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Current Ratio (current + ratio)
Kinds of Current Ratio Selected AbstractsInkjet-Printed Single-Droplet Organic Transistors Based on Semiconductor Nanowires Embedded in Insulating PolymersADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Jung Ah Lim Fabrication of organic field-effect transistors (OFETs) using a high-throughput printing process has garnered tremendous interest for realizing low-cost and large-area flexible electronic devices. Printing of organic semiconductors for active layer of transistor is one of the most critical steps for achieving this goal. The charge carrier transport behavior in this layer, dictated by the crystalline microstructure and molecular orientations of the organic semiconductor, determines the transistor performance. Here, it is demonstrated that an inkjet-printed single-droplet of a semiconducting/insulating polymer blend holds substantial promise as a means for implementing direct-write fabrication of organic transistors. Control of the solubility of the semiconducting component in a blend solution can yield an inkjet-printed single-droplet blend film characterized by a semiconductor nanowire network embedded in an insulating polymer matrix. The inkjet-printed blend films having this unique structure provide effective pathways for charge carrier transport through semiconductor nanowires, as well as significantly improve the on-off current ratio and the environmental stability of the printed transistors. [source] Preparation and Memory Performance of a Nanoaggregated Dispersed Red 1-Functionalized Poly (N -vinylcarbazole) Film via Solution-Phase Self-AssemblyADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Xiao-Dong Zhuang Abstract A nanoaggregated dispersed red 1-grafted poly(N -vinylcarbazole) (abbreviated PVDR) is self-assembled via ,,, stacking interactions of the carbazole groups in the polymer system after adding a solution of PVDR in N,N -dimethylformamide to dichloromethane. Upon self-assembly, the nanoaggregated PVDR film displays helical columnar stacks with large grain sizes, whereas a non-aggregated PVDR film exhibits an amorphous morphology with smaller grain size. A write-once read-many-times (WORM) memory device is shown whereby a pre-assembled solution of PVDR is spin-coated as the active layer and is sandwiched between an aluminum electrode and an indium-tin-oxide (ITO) electrode. This device shows very good memory performance, with an ON/OFF current ratio of more than 105 and a low misreading rate through the precise control of the ON and OFF states. The stability of the nanoaggregated PVDR device is much higher than that of the non-nanoaggregated PVDR device. This difference in device stability under constant voltage stress can be mainly attributed to the difference in the film crystallinity and surface morphology. No degradation in current density was observed for the ON- and OFF-states after more than one hundred million (108) continuous read cycles indicating that both states were insensitive to the read cycles. These results render the nanoaggregated PVDR polymer as promising components for high-performance polymer memory devices. [source] Improving the ON/OFF Ratio and Reversibility of Recording by Rational Structural Arrangement of Donor,Acceptor MoleculesADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Ying Ma Abstract Organic molecules with donor,acceptor (D,A) structure are an important type of material for nanoelectronics and molecular electronics. The influence of the electron donor and acceptor units on the electrical function of materials is a worthy topic for the development of high-performance data storage. In this work, the effect of different D,A structures (namely D,,,A,,,D and A,,,D,,,A) on the electronic switching properties of triphenylamine-based molecules is investigated. Devices based on D,,,A,,,D molecules exhibit excellent write,read,erase characteristics with a high ON/OFF ratio of up to 106, while that based on A,,,D,,,A molecules exhibit irreversible switching behavior with an ON/OFF ratio of about (3.2,×,101),(1,×,103). Moreover, long retention time of the high conductance state and low threshold voltage are observed for the D,A switching materials. Accordingly, stable and reliable nanoscale data storage is achieved on the thin films of the D,A molecules by scanning tunneling microscopy. The influence of the arrangement of the D and A within the molecular backbone disclosed in this study will be of significance for improving the electronic switching properties (ON/OFF current ratio and reversibility) of new molecular systems, so as to achieve more efficient data storage through appropriate design strategies. [source] High-Performance Photoresponsive Organic Nanotransistors with Single-Layer Graphenes as Two-Dimensional ElectrodesADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Yang Cao Abstract Graphene behaves as