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Recyclable organic bilayer piezoresistive cantilever for torque magnetometry at cryogenic temperatures
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In this article we demonstrate that a migration of iodine species and chemical transformation in a moist environment induced by a voltage-biased Pt electrode is able to alter the color and degree of charge transfer in a layer of the 2D organic molecular metal (BEDO-TTF)2.4I3 [BEDO = bis(ethylenedioxy)tetrathiafulvalene] self-assembled at the surface of a polycarbonate film. These effects produce a reversible electrochromic behavior of the layer with low operating voltages and fast operation times. Adjuvant with electrochromism, this flexible material exhibits rectifying behavior whose I-V curves are dependent on the voltage sweep directions. These results open new possibilities for the design and fabrication of organic flexible materials for soft electrochromic and rectifying components. The easy working principle ensures reliability, low power consumption, and versatility through its implementation into simple devices. Such working principle has been confirmed by temperature dependent resistance measurements, X-Ray, EDX-SEM, and conducting-AFM studies. Migration and chemical transformation of iodine species in the organic salt has been utilized to make dual functional devices that can operate at low voltages. An international team led by Dr. Eden Steven from Florida State University, USA and Elena Laukhina from Ciber-BBN (ICMAB-CSIC), Spain develops flexible electrochromic and rectifying components based on bi-layered thin films of a molecular metal. The thin film consists of a thin polycarbonate substrate and a metallic triiodide salt of an organic molecule BEDO-TTF which undergoes losses or restore of I3- anions under forward or reverse biases in the presence of water, respectively, resulting in discoloration/coloration and electrical rectifying behavior. The simple working principle and the versatile functionalities shown here enable promising design and fabrication of organic electrochromic and rectifying devices in the near future.
The paper is addressed to the modern technologies that need to be instrumented with flexible highly sensitive pressure sensors. We present and discuss a design approach for engineering compact flexible layered pressure sensors that contain the polycrystalline layer of the β-(BEDT-TTF)2I3 organic molecular metal as a highly piezo-resistive component. The strategy is based on the integration of the pressure sensing β-(BEDT-TTF)2I3/polycarbonate bilayer film and a set of gold electrodes into one compact multi-layer design. The pressure test demonstrated that the developed sensor construction measures pressure up to 500 bars with outstanding electrical response.
Preparation and properties of surface-conductive polymer composites based on a recently synthesized electron-donor, methylenedithio-tetraselenefulvalene (MDT-TSF) are described. Polycarbonate and bio-degradable polyester polylactide are used as polymer matrices. The obtained surface-conductive materials with MDT-TSF polyiodides show high, metal-like conductivities, indicating that MDT-TSF is one of the best donors for conductive composites.
Since their discovery, organic conductors have attracted fundamental and device physics interest due to their diverse physical properties. However, conventional electrochemical growth methods produce millimeter-sized crystals that do not translate to the fabrication of large-scale thin-film devices. Of late a chemical-vapor annealing method has been proved to be capable of growing a conductive polycrystalline layer of (BEDT-TTF)2I3 molecular conductor on the surface of soluble polycarbonate (PC) thin films in a bilayer configuration. (Here BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene.) This has resulted in efficient piezoresistive organic molecular sensors. Conversely, solubility and other incompatibilities limit the direct application of the crystallite growth method to other substrates with arbitrary shape and composition. Here we report methods to circumvent these limitations. Specifically, we demonstrate the transfer of the active layer of a PC/(BEDT-TTF)2I3 bilayer film from the non-porous parent PC substrate to porous and humidity-dependent Bombyx mori silk target substrates. SEM analysis, temperature dependent resistance, and electromechanical measurements show no significant damage to the transferred (BEDT-TTF)2I3 layer. The silk/(BEDT-TTF)2I3 bilayer films exhibit additional functions that can be used for humidity sensing, electric current-driven actuators, and strain detection. Of particular significance is the piezoresistive function of the porous silk bilayer structure that allows the investigation of multi-stage diffusion processes.
Understanding the compatibility between spider silk and conducting materials is essential to advance the use of spider silk in electronic applications. Spider silk is tough, but becomes soft when exposed to water. Here we report a strong affinity of amine-functionalised multi-walled carbon nanotubes for spider silk, with coating assisted by a water and mechanical shear method. The nanotubes adhere uniformly and bond to the silk fibre surface to produce tough, custom-shaped, flexible and electrically conducting fibres after drying and contraction. The conductivity of coated silk fibres is reversibly sensitive to strain and humidity, leading to proof-of-concept sensor and actuator demonstrations.
This study is stimulated by the discovery of high sensitivity of nanostructured layers of organic semiconductor α′-BEDT-TTF)2IxBr3-x [BEDT-TTF = bis(ethylendithio)-tetrathiafulvalene] to heat radiation. We present the development and assessment of the flexible lightweight highly sensitive film-based thermistor as (i) a separate sensor, (ii) a sensor integrated in e-textile and (iii) a sensor embedded in a wireless sensor node. Wireless Sensor Networks (WSN) and Internet of Things (IoT), being two promising technologies, have already been applied in a number of monitoring scenarios. In spite of great progress achieved in sensing technologies and wireless embedded systems there is a gap in multidisciplinary research aimed at investigating the aggregate potential of these technologies. Experimental results demonstrate that the developed bi-layer organic thermistor has high potential for environmental and biomedical monitoring. They can be used as a part of wearable units or as sensing units on board of wireless sensing devices.
