An optimization technique is coupled with crystal plasticity based finite element (CPFE) computations to aid the microstructural design of a wrought magnesium alloy for improved strength and ductility. The initial microstructure consists of a collection of sub-micron sized grains containing deformation twins. The variables used in the simulations are crystallographic texture, and twin spacing within the grains. It is assumed that plastic deformation occurs mainly by dislocation slip on two sets of slip systems classified as hard and soft modes. The hard modes are those slip systems that are inclined to the twin planes and the soft mode consists of dislocation glide along the twin plane. The CPFE code calculates the stress-strain response of the microstructure as a function of the microstructural parameters and the length-scale of the features. A failure criterion based on a critical shear strain and a critical hydrostatic stress is used to define ductility. The optimization is based on the sequential generation of an initial population defined by the texture and twin spacing variables. The CPFE code and the optimizer are coupled in parallel so that new generations are created and analyzed dynamically. In each successive generation, microstructures that satisfy at least 90% of the mean strength and mean ductility in the current generation are retained. Multiple generation runs based on the above procedure are carried out in order to obtain maximum strength-ductility combinations. The implications of the computations for the design of a wrought magnesium alloy are discussed. Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.

Skutterudites are known to be efficient thermoelectric (TE) materials in the temperature range from 600 K to 900 K. Dimensionless figure of merit (ZT) for filled skutterudite TE materials have been reported as ca. 1 at 800 K. Novel nano- engineering approaches and filling of the skutterudites crystal can further improve the transport properties and ultimately the ZT. Although classified among the promising TE materials, research on their large-scale production via bottom up synthetic routes is rather limited. In this work, large quantity of cobalt antimonide (CoSb3) based skutterudites nanopowder (NP) was fabricated through a room temperature co-precipitation precursor method. Dried precipitates were process by thermo-chemical treatment steps including calcination (in air) and reduction (in hydrogen). CoSb3 NPs were then mixed with silver (Ag) nanoparticles at different weight percentages (1%, 5% and 10% by wt) to form nanocomposites. Skutterudite NP was then consolidated by Spark Plasma Sintering (SPS) technique to produce highly dense compacts while maintaining the nanostructure. Temperature dependent TE characteristics of SPS’d CoSb3 and Ag containing nanocomposite samples were evaluated for transport properties, including thermal conductivity, electrical conductivity and Seebeck coefficient over the temperature range of 300 - 900 K. Physicochemical, structural and microstructural evaluation results are presented in detail.

Long term stability has been a crucial issue for the future applications of the solid oxide fuel cells (SOFCs). Current collectors for the cathodes have been among the most vulnerable components of the SOFCs due to their operation in oxidizing atmospheres at relatively high temperatures. Ag and Ag based LSM (lanthanum-strontium manganite) composites were studied to develop highly stable and low-cost current collectors compatible with other fuel cell components. In this study, no degradation was observed in the electrical conductivity and the porous microstructure of the Ag-LSM composite current collectors after 600 hours of operation at 800oC in air.

A high-throughput methodology is applied for the discovery and optimization of novel catalyst formulations to convert readily available hydrocarbon-based JP-8 fuel directly into a lighter hydrocarbon product suitable for portable power applications utilizing LPG-powered fuel cells. In addition to catalytic cracking challenges, JP-8 cracking poses other challenges including high sulfur content (up to 3,000 ppmw) and significant concentration of aromatics, which are precursors to coking. An existing 16-channel high-throughput reactor system was modified for the JP-8 catalytic cracking studies. The catalyst support material was of primary importance in determining cracking activity. Alumina-based catalytic materials demonstrate the greatest activity for conversion of JP-8 to LPG during catalytic cracking at reactor temperatures above 600°C. This is attributed to the importance of acidic reaction sites within the structure of the catalytic support. The addition of noble metals to the alumina-based materials does not yield significant improvements in JP-8 conversion.

The selective formation of porous silicon in nanowires is observed in Si/Ge epitaxial layers along Ge layers grown by molecular beam epitaxy on a Si(100) substrate after metal-assisted chemical etching in aqueous HF-H2O2 solution. We assume that Ge layers serve as channels for a hole current out of the semiconductor to sustain the dissolution reaction. The tunnelling of holes through the potential barrier at the semiconductor surface is assumed to be the dominating mechanism of the hole transfer to the electrolyte.

RED is a technique we have developed for stand-off detection of trace explosives using infrared (IR) photo-thermal imaging [1,2,3]. RED incorporates compact IR quantum cascade lasers tuned to strong characteristic absorption bands and may be used to illuminate explosives present as particles on a surface. An IR focal plane array is used to image the surface and detect any small increase in the thermal emission upon laser illumination. We have previously demonstrated the technique at several meters to 10’s of meters of stand-off distance indoors and in field tests [4,5], while operating the lasers below the eye-safe intensity limit (100 mWcm2) [6]. Sensitivity to traces of explosives as small as a nanogram has been demonstrated. By varying the incident wavelength slightly, we can readily show selectivity between individual explosives such as TNT and RDX. Using a sequence of lasers at different wavelengths, we increase both sensitivity and selectivity. A complete detection protocol can be performed in a sub-second time domain. More recently, RED has been used to emphasize measurements with cooled detectors in addition to examining the utility of filtering the collected thermal emission signal which is rich in analyte-specific spectroscopic information. A next generation RED system and detection algorithm is being developed to take advantage of these more powerful features. This manuscript will include an overview of the approach and recent experimental results.