a robust semimetal with the high electrical conductivity stemming from its high-quality tight two-dimensional crystallographic lattice. It is therefore a promising electrode material. Here, a general methodology for making stable photoresponsive field effect transistors, whose device geometries are comparable to traditional macroscopic semiconducting devices at the nanometer scale, using cut graphene sheets as 2D contacts is detailed. These contacts are produced through oxidative cutting of individual 2D planar graphene by electron beam lithography and oxygen plasma etching. Nanoscale organic transistors based on graphene contacts show high-performance FET behavior with bulk-like carrier mobility, high on/off current ratio, and high reproducibility. Due to the presence of photoactive molecules, the devices display reversible changes in current when they are exposed to visible light. The calculated responsivity of the devices is found to be as high as ,8.3,A,W,1. This study forms the basis for making new types of ultrasensitive molecular devices, thus initiating broad research interest in the field of nanoscale/molecular electronics. [source] Hybrid Nanoparticle/Organic Devices with Strong Resonant Tunneling BehaviorsADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Tianhang Zheng Abstract A hybrid nanoparticle/organic device consisting of small molecule organic semiconductors and Ag nanoparticles is reported. The single device exhibits unusual properties of organic resonant tunneling diode (ORTD) at low driving voltage region and offers light emission at high voltage. For ORTD, a strong negative differential resistance behavior is demonstrated at room temperature. The current resonance with the peak-to-valley current ratio of over 4.6 and narrow linewidth of only ,1.4,V is achieved. A detailed operating mechanism of the charging and emission modes is proposed, which can be discussed in terms of the strong charge-trapping effect of Ag nanoparticles. The repeatable operations of hybrid device show the mutual influences between two modes and the light emission properties of the ORTD are also discussed. [source] A New Carbazole-Constructed Hyperbranched Polymer: Convenient One-Pot Synthesis, Hole-Transporting Ability, and Field-Effect Transistor PropertiesADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Zhong'an Li Abstract A new hyperbranched polymer (HB-car), constructed fully by carbazole moieties, is successfully synthesized through a one-pot Suzuki coupling reaction. The resultant polymer is well-characterized, and its hole-transporting ability is studied carefully. The device, in which HB-car is utilized as a hole-transporting layer and tris-(8-hydroxyquinoline) aluminum as an electron-emitting layer as well as electron-transporting layer, gives a much higher efficiency (3.05,cd A,1), than that of a poly(N -vinylcarbazole) based device (2.19,cd A,1) under similar experimental conditions. The remarkable performance is attributed to its low energy barrier and enhanced hole-drifting ability in the HB-car based device. In addition, for the first time, a field-effect transistor (FET) based on the hyperbranched polymer is fabricated, and the organic FET device shows that HB-car is a typical p -type FET material with a saturation mobility of 1,×,10,5,cm2 V,1 s,1, a threshold voltage of ,47.1,V, and an on-to-off current ratio of 103. [source] Synthesis, Characterization, and Field-Effect Transistor Performance of Thieno[3,2-b]thieno[2,,3,:4,5]thieno[2,3-d]thiophene DerivativesADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Ying Liu Abstract The synthesis, characterization, and field-effect transistor (FET) properties of a new class of thieno[3,2-b]thieno[2,,3,:4,5]thieno[2,3-d]thiophene derivatives are described. The optical spectra of their films show the presence of stronger interactions between molecules in the solid state. Thermal analyses reveal that the three materials are thermally stable and have no phase transitions at low temperature. The crystal structures are determined, and show ,-stacked structures and intermolecular S···S contacts. These organic materials exhibit p-type FET behavior with hole mobilities as high as 0.14,cm2,V,1,s,1 and an on/off current ratio of 106. These results indicate that thieno[3,2-b]thieno [2,,3,:4,5]thieno[2,3-d]thiophene, as a linear ,-conjugated system, is an effective building block for developing high-performance organic semiconductors. [source] Influence of Electric Field on Microstructures of Pentacene Thin-Films in Field-Effect Transistors,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2008L. Cheng Abstract We report on electric-field-induced irreversible structural modifications in pentacene thin films after long-term operation of organic field-effect transistor (OFET) devices. Micro-Raman spectroscopy allows for the analysis of the microstructural modifications of pentacene in the small active channel of