Integrity and lifetime of reactor pressure vessels are practically determined by their material resistance against fast/non-ductile failure and consequently by their radiation damage resulting in irradiation embrittlement and hardening. Mechanism of irradiation embrittlement of RPV materials depends on selected materials and operation conditions but their values depend in a large extent on reactor design, i.e. on neutron flux/fluence depending on RPV wall. Generally, new RPV design allows smaller neutron fluences but absolute value of irradiation embrittlement still depends on a choice of RPV material. Even though radiation damage (especially irradiation embrittlement) is important for RPV behavior, integrity and lifetime depends, in principle, on final value of applied fracture mechanics parameter –transition temperature. Thus, its initial value as well as its shift due to irradiation embrittlement is of interest but only the embrittlement can be affected during operation.

Determining upconversion parameters is of high interest in laser material development. For many materials these parameters cannot be directly measured by experimental methods. These upconversion coefficients appear as unknown parameters in the laser rate equations, which are a system of coupled nonlinear differential equations that are used to model the dynamics of population densities in different energy levels. In this paper we propose the well-established system theoretic tools pertaining to the system inversion to be applied in this case. The unknown parameters can be considered as the inputs and the fluorescence signals can be considered as the outputs of the dynamical system. Therefore the determination of the unknown upconversion rates in the system equations from the output data is a classical system inversion problem. In this paper we demonstrate how to compute the unknown coefficients in the rate equations from the experimental emission data utilizing this method.

Cadmium Zinc Telluride (CZT) semiconductor crystal properties have been studied extensively with a focus on correlations to their radiation detector performance. The need for defect-free CZT crystal is imperative for optimal detector performance. Extended defects like Tellurium (Te) inclusions, twins, sub-grain boundaries, and dislocations are common defects found in CZT crystals; they alter the electrical properties and, therefore, the crystal's response to high energy radiation. In this research we studied the extended defects in CZT crystals from two separate ingots grown using the low-pressure Bridgman technique. We fabricated several detectors cut from wafers of two separate ingots by dicing, lapping, polishing, etching and applying gold metal contacts on the main surfaces of the crystals. Using infrared (IR) transmission microscope we analyzed the defects observed in the CZT detectors, showing three dimensional scans and plot size distributions of Te inclusions, twins and sub-grain boundaries observed in particular regions of the CZT detectors. We characterized electrical properties of the detectors by measuring bulk resistivity and detector response to gamma radiation. We observed that CZT detectors with more extended defects showed poor opto-electrical properties compared to detectors with fewer defects.

The BiCuSeO has been proved to be one of the best oxide-based thermoelectric materials in recent years. Its electric properties have been widely studied, yet the lattice thermal conductivity was only discussed roughly. Our investigation suggests that the anharmonic vibration and the interlayer-interaction plays the crucial role in reducing the intrinsic lattice thermal conductivity. The thermal conductivity has been calculated based on quasi-harmonic approximation and detailed contribution have been discussed. The calculated data have good agreement with the experimental data.

Stabilized Au NPs were directly deposited on nanostructured ZnO and ZrO2 by a simple one-step strategy based on sacrificial anode electrolysis. The annealed nanocomposites are proposed as active layers in resistive gas sensors for low-cost processes. Results on the performance of gas sensors based on pristine and Au-doped MOx nanostructured thin films, used for the detection of NO2 gas, were reported at an operating temperature of 300°C, evaluating the effects of the MOx chemical composition and morphology, and the Au-doping.

We present a detailed study of memory performance of titanium oxide (TiO2-x)-based resistive switching memories by modifying critical parameters of the films involved in the memory stack grown by reactive sputtering at room temperature. The device includes a Ti nanolayer at the Au/TiO2-x interface and it is defined by the following material stack: Au/Ti/TiO2-x/Au/SiO2/Si. We investigate the memory performance optimization of the device in terms of the Ti nanolayer thickness using as a starting point for the TiO2-x growth conditions these identified by varying the ratio of oxygen concentration to argon concentration by our previous results. Due to the superb ability of Ti to absorb oxygen atoms from the dielectric matrix, a large amount of oxygen vacancies is created, which are crucial for the stable function of the memory devices. We observe the existence of an optimum Ti thickness that if further increased gradually degrades the resistive switching behavior. The induced interface oxide thickness is found also to affect the fluctuation of the ON/OFF processes. In terms of electrical performance self-rectifying characteristics were recorded for all samples in the both resistance states. We then demonstrate that at least five-level resistance states could be obtained by modifying the compliance current, exhibiting excellent resistance uniformity and retention capability. The results are supported by C-AFM measurements demonstrating the scaling potential of the large area device discussed above.

