Alexandre Carella

Highly Flexible Transparent Film Heaters Based on Random Networks of Silver Nanowires

AbstractWe demonstrate a new concept for the fabrication of flexible transparent thin film heaters based on silver nanowires. Thanks to the intrinsic properties of random networks of metallic nanowires, it is possible to combine bendability, transparency and high heating performances at low voltage, typically below 12 V which is of interest for many applications. This is currently not possible with transparent conductive oxide technologies, and it compares well with similar devices fabricated with carbon nanotubes or graphene. We present experiments on glass and poly(ethylene naphthalate) (PEN) substrates (with thicknesses of 125 μm and extremely thin 1.3 μm) with excellent heating performances. We point out that the amount of silver necessary to realize the transparent heaters is very low and we also present preliminary results showing that this material can be efficiently used to fabricate photochromic displays. To our knowledge, this is the first report of metallic nanowire-based transparent thin film heaters. We think these results could be a useful approach for the engineering of highly flexible and transparent heaters which are not attainable by existing processes.

Improvement of the Seebeck coefficient of PEDOT:PSS by chemical reduction combined with a novel method for its transfer using free-standing thin films

A simple method for improving the Seebeck coefficient of PEDOT:PSS up to 161 μV K−1 is presented and combined with a new process for transferring thick (>10 μm) films of PEDOT:PSS onto substrates with various shapes, and in particular onto flexible substrates. These reduced transferred films have been used in combination with a nickel ethylenetetrathiolate coordination polymer to fabricate cheap and flexible heat flux sensors.

Synthesis and purification of long copper nanowires. Application to high performance flexible transparent electrodes with and without PEDOT:PSS

AbstractWe demonstrate the hydrothermal synthesis of long copper nanowires based on a simple protocol. We show that the purification of the nanowires is very important and can be achieved easily by wet treatment with glacial acetic acid. Fabrication of random networks of purified copper nanowires leads to flexible transparent electrodes with excellent optoelectronic performances (e.g., 55 Ω/sq. at 94% transparency). The process is carried out at room temperature and no post-treatment is necessary. Hybrid materials with the conductive polymer PEDOT:PSS show similar properties (e.g., 46 Ω/sq. at 93% transparency), with improved mechanical properties. Both electrodes were integrated in capacitive touch sensors.

Improvements in purification of silver nanowires by decantation and fabrication of flexible transparent electrodes. Application to capacitive touch sensors

Transparent flexible electrodes made of metallic nanowires, and in particular silver nanowires (AgNWs), appear as an extremely promising alternative to transparent conductive oxides for future optoelectronic devices. Though significant progresses have been made the last few years, there is still some room for improvement regarding the synthesis of high quality silver nanowire solutions and fabrication process of high performance electrodes. We show that the commonly used purification process can be greatly simplified through decantation. Using this process it is possible to fabricate flexible electrodes by spray coating with sheet resistance lower than 25 Ω sq⁻¹ at 90% transparency in the visible spectrum. These electrodes were used to fabricate an operative transparent flexible touch screen. To our knowledge this is the first reported AgNW based touch sensor relying on capacitive technology.

Design and synthesis of the active part of a potential molecular motor

The design and synthesis of a ruthenium complex are described, together with its physico-chemical properties, showing its potential to work as a single molecule rotary motor.

Synthesis and Reactivity of [Penta(4‐halogenophenyl)cyclopentadienyl][hydrotris(indazolyl)borato]ruthenium(II) Complexes: Rotation‐Induced Fosbury Flop in an Organometallic Molecular Turnstile

The preparation of ruthenium(II) complexes coordinated to a penta(4-halogeno)phenylcyclopentadienyl ligand and to the hydrotris(indazolyl)borate ligand are detailed. Our strategy involves first the coordination of the penta(4-bromo)phenylcyclopentadienyl ligand by reaction with the ruthenium-carbonyl cluster followed by the coordination of the tripodal ligand. The pentabrominated precursor was successfully converted to the pentaiodinated derivative by using the Klapars-Buchwald methodology, applied for the first time on organometallic substrates. Cross-coupling reactions were performed on both pentabromo and pentaiodo complexes to introduce in a single step the five peripheric ferrocenyl fragments required to obtain a potential molecular motor. The two ligands present in the ruthenium complexes undergo a correlated rotation that was established both experimentally by NMR experiments and an X-ray diffraction study, and theoretically by DFT calculations. The potential-energy curve obtained by DFT revealed the energy barrier of the gearing mechanism to be only 4.5 kcal mol(-1). These sterically highly constrained complexes can be regarded as organometallic molecular turnstiles.