OFET during device operation. The results suggest that the herringbone packing of pentacene molecules in a solid film is affected by an external electric field, particularly the source-to-drain field that parallels the a,b lattice plane. The analysis of vibrational frequency and Davydov splitting in the Raman spectra reveals a singular behavior suggesting a reduced separation distance between pentacene molecules after long-term operations and, thus, large intermolecular interactions. These results provide evidence for improved OFET performance after long-term operation, related to the microstructures of organic semiconductors. It is known that the application of large electric fields alters the semiconductor properties of the material owing to the generation of defects and the trapping of charges. However, we first suggest that large electric fields may alter the molecular geometry and further induce structural phase transitions in the pentacene films. These results provide a basis for understanding the improved electronic properties in test devices after long-term operations, including enhanced field-effect mobility, improved on/off current ratio, sharp sub-threshold swing, and a slower decay rate in the output drain current. In addition, the effects of source-to-drain electric field, gate electric field, current and charge carriers, and thermal annealing on the pentacene films during OFET operations are discussed. [source] Photoresponse Properties of CdSe Single-Nanoribbon Photodetectors,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2007Y. Jiang Abstract Photodetectors are fabricated from individual single-crystal CdSe nanoribbons, and the photoresponse properties of the devices are studied systematically. The photodetector shows a high sensitivity towards excitation wavelength with a sharp cut-off at 710,nm, corresponding to the bandgap of CdSe. The device exhibits a high photo-to-dark current ratio of five orders of magnitude at 650,nm, and can function with excellent stability, reproducibility, and high response speed (<,1,ms) in a wide range of switching frequency (up to 300,Hz). The photocurrent of the device shows a power-law dependence on light intensity. This finding together with the analysis of the light intensity-dependent response speed reveals the existence of various traps at different energy levels (shallow and deep) in the bandgap. Coating with a thin SiO2 isolating layer increases the photocurrent but decreases the response speed of the CdSe nanoribbon, which is attributed to reduction of recombination centers on ribbon surface. [source] High-Current-Density CuO x/InZnOx Thin-Film Diodes for Cross-Point Memory Applications,ADVANCED MATERIALS, Issue 16 2008Bo Soo Kang Room-temperature-deposited CuOxInZnOx thin-film heterojunction diodes show a high current density of 3.5,×,104,A cm,2 and a high on/off current ratio of 106 (see figure). The oxide diode is a promising switch element for three-dimensional stackable memory devices, where high-temperature-prepared silicon diodes are difficult to apply. [source] High-Performance Programmable Memory Devices Based on Hyperbranched Copper Phthalocyanine Polymer Thin Films,ADVANCED MATERIALS, Issue 9 2008Seungchel Choi Electrically programmable fuse-type polymer memory devices based on hyperbranched copper phthalocyanine polymer thin films are fabricated. The devices have novel write-once-read-many (WORM) memory characteristics, with a high ON/OFF current ratio (of 106) and a high electrical stability, thus opening up the possibility of a low-cost mass production of high-performance, nonvolatile polymer memory devices. [source] Self-Organized Organic Thin-Film Transistors on Plastic,ADVANCED MATERIALS, Issue 8 2004Y. Choi The development of the self-organized growth of pentacence thin films on the channel region of a thin-film transistor (TFT) using surface modifications induced by organic vapor phase deposition is reported (see Figure). A bottom-contact TFT on plastic using an organic gate insulator of cross-linked poly-(4-vinylphenol) exhibited a field-effect mobility of 1.2 cm2/Vs and an on/off current ratio of ,,107. [source] Population trends and habitat use of Harlequin Ducks in Rhode IslandJOURNAL OF FIELD ORNITHOLOGY, Issue 3 2007Christine M. Caron ABSTRACT To assess population trends of Harlequin Ducks (Histrionicus histrionicus) in Rhode Island (U.S.A.), we analyzed Christmas Bird Counts and other historical surveys and also conducted surveys during the winter of 2005,2006. We estimated sex and age ratios, evaluated the effects of tidal regime and time of day on survey precision, and quantified habitat use. The population in Rhode Island experienced logistic growth from 1976 to 2004, with approximately 150 birds now wintering at three primary sites in the state. We estimated that the current ratio of males to females in the region was 1.6:1 (62% males) and that 13% of males were first-winter birds. Most