The isothermal oxidation-sulfidation of Fe-40Al based intermetallics alloys in N2/SO2 gas mixture at 625, 700 and 775°C were evaluated. Fe40Al, Fe40Al+0.1B, Fe40Al+0.1B+10Al2O3 alloys were produced by atomization and deposition. Isothermal gas exposition was reached during 48 hours. FeAl based alloys showed good sulfidation resistance, presenting both small weight gain and weight change fluctuations. At 625°C, the Fe40Al+0.1B alloy had the biggest weight gain; on the other hand the Fe40Al alloy exhibited the biggest sulfidation resistance. At 700 and 775°C, the Fe40Al+0.1B alloy presented the smallest weight gain, however Fe40Al alloy presented higher weight gain, that is to say, the smallest sulfidation resistance at those temperatures. The variation in the weight gain curves were discussed in terms of formation and detachment of sulfides, and by local attack on the alloy surface as the temperature increasing. The results are supplemented with characterization by SEM and analysis of X-rays dispersion.

To obtain highly dispersed and highly active catalysts by impregnating of active species onto the monolith directly, cordierite honeycomb ceramics were modified by nitric acid solution of 68wt%. Effects of acid treatment temperature and time on the performance of cordierite were investigated. Specific surface area, pore size distribution, morphology and structure of cordierite were characterized by N2-physical adsorption, SEM, XRD, respectively. Concentrations of ions in the acid solution were measured by AAS. It is shown that the corrosion content of cordierite increases and more micropores are generated with increasing time of acid treatment, leading to an upward trend of specific surface area. The coefficient of thermal expansion and compression strength decrease obviously at a higher temperature, which is mainly attributed to the removal of Al and Mg ions from the silicate structure and delayed formation of free amorphous silica on the surface of the cordierite. The optimal modification process of cordierite matrix acid erosion is at 110°C for 6 h.

Gallium nitride (GaN) is a robust piezoelectric semiconductor with excellent thermal and chemical stability, making it an attractive material for surface acoustic wave (SAW) sensors operating in high temperature and harsh environments. The sensitivity of SAW devices is proportional to the square of the operating frequency. Therefore, high operating frequencies into the GHz regime are desirable for SAW sensors. For GaN, this requires sub-micron interdigital transducers (IDTs) when devices are designed to operate at the fundamental Rayleigh mode frequency. The necessity for sub-micron IDTs can increase fabrication costs and complexity. By designing SAW devices to operate at harmonic frequencies, GHz operation can be realized with relatively large IDTs, resulting in simpler and more cost effective solutions for GaN based SAW sensors. Devices have previously been designed to operate at the 5th and higher harmonics on lithium niobate, but there are no reports of using this technique on GaN in the literature. In this study, GaN thin films have been grown via metal organic vapor phase epitaxy on sapphire substrates. SAW devices designed to operate at the fundamental frequency and higher harmonics have been fabricated and measured. Operating frequencies greater than 2 GHz have been achieved using IDTs with 5 μm fingers. In addition, reduction of electromagnetic feedthrough around the 5th and 7th harmonic is demonstrated through varying ground electrode geometries.

A triple-shape material based on the two crystallizable segments poly(ω‑pentadeca-lactone) and poly(ε-caprolactone) was synthesized by crosslinking star-shaped precursors. A newly developed programming procedure (TSCP2) was applied in order to achieve triple-shape behavior. The application of this modified triple-shape creation procedure enabled triple-shape capability by influencing the crystallization behavior of the two switching segments in these copolymer networks, which partly show no two distinct and separated melting points. The influence of molecular weight and content of the poly(ε-caprolactone) segment on the triple-shape effect programmed by application of TSCP2 was investigated.

We describe a scalable synthesis process for the production and patterning of polymer matrix nanocomposites (PMNCs) using femtosecond laser irradiation to target specific functional behaviors. A modified, in situ chemical vapor deposition (CVD), nanoinfusion process was used to nucleate and grow nanoparticles in the bulk of an optically transparent polytetrafluoroethylene-co-hexafluoropropylene (FEP) polymer matrix. Metallic nanoparticles synthesized with this process can have a strong optical absorption at their surface plasmon resonance (SPR) frequency and we have utilized this property to selectively irradiate and pattern nanocomposites via femtosecond, photothermal heating. If the nanoparticle environment includes species used for chemical vapor deposition, the heat causes a localized decomposition of the precursor species in the immediate vicinity of the nanoparticle leading to a variety of core-shell nanostructures. Using this processing scheme, we have grown shells of tungsten oxide around silver nanoparticles within the polymer matrix resulting in a 40 nm red shift in the SPR of the silver nanoparticles in regions of the material exposed to femtosecond laser pulses. This process has also been adapted to polymers containing tungsten oxide nanoparticles so that the photocatalytic behavior of the particles could be used to the decompose precursor species in the immediate vicinity of the irradiated nanoparticles. These results demonstrate that, by using optical masks and laser processing, it is possible to synthesize nanocomposites with a high degree of control over the location, composition, size, and distribution of nanoparticles within a polymer matrix resulting in patterned materials with tailored electrical, optical, and photocatalytic properties.

