Phase formation mechanisms associated with the vitrification of Savannah River Site (SRS) Sludge Batch 4 (SB4) high level waste surrogate with high iron and aluminum contents were studied by infrared spectroscopy (IRS), X-ray diffraction (XRD) and optical microscopy. Two mixtures at 50 wt.% SB4 waste loading were prepared as slurries with a water content of ∼50 wt% using a waste surrogate and commercially available Frit 503-R4 (Li2O – 8 wt%, B2O3 – 16 wt%, SiO2 – 76 wt%) or mixture of chemicals (LiOH·H2O, H3BO3, SiO2). The mixtures were air-dried at a temperature of 115 °C and heat-treated at 500, 700, 900, 1000, 1100, 1200, and 1300 °C for 1 hr at each temperature. IR spectra and XRD patterns of the products heat-treated at each temperature were recorded. In both the mixtures phase formation reactions started at low temperatures and yielded intermediate phases (sodalite, pyroxene-type, nepheline), and the reactions were mostly completed within the temperature range between 1000 and 1100 °C. The glassy materials prepared at 1200 and 1300 °C were composed of vitreous phase and magnetite/trevorite type spinel.

Formation of carbon nanospheres is typically relegated to two costly methods. Chemical vapor deposition produces uniform spheres safely anchored to a substrate but at the cost of being slow and expensive to run. Arc discharge of a carbon target produces soot containing a low density of random spheres that must be laboriously sorted. An alternative approach is to fabricate carbon nanospheres through the pyrolysis of organic feedstock. This paper presents the findings from an investigation into using pectin as a pre-cursor material for pyrolysis. The pectin is combined with different saccharides - sucrose, dextrose, and fructose and processed in aqueous solution until a gel set. The gel is then thermally processed in a nitrogen environment at 500 °C. The resultant carbon material is examined under SEM. Images confirm the formation of nanospheres and other microscale and nanoscale structures. The pectin, a naturally derived product from plant materials, is a renewable source of materials which can be used to form nanotechnologies for many energy-related applications.

The Sellafield Waste Vitrification Plant (WVP) immobilises highly active liquors produced during reprocessing of spent nuclear fuel by bonding the fission products as metal oxides into a borosilicate glass matrix. This provides a stable and durable waste form suitable for safe long term storage and ultimate disposal.

WVP was commissioned with feed from reprocessing of Magnox reactor fuel. This material is relatively low in fission product content per tonne of fuel, but contains significant Al and Mg from fuel cladding. WVP also routinely treats a blended feed made from a mixture of Magnox and Oxide reprocessing products. The Oxide fuel from Light Water Reactor (LWR) and Advanced Gas Cooled (AGR) power stations is of higher burnup and contains more fission products per tonne of fuel, also Gd and other process additives. Blending allows 25% incorporation of waste oxides by weight in glass to be achieved routinely.

Recent programmes of development work in WVP have been aimed at increasing incorporation rates for these feeds, to reduce the number of waste containers produced for disposal. Work has also focussed on increasing the throughput of WVP, to more rapidly treat current stocks of liquid reprocessing waste, both by increasing the feed rate and by improving the lifetime of key components to improve plant availability.

Future challenges for WVP include flowsheet changes to treat historic stocks of reprocessing wastes containing high U, Fe and Cr. Washout of solids from the base of waste storage tanks in preparation for decommissioning is also likely to give high Mo feeds. Development of flowsheet and glass formulation to accept these changes in feed composition will be a key objective of future work.

The goal of this study is to investigate the fundamental relationship between the extent of crosslinking and shape-memory behavior of amorphous, (meth)acrylate-based polymer networks. The polymer networks were produced by copolymerization of tert-butyl acrylate (tBA) and poly(ethylene glycol) dimethacrylates of differing molecular weights (PEGDMA). Polymer compositions were tailored via the amount (weight percent (wt%)) and molecular weight of the PEGDMA crosslinking agents added to produce four materials with varying levels of crosslinking (0, 2, 10, and 40 wt% crosslinking agent corresponding to 0, 0.6, 3.2, and 16.6 mole%) and nearly equal glass transition temperatures (Tg ). The effect of crosslinking on deformation limits and free-strain recovery is evaluated. Near complete strain recovery was demonstrated by all materials; however, absolute recovery strain decreased with increasing crosslinking due to a corresponding decrease in strain-to-failure. The results provide insights regarding the link between polymer structure, deformation limits, and strain-recovery capabilities of this class of shape-memory polymers. An improved understanding of this relationship is pivotal for optimizing system response for a wide range of shape-memory applications.