Harlequin Ducks were observed in rocky habitats within 50 m of the shore or offshore islands. We detected the greatest numbers of birds, with the least amount of variation, during morning surveys at low tide, suggesting that this may be the most appropriate time for population monitoring. Increases in the Rhode Island population and male-biased sex ratios may indicate a local population recovery resulting from a hunting ban initiated in 1990. Although most Harlequin Ducks in eastern North America winter in Maine, the population in Rhode Island represents one of the largest in the southern part of their range. SINOPSIS Para determinar las tendencias poblacionales de arlequines (Histrionicus histrionicus), en Rhode Island, analizamos los conteos navideños, otros censos históricos y además llevamos a cabos censos durante el invierno de 2005,2006. Cuantificamos el uso de habitat, estimamos la tasa de edad y sexos y evaluamos el efecto del régimen de mareas y la hora del dia en la presición de los censos. La población de patos arlequines experimentó un crecimiento logístico de 1976,2004, con unos 150 patos pasando el invierno en tres localidades primarias, del estado. Estimamos una tasa de 1.6:1 de machos a hembras (62% de machos), siendo un 13% de los machos individuos de primer invierno. La mayoría de las aves fueron observadas en hábitats rocosos a unos 50 m de la playa o en islas cerca de la playa. Detectamos el mayor número de aves, con la menor variación, en los censos que se llevaron a cabo durante la marea baja, lo que sugiere que este es el momento más apropiado para monitorear sus poblaciones. El aumento de estas aves en Rhode Island, el sesgo en su sexo, hacia mayor cantidad de machos, pudiera indicar, de un recobro poblacional como resultado la prohibición de su cacería a partir de 1990. Aunque la mayoría de los arlequines de la parte este de los EUA pasan el invierno en Maine, la población de Rhode Island representa una de las mayores en la parte sur de su distribución. [source] 2,7-Carbazolenevinylene-Based Oligomer Thin-Film Transistors: High Mobility Through Structural Ordering,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2005N. Drolet Abstract We have fabricated organic field-effect transistors based on thin films of 2,7-carbazole oligomeric semiconductors 1,4-bis(vinylene-(N -hexyl-2-carbazole))phenylene (CPC), 1,4-bis(vinylene-(N,-methyl-7,-hexyl-2,-carbazole))benzene (RCPCR), N -hexyl-2,7-bis(vinylene-(N -hexyl-2-carbazole))carbazole (CCC), and N -methyl-2,7-bis(vinylene-(7-hexyl- N -methyl-2-carbazole))carbazole (RCCCR). The organic semiconductors are deposited by thermal evaporation on bare and chemically modified silicon dioxide surfaces (SiO2/Si) held at different temperatures varying from 25 to 200,°C during deposition. The resulting thin films have been characterized using UV-vis and Fourier-transform infrared spectroscopies, scanning electron microscopy, and X-ray diffraction, and the observed top-contact transistor performances have been correlated with thin-film properties. We found that these new ,-conjugated oligomers can form highly ordered structures and reach high hole mobilities. Devices using CPC as the active semiconductor have exhibited mobilities as high as 0.3,cm2,V,1,s,1 with on/off current ratios of up to 107. These features make CPC and 2,7-carbazolenevinylene-based oligomers attractive candidates for device applications. [source] Self-Assembly and Electronics of Dipolar Linear Acenes,ADVANCED MATERIALS, Issue 4 2005Q. Miao Linear acenes terminated with quinones demonstrate that electrostatic complementarity is a viable self-assembly motif for organic semiconductors. An organic field-effect transistor with co-facial, head-to-tail stacks with ,-surfaces 0.1,Å closer together than the aromatic planes of graphite is fabricated. The field-effect mobilities and ON/OFF current ratios are high enough to be useful in flexible electronic applications. [source] Resistive switching polymer materials based on poly(aryl ether)s containing triphenylamine and 1,2,4-triazole moietiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2008Kun-Li Wang Abstract A series of poly(aryl ether)s were successfully prepared via aromatic nucleophilic substitution reaction from various bisphenols and a novel bipolar aryl difluoride monomer containing electron-donor triphenylamine and electron-acceptor 1,2,4-triazole moieties. The poly(aryl ether)s exhibited excellent solubility in organic solvents such as dimethylformamide, chloroform, and tetrahydrofuran at room temperature. The poly(aryl ether)s showed high thermal stability with Td10 higher than 500 °C and glass transition temperatures (Tg) higher than 187 °C. The thin films of the poly(aryl ether)s indicated bistable resistive switching behavior with ON/OFF current ratios as high as 103. The switching on and switching off bias voltages of the poly(aryl ether)s were affected by the bisphenol