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Ta-doped SnO 2 films with high conductivity and high optical transparency have been successfully fabricated using the rf-sputtering method, and their electrical transport properties have been investigated. All films reveal degenerate semiconductor (metal) characteristics in electrical transport properties. For the thick films (t ∼ 1 μ m with t being the thickness) deposited in pure argon, the electron–phonon scattering alone cannot explain the temperature-dependent behaviors of resistivity, the interference effect between electron–phonon and electron–impurity scattering should be considered. For t ≲ 36 nm films, both the conductivity and the Hall coefficient show a linear relation with the logarithm of temperature (ln ⁡ T) from ∼ 100 K down to liquid helium temperature. The ln ⁡ T behaviors of conductivity and Hall coefficient cannot be explained by the Altshuler-Aronov type electron–electron interaction effect but can be quantitatively interpreted by the electron–electron interaction effects in the presence of granularity. Our results not only provide strong support for the theoretical results on the electron–phonon–impurity interference effect, but also confirm the validity of the theoretical predictions of charge transport in granular metals in a strong coupling regime. [ABSTRACT FROM AUTHOR]

The ability to tune the performance of acoustic metamaterials without structural modifications or complex active control circuits is a remarkable challenge. In this work, we present a square piezoelectric side-branch (PSB) pipe-type structure that consists of the piezoelectric composite sheets (PCSs) on its sidewall and propose the corresponding equivalent electroacoustic circuit model. Compared with the traditional side-branch, theoretical and numerical results show that the thickness of the PSB can be up to λ / 200 , and the tunable phase shift of the transmitted wave in the PSB pipe can achieve nearly 2 π by adjusting the capacitances that are connected to the PCSs. The experiment for a square pipe with one PCS is also given to prove the phase control ability of the PSB model. Furthermore, we show that by merely adjusting the external capacitances of the PCSs, switching the functions between the 45° extraordinary transmission and the acoustic focusing for the same incident wave can be exactly realized. Our work provides a promising potential in active controls and integration designs of acoustic metamaterials and devices. [ABSTRACT FROM AUTHOR]

Continuously and widely tunable lasers, actively stabilized on a frequency reference, are broadly employed in atomic, molecular, and optical (AMO) physics. The frequency-stabilized optical frequency comb (OFC) provides a novel optical frequency reference, with a broadband spectrum that meets the requirement of laser frequency stabilization. Therefore, we demonstrate a frequency-stabilized and precisely tunable laser system based on it. In this scheme, the laser frequency locked to the OFC is driven to jump over the ambiguity zones, which blocks the wide tuning of the locked laser, and tuned until the mode hopping happens with the always-activated feedback loop. Meanwhile, we compensate the gap of the frequency jump with a synchronized acoustic optical modulator to ensure the continuity. This scheme is applied to an external cavity diode laser (ECDL), and we achieve tuning at a rate of about 7 GHz/s, with some readily available commercial electronics. Furthermore, we tune the frequency-stabilized laser only with the feedback of diode current, and its average tuning speed can exceed 100 GHz/s. Due to the resource-efficient configuration and the simplicity of completion, this scheme can be referenced and can find wide applications in AMO experiments. [ABSTRACT FROM AUTHOR]

In the air coherent detection of the terahertz (THz) technique, a high voltage signal with a square waveform offers a modulated biased field over the air sensor. In this technique, a temporal THz waveform can be obtained routinely. However, its field strength has to be calibrated separately by other techniques. In this paper, we propose a method to calibrate the field strength of the THz pulse by means of applying a positive square wave instead of an alternating square wave as the modulated biased field. In this method, the ratio of the THz signal to the background signal is used for the calibration of the field strength of the THz pulse. Using this method, both the waveform and the electric field strength of the THz pulse can be easily obtained. [ABSTRACT FROM AUTHOR]

We report on the epitaxial growth of antimony-based GaSb/Ga1−xInxSb/GaSb quantum wells (QWs) on the (111) plane. Different from the more common (001) heterostructures, (111) structures offer certain advantages in electronic properties, such as the existence of the strain-induced piezoelectric effect, as well as a large effective mass of hole carriers along the growth axis. In the present work, we found that high-quality QWs can be successfully grown using a GaSb buffer layer on a vicinal GaAs (111)B substrate. Due to the presence of the piezoelectric field and the surface states, hole carriers are introduced in the QW without intentional doping. Electrical transport measurements on an x = 0.1 sample at 300 mK show that the QW has a two-dimensional hole gas (2DHG) density of 6.7 × 1011 cm−2 and a mobility of 28 000 cm2/Vs. The 2DHG exhibits clear Shubnikov–de Haas oscillations and the integer quantum Hall effect under a perpendicular magnetic field. [ABSTRACT FROM AUTHOR]

