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In this study oxygen permeability in dispersion barriers produced from poly(vinyl alcohol) (PVOH) and kaolin clay blends coated onto polymeric supports was investigated. To determine the oxygen permeability, two measurement methods were used: the oxygen transmission rate (OTR) and the ambient oxygen ingress rate (AOIR). It was found that with increasing kaolin content the oxygen permeability increased, up to about 5 wt% kaolin, whereafter the oxygen permeability decreased, as was expected. The increased (> 5%) kaolin loading lowered the diffusion because of an increased tortuosity. Structural information about the dispersion-barrier coatings, such as kaolin orientation and polymer crystallinity, was obtained from Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Kaolin orientation was influenced by the drying temperature, the thickness of the samples, and the kaolin concentration. The polymer crystallinity increased in thicker samples. The drying temperature did not show any clear effect on the crystallinity of thin samples, while for the thicker barriers, combined with a kaolin concentration lower than 20 wt%, a higher crystallinity was achieved at lower drying temperatures. This study demonstrates the strong influence of chemical and physical structures on the permeability of the investigated coatings. [ABSTRACT FROM AUTHOR]

Abstract: The growth of thin 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) films on a 3C-SiC(001)c(2×2) substrate has been studied by means of photoelectron spectroscopy (PES) and atomic force microscopy (AFM). In the first monolayer the molecules interact with the substrate mainly through the O atoms in the end groups of the molecule. The O atoms have a higher binding energy in the first molecular layer compared to the following layers. No chemical shifts are observed in the Si 2p spectra or in the C 1s spectra from the perylene core of the molecules. From the VB spectra and LEED pattern we conclude that the substrate remains in the c(2×2) reconstruction after PTCDA deposition. For thicker films a Stranski–Krastanov film growth was observed with flat lying molecules relative to the substrate. [Copyright &y& Elsevier]

We have studied the thin film formation and the electronic structure of the organic molecular semiconductor 3,4,9,10 perylene tetracarboxylic dianhydride (PTCDA), on clean and on hydrogen-passivated Si(001) surfaces. The studies were made by means of high resolution X-ray photoelectron spectroscopy (HRXPS), angle-resolved photoelectron spectroscopy (ARPES), near edge X-ray absorption fine structure (NEXAFS) and low energy electron diffraction (LEED). On the H passivated surface the changes in the electronic structure of the substrate and the molecules with increasing film thickness are very small. The molecular orbitals show a dispersive behavior, indicating that the PTCDA layers are ordered. On the reactive clean surface the anhydride groups of the molecule interact with the substrate as indicated by changes in the core level binding energies. This results in a much lower ordering in the film compared to PTCDA on a passivated silicon surface. There is no sign of decomposition of the molecule because of the more reactive substrate. [Copyright &y& Elsevier]

We have studied the interface and thin film formation of the organic molecular semiconductor 3,4,9,10 perylene tetracarboxylic dianhydride (PTCDA) on clean and on hydrogen passivated Si(001) surfaces. The studies were made by means of high resolution X-ray photoelectron spectroscopy (HRXPS), near edge X-ray absorption fine structure (NEXAFS), low energy electron diffraction (LEED), and atomic force microscopy (AFM). On the passivated surface the LEED pattern is somewhat diffuse but reveals that the molecules grow in several ordered domains with equivalent orientations to the substrate. NEXAFS shows that the molecules are lying flat on the substrate. The Si 2p XPS line shape is not affected when the film is deposited so it can be concluded that the interaction at the interface between PTCDA and the substrate is weak. The evolution of the film formation appears to be homogeneous for the first monolayer with a nearly complete coverage of flat lying molecules based on the XPS attenuation. For layer thickness of 0.5–2 monolayers (ML) the molecules start to form islands, attracting the molecules in between, leaving the substrate partly uncovered. For thicker films there is a Stranski–Krastanov growth mode with thick islands and a monolayer thick film in between. For the clean surface the ordering of the film is much lower and angle resolved photoelectron spectroscopy (ARPES) of the molecular orbitals have only a small dependence of the emission angle. NEXAFS shows that the molecules do not lie flat on the surface and also reveal a chemical interaction at the interface. [Copyright &y& Elsevier]