We suggest a new method for fabricating diamond nanoclusters by employing a coaxial arc plasma gun. Diamond powder comprised of diamond nanoclusters and amorphous carbon was fabricated in vacuum and a hydrogen atmosphere, and the diamond crystallite sizes were estimated to be 1.8, 2.3, and 2.3 nm for the powders prepared at hydrogen pressures of 0, 53.3, and 159.6 Pa respectively, from the X-ray diffraction peaks. The hydrogen ambient gas is not necessarily required for the diamond nanoclusters formation. We consider that this method enables us to form diamond nanoclusters in nucleation owing to a supersaturated condition at a facing plate located in front of an arc plasma gun.

Thermal stability, hydration and mechanical properties of thermally cross-linked Sulfonated Aromatic Polymers (SAP) with high ionic exchange capacity (IEC) were measured and compared to untreated samples. The formation of cross-linking greatly stabilizes SAP in terms of thermal, mechanical, and hydrolytic degradation: they can resist in water even at a temperature of 145 °C with improved mechanical properties. Acid-base titration and FTIR spectra consistently indicate that SAP microstructure stabilization is related to cross-linking of the polymer chains by SO2 bridges, which is promoted by temperature.

We demonstrate the highly reflective broadband a-Si distributed Bragg reflector fabricated by oblique angle deposition. By tuning the refractive index of a-Si film, the high index contrast material system was achieved. The broadband reflective characteristics of a-Si distributed Bragg reflector were investigated by calculation and fabrication. The broad stop band (Δλ/λ=33.7%, R>99%) with only a five-pair a-Si distributed Bragg reflector was achieved experimentally at center wavelength of 650, 980, and 1550 nm. The size-, feature- and substrate-independent method for highly reflective Bragg reflectors was realized by simple oblique angle evaporation.

A water-based BaTiO3 precursor solution, suited for ink-jet printing of hetero-epitaxial BaTiO3 layers on LaAlO3 single-crystal substrates was developed. First, a study on the simultaneous stabilization of Ba2+ and Ti4+ions in a neutral, aqueous environment was performed. Thermal analysis of the precursor was used to select appropriate temperature programs and the rheology of the solutions is studied to optimize dipcoating and later ink-jet printing parameters. On both substrates, it was possible to obtain epitaxial layers of about 200 nm thickness after sintering at temperatures above 1000 °C. Currently, we are adapting the thermal program and heating atmosphere in order to reduce the sintering temperatures, decrease the surface roughness and increase density.

The unique structure and properties of graphene initiated broad fundamental and technological research, and highlighted graphene as a new candidate for various applications such as energy storage, solar cells and electronic devices. Chemical vapor deposition (CVD) has been utilized for industrial large-scale synthesis of graphene. Regardless of the synthesis process, graphene should be transferred to arbitrary substrates for different applications. The transfer processes, introduce defects such as wrinkles and cracks in graphene which compromise the properties and applications. In recent years, fundamental research has been focused on characterization of graphene to develop new techniques for large-scale, high-resolution graphene metrology. Herein, a complementary high throughput metrology technique using fluorescent quenching is further investigated for different fluorescent dyes to characterize CVD synthesized graphene.

Physical properties of filaments in Cu/HfO2/Pt conducting-bridge memory (CB-RAM) were investigated basing on direct observation by conducting atomic force microscopy (C-AFM) and energy dispersive X-ray spectroscopy (EDS), R-T characteristics until liquid nitrogen temperature, and I-V characteristics both in air and in vacuum. As a result, physical picture of filaments in Cu/HfO2/Pt structures was revealed. Filaments consist of Cu containing large residual resistance and the cross-sectional area of the filament, S fila, was roughly proportional to set voltage, V set, even when current compliance was kept constant. Interestingly, resistivities of filaments are same among all the filaments in different samples and are invariant even after repetitive switching that changes resistance of the filaments. Cu/HfO2/Pt obeyed the universal relation that reset current, I reset, is proportional to the inverse of resistance in a low resistance state, 1/R LRS, which is known to be applicable to oxygen-migration-based resistive switching memories such as Pt/NiO/Pt. Considering the invariance of resistivity of the filament, this suggests the fact that I reset is decided dominantly by S fila. In addition, it was suggested that moisture is necessary for dissolution and migration of Cu to form filaments.

