Following Chemical Charge Trapping in Pentacene Thin Films by Selective Impurity Doping and Wavelength‐Resolved Electric Force Microscopy

Charge trapping is one of several factors that limit the performance of organic electronic materials, yet even in pentacene, a prototypical small‐molecule semiconductor, the precise chemical nature of charge trapping remains poorly understood. Here the effects of three chemical trap‐precursor candidates are examined by layering thin‐film pentacene transistors with different pentacene defect species. The resulting charge trapping is studied in each device via scanning‐probe electric force microscopy coupled with variable‐wavelength sample illumination. Firstly, it is found that layering with pentacen‐6(13H)‐one (PHO) readily produces uniform charge trapping everywhere in the transistor channel, as expected for an active blanket‐deposited trap‐precursor. However, layering with 6,13‐dihydropentacene (DHP) produces fewer, more‐isolated traps, closely resembling the surface potential distribution in pristine pentacene thin films. Secondly, the rates of trap‐clearing versus illuminating wavelength (trap‐clearing spectra) are measured, revealing enhanced trap‐clearing rates at wavelengths assigned to the absorption of either pentacene or the charged trap species. The trap‐clearing spectrum for the PHO‐layered sample closely resembles the spectrum obtained from pentacene aged in a working transistor, while the trap‐clearing spectrum for the DHP‐layered sample resembles the spectrum observed in pristine pentacene. We conclude that PHO competently creates traps in pentacene that match the expected trap‐clearing spectrum for degraded pentacene, while DHP does not, and that the chemical trap species in aged pentacene is very likely PHO⁺.     

Modelling of the Am(III) – Cm(III) kinetic separation effect observed during metal ion extraction by bis-(1,2,4)-triazine ligands

The kinetic separation effect was observed leading to a separation factor for Am(III) over Cm(III) as high as 7.9 by using 2,9-bis-(1,2,4-triazin-3-yl)-1,10-phenantroline (BTPhen) ligands in our recent study. In an attempt to explain the observed tendencies, several kinetic models were tested. A model based on mass transfer as the rate-controlling process was found to best describe the kinetic data and allowed to simulate the dependence of Am/Cm separation factor on time. The calculated values of the overall mass-transfer coefficients confirmed that the observed kinetic effect was caused by the different rates of Am(III) and Cm(III) extraction. This kinetic separation phenomenon and its explanation paves the way for potential new approaches to separation of metal ions with very similar properties, such as the adjacent minor actinides Am(III) and Cm(III).     

Quantification of Microstructural Evolution in Grain Boundary Networks

In this work, the effect of grain boundary engineering (GBE) on the structure and connectivity of networks of two types of boundaries was quantified. General high angle boundaries and “special” Σ = 3 and Σ = 9 coincident site lattice boundaries were considered. The effect of GBE processing was to increase the population and length of special boundaries and to disrupt the network of high-angle grain boundaries (HAGBs) in the microstructure. The GBE processing resulted in an increase in the population of special boundaries as determined by line length fraction from approximately 37% to approximately 57%. The connectivity of the special boundaries, as determined by topological analysis, increased by a factor of 4, while the connectivity of HAGBs decreased by an order of magnitude. Cluster sizes in the special boundary network increased across the range of sizes, and the maximum cluster size of HAGBs decreased significantly. The metrics reported here allow for a quantitative analysis of grain boundary connectivity in microstructures, as well as for a quantitative means of comparison of microstructures. These metrics will be used in simulations of diffusional creep, with the aim of quantifying structure–property relationships in grain boundary engineered systems.     

Distance-Dependent Electronic Interactions Across DNA Base Pairs: Charge Transport,Exciton Coupling,and Energy Transfer

The π-stacked bases of B-DNA constitute a helical ruler present nowhere else in nature. When two chromophores are placed at the ends of a base-pair domain with fixed orientations of their transition dipole moments, insertion of an additional base pair between the chromophores increases the distance between the chromophores by ca. 3.4 Å and the angle between their transition dipoles by ca. 36°. The consequences of these changes on the dynamics and efficiency of photoinduced charge transport and upon exciton-coupled circular dichroism and fluorescence resonance energy transfer are discussed.     

Emulsifying properties of soy protein isolate fractions obtained by isoelectric precipitation

Soy protein isolate (SPI) fractions were produced by isoelectric precipitation based on results of isoelectric focusing carried out on the crude soy extract. The fractions were produced from crude protein extract (pH 9.0) sequentially and non‐sequentially at isoelectric points (pIs) of 5.6, 5.1 and 4.5. Emulsions stabilised by soy proteins with pIs between 5.6 and 5.1 had the highest (P < 0.01) emulsion stability index (ESI), while those stabilised with proteins having pIs between 5.1 and 4.5 resulted in the lowest ESI for sequentially precipitated fractions. Non‐sequential fractionation at pI 5.1 produced fractions with higher emulsifying activity index (EAI) than sequential fractionation. SDS‐PAGE profiles indicated that the fractions exhibiting high functionality in terms of ESI and EAI were also richer in 7S globulin protein subunits. © 2001 Society of Chemical Industry     

Engineering magnetic nanocomposite microstructures

The realization of high energy densities in permanent magnetic materials requires careful control of both the composition and the processing conditions to develop appropriate microstructures. In this paper, we will show that manipulation of multiple alloying additions leads to the synthesis of magnetically optimum nanoscale metal matrix composite microstructures in a 9-element modified Nd-Fe-B alloy. The development of composite microstructures in hard magnetic materials is a novel concept resulting in many beneficial effects on the resulting structure/processing/property relationships.     

Ageing-a perspective

Ageing is a gradual change of state and property that usually leads to a degree of malfunction. The primal process in all cases is that the chemical and physical bonds between the atoms of the substance are repeatedly broken, reorganized, and reformed in new configurations. The author lends considerable insight into the mechanics of ageing, especially electrical failure involving insulation     

A design optimization strategy for creating devices that traverse the Pareto frontier over time

In some instances, the performance or function that is needed by a product naturally and predictably changes over time. Providing solutions that anticipate, account for, and allow for these changes is a significant challenge to manufacturers and design engineers. In this paper, a multiobjective optimization design method involving the strategic use of a series of optimization formulations is introduced to design products that adapt to changing needs by moving from one location on the Pareto frontier to another through the addition of a module. The design of a simple unmanned air vehicle is used to demonstrate implementation of the method, and results in the development of one aircraft platform and two module designs that adapt the aircraft to perform optimally for the particular mission at hand, thus optimally satisfying all three different mission profiles individually. The authors conclude that the developed method provides a new and general framework for selecting platform and module designs, and is capable of providing a set of designs based on predicted changes in needs.