243 research outputs found

    Unipolar resistive switching in metal oxide/organic semiconductor non-volatile memories as a critical phenomenon

    Get PDF
    Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 10(17) m(-2). We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching. (C) 2015 Author(s).Dutch Polymer Institute (DPI), BISTABLE [704]; Fundacao para Ciencia e Tecnologia (FCT) through the research Instituto de Telecommunicacoes (IT-Lx); project Memristor based Adaptive Neuronal Networks (MemBrAiNN) [PTDC/CTM-NAN/122868/2010]; European Community Seventh Framework Programme FP7', ONE-P [212311]; Dutch Ministry of Education, Culture and Science (Gravity Program) [024.001.035]info:eu-repo/semantics/publishedVersio

    Electrical conduction of LiF interlayers in organic diodes

    Get PDF
    An interlayer of LiF in between a metal and an organic semiconductor is commonly used to improve the electron injection. Here, we investigate the effect of moderate bias voltages on the electrical properties of Al/LiF/poly(spirofluorene)/Ba/Al diodes by systematically varying the thickness of the LiF layer (2-50 nm). Application of forward bias V below the bandgap of LiF (V < E-g similar to 14 V) results in reversible formation of an electrical double layer at the LiF/poly(spirofluorene) hetero-junction. Electrons are trapped on the poly(spirofluorene) side of the junction, while positively charged defects accumulate in the LiF with number densities as high as 10(25)/m(3). Optoelectronic measurements confirm the built-up of aggregated, ionized F centres in the LiF as the positive trapped charges. The charged defects result in efficient transport of electrons from the polymer across the LiF, with current densities that are practically independent of the thickness of the LiF layer. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.Fundacao para Ciencia e Tecnologia (FCT) through the research Instituto de Telecommunicacoes (IT-Lx); project Memristor based Adaptive Neuronal Networks (MemBrAiNN) [PTDC/CTM-NAN/122868/2010]; KAU [71-100-35-HiCi]; European Community [212311]; ONE-P; Dutch Ministry of Education, Culture and Science [024.001.035]info:eu-repo/semantics/publishedVersio

    Magnetization of Greenland ice and its relationship with dust content

    Get PDF
    We estimate the concentration of fine magnetic particles in ice samples from the North Greenland Ice Core Project core from the central Greenland ice sheet, using low-temperature (77K) isothermal remanent magnetization (IRM) analysis and compare it with the mass concentration of aerosol dust. Samples were taken from six climatic intervals, spanning the time from the Holocene (Preboreal) back to the Last Glacial Dansgaard/Oeschger cycle 5. The mean IRM intensity of the ice varies by a factor of 3 from glacial to interglacial stages, being lower during interglacials. The IRM acquisition curves of the ice do not quite saturate at the maximum available field of 0.8 T and show a relatively broad coercivity, which is compatible with a mixture of maghemite or magnetite and hematite. Comparison of the IRM intensity and total dust mass shows a remarkably good correlation but also reveals a large background magnetization, which may be essentially constant over the different climatic stages. IRM suggests that the dust properties are independent of the background signal and that the dust aerosol has a magnetization within about 30% of pristine loess from the Chinese Loess Plateau, which is considered to have the same source in the same east Asian deserts as dust in Greenland ice. Ice contamination and the flux of extraterrestrial dust particles were considered in order to explain the origin of the background magnetization. Nevertheless, we could not find a convincing explanation for this signal, which represents a considerable part of the IRM signal and is the dominant component during interglacial intervals, without invoking the presence of undetected dust mass. The alternative hypothesis of a varying magnetization of the ice dust at different climatic periods would suggest that different sources of aerosol are active during different climatic periods. This, however, has not proven to be the case so far for studies of the provenance of dust in Greenland ice

    Trapping of electrons in metal oxide-polymer memory diodes in the initial stage of electroforming

    Get PDF
    Metal oxide-polymer diodes require electroforming before they act as nonvolatile resistive switching memory diodes. Here we investigate the early stages of the electroforming process in Al/Al2O3 /polyspirofluorene /Ba/Al diodes using quasistatic capacitance-voltage measurements. In the initial stage, electrons are injected into the polymer and then deeply trapped near the polyspirofluorene-Al2O3 interface. For bias voltages below 6 V, the number of trapped electrons is found to be CoxideV/q with Coxide as the geometrical capacitance of the oxide layer. This implies a density of traps for the electrons at the polymer-metal oxide interface larger than 31017 m−2

    Nitisinone Arrests but Does Not Reverse Ochronosis in Alkaptonuric Mice.

