bluuebunny/crossref_metadata_2025 huggingface dataset:
Diamond-like Carbon Film Coating for Tissue Engineering
Authors: Ohgoe Yasuharu , Matsuo Haruki , Nonaka Kazuhiro , Yaguchi Toshiyuki , Kanasugi Kazuya , Hirakuri Kenji , Funakubo Akio , Fukui Yasuhiro
Published: August 2010

In this study, we focus on effect of diamond-like carbon (DLC) coating on scaffold for tissue engineering. DLC film was deposited on segmented polyurethane (SPU) scaffold sheet which consists of micro SUP fibers. Structural and compositional effects of the DLC film coating were investigated on cell growth as an investigation of biological response. The surface composition, morphology, structures, and wettability of the DLC film coating was estimated by using X-ray photoelectron spectrometer (XPS), Scanning Electron Microscope (SEM), Ar-laser Raman spectrophotometer (Raman), and contact angle measurement. And then, human umbilical vein endothelial (HUV-EC-C) cells were grown on the DLC coated scaffold sheet. The results presented here suggest that DLC film coating is promising approach to improve biological for tissue engineering.
Electrical and structural properties of ultrathin polycrystalline and epitaxial TiN films grown by reactive dc magnetron sputtering
Authors: Magnus Fridrik , Ingason Arni Sigurdur , Olafsson Sveinn , Gudmundsson Jon Tomas
Published: August 2010

Ultrathin TiN films were grown by reactive dc magnetron sputtering on amorphous SiO2 substrates and single-crystalline MgO substrates at 600°C. The resistance of the films was monitored in-situ during growth to determine the coalescence and continuity thicknesses. TiN films grown on SiO2 are polycrystalline and have coalescence and continuity thicknesses of 8 Å and 19 Å, respectively. TiN films grow epitaxially on the MgO substrates and the coalescence thickness is 2 Å and the thickness where the film becomes continuous cannot be resolved from the coalescence thickness. X-ray reflection measurements indicate a significantly higher density and lower roughness of the epitaxial TiN films.
Rutherford Backscattering Spectrometry Analysis of Growth Rate and Activation Energy for Self-formed Ti-rich Interface Layers in Cu(Ti)/Low-k Samples
Authors: Kohama Kazuyuki , Ito Kazuhiro , Mori Kenichi , Maekawa Kazuyoshi , Shirai Yasuharu , Murakami Masanori
Published: August 2010

A new fabrication technique to prepare ultra-thin barrier layers for nano-scale Cu wires was proposed in our previous studies. Ti-rich layers formed at the Cu(Ti)/dielectric-layer interfaces consisted of crystalline TiC or TiSi and amorphous Ti oxides. The primary control factor for Ti-rich interface layer composition was the C concentration in the dielectric layers rather than the formation enthalpy of the Ti compounds. To investigate Ti-rich interface layer growth in Cu(Ti)/dielectric-layer samples annealed in ultra high vacuum, Rutherford Backscattering Spectrometry (RBS) was employed in the present study. Ti peaks were obtained only at the interface for all the samples. Molar amounts of Ti atoms segregated to the interface (n) were estimated from Ti peak areas. Thenvalue was defined byn=Z·exp(-E/RT) · tm, whereZis a preexponential factor andEthe activation energy for the reaction. TheZ,E, andmvalues were estimated from plots of lognvs logtand lognvs 1/T. Themvalues are similar in all the samples. TheEvalues for Ti atoms reacting with the dielectric layers containing carbon (except SiO2) tended to decrease with decreasing C concentration (decreasingk), while reaction rate coefficients (Z·exp(-E/RT)) were insensitive to C concentration in the dielectric layers. These factors lead to conclusion that growth of the Ti-rich interface layers is controlled by chemical reactions of the Ti atoms with the dielectric layers represented by theZandEvalues, rather than diffusion in the Ti-rich interface layers.
Photonic Crystal Structures as Spectral Control for Thermophotovoltaic Energy Conversion
Authors: Fourspring Patrick Michael
Published: August 2010

Spectral control is an enabling technology for greater than 10% efficient thermophotovoltaic (TPV) energy conversion [1-3]. Without control of the spectral distribution of photons reaching a TPV cell, the efficiency of a TPV energy conversion system suffers dramatically. Spectral control is the selection, design, and development of materials and structures used in TPV energy conversion systems to maximize the net flux of convertible (above band gap) photons, minimize the net flux of unconvertible (below band gap) photons, and recuperate (or reflect) any net flux of unconvertible (below band gap) photons that reach the TPV cell back to the radiating surface. Front surface, tandem filters consisting of an edge pass filter (short pass) in series with a highly doped, epitaxially grown layer have achieved the highest energy weighted spectral efficiency to date.

The performance, however, of these tandem filters is limited by at least two fundamental physical phenomena: the variation in performance with the incident angle of the photons and absorption in the filter materials. Three dimensional (3D), photonic crystal structures offer a potential solution to these fundamental limitations of tandem filters as well as the potential of spectral control for the radiating surfaces of TPV energy conversion system. First, 3D photonic crystal structures, in theory, perform equally for all incident angles. Second, the fabrication techniques for 3D photonic crystal structures may allow the use of materials (such as crystalline Si) with less absorption in the spectral range of interest (1-15μm) than the materials currently used in tandem filters. The fabrication techniques for 3D photonic crystal structures may also allow the use of high temperature (1000°C) materials for use as radiating surface spectral control. If so, 3D photonic crystal structures may be used to mitigate several of the inefficiencies associated with TPV systems.