The nanocrystalline molybdenum oxide embedded Zr-doped HfO2 high-k nonvolatile memory device has been fabricated using the one pumpdown sputtering process and a rapid thermal annealing step. The majority embedded molybdenum existed in the MoO3 nanocrystal form but a small amount of metallic molybdenum was also detected. The memory function of this device was based on the hole trapping-and-detrapping mechanism. The embedded nanocrystals retained charges after the breakdown of the high-k stack. The charge storage capacity was influenced by light exposure, especially the wavelength. The silicon/high-k interface was also affected by the exposed light. This study provided an insight of the function of the embedded nanocrystals and the light effects on the device.

SiO2-Al2O3-Y2O3 glasses exhibit high glass transition temperatures, water corrosion resistance and good mechanical properties. These properties suggest that yttrium aluminosilicate glasses could potentially replace the borosilicate glasses usually used for immobilization of nuclear wastes. At the same time, yttrium can be used to simulate actinides.

During waste immobilization, crystallization of the glassy matrix must be avoided or at least controlled, thus, the understanding of glass crystallization kinetics is essential.

We found by XRD that the crystalline phases present on heat treatments are yttrium disilicate and sillimanite/mullite. By optical microscopy on polished cross-sections we could only identify highly yttrium enriched crystals which we associate with yttrium disilicate crystals.

In this paper we measure the surface density of nucleation sites Ns in as obtained splat cooled pieces obtaining values of about 1.5 · 1011 nucleus · m-2. Crystal growth rate U in the temperature range 1000-1040 o C varies in the range 8-13 μm · h-1. These data are useful for designing sintering or melting thermal paths of YAS glasses in order to control their microstructure. We show the effect of glass particle size on DTA results: crystallization peaks moves towards lower temperatures for smaller particle size, which confirms that mainly surface nucleation is taking place on heating.

A set of hot rolled 7xxx aluminum alloys with modification of processing conditions were analyzed on their fatigue life time as well as the internal microstructure using 3D computed X-ray tomography with a lab scale scanner and optical microscopy. It is shown that for conventional hot rolling conditions many large (>300μm) casting pores were retained in the material. With modifications of the rolling conditions the size and density distribution of the retained casting pores were significantly reduced, leading to greatly improved fatigue life times.

Using advanced first-principles calculations, we have studied the structural and electronic properties of graphene/α-Al2O3 interfaces and show that α -Al2O3 is an ideal gate dielectric material for graphene transistors. Clean interface exists between graphene and Al-terminated (or hydroxylated) Al2O3 and the valence band offsets for these systems are large enough to create injection barrier. Remarkably, a band gap of ~180 meV can be induced in graphene layer adsorbed on Al-terminated surface, which is significantly larger than graphene on other popular substrates.

In this work, we have studied the structure and mechanics of fish scales from striped bass (Morone saxatilis). This scale is about 200-300 μm thick and consists of a hard outer bony layer supported by a softer cross-ply of collagen fibrils. Puncture tests with a sharp needle indicated that a single fish scale provides a high resistance to penetration which is superior to polystyrene and polycarbonate, two engineering polymers that are typically used for light transparent packaging or protective equipment. Under puncture, the scale undergoes a sequence of two distinct failure events: First, the outer bony layer cracks following a well defined cross-like pattern which generates four “flaps” of bony material. The deflection of the flaps by the needle is resisted by the collagen layer, which in biaxial tension acts as a retaining membrane. Remarkably this second stage of the penetration process is highly stable, so that an additional 50% puncture force is required to eventually penetrate the collagen layer. The combination of a hard layer that can fail in a controlled fashion with a soft and extensible backing layer is the key to the resistance to penetration of individual scales.

