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Now showing items 1 - 16 of 5088

  • Low-Voltage Solution-Processed Hybrid Light-Emitting Transistors

    Chaudhry, Mujeeb Ullah   Tetzner, Kornelius   Lin, Yen-Hung   Nam, Sungho   Pearson, Christopher   Groves, Chris   Petty, Michael C.   Anthopoulos, Thomas D.   Bradley, Donal D. C.  

    We report the development of low operating voltages in inorganic-organic hybrid light-emitting transistors (HLETs) based on a solution-processed ZrOx gate dielectric and a hybrid multilayer channel consisting of the heterojunction In2O3/ZnO and the organic polymer "Super Yellow" acting as n- and p-channel/emissive layers, respectively. Resulting HLETs operate at the lowest voltages reported to-date (<10 V) and combine high electron mobility (22 cm(2)/(V s)) with appreciable current on/off ratios (approximate to 10(3)) and an external quantum efficiency of 2 X 10(-2)% at 700 cd/m(2). The charge injection, transport, and recombination mechanisms within this HLET architecture are discussed, and prospects for further performance enhancement are considered.
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  • UV-Assisted Low Temperature Oxide Dielectric Films for TFT Applications

    Hwang, Jaeeun   Lee, Kyungmin   Jeong, Yesul   Lee, Yong Uk   Pearson, Christopher   Petty, Michael C.   Kim, Hongdoo  

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  • Model for large-area monolayer coverage of polystyrene nanospheres by spin coating

    Chandramohan, Abhishek   Sibirev, Nikolai V.   Dubrovskii, Vladimir G.   Petty, Michael C.   Gallant, Andrew J.   Zeze, Dagou A.  

    Nanosphere lithography, an inexpensive and high throughput technique capable of producing nanostructure (below 100 nm feature size) arrays, relies on the formation of a monolayer of self-assembled nanospheres, followed by custom-etching to produce nanometre size features on large-area substrates. A theoretical model underpinning the self-ordering process by centrifugation is proposed to describe the interplay between the spin speed and solution concentration. The model describes the deposition of a dense and uniform monolayer by the implicit contribution of gravity, centrifugal force and surface tension, which can be accounted for using only the spin speed and the solid/liquid volume ratio. We demonstrate that the spin recipe for the monolayer formation can be represented as a pathway on a 2D phase plane. The model accounts for the ratio of polystyrene nanospheres (300 nm), water, methanol and surfactant in the solution, crucial for large area uniform and periodic monolayer deposition. The monolayer is exploited to create arrays of nanoscale features using 'short' or 'extended' reactive ion etching to produce 30-60 nm (diameter) nanodots or 100-200 nm (diameter) nanoholes over the entire substrate, respectively. The nanostructures were subsequently utilized to create master stamps for nanoimprint lithography.
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  • Control of droplet morphology for inkjet-printed TIPS-pentacene transistors

    Lee, Myung Won   Ryu, Gi Seong   Lee, Young Uk   Pearson, Christopher   Petty, Michael C.   Song, Chung Kun  

    We report on methods to control the morphology of droplets of 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-PEN), which are then used in the fabrication of organic thin film transistors (OTFTs). The grain size and distribution of the TIPS-PEN were found to depend on the temperature of the droplets during drying. The performance of the OTFTs could be improved by heating the substrate and also by changing the relative positions of the inkjet-printed droplets. In our experiments, the optimum substrate temperature was 46 degrees C in air. Transistors with the TIPS-PEN grain boundaries parallel to the current flow between the source and drain electrodes exhibited charge carrier mobilities of 0.44 +/- 0.08 cm(2)/V s. (C) 2012 Elsevier B.V. All rights reserved.
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  • Improved memory behaviour of single-walled carbon nanotubes charge storage nodes

    Alba-Martin, Maria   Firmager, Timothy   Atherton, Joseph   Rosamond, Mark C.   Ashall, Daniel   Al Ghaferi, Amal   Ayesh, Ahmad   Gallant, Andrew J.   Mabrook, Mohammed F.   Petty, Michael C.   Zeze, Dagou A.  