A novel explanation of the quasi-elastic release phenomenon in shock-compressed aluminum is presented. A dislocation-based model, taking into account dislocation substructures and evolution, is applied to simulate the elastic-plastic response of both single-crystal and polycrystalline aluminum. The calculated results are in good agreement with experimental results from not only the velocity profiles but also the shear strength and dislocation density, which demonstrate the accuracy of our simulations. Simulated results indicate that dislocation immobilization during dynamic deformation results in a smooth increase in the yield stress, which leads to the quasielastic release, while the generation of dislocations caused by the plastic release wave results in the appearance of a transition point between the quasi-elastic release and the plastic release in the profile. [ABSTRACT FROM AUTHOR]

The gate-defined quantum dot is regarded as one of the basic structures required for scalable semiconductor quantum processors. Here, we demonstrate a structure that contains three quantum dots scaled in series. The electron number of each dot and the tunnel coupling between them can be tuned conveniently using splitting gates. We tune the quantum dot array asymmetrically such that the tunnel coupling between the right dot and the central dot is much larger than that between the left dot and the central dot. When driven by microwaves, the sidebands of the photon-assisted tunneling process appear not only in the left-to-central dot transition region but also in the left-to-right dot transition region. These sidebands are both attributed to the left-to-central transition for asymmetric coupling. Our result shows that there is a region of a triple quantum dot structure that remains indistinct when studied with a normal two-dimensional charge stability diagram; this will be helpful in future studies of the scalability of quantum dot systems. [ABSTRACT FROM AUTHOR]

We carry out numerical simulations of oscillatory Rayleigh–Bénard convection under lateral periodic conditions over the Rayleigh number range of 10 6 ≤ Ra ≤ 10 8 and the vibration frequency range of 0 ≤ ω ≤ 1000. It is demonstrated that high-frequency vibration achieves a significant enhancement of the intensity of convective flows and the heat-transport efficiency. The phase decomposition method is adopted to distinguish between the vibration-generated oscillatory flows and the fluctuating fields. It is shown that although the contribution of oscillatory flows on heat transport vanishes, the oscillating properties in near-wall regions introduce a strong shear effect to increase the intensity of fluctuating velocities both in the bulk regime and within boundary layers, destabilize thermal boundary layers, and trigger massive eruptions of thermal plumes, which achieves an enhancement of heat transfer. Our results further reveal a universal scaling law between the vibrational Reynolds and Rayleigh numbers, i.e., Re vib ∼ Ra vib 1 / 2 , which can be well described by our proposed analytical model. Moreover, it is shown that vibrational influences are different for the fluctuating velocity and temperature fields. [ABSTRACT FROM AUTHOR]

The reduced graphene oxide/cobalt ferrite (rGO/Co-Fe) magnetic composite particle was synthesized via a solvothermal process and employed as the magnetorheological (MR) material. The morphology of rGO/Co-Fe was observed by SEM, the chemical structure was confirmed by FT-IR, and the rheological properties of rGO/Co-Fe when suspended in silicone oil were studied by a rotational rheometer under different magnetic field strengths. Along with shear stress curves of rGO/Co-Fe based MR fluid tested in a controlled shear rate mode, their magnetic field strength-dependent yield stresses were observed to fit the universal yield stress function well. [ABSTRACT FROM AUTHOR]

The dependence of periodic structures and ablated areas on temporal pulse shaping is studied upon irradiation of fused silica by femtosecond laser triple-pulse trains. Three types of periodic structures can be obtained by using pulse trains with designed pulse delays, in which the threedimensional nanopillar arrays with ~100-150 nm diameters and ~200 nm heights are first fabricated in one step. These nanopillars arise from the break of the ridges of ripples in the upper portion, which is caused by the split of orthogonal ripples in the bottom part. The localized transient electron dynamics and corresponding material properties are considered for the morphological observations. [ABSTRACT FROM AUTHOR]

