TCNQ nanoparticles (mean diameter of about 35 nm) as electrode material in organic field-effect transistors are also reported.

From molecule-based (super)conductors to thin films, nanowires and nanorings

Thin films of (TTF)(TCNQ) (TTF=tetrathiafulvalene, TCNQ=tetracyanoquinodimethane) are deposited on Si (001), KBr, and stainless steel conversion coatings (SSCC) using chemical vapor deposition. These films are characterized by IR, XRD, conductivity measurements, and SEM. Conducting nanowires and nanorings of (TTF)(TCNQ) and nanowires of (TTF)[Ni(dmit) 2 ] 2 (typically, 20 nm×20 μm) are prepared by successively dipping SSCC in acetonitrile solutions of TTF and TCNQ, or (TTF) 3 (BF 4 ) and (Bu 4 N)[Ni(dmit) 2 ], respectively. These nanowires are observed by SEM. The (TTF)(TCNQ) nanowires are also observed by TEM and AFM and characterized by current-voltage measurements. Nanowires of (TTF)[Ni(dmit) 2 ] 2 are also obtained on silicon conversion coatings (SiCC) and characterized by Raman spectroscopy.

Charge injection from organic charge-transfer salts to organic semiconductors

Highly conducting films of organic charge-transfer (CT) salts are fabricated by a solution process from the dispersions stabilized by poly(vinylpyrrolidone). This method provides a general way to obtain conducting films of nonvolatile organic cation- and anion-radical salts with inorganic counter ions. Carrier injection from organic CT salts to organic semiconductors is investigated by using these films as electrodes in organic field-effect transistors. Efficient hole injection is observed not only from organic cation-radical salts but also from anion-radical salts to pentacene and sexithiophene. Electron injection is dominant from both types of CT salts to C60, but hole injection and ambipolar characteristics are observed for cation-radical salts. The Fermi levels of the CT salts are discussed on the basis of these observations.

Tetrathiafulvalene-based conducting deposits on silicon substrates

Tetrathiafulvalene-based molecular conductors, namely [TTF][TCNQ], (TTF)6[N(C2H5)4](HPM12O40) (M = W, Mo), and TTF[Ni(dmit)2]2 have been processed as thin films on microrough (001)-oriented silicon substrates using three different techniques. CVD-grown [TTF][TCNQ] deposits consist of platelets (10 × 5 µm) and filaments (diameter ∼1 µm). CN stretching modes in the infrared spectrum and CC stretching modes in the Raman spectrum are in agreement with a charge transfer of ∼0.6 from the TTF donor to the TCNQ acceptor. The N(1s) photoelectron spectrum confirms the presence of a reduced tetracyanoquinodimethane moiety. The films exhibit a semiconducting behaviour with a room-temperature conductivity of ∼0.4 S cm−1. Deposits of (TTF)6[N(C2H5)4](HPW12O40) are electrodeposited on microrough Si(001) at constant current from TTF and [N(C2H5)4]3(PW12O40) in acetonitrile solution. The films are made of stacked sheets (5 < thickness < 25 µm). Vibrational spectra, conductivity measurements and magnetic susceptibility data are similar to those obtained on single crystals of (TTF)6[N(C2H5)4](HPW12O40) grown on a platinum electrode. Thin films of TTF[Ni(dmit)2]2 are grown on microrough Si(001) by an adsorption process in organic solution. The deposits are characterized by Raman micro-probe and exhibit a pseudo-metallic behaviour with a room-temperature conductivity of about 2 S cm−1.

MOCVD-Processed Ni Films from Nickelocene. Part II: Carbon Content of the Deposits†

In this study, results are reported on the composition and the electrical and magnetic properties of thin films of nickel deposited by metal-organic CVD (MOCVD) from nickelocene. It was found that the films contain carbon, whose content decreases with increasing deposition pressure and hydrogen flow rate and with decreasing molar fraction of the precursor. Ferromagnetic properties, namely saturation magnetization, Curie temperature, and also electrical conductivity of the films decrease with increasing carbon content. The evolution of the saturation magnetization Ms of the films with measurement temperature follows Blochs law. Carbon is found in the films in different forms, namely carbidic (interstitial), aliphatic, or cyclic. Deposition of these forms is discussed and is correlated with the variations of the properties of the films.

Colloidal Solutions of Organic Conductive Nanoparticles

Although molecular metals have been known for decades, their insolubility, low vapor pressure, and synthesis routes have prevented them from being integrated into electronic devices. We have prepared stable colloidal solutions of the organic metal TTF-TCNQ that overcome such difficulties. The solutions contain well-dispersed nanoparticles stabilized by long alkyl chain amines. They afford soluble powders by evaporation and homogeneous thin films by drop-casting. Powders and films show room temperature conductivities in the 0.01-0.1 S cm(-1) range.