Several omnibus tests have been developed to assess the fit of a regression model. But many of these lack-of-fit tests focus on the simple regression setting. Here, we focus on multiple logistic regression. Pearson's well-known chi-square test statistic and the deviance statistic are no longer valid in the case that the model contains one or more continuous covariates. To overcome this difficulty, Hosmer and Lemeshow proposed a Pearson type statistic based on groups defined by the so-called deciles of risk. We propose a test statistic that is similar in approach to the Hosmer and Lemeshow statistic in that the observations are classified into distinct groups. In the procedure proposed here however, the grouping is not according to probabilities fitted under the null model. We use a recursive partitioning algorithm to divide the sample space into different groups. This generally allows for a more powerful assessment of the model fit. Simulations are carried out to compare the results of the proposed test to that of Hosmer and Lemeshow. Three data examples illustrate the performance of the tree based lack-of-fit test, in comparison to several other tests. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Ag/Si(111)- √3 × √3 surface and studied by scanning tunneling microscopy/spectroscopy and low energy electron diffraction (LEED). The growth mode was characterized as layer-by-layer growth with a single molecular unit cell in a short range order. The growth of the first two monolayers involves a molecule/substrate superstructure and a molecule/molecule superstructure. At higher coverages, the molecules in each layer were found to align so that unit cells are on top of each other. The experimentally obtained LEED pattern is described as a combination of patterns from the molecular unit cell and the molecule/substrate superstructure. The electronic structure was found to be strongly dependent on the film thickness for the first few layers: Several extra states are found at low coverages compared to higher coverages resulting in a very small pseudo gap of 0.9 eV for the first layer, which widens up to 4.0 eV for thicker films. [ABSTRACT FROM AUTHOR]

Abstract: When creating thin films of polymer blends, interesting morphologies are formed because of phase separation. In particular for conjugated polymers, which are used as active material in optoelectronic devices, it is very important to understand the parameters that influence the phase separation process and to achieve control over the morphology. The overall goal of this blend morphology study is to contribute to the design of device structures with desired performance. Here we present results of morphology studies on thin films of polyfluorene-based blends with the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The polymers used are poly(9,9-dioctylfluorene) (F8) and four different copolymers of F8. The thin films are spin coated from chloroform solutions onto silicon substrates and their surface morphology is imaged by tapping mode atomic force microscopy (AFM). We observe that the size and the shape of the domains in the film depend on the structure of the polymer. The nature of the monomer that, together with F8, is building the repeating unit in the copolymers has a strong effect on the phase separation in the polymer: PCBM blend. Since phase separation is influenced by interactions between components of the blend and the solvent, these results indicate that the degree of chemical interaction between polymer, solvent and PCBM, is different for the different blends. For the systems that form larger domains there is a clear correlation between the domain size (area) and the polymer/PCBM blend ratio. We also observe that the spin speed affects the thickness of the films and that the domain size increases with increasing thickness, primarily due to longer drying times. [Copyright &y& Elsevier]

Oxyhydride of yttrium (YHO) belongs to an emerging class of materials, with oxide and hydride anions sharing the same sites in the lattice. Under sunlight irradiation, the material is transparent to visible light with transparency exceeding 85% and can absorb about 10% of sunlight. Furthermore, increasing light transmittance in the visible light enhanced the self-cleaning properties of the coated materials, making these materials promising candidates for smart windows applications. However, the light-absorbing properties of the materials were increased with exposure time, and in the photodarkening state, they can absorb about 40% of sunlight. Kelvin probe measurements show work function values between 2.9 and 4.2 ​eV for YHO, depending on the H 2 /Ar pressure in the deposition chamber. Using the Kelvin probe, we demonstrate that the work function decreases with decreasing deposition pressure and hydrogen flow. Measurements under solar light reveal a decrease of work function by 0.2 ​eV followed by a slow relaxation with the light off. Moreover, the self-cleaning test shows that the oxyhydroxide thin films have excellent photocatalytic activity and total self-cleaning in 40 ​h. [Display omitted] • Photochromic yttrium oxyhydride (YHO) films are grown by reactive magnetron sputtering. • The light-absorbing properties increase with exposure time and in the photodarkening state and absorb about 40% of sunlight. • The yttrium oxyhydride coatings exhibited excellent self-cleaning ability. [ABSTRACT FROM AUTHOR]