Turbulent Rayleigh-Bénard convection in a square cavity with rough horizontal walls is investigated at a fixed Prandtl number Pr = 0.7 over the Rayleigh number range of 106 ≤ Ra ≤ 109. We have proposed five models with rough elements of the same height but different spatial distributions to evaluate their influences on the heat transport and flow structures of the system. It is found that the flow reversal can be promoted at a Rayleigh number around 107. In all the rough models, the heat transfer is impeded at a low Ra and enhanced at a Rayleigh number beyond a critical value. Interestingly, the heat transfer and flow structure can be clustered by the sparsity of the rough element distribution. Different scaling exponents for heat transfer are identified for sparsely distributed rough models and compactly distributed models. On the other hand, the spatial distribution of rough elements has little effect on the scaling of the Reynolds number. [ABSTRACT FROM AUTHOR]

The effect of light irradiation on the characteristics of organic field-effect transistors containing sexithiophene (6-T) and pentacene was examined. Organic phototransistors (OPTs) in which 6-T and pentacene were incorporated were fabricated. Their response behaviors were investigated under conditions of irradiation by either modulated or continuous ultraviolet light with various intensities. Both devices showed two distinguishable responses, i.e., fast and slow responses from photoconductive and photovoltaic effects, respectively. The fast response is mainly the result of the generation of mobile carriers by the absorption of a photon energy higher than the band gap energy of the semiconductor and, subsequently, an increase in conductance via a greater flow of photogenerated mobile carriers into the channel layer. On the other hand, the slow response, which was confirmed by a light induced shift in the threshold voltage (Vth) or the switch-on voltage (VO), is the result of a slow release of accumulated and trapped electrons in the semiconductor-gate dielectric interface. The VO is defined as the flatband voltage of devices. Below the VO, the channel current with the gate voltage is off current, and the channel current increases with the gate voltage above the VO. The speed of release of the accumulated charge was dependent on the type of semiconductor used. Pentacene OPTs showed a particularly long retention time. Even after storage for ten days, the shifted VO (or Vth) for the pentacene OPTs by light irradiation was not restored to the original value of the fresh devices. We conclude that this long sustained Vth shift renders them attractive for use in “light-addressable nonvolatile memory devices.” [ABSTRACT FROM AUTHOR]

Solid films of CdSe colloidal quantum dots are conductive when reduced by electrochemistry. The dark conductivity and the photoconductivity of these n-type CdSe nanocrystalline solids have been investigated as a function of film treatment. When the films are treated with NaOH, a carrier mobility of ∼10-2 cm2/V s and a charging/discharging time of ∼10 ms are obtained. Under an excitation intensity of ∼0.75 mW/cm2, a significant photoconductivity of ∼10-3 S cm-1 has been observed. The high mobility allowed demonstrating the operation of a field effect transistor. [ABSTRACT FROM AUTHOR]

We report the solid-state optical gain characteristics of a spiroanthracenefluorene polymer, namely, poly(9-spiro(10,10-bis(2-ethylhexyl)-10H-anthracene)fluorene) (PEHSAF), specifically designed for thermal stability. An efficient stimulated emission occurs at λ=445 nm under amplified spontaneous emission conditions for asymmetric slab waveguide structures. The modal gain and propagation loss coefficients were found to be g<=38 cm-1 and α=0.8 cm-1, respectively. The PEHSAF stimulated emission characteristics are shown to be thermally stable in vacuo for temperatures up to 250 °C. Surface-emitting distributed feedback lasers have been fabricated by spin-coating PEHSAF onto one-dimensional grating structures. The lasers operate in the blue spectral region and exhibit low oscillation thresholds (>=18 nJ) and relatively high slope efficiencies (<=5%). Varying the PEHSAF film thickness allows the tuning of the emission wavelength within a 16 nm window. [ABSTRACT FROM AUTHOR]