The homogeneity of the Schottky barrier potential of reactively sputtered PdOy/ZnO Schottky contacts has been investigated by light beam-induced current measurements on the micrometer scale. It is found that a metallic capping layer, acting as an equipotential surface, is not necessary for PdOy/ZnO Schottky contacts in contrast to AgxO/ZnO Schottky diodes. Further, we probed the generated photocurrent of a ZnO-based metal-semiconductor field-effect transistor for a closed and open channel, respectively. The photocurrent is, in general, one order of magnitude larger for closed channel conditions. The position of maximum photocurrent generation shifts towards the drain for higher source drain voltages for closed channel conditions, whereas it is nearly independent of the source drain potential for an open channel.

We have examined the Large Particle Count (LPC) analytical method to see whether there are opportunities to improve both the accuracy and precision in hope of improving the utility of the LPC measurement. We have identified weaknesses in the current method that limit both its accuracy and its precision, and which can introduce count errors in excess of a factor of 10. We propose modifications to the current method which result in both accuracy and precision improvements. We recommend these improvements as absolutely necessary for any experiments designed to test the correlation between LPC and defectivity.

Bioactive glass is known for its potential as a bone scaffold due to its ability to stimulate osteogenesis and differentiation of stem cells into bone cells. In an attempt to investigate if we can increase these potentials, we decorated the structure of the bioactive glass made by the sol-gel technique with 3 peptides sequences from different proteins known for their potentials to stimulate the osteogensis process (fibronectin, BMP-2 and protein kinase CKI). This material was tested with Human Mesenchymal Stem Cells (hMSCs) and MC-3T3 preosteoblasts to see the difference in the effect on uncommitted and committed cells. The bioactive glass sol with and without the peptides was dip coated onto glass cover slips, leading to a film of the material, surface decorated with the peptides of choice. The two cell types were seeded onto the materials in standard proliferation medium without additives for differentiation induction. Cells were also grown on tissue culture treated cover slips with and without differentiation induction media as positive and negative controls, respectively. The cells were grown on the materials for a total of five weeks, and were tested at four time points (weekly from week two) by immunocytochemical assays to investigate the levels of different osteogenic markers (osteopontin, osteocalcin and osteonectin) and by qRT-PCR to investigate the mRNA potential of the same proteins. On the native bioactive glass samples, the hMSCs and the MC-3T3s adhered poorly. On peptide-decorated samples, the hMSC adhered poorly, however, the MC-3T3 cells appear to differentiate at a rate that is equal to or faster than the positive control, indicating that the peptide effect is similar to that achieved by traditional BMP-2 soluble protein techniques. This supports our hypothesis that adding specific peptide sequences known for their effects in cells adhesion, proliferation and differentiation can increase the potential of the bioactive glass as a scaffold for bone tissue engineering. The data, however, leads to some questions regarding the MC-3T3 cell model for use in further studies.

A novel technique to form periodically nanostructured Si surface morphologies based on nanosphere lithography (NSL) and He ion implantation induced swelling is studied in detail. It is shown that by implantation of keV He ions through the nanometric openings of NSL masks regular arrays of hillocks and rings can be created on silicon surfaces. The shape and size of these surface features can be easily controlled by adjusting the ion dose and energy as well as the mask size. Feature heights of more than 100 nm can be obtained, while feature distances are typically 1.15 or 2 (hillock or ring) nanosphere radii, which are chosen to be between 100 and 500 nm in this study. Atomic force and scanning electron microscopy measurements of the surface morphology are supplemented by cross-sectional transmission electron microscopy, revealing the inner structure of hillocks to consist of a central cavity surrounded by a hierarchical arrangement of smaller voids. The surface morphologies developed here have the potential to be useful for fixing and separating nano-objects on a silicon surface.

