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Pentacene
Terms modified by Pentacene Selected AbstractsThe Role of OTS Density on Pentacene and C60 Nucleation, Thin Film Growth, and Transistor PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Ajay Virkar Abstract In organic thin film transistors (OTFTs), charge transport occurs in the first few monolayers of the semiconductor near the semiconductor/dielectric interface. Previous work has investigated the roles of dielectric surface energy, roughness, and chemical functionality on performance. However, large discrepancies in performance, even with apparently identical surface treatments, indicate that additional surface parameters must be identified and controlled in order to optimize OTFTs. Here, a crystalline, dense octadecylsilane (OTS) surface modification layer is found that promotes two-dimensional semiconductor growth. Higher mobility is consistently achieved for films deposited on crystalline OTS compared to on disordered OTS, with mobilities as high as 5.3 and 2.3,cm2,V,1,s,1 for C60 and pentacene, respectively. This is a significant step toward morphological control of organic semiconductors which is directly linked to their thin film charge carrier transport. [source] A Computational Study of the Sub-monolayer Growth of PentaceneADVANCED FUNCTIONAL MATERIALS, Issue 13 2006D. Choudhary Abstract A computational study of organic thin-film growth using a combination of ab,initio based energy calculations and kinetic Monte Carlo (KMC) simulations is provided. A lattice-based KMC model is used in which binding energies determine the relative rates of diffusion of the molecules. This KMC approach is used to present "landscapes" or "maps" that illustrate the possible structural outcomes of growing a thin film of small organic molecules, represented as a two-site dimer, on a substrate in which the strength of organic,substrate interactions is allowed to vary. KMC provides a mesoscopic-scale view of sub-monolayer deposition of organic thin films on model substrates, mapped out as a function of the flux of depositing molecules and the temperature of the substrate. The morphology of the crystalline thin films is shown to be a strong function of the molecule,molecule and molecule,substrate interactions. A rich variety of maps is shown to occur in which the small organic molecules either stand up or lie down in a variety of different patterns depending on the nature of the binding to the surface. In this way, it is possible to suggest how to tailor the substrate or the small organic molecule in order to create a desired growth habit. In order to demonstrate how this set of allowable maps is reduced in the case where the set of energy barriers between substrate and organic molecule are reliably known, we have used Gaussian,98 calculations to establish binding energies for the weak van der Waals interactions between a),pairs of pentacene molecules as a function of orientation and b),pentacene and two substrates, silicon surfaces passivated with cyclopentene molecules and a crystalline model of silicon dioxide. The critical nucleation size and the mode of diffusion of this idealized two-site dimer model for pentacene molecules are found to be in good agreement with experimental data. [source] Cover Picture: Microscopic Evidence for Spatially Inhomogeneous Charge Trapping in Pentacene (Adv. Mater.ADVANCED MATERIALS, Issue 11 200511/2005) Abstract Trapped charge has been observed in polycrystalline pentacene films by electric force microscopy in work reported by Muller and Marohn on p.,1410. The cover shows an optical fiber watching the motion of a metal-coated cantilever hovering over a polycrystalline pentacene film. The film occupies the 6.5,,,m gap in a working field-effect transistor. Trapped charge (dark blue and black areas in the pentacene) appears as large patches randomly distributed throughout the device, implying that long-lived traps in polycrystalline pentacene are not correlated with grain boundaries. [source] Efficient Isomer-Pure Synthesis of a Benzo[b]thiophene Analogue of Pentacene.CHEMINFORM, Issue 31 2004Brigitte Wex Abstract For Abstract see ChemInform Abstract in Full Text. [source] Pentacene-Based Polycyclic Aromatic Hydrocarbon Dyads with Cofacial Solid-State ,-StackingCHEMISTRY - A EUROPEAN JOURNAL, Issue 46 2009Dan Lehnherr Give me five! Pentacene-based polycyclic aromatic hydrocarbon (PAH) dyads are synthesized via an unsymmetrical pentacene building block. These molecules exhibit cofacial solid-state ,-stacking as a result of the large aromatic chromophores. The choice of the PAH attached to the pentacene (see picture) influences the electronic properties as determined by UV/Vis absorption/emission spectroscopy and cyclic voltammetry. [source] Fabrication and evaluation of complementary logic circuits using zinc oxide and pentacene thin film transistorELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 9 2009Hiroyuki Iechi Abstract We fabricated hybrid complementary inverters with n-channel zinc oxide (ZnO) transistors as the n-type inorganic material and p-channel organic transistors using pentacene as the p-type organic material. The complementary inverter exhibited a large voltage gain of 10 to 12 and a cutoff frequency of 0.5 kHz. ZnO thin film transistors show n-type semiconducting properties having field-effect mobility of 2.1×10,3 cm2/Vs. On the other hand, pentacene thin film transistors show p-type semiconducting properties having field-effect mobility of 3.2×10,2 cm2/Vs. We describe basic charge transfer characteristics of ZnO thin films. The results obtained here demonstrate that it is important for the transistor using ZnO to be injected charge from electrode to semiconducting material effectively. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(9): 36,42, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10085 [source] Ultrathin, Organic, Semiconductor/Polymer Blends by Scanning Corona-Discharge Coating for High-Performance Organic Thin-Film TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Hee Joon Jung Abstract A new thin-film coating process, scanning corona-discharge coating (SCDC), to fabricate ultrathin tri-isopropylsilylethynyl pentacene (TIPS-PEN)/amorphous-polymer blend layers suitable for high-performance, bottom-gate, organic thin-film transistors (OTFTs) is described. The method is based on utilizing the electrodynamic flow of gas molecules that are corona-discharged at a sharp metallic tip under a high voltage and subsequently directed towards a bottom electrode. With the static movement of the bottom electrode, on which a blend solution of TIPS-PEN and an amorphous polymer is deposited, SCDC provides an efficient route to produce uniform blend films with thicknesses of less than one hundred nanometers, in which the TIPS-PEN and the amorphous polymer are vertically phase-separated into a bilayered structure with a single-crystalline nature of the TIPS-PEN. A bottom-gate field-effect transistor with a blend layer of TIPS-PEN/polystyrene (PS) (90/10 wt%) operated at ambient conditions, for example, indeed exhibits a highly reliable device performance with a field-effect mobility of approximately 0.23 cm2 V,1 s,1: two orders of magnitude greater than that of a spin-coated blend film. SCDC also turns out to be applicable to other amorphous polymers, such as poly(, -methyl styrene) and poly(methyl methacrylate) and, readily combined with the conventional transfer-printing technique, gives rise to micropatterned arrays of TIPS-PEN/polymer films. [source] Organic Electronics: High Tg Cyclic Olefin Copolymer Gate Dielectrics for N,N,-Ditridecyl Perylene Diimide Based Field-Effect Transistors: Improving Performance and Stability with Thermal Treatment (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Mater. Abstract A novel application of ethylene-norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field-effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally-treated N,N, -ditridecyl perylene diimide (PTCDI-C13)-based n-type FETs using a COC/SiO2 gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95° ± 1°) and high thermal stability (glass transition temperature = 181 °C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI-C13 domains grown on the COC/SiO2 gate dielectric increases significantly. The resulting n-type FETs exhibit high atmospheric field-effect mobilities, up to 0.90 cm2 V,1 s,1 in the 20 V saturation regime and long-term stability with respect to H2O/O2 degradation, hysteresis, or sweep-stress over 110 days. By integrating the n-type FETs with p-type pentacene-based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized. [source] High Tg Cyclic Olefin Copolymer Gate Dielectrics for N,N,-Ditridecyl Perylene Diimide Based Field-Effect Transistors: Improving Performance and Stability with Thermal TreatmentADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Jaeyoung Jang Abstract A novel application of ethylene-norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field-effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally-treated N,N, -ditridecyl perylene diimide (PTCDI-C13)-based n-type FETs using a COC/SiO2 gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95° ± 1°) and high thermal stability (glass transition temperature = 181 °C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI-C13 domains grown on the COC/SiO2 gate dielectric increases significantly. The resulting n-type FETs exhibit high atmospheric field-effect mobilities, up to 0.90 cm2 V,1 s,1 in the 20 V saturation regime and long-term stability with respect to H2O/O2 degradation, hysteresis, or sweep-stress over 110 days. By integrating the n-type FETs with p-type