Synthesis of triester-functionalized molecular motors incorporating bis-acetylide trans-platinum insulating fragments

Bis-ferrocene compounds linked either by two triple bonds (1,4-di(ferrocenyl)butadiyne 1), or by the triple bond–platinum–triple bond sequence (trans-bis(ferrocenylethynyl)bis(triethylphosphine)platinum(II), 2) have been synthesized. The electronic coupling between the ferrocene groups has been estimated from the intensity of the intervalence transition in the electrochemically generated mixed valence complexes. Upon insertion of a platinum fragment a weak attenuation was observed, with the Vab parameter decreasing from 0.036 eV for 1 to 0.025 eV for 2. A theoretical study has also been performed, using a combination of DFT for geometry optimization and Extended Huckel Theory for the estimation of the electronic coupling. It was found that the electronic coupling decreases from 0.090 eV for 1 to 0.022 eV for a model of 2. In a second part of this work, we describe the synthesis of two molecular motors incorporating the ligand hydrotris[6-(ethoxycarbonyl)indazol-1-yl]borate which exhibits three pendant ester groups dedicated to be anchored onto an oxide surface. This stator is connected through a ruthenium centre to a pentasubstituted cyclopentadienyl rotor bearing ferrocene terminal electroactive groups, linked either by a phenylethynyl spacer (complex 4) or a spacer containing bis-acetylide trans-platinum insulating fragments (complex 8).

Sub-ppm Detection of Nerve Agents Using Chemically Functionalized Silicon Nanoribbon Field-Effect Transistors†

Organophosphorus compounds (OPs) represent one of the most important and lethal classes of chemical warfare agents (e.g. sarin, tabun, soman). Highly active volatile OPs are powerful inhibitors of acetylcholinesterase, which is a critical enzyme of the nervous system. The ease of manufacturing OPs based on inexpensive starting materials makes these agents a weapon of choice for terrorist attacks. Thus, the rapid sensing of these nerve agents has recently become an increasingly important research goal. Various approaches have been reported for the detection of these chemical warfare agents including colorimetric and fluorimetric spectroscopies, enzymatic assays, piezoelectric devices, single-walled carbon nanotube resistors and capacitors. However, these systems are plagued by limitations such as slow response time, moderate selectivity, operational complexity, or limited portability. Field-effect transistors (FET) based on nanomaterials such as semiconducting nanowires, nanoribbons, or carbon nanotubes have been recently explored for chemical and biological detection. Their high effectiveness is mainly ascribed to an extreme sensitivity to electrostatic changes at the surface of the semiconductor and/or modifications of the Schottky barrier at the semiconductor/metal interface. A charge generation in the vicinity of the semiconductor of a FET is known to alter the electrical properties of the device. Several research groups have independently developed a series of small-molecule fluorescent sensors for OPs detection. They investigated organic moieties reactive towards OPs by formation of a phosphate ester intermediate and subsequent intramolecular nucleophilic substitution, which led to an ammonium salt and thus charge formation. We thought monitoring this charge generation with a functionalized FET could be a particularly promising approach. Herein, we report the development of an OPs chemical sensor based on highly sensitive silicon nanoribbon field-effect transistors (SiNR-FETs) functionalized with compound 1 (Scheme 1).

Technomimetic molecules: synthesis of ruthenium(II) 1,2,3,4,5-penta(p-bromophenyl)cyclopentadienyl hydrotris(indazolyl)borate, an organometallic molecular turnstile

A short route to prepare a ruthenium complex with a pentaphenyl substituted cyclopentadienyl and a hydrotris(indazolyl)borate ligand is described: this complex can be seen as an organometallic molecular turnstile.

A star-shaped ruthenium complex with five ferrocenyl-terminated arms bridged by trans-platinum fragments

We present the synthesis of the new heteropolytopic penta(4-ethynylphenyl)cyclopentadiene ligand, its complexation through the Cp ring to ruthenium tris(indazolyl)borate and through the terminal alkyne groups to five ferrocenyl ethynyl platinum units, yielding an undecanuclear heterotrimetallic complex.