We extend the McPherson Model for silicon-oxygen bond-breakage derived for a single SiO4 tetrahedron to capture the influence of the whole lattice. Several pair-wise potentials have been compared in the model including Mie-Grüneisen as well as diverse forms of TTAM/BKS. The contribution of the whole lattice substantially increases the activation energy for the Si-O bond rupture. The corresponding small transition rate of a non-distorted Si-O bond suggests that the interaction with the electric field alone can not be responsible for the bond-breakage and the contribution of other components such as energy delivered by particles and/or bond weakening is required.ü

The present work details, to our knowledge, the first examination of the influence of blue-light radiation on the optical properties of organic luminescent films in attempting to develop an indicator dosimeter for phototherapy of neonatal jaundice. Jaundice is the most common problem encountered in newborns due to immature functioning in the liver. The operating principle of the device is based on the optical response of poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene (MEH-PPV) and tris(8-hydroxyquinolinato) aluminum (Alq3) materials dispersed in polystyrene (PS) matrix (denoted as PS/MEH-PPV/Alq3). It is observed a blue-shift on the photoluminescence of PS/MEH-PPV/Alq3 system from red to orange-yellow, and then to green as function of the blue-light radiation exposure time. The result is attributed to the spectral overlap between emission of Alq3 and absorption of MEH-PPV. The optical response of PS/MEH-PPV/Alq3 to radiation was investigated to design a low-cost (< US$ 0.05) “smart” sensor to represent easily the radiation dosage normally used in blue-light phototherapy. The basic idea behind this concept considers the sensor as a traffic light device, where red represents underdose and green the prescription dose or overdose, while orange-yellow suggests that radiation therapy is an ongoing process. This personal real-time radiation dosimeter appears here as a key requirement for successful development of innovations in effective management of the radiation dose planning before treatment of neonatal where control of dose absorption of infants is extremely important.

We report thermal diffusivity measurements for samples of silicon, gallium arsenide and cupper by means of the photoacoustic technique in a heat transmission configuration in order to obtain a comparison between the results obtained with the use of the conventional RG-model and our SP-model (based in a square periodical heat source) in the fitting process to the experimental data. Our results show that our SP-model is accurate to obtain a good fitting with the experimental data and it improves notably the results obtained with the RG-model.

Crystal and interfacial structures of oxide nanoparticles in 16Cr-4Al-2W-0.3Ti-0.3Y2O3 ODS ferritic steel have been examined using high-resolution transmission electron microscopy (HRTEM) techniques. Oxide nanoparticles with a complex-oxide core and an amorphous shell were frequently observed. The crystal structure of complex-oxide core is identified to be mainly monoclinic Y4Al2O9 (YAM) oxide compound. Orientation relationships between the oxide and matrix are found to be dependent on the particle size. Large particles (> 20 nm) tend to be incoherent and have a spherical shape, whereas small particles (< 10 nm) tend to be coherent or semi-coherent and have a faceted interface. The observations of partially amorphous nanoparticles lead us to propose three-stage mechanisms in order to rationalize the formation of oxide nanoparticles containing core/shell structures in as-fabricated ODS steels.

The valence band discontinuity (offset) between a-Si:H-based intrinsic thin layers and c-Si substrates was estimated using ultraviolet photoelectron spectroscopy (UPS) in combination with x-ray photoelectron spectroscopy (XPS). A core level shift measured by XPS was utilized to correct the shifts of UPS spectra after UV light illumination. Thin films of a-Si:H, a-SiO:H and a-SiC:H were prepared by plasma-enhanced chemical vapor deposition (PECVD) using SiH4, CO2 and CH4 gases. The valence band offset of 0.11 eV was obtained from the a-Si:H/c-Si heterojunction, whereas 0.27 eV was obtained from the a-SiO:H/c-Si heterojunction. Moreover, the valence band offset between the c-Si and the a-SiC:H deposited with [CH4]=10 SCCM and [CH4]=20 SCCM were determined to be 0.25 eV and 0.36 eV, respectively. The c-Si-based heterojunction solar cells with estimated i layer in this study were fabricated, reduction of FF with increasing the valence band offset was observed. It is likely that increasing of the valence band offset contributes to the reduction of FF.