    Get PDF
    Alkaptonuria (AKU) is an ultrarare autosomal recessive disorder resulting from a deficiency of homogentisate 1,2 dioxygenase (HGD), an enzyme involved in the catabolism of phenylalanine and tyrosine. Loss of HGD function prevents metabolism of homogentisic acid (HGA), leading to increased levels of plasma HGA and urinary excretion. Excess HGA becomes deposited in collagenous tissues and subsequently undergoes polymerisation, principally in the cartilages of loaded joints, in a process known as ochronosis. This results in an early-onset, devastating osteoarthropathy for which there is currently no effective treatment. We recently described the natural history of ochronosis in a murine model of AKU, demonstrating that deposition of ochronotic pigment begins very early in life and accumulates with age. Using this model, we were able to show that lifetime treatment with nitisinone, a potential therapy for AKU, was able to completely prevent deposition of ochronotic pigment. However, although nitisinone has been shown to inhibit ochronotic deposition, whether it can also facilitate removal of existing pigment has not yet been examined. We describe here that midlife administration of nitisinone to AKU mice arrests further deposition of ochronotic pigment in the tibiofemoral joint, but does not result in the clearance of existing pigment. We also demonstrate the dose-dependent response of plasma HGA to nitisinone, highlighting its efficacy for personalised medicine, where dosage can be tailored to the individual AKU patient

    Lithium fluoride injection layers can form quasi-Ohmic contacts for both holes and electrons

    Get PDF
    Thin LiF interlayers are typically used in organic light-emitting diodes to enhance the electron injection. Here, we show that the effective work function of a contact with a LiF interlayer can be either raised or lowered depending on the history of the applied bias. Formation of quasi-Ohmic contacts for both electrons and holes is demonstrated by electroluminescence from symmetric LiF/polymer/LiF diodes in both bias polarities. The origin of the dynamic switching is charging of electrically induced Frenkel defects. The current density-electroluminescence-voltage characteristics can qualitatively be explained. The interpretation is corroborated by unipolar memristive switching and by bias dependent reflection measurements. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License

    Opto-electronic characterization of electron traps upon forming polymer oxide memory diodes

    Get PDF
    Metal-insulator-polymer diodes where the insulator is a thin oxide (Al2O3) layer are electroformed by applying a high bias. The initial stage is reversible and involves trapping of electrons near the oxide/polymer interface. The rate of charge trapping is limited by electron transport through the polymer. Detrapping of charge stored can be accomplished by illuminating with light under short-circuit conditions. The amount of stored charge is determined from the optically induced discharging current transient as a function of applied voltage and oxide thickness. When the charge density exceeds 8 1017/m2, an irreversible soft breakdown transition occurs to a non-volatile memory diode

    Relation between the electroforming voltage in alkali halide-polymer diodes and the bandgap of the alkali halide

    Get PDF
    Electroforming of indium-tin-oxide/alkali halide/poly(spirofluorene)/Ba/Al diodes has been investigated by bias dependent reflectivity measurements. The threshold voltages for electrocoloration and electroforming are independent of layer thickness and correlate with the bandgap of the alkali halide. We argue that the origin is voltage induced defect formation. Frenkel defect pairs are formed by electron-hole recombination in the alkali halide. This self-accelerating process mitigates injection barriers. The dynamic junction formation is compared to that of a light emitting electrochemical cell. A critical defect density for electroforming is 10(25)/m(3). The electroformed alkali halide layer can be considered as a highly doped semiconductor with metallic transport characteristics. (C) 2014 Author(s)
    corecore