Change in the light-induced minority carrier effective lifetime τeff of crystalline silicon caused by rapid laser heating is reported. The top surface of n- and p-type silicon substrates with thicknesses of 520 μm coated with thermally grown SiO2 layers were heated by a 940 nm semiconductor laser for 4 ms. τeff was measured by a method of microwave absorption caused by carriers induced by 620 nm light illumination at 1.5 mW/cm2. τeff for light illumination of the top surfaces was decreased to 1.0x10-5 and 4.8x10-6 s by laser heating at 5.0x104 W/cm2 for n- and ptype 520-μm-thick silicon substrates, respectively. The decrease in τeff resulted from the generation of defect states associated with the carrier recombination velocity at the top surface region, S top. Laser heating increased S top to 6000 and 10000 cm/s for n- and p-type silicon samples, respectively. Heat treatment at 400oC for 4h markedly decreased S top to 21 and 120 cm/s, respectively, for n- and p-type silicon samples heated at 5.0x104 W/cm2. Laser heating at 4.0x104 W/cm2 for 4 ms was also applied to samples treated with Ar plasma irradiation at 50 W for 60 s, which decreased τeff (top) to 2.0x10-5 s and 3.9x10-6 s for n- and p-type silicon samples, respectively. Laser heating successfully increased τeff (top) to 2.8x10-3 and 4.1x10-4 s for n- and p-type samples, respectively. Laser irradiation at 4x104 W/cm2played a role of curing recombination defect sites.

We report a theoretical investigation of changes in the electronic structure of americium metal due to applied pressure. We employ a variant of the LDA+DMFT method that takes into account not only the correlations among the 5f electrons, but also the feedback of these correlations on the rest of the system by means of an appropriate adjustment of the electronic charge density. We observe only minor modification of the electronic structure in the compressed lattice, which is in accord with recent resonant x-ray spectroscopy experiments.

A full-scale water physical model of a degassing unit is built and used to evaluate the performance of several impeller designs. Four impeller designs are tested: a) one smooth not commercial impeller for reference purposes, b) a commercial design by FOSECO®, called standard impeller in this work, c) a commercial design by FOSECO® with notches, and d) a new design proposed in this work. Since the physical model is easy and safe to operate, a full experimental design is performed to evaluate the effect of the most important process variables, such as impeller rotating speed, gas flow rate, impeller design and the point of gas injection (a conventional gas injection through the shaft and a novel method of injecting gas through the bottom of the ladle) on the kinetics of oxygen desorption of water which is similar to dehydrogenation of liquid aluminum. The new design of impeller proposed in this work shows the best performance in degassing of all impellers tested in this study. It is found that the rotor speed and its design are the most significant variables affecting degassing kinetics, and therefore the analysis of the existing commercial impeller designs may be useful to optimize the fluid dynamics of the process, which in turn would increase efficiency and productivity of the process. Finally, the novel gas injection method through the bottom, proposed by our own group, presents slightly faster degassing kinetics than the conventional injection of purge gas in the conventional way through the impeller.

We present the fabrication and characterization of low-temperature ambipolar thin-film transistors (TFTs) based on hydrogenated amorphous silicon-germanium (a-SiGe:H) as active layer. Inverted staggered a-SiGe:H TFTs were fabricated on Corning glass. Spin-on glass silicon dioxide was used as gate dielectric to improve the quality of the dielectric-semiconductor interface. For positive gate bias the transfer characteristic showed n-type TFT behavior, while for negative gate bias p-type behavior was observed. The n-type region exhibits subthreshold slope of 0.45 V/decade while the p-type region shows a subthreshold slope of 0.49 V/decade.

Research has been carried out to optimize the consolidation stage for the immobilization of pyrochemical wastes with a sodium aluminophosphate glass. The alternative techniques of hot pressing and hot isostatic pressing of the calcined wastes with the glass have been investigated. This has been performed on simulant waste material and the products investigated by scanning electron microscopy and X‑ray diffraction. The consolidation techniques were compared to each other and to the original process for suitability as a waste-form.

The solar cells employed in low to medium (50 to 200 suns) concentration photovoltaic (CPV) are usually mono-crystalline silicon. Laser Groove Buried Contacts (LGBC) are preferred to screen printing in these cells due to the high currents generated in the system. In this paper, we report on the use of Coherence Correlation Interferometry (CCI) to accurately measure the width and depth of the laser-ablated grooves. In addition, the technique is also used to measure the surface roughness at the bottom of the trenches, since this can determine the success of the subsequent plating process, and at the top surface to optimize the debris control and obtain clean surfaces and well-shaped groove edges. The laser ablation process was also optimized to obtain the groove aspect ratio and surface quality required. Process parameters to be controlled include laser power, pulse energy, stage speed and focal length. The CCI technique is capable of providing all the groove and surface metrology required for this process optimization.

