Cobalt and silver nanocoatings for reactor dosimetry.

Activation foils are an important tool for the characterization of neutron fields. Some of the materials that are used in these foils have large interaction cross-sections that cause unwanted self-shielding effects. In practice experimenters minimize these effects by using aluminium alloys. An alternative approach can be a nanocoating of a pure material on a carrier. The validity of this approach is investigated in this work. Nanocoatings can be more flexible compared to alloys and can probably reduce the number of required post-irradiation gamma spectrometry measurements. Cobalt and silver nanocoatings were deposited by physical vapour deposition on nickel and aluminium carrier foils. The nanocoatings were tested in two irradiation campaigns in the Belgian Reactor 1 at SCK CEN. By depositing nanocoatings with different thickness and determining the corresponding number of activated atoms the inherent flexibility of the technique is demonstrated. When the dosimeters were punched from the carrier foils, the metal cylindrical punch damaged the nanocoatings which increased the spread on the number of atoms between different dosimeters. This is prevented by including a Ti interlayer of 5 nm between the carrier and the cobalt and silver layers. It was shown that this results in a coating with good homogeneity or minimal spread. This study shows that applying nanocoatings on a carrier is a valid technique to make dosimeters.

Effectiveness of Ligand Denticity-Dependent Oxidation Protection in Copper MOD Inks.

The recent cost-driven transition from silver- to copper-based inks for printing on flexible substrates is connected with new key challenges. Given the high oxidation sensitivity of copper inks before, during, and after the curing process, the conductivity and thereby the device performance can be affected. Strategies to limit or even avoid this drawback include the development of metal organic decomposition (MOD) inks with selected "protective" ligands. In this study, the influence of the ligand on the oxide formation during the ink decomposition process is described using a wide variety of in situ characterization techniques. It is demonstrated that bidentate ligands provide an improved oxidation barrier, although the copper preservation mechanism has its limits: oxygen can interfere in every reduction pathway depending on the curing duration and atmospheric conditions. The generated insights can be applied in the further evolution toward ambient-curable copper MOD inks.

TiO2-coated luminescent porous silicon micro-particles as a promising system for nanomedicine.

Porous silicon (pSi) is a sponge-like material obtained by electrochemical etching of a crystalline silicon wafer. Due to quantum confinement effects, this material is photoluminescent and this is a fundamental property from the perspective of bioimaging applications. Limitations in nanomedicine to the use of photoluminescent pSi structures are mainly due to optical quenching in an aqueous environment and to the adverse effects of reactive groups introduced by etching procedures. In this work, we exploited an inorganic TiO2 coating of pSi microparticles by Atomic Layer Deposition (ALD) that resulted in optical stability of pSi particles in a biological buffer (e.g. PBS). The use of a rotary reactor allows deposition of a uniform coating on the particles and enables a fine tuning of its thickness. The ALD parameters were optimized and the photoluminescence (PL) of pSi-TiO2 microparticles was stabilized for more than three months without any significant effect on their morphology. The biocompatibility of the coated microparticles was evaluated by analyzing the release of cytokines and superoxide anion (O2 -) by human dendritic cells, which play an essential role in the regulation of inflammatory and immune responses. We demonstrated that the microparticles per se are unable to significantly damage or stimulate human dendritic cells and therefore are suitable candidates for nanomedicine applications. However, a synergistic effect of the microparticles with bacterial products, which are known to stimulate immune-response, was observed, indicating that a condition unfavorable to the use of inorganic nanomaterials in biological systems is the presence of infection diseases. These results, combined with the proved PL stability in biological buffers, open the way for the use of pSi-TiO2 microparticles as promising materials in nanomedicine, but their ability to increase immune cell activation by other agonists should be considered and even exploited.

Te-based chalcogenide materials for selector applications.

The implementation of dense, one-selector one-resistor (1S1R), resistive switching memory arrays, can be achieved with an appropriate selector for correct information storage and retrieval. Ovonic threshold switches (OTS) based on chalcogenide materials are a strong candidate, but their low thermal stability is one of the key factors that prevents rapid adoption by emerging resistive switching memory technologies. A previously developed map for phase change materials is expanded and improved for OTS materials. Selected materials from different areas of the map, belonging to binary Ge-Te and Si-Te systems, are explored. Several routes, including Si doping and reduction of Te amount, are used to increase the crystallization temperature. Selector devices, with areas as small as 55 × 55 nm2, were electrically assessed. Sub-threshold conduction models, based on Poole-Frenkel conduction mechanism, are applied to fresh samples in order to extract as-processed material parameters, such as trap height and density of defects, tailoring of which could be an important element for designing a suitable OTS material. Finally, a glass transition temperature estimation model is applied to Te-based materials in order to predict materials that might have the required thermal stability. A lower average number of p-electrons is correlated with a good thermal stability.

Magnetic and electrical characterization of nickel-rich NiFe thin films synthesized by atomic layer deposition and subsequent thermal reduction.

