bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Energy Electron Microscopy for Semiconductor Applications
Authors: Mankos Marian , Spasov Vassil , Han Liqun , Kojima Shinichi , Jiang Ximan , Harb Salam , Grella Luca , Czarnik Cory
Published: April 2011

A novel low energy electron microscope (LEEM) aimed at improving the throughput and extending the applications for semiconductor devices has been developed. A dual beam approach, where two beams with different landing energies illuminate the field of view, is used to mitigate the charging effects when the LEEM is used to image semiconductor substrates with insulating or composite (insulator, semiconductor, metal) surfaces. We have experimentally demonstrated this phenomenon by imaging a variety of semiconductor device wafers without deleterious charging effects. Results from several important semiconductor device layers will be illustrated in detail.
Using the Focused Ion Beam to Perform Serial Sectioning of Micron-Sized Particles for Coordinated Nanoscale Analysis
Authors: Bassim Nabil D. , De Gregorio Bradley T. , Stroud Rhonda M.
Published: April 2011

Standard Focused Ion Beam (FIB) lift-out methods for production of transmission electron microscopy (TEM) thin sections destroy many cubic microns of material in order to produce a single 100-nm thick section. Microtome sectioning, in contrast, allows serial sectioning of adjacent multiple 100-nm sections, without loss of materials between sections, but lacks site specificity. In order to maximize the yield of analyzable material in thin section form from valuableone-of-a kind- micron-sized samples, we have developed serial sectioning techniques that combine FIB lift-out with microtomy. In this paper, we show an example of sectioning and subsequent TEM analysis of simulated cometary residues which resemble impact craters collected during the NASA Stardust Mission. These techniques may be generalized to any one-of-a-kind sample for which preserving analyzable volume is critical, such as forensic analysis of dust particles, failure analysis and electronic device sectioning.
Cell Self Assembly of Intracellular Interface Using Cell Migration
Authors: Hoshino Takayuki , Konno Tomohiro , Ishihara Kazuhiko , Morishima Keisuke
Published: April 2011

A cell-driven self-assembly of intracellular nano-device was proposed for bio-hybrid interface. This cells-driven self-assembly employed cell migration force to insert a conductive nanoneedle which would be worked as intracellular electrode. Such a nanoneedle was fabricated in the bottom of a microwell using focused ion beam induce deposition. The microwell structure with a coating of cell adhesion molecules was employed as the scaffold of the cell migration. A glass plate with the microwells had a non cell binding coating of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer as an anti-biofouling material. Thus a cell adhered only on the wall of a microwell then the cell migrated into the microwell. Adhesion force and migration force induced self-insertion of the nanoneedle into a live cell body using the cell's own migration force. The inserted nanoneedle was made of electrical conductive tungsten, so the intracellular nanoneedle might extract intracellular potential more precisely than extracellular electrode, while inducing much less damage to cells. In the future, the technique of cell-driven self-insertion of nanoneedle may be integrated with multi electrode arrays for developing long-lasting measurements device on cellular network researches, or the risk assessment of the nanomaterials on cellular activities.
The End Group Modification of Phospholipid Polymer Brush Grafted on Ferric Oxide Nanoparticles for Diagnostics
Authors: Matsuno Ryosuke , Ishihara Kazuhiko
Published: April 2011

Nanoparticles are widely applied as diagnostic reagents, drug-delivery carriers or bioaffinity beads. In particular, magnetic particles have been widely used in the study of biomedical applications. When we look ahead to the future, it is needed to construct precisely designed surface containing such as high bioaffinity and capability to capture of small amount protein or specific protein among various protein. As a method to construct precisely designed biocompatible polymer surface, atom transfer radical polymerization (ATRP) was widely used as a living free radical polymerization. ATRP has advantages such as control of molecular weight, narrow polydispersivity, easy synthesis of block copolymer, and preparation of high density polymer brush under mild condition. Previously, we have demonstrated synthesis of poly (2-methacryloyloxyethyl phosphorylcholine (MPC)) brush on ferric oxide (Fe3O4) by ATRP from immobilized initiator includes bromine that ATRP moiety. Here, it is known that poly(MPC) has been not affected for reduction of nonspecific binding, salt concentrations, pH and temperature. In this state, the poly(MPC)-grafted Fe3O4 could not be used for diagnostic material and collection material using magnetic interaction because poly(MPC) suppress protein adsorption. To introduce immobilization part for protein, p-nitrophenyloxycarbonyl polyethylene glycol methacrylate (MEONP) monomer that has active ester was polymerized as a block component. The poly(MPC-b-MEONP)-grafted Fe3O4 could capture proteins via active ester to amine of proteins. However, on careful consideration, this immobilization method had disadvantage for capture protein because immobilization part located in the side chain, not locate most outer surface. We focused on bromine (Br) located on end group of poly(MPC) brush, probably locate most outer surface. If the end group would be modified easily, the technique will be most effective modification. We adapted the reduction from azide (N3) to amine (NH2), after Br was exchanged to N3. This reduction has been called “staudinger reduction”. Generally, Click chemistry that reaction between N3 and alkyne is famous as a reaction of N3. On the other hand, the modification technique has wide application range due to amine group. At first, bromine was converted into azide, N3 using NaN3. Furthermore, the N3 was reduced to NH2 using PPh3 and H2O. The purification of magnetic nanoparticles with end group modified poly(MPC) brush was easy because of use of external magnetic interaction. The surface characterization at each step was estimated by XPS and FT-IR spectrum measurement. The absorbance signal attributed to N3 was appeared around 2000 cm-1 from FT-IR spectrum and N1s signal according to NH2 was observed at 399 eV from XPS measurement. The surface NH2 could react to carboxyl group or convert into other functional groups easily. The end group modification will be a useful for various bioaffinity bead applications.
Self-assembled Materials Containing Complementary Nucleobase Molecular Recognition
Authors: Smitthipong Wirasak , Chworos Arkadiusz , Lin Brian , Neumann Thorsten , Gajria Surekha , Jaeger Luc , Tirrell Matthew
Published: April 2011