We report a study of InGaN and InAlN epilayers grown on GaN/Sapphire substrates by microfocused three-dimensional X-ray Reciprocal Space Mapping (RSM). The analysis of the full volume of reciprocal space, while probing samples on the microscale with a focused X-ray beam, allows us to gain uniquely valuable information about the microstructure of III-N alloy epilayers. It is found that “seed” InGaN mosaic nanocrystallites are twisted with respect to the ensemble average and strain free. This indicates that the growth of InGaN epilayers follows the Volmer-Weber mechanism with nucleation of “seeds” on strain fields generated by the a-type dislocations which are responsible for the twist of underlying GaN mosaic blocks. In the case of InAlN epilayer formation of composition gradient was observed at the beginning of the epitaxial growth.

In this work, we study the effects of implanted hydrogen ions on defect formation and impurity redistribution in ZnO crystals implanted with silver ions. Hydrogen was first implanted at room temperature in ZnO with energy of 30 keV to a dose of 2 × 1016 /cm2. The ZnO samples with and without prior H implantation were implanted with Ag ions at four different energies, 30, 75, 150, and 350 keV, to doses 3.3×1013, 4.2×1013, 8.3×1013 and 3.4×1014 /cm2, respectively, resulting in a uniform concentration profile of Ag from the surface to depth ~ 150 nm. These samples were annealed at temperatures 850-1050°C for 30 minutes in an oxygen gas flow. The distribution of Ag atoms, either aligned or nonaligned along the crystalline directions, were measured by Rutherford backscattering (RBS) combined with ion channeling. Following Ag ion implantation, the damage level in the ZnO lattice, measured along the <10-11> crystalline direction is higher in the sample without H ion implantation than the sample with H. Lattice damage was found to recover faster in the sample without H implantation than the sample with H, e.g., for Zn signals, the normalized RBS yield χmin for the without H-implanted sample dropped from 27.5% following Ag implantation to 4.3% after annealing at 1050 ˚C, whereas the Zn χmin value for the sample with H implant decreased from 17.6% following Ag implantation to 5.3% after annealing at 1050 ˚C. On the other hand, the χmin values for the Ag dopants before annealing in the H-implanted sample are the same in the sample without H. Post-Ag-implantation annealing resulted in much higher χmin values for Ag in the sample with H implant. For the as-implanted samples, 26.6% of the implanted Ag atoms are on substitutional sites in the sample with H, as compared to 30.3% of the implanted Ag being on the substitutional sites in the sample without H. After annealing at 1050 ˚C, the fraction of substitutional Ag is 73.7% in the H-implanted sample, in contrast to the fraction of 61.6% for substitutional Ag in the sample without H implant. Similar to other oxide crystals, H ion implantation and thermal annealing can result in the formation of nanocavities in the ZnO lattice. We discuss these findings in the context of the effects of nanocavities on formation and annihilation of point defects as well as on impurity diffusion and trapping in ZnO crystals.

Natural materials have often a defined multilevel hierarchy which governs their macroscopic mechanical properties. Cork, sponge and bone are only a few examples. These materials are generally heterogeneous and can exhibit a cellular pattern, i.e. a partition of a solid with voids, at multiple levels of the structural hierarchy. It is well known that the arrangement of the voids plays a major role in the overall performance of the material. Furthermore, it has been demonstrated that the nesting of cellular patterns at different levels confers remarkable mechanical properties to the structure.

This paper presents a multiscale approach to the analysis of a hierarchical structure which exhibits nested levels of lattice, i.e. regular periodic patterns of voids occur at different length scales. A number of three-dimensional topologies as well as the effect of lattice geometry parameters have been investigated. The results of the analysis are plotted onto material property charts. The visualization of the properties helps gain insight into the contribution that each hierarchical layer imparts to the overall properties of a component hierarchically structured with lattice materials.

Anodic aluminum oxide (AAO) membranes were fabricated in a mild two-step anodization procedure. The voltage was varied during both anodization steps to control the pore size and morphology of the AAO membranes. Pore sizes ranged from 34 nm to 117 nm. Characterization of the pore structure was performed by scanning electron microscopy (SEM). To assess the potential of the AAO membranes as a neuronal differentiation platform, C17.2 neural stem cells (NSCs), an immortalized and multipotent cell line, were used. The NSCs were forced to differentiate via serum-withdrawal. Cellular growth was characterized by immunocytochemistry (ICC) and SEM. ImageJ software was used to obtain phenotypic cell counts and neurite outgrowth lengths. Results indicate a highly tunable correlation between AAO nanopore sizes and differentiated cell populations. By selecting AAO membranes with specific pore size ranges, control of neuronal network density and neurite outgrowth length was achieved.