Organic phototransistors (OPTs) were fabricated from pentacene and copper phthalocyanine (CuPC) based on the geometry of organic field-effect transistors (OFETs); and the effect of the wavelength of the incident light source on their performance was examined. High performance OFETs with pentacene and CuPC were fabricated and the characteristics of the OPTs were examined under UV and visible-light irradiations with top illumination. The CuPC and pentacene OPTs show a high responsivities of 0.5–2 and 10–50 A/W and maximum IPh/IDark of 3000 and 1.3×105, respectively, under 365 nm UV light. However, under visible light, at a wavelength of 650 nm, the pentacene OPTs had 100 times less responsivity, 0.15–0.45 A/W, and a IPh/IDark of 1000, even though an absorption coefficient three times larger was observed at this wavelength than at 365 nm. A strong correlation was found between the performance of the OPTs and the incident photon to current conversion efficiency spectra of an organic semiconductor. The strong dependence on the wavelength of incident light of the performance of the prepared OPTs can be explained by an internal filter effect in which light with a large absorption coefficient is filtered at the top surface and through the bulk of the film when light is directed onto the opposite side of the OFET gate electrode. Thus, light cannot efficiently contribute to the generation of charge carriers in the channel regions that were formed in the first two molecular layers adjacent to the dielectric interface. Consequently, the most efficient OPTs were produced when the following conditions of incident light were satisfied: The photon energies (or frequencies) should be (i) larger than the band gap and (ii) have a relatively small absorption coefficient, since the light can penetrate down to the channel layer more efficiently when it is near the dielectric interface without any loss in absorption through the film. [ABSTRACT FROM AUTHOR]

The intraband relaxation between the 1Pe and 1Se state of CdSe colloidal quantum dots is studied by pump-probe time-resolved spectroscopy. Infrared pump-probe measurements with ∼6-ps pulses show identical relaxation whether the electron has been placed in the 1Se state by above band-gap photoexcitation or by electrochemical charging. This indicates that the intraband relaxation of the electrons is not affected by the photogenerated holes which have been trapped. However, the surface ligands are found to strongly affect the rate of relaxation in colloid solutions. Faster relaxation (<8 ps) is obtained with phosphonic acid and oleic acid ligands. Alkylamines lead to longer relaxation times of ∼10 ps and the slowest relaxation is observed for dodecanethiol ligands with relaxation times ∼30 ps. It is concluded that, in the absence of holes or when the holes are trapped, the intraband relaxation is dominated by the surface and faster relaxation correlates with larger interfacial polarity. Energy transfer to the ligand vibrations may be sufficiently effective to account for the intraband relaxation rate. [ABSTRACT FROM AUTHOR]

The effect of keto defects in fluorene units on the performance of organic field-effect transistors (OFETs) was examined based on fluorene end-capped fused bithiophenes (BFTT) and biphenyl end-capped fused bithiophene oligomers (BPTT). The formation of keto defects after various periods of UV illumination in air on BFTT films was confirmed by the increase of the long-wavelength emission at 2.1-2.3 eV in the photoluminescent sPLd spectrum and the generation of a Fourier transfer infrared (FTIR) peak at 1721 cm-1, corresponding to the carbonyl stretching mode of the fluorenone moiety. For both BPTT films irradiated in air and BFTT in nitrogen, i.e., a keto-free system, no increase in long-wavelength emission in the PL spectrum, was found and the peak corresponding to the carbonyl stretching mode of the fluorenone moiety was absent in the FTIR spectrum. The threshold voltage, i.e., switch-on voltage, of the OFETs was increased and the field-effect mobility and on-state drain current were rapidly decreased after the formation of ketonic defects, since these defects induce the formation of numerous trap sites in the band gap of the semiconducting conjugated oligomer. The density of trap sites (Nt) generated after the formation of keto defects was determined using space-charge-limited current spectroscopy. A Nt of around 2.7 ×1015 cm-3 was found for the BFTT film due to the formation of keto defects after 6 h of UV irradiation. [ABSTRACT FROM AUTHOR]

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 (<10 V) and high operational stability are achieved by the s-SWNT-FETs with polystyrene/CEP bilayer gate dielectrics. In addition, this indicates that the interface between the s-SWNTs and the low-k insulator is of critical importance for efficient charge transport. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

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 margin, and transmission-gates. In addition, we developed and characterized information storage circuits like D-Latches and D-Flip-Flops consisting of 16 transistors, demonstrating both their static and dynamic performances and thus the suitability of this technology for more complex circuits such as display addressing logic. [ABSTRACT FROM AUTHOR]