There is increased interest towards the application of carbon based nanomaterials to biosensors since these can be used to quickly detect presence of the toxins in food, agricultural and environmental systems. The accurate, faster and early detection of food toxins is presently very important for ensuring safety and shelf life of agricultural commodities resulting from food contamination. The carbon materials (CNTs) and recently discovered graphene have been predicted to be promising candidates in the development of electrochemical biosensor owing to their exceptionally large surface area and interesting electrochemical properties. We focus on some of the recent results obtained in our laboratories pertaining to the development of biosensors based on multi-walled carbon nanotubes and graphene for mycotoxin(aflatoxin ) detection.

A protective coating was built and assessed in order to reduce the degradation of metallic substrates caused by corrosion damage. Hence, a set of coatings with different configurations, in terms of layer arrangement, was produced by flame-spraying of composite powder (AISI 316L stainless steel coated with an α-alumina layer) onto an AISI 1018 steel substrate. In order to ensure a homogeneous dispersion of phases, a correlation was established between the operating parameters of thermal spraying (roughness and surface temperature of substrate, spraying distance, passing speed) and the splat formation. Then, corrosion damage caused in the coated samples by exposure to a salt spray was monitored through weight measurements and observations with optical and scanning electron microscopy. The results show that corrosion still remains in all cases; however, it proceeds at lower rates for coatings made with composite particles plus an α-alumina layer. The weight loss due to corrosion damage was reduced in approximately 94% as compared with the substrate without protection. Coating adhesion was also improved by an increased substrate roughness, with no need for an intermediate layer.

We study how the period of transient thermal gradient impacts on morphologies of nanostructures on the Si(001) surface. Strain-free, self-assembled nanodots as well as periodic nanowires are fabricated directly on Si(001) surfaces by applying high power laser pulses on the surface interferentially. The morphologies of the nanostructures are studied by atomic force microscopy. Generally, the laser irradiated surfaces show nanowires but nanodots are also observed. The nanowire width increases with interference period. The narrowest nanowires observed have the width smaller than 50 nm, which is four times smaller than the interference period while the nanodots have a base width of 43 nm and height of 8 nm.

Deep borehole disposal (or DBD) is now seen as a viable alternative to the (comparatively shallow) geologically repository concept for disposal of high level waste and spent nuclear fuel. Based on existing oil and geothermal well technologies, we report details of investigations into cementitious grouts as sealing/support matrices (SSMs) for waste disposal scenarios in the DBD process where temperatures at the waste package surface do not exceed ∼190ºC. Grouts based on Class G oil well cements, partially replaced with silica flour, are being developed, and the use of retarding admixtures is being investigated experimentally. Sodium gluconate appears to provide sufficient retardation and setting characteristics to be considered for this application and also provides an increase in grout fluidity. The quantity of sodium gluconate required in the grout to ensure fluidity for 4 hours at 90, 120 and 140°C is 0.05, 0.25 and 0.25 % by weight of cement respectively. A phosphonate admixture only appears to provide desirable retardation properties at 90°C. The presence of either retarder does not affect the composition of the hardened cement paste over 14 days curing and the phases formed are durable under conditions of high temperature and pressure.

Ferritic stainless steels are widely used in transportation industry due to their exceptional performance regarding mechanical and corrosion properties. However, after a welding process, joints feature the sensitizing phenomenon because of the heat exchange from the torch affecting mechanical properties and corrosion resistance. This work describes the behavior firstly of mechanical properties of weld joints of ferritic stainless steel as base material without and with filler material (AISI 308L) by gas tungsten arc welding (GTAW). Operating parameters such as arc voltage, welding currrent, welding speed, feed speed, shielding gas flow were evaluated. Secondly, samples of weld joints were coated by flame spraying of composite particles in order to reduce the weight loss induced by corrosion in a salt spray (fog) apparatus. Changes induced from GTAW on the heat affected zone and Thermal Spraying on corrosion resistance, were monitored by optical and scanning electron microscopy, microhardness and longitudinal tensile testing. Results show that GTAW helps to control the size and the microstructure of heat affected zone improving simultaneously the mechanical properties. Meanwhile, welded joints covered by composite coatings feature a lower damage provided that the ceramic phase has been homogeneously dispersed.

Biomolecules have been traditionally immobilised onto surfaces using wet chemical techniques for various medical applications. Recent decades have seen plasma methods being used to prepare these surfaces through various forms of surface modification, but the direct exposure of biomolecules to plasma has been avoided due to fears that the molecules would be denatured by the energetic plasma species. Recent results are now demonstrating that direct plasma deposition of biomolecule coatings can be achieved. This creates the possibility to directly modify the surface of implants without any form of surface pre-treatment and this opens up the possibility to alter the healing processes. Materials such as collagen, chitosan, catalase and heparin can be effectively deposited onto surfaces with minimal impact on biological performance and without any chemical binders, linkers or impurities. The performance of these materials has been characterised using both in vitro and in vivo methodologies. In a further step, the results of a preclinical trial are presented which reveal that direct deposition of biomolecules onto open wounds can also be achieved and the impact of this on wound healing is measured in an immunocompromised animal model. A non-thermal plasma device was used to deliver collagen on to chronic wounds and the treatment was shown to promote wound closure in a rabbit wound healing model.