The conclusion of this assessment is that 3D, photonic crystal structures can, in theory, provide near perfect TPV spectral control. If so, these structures may allow a 20% improvement over the performance achieved by tandem filters. Realizing this potential for TPV spectral control, however, will likely require significant development. At least two major challenges exist:

• Design techniques will likely need to be developed that will allow the analysis and design of 3D photonic crystal structures.

• Fabrication techniques will need to be developed for these structures that provide sufficient fidelity to a design to achieve the required performance and can be scaled to provide the area required for a given TPV application.
Fabrication of Cu(In,Ga)Se2 Films by a Combination of Mechanochemical Synthesis, Wet Bead Milling, and a Screen Printing/sintering Process
Authors: Kubo Junya , Matsuo Yoshihiro , Wada Takahiro , Yamada Akira , Konagai Makoto
Published: August 2010

We prepared fine Cu(In,Ga)Se2 (CIGS) powder suitable for screen printing using a mechanochemical synthesis and wet bead milling. Particulate precursors were deposited in a layer by a screen-printing technique, and the porous precursor layer was sintered into a dense polycrystalline film by atmospheric-pressure firing in an N2 gas atmosphere. The microstructure of CIGS powder and fired CIGS film were observed in an SEM. The wet bead milling was effective for the reduction and homogenization of the average grain size of CIGS powder. The CIGS grains in the film were well sintered and the size of CIGS grains was as large as about 2 μm. The CIGS solar cell showed an efficiency of 3.1%, with Voc of 0.279 V, Jsc of 28.8 mA/cm2 and FF of 0.386.
Fabrication of TiO2 Nanobelt Network for Dye-Sensitized Solar Cells
Authors: Li Haiyan , Jiao Jun
Published: August 2010

Interconnected TiO2 nanobelt networks were prepared to serve as anode materials. The aim is to enhance the electron transport through the anode of dye-sensitized solar cells. Using an alkaline hydrothermal procedure and by controlling the reaction time, two kinds of nanostructures were synthesized: TiO2 nanobelts and the mixture of TiO2 nanobelts/TiO2 nanoparticles. This investigation suggests that TiO2 nanobelts are the result of the rearrangement of the [Ti(OH)6]2- monomers formed during the erosion process of TiO2 nanoparticles. The nanostructures of as-synthesized nanobelts were woven and interconnected, resulting in networks after an annealing process. Raman analysis indicates that both kinds of nanostructures were pure anatase. Electrical characterization suggests that the conductivities of these TiO2 nanobelt networks were higher than those of the TiO2 nanoparticle films. Under simulated sunlight with an intensity of AM 1.5 G, the solar cells made of TiO2 nanobelt networks show exceptional photocurrent in comparison to those made of TiO2 nanoparticles.
A III-nitride Layered Barrier Structure for Hyperspectral Imaging Applications
Authors: Bell Douglas , Tripathi Neeraj , Grandusky James , Jindal Vibhu , Shahedipour-Sandvik Fatemeh
Published: August 2010

We report on a novel photodetector structure based on III-nitride materials. A layered configuration is used to create a barrier with voltage-tunable height. The barrier is used as a filter on photoexcited holes and electrons, and could form the basis for a dynamically tunable pixel in a hyperspectral imaging array. This would eliminate the need for external gratings and filters used in conventional hyperspectral instruments; in addition, the tunability of pixels allows decrease of the array dimension by one. The III-nitride materials family is a good candidate for this device, combining large band offsets with the ability for epitaxial growth. We have demonstrated the feasibility of using III-nitride materials to fabricate layered tunnel barriers, and have demonstrated tunability of photodetection using these structures. External quantum efficiencies of > 12% have been achieved with prototype devices.
Polymer-Titania Composites for Photocatalysis of Organics in Aqueous Environments
Authors: Coutinho Cecil A , Gupta Vinay K
Published: August 2010

Microcomposites composed of titanium dioxide nanoparticles embedded within cross-linked, thermally responsive microgels of poly(N-isopropylacrylamide) were prepared. These microcomposites showed rapid sedimentation, which is useful for gravity separation of the titania nanoparticles in applications such as environmental remediation. To investigate the degradation kinetics using these microcomposites in aqueous suspensions, methyl orange was employed as a model contaminant. The decline in the methyl orange concentration was monitored using UV-Vis spectroscopy. Degradation of methyl orange was also measured using only nanoparticles TiO2 (DegussaTM P25) for comparison with the microcomposites. Experiments were performed at different pH conditions that spanned acidic, neutral, and basic conditions to gain insight into the interplay of TiO2 surface charge, ionization of the polyelctrolyte chains in the microcomposites, and ionization of the methyl orange.
TiO2 anatase nanotubes for the purification of uranium,arsenic and lead containing water: an X-ray Photoelectron Spectroscopy study
Authors: Bonato Marco , Ragnarsdottir Kristin Vala , Allen Geoffrey C.
Published: August 2010

TiO2 anatase nanotubes synthesised via anodic oxidation were used as adsorbent for the uptake of U and Pb from aqueous solution and the photoremoval of As(III). An X-ray photoelectron spectroscopy study of the sorbent medium surface revealed a high adsorption of U and Pb at pH 8. The adsorption of the uranyl ion was enhanced in an anoxy (N2) atmosphere, because this prevents the formation of very stable carbonyl complexes. As(III) was adsorbed on TiO2 but in the presence of O2 and UV light was oxidized to As(V). XPS analysis revealed that in the pH range 3-9 As(V) was always the major species detected at the surface of the titania photocatalyst.
The US Department of Energy's Working Group on Photoelectrochemical Hydrogen Production: Promoting Technology-Enabling Breakthroughs in Semiconductor Materials Research
Authors: Garland Roxanne , Miller Eric L.
Published: August 2010

Photoelectrochemical (PEC) hydrogen production, using sunlight to split water, is an important enabