Search

Solution-processed semiconducting carbon nanotube transistors with a high mobility and an ON/OFF ratio are the most promising for use in flexible electronics. In this paper, we report low-k/high-k bilayer polymer dielectrics for solution-processed semiconducting single-walled carbon nanotube (s-SWNT) field-effect transistors (s-SWNT-FETs) with efficient charge transport and operation at low voltage. Thin low-k polystyrene (10 nm) is used for the first contact insulator with a channel in order to passivate the dipolar disorder induced by high-k insulators. The second gate insulator for low voltage operation is cyanoethyl pullulan (CEP), which is an environmentally friendly high-k insulator based on cellulose. Moreover, poly[(vinylidenefluoride-co-trifluoroethylene) is chosen as a single layer dielectric for comparison. A reasonably low operational voltage (

Nitrogen-doped p-type ZnO (ZnO:N) films have been achieved by ultrasonic spray pyrolysis at atmosphere. The high structural quality of the obtained films was confirmed by x-ray diffraction, scanning electron microscopy, and photoluminescence spectra. Hall-effect and Seebeck-effect measurements indicate that the obtained p-type ZnO film shows a low resistivity of 3.02×10−2Ωcm, high carrier concentration of 8.59×1018cm−3, high mobility of 24.1cm2∕Vs, and high Seebeck coefficient of 408.2μV∕K at room temperature. Furthermore, the two-layer structured ZnO p–n homojunctions were prepared by depositing n-type ZnO layer on p-type ZnO:N layer. The current–voltage curve derived from the two-layer structure clearly shows the typical rectifying characteristic of p–n junctions.

The effect of ketonic defects on electrical properties, i.e., the performance of organic field-effect transistors (OFETs) was examined in fluorene end capped fused bithiophene oligomers (BFTT). The long wavelength emission at 2.1–2.3eV resulting from the ketonic defects was observed in photoluminescence spectra of BFTT films after UV irradiation in air. In addition, the peak corresponding to the carbonyl stretching mode of the fluorenone moiety at 1721cm−1 was also apparent after UV irradiation for periods longer than 6h in air. These observations confirm that ketonic defects are present in the fluorene units of BFTT after photo-oxidation. The threshold voltage (Vth), i.e., switch-on voltage, of OFETs was increased and field-effect mobility (μFET) was decreased after the formation of the ketonic defects, since these defects induce the formation of numerous trap sites in the bandgap of the semiconducting conjugated oligomer.

The N–In codoped p-type ZnO films have been prepared by ultrasonic spray pyrolysis. X-ray photoelectron spectroscopy analysis confirmed the presence of nitrogen and indium in the codoped films, and the incorporation of indium causes the change in the chemical state of nitrogen, which promotes the formation of p-type conduction. Low resistivity of 1.7×10−2 Ω cm, high carrier concentration of 2.44×1018 cm−3 and Hall mobility of 155 cm2 V−1 s−1 at room temperature for the codoped films were obtained. A conversion from p-type conduction to n type in a range of temperature has been identified by the measurement of Seebeck and Hall effect.

We report the fabrication and characteristics of surface relief grating on the end surface of silica optical fiber with a diameter of 125 μm. One- and two-dimensional gratings were inscribed on the fiber surface covered with azo polymer thin-film layer using interferometric methods. Diffraction beam patterns of the zeroth and the first order due to surface relief gratings were observed using a 635 nm laser, and the relation between the measured diffraction beam pattern and the grating period was also investigated.

Polymeric wavelength filters with Bragg gratings have been fabricated using holographic surface relief gratings on azobenzene polymer films. In order to fabricate Bragg gratings on polymer waveguides, we used holographic surface relief gratings on the azobenzene polymer film as an etch mask and the grating patterns were transferred to the polymer waveguides by O2 reactive ion etching. The grating period was ∼500 nm and the depth was ∼30 nm with a 10-mm-long Bragg grating length. A transmission dip of −15 dB at the Bragg wavelength and a 3-dB-transmission bandwidth of ∼0.2 nm were obtained from the device.

We present an experimental strategy via X-ray irradiation combined with time-resolved X-ray diffraction to reduce a coercive field of ferroelectric thin films. We found in real-time that X-ray irradiation enables the irreversible phase transition from a polar to non-polar phase in ferroelectric poly(vinylidene fluoride-trifluoroethylene) thin films. The non-polar regions act as initial nucleation sites for opposite domains thus reducing the coercive field, directly related to the switching of domains, by 48%.

Significant effects of the modulation depth (h) on a three-dimensional (3D) colloidal self-assembly with symmetric and asymmetric two-dimensional (2D) templates are demonstrated. When the ratio “h/D” of the surface modulation (h) to the diameter of the bead (D) exceeded 0.35, then 3D square array patterns were obtained, and when the ratio h/D was from 0.28 to 0.35, pseudo-{110} structure resulted. When the ratio h/D was less than 0.28, the 3D crystallization of colloids was not observed but regular tetragonal or hexagonal clusters were formed in a 2D pattern.

We present microstructure and magnetic properties of Sm2(Fe, Si)17Cx/α-Fe nanocomposite magnets prepared under a pressure of 4 GPa at a temperature of 923 K. A high-pressure experiment was carried out in a belt-type pressure apparatus. Analyses of x-ray diffraction and transmission electron microscopy show that the nanocomposite magnets have a grain size of 6–8 nm, which provides a strong exchange coupling between hard and soft magnetic phases. As a result, the magnets have, compared with nanocomposite magnets prepared under normal pressure, a significant increase in both coercivity, from 132 to 500 kA/m, and remanent magnetization, from 0.68 to 0.83Ms.

Propagation of intense circularly polarized laser pulses in strongly magnetized inhomogeneous plasmas is investigated. It is shown that a left-hand circularly polarized laser pulse propagating up the density gradient of the plasma along the magnetic field is reflected at the left-cutoff density. However, a right-hand circularly polarized laser can penetrate up the density gradient deep into the plasma without cutoff or resonance and turbulently heat the electrons trapped in its wake. Results from particle-in-cell simulations are in good agreement with that from the theory. (c) 2015 AIP Publishing LLC.

Direct formation of surface relief gratings at modest intensities on azobenzene polymers has recently been accomplished. Unusual optical erasure of these surface relief gratings was observed. It is found that the optical erasure is dependent on the polarization state of the erasing beam as well as that of the recording beams used to form the gratings. Thus, gratings when formed memorize the polarization states which created them and influence their erasure behaviors accordingly. Direct transfer of patterns by photoprinting through a phase mask has been achieved.

A model for the formation of holographic surface relief gratings in azobenzene functionalized polymers is presented. Forces leading to migration of polymer chains upon exposure to light in the absorption band of the azo chromophore are attributed to dipoles interacting with the gradient of the electric field present in the polymer material. Efficient trans–cis cycling in the azobenzenes allows cooperative movement of the chromophores under the influence of gradient forces.

Experimental studies on the recording of surface relief gratings on azobenzene containing polymer films using laser beams with different polarizations were carried out. The results indicate that the localized variations of light intensity and alternation of the resultant electric field polarization in the film are essential to the formation of the surface relief gratings.

We report observation of holographic surface relief gratings with relatively large amplitude on a second order nonlinear optical polymeric material. Surface relief gratings on these polymer films were created upon exposure to polarized Ar+ laser beams at 488 nm without any subsequent processing steps. The surface structure of the relief gratings was investigated by atomic force microscopy. The depth of the surface relief in a typical case was 120 nm which is approximately 20% of the original film thickness. The diffraction efficiency of gold‐coated gratings was investigated as a function of wavelength and capability of recording orthogonal gratings on the same film was demonstrated.

Novel aromatic and aliphatic polyimides exhibiting sizable second‐order nonlinear optical properties and long term thermal and temporal stability were synthesized. Detailed physical characterization revealed that the polymers are stable up to 300 °C with high glass transition temperatures (≳200 °C). Exceptional thermal stabilities at elevated temperatures were observed even at 150 °C.

Ambipolar semiconducting polymers, characterized by both high electron (μe) and hole (μh) mobility, offer the advantage of realizing complex complementary electronic circuits with a single semiconducting layer, deposited by simple coating techniques. However, to achieve complementarity, one of the two conduction paths in transistors has to be suppressed, resulting in unipolar devices. Here, we adopt charge injection engineering through a specific interlayer in order to tune injection into frontier energy orbitals of a high mobility donor-acceptor co-polymer. Starting from field-effect transistors with Au contacts, showing a p-type unbalanced behaviour with μh = 0.29 cm2/V s and μe = 0.001 cm2/V s, through the insertion of a caesium salt interlayer with optimized thickness, we obtain an n-type unbalanced transistor with μe = 0.12 cm2/V s and μh = 8 × 10−4 cm2/V s. We applied this result to the development of the basic pass-transistor logic building blocks such as inverters, with high gain and good noise ma...

The use of a solution-processed gold chloride (AuCl3) as an anode interfacial modifier was investigated for high-performance polymer solar cells (PSCs). Kelvin probe, 4-point probe, and X-ray photoelectron spectroscopy studies demonstrated that AuCl3 increases the indium-tin-oxide (ITO) work-function and decreases the ITO sheet resistance, because of Au nanoparticle formation and Cl adsorption by the AuCl3 treatment to induce a p-doping effect, thereby improving the built-in potential and interface resistance. As a result, the introduction of AuCl3 by simple solution processing remarkably improved cell-performances, indicating that AuCl3 is an efficient anode interfacial modifier for enhancing PSC-performance.

Three-dimensional particle-in-cell simulations show that the anisotropic collapse of a plasma microshell by impact of two oppositely directed intense laser pulses can create at the center of the shell cavity a submicron-sized plasma of high density and temperature suitable for generating fusion neutrons.

Pentacene organic field-effect transistors (OFETs) were fabricated with multilayer graphene films as the source and drain electrodes. The electrical properties of graphene electrode OFETs were monitored as the fabrication conditions were varied with surface treatments on the dielectric layer and substrate. With surface treatments, the performance of the graphene-electrode pentacene OFETs were significantly enhanced; the output currents increased by more than tenfold, and the mobility increased to levels as high as 1.2 cm2/V s. Our results may foster the wide application of graphene electrodes in OFETs and other types of organic electronic devices.

Enhanced performance of inverted polymer solar cells (PSCs) is demonstrated by indium tin oxide (ITO) interfacial tuning via a water-soluble polyfluorene (WPF-6-oxy-F). Kelvin probe studies and dark current-voltage curves demonstrated that the WPF-6-oxy-F layer reduces the ITO work-function because of the favorable interfacial dipole formed by the WPF-6-oxy-F interlayer, thereby enhancing the built-in potential and reducing the interface resistance. As a result, introduction of the WPF-6-oxy-F by simple solution processing into the inverted PSCs dramatically enhanced cell-performances. This approach could be very beneficial and an important step for the future development of all-solution-processed or roll-to-roll processed PSCs.

We demonstrate the fabrication of inverted-structure organic solar cells (OSCs) with graphene cathodes. The graphene film used in this work was work-function-engineered with an interfacial dipole layer to reduce the work function of graphene, which resulted in an increase in the built-in potential and enhancement of the charge extraction, thereby enhancing the overall device performance. Our demonstration of inverted-structure OSCs with work-function-engineering of graphene electrodes will foster the fabrication of more advanced structure OSCs with higher efficiency.

Polymer light-emitting diodes(PLEDs) and light-emitting electrochemical cells (LECs) were fabricated using a water-soluble conjugated polymer with ion-conducting side chains. The water-soluble polymer was spin-coated on the emitting layer of a PLED and was used as an electron-injecting layer. The PLED showed enhanced performance with LEC behavior due to both the mobile ions and ion-conducting side groups of the polymer. A single-component and single-layer device was also fabricated, which showed typical LEC behavior with 1.13% maximum external quantum efficiency after complete ion migration.

We report the characteristics of a p-n heterojunction diode comprised of a poly(3,4-ethylene-dioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) as the hole-conducting p-type polymer and n-type ZnO nanowall networks. ZnO nanowall networks were synthesized on a GaN/sapphire substrate without metal catalyst using hot-wall type metal organic chemical vapor deposition. The p-n heterojunction diodes of PEDOT:PSS/ZnO nanowall exhibited a space charge limited current phenomena at forward bias and a transient reverse current recovery when a sudden reverse bias was applied from the forward bias condition. The minority carrier lifetime was estimated to be ∼2.5 μs.

To enhance solar harvesting in organic solar cells, uniform-sized metal nanoparticles of ∼13 nm were incorporated to the device via pulse-current electrodeposition, which is a kind of simple and quick solution process that can control the density and size of metal nanoparticles. By incorporating plasmonic Ag nanoparticles on surface modified transparent electrodes, overall power conversion efficiency was increased from 3.05% to 3.69%, mainly resulting from the improved photocurrent density as a result of enhanced absorption of the photoactive conjugate polymer due to the high electromagnetic field strength in the vicinity of the excited surface plasmons.

This letter reports on reversible switching behavior of metal-insulator-metal type nonvolatile organic memory devices using polyfluorene-derivative (WPF-oxy-F) single layer film. The current-voltage (I-V) characteristics showed that the WPF-oxy-F single layer film has two distinguished resistance states, low resistance state and high resistance state, with four orders of on/off ratio (Ion∕Ioff∼104). From the analysis of I-V curves, area dependent I-V characteristics, and current images obtained by conducting atomic force microscopy we propose that the space charge limited current with filamentary conduction is a potential mechanism for the reversible switching behavior of WPF-Oxy-F memory devices.

We report the effects of gate bias sweep rate on the electronic characteristics of ZnO nanowire field-effect transistors (FETs) under different environments. As the device was swept at slower gate bias sweep rates, the current decreased and threshold voltage shifted to a positive gate bias direction. These phenomena are attributed to increased adsorption of oxygen on the nanowire surface by the longer gate biasing time. Adsorbed oxygens capture electrons and cause a surface depletion in the nanowire channel. Different electrical trends were observed for ZnO nanowire FETs under different oxygen environments of ambient air, N2, and passivation.

We report here a simple and easy method of fabricating arranged inorganic nanowire architecture via electrospinning method equipped with a devised collector and demonstrate hybrid photovoltaic cells that are fashioned of planar-aligned TiO2 nanowire architectures such as uniaxially aligned nanowires and multiple layers of cross-aligned nanowire arrays with poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene]. The power conversion efficiency can be significantly improved by at least 70% under 1sun condition depending on the degree of aligning TiO2 nanowire arrays through enhancing charge collection and transport rate, as well as facilitating the polymer infiltration as compared to a randomly collected TiO2 nanowire electrode.

We investigated preferentially oriented pentacene grains on rubbed polyimide (PI) layers under various conditions, such as substrate temperature and cumulative rubbing number. In case of pentacene thin films deposited on rubbed PI at room temperature (RT), compared to unrubbed, the field-effect mobilities were improved by two- to threefold in contrast to the cases of elevated temperature. From the results of crystalline in-plane orientation and thin-film versus bulk-phase ratio, we proposed that pentacence crystalline orientation on a rubbed PI layer could be more favorable at RT, whereas the heating energy might weaken the interaction energy between pentacene molecules and aligned PI layer.