moiety. The good resistive switching behavior of the poly(aryl ether)s made them promising candidates for future nonvolatile memory applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6861,6871, 2008 [source] Correction of mass spectrometric isotope ratio measurements for isobaric isotopologues of O2, CO, CO2, N2O and SO2RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2008Jan Kaiser Gas isotope ratio mass spectrometers usually measure ion current ratios of molecules, not atoms. Often several isotopologues contribute to an ion current at a particular mass-to-charge ratio (m/z). Therefore, corrections have to be applied to derive the desired isotope ratios. These corrections are usually formulated in terms of isotope ratios (R), but this does not reflect the practice of measuring the ion current ratios of the sample relative to those of a reference material. Correspondingly, the relative ion current ratio differences (expressed as , values) are first converted into isotopologue ratios, then into isotope ratios and finally back into elemental , values. Here, we present a reformulation of this data reduction procedure entirely in terms of , values and the ,absolute' isotope ratios of the reference material. This also shows that not the absolute isotope ratios of the reference material themselves, but only product and ratio combinations of them, are required for the data reduction. These combinations can be and, for carbon and oxygen have been, measured by conventional isotope ratio mass spectrometers. The frequently implied use of absolute isotope ratios measured by specially calibrated instruments is actually unnecessary. Following related work on CO2, we here derive data reduction equations for the species O2, CO, N2O and SO2. We also suggest experiments to measure the required absolute ratio combinations for N2O, SO2 and O2. As a prelude, we summarise historic and recent measurements of absolute isotope ratios in international isotope reference materials. Copyright © 2008 John Wiley & Sons, Ltd. [source] Syntheses, Phase Behavior, Supramolecular Chirality, and Field-Effect Carrier Mobility of Asymmetrically End-Capped Mesogenic OligothiophenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2009Qingwei Meng Dr. Abstract Supramolecular chirality and liquid crystalline OFET: Achiral end-capped oligothiophenes can be tuned to exhibit supramolecular chirality with unique striped textures showing distinct circular dichroism signals as well as a highly ordered SmE phase that leads to high hole carrier mobility. A novel series of asymmetrically end-capped mesogenic oligothiophenes, with various oligothiophene core lengths, alkoxy tail lengths, and molecular polarities through introducing alkylsulfanyl or alkylsulfonyl functionalities as the terminal group, have been synthesized by palladium-catalyzed Suzuki cross-coupling and Kumada cross-coupling reactions as key steps. For the single end-capped oligothiophenes, CmO-Ar-OT(4)-H in which m=10, 12, 14, 16, and 18, all of these oligomers exhibited a broad temperature range of highly ordered smectic E and enantiotropic nematic phases, apart from the one with the longest octadecyloxy tail. For the double end-capped series C10O-Ar-OT(n)-R, R=Ph-SC6 or Ph-SO2C6 in which n=1, 2, 3, and 4, oligomers with more than one thiophene ring exhibited smectic A and smectic C phases, various crystal polymorphs and/or unusual low-temperature condensed phases. In the nonpolar, alkylsulfanylphenyl-substituted oligothiophene series, both the crystal/solid melting point and mesogenic clear point increased significantly with an increasing oligothiophene conjugation length. In the polar, alkylsulfonylphenyl-substituted oligothiophene series, all the oligomers showed increased melting points, but decreased mesogenic temperature intervals than those of their corresponding alkylsulfanyl counterparts. Remarkably, two different helical structures showing distinct striated textures or striped patterns were observed with a pitch of several to tens of micrometers under a polarized optical microscope upon cooling from their preceding fluidic smectic phases. The unusual twisted smectic layer structures in the thin solid films exhibiting distinct supramolecular chirality of both handednesses, revealed by circular dichroism measurements, were further confirmed by XRD analyses characterized by a sharp layer reflection together with its higher orders and diffuse wide-angle scatterings. In addition, initial studies showed that the highly ordered smectic phase of the single end-capped oligothiophenes can be utilized to improve field-effect charge mobility. C10O-Ar-OT(4)-H showed a hole mobility of 0.07,cm2,V,1,s,1 when deposited on octyltrichlorosilane-treated substrates at 140,°C and the on/off current ratios reached 5×105; on the other hand, its mobility was only 8×10,3,cm2,V,1,s,1 on the same substrate when deposited at room temperature. [source] | |||||||||||||