Studies were made into the influence of oversized rare-earth atoms on the processes of radiation defect accumulation and annealing in two-component zirconium alloys. Zr and Zr-X alloys (where X = Sc, Dy, Y, Gd and La) have been irradiated with 2 MeV electrons at 82 K. The radiation-induced resistivity has been measured in situ as a function of dose. As compared to unalloyed zirconium, the alloys have exhibited a decrease in the resistivity gain, this decrease being proportional to both the concentration and the size of dopant atoms. A possible explanation for the effect is offered. The difference between the recovery processes in zirconium and in its alloys has been studied. To this end, the irradiated specimens were subjected to isochronal annealing at temperatures between 82 and 350 K. It is shown that Dy, Y, Gd and La atoms trap interstitial atoms at stage I of the recovery. The dissociation of interstitial-impurity complexes takes place at stage II. In zirconium alloys with Dy, Y and Gd, splitting of recovery stage III into two substages has been revealed. The Zr-La alloy has not shown this splitting. Isothermal annealing data were used to determine the activation energies of recovery stages, and also to calculate the activation energy spectra for zirconium and its alloys. The oversized atoms of rare-earth metals are shown to interact effectively with both the interstitials and the vacancies in the zirconium matrix. This effect must be taken into account when developing new radiation-resistant Zr-base alloys or modifying the ones already existing.

This paper reports on a multi-faceted evaluation of science communication workshops conducted during the summer of 2009 with Research Experience for Undergraduate (REU) students from the Center for High-rate Nanomanufacturing and the Harvard University School of Engineering and Applied Sciences, in a partnership between the Museum of Science, Boston Strategic Projects department and faculty from the Nanoscale Science and Engineering Centers headquartered at Harvard and at Northeastern Universities. The workshops were shown to (1) increase student interest in exploring and understanding the broader impacts of research, and (2) increase student knowledge, confidence and practice of communication skills for both professional and non-professional audiences.

There is an increasing amount of experimental evidence that the plastic behavior of crystals changes at micro- and nano-scales in a way that is not necessarily captured by state-of-the-art plasticity models. In this paper, length scale effects in the plasticity of crystals are analyzed by means of direct numerical simulations that resolve the scale of the carriers of plasticity, i.e., the dislocations. A computationally efficient, atomistically informed dislocation dynamics framework which has the capability of reaching high dislocation densities and large strains at moderately low strain rates in finite volumes is recalled. Using this theoretical framework, a new type of size effect in the hardening of crystals subject to nominally uniform compression is discovered. In light of such findings, behavior transitions in the space of meaningful structural parameters, from forest-hardening dominated regime to an exhaustion hardening dominated regime are discussed. Various scalings of the flow stress with crystal size emerge in the simulations, which are compared with recent experimental data on micro- and nano-pillars.

In order to reduce the power-generating cost of silicon solar cells, it is necessary to achieve a high conversion efficiency using a thinner crystalline silicon (c-Si) substrate. The HIT (Heterojunction with Intrinsic Thin-layer) solar cell is an amorphous silicon (a-Si) / c-Si heterojunction solar cell that exhibits the potential to make this possible. Our recent R&D activities have achieved the world’s highest conversion efficiency of 23.0% with a practical sized (100.4 cm2) HIT solar cell, by improving the quality of the surface passivation, reducing the optical absorption loss and reducing the resistance loss. We have also developed a HIT solar cell with a thickness of only 98 mm, which has a very high conversion efficiency of 22.8%. This value is comparable to that of the conventional HIT solar cell, which has a thickness of more than 200 mm. Moreover, we have fabricated HIT solar cells using thinner c-Si substrates (96 to 58 μm), and found that the Voc increased with decreases in the substrate thickness, and reached an extremely high value of 0.745 V with a thickness of only 58 μm. This indicates that the surface recombination velocity of the HIT structure is extremely low due to the excellent passivation of the c-Si surface.

