Hysteresis in Conjugated Polymer Thin Film Transistors Generated by Chain Relaxation

The hysteresis phenomenon in a polymer thin film transistor (PTFT) with either poly(3‐hexylthiophene), poly(3‐dodecylthiophene), or poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene] is investigated over a wide range of temperatures, and found to be generated by the delay in main chain ring distortion with an applied electric field. In the temperature range for side chain relaxation, main chain motion induced by side chain motion already starts such that polarization of the main chain by the applied electric field is permitted but in a limited extent and is not in phase with the variation in electric field. In the main chain relaxation temperature range, the extent of segmental motion increases, which leads to the main chain being more realignable by the applied electric field and thus a reduced hysteresis. After main chain relaxation is complete, the ring can distort more freely and chain segments are able to realign in phase with the applied electric field, which leads to a leveling off of the hysteresis. This investigation shows for first time that the chain relaxation in conjugated polymers is the origin of the hysteresis in PTFT devices.     

引导未来生活的小发明

每年的发明展上，总能看到一些“慧眼识珠”的投资者或商家的身影，一旦寻到极具市场潜力的新点子，立马实现量产，推向市场。     

Structure Tuning of Crown Ether Grafted Conjugated Polymers as the Electron Transport Layer in Bulk‐Heterojunction Polymer Solar Cells for High Performance

A series of novel electron transport (ET) polymers composed of different conjugated main chains (fluorene, thiophene, and 2,7‐carbazole) and crown ether side chain (crown ether, aza‐crown ether and amine) is presented for bulk‐heterojunction polymer solar cells with poly(3‐hexylthiophene) (P3HT) or poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo [1,2‐b:4,5‐b′] dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]](PTB7) as the active polymer and aluminum metal as the cathode. Unexpectedly, it is found that the main chain of ET polymers has a greater effect on the interfacial dipole than the side chain, even when attaching a high polarity group. The electron‐rich bridge atom of the main chain may also contribute appreciably to the interfacial dipole. When used as the ET layer, all of these polymers can generate an optical interference effect for redistribution of the optical electric field as an optical spacer and, therefore, allow more light to be absorbed by the active layer, thus leading to an increase in short‐circuit current density. They can also block hole diffusion to the cathode and prevent electron–hole recombination during the ET process. Among the five ET polymers investigated, PCCn6 is the most effective one, providing a remarkable improvement in the power conversion efficiency (measured in air) of the device to 8.13% compared to 5.20% for PTB7:[6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM).     

The effect of the CH4 level on the morphology,microstructure, phase purity and electrochemical properties of carbon films deposited by microwave-assisted CVD from Ar-rich source gas mixtures

Carbon thin films were deposited on Si substrates by microwave-assisted chemical vapor deposition (CVD) using variable CH₄ levels in an Ar/H₂ (Ar-rich) source gas mixture. The relationship between the CH₄ concentration (0.5 to 3 vol.%) in the source gas and the resulting film morphology, microstructure, phase purity and electrochemical behavior was investigated. The H₂ level was maintained constant at 5% while the Ar level ranged from 92 to 94.5%. The films used in the electrochemical measurements were boron-doped with 2 ppm B₂H₆ while those used in the structural studies were undoped. Boron doping at this level had no detectable effect on the film morphology or microstructure. Relatively smooth ultrananocrystalline diamond (UNCD) thin films, with a nominal grain size of ca. 15 nm, were only formed at a CH₄ concentration of 1%. At the lower CH₄ concentration (0.5%), faceted microcrystalline diamond was the predominant phase formed with a grain size of ca. 0.5 µm. At the higher CH₄ concentration (2%), a diamond-like carbon film was produced with mixture of sp²-bonded carbon and UNCD. Finally, the film grown with 3% CH₄ was essentially nanocrystalline graphite. The characteristic voltammetric features of high quality diamond (low and featureless voltammetric background current, wide potential window, and weak molecular adsorption) were observed for the film grown with 1% CH_4, not the films' grown with higher CH₄ levels. The C₂ dimer level in the source gas was monitored using the Swan band optical emission intensity at 516 nm. The emission intensity and the film growth rate both increased with the CH₄ concentration in the source gas, consistent with the dimer being involved in the film growth. Importantly, C₂ appears to be involved in the growth of the different carbon microstructures including microcrystalline and ultrananocrystalline diamond, amorphous or diamond-like carbon, and nanocrystalline graphite. In summary, the morphology, microstructure, phase purity and electrochemical properties of the carbon films formed varied significantly over a narrow range of CH₄ concentrations in the Ar-rich source gas. The results have important implications for the formation of UNCD from Ar-rich source gas mixtures, and its application in electrochemistry. Characterization data by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), visible-Raman spectroscopy and electrochemical methods are presented.     

Electrically conductive material made from CNT and PTFE

Carbon nanotube (CNT)-filled Polytetrafluoroethylene (PTFE) film is successfully formed by using dispersion fluids of CNT and PTFE. The CNTs were uniformly dispersed and connected to each other within this film. The connection of the CNTs with one another facilitated electrical conduction. The conductivity of this film was dependent on the concentration of CNTs within the film. A PTFE film with a CNT concentration of 90% showed an electrical conductivity of 20 S/cm.     