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A novel transparent touch sensor was fabricated with a drop-on-demand inkjet printing technique on borosilicate glass and flexible polyethylene terephthalate (PET) substrates. Conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (
Pedot:
PSS) and dielectric poly(methylsiloxane) were deposited on a desired area to form a capacitive touch sensor structure. The properties of the printed sensors (optical transparency, electrical resistance and touch sensing performance) were investigated with varying
Pedot:
PSS printing passes. A novel transparent touch sensor fabricated with an all-inkjet-printing method is demonstrated for the first time. This process holds industrially viable potential to fabricate transparent touch sensors with an inkjet printing technique on both rigid and flexible substrates for a wide range of applications.
Bilayer films, composed of a thin-layer of pyroresistive submicrometer-sized crystals on top of a polymeric thin film, can be used both as a direct-contact thermometer and as passive infrared sensor. These materials are capable of detecting, radiation of a wide-range of wavelengths very rapidly and reversibly, as well as recognizing distant objects with applications in robotics, biomedicine, and human health care
We developed a lightweight flexible keyboard with a touch sensor fabric that consists of conductive polymer-coated fibers. In our sensor fabric, the conductive polymer-coated fibers, which are sensing electrodes, are woven at a 2-cm pitch and the rest of the fabric is filled with pristine polyester fibers. The sensing principle for human touch detection is the measurement of the capacitance between the conductive polymer-coated sensing fibers and human fingers. The keyboard system consists of the touch sensor fabric, a capacitance measurement circuit, a signal processing circuit and software for entering characters into a personal computer (PC). The fabricated fabric has a large area, 20.5 cm × 12.5 cm, and weighs only 9 g, making it large enough for touch input and light enough to carry. In addition, the sensing electrode is bendable to a diameter of 1 mm because the sensor electrode is not inorganic material but rather polymer. When the sensor is touched, the capacitance between fiber and finger is increased by 2 pF, which is large enough to be detected with conventional capacitance measurement circuits. Finally, the keyboard input is demonstrated with our fabricated fabric sensors. This technology will lead to the development of keyboards that are especially well suited for wearable and portable electronic devices.
We present a study of the influence of the iodine/solvent annealing temperature on the properties of piezoresistive bilayer films with layers of α-(BEDT-TTF)2I3 [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene]. The formation of the conductive layers was tested by XRD, direct current (dc) conductivity measurements, and SEM, and the electromechanical properties have also been studied. We demonstrate that it is possible to form bilayer (BL) films with an invariant gauge factor of ca. 10 but with the temperature dependence of the resistance variable from metallic to semiconductor-like by control of the annealing temperature. This control even permits the preparation of a BL film with temperature-independent resistance.
Conducting reticulate doped polymer (RDP) films with transparent appearance were prepared by the two-step method. Polycarbonate films were doped with the bis(ethylenedioxy) tetrathiafulvalene (BEDO-TTF) complex of ReO4-, Br-, C(CN)(3), or C2O42-, the surface resistivities of which were 1.5, 1.4, 30, and 8.0 k Omega/square, respectively. The films containing ReO4 and Br complexes showed quasi-reversible humidity dependent behaviors, in which the resistivity and interconducting- layer distance were increased and decreased, respectively, in dry atmosphere. The ReO4 containing film exhibited better reversibility, while the existence of two kinds of crystal structures was proved for the Br complex. [GRAPHICS] (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Highly sensitive single-wall carbon nanotube/graphite nanoplatelet (SWCNT/GNP) hybrid thin-film sensors are developed, which possess the unique capability for self-temperature compensation. This unique property in combination with their high gauge sensitivity and large reversible extensibility promises the SWCNT/GNP hybrid thin film piezoresistive sensors for a wide range applications, such as in man-machine interaction and body monitoring.
Criteria for the selection of molecular metals as the active components of conducting hi-layer composite films are presented and discussed. it is shown that two-dimensional (2D) organic metals with halide or trihalides anions have some advantages over other molecular metals for the conducting hi-layer composite film preparation.