pentacene-based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized. [source] Variable Temperature Mobility Analysis of n-Channel, p-Channel, and Ambipolar Organic Field-Effect TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Joseph A. Letizia Abstract The temperature dependence of field-effect transistor (FET) mobility is analyzed for a series of n-channel, p-channel, and ambipolar organic semiconductor-based FETs selected for varied semiconductor structural and device characteristics. The materials (and dominant carrier type) studied are 5,5,,,-bis(perfluorophenacyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (1, n-channel), 5,5,,,-bis(perfluorohexyl carbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (2, n-channel), pentacene (3, p-channel); 5,5,,,-bis(hexylcarbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (4, ambipolar), 5,5,,,-bis-(phenacyl)-2,2,: 5,,2,:5,,2,,,-quaterthiophene (5, p-channel), 2,7-bis((5-perfluorophenacyl)thiophen-2-yl)-9,10-phenanthrenequinone (6, n-channel), and poly(N -(2-octyldodecyl)-2,2,-bithiophene-3,3,-dicarboximide) (7, n-channel). Fits of the effective field-effect mobility (µeff) data assuming a discrete trap energy within a multiple trapping and release (MTR) model reveal low activation energies (EAs) for high-mobility semiconductors 1,3 of 21, 22, and 30,meV, respectively. Higher EA values of 40,70,meV are exhibited by 4,7 -derived FETs having lower mobilities (µeff). Analysis of these data reveals little correlation between the conduction state energy level and EA, while there is an inverse relationship between EA and µeff. The first variable-temperature study of an ambipolar organic FET reveals that although n-channel behavior exhibits EA,=,27,meV, the p-channel regime exhibits significantly more trapping with EA,=,250,meV. Interestingly, calculated free carrier mobilities (µ0) are in the range of ,0.2,0.8,cm2,V,1 s,1 in this materials set, largely independent of µeff. This indicates that in the absence of charge traps, the inherent magnitude of carrier mobility is comparable for each of these materials. Finally, the effect of temperature on threshold voltage (VT) reveals two distinct trapping regimes, with the change in trapped charge exhibiting a striking correlation with room temperature µeff. The observation that EA is independent of conduction state energy, and that changes in trapped charge with temperature correlate with room temperature µeff, support the applicability of trap-limited mobility models such as a MTR mechanism to this materials set. [source] Electronic Structure and Geminate Pair Energetics at Organic,Organic Interfaces: The Case of Pentacene/C60 HeterojunctionsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Stijn Verlaak Abstract Organic semiconductors are characterized by localized states whose energies are predominantly determined by electrostatic interactions with their immediate molecular environment. As a result, the details of the energy landscape at heterojunctions between different organic semiconductors cannot simply be deduced from those of the individual semiconductors, and they have so far remained largely unexplored. Here, microelectrostatic computations are performed to clarify the nature of the electronic structure and geminate pair energetics at the pentacene/C60 interface, as archetype for an interface between a donor molecule and a fullerene electron acceptor. The size and orientation of the molecular quadrupole moments, determined by material choice, crystal orientation, and thermodynamic growth parameters of the semiconductors, dominate the interface energetics. Not only do quadrupoles produce direct electrostatic interactions with charge carriers, but, in addition, the discontinuity of the quadrupole field at the interface induces permanent interface dipoles. That discontinuity is particularly striking for an interface with C60 molecules, which by virtue of their symmetry possess no quadrupole. Consequently, at a pentacene/C60 interface, both the vacuum-level shift and geminate pair dissociation critically depend on the orientation of the pentacene ,-system relative to the adjacent C60. [source] Azeotropic Binary Solvent Mixtures for Preparation of Organic Single CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Xiaoran Li Abstract Here, a new approach is introduced to prepare large single crystals of ,-conjugated organic molecules from solution. Utilizing the concept of azeotropism, single crystals of tri-isopropylsilylethynyl pentacene (TIPS-PEN) with dimensions up to millimeters are facilely self-assembled from homogeneous solutions comprising two solvents with opposing polarities and a positive azeotropic point. At solvent compositions close to the azeotropic point, an abrupt transition of morphology from polycrystalline thin-films to large single crystals is found. How to adjust the initial ratio of the binary solvents so that the change in solvent composition during evaporation favors the specific H-aggregation and promotes an efficient self-assembly of TIPS-PEN is explained. The charge-carrier (hole) mobilities are substantially enhanced by a factor of 4 from the morphology of thin-films to large single crystals used as active layer in field-effect transistors. Additionally, this approach is extended to other ,,, stacked organic molecules to elucidate its broad applicability. [source] The Role of OTS Density on Pentacene and C60 Nucleation, Thin Film Growth, and Transistor PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Ajay Virkar Abstract In organic thin film transistors (OTFTs), charge transport occurs in the first few monolayers of the semiconductor near the semiconductor/dielectric interface. Previous work has investigated the roles of dielectric surface energy, roughness, and chemical functionality on performance. However, large discrepancies in performance, even with apparently identical surface treatments, indicate that additional surface parameters must be identified and controlled in order to optimize OTFTs. Here, a crystalline, dense octadecylsilane (OTS) surface modification layer is found that promotes two-dimensional semiconductor growth. Higher mobility is consistently achieved for films deposited on crystalline OTS compared to on disordered OTS, with mobilities as high as 5.3 and 2.3,cm2,V,1,s,1 for C60 and pentacene, respectively. This is a significant step toward morphological control of organic semiconductors which is directly linked to their thin film charge carrier transport. [source] Non-volatile Ferroelectric Poly(vinylidene fluoride- co -trifluoroethylene) Memory Based on a Single-Crystalline Tri-isopropylsilylethynyl Pentacene Field-Effect TransistorADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Seok Ju Kang Abstract A new type of nonvolatile ferroelectric poly(vinylidene fluoride- co -trifluoroethylene) (P(VDF-TrFE)) memory based on an organic thin-film transistor (OTFT) with a single crystal of tri-isopropylsilylethynyl pentacene (TIPS-PEN) as the active layer is developed. A bottom-gate OTFT is fabricated with a thin P(VDF-TrFE) film gate insulator on which a one-dimensional ribbon-type TIPS-PEN single crystal, grown via a solvent-exchange method, is positioned between the Au source and drain electrodes. Post-thermal treatment optimizes the interface between the flat, single-crystalline ab plane of TIPS-PEN and the polycrystalline P(VDF-TrFE) surface with characteristic needle-like crystalline lamellae. As a consequence, the memory device exhibits a substantially stable source,drain current modulation with an ON/OFF ratio hysteresis greater than 103, which is superior to a ferroelectric P(VDF-TrFE) OTFT that has a vacuum-evaporated pentacene layer. Data retention longer than 5,×,104 s is additionally achieved in ambient conditions by incorporating an interlayer between the gate electrode and P(VDF-TrFE) thin film. The device is environmentally stable for more than 40 days without additional passivation. The deposition of a seed solution of TIPS-PEN on the chemically micropatterned surface allows fabrication arrays of TIPS-PEN single crystals that can be potentially useful for integrated arrays of ferroelectric polymeric TFT memory. [source] Enhancement of Carrier Mobilities of Organic Semiconductors on Sol,Gel Dielectrics: Investigations of Molecular Organization and Interfacial Chemistry EffectsADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Tommy Cahyadi Abstract The dielectric-semiconductor interfacial interactions critically influence the morphology and molecular ordering of the organic semiconductor molecules, and hence have a profound influence on mobility, threshold voltage, and other vital device characteristics of organic field-effect transistors. In this study, p-channel small molecule/polymer (evaporated pentacene and spin-coated poly(3,3,;-didodecylquarterthiophene) , PQT) and n-channel fullerene derivative ({6}-1-(3-(2-thienylethoxycarbonyl)-propyl)-{5}-1-phenyl-[5,6]-C61 , TEPP-C61) show a significant enhancement in device mobilities ranging from ,6 to ,45 times higher for all classes of semiconductors deposited on sol,gel silica gate-dielectric than on pristine/octyltrichlorosilane (OTS)-treated thermally grown silica. Atomic force microscopy, synchrotron X-ray diffraction, photoluminescence/absorption, and Raman spectroscopy studies provide comprehensive evidences that sol,gel silica dielectrics-induced enhancement in both p- and n-channel organic semiconductors is attributable to better molecular ordering/packing, and hence reduced charge trapping centers due to lesser structural defects at the dielectric-semiconductor interface. [source] Solution-Deposited Zinc Oxide and Zinc Oxide/Pentacene Bilayer Transistors: High Mobility n-Channel, Ambipolar, and Nonvolatile Devices,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2008Bhola Nath Pal Abstract A solution processed n-channel zinc oxide (ZnO) field effect transistor (FET) was fabricated by simple dip coating and subsequent heat treatment of a zinc acetate film. The field effect mobility of electrons depends on ZnO grain size, controlled by changing the number of coatings and zinc acetate solution concentration. The highest electron mobility achieved by this method is 7.2,cm2 V,1 s,1 with On/Off ratio of 70. This electron mobility is higher than for the most recently reported solution processed ZnO transistor. We also fabricated bilayer transistors where the first layer is ZnO, and the second layer is pentacene, a p-channel organic which is deposited by thermal evaporation. By changing the ZnO grain size (or thickness) this type of bilayer transistor shows p-channel, ambipolar and n-channel behavior. For the ambipolar transistor, well balanced electron and hole mobilities are 7.6,×,10,3 and 6.3,×,10,3,cm2 V,1 s,1 respectively. When the ZnO layer is very thin, the transistor shows p-channel behavior with very high reversible hysteresis. The nonvolatile tuning function of this transistor was investigated. [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] Organic Thin Film Transistors with Polymer Brush Gate Dielectrics Synthesized by Atom Transfer Radical PolymerizationADVANCED FUNCTIONAL MATERIALS, Issue 1 2008C. Pinto Abstract Low operating voltage is an important requirement that must be met for industrial adoption of organic field-effect transistors (OFETs). We report here solution fabricated polymer brush gate insulators with good uniformity, low surface roughness and high capacitance. These ultra thin polymer films, synthesized by atom transfer radical polymerization (ATRP), were used to fabricate low voltage OFETs with both evaporated pentacene and solution deposited poly(3-hexylthiophene). The semiconductor-dielectric interfaces in these systems were studied with a variety of methods including scanning force microscopy, grazing incidence X-ray diffraction and neutron reflectometry. These studies highlighted key differences between the surfaces of brush and spun cast polymethyl methacrylate (PMMA) films. [source] Orders-of-Magnitude Reduction of the Contact Resistance in Short-Channel Hot Embossed Organic Thin Film Transistors by Oxidative Treatment of Au-Electrodes,ADVANCED FUNCTIONAL MATERIALS, Issue 15 2007B. Stadlober Abstract In this study we report on the optimization of the contact resistance by surface treatment in short-channel bottom-contact OTFTs based on pentacene as semiconductor and SiO2 as gate dielectric. The devices have been fabricated by means of nanoimprint lithography with channel lengths in the range of 0.3,,m,<,L,<,3.0,,m. In order to reduce the contact resistance the Au source- and drain-contacts were subjected to a special UV/ozone treatment, which induced the formation of a thin AuOx layer. It turned out, that the treatment is very effective (i),in decreasing the hole-injection barrier between Au and pentacene and (ii),in improving the morphology of pentacene on top of the Au contacts and thus reducing the access resistance of carriers to the channel. Contact resistance values as low as 80,,,cm were achieved for gate voltages well above the threshold. In devices with untreated contacts, the charge carrier mobility shows a power-law dependence on the channel length, which is closely related to the contact resistance and to the grain-size of the pentacene crystallites. Devices with UV/ozone treated contacts of very low resistance, however, exhibit a charge carrier mobility in the range of 0.3,cm2,V,1,s,1,<,,,<,0.4,cm2,V,1,s,1 independent of the channel length. [source] Surface-Modified High- k Oxide Gate Dielectrics for Low-Voltage High-Performance Pentacene Thin-Film Transistors,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2007S. Kim Abstract In this study, pentacene thin-film transistors (TFTs) operating at low voltages with high mobilities and low leakage currents are successfully fabricated by the surface modification of the CeO2,SiO2 gate dielectrics. The surface of the gate dielectric plays a crucial role in determining the performance and electrical reliability of the pentacene TFTs. Nearly hysteresis-free transistors are obtained by passivating the devices with appropriate polymeric dielectrics. After coating with poly(4-vinylphenol) (PVP), the reduced roughness of the surface induces the formation of uniform and large pentacene grains; moreover, ,OH groups on CeO2,SiO2 are terminated by C6H5, resulting in the formation of a more hydrophobic surface. Enhanced pentacene quality and reduced hysteresis is observed in current,voltage (I,V) measurements of the PVP-coated pentacene TFTs. Since grain boundaries and ,OH groups are believed to act as electron traps, an OH-free and smooth gate dielectric leads to a low trap density at the interface between the pentacene and the gate dielectric. The realization of electrically stable devices that can be operated at low voltages makes the OTFTs excellent candidates for future flexible displays and electronics applications. [source] A Computational Study of the Sub-monolayer Growth of PentaceneADVANCED FUNCTIONAL MATERIALS, Issue 13 2006D. Choudhary Abstract A computational study of organic thin-film growth using a combination of ab,initio based energy calculations and kinetic Monte Carlo (KMC) simulations is provided. A lattice-based KMC model is used in which binding energies determine the relative rates of diffusion of the molecules. This KMC approach is used to present "landscapes" or "maps" that illustrate the possible structural outcomes of growing a thin film of small organic molecules, represented as a two-site dimer, on a substrate in which the strength of organic,substrate interactions is allowed to vary. KMC provides a mesoscopic-scale view of sub-monolayer deposition of organic thin films on model substrates, mapped out as a function of the flux of depositing molecules and the temperature of the substrate. The morphology of the crystalline thin films is shown to be a strong function of the molecule,molecule and molecule,substrate interactions. A rich variety of maps is shown to occur in which the small organic molecules either stand up or lie down in a variety of different patterns depending on the nature of the binding to the surface. In this way, it is possible to suggest how to tailor the substrate or the small organic molecule in order to create a desired growth habit. In order to demonstrate how this set of allowable maps is reduced in the case where the set of energy barriers between substrate and organic molecule are reliably known, we have used Gaussian,98 calculations to establish binding energies for the weak van der Waals interactions between a),pairs of pentacene molecules as a function of orientation and b),pentacene and two substrates, silicon surfaces passivated with cyclopentene molecules and a crystalline model of silicon dioxide. The critical nucleation size and the mode of diffusion of this idealized two-site dimer model for pentacene molecules are found to be in good agreement with experimental data. [source] Extracting Parameters from the Current,Voltage Characteristics of Organic Field-Effect TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 11 2004G. Horowitz Abstract Organic field-effect transistors were fabricated with vapor-deposited pentacene on aluminum oxide insulating layers. Several methods are used in order to extract the mobility and threshold voltage from the transfer characteristic of the devices. In all cases, the mobility is found to depend on the gate voltage. The first method consists of deriving the drain current as a function of gate voltage (transconductance), leading to the so-called field-effect mobility. In the second method, we assume a power-law dependence of the mobility with gate voltage together with a constant contact resistance. The third method is the so-called transfer line method, in which several devices with various channel length are used. It is shown that the mobility is significantly enhanced by modifying the aluminum oxide layer with carboxylic acid self-assembled monolayers prior to pentacene deposition. The methods used to extract parameters yield threshold voltages with an absolute value of less than 2 V. It is also shown that there is a shift of the threshold voltage after modification of the aluminum oxide layer. These features seem to confirm the validity of the parameter-extraction methods. [source] Driving High-Performance n- and p-type Organic Transistors with Carbon Nanotube/Conjugated Polymer Composite Electrodes Patterned Directly from SolutionADVANCED MATERIALS, Issue 37 2010Sondra L. Hellstrom We report patterned deposition of carbon nanotube/conjugated polymer composites from solution with high nanotube densities and excellent feature resolution. Such composites are suited for use as electrodes in high-performance transistors of pentacene and C60, with bottom-contact mobilities of > 0.5 and > 1 cm2 V,1 s,1, respectively. This represents a clear step towards development of inexpensive, high-performance all-organic circuits. [source] Three-Dimensional Atomic Force Microscopy , Taking Surface Imaging to the Next LevelADVANCED MATERIALS, Issue 26-27 2010Mehmet Z. Baykara Abstract Materials properties are ultimately determined by the nature of the interactions between the atoms that form the material. On surfaces, the site-specific spatial distribution of force and energy fields governs the phenomena encountered. This article reviews recent progress in the development of a measurement