The reaction mechanism of BaCO3+CaCO3+TiO2 by solid state methods has been studied in this work using thermal analysis (DSC-TG) from 500 to 1500 °C and in situ X-ray diffraction (XRD) from room temperature to 800 °C. In the mixed powders, the CaO is firstly formed followed by presence of an intermediate Ba2TiO4 phase and finally the formation of CaTiO3, BaTiO3 and/or (Ba,Ca)TiO3, where the presence of CaO or CaTiO3 (CT) has slowed down the formation of BaTiO3 (BT). Raman microscopy of a BT-CT diffusion couple has shown that Ca2+ firstly diffuses into the BT grain boundaries and then into the BT core.

The insertion of reprocessed fuel spiked with thorium in a typical PWR fuel element considering (TRU-Th) cycle was simulated using different fissile materials that varied from 5.5% to 7.0%. The reprocessed fuels were obtained using the ORIGEN 2.1 code from a burned PWR standard fuel (33,000 MWd/tHM burned), with 3.1% of initial enrichment, which was remained in the cooling pool for five years and then reprocessed using UREX+ technique. The kinf, hardening spectrum and the fuel evolution during the burnup were evaluated. This study was performed using the SCALE 6.0

Undoped and Li-doped ZnO films were fabricated by screen printing approach on sapphire substrate. The effect of Li doping and annealing temperature on the luminescent, optical, electrical and structural properties of the films has been investigated by the photoluminescence (PL), Raman scattering, conductivity, Atomic Force microscopy and X-ray diffraction (XRD) methods. The XRD study revealed that the films have polycrystalline wurtzite structure with grain sizes ranging from 26 to 38 nm. In the undoped ZnO films, the increase of annealing temperature from 800 to 1000 °C resulted in the increase of the grain sizes, film conductivity and the intensity of the ultraviolet PL. The introduction of Li of low concentration of 0.003 wt % at 800 °C or 900 °C allows producing the low-resistive films with enhanced ultraviolet PL and reduced density of crystalline defects. Highly doped films (with 0.3 wt % of Li) were found to be semi-insulating with deteriorated PL properties irrespectively of the annealing temperature. It is shown that introduction of Li in the ZnO films affects their PL spectra mainly via the evolution of the film crystallinity and the density of intrinsic defects.

Anatase titania has been widely used for several applications such as photocatalysis and solar cells. Sol-gel is a conventional route to obtain amorphous titania and, either post-annealing or a post-hydrothermal treatment are necessary to obtain anatase crystalline phase. It is well known that the synthesis conditions affect in the particle size, surface area and grain size of the titania. In this work regular nanoparticles of anatase titania (TiO2) were obtained by an easy ultrasound-assisted synthesis; the nanoparticles were undergone to either a hydrothermal treatment at 130 °C and/or to an annealing at 450°C. Nanoparticles powder with a crystal size of about 8-10 nm were re-dispersed in aqueous solution at different concentrations (5 to 20mg/mL). Poly (3-hexylthiophene) (P3HT) microfibers were immersed into the TiO2 nanoparticles solution for 24 h and they were dried at 80°C for 1 h in order to form the bulk heterojunction. P3HT:TiO2 heterojunctions were characterized by SEM and EDS. According to SEM results at low concentration (5 mg/mL), the covering of the P3HT microfibers is poor and at high concentration (20 mg/mL) the microfibers were seen cracked. The best homogeneous covering onto the P3HT microfibers was obtained at 10mg/mL of titania nanoparticles; it could be the optimal concentration to build bulk heterojunction for hybrid solar cells.

In this study, thiol-epoxy polymer composites are explored as candidates for high-temperature die attach applications. We present a polymer composite processing technique for die attach adhesives with low cure-stress. Lap shear samples of both a polymer adhesive and current industry adhesives were subjected to tensile testing and die shear strength was compared. At 260 °C, the candidate polymer adhesive exhibited a die shear strength of 0.500 MPa in comparison with 1.35 MPa and 0.258 MPa for two control adhesives. While samples showed less variation in properties in die shear strength between room temperature and 260 °C, the absolute die shear strength values were inferior to commercial adhesives at both room and elevated temperatures. We hypothesize that low cure stress networks, such as the thiol-epoxies presented, provide a compelling choice to engineer new die attach adhesives, but realize that further network refining is needed including the addition of adhesion promoters and other additives, a task better suited to industrial research with a focus in properties optimization.