Here we report the nucleic acid/cationic amphiphile based-materials in which we exchange the counter-ions of the polyanionic backbone of the nucleic acids with the cationic amphiphiles to form self-assembled transparent films with the thickness of several microns. Predominantly, single stranded poly(A), poly(U) and double stranded poly(AU) were employed for these studies. Small-angle X-ray scattering (SAXS) experiments suggested lamellar-like structure for all the film samples. However, the molecule length as well as the molecular structure of nucleic acids can affect the topology and mechanical properties of these films. Complementary base-paring of poly(AU) is reported here with comparison to poly(A) and poly(U) complexes.
Collagen Matrix Alignment Using Inkjet Printer Technology
Authors: Deitch Sandra , Kunkle Catherine , Cui Xiaofeng , Boland Thomas , Dean Delphine
Published: April 2011

Collagen fiber orientation plays an important role in many cell properties and actionsin vivo. Collagen and other matrix proteins are aligned in many tissues during normal functioning. For example, cardiomyocytes align in the heart to produce a synchronously beating tissue. The extra-cellular matrix environment, including collagen, is aligned along the cells. This matrix helps with cell adhesion and the alignment of the fibers also contributes to the anisotropic mechanical property of the tissue. While it is easy to replicate randomly oriented collagenin vitro, it is much more difficult to create aligned collagen matrices for cell culture. In this work, a novel inkjet printer-based collagen alignment technique was established. A 1 mg/ml rat tail collagen type I solution was printed, using a modified HP DeskJet 500 printer, onto plasma cleaned and UV sterilized glass slides. The collagen was printed in an eight line pattern, designed in Microsoft Word with 87.5 μm by 23.1 mm lines. The pattern was printed three successive times on each slide to complete the alignment. Immunofluorescence imaging of primary antibodies specific to collagen type I indicated that the heat involved in the printing process was not great enough to denature the collagen. The extent of collagen alignment was quantified using atomic force microscopy and compared to random collagen films and collagen films aligned using a mechanical scraping method. Additionally, neonatal rat cardiomyocytes were cultured on the aligned matrices. These cells require extracellular matrix alignment to maintain their in vivo-like phenotype during in vitro culture. The cells grew along the lines of collagen and coordinated beating, indicating the success of the aligned matrix. This collagen alignment technique is cheap, fast, precise, and easy to use in comparison to other current techniques. It can be used to align collagen on any type of substrate, such as a gel, which makes it a useful tool in many applications. This technique may also be used to align other extra-cellular matrix proteins and could even be used to create a three dimensional construct with varying fiber orientations.
Biocompatibility, Bioactivity and Mechanical Properties of Portland Cement and Portland Cement-Metakaolin Blends for Bone Tissue Engineering Applications
Authors: Gallego Daniel , Higuita Natalia , Garcia Felipe , Posada Olga M. , Lopez Luis E. , Litsky Alan S. , Hansford Derek J.
Published: April 2011

We studied the potential applications of Portland cement and Portland cement-Metakaolin blends as scaffolding materials for load bearing bone tissue engineering. Cementitious pastes were prepared by mixing Portland cement and Metakaolin at different ratios (100:0, 85:15), and hydrated under a concentrated CO2 atmosphere (carbonated pastes). Pastes fabricated similarly, but hydrated under normal atmospheric conditions were used for comparison (non-carbonated pastes). Compressive tests were run to evaluate the mechanical properties of the pastes. The bioactivity of the samples was tested in a simulated body fluid (SBF) solution for 1 and 4 days. Sample morphology and chemistry were characterized via scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. The cytocompatibility was studied using human osteosarcoma (HOS) cell cultures and the direct contact assay. Mechanical characterization did not show significant differences in the compressive strength of the blends compared to pure cement controls. The bioactivity test revealed that the pastes induced surface precipitation of calcium phosphate (CaP) when exposed to the SBF solution (as confirmed by SEM and EDS). Non-carbonated pastes induced early CaP precipitation. Cytocompatibility experiments showed that the carbonated blends allowed adequate cell growth. Non-carbonated blends presented a highly cytotoxic behavior. The introduction of Metakaolin did not affect the cytocompatibility of the samples. These results show that Portland cement and Portland cement-Metakaolin blends could present suitable characteristics for applications as scaffolding materials in load bearing bone tissue engineering.
Electrospun Gelatin/Hydroxyapatite Nanocomposite Scaffolds for Bone Tissue Engineering
Authors: Catledge Shane , Tyagi Parul , Koopman Mark , Stanishevsky Andrei , Vohra Yogesh K.
Published: April 2011