The syntheses, structures, selected physical properties, and band electronic structures of three copper (I) dicyanamide halide salts of bis(ethylenedithio)tetrathiafulvalene [kappa-(ET)2Cu[N(CN)2]X, where X = Cl, Br, and I] are discussed. X-ray crystallographic studies demonstrate that the three derivatives are isostructural. The bromide salt is an ambient pressure superconductor with an inductive onset at 11.6 K and a resistive onset at 12.5 K. kappa-(ET)2Cu[N(CN)2]Cl exhibits the highest reported superconducting transition temperature (T(c) = 12.8 K, 0.3 kbar) for an organic superconductor, once a semiconductor-semiconductor transition (42 K) is suppressed. The application of GE varnish or Apiezon N grease to crystals of kappa-(ET)2Cu[N(CN)2]Cl provides sufficient stress to induce superconductivity at "ambient pressure". Crystals of the iodide remain metallic to approximately 150 K, where they become weakly semiconductive. No sign of superconductivity was detected at pressures (hydrostatic and shearing) up to 5.2 kbar and at temperatures as low as 1.1 K. The band electronic structures of the three salts are essentially identical. The differences in superconducting properties are explained in terms of differences in lattice softness, which are strongly influenced by short C-H...donor and C-H...anion contacts.
A new method of preparing conductive polymer composites by growing crystalline networks of conductive additives in polymer matrices (reticulate doping) is described. The method consists of treating the polymer containing molecularly dispersed donor additive with acceptor/solvent vapors. In the swollen polymer layer simultaneously CT complex formation and crystallization takes place which for proper conditions leads to the formation of a network of the CT complex crystallites, making the film surface-conducting.
The preparation and properties of surface conductive films using several electron donors and an iodine acceptor are described. The films obtained show surface resistivities of 104–106 ohm and are generally stable under ambient conditions.
Electric properties of conducting reticulate doped polymeric films, containing ET polyiodide crystalline network, have been investigated. In order to improve their conducting properties they were annealed in iodine vapors. It was found, that certain conditions of thermal treatment lead to metal-like state, stable down to helium temperatures. The overall decrease of resistivity R300K/R4.2K reaches 45. At some conditions of the thermal treatment an accelerated decrease of resistivity is observed below 7 K, vanishing with application of magnetic field, thus giving the first evidence of the (incomplete) superconducting transition in polymeric organic composite material.
The thermal expansion of polymers is investigated from 4.2 K to room temperature. Samples of thermoplastic polymers and a weakly cross-linked epoxy resin were used with an inductive dilatometer. Thermal expansion data are presented.
New conducting bilayer films (BL-film) containing (BEDT-TTF)(2)(I3Br1-x)(3) molecular metals as active components have been prepared. The effect of various parameters of the BL-film preparation on the conducting layer composition was systematically studied by X-ray, Raman, EPR, and SEM. It was shown that the conducting layer of new BL-films is formed by "c " oriented (BEDT-TTF)(2)(IxBr1-x)(3) nanocrystals which contain a set of the IBr2-, I2Br-, and/or I-3(-) anions. It was found that the alpha' --> beta phase transition takes place in the (BEDT-TTF)(2)(IxBr1-x)(3) nanocrystals under film annealing. Some of the new composite BL-films, being flexible and transparent, reveal a metal-like temperature dependence of resistance down to nitrogen temperature.
The properties of five new highly conducting salts of TMTSF, (TMTSF)2X, X = PF6-, AsF6-, SbF6-, BF4- and NO3- are reported. The measurements include d.c. and m.w. conductivity, thermopower, optical reflectivity, magnetic susceptibility and 19F-NMR. Preliminary structural data indicate uniform donor stacks. Metal to insulator transitions in four materials occur below 20 K, where specific conductivities higher than 105 (Ω-cm)−1 are observed for two salts (X = PF6- and NO3-).
The low temperature thermal expansion of several aluminium, nickel, copper, and iron base alloys was measured from liquid hydrogen temperature to room temperature. Both the thermal contraction from room temperature, (L293 − LT)/L293, and the thermal expansion coefficient, (1/L293)/(dL/dT), are tabulated as a function of temperature. Comparison of similar alloys and alloy conditions led to the general conclusions that: (a) relatively large changes in composition are required to produce significant changes in the thermal expansion, (b) thermal treatment or condition has little effect except when it produces a basic structure change, and (c) the thermal expansion coefficient at room temperature is a good indicator of the total length change to a low temperature.
Electronics that are capable of intimate, non-invasive integration with the soft, curvilinear surfaces of biological tissues offer important opportunities for diagnosing and treating disease and for improving brain/machine interfaces. This article describes a material strategy for a type of bio-interfaced system that relies on ultrathin electronics supported by bioresorbable substrates of silk fibroin. Mounting such devices on tissue and then allowing the silk to dissolve and resorb initiates a spontaneous, conformal wrapping process driven by capillary forces at the biotic/abiotic interface. Specialized mesh designs and ultrathin forms for the electronics ensure minimal stresses on the tissue and highly conformal coverage, even for complex curvilinear surfaces, as confirmed by experimental and theoretical studies. In vivo, neural mapping experiments on feline animal models illustrate one mode of use for this class of technology. These concepts provide new capabilities for implantable and surgical devices.
In polymeric composite thin films it is possible to translate elastic elongations of the film into reversible nanoscale deformations of the soft organic-crystal components, leading to films with extreme sensitivity to strain changes with durable, fast, and completely reversible responses. Simple prototypes (see image), demonstrate that these sensors are highly promising for a wide range of applications. (Figure Presented)