Highlights: [•] We reproduced the C K-edge NEXAFS spectrum of PCBM by DFT simulations. [•] The experimental peaks were assigned to specific molecular moieties. [•] C-atoms contributing to the high-energy shoulder of the first peak were identified. [Copyright &y& Elsevier]

Estimations of ochratoxin A (OTA) and 4-deoxynivalenol (DON) exposure of the Belgian population through beer consumption were made using the results of the recent Belgian food survey and the compiled data set of OTA and DON levels in conventionally and organically produced beers in 2003-05. For the consumers of organic beers, the daily intake of OTA was 0.86 (in 2003), 1.76 (in 2004) and 0.72 (in 2005) ng kg-1 body weight (bw), considering the mean beer consumption (0.638 litres) and the average level of OTA in 2003, 2004 and 2005, respectively. Using the 97.5th percentile of beer consumption (1.972 litres), the corresponding OTA daily intakes were 2.65, 5.44 and 2.24 ng kg-1 bw, which are close or above the tolerable daily intake (TDI) of 5 ng kg-1 bw. For the consumers of conventional beers, the OTA intakes were low: 0.23, 0.23 and 0.11 ng kg-1 bw day-1 for the average beer consumption, in 2003, 2004 and 2005 against 0.72, 0.73 and 0.34 ng kg-1 bw day-1 when the 97.5th percentile level was considered. As for the DON intake, the estimates were quite low for both conventional and organic beer consumers when the provisional maximum TDI (PMTDI) of 1 µg kg-1 bw was considered. Average consumption of organic beer led to daily intakes of 0.05 and 0.04 µg DON kg-1 bw in 2003 and 2004, respectively, whilst for conventional beer, daily intakes were 0.07 and 0.05 µg DON kg-1 bw. At the 97.5th percentile level of beer consumption, daily intakes of 0.15 and 0.13 µg kg-1 bw were obtained for organic beers against 0.23 and 0.17 µg kg-1 bw for conventional ones. The results showed that beer could be an important contributor to OTA exposure in Belgium, even though a declining trend seems to be apparent during the last year of monitoring. Therefore, efforts should be devoted to maintain the OTA levels as low as reasonably achievable, especially for organic beer. [ABSTRACT FROM AUTHOR]

A database has been compiled with the levels of important contaminants (mycotoxins, heavy metals and pesticides) measured from 2002 to 2005 in winter wheat (Triticum aestivum) grown in Belgium according to the organic and conventional farming systems. Assuming no further change in contaminant levels during cereal processing and during the preparation of foodstuffs, conservative intakes are estimated for the consumers of cereal-based products such as flour, bread, breakfast cereals, dough and pastry. The results show that for the consumer of organic foodstuffs, estimated daily intakes are 0.56 µg deoxynivalenol (DON), 0.03 µg zearalenone (ZEA), 0.19 µg Cd, 0.28 µg Pb and 0.0006 µg Hg kg-1 body weight, taking into account the average contaminant levels in unprocessed grains and the average cereal products consumptions in Belgium. For the consumers of conventional foodstuffs, the corresponding estimated daily intakes are 0.99 µg DON, 0.06 µg ZEA, 0.17 µg Cd, 0.12 µg Pb and 0.0007 µg Hg kg-1 body weight. In addition, it appears that for the consumers of conventional products, intakes of some post-harvest insecticides have to be taken into account (0.11 µg chlorpyriphos-methyl, 0.2 µg dichlorvos and 0.24 µg pirimiphos-methyl kg-1 bw). When expressed as a percentage of the tolerable/acceptable daily intake (TDI/ADI), it seems that the corresponding estimated (conservative) intakes are the highest for DON (56% for organic and 99% for conventional cereal products), ZEA (16% for organic and 32% for conventional cereal products), and Cd (19% for organic and 17% for conventional cereal products), all other estimated intakes of contaminants (including pesticides) being lower than 10% of the TDI/ADI. [ABSTRACT FROM AUTHOR]