Electrospun composite scaffolds were prepared by mixing gelatin with nanoparticles of hydroxyapatite (nanoHA) in 2,2,2-trifluoroethanol (TFE) solution. The fibrous composite scaffolds with nanoHA content from 0 to 40 wt% were compared in terms of structure and morphology via x-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that dispersion of nanoHA in the scaffolds is uniform for 0%, 10%, 20%, and 30% nanoHA content, but significant nanoHA agglomeration can be observed for scaffolds with 40% nanoHA. In order to study the effect of nanoHA content on mechanical properties at the nanoscale level, the fibrous scaffolds were pressed into dense pellets and tested by nanoindentation to determine Young's modulus. Young's modulus was found to increase linearly with nanoHA content, reaching unexpectedly high values of 10.2 ± 0.8 GPa. Results are compared with other polymer/HA composites including those made with polycaprolactone or collagen.
A Novel Electrospun Dendrimer-Gelatin Hybrid Nanofiber Scaffold for Tissue Regeneration and Drug Delivery
Authors: Smith-Freshwater Alicia P , Bowlin Gary L , Yang Hu
Published: April 2011

Gelatin has been widely used to develop tissue engineering scaffolds because it has many attractive properties. Dendrimer provides a versatile, compositionally and structurally controlled architecture to construct nanomedicine. This study was aimed at developing a novel electrospun dendrimer-gelatin nanofiber scaffold to best mimic natural extracellular matrix (ECM) to promote tissue formation and serve as a reservoir for controlled drug delivery. Starburst™ polyamidoamine (PAMAM) dendrimer G3.5 was covalently bonded to the gelatin backbone and electrospun into nanofibers. Doxycycline (DC), which is an effective antibiotic that has the ability to inhibit matrix metalloproteinase, was encapsulated into the nanofiber scaffold. The electrospun DC-gelatin scaffold provides a bacterial free environment for cell growth and tissue regeneration. The resulting dendrimer-gelatin nanofiber scaffold achieved a unique structural configuration where covalently bound three-dimensional dendritic nanospheres were evenly distributed along the elongated dimension of the nanofiber, and both dendrimer and gelatin had numerous functional groups suitable for accommodating multiple functional entities and high payload of drugs. The development of this new scaffold with the capability of delivering multiple functional entities was an important step towards the use of bioactive nanofibers to facilitate tissue regeneration and controlled drug release.
Nanomonitors: Nanomaterial Based Devices Towards Clinical Immunoassays
Authors: Prasad Shalini , Bothara Manish , Reddy Ravikiran , Carruthers John , Barrett Thomas
Published: April 2011

The immobilization of biomolecules on a solid substrate and their localization in “small” regions are major requirements for a variety of biomedical diagnostic applications, where rapid and accurate identification of multiple biomolecules is essential. In this specific application we have fabricated nanomitors for identifying specific protein biomarkers based on the electrical detection of antibody-antigen binding events.

The nanomonitor, lab-on-a-chip device technology is based on electrical detection of protein biomarkers. It is based on developing high density, low volume multi-well plate devices. The scientific core of this technology lies in integrating nanomaterial with micro fabricated chip platforms and exploiting the improve surface area to volume to improve the detection.

The devices that have been developed utilize electrical detection mechanisms where capacitance and conductance changes due to protein binding are used as “signatures” for biomarker profiling. In comparison to optical methods, the electrical detection technique is non-invasive as well as a label free. The signal acquisition is simple and it uses the existing data acquisition and signal analysis methods
Culture of Insect Heart Muscle Tissue and Its Applicability to Bio-Actuators
Authors: Akiyama Yoshitake , Iwabuchi Kikuo , Furukawa Yuji , Morishima Keisume
Published: April 2011

An insect heart (dorsal vessel) is well suited as an environmentally robust bioactuator since insect tissue is generally robust over culture conditions compared with mammalian tissue. In this paper, the applicability of a caterpillar dorsal vessel to a bioactuator was assessed by fabricating a micropillar actuator driven by dorsal vessel tissue and evaluating the response to electrical pulse stimuli. The actuator worked autonomously for more than 90 days at 25 °C without any maintenance. The average frequency and displacement for 30 s on the 28th day of culturing were 0.83 Hz and 41 μm, respectively. Furthermore, as a regulation method for the dorsal vessel, electrical pulse stimuli were applied to the micropillar actuator. The contractile delay was about 50 ms. A twitch contraction was evoked by electrical pulse stimulus at 20 ms in duration and 10 volts in amplitude. A tetanic contraction was observed when stimuli over 10 Hz were applied.
Fabrication of Ring-shaped Bioactuator Powered by Cardiomyocytes
Authors: Horiguchi Hiroshi , Akiyama Yoshitake , Morishima Keisuke
Published: April 2011