    To investigate their memory behaviours, single-walled carbon nanotubes (SWCNTs) were embedded in the floating gate of a hybrid metal-insulator-semiconductor structure using layer-by-layer deposition, and polymethylmethacrylate (PMMA) as the dielectric. Unlike longer SWCNT-based structures, shortened SWCNTs were shown to exhibit reliable and large memory windows by virtue of a better encapsulation which reduces charge leakage. The capacitance-voltage characteristics of the devices were consistent with electron injection into the SWCNT charge storage elements (in the floating) from the top electrode through the PMMA, using localized defects and crossing the PMMA energy barrier. In terms of material formulation, a combination of SWCNTs dispersed in sodium dodecyl sulfate and polyethyleneimine used as charge storage elements in the floating gate was shown to lead to repeatable and reliable memory characteristics. Fast switching and very large memory windows (similar to 7V) exhibiting high charge density (2.6 x 10(12) cm(-2)) and charge retention in excess of similar to 76% were achieved under a +/- 10V sweep voltage range. These results suggest that SWCNTs could lead to improved memory behaviour with the potential for application in plastic electronics.
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  • Evolution-in-materio:solving computational problems using carbon nanotube-polymer composites

    Mohid, Maktuba   Miller, Julian F.   Harding, Simon L.   Tufte, Gunnar   Massey, Mark K.   Petty, Michael C.  

    Evolution-in-materio uses evolutionary algorithms to exploit properties of materials to solve computational problems without requiring a detailed understanding of such properties. We show that using a purpose-built hardware platform called Mecobo, it is possible to solve computational problems by evolving voltages and signals applied to an electrode array covered with a carbon nanotube-polymer composite. We demonstrate for the first time that this methodology can be applied to function optimization and also to the tone discriminator problem (TDP). For function optimization, we evaluate the approach on a suite of optimization benchmarks and obtain results that in some cases come very close to the global optimum or are comparable with those obtained using well-known software-based evolutionary approach. We also obtain good results in comparison with prior work on the tone discriminator problem. In the case of the TDP we also investigated the relative merits of different mixtures of materials and organizations of electrode array.
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  • A pentacene-based organic thin film memory transistor RID A-4639-2009

    Mabrook, Mohammed F.   Yun, Youngjun   Pearson, Christopher   Zeze, Dagou A.   Petty, Michael C.  

    An organic memory device based on a pentacene thin film transistor is demonstrated. Gold nanoparticles have been used as the charge storage elements while a thin film of polymethylmethacrylate formed the gate insulator. The electrical characteristics and the memory behavior of the organic thin film memory transistor (OTFMT) are reported. Under an appropriate gate bias (1 s pulses), the gold nanoparticles are charged and discharged, resulting in significant threshold voltage shifts of the OTFMT. The detailed programing and erasing procedures are reported.
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  • An Ion Sensitive Organic Field-Effect Transistor Incorporating the Ionophore Valinomycin

    Ritjareonwattu, Supachai   Yun, Youngjun   Pearson, Christopher   Petty, Michael C.  

    We report on the effect of depositing the ionophore valinomycin onto the polymethylmethacrylate (PMMA) gate insulator of an ion-sensitive organic field-effect transistor (ISOFET) based on poly(3-hexylthiophene). The ionophore was deposited onto the PMMA using the Langmuir-Blodgett (LB) technique; thin films based on pure valinomycin and those in which valinomycin was mixed with arachidic acid were investigated. The pH sensitivity of the reference ISOFET could be improved significantly when the devices were coated with an LB film of arachidic acid. However, the response to K+ was low. By adding a small amount (5% w/ w) of the ionophore valinomycin to the fatty acid LB film, an improved response to potassium ions was achieved, but no selectivity over sodium. It was necessary to use an LB membrane of pure valinomycin in order to realise an ISOFET with some K+ selectivity. We suggest that the presence of the ionophore in the fatty acid matrix disrupts the packing of the hydrocarbon chains in the mixed LB film and that the monovalent ion response originates from interactions with the carboxylic acid groups in the fatty acid. In contrast, for the case of the pure valinomycin coating, it is thought that K+ response is controlled by complex formation with the ionophore.
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  • Stable white light emission from an externally modified organic light-emitting device

    Giner-Casares, Juan J.   Martin-Romero, Maria T.   Camacho, Luis   Cocho Martinez, Blanca   Cadd, Duncan   Pearson, Christopher   Petty, Michael C.  

    A blue organic light-emitting device, based on an iridium phosphorescent dopant in a polyvinylcarbazole host, has been modified by the addition of an external CaS:Eu inorganic phosphor layer. By incorporating a surfactant in the phosphor mixture, a uniform coating could be achieved by drop-casting. The resulting hybrid device exhibited white light emission, with Commission Internationale de l'Eclairage, CIE (x, y) coordinates of x =3D 0.32, y =3D 0.35. No significant change in these coordinates was observed for current densities in the range 25-510 A m(-2). The maximum power efficiencies of the white device was 2.3 lm W-1 at a brightness of 254 cd m(-2). (C) 2010 Elsevier B.V. All rights reserved.
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  • Memory effects in hybrid silicon-metallic nanoparticle-organic thin film structures

    Mabrook, Mohammed F.   Pearson, Christopher   Kolb, Dan   Zeze, Dagou A.   Petty, Michael C.  

