We report a low cost and high throughput electrochemical anodic oxidation method to enhance the metal-semiconductor contact between a silver electrode and an organic semiconductor in a rectifying diode application. The oxidized layer enhances the contact properties, leading to better device performance. Three different anodic oxide thicknesses were used in the study. Current-voltage and AC rectification measurements were used to characterize the printed devices. The DC output voltage of the half-wave rectifier increased consistently as a function of the oxide thickness. This procedure points toward a cost-effective way to optimize printed organic devices.

Silicon carbide power devices are purported to be capable of operating at very high temperatures. Current commercially available SiC MOSFETs from a number of manufacturers have been evaluated to understand and quantify the aging processes and temperature dependencies that occur when operated up to 350°C. High temperature constant positive bias stress tests demonstrated a two times increase in threshold voltage from the original value for some device types, which was maintained indefinitely but could be corrected with a long negative gate bias. The threshold voltages were found to decrease close to zero and the on-state resistances increased quite linearly to approximately five or six times their room temperature values. Long term thermal aging of the dies appears to demonstrate possible degradation of the ohmic contacts. This appears as a rectifying response in the I-V curves at low drain-source bias. The high temperature capability of the latest generations of these devices has been proven independently; provided that threshold voltage management is implemented, the devices are capable of being operated and are free from the effects of thermal aging for at least 70 hours cumulative at 300°C.

Transmission electron microscopy has been used to investigate the morphological development of the perovskite (P-) Ti3AlC carbides in the γ matrix of a Ti-45Al-5Nb-0.75C alloy during annealing. P-Ti3AlC carbides in the γ matrix initially have a needle-like shape but during annealing at 800 °C they change to a plate-like shape. In the needle-like shape the carbides are orientated parallel to the [001] direction of the matrix. They extend along the [100]γ or [010]γ direction into plates later and subsequently split into sub particles after extended annealing. It is proposed that the elastic interaction energy between the split sub domains may be the reason that this decomposition into sub-particles is energetically favorable.

Calcium sulfide (CaS) nanoparticles are cadmium free fluorescent nanostructures with potential applications in nanomedicine and photovoltaic cells. We report on the synthesis and optical properties of CaS nanoparticles prepared by the reaction of Ca(CH3CO2)2 and DMSO in a microwave. The absorption spectra of CaS prepared from this method consists of a well-defined peak in the UV and a long wavelength tail that extends above 700 nm. Emission bands centered at around 500 nm with a long wavelength tail that extends above 600 nm are observed upon excitation at 405 nm. STM measurements reveal the formation of CaS nanoparticles with an average diameter of (3.2 ± 0.7) nm. The direct and indirect band gaps are estimated to be (0.403 ± 0.003) eV and (4.135 ± 0.006) eV, respectively. Theoretical calculations on small CaS clusters are used to establish the physical properties of calcium sulfide nanoclusters, including the optical absorption spectra. Unique to CaS nanostructures is the absorption of light at wavelengths longer that in the bulk material instead of the blue shift associated with quantum confinement effects in semiconductors. Indeed, the strong absorption bands in the visible region of the spectra of the CaS nanostructures do not have a counterpart in the gas or solid phases. The optical absorption spectra are proposed to have a significant contribution from indirect transitions which are discussed in terms of the dispersion of the phonon frequency.

In the present work, we report the synthesis and characterization of NaNbO3 particles obtained by microwave-assisted hydrothermal method from Nb2O5 and NaOH. The synthesis was made at different periods at 180 °C and 300W. The crystallization of NaNbO3 structures produced Na2Nb2O6.H2O in the intermediate phase with fiber-like morphology, and this is associated with the synthesis time. Pure orthorhombic NaNbO3 with cube-like morphology originates after synthesizing for 240 minutes. To verify the remnant polarization of particles, films were obtained by electrophoresis process and sintered at 800°C for 10 minutes in a microwave furnace. The films characterization indicated that films of niobate with fiber-like morphology present remaining polarization, and the morphology of cubes did not show remaining polarization. Considering these results, it can be concluded that the morphology implemented ferroelectric property of NaNbO3.

A novel process for the formation of pairs of opposing metallic nanotips within linear trenches on a silicon wafer is investigated in detail. The process is based on a spreading knife technique typically used in nanosphere lithography to generate monolayers of colloidal polystyrene beads. Here it is applied to initiate self-assembly of spheres in long linear trenches acting as a template for the sphere arrangement. The optimum blade velocity to deposit the spheres selectively and densely packed in the trench depends on the trench surface fraction and can be described by a modified Dimitrov model. It is demonstrated that the spheres can be used as a shadow mask to deposit metallic nanotips in a channel, which are electrically interconnected on each side of the trench, possibly enabling the control and manipulation of nanoobjects in the channel.