We have proposed a novel use of pulsating living cells as a driving source for a micro bio-actuator. Cardiyomyocytes contract autonomously using chemical energy. But, contractile force of a single cardiomyocyte is not enough to actuate a micro robot or a mechanical system. So it is necessary to reconstruct cardiomyocytes to increase the ability to contract. We focused on the reconstruction of cardiomyocytes using a basement membrane protein mixture. In this paper, we fabricated a prototype cardiomyocyte gel structure. We confirmed that the ring-shaped cardiomyocyte gel structure condensed around the central cylinder within the PDMS mold and contracted synchronously and autonomously.
Zone-Specific Changes in Micromechanical, Biochemical, and Structural Properties in Articular Cartilage from a Rabbit Joint Flexion Model
Authors: Li Cheng , King Karen B. , Pruitt Lisa A.
Published: April 2011

Metacarpophalangeal (MCP) joint proximal bone-cartilage specimens from the fourth digit were collected from repetitively flexed and non-flexed (control) paws of four New Zealand White rabbits. The specimens were cryo-fractured to reveal a sagittal cut containing the cartilage zones of different collagen microstructure. Nanoindentation, Fourier Transform infrared microspectroscopic imaging (FTIRMI), and histology were performed on a region of interest (ROI) ∼400 microns wide and through the thickness of the cartilage with two goals in mind: (1) to examine the effect of collagen network structure (random in the mid zone versus organized in the deep zone) on the biomechanical and biochemical properties of cartilage; and (2) to understand the changes in these properties due to physical forces. We found that zone microstructure significantly affected the measurement of the local relaxed modulus measured by nanoindentation. The deep zone had a higher modulus than the mid zone (Wilcoxon paired test, p<0.05). We also found that flexion significantly decreased the proteoglycan content in both the mid and deep zones (Wilcoxon paired test, p<0.05), suggesting indirect repetitive loading in the rabbit paw can be damaging to the joint via down regulating proteoglycan synthesis in the mid and deep zone cartilage. This is the first study to simultaneously report the local zone-specific mechanical and biochemical properties in the rabbit joint flexion model.
Characterisation of Cell Adhesion to Substrate Materials and the Resistance to Enzymatic and Mechanical Cell-Removal
Authors: Griffiths Helen Jane , Harvey John G , Dean James , Curran James A , Markaki Athina E , Clyne T William
Published: April 2011

Cell-implant adhesive strength is important for prostheses. In this paper, an investigation is described into the adhesion of bovine chondrocytes to Ti6Al4V-based substrates with different surface roughnesses and compositions. Cells were cultured for 2 or 5 days, to promote adhesion. The ease of cell removal was characterised, using both biochemical (trypsin) and mechanical (accelerated buoyancy and liquid flow) methods. Computational fluid dynamics (CFD) modelling has been used to estimate the shear forces applied to the cells by the liquid flow. A comparison is presented between the ease of cell detachment indicated using these methods, for the three surfaces investigated.
Three Dimensional Morphology and Compressive Behaviour of Sintered Biodegradable Composite Scaffolds
Authors: Ghassemieh Elaheh
Published: April 2011

Porous poly-L-lactide acid (PLA) scaffolds are prepared using polymer sintering and porogen leaching method. Different weight fractions of the Hydroxyapatite (HA) are added to the PLA to control the acidity and degradation rate. The three dimensional morphology and surface porosity are tested using micro CT, optical microscopy and scanning electron microscopy (SEM). Results indicate that the surface porosity does not change by addition of HA. The micro Ct examinations show slight decrease in the pore size and increase in wall thickness accompanied with reduced anisotropy for the scaffolds containing HA. SEM micrographs show detectable interconnected pores for the scaffold with pure PLA. Addition of the HA results in agglomeration of the HA which blocks some of the pores. Compression tests of the scaffold identify three stages in the stress-strain curve. The addition of HA adversely affects the modulus of the scaffold at the first stage, but this was reversed for the second and third stages of the compression. The results of these tests are compared with the cellular material model. The manufactured scaffold have acceptable properties for a scaffold, however improvement to the mixing of the phases of PLA and HA is required to achieve better integrity of the composite scaffolds.
Microstructures in the Formation of Chemical Gardens
Authors: Sainz-Diaz C. Ignacio , Escribano Bruno , Cartwright Julyan
Published: April 2011

Chemical gardens are biomimetic structures in the form of plants formed by a combination of salts which precipitate by a combination of convection forced by osmosis, free convection and chemical reactions. Chemical gardens may be implicated in other phenomena of industrial interest which involve precipitation across a colloidal gel membrane which separates two different aqueous solutions, for example, in cement technology and metal corrosion process. However, the variation in chemical composition, morphology and mechanical properties of the different surfaces of these formations is not well known yet. Several salts in different concentrations and conditions have been explored under terrestrial gravity and microgravity. The chemical garden structures have been characterised by morphology analysis, scanning electron microscopy, chemical analysis and x-ray diffraction, correlating these data with the biomimetic growth and the physical-chemical nanoprocesses involved in it. This approach can also be useful for the analysis of biomaterials with interesting biomechanical properties.
The Hydrolysis and Oxidation Behavior of Lithium Borohydride and Magnesium Hydride Determined by Calorimetry
Authors: Brinkman Kyle , Gray Joshua R. , Hardy Bruce , Anton Donald L.
Published: April 2011