Nickel-rich NiFe thin films (Ni92Fe8, Ni89Fe11 and Ni83Fe17) were prepared by combining atomic layer deposition (ALD) with a subsequent thermal reduction process. In order to obtain Ni x Fe1-x O y films, one ALD supercycle was performed according to the following sequence: m NiCp2/O3, with m = 1, 2 or 3, followed by one FeCp2/O3 cycle. The supercycle was repeated n times. The thermal reduction process in hydrogen atmosphere was investigated by in situ x-ray diffraction studies as a function of temperature. The metallic nickel iron alloy thin films were investigated and characterized with respect to crystallinity, morphology, resistivity, and magnetism. As proof-of-concept magnetic properties of an array of Ni83Fe17, close to the perfect Permalloy stoichiometry, nanotubes and an isolated tube were investigated.

Nanostructured TiO2/carbon nanosheet hybrid electrode for high-rate thin-film lithium-ion batteries.

Heterogeneous nanostructured electrodes using carbon nanosheets (CNS) and TiO2 exhibit high electronic and ionic conductivity. In order to realize the chip level power sources, it is necessary to employ microelectronic compatible techniques for the fabrication and characterization of TiO2-CNS thin-film electrodes. To achieve this, vertically standing CNS grown through a catalytic free approach on a TiN/SiO2/Si substrate by plasma enhanced chemical vapour deposition (PECVD) was used. The substrate-attached CNS is responsible for the sufficient electronic conduction and increased surface-to-volume ratio due to its unique morphology. Atomic layer deposition (ALD) of nanostructured amorphous TiO2 on CNS provides enhanced Li storage capacity, high rate performance and stable cycling. The amount of deposited TiO2 masks the underlying CNS, thereby controlling the accessibility of CNS, which gets reflected in the total electrochemical performance, as revealed by the cyclic voltammetry and charge/discharge measurements. TiO2 thin-films deposited with 300, 400 and 500 ALD cycles on CNS have been studied to understand the kinetics of Li insertion/extraction. A large potential window of operation (3-0.01 V); the excellent cyclic stability, with a capacity retention of 98% of the initial value; and the remarkable rate capability (up to 100 C) are the highlights of TiO2/CNS thin-film anode structures. CNS with an optimum amount of TiO2 coating is proposed as a promising approach for the fabrication of electrodes for chip compatible thin-film Li-ion batteries.

Catalytic activation of OKO zeolite with intersecting pores of 10- and 12-membered rings using atomic layer deposition of aluminium.

Tetrahedral framework aluminium was introduced in all-silica zeolite -COK-14 using Atomic Layer Deposition (ALD) involving alternating exposure to trimethylaluminium and water vapour. The modification causes permanent conversion of the originally interrupted framework of -COK-14 to a fully connected OKO type framework, and generates catalytic activity in the acid catalysed hydrocarbon conversion reaction.

Determination of anabolic steroids in dietary supplements by liquid chromatography-tandem mass spectrometry.

Nineteen different dietary supplements, ordered through the internet and intercepted by the Belgian pharmaceutical inspection at the post office, were analyzed by means of liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the presence of anabolic steroids. After a methanolic extraction the samples were screened for the presence of 49 compounds. This resulted in almost 60% of the samples being suspected of containing one of these 49 anabolic compounds and being subjected to a confirmatory product ion scan. In all of these suspected samples we were able to confirm at least one anabolic steroid with concentrations between 0.01 and 2.5 mg unit(-1) (unit: one capsule or tablet or for liquids: the prescribed dose). The anabolic steroids that was mostly encountered was testosterone (50%) followed by beta-boldenone (25%). These results once more confirm the dubious reputation of over-the-counter dietary supplements.

An off-normal fibre-like texture in thin films on single-crystal substrates.

In the context of materials science, texture describes the statistical distribution of grain orientations. It is an important characteristic of the microstructure of polycrystalline films, determining various electrical, magnetic and mechanical properties. Three types of texture component are usually distinguished in thin films: random texture, when grains have no preferred orientation; fibre texture, for which one crystallographic axis of the film is parallel to the substrate normal, while there is a rotational degree of freedom around the fibre axis; and epitaxial alignment (or in-plane texture) on single-crystal substrates, where an in-plane alignment fixes all three axes of the grain with respect to the substrate. Here we report a fourth type of texture--which we call axiotaxy--identified from complex but symmetrical patterns of lines on diffraction pole figures for thin films formed by solid-state reactions. The texture is characterized by the alignment of planes in the film and substrate that share the same d-spacing. This preferred alignment of planes across the interface manifests itself as a fibre texture lying off-normal to the sample surface, with the fibre axis perpendicular to certain planes in the substrate. This texture forms because it results in an interface, which is periodic in one dimension, preserved independently of interfacial curvature. This new type of preferred orientation may be the dominant type of texture for a wide class of materials and crystal structures.