Abstract: Acrylamide has recently been found in a range of heat treated food items. As it is a neurotoxic agent and a probable, human carcinogen (IARC 2A), human exposure to this chemical might constitute an important public health issue. The purpose of the study was to estimate the acrylamide intake in Flemish adolescents (based on 7-day food record) and to evaluate the possible health risks due to the exposure. The Belgian Federal Agency for the Safety of the Food Chain collected 150 food items from different supermarkets and restaurants to analyse the acrylamide level. The limit of quantitation was 30μg acrylamide/kg foodstuffs. Exposure modelling was based on Monte Carlo simulations. The estimated dietary intake of acrylamide per person given as the 5th, 50th and 95th percentile were 0.19, 0.51 and 1.09μg/kgbw/d. Bread, despite its low acrylamide content, is relevant as a source of acrylamide exposure at the lower percentiles. At higher percentiles the contribution of French fries and crisps is more important. It must be emphasised that the exposure assessment has several limitations. Risk of neurotoxicity seems negligible. The relevance of current intake levels in terms of cancer risk remains a subject of debate. [Copyright &y& Elsevier]

Using annealing in an ammonia atmosphere in combination with Ga adsorption and desorption, polar surfaces of ex situ grown GaN(0001) epilayers can be prepared towards clean and stoichiometric conditions. This combination of surface treatments also improves the surface crystalline order and chemical homogeneity, as observed in photoelectron spectra, in low energy electron diffraction (LEED) patterns, and of the coefficient of variation (Cvar) of the Ga3d intensity in the spectromicroscopy images. The lateral resolution limit of the spectromicroscopy images is 2μm. The surface improvements during NH3 annealing show saturation effects. The best surface quality in terms of the crystalline order and chemical homogeneity was found after annealing at 800°C in NH3, followed by Ga adsorption and finally desorption by annealing in a NH3 atmosphere. [Copyright &y& Elsevier]

Deals with use of self-organized discotic liquid crystals to create thin films with structures optimized for use in photodiodes. Photoinduced charge transfer between the hexabenzocoronene and perylene; Commercial applications in optoelectronic technologies; High performance of crystalline organics in a solution-processed photovoltaic device.

Presents an erratum of the article 'Ultraviolet--Visible Near-Field Microscopy of Phase-Separated Blends of Polyfluorene-Based Conjugated Semiconductors' appearing in the 2001 issue of the journal 'Applied Physics Letters'.

We have used fluorescence scanning near-field microscopy to characterize polymer blends for electroluminescent applications, and thereby identify compositional nonhomogeneities. In particular, we have focused on the binary system constituted by poly(9,9′-dioctylfluorenealt-benzothiadiazole) and poly(9,9′-dioctylfluorene) (PFO), known to give efficiencies of up to 22 cd/A in light-emitting devices with suitable electrodes. Our primary aim was the assignment of the morphological features revealed in shear-force and atomic-force images of spin-coated films, and suggestive of phase separation on a 300-nm-length scale. From analysis of the fluorescence images (325 and 488 nm excitation), and quantitative correlation of optical and topographic data, we identify the raised features with PFO-rich regions. However, the limited variation in fluorescence intensity reveals a high extent of mixing within each phase on the length scale accessible in our experiment, approximately 100 nm for our focused-ion-beam-processed probe apertures. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]