Lithium borohydride, magnesium hydride and the 2:1 “destabilized” ball milled mixtures (2LiBH4:MgHM2) underwent liquid phase hydrolysis, gas phase hydrolysis and air oxidation reactions monitored by isothermal calorimetry. The experimentally determined heats of reaction and resulting products were compared with those theoretically predicted using thermodynamic databases. Results showed a discrepancy between the predicted and observed hydrolysis and oxidation products due to both kinetic limitations and to the significant amorphous character of observed reaction products. Gas phase and liquid phase hydrolysis were the dominant reactions in 2LiBH4:MgH2 with approximately the same total energy release and reaction products; liquid phase hydrolysis displayed the maximum heat flow for likely environmental exposure with a peak energy release of 6 (mW/mg).
Hydrogen Storage Properties of a Combined Li3AlH6-LiBH4 System
Authors: Choi Young Joon , Lu Jun , Sohn Hong Yong , Fang Zak
Published: April 2011

Lithium based complex hydrides, including lithium aluminum hydrides and lithium borohydride (LiAlH4, Li3AlH6 and LiBH4), are among the most promising materials due to their high hydrogen contents. In the present work, we investigated the hydrogen storage properties of a new combined system of Li3AlH6-LiBH4. The samples were made with small amounts of catalyst under low energy milling conditions. Thermogravimetric analysis (TGA) of a Ti-doped Li3AlH6/2LiBH4 indicated that the degree of hydrogen release reached 7.3 wt. % by the time the sample reached 450iÆc under a heating rate of 2iÆC/min. This increased to 8.8 wt. % when the sample was held at 450iÆCfor additional 8 hours minutes under this condition. The dehydrogenation product was a mixture of LiH and AlB2. This product could be rehydrogenated up to 3.8 wt. % under 24.1 MPa hydrogen pressure and 450iÆC.
Surface Enhanced Raman Spectroscopy and Cyclic Voltammetry Studies of Ni-rich Oxide Nanowires as Electrode Materials
Authors: Nguyen Que Anh , Bhargava Yash V. , Thorne Shawn A. , Cohen-Hyams Tzipi , Devine Thomas M.
Published: April 2011

A novel electrode material for Ni metal hydride batteries, composed of electrochemically synthesized, Ni-rich oxide nanowires, was investigated in this study. The nanowires, grown on Alloy 600 in a high-temperature, high-pressure aqueous electrolyte, are typically 25nm in diameter and 5-10um long. Cyclic voltammetry, with surface enhanced Raman spectroscopy (SERS) suggests that anodic polarization of the wires converts Ni2+ species to Ni3+, present as γ–-NiOOH, the chemical phase involved in the charge/discharge reaction in Ni-MH batteries. The reversibility of the reaction was confirmed via multiple polarization cycles and SEM imaging. In addition, the current density and polarization behavior of the nanowires in 0.01M KOH solution is compared to that of planar NiO and Alloy 600. Results suggest that the nanowires, due to their higher surface area, achieves at least 10 times the current density (for a given apparent area) of the non-nanowire samples.
Thermoelectric Properties of YbBiPt and YBiPt Thin Films
Authors: Guner Sadik , Budak Satilmis , Muntele Claudiu I , Ila Daryush
Published: April 2011

Monolayer thin films of YbBiPt and YBiPt have been produced with 560 nm and 394 nm thick respectively in house and their thermoelectric properties were measured before and after MeV ion bombardment. The energy of the ions were selected such that the bombarding Si ions stop in the silicon substrate and deposit only electronic energy by ionization in the deposited thin film. The bombardment by 5.0 MeV Si ions at various fluences changed the homogeneity as well as reducing the internal stress in the films thus affecting the thermal, electrical and Seebeck coefficient of thin films. The stoichiometry of the thin films was determined using Rutherford Backscattering Spectrometry, the thickness has been measured using interferometry and the electrical conductivity was measured using Van der Pauw method. Thermal conductivity of the thin films was measured using an in-house built 3ω thermal conductivity measurement system. Using the measured Seebeck coefficient, thermal conductivity and electrical conductivity we calculated the figure of merit (ZT). We will report our findings of change in the measured figure of merit as a function of bombardment fluence.
Effects of Mg Content on Zn1-xMgxO:Al Transparent Conducting Films
Authors: Li Xiaonan , Ray Hannah , Perkins Craig L. , Noufi Rommel
Published: April 2011

Conductive zinc oxide (ZnO) films are used extensively as transparent electrodes in thin-film photovoltaic solar cells. Compared with the widely used indium tin oxide (ITO) and tin oxide (SnO2), ZnO has a smaller optical bandgap. ZnO is commonly used as a front contact for copper indium gallium diselenide (CIGS) solar cells, but it forms a small, unfavorable conduction-band offset with the CdS layer. The optical bandgap of ZnO could easily be engineering by alloying with MgO or CdO. In this work, we try to optimize the ZnO for CIGS solar cells. The optical and electrical properties of Zn1-xMgxO:Al films fabricated by co-sputtering were studied. Two targets: ZnO:Al and MgO, were used. The ratio of ZnO/MgO was varied continuously on the 6”x6” glass substrate, and the effects of composition on the properties of the Zn1-xMgxO:Al films were investigated. The carrier concentration and mobility of the Zn1-xMgxO:Al films decreased quickly with increasing Mg content. However, the optical properties of the Zn1-xMgxO:Al films do not vary linearly with Mg content, as reported by most papers. The observed optical bandgap of Zn1-xMgxO:Al films is actually first narrowed, then increased with the Mg content. The shift in optical bandgap from narrow to wide occurs at around a composition of x = 0.07. After the point of x = 0.07, the bandgap width star increase but film sheet resistance already too low. Our result therefore suggests that the alloyed Zn1-xMgxO:Al does not benefit the CIGS solar cell.
Light management issues in intermediate band solar cells
Authors: Martí Antonio , Antolín Elisa , Cánovas Enrique , Linares Pablo García , Luque Antonio
Published: April 2011