The condensation of hydrazides with aldehydes has been found to be a simple and rapid method for synthesizing catechol-terminated coating reagents for magnetite nanoparticles. This approach allowed the production of biotin- and polyethylene glycol-functionalized nanoparticles, whose interaction with 3T3 fibroblast cells has been assessed. The cellular location of these nanoparticles was imaged by fluorescence microscopy, which was made possible by co-coating with a porphyrin-catechol conjugate. Images show significant interactions between biotinylated nanoparticles and 3T3 fibroblasts, but those with a polyethylene glycol coating did not interact.

A MEMS floating element shear stress sensor has been developed for flow testing applications, targeted primarily in ground and flight testing of aerospace vehicle and components. However, concerns remain about the interaction of the flow with the mechanical elements of the structure at the micro-scale. In particular, there are concerns about the validity of laminar flow cell calibration to measurement in turbulent flows, and the extent to which pressure gradients may introduce errors into the shear stress measurement. In order to address these concerns, a numerical model of the sensor has been constructed.

In this paper, a computational fluid dynamics (CFD) model is described. The CFD model directly models a laminar flow cell experiment that is used to calibrate the shear sensor. The computational model allows us to quantify the contributions (e.g. pressure gradient vs. shear, top surface vs. lateral surfaces) to the sensor output in a manner that is difficult by purely experimental means. The results are compared to experimental data, validating the model and resulting in the following: Surface shear stress contributes approximately 40% of the total flow direction force; pressure gradient effects contribute nearly 45% for the textured shuttle described here; lift forces and pitching moments are non-zero. Thus, it is found that flow interactions are complex and that it is insufficient to simply assume that flow forces on the sensor are the top area multiplied by wall shear, as is sometimes done. Pressure gradient effects, at least, must be included for accurate calibration.

Regenerative engineering was conceptualized by bridging the lessons learned in developmental biology and stem cell science with biomaterial constructs and engineering principles to ultimately generate de novo tissue. We seek to incorporate our understanding of natural tissue development to design tissue-inducing biomaterials, structures and composites than can stimulate the regeneration of complex tissues, organs, and organ systems through location-specific topographies and physico-chemical cues incorporated into a continuous phase. This combination of classical top-down tissue engineering approach with bottom-up strategies used in regenerative biology represents a new multidisciplinary paradigm. Advanced surface topographies and material scales are used to control cell fate and the consequent regenerative capacity.

Musculoskeletal tissues are critical to the normal functioning of an individual and following damage or degeneration they show extremely limited endogenous regenerative capacity. The increasing demand for biologically compatible donor tissue and organ transplants far outstrips the availability leading to an acute shortage. We have developed several biomimetic structures using various biomaterial platforms to combine optimal mechanical properties, porosity, bioactivity, and functionality to effect repair and regeneration of hard tissues such as bone, and soft tissues such as ligament and tendon. Starting with simple structures, we have developed composite and multi-scale systems that very closely mimic the native tissue architecture and material composition. Ultimately, we aim to modulate the regenerative potential, including proliferation, phenotype maturation, matrix production, and apoptosis through cell-scaffold and host –scaffold interactions developing complex tissues and organ systems.

We discuss methods to describe the evolution of dislocation systems in terms of a limited number of continuous field variables while correctly representing the kinematics of systems of flexible and connected lines. We show that a satisfactory continuum representation may be obtained in terms of only four variables. We discuss the consequences of different approximations needed to formulate a closed set of equations for these variables and propose a benchmark problem to assess the performance of the resulting models. We demonstrate that best results are obtained by using the maximum entropy formalism to arrive at an optimal estimate for the dislocation orientation distribution based on its lowest-order angular moments.

A new peptide amphiphile (PA) called C16-W3K has hierarchical structures, presenting unique solution states, micelle structures, and secondary structures. In this work, the effects of salt (sodium dihydrogenorthophosphate) concentration on the hierarchical structural transitions of the C16-W3K solution due to its active hydrogen bonding in the peptide were discussed. In order to analyze the effects of salt on the structural transitions, the mechanical and structural analyses were conducted by viscosity measurements, transmission electron microscopy (TEM), and circular dichroic (CD) spectroscopy. It was found that the C16-W3K solutions with different salt concentrations presented different multi-scale structural transitions from spherical micelles with α-helix molecular conformations in the sol state to wormlike micelles with β-sheet conformations in the gel state. Additionally, we found that the speed of transition increased as the salt concentration increased and the conformational ratio of β-sheet to α-helix in the solutions increased with the increase in the salt concentration.