mode called three-dimensional atomic force microscopy (3D-AFM) that allows the dense, three-dimensional mapping of these surface fields with atomic resolution. Based on noncontact atomic force microscopy, 3D-AFM is able to provide more detailed information on surface properties than ever before, thanks to the simultaneous multi-channel acquisition of complementary spatial data such as local energy dissipation and tunneling currents. By illustrating the results of experiments performed on graphite and pentacene, we explain how 3D-AFM data acquisition works, what challenges have to be addressed in its realization, and what type of data can be extracted from the experiments. Finally, a multitude of potential applications are discussed, with special emphasis on chemical imaging, heterogeneous catalysis, and nanotribology. [source] High-Mobility Nonvolatile Memory Thin-Film Transistors with a Ferroelectric Polymer Interfacing ZnO and Pentacene ChannelsADVANCED MATERIALS, Issue 42 2009Kwang H. Lee Nonvolatile memory ferroelectric thin-film transistors (FeTFT) with P(VDF-TrFE) polymer are demonstrated with both n-channel ZnO and p-channel pentacene. A high mobility of ,1,cm2 V,1 s,1 and large memory window of ,20,V are achieved through the organic ferroelectric, inorganic channel hybrid device of ZnO-FeTFT. WRITE/ERASE states are clearly distinguished by ±20,V switching for ZnO- and pentacene-FeTFTs. [source] Effect of Traps on Carrier Injection and Transport in Organic Field-effect TransistorIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2010Martin Weis Non-member Abstract This study illustrates effect of traps on the charge injection and transport in the organic field-effect transistor (OFET). Here are included silicon nanoparticles (NPs) on a semiconductor-gate insulator interface, which work as trapping centers of charge carriers. Charge transport and injection phenomena are investigated by electrical measurements in presence of traps with designed densities. We find that OFETs with a low concentration of intrinsic carriers, such as a pentacene, are extremely sensitive to the internal electric fields. A significant threshold voltage shift due to trapped charge is observed, with a possibility to tune it by controlling the NP density. We demonstrate that the NP film can serve to design the amount of the accumulated charge in OFET and thus change the space-charge-limited conditions to the injection-limited conditions. A detailed analysis of pentacene OFET based on dielectric properties and the Maxwell-Wagner model reveals the internal electric field created by NPs. Additionally, the effect of NPs is discussed with respect to effective mobility, and its decrease is related to deceleration of carrier propagation by the trapping effect as well as low injection due to the increase of the carrier injection barrier by the internal field. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Direct Condensation Method for the Preparation of Organic-Nanoparticle DispersionsADVANCED MATERIALS, Issue 24 2009Stefan Köstler Organic nanoparticle dispersions are prepared via a versatile technique. Particles are formed by evaporation of aromatic hydrocarbons (like pentacene, rubrene, and tetracene) in an inert atmosphere and condensation of the vapor in a liquid medium. This allows the preparation of stable and concentrated dispersions of organic nanoparticles, showing interesting optical properties and potential applications in organic electronics and sensors. [source] Multibit Storage of Organic Thin-Film Field-Effect TransistorsADVANCED MATERIALS, Issue 19 2009Yunlong Guo Organic thin-film field-effect transistor (OTFT) multibit storage devices are fabricated based on pentacene or copper phthalocyaine (CuPc) with normal polymer modifying layers of polystyrene (PS) or polymethylmethacrylate (PMMA). The devices shows excellent multibit storage properties in a single OTFT using electric and light-assisted programs. [source] Pentacene Nanostructures on Surface-Hydrophobicity-Controlled Polymer/SiO2 Bilayer Gate-Dielectrics,ADVANCED MATERIALS, Issue 19 2007H. Yang New evidence of a pentacene "bulk phase", which shows a different layer orientation from the "thin-film phase", was discovered. Thin films prepared on surface-hydrophobicity-controlled polymer/SiO2 dielectrics, were studied by using 2D grazing-incidence X-ray diffraction. [source] Thickness Dependence of Mobility in Pentacene Thin-Film Transistors,ADVANCED MATERIALS, Issue 14 2005R. Ruiz The field-effect mobility of pentacene transistors saturates when six,monolayers of pentacene are deposited on the gate dielectric. This saturation is not caused by the formation of islands, as the early stages of growth have been found to take place in a layer-by-layer fashion, and layer completion continues well past six,monolayers (see Figure). [source] | |||||||||||||||||||