This paper discusses several topics related to light management that improve our understanding of the performance and potential of the intermediate band solar cell (IBSC). These topics are photon recycling, photon selectivity and light confinement. It is found that neglecting photon recycling leads to underestimate the limiting efficiency of the IBSC in 7 points (56.1 % vs 63.2 %). Light trapping allows to effectively absorbing photons whose energy is associated to the weakest of the optical transitions in the IBSC, allowing also for higher efficiencies with lower device thickness. The impact of photon selectivity on the cell performance is also discussed.
Up Conversion for Photovoltaics
Authors: Conibeer Gavin , Shalav Avi , Trupke Thorsten , Green Martin
Published: April 2011

An up-converter (UC) absorbs two or more low-energy photons and emits a single high-energy photon. A down-converter (DC) absorbs a single high-energy photon and emits two or more low energy photons. The current work extends previous limiting efficiency analysis to a combination of UC and DC; an up converter with two levels; and to compare analyses using real air mass data with that modelling the sun as a blackbody. Analysis has been carried out both with the band gap of the cell as an optimized parameter and at a fixed value of 1.1eV. All of UC, DC and two level UC are shown to improve efficiencies for both spectra. Combined UC/DC improves the efficiency further for the 1.1eV band gap but gives a lower efficiency for the optimised band gap. The explanation for this unexpected result is presented based on the small coupling losses that result from absorption/re-emission in the DC. The limiting efficiencies of such an approach are very similar to several other third generation concepts such as impurity PV, Intermediate Band solar cells or three level tandems. However in practice the UC (or DC) approach has the advantage that the optical properties of the UC are decoupled from the electrical properties of the PV cell, and hence each can be optimised independently. This means that it may be the simplest third generation approach to implement using existing PV cells, if a reasonable UC efficiency can be obtained. Nonetheless experimental work on realising UC is at an early stage. Some of the work on rare earth doped UC is reviewed together with the potential to improve the spectral sensitivity to below band gap radiation.
Light Trapping in μc-Si:H Thin-film Solar Cells by Back Surface Reflector with Grating Structure Fabricated by Self-ordering Process
Authors: Sai Hitoshi , Fujiwara Hiroyuki , Kondo Michio
Published: April 2011

Back surface reflectors (BSRs) with grating structures have been developed to enhance light trapping in thin-film microcrystalline Si (μc-Si:H) solar cells. As a grating structure, a periodic honeycomb-like dimple pattern with periods of 100 ˜ 450 nm has been fabricated on Al substrates by a self-ordering process using anodic oxidation of Al. A clear diffraction effect by the grating structure has been confirmed on the patterned Al using angle-dependent reflection measurement. From quantum efficiency measurements, we found that the periodically patterned BSR can confine the incident light effectively, especially at longer wavelengths. Nevertheless, short circuit current densities obtained from the patterned BSRs are rather comparable to that obtained from the random textured substrate. For further improvement of the light-trapping effect by the grating structure, it is necessary to realize higher diffraction efficiencies while maintaining high total reflectivity on the BSR structure.
Nanoimprint Lithography of Light Trapping Structures in Sol-gel Coatings for Thin Film Silicon Solar Cells
Authors: Heijna Maurits , Loffler Jochen , Van Aken Bas , Soppe Wim , Borg Herman , Peeters Patrick
Published: April 2011

For thin-film silicon solar cells, light trapping schemes are of uppermost importance to harvest all available sunlight. Typically, superstrates with randomly textured TCO front layers are used to scatter the light diffusively in pin-cells on glass. Here, we investigate methods to texture opaque substrates with both random and periodic textures, for use in nip-cells on metal foil. We applied an electrically insulating SiOx-polymer coating on a stainless steel substrate, and textured this barrier layer by nanoimprint. On this barrier layer the back contact is deposited for further use in the solar cell stack. Replication of masters with various random and periodic sub-micron patterns was tested, and, using scanning electron microscopy, replicas were found to compare well with the originals. The embossing of the barrier layer does not diminish its electrically isolating properties, and thus adds extra functionality to this layer. Masters with U-grooves of various sub-micrometer widths have been used to investigate the optimal dimensions of regular patterns for light trapping in the silicon layers. Angular reflection distributions were measured to evaluate the light scattering properties of both periodic and random patterns. These periodic patterns, comprising diffraction gratings, show promising results in scattering the light to specific angles, enhancing the total internal reflection in the solar cell.
Highly Conductive In4Sn3O12 Films Prepared by Pulsed Laser Deposition
Authors: O'Neil David H , Kuznetsov Vladimir , Jacobs Robert , Jones Martin O , Edwards Peter P
Published: April 2011