As one of statistical characteristics of turbulent flow, space-time correlation is important when studies contribute to understanding of the mechanism of sound radiation and wave scattering by turbulence. This paper combines large-eddy simulations (LES) with the lattice Boltzmann method (LBM) to study the effects of subgrid models on time correlations in decaying isotropic turbulence. The performance of the inertial-range (IR) consistent model and the classical Smagorinsky model is evaluated in terms of two-time Eulerian velocity correlations at the LBM framework. The present study compares the correlations evaluated by LES and the direct numerical simulations based on the lattice Boltzmann equation and Navier–Stokes (NS) equations, respectively. It shows that the lattice Boltzmann subgrid models yield an underestimation of the magnitude of the time correlation on different time intervals and on a variety of wavenumber modes, similar to NS subgrid models. It is also observed that the calculated decorrelation time scale is in good agreement with the theoretical analysis for the Eulerian time microscale and scales nearly as τ(k)∝(Vk)-1. It appears that τ(k) may be either underestimated or overestimated depending on the shape of initial energy spectrum to some extent. Furthermore, compared to the classical Smagorinsky model with different initial spectra, the IR consistent subgrid model shows promising performance on the prediction of the time-space correlations in turbulent flows. [ABSTRACT FROM AUTHOR]

A mathematical model representing the relation between pulling up speed, time and aspect ratio is reported, accordingly the axially pull-up electrochemical etching method for fabricating nanoprobes is proposed. The tungsten probes with predetermined shape and aspect ratio according to the model were successfully produced with this method. Then the probes were installed inside a micromanipulation system to manipulate the carbon nanotubes and measure their current-voltage (I-V) characteristics. The probe fabrication and application experiments demonstrated the reasonability and reliability of the model and method developed in this note. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 1 sun 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The submicroscaled octadecyltrichlorosilane (OTS) line patterns on gate-dielectric surfaces were introduced into the fabrication of organic field effect transistors (OFETs). These spin-cast regioregular poly(3-hexylthiophene) films on soft-lithographically patterned SiO2 surfaces yielded a higher hole mobility (∼0.072 cm2/V s) than those of unpatterned (∼0.015 cm2/V s) and untreated (∼5×10-3 cm2/V s) OFETs. The effect of mobility enhancement as a function of the patterned line pitch was investigated in structural and geometric characteristics. The resulting improved mobility is likely attributed to the formation of efficient π-π stacking as a result of guide-assisted, local self-organization-involved molecular interactions between the poly(3-hexylthiophene) polymer and the geometrical OTS patterns. [ABSTRACT FROM AUTHOR]

The use of periodic submicrometer structures as an efficient light-trapping scheme was investigated for high performance organic solar cells (OSCs) based on poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61. The gratings on an active layer are achieved by a soft lithographic approach using photoinduced surface-relief gratings (SRGs) on azo polymer films and poly(dimethylsiloxane) as a master and stamp, respectively. Incident photon to current conversion efficiency and the power conversion efficiency of OSC with gratings increased primarily due to enhanced short circuit current density, indicating that SRGs induce further photon absorption in active layers by increasing the optical path length and light trapping. [ABSTRACT FROM AUTHOR]

Indium tin oxide (ITO) substrates modified with self-assembled monolayers (SAMs) were used to control the anode work function and active layer morphology of organic solar cells based on poly(3-hexylthiophene)/[6:6]-phenyl-C61 butyric acid methyl ester heterojunctions. By using SAMs with the terminal groups –NH2, –CH3, and –CF3, the authors were able to control the hole injection barrier of the ITO closer to the highest occupied molecular orbital level of active layer and surface energy of the ITO substrate. A solar cell device with CF3 SAM treated ITO was found to exhibit high efficiency performance, about 3.15%. [ABSTRACT FROM AUTHOR]

The authors report on a spray deposition method as a cost-efficient technique for the fabrication of organic solar cells (OSCs). Active layers of OSCs were fabricated using conventional handheld airbrushes. Although the spray deposited film showed a relatively rougher surface than spin coated ones, pinhole-free and constant thickness films could be obtained. An optimized OSC showed 2.83% of power conversion efficiency and 52% of incident photon to current conversion efficiency even though the device was fabricated in air. The performance of sprayed OSCs was comparable to that of the spin coated devices fabricated in air. [ABSTRACT FROM AUTHOR]