Reuse of Industrial Sludge as Pelletized Aggregate for Concrete

Industrial sludge is generated at a rate of 100 metric tons∕day, from a copper slag recycling plant. The industrial sludge is currently being landfilled. However, limited availbility of landfill sites has raised the need of an alternative disposal. A renewed interest in converting the industrial sludge into construction materials has been prompted to achieve a viable disposal option in saving the depleting natural resources of raw materials as well as the environment. This study describes the use of sintered sludge pellets as a complete replacement for regular granite aggregates in concrete. The pelletized sludge was fired to a temperature of 1,135°C at which the sintering process occurs, producing a hard fused basalt-like mass. In comparison with normal granite aggregates, the sintered sludge pellets display a higher aggregate strength, a higher porosity, and a lower aggregate density that manifests attributes better than that required of construction aggregates. The concrete cast with the pelletized aggregtes achieved a compressive strength of 38.5 N∕mm2 after 28 days and was comparable to the control specimen. Leaching tests conducted on the sludge pellets and concrete showed that all leachate contamination levels determined using the column leaching test are within acceptable ranges after 130 days of stabilization. The experimental results indicated that a complete replacement of conventional aggregates with sintered sludge pellets for structural concrete is both technically and environmentally feasible.     

Effect of prior heat treatment on wear behaviour of 0·23% carbon dual phase steel

The present study is aimed at understanding the effect prior heat treatment on the high-stress abrasive wear response of 0·.23% carbon dual phase steel. As-received steel was subjected to annealing, normalising and hardening treatment prior to actual dual phase heat treatment. These steels along with the as-received steel were intercritically annealed at 745°C followed by water quenching in order to produce dual phase microstructures. Abrasion tests were carried out at varying sliding distances with a 40 μm abrasive and at 7 N applied load. Wear test at varying loads were also performed for the steel that showed maximum wear resistance. Dual phase treatment resulted in improved overall wear response. The wear resistance for the steel with prior annealing treatment (DPLA-1) and for the steel with prior hardening treatment (DPLA-3) improved over the entire range of sliding distance. It was also found that the wear rate increased with applied load for DPLA-1 steel.

Cette étude vise à comprendre l’effet du traitement thermique antérieur sur la réponse à l’usure par abrasion à contrainte élevée de l’acier biphasé à 0·23% de carbone. On a soumis l’acier brut d’usinage à un traitement de recuit, à un traitement de normalisation ainsi qu’à un traitement d’endurcissement avant le traitement thermique actuel de structure biphasée. On a effectué un traitement de recuit intercritique à 745°C de ces aciers ainsi que de l’acier brut d’usinage, suivi par trempe à l’eau afin de produire des microstructures biphasées. On a effectué un essai d’abrasion sur des distances variées de glissement avec un abrasif de 40 μm et une charge appliquée de 7 N. On a également effectué un essai d’usure avec diverses charges de l’acier ayant montré la meilleure résistance à l’usure. Le traitement de structure biphasée améliorait globalement la réponse à l’usure. L’acier avec traitement de recuit antérieur (DPLA-1) ainsi que l’acier avec traitement d’endurcissement antérieur (DPLA-3) ont montré une amélioration sur toute la gamme de distance de glissement. La vitesse d’usure de l’acier DPLA-1 augmentait avec l’application de la charge.     

Dynamic response of an elastic fence under wind action

Abstract

The along‐wind response of a surface‐mounted elastic fence under the action of wind was investigated numerically. In the computations, two sets of equations, one for the simulation of the unsteady turbulent flow and the other for the calculation of the dynamic motion of the fence, were solved alternatively. The resulting time‐series tip response of the fence as well as the flow fields were analyzed to examine the dynamic behaviors of the two.

Results show that the flow is unsteady and is dominated by two frequencies: one relates to the shear layer vortices and the other one is subject to vortex shedding. The resulting unsteady wind load causes the fence to vibrate. The tip deflection of the fence is periodic and is symmetric to an equilibrium position, corresponding to the average load. Although the along‐wind aerodynamic effect is not significant, the fluctuating quantities of the tip deflection, velocity and acceleration are enhanced as the fundamental frequency of the fence is near the vortex or shedding frequency of the flow due to the occurrence of resonance. In addition, when the fence is rather soft, a higher mode response can be excited, leading to significant increases in the variations of the tip velocity and acceleration.     

Optical and electrochemical properties of optically transparent,boron-doped diamond thin films deposited on quartz

The optical and electrochemical properties of transparent, boron-doped diamond thin film, deposited on quartz, are discussed. The films were deposited by microwave-assisted chemical vapor deposition, for 1-2 h, using a 0.5% CH4/H2 source gas mixture at 45 Torr and 600 W of power. A high rate of diamond nucleation was achieved by mechanically scratching the quartz. This pretreatment leads to the formation of a continuous film, in a short period of time, which consists of nanometer-sized grains of diamond. The thin-film electrode was characterized by cyclic voltammetry, atomic force microscopy, and UV-visible absorption spectrophotometry. The film's electrochemical response was evaluated using Ru(NH3)6(3+/2+) in 1 M KCl, Fe(CN)6(3-/4-) in 1 M KCl, and chlorpromazine (CPZ) in 10 mM HClO4. The film exhibited a low voltammetric background current and a stable and active voltammetric response for all three redox systems. The optical transparency of the polycrystalline film in the visible region was near 50% and fairly constant between 300 and 800 nm. The optical and electrical properties were extremely stable during 48-h exposure tests in various aqueous (HNO3, NaOH) solutions and nonaqueous (e.g., chlorinated) solvents. The properties were also extremely stable during anodic and cathodic potential cycling in harsh aqueous environments. This stability is in stark contrast to what was observed for an indium-doped tin oxide thin film coated on quartz. The spectroelectrochemical response (transmission mode) for CPZ was studied in detail, using a thin-layer spectroelectrochemical cell. Thin-layer voltammetry, potential step/ absorption measurements, and detection analytical figures of merit are presented. The results demonstrate that durable, stable, and optically transparent diamond thin films, with low electrical resistivity (approximately 0.026 omega x cm) laterally through the film, can be deposited on quartz.