Highly conductive (> 103 Ω-1cm-1) and transparent (∼ 90%) In4Sn3O12 films have been deposited using pulsed laser deposition (PLD) on glass substrates held at a temperature of 500°C under varying pressures of oxygen (2.5 mTorr ≤ PO2 ≤ 15 mTorr). The crystallinity and the roughness of the films were found to increase with the pressure of oxygen used during deposition. Electron concentrations of the order of 5×1020 cm-3 and mobilities as high as 30 cm2V-1s-1 were derived from the measurement of Hall coefficients. Both the electronic transport and optical properties of the films were found to be strongly sensitive to the pressure of oxygen used during deposition.
Robust Design of Advanced Thermoelectric Conversion Systems: Probabilistic Design Impacts on Specific Power and Power Flux Optimization
Authors: Hendricks Terry J , Karri Naveen K.
Published: April 2011

Advanced, direct thermal energy conversion technologies are receiving increased research attention in order to recover waste thermal energy in advanced vehicles and industrial processes. Advanced thermoelectric (TE) systems necessarily require integrated system-level analyses to establish accurate optimum system designs. Past system-level design and analysis has relied on well-defined deterministic input parameters even though many critically important environmental and system design parameters in the above mentioned applications are often randomly variable, sometimes according to complex relationships, rather than discrete, well-known deterministic variables. This work describes new research and development creating techniques and capabilities for probabilistic design and analysis of advanced TE power generation systems to quantify the effects of randomly uncertain design inputs in determining more robust optimum TE system designs and expected outputs. Selected case studies involving stochastic TE .material properties demonstrate key stochastic material impacts on power, optimum TE area, specific power, and power flux in the TE design optimization process. Magnitudes and directions of these design modifications are quantified for selected TE system design analysis cases.
Electronic Phase Transitions in F-electron Metals at High Pressures: Synchrotron X-ray Spectroscopic Studies on GD to 100 GPa
Authors: Yoo Choong-Shik , Maddox Brian , Iota Valentin
Published: April 2011

Unusual phase transitions driven by electron correlation effects occur in many f-electron metals (lanthanides and actinides alike) from localized phases to itinerant phases at high pressures. The dramatic changes in atomic volumes and crystal structures associated with some of these transitions signify equally important changes in the underlying electronic structure of these correlated f-electron metals. Yet, the relationships among the crystal structure, electronic correlation and electronic structure in f-electron metals have not been well understood. In this study, utilizing recent advances in third-generation synchrotron x-ray spectroscopies and high-pressure diamond-anvil cell technologies, we describe the pressure-induced spectral changes across the volume collapse transition in Gd at 60 GPa and well above. The spectral results suggest that the f-electrons of high-pressure Gd phases are highly correlated even at 100 GPa – consistent with the Kondo volume collapse model and the recent experimental evidence of strong electron correlation of α-Ce.
Quantifying the Importance of Orbital Over Spin Correlations in δ-Pu Within Density-Functional Theory
Authors: Soderlind Per
Published: April 2011

The electronic structure of plutonium is studied within the density-functional theory (DFT) model. Key features of the electronic structure are correctly modeled and bonding, total energy, and electron density of states are all consistent with measure data, although the prediction of magnetism is not consistent with many observations. Here we analyze the contributions to the electronic structure arising from spin polarization, orbital polarization, and spin-orbit interaction. These effects give rise to spin and orbital moments that are of nearly equal magnitude, but anti-parallel, suggesting a magnetic-moment cancellation with a zero total moment. Quantifying the spin versus orbital effects on the bonding, total energy, and electron spectra it becomes clear that the spin polarization is much less important than the orbital correlations. Consequently, a restricted DFT approach with a non-spin polarized electronic structure can produce reasonable equation-of-state and electron spectra for δ-Pu when the orbital effects are accounted for. Hence, we present two non-magnetic models. One in which the spin moment is canceled by the orbital moment and another in which the spin moment (and therefore the orbital moment) is restricted to zero.
Theoretical Studies of Spectral Properties of Plutonium
Authors: Zhu Jian-Xin , McMahan A.K. , Jones M.D. , Durakiewicz T. , Joyce J.J. , Wills J.M. , Albers R.C.
Published: April 2011

By combining the local density approximation (LDA) with dynamical mean field theory (DMFT), we report a systematic analysis of the spectral properties of δ-plutonium with varying 5f occupancy. The LDA Hamiltonian is extracted from a tight-binding (TB) fit to full-potential linearized augmented plane-wave (FP-LAPW) calculations. The DMFT equations are solved by the exact quantum Monte Carlo (QMC) method and the Hubbard-I approximation. We show the strong sensitivity of the spectral properties to the 5f occupancy, which suggests using this occupancy as a fitting parameter in addition to the Hubbard U. By comparing with PES data, we conclude that the “open shell” 5f5 configuration gives the best agreement, resolving the controversy over 5f “open shell” versus “close shell” atomic configurations in δ-Pu.
Testing of Uranium Dioxide Containing Different Levels of Alpha Activity Under Anaerobic and Reducing Conditions
Authors: Ödegaard-Jensen Arvid , Oversby Virginia
Published: April 2011