    We report on the electrical behaviour of metal-insulator-semiconductor (MIS) structures fabricated on silicon substrates and using organic thin films as the dielectric layers. These insulating thin films were produced by different methods, including spin-coating (polymethylmethacrylate), thermal evaporation (pentacene) and Langmuir-Blodgett deposition (cadmium arachidate). Gold nanoparticles, deposited at room temperature by chemical self-assembly, were used as charge storage elements. In all cases, the MIS devices containing the nanoparticles exhibited hysteresis in their capacitance versus voltage characteristics, with a memory window depending on the range of the voltage sweep. This hysteresis was attributed to the charging and discharging of the nanoparticles from the gate electrode. A maximum memory window of 2.5 V was achieved by scanning the applied voltage of an Al/pentacene/Au nanoparticle/SiO2/P-Si structure between 9 and -9 V. (C) 2008 Elsevier B.V. All rights reserved.
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  • Electrical behavior of memory devices based on fluorene-containing organic thin films

    Dimitrakis, Panagiotis   Normand, Pascal   Tsoukalas, Dimitris   Pearson, Christopher   Ahn, Jin H.   Mabrook, Mohammed F.   Zeze, Dagou A.   Petty, Michael C.   Kamtekar, Kiran T.   Wang, Changsheng   Bryce, Martin R.   Green, Mark  

    We report on switching and negative differential resistance (NDR) behaviors of crossed bar electrode structures based on Al/organic layer/Al devices in which the organic layer was a spin-coated layer of 7-{4-[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl}-9,9-dihexyl-N, N-diphenyl-fluoren-2-amine. The addition of gold nanoparticles (0.5 wt %) did not change the switching behavior of thicker film structures; however, devices incorporating the nanoparticles showed more reproducible characteristics. In most cases, a "forming" process, in which a large positive voltage was applied to the top Al electrode, was required before the NDR and conductivity switching were observed. Three different electrical conductivity mechanisms have been identified: Poole-Fretikel conductivity in unformed structures, linear current versus voltage characteristics for the ON state in formed devices, and superlinear current versus voltage behavior for the OFF state in formed devices. Models based on metallic filaments or on the injection and storage of charge do not explain all our experimental observations satisfactorily. Instead, an explanation based on the formation of nanocrystalline regions within the thin film is suggested. The devices can be used as two-terminal memory cells operating with unipolar voltage pulses. (C) 2008 American Institute of Physics.
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  • A Versatile Nanopatterning Technique Based on Controlled Undercutting and Liftoff RID C-3149-2012

    Rosamond, Mark C.   Gallant, Andrew J.   Petty, Michael C.   Kolosov, Oleg   Zeze, Dagou A.  

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  • Handbook of Organic Materials for Electronic and Photonic Devices || Organic electronic memory devices

    Petty, Michael C.  

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  • Effects of hydrogen plasma treatment on the electrical behavior of solution-processed ZnO transistors

    Jeong, Yesul   Pearson, Christopher   Lee, Yong Uk   Ahn, Kyun   Cho, Chae-Ryong   Hwang, Jaeeun   Kim, Hongdoo   Do, Lee-Mi   Petty, Michael C.  

    The effects of hydrogen plasma treatment on the active layer of top-contact zinc oxide thin film transistors are reported. The transfer characteristics of the reference devices exhibited large hysteresis effects and an increasing positive threshold voltage (V-TH) shift on repeated measurements. In contrast, following the plasma processing, the corresponding characteristics of the transistors exhibited negligible hysteresis and a very small V-TH shift; the devices also possessed higher field effect carrier mobility values. These results were attributed to the presence of functional groups in the vicinity of the semiconductor/gate insulator interface, which prevents the formation of an effective channel. (C) 2014 AIP Publishing LLC.
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  • Solution-processed SiO2 gate insulator formed at low temperature for zinc oxide thin-film transistors

    Jeong, Yesul   Pearson, Christopher   Kim, Hyun-Gwan   Park, Man-Young   Kim, Hongdoo   Dod, Lee-Mi   Petty, Michael C.  

    We report on the low-temperature formation (180 degrees C) of a SiO2 dielectric layer from solution-processed perhydropolysilazane. A bottom-gate zinc oxide thin-film transistor has subsequently been fabricated that possesses a carrier mobility of 3 cm(2) V s(-1), an on/off ratio of 10(7) and minimal hysteresis in its transfer and output characteristics.
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  • [Wiley Series in Materials for Electronic and Optoelectronic Applications] Molecular Electronics ||

    Petty, Michael C.  

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