This paper reports a NEMS (Nano Electro Mechanical Syetems) tunable color filter based on subwavelength grating with high color uniformity and low drive voltage. We newly proposed a GVG (Ground-Voltage-Ground) type tunable color filter deployed with a parallel-plate actuator with three pairs of electrode to decrease a crosstalk of an electrostatic attraction force between each actuator. The proposed structure was fabricated using an SOI wafer. The color tuning using was demonstrated by applying the drive voltage of 6.7 V. The reflected light intensity was decreased by 34 % at 680 nm wavelength. The color uniformity was also obtained in the filter area by reducing the variation of the displacement on one-dimensional arrayed actuators.

We have studied the effect of pentacene purity and evaporation rate on low-voltage organic thin-film transistors (OTFTs) prepared solely by dry fabrication techniques. The maximum field-effect mobility of 0.07 cm2/Vs was achieved for the highest pentacene evaporation rate of 0.32 Å/s and four-time purified pentacene. Four-time purified pentacene also led to the lowest threshold voltage of -1.1 V and inverse subthreshold slope of ∼100 mV/decade. In addition, pentacene surface was imaged using atomic force microscopy, and the transistor channel and contact resistances for various pentacene evaporation rates were extracted and compared to field-effect mobilities.

Cylindrical porous polycaprolactone (PCL) scaffolds containing 25, 35, and 50 wt% demineralized bone matrix (DBM) were fabricated using a salt-leaching method for application in bone engineering. In the present work, PCL-DBM scaffolds were monitored for calcium and phosphorus deposition in both deionized (DI) water and simulated body fluid (SBF) for time periods of 5, 10, 15, and 20 days at 37°C under constant rotation. An in vitro assessment of the bioactivity of synthetic materials using SBF under physiological conditions can be used as a barometer of scaffold behavior in vivo. DBM, an osteoinductive material, was used to gauge if there was a correlation between the concentration of DBM within a scaffold and the apatite formation on its surface. Biochemical assays, alizarin red S staining, and scanning electron microscopy (SEM) with elemental analysis of calcium and phosphorus were consistent in that they confirmed that PCL scaffolds containing 35 wt% DBM in SBF at 14 days post-immersion showed signs of early apatite formation.

Aim of this work was to realize free-standing conductive nanofilms having very large surface area with typical nano-scale thickness (40-120 nm) by modifying existing approaches for nanostructured thin films assembly. We tested and optimized two different fabrication methods for the obtainment of free-standing conductive ultra-thin nanosheets based on the conductive polymer poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS). Supporting Layer and Sacrificial Layer techniques permitted the obtainment of single layer nanofilms that can be released in water and of LbL multilayer nanosheets (PEDOT:PSS/Polyelectrolytes) that can be released in acetone, respectively. Here we describe the details of both the proposed fabrication methods and compare the properties of the realized nanosheets in terms of thickness, contact angle and conductivity. Interestingly, the realized free-standing nanosheets, despite their low thickness, are very robust and compliant while maintaining their structure and functionality. Possible applications are foreseen in the field of sensing and actuation, as well as in the biomedical field, e.g. as smart conductive substrates for cell culturing and stimulation.

The nano-scale friction on crystalline gold surfaces can be systematically varied by changing the oxidation state of the surfaces through an applied electrochemical potential. We present experimental results from high-resolution friction force microscopy, where the atomic structure of the surface is reflected in lateral force maps. While the oxidation of gold surfaces always brings upon a significant increase in friction, the situation is more complex in the potential regime where only sulfate anions are adsorbed. The influence of adsorbed anions on friction depends on electrochemical potential and on normal load, demonstrating that electrochemical processes and sliding dynamics are altered in the confinement of the tip-sample contact.

The gold nanoparticles (AuNPs) conjugated with carbon nanotubes (CNTs) and/or biomolecules such as DNA are synthesized using a novel plasma technique combined with introduction of ionic liquids or aqueous solution for application to life sciences.

First, we successfully generate the gas-liquid interfacial discharge plasma (GLIDP) using an ionic liquid, in which the large sheath electric field is formed on the ionic liquid and the plasma ion irradiation to the ionic liquid with high energy is realized.

Second, it is found that the high energy ion irradiation to the ionic liquid is effective for the synthesis of the AuNPs. Furthermore, the controlled ion irradiation to the ionic liquid including a carboxyl group can realize the density-controlled synthesis of the AuNPs on the CNTs by dissociation of the ionic liquid and the controlled functionalization of the CNTs by the dissociated carboxyl group.

Third, the size- and morphology-controlled AuNPs covered with DNA are synthesized using the GLIDP with aqueous solution, where DNA prevents the AuNPs from further clustering, resulting in the small-sized AuNPs. The synthesized AuNPs conjugated with DNA can be encapsulated into the CNTs using the DC electric field. The CNTs work as vectors to deliver DNA into living cells because the CNTs have the unique ability to easily penetrate cell membranes with low cytotoxicity.