Sweden plans to dispose of spent nuclear reactor fuel in a deep geologic repository in granitic rock. The conditions in the repository in the long term will be reducing and water is not expected to contact the fuel until after more than 1000 years. At that time, most of the beta- and gamma-active nuclides will have decayed away and the radiation will be dominated by alpha decay. In order to simulate the radiolysis field for dissolution of spent fuel with age more than 1000 years we have used uranium dioxide containing 5% U-235 and 0, 5, or 10% U-233. The 10% U-233 gives an alpha activity appropriate to about 3000 years after disposal. Samples were testied in a synthetic groundwater with low ionic strength and with the chemical composition dominated by sodium bicarbonate and calcium chloride. Tests were run in triplicate using an atmosphere of nitrogen (1atm), hydrogen (10 bar), hydrogen (10 bar) plus an iron strip in the solution, nitrogen (1 atm) plus an iron strip in the solution, hydrogen (10 bar) plus an iron strip in the solution, hydrogen (10 bar) without the iron strip. Each of these test conditions was run for 2 consecutive periods of at least 21 days. The results showed that the dissolution behavior of the samples was the same for both nitrogen atmosphere and hydrogen atmosphere. The amount of U dissolved under these conditions clearly showed the enhancement of dissolution due to oxidation of the sample surface by radiolysis products. When an iron strip was added to the solution, the amount of dissolution decreased dramatically indicating that the Fe(II) ions released from the corroding iron were able to react with most of the radiolysis products before they could oxidize the uranium dioxide surface.
Orbital Hybridization in Uranium Compounds and its Influence on Electronic Properties
Authors: Wang Wei , Zhang Hong , Liu Guokui
Published: April 2011

Computational analysis and modeling of spectroscopic properties of trivalent uranium in crystals of hexagonal symmetry have been conducted with inclusion of the crystal-field induced orbital hybridization between the 5f3 and 5f26d configurations. It is shown that, in the absorption spectrum with energy above 20,000 cm-1, the mixing of 5f3 and 5f26d states is significant. The spectrum in this region cannot be interpreted by the conventional model of crystal field theory. The Judd-Ofelt theory is completely failed in predicating the intensities of optical absorption from the ground state to the configuration mixed excited states. A new Hamiltonian including the odd ranks of crystal field interaction is diagonalized on the bases of all 5f3 and 5f26d states. A simulation of absorption spectrum is optimized in comparison with the experimental spectrum for determination of the Hamiltonian parameters.
Spin-Orbit Coupling Versus Exchange Interaction in Actinide Metals
Authors: van der Laan Gerrit , Moore Kevin Thomas
Published: April 2011

The electronic structure of the actinide metals, Th, U, Np, Pu, Am, and Cm, is investigated using electron energy-loss spectroscopy (EELS) in a transmission electron microscope, together with many-electron spectral calculations. At theN4,5edge, sum rule analysis gives the angular part of the spin-orbit interaction per hole, showing that while light metals (Th and U) followLScoupling, heavier metals (Pu, Am, and Cm) follow intermediate coupling of the 5fstates. The intermediate coupling is near thejjlimit for Pu and Am, but strongly shifted towards theLScoupling limit for Cm. At theO4,5edge many-electron spectral calculations show that the prepeak corresponds to a “forbidden” transition.
Multi Scale Study of Self-irradiation Effects in Plutonium Alloys
Authors: Berlu Lilian , Rosa Gaëlle , Jomard Gérald
Published: April 2011

Experimental measurements have shown that plutonium alloys exhibit changes of their macroscopic as well as microscopic properties. For example, a swelling of plutonium alloys was observed with aging with dilatometry and X-ray diffraction. The main idea to explain these changes rises in self irradiation undergoing by those materials. Plutonium α decay is at the origin of displacements cascades creating a large amount of structural defects. These later by anihilation and recombination give rise to larger defects such as voids and clusters. The aim of this work is to study the occurrence of such phenomena combining ab-initio, molecular dynamic and Monte Carlo methods in a coherent multi-scale approach which would help to understand long term behavior of structural defects and consequences of self irradiation. We show that plutonium does not seem to behave like other metals under ion irradiation. We discuss results obtained for high energy displacements cascade simulations. After parametric study of displacements cascade simulations combining temperature and cascade energy has been exposed, superposition of low energies displacements cascades is discussed as a method to construct realistic defect microstructures and to reach a rational use of computational time. At the end, we will present results of preliminary Monte Carlo simulations based on our molecular dynamic data which show that the spatial correlation of the stable defects populations created by the cascades seems to have a great influence on the predicted swelling.
Direct Energy Conversion Nano-hybrid Fuel
Authors: Popa-Simil Liviu
Published: April 2011

Most of the exothermic nuclear reactions transfer the mass defect or binding and surplus energy into kinetic energy of the resulting particles. These particles are traveling through material lattices, interacting by ionization and nuclear collisions. Placing an assembly of conductive-insulating layers in the path of such radiation, the ionization energy is transformed into charge accumulation by polarization. The result is a super-capacitor charged by the moving particles and discharged electrically. Another more promising solution is to use bi-material nanoparticles organized such as to act like a serial connection and add the voltage. A spherical symmetry fission products source coated in several nano-layers is desired for such structures. The system may operate as dry or liquid-immersed battery, removing the fission products from the fissile material. There is a tremendous advantage over the current heat flow based thermal stabilization system allowing a power density up to 1000 times higher.