High efficiency silicon solar cells demand the use of high lifetime silicon wafers. Characterization of boules and bricks before wafering allows poor quality material to be rejected before expensive processing steps. This paper extends simulation techniques previously used in quasi-steady-state-photoconductance to transient photoconductance decay measurements of high lifetime bulk samples. Simulated photogenerated carrier density profiles allow estimation of the bulk lifetime of a thick silicon sample with high surface recombination velocity.

Ordered arrays of gold particles have been fabricated on gold-coated Si(100) surfaces by pre-patterning the surface with a nanoindenter. During thermal annealing the Au is observed to accumulate within the residual indents. Once nucleated, the Au particles grow at the expense of smaller surface particles via an Ostwald-ripening process. The size of the Au particles is controlled by the initial thickness of the deposited Au layer, the size of the indentation (which is controlled with a high degree of precision), and the annealing conditions. Particles of ˜200 nm dimensions are formed in indents of ˜1 μm dimensions whilst nanoparticles of ˜20 nm are observed in the smallest indents made (˜50 nm). We have also demonstrated patterning of Au by indentation of a Au layer sandwiched between two SiO2 films deposited on Si by plasma-enhanced chemical vapour deposition. Here, cracking of the SiO2 layer occurs allowing Au to diffuse to the surface at the indented locations during post-indentation annealing.

We developed a BioMEMS device to study cell- mitochondrial physiological functionalities. The pathogenesis of many diseases including obesity, diabetes, heart failure as well as aging has been linked to functional defects of mitochondria. This is understandable as the mitochondria produces up to 90% of ATP, and plays a critical role in cell signaling and apoptosis. The synthesis of ATP is determined by the electrical potential across the inner mitochondrial membrane (IMM) and by the pH difference due to proton flux across it. Therefore, electrical characterization by E-fields with complementary chemical testing was used here. Mitochondrial ion channels present in the IMM control specific ion fluxes, and maintain ion homeostasis, matrix volume, IMM potential etc and thus serve a central role in cell growth and death related processes. Defects in ion channels (Channelopathies) are being attributed to many diseases like cancer, neurodegeneration, etc. Complete physiological roles of various ion channels and their interactions are still unknown, hindering the development of targeted therapeutic agents. The BioMEMS device was fabricated as an SU-8 based microfluidic system with gold electrodes on SiO2/Si wafers for electromagnetic interrogation. Ion Sensitive Field Effect Transistors (ISFETs) were incorporated for proton studies important in electron transport chain, together with monitoring Na+, K+, Ca++ions for ion channel studies. ISFETs are chemically sensitive MOSFET devices, their threshold voltage is directly proportional to the electrolytic H+ ion variation. These ISFETs (sensitivity ˜55 mV/pH for H+) were further realized as specific ion sensitive CHEMFETs by depositing a poly-HEMA layer sandwiched between the gate and a final specific ion sensitive membrane. Electrodes for dielectric spectroscopy studies of mitochondria were designed as 2- and 4-probe structures for optimized operation over a wide frequency range. In addition, to limit polarization effects (which masks actual impedance for high conductivity solutions at low frequencies), a 4-electrode set-up with unique meshed pickup electrodes (7.5×7.5 μm2 loops with 4 μm wires) was fabricated. An electrical model was developed for the mitochondrial sample, and its frequency response correlated with impedance spectroscopy experiments of sarcolemmal mitochondria. Using the mesh electrode structure, we obtained a reduction of 83.28% in impedance at 200 Hz. COMSOL simulations of selected electrical structures in this sensor were compared with experimental results to better understand the physical system. The simultaneous measurement of membrane potential, ion concentrations and pH would enhance diagnostics and studies of mitochondrial diseases.