We report a study on the wetting and spreading of hydrazine-CZTS solution on a series of solid surfaces. The work of adhesion between a hydrazine solution and soda-lime glass, Si, graphite, ITO, SnO2, ZnO, CdS, In2S3, Cu, Au, Ag, Al, Ni, Mo, and carbon single-walled nanotubes was calculated using observed contact angles and the areas of the interface. The surface roughness of drop-casted CZTS precursor films was lower on surfaces with better hydrazine wettability. This suggests that the surface roughness of solution-processed films can be controlled by altering the wetting behavior of the solution on the substrate.

The synthesis of hexadecylamine capped (HDA) CdTe and PbTe via a simple hybrid solution based high temperature route is described. In this method the tellurium is first reduced to form the telluride salt followed by reaction with the metal salt and finally thermolysis in a coordinating solvent. The metal salt and reaction temperature played an important role in the morphology and growth mechanism of the particles. The CdTe particles where in the form of rods and spheres whereas the PbTe nanoparticles were in the form of nanowires. The oriented attachment mechanism is proposed for the growth of elongated particles under certain reaction conditions.

Core-shell quantum dots (QDs) with enhanced photostability compared with bare QDs are promising light absorbers for solar cell applications. In this work, electron injection from excited CdSe/ZnS QDs to Zinc Oxide (ZnO) nanowires (NWs) prepared by two techniques were demonstrated. Arrays of ZnO NWs were fabricated by hydrothermal growth and etching. ZnO NWs were sensitized with hydrophobically ligated colloidal CdSe/ZnS QDs. The electron transfer dynamic in QD/ZnO NW architecture was examined using photoluminescence (PL) and decay lifetime analyses. The quenching of the QD emission peak and lowered average lifetime in QD/ZnO NW architecture confirms the deactivation of the excited QDs via electron transfer to ZnO NWs. Electron transfer was enhanced by using smaller QDs. This study provides insight on charge transfer dynamics at the QD/ZnO NW interface in order to engineer high performance quantum dot sensitized solar cells (QDSSCs).

In this work high-temperature X-ray diffraction has been used to investigate thermal and chemical expansion as well as overall phase stability for various cathode materials: Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF), La0.3Sr0.7CoO3 (LSC37), La0.6Sr0.4CoO3 (LSC64) and La0.6Sr0.4Fe0.8Co0.2O3 (LSCF), as a function of temperature in reducing conditions. When perovskites materials are under a low oxygen partial-pressure condition, the lattice parameter and overall dimension increase. Their chemical expansion has comparable values. From the viewpoint of the stability of these phases, the high-temperature X-ray diffraction results indicate no phase decomposition can be one of the reasons for material failure at the current experimental oxygen partial pressure. LSF is most stable, while LSC and LSCF form oxygen vacancy-ordered phases and then decompose when heated to 1000°C under atmospheres with pO2 as low as 10-5 atm.

Zirconolite (CaZrTi2O7), a durable and compositionally flexible titanate ceramic for the immobilization of separated actinides, is currently the UK’s preferred candidate phase for the immobilization of plutonium dioxide arising from aqueous reprocessing. Here, its suitability as a waste-form for actinide chlorides arising from pyrochemical reprocessing is investigated through synthesis via a molten salt mediated reaction using a number of different salt eutectics (MgCl2:NaCl, CaCl2:NaCl and KCl:NaCl). It is found that the effectiveness of the molten salt synthesis of zirconolite is governed by the solubility of ZrO2 in the salt medium used; the synthesis proceeding via the formation of a perovskite (CaTiO3) intermediate which then reacts with ZrO2 to form zirconolite via a solution-diffusion mechanism. Most notably, in the KCl:NaCl eutectic different zirconolite polytypes are formed at different synthesis temperatures, with zirconolite-3T forming at 900 °C, giving way to zirconolite-2M at 1200 °C.

A RF magnetron sputtering method was used to prepare Mg2Si films at 300-400oC on (001) Al2O3 substrates from a Mg disc target with Si chips. Mg deposition was not detected at 400°C from a pure Mg disc target without Si chips due to the high vapor pressure of Mg. However, the amount of Mg deposition increased with the increase in Si/(Mg+Si) area ratio of the target surface together with the increase of the Si deposition. The obtained films had a stoichiometric composition of Si/(Mg+Si)=0.33 that consisted of the well crystalline Mg2Si single phase regardless of Si/(Mg+Si) area ratio of the target surface. This showed the existence of a “process window” against supply ratio of Si/(Mg+Si) for Mg2Si single phase films with a stoichiometric composition. This is considered to be due to the vaporization of the excess Mg prepared under the Mg excess condition as reported by Mahan et al. for Mg2Si films prepared at 200°C by ultra-high vacuum evaporation.

This is a preliminary report of a neutron scattering experiment used to investigate 4f electron behavior in Ce.