To produce surface plasmons, silver nanostructures were fabricated using a thermal evaporation method and the surface plasmon wavelength was tuned via an annealing. These nanostructures were located between the indium tin oxide (ITO) and poly(3,4-ethylenedioxy thiophene)/poly(styrenesulfonate) for the coupling of the surface plasmon resonance with organic fluorophores. To prevent the quenching of emission, spacer was placed between the light emitting polymers and the ITO substrate. As a result, the authors were able to observe an increase in photoluminescence of conjugated polymers using the silver nanostructures. [ABSTRACT FROM AUTHOR]

Tungsten trioxide (WO3) nanowires were synthesized by thermal evaporation of tungsten powder in two steps: tungsten suboxide (WO3-x) nanowires were synthesized, and then oxidized in O2 ambient and transformed into WO3 nanowires. Raman spectroscopy was applied to study the thermochromic phase transition of one-dimensional WO3 nanowires. From the temperature dependence of the characteristic mode at 33 cm-1 in WO3, the phase transition temperature was determined. It was found that the phase transition of WO3 nanowires was reversible and the phase transition temperatures were even lower than that of WO3 nanopowder. [ABSTRACT FROM AUTHOR]

A thermally cross-linkable perfluorocyclobutane (PFCB) polymer was synthesized and examined for use as the gate dielectric in organic thin film transistors (OTFTs). The PFCB polymer showed good solvent and process resistance during the photolithographic patterning of the electrodes. Bottom contact OTFTs were fabricated with poly(3-hexylthiophene)-2,5-diyl (P3HT) as the semiconductor, either spin cast or dip coated, on the PFCB gate dielectric. OTFTs fabricated with dip-coated P3HT showed a field effect mobility of 1.8×10-3 cm2/V s and a high on/off current ratio of 8.3×106 in the saturation regime, with a source-drain voltage of VD=-50 V. [ABSTRACT FROM AUTHOR]

We have demonstrated the enhancement of the output power of ultraviolet GaN-based light-emitting diodes (LEDs) by using one-dimensionally nanopatterned Cu-doped indium oxide(CIO)/indium tin oxide (ITO) p-type contact layers. The one-dimensional (1D) nanopatterns (250 nm in width and 100 nm in depth) are defined using a TiO2 1D nanomask fabricated by means of a surface relief grating technique. When fabricated with the nanopatterned p-contact layers, the output power of LEDs is improved by 40 and 63% at 20 mA as compared to those fabricated with the unpatterned CIO/ITO and conventional Ni/Au contacts, respectively. [ABSTRACT FROM AUTHOR]

Solid films of n-type Mn2+/CdSe colloidal quantum dots show a positive magnetoresistance. At 0.3 K the film resistance is increased by up to 150% at 10 T. The variable range hopping model quantitatively accounts for the magnetoresistance at low field. [ABSTRACT FROM AUTHOR]

The light collected from inductively coupled CH4/N2 and N2 plasmas is strongly affected by wall reflection. Since wall reflectivity varies with wavelength, the effect can lead to a significant error in the electron temperature determined by the line-ratio method. [ABSTRACT FROM AUTHOR]

We report highly photosensitive organic phototransistors (OPTs) based on a 2,5-bis-biphenyl-4-yl-thieno[3,2-b]thiophene (BPTT). The measured maximum sensitivity and the ratio of photocurrent to dark current (Iph/Idark) in BPTT OPTs were 82 A/W and 2.0×105 under 380 nm UV light with 1.55 mW/cm2, respectively. The prepared OPTs show a photocurrent response similar to the absorption spectrum of BPTT. The major mechanisms for photocurrent amplification in this device were verified from experimental results as photovoltaic (turn-on) and photocurrent effect (turn-off) by a fitting to theoretic equations. [ABSTRACT FROM AUTHOR]

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 2.1–2.3 eV 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 1721 cm-1 was also apparent after UV irradiation for periods longer than 6 h 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. [ABSTRACT FROM AUTHOR]

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 O[sub 2] 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. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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.© 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Explores the synthesis of novel aromatic and aliphatic polyimides. Exhibition of sizable second-order nonlinear optical properties and temporal stability; Determination of the high glass transition temperatures; Observation of exceptional thermal stabilities at elevated temperature.

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. [ABSTRACT FROM AUTHOR]

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. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]