Organic-based magnets are intriguing materials with unique magnetic and electronic properties that can be tailored by chemical methodology. By using molecular layer deposition (MLD), we demonstrate the thin film fabrication of V[TCNE: tetracyanoethylene]x, of the first known room temperature organic-based magnet. The resulting films exhibit improvement in surface morphology, larger coercivity (80 Oe), and higher Curie temperature/thermal stability (up to 400 K). Recently, the MLD method has been widely studied to implement fine control of organic film growth for various applications. This work broadens its application to magnetic and charge transfer materials and opens new opportunities for metal–organic hybrid material development and their applications in various multilayer film device structures. Finally, we demonstrate the applicability of the multilayer V[TCNE]x as a spin injector combining LSMO, an standard inorganic magnetic semiconductor, for spintronics applications.Keywords: magnetic semiconductor; molecular layer deposition; organic spintronics; organic-based magnet; V[TCNE]x;

The ion-induced reprecipitation of the emeraldine base form of polyaniline from an aqueous-organic binary solution is a facile method for obtaining polymer nanoparticles and microscale clusters. The hydrophobic collapse and aggregation that accompanies the addition of various cosolutes induces changes in the peak wavelength and linewidth of the main exciton absorption. In particular, we find that the addition of ionic cosoutes leads to a redshifting and broadening of this spectroscopic feature, with divalent coions exhibiting an additional hypsochromic reversal at high concentrations. The denaturant urea, in contrast, causes a blueshift and line-narrowing at all concentrations. Using a quantitative Lorentz fit, we show how the redshifting and broadening of this spectral feature can be attributed, at least in part, to the forced planarization of the polymer chains in the collapsed state.Highlights► Adding monovalent cosolutes to polyaniline suspensions causes the chains to collapse. ► The forced planarization of the polymer leads to a redshifting and broadening of the exciton absorption peak. ► Urea decreases the hydrophobic interaction and therefore has the opposite effect. ► Divalent coions cause redshifting at low concentrations, then a hypsochromic reversal. ► We preformed a quantitative spectral analysis to study the magnitude of these changes.

We report a study of the electrical bistability and bias-controlled spin valve effect in an organic device using rubrene (C42H28) as an organic semiconductor channel. The half-metallic La0.7Sr0.3MnO3 (LSMO) and Fe are used as the two ferromagnetic electrodes. The device displays reproducible switching between a low-impedance (ON) state and a high-impedance (OFF) state by applying different polarities of high biases. In the ON state, the device shows a spin valve effect with magnetoresistance values up to 3.75%. The observed spin valve effect disappears when the device recovers to the initial OFF state.

We studied magnetoresistance (MR) in La2/3Sr1/3MnO3 (LSMO)/organic semiconductor (OSC)/Fe heterojunction devices using rubrene (C42H28) as an organic semiconductor. Efficient spin polarized tunneling using a hybrid barrier (oxide (1.2 nm)/rubrene (5 nm)) was observed. Devices with a thin layer of rubrene as the barrier may have magnetic clusters and/or pinholes in the barrier, which could explain significant variations of MR among devices. As the thickness of the rubrene layer is increased, device current becomes strongly limited by carrier injection resulting in strong temperature and bias dependent device resistance. The carrier injection in these devices can be described with thermionic field emission at the metal/OSC interface and is analyzed with both empirical and theoretical models. The effect of carrier transport through the spacer on the magnetoresistance for organic-based spin valve is discussed. The observed giant magnetoresistance (GMR) in 20 nm rubrene device demonstrates the spin polarized carrier injection and transport through the rubrene OSC layer.

We report the operation of spin-valve structures formed from arrays of aligned carbon nanotubes grown and embedded in porous anodized aluminum oxide. The devices incorporate cobalt nanoparticles acting as both a ferromagnetic layer and carbon nanotube array-growing catalysts, requiring only one deposited ferromagnetic layer as the other magnetic electrode. A peak in the resistance occurs clearly as a result of the reversal of the magnetization of the electrodes. Device magnetoresistance ratios reach 1.5% at 40 K, yielding an estimate of the maximum spin scattering length of 2 μm at temperatures up to 40 K. This device architecture presents not only an opportunity for massively parallel patterned circuits with devices the size of an individual nanotube diameter, but also the potential for multi-state switching devices with the selective incorporation of various ferromagnetic catalyst nanoparticles of different coercive fields within the same porous anodized aluminum oxide array.

A novel optical biosensing platform utilizing the unique solubility and chemochromic properties of polyaniline is presented. A facile, ion-induced reprecipitation method leads to the entrapment of a chosen oxidoreductase enzyme, which, in the presence of its associated substrate, catalyzes a reversible redox change in the host polymer. This change is monitored via the UV–vis absorption and subsequently analyzed to fit a Michaelis–Menten model. Here, in vitro prototype devices demonstrate selective sensing of glucose, choline, and uric acid, and the potential to be adapted for use as part of real-time in vivo monitoring systems is discussed.

We introduce a novel method for fabricating nano- and microscale polyaniline particles containing an entrapped oxidoreductase enzyme for use in biosensing applications. This facile process utilizes the reprecipitation of the emeraldine base form of polyaniline from an aqueous−organic suspension, with hydrophobic collapse and subsequent cross-linking of the polymer induced by adjusting the ionic strength beyond a critical threshold. We present UV−vis spectroscopy data, including a quantitative treatment of the spectral line width, along with dynamic light scatting results, to explain the conformation changes in the polyaniline chains that accompany this transition. The resultant aggregated supermolecular polyaniline formations immobilize enzymes via gelation entrapment, augmented by electrostatic attraction, without the need for harsh reaction conditions or additional reagents. Because of its strong optical features at visible wavelengths that can serve as probes for chain conformation, oxidation state, and protonation level, polyaniline may act as a model system for the study of hydrophobic and ion screening effects in proteins and other foldamers.

We present experimental results regarding the effects of applied pressure on the morphology and electrical conductivity of polyaniline/HClO4 nanostructures synthesized via dilute polymerization. By applying a local pressure of 4000 psi (28 MPa) to the nanostructured network, the morphology of the network was transformed to that of a continuous film. The conductivity shows a concomitant increase for the temperature range of 250–300 K. We assign this enhancement of room temperature conductivity to an increase in the effective contact areas between the previously fibrous structures leading to a shorter charge transport path length as the morphology of the film is transformed from a nanostructured network to a continuous film.

A novel, simple, and scalable technique to control the formation of the nanofibers of polyaniline and its derivatives via porous membrane controlled polymerization (PMCP) is reported. Through appropriate synthesis conditions, there are nearly 100% nanofibers formed with diameters tunable from 20nm to 250nm via the selection of pore diameter, monomer, counterions, and polymerization conditions. The nanofiber lengths vary from sub-micrometre to several micrometres. A single nanofiber can be easily isolated from the agglomeration. X-Ray diffraction patterns show that doped polyaniline nanofibers are substantially crystalline.

A novel, simple, and scalable technique to control the formation of the nanofibers of polyaniline and its derivatives via porous membrane controlled polymerization (PMCP) is reported. Through appropriate synthesis conditions, there are nearly 100% nanofibers formed with diameters tunable from 20nm to 250nm via the selection of pore diameter, monomer, counterions, and polymerization conditions. The nanofiber lengths vary from sub-micrometre to several micrometres. A single nanofiber can be easily isolated from the agglomeration. X-Ray diffraction patterns show that doped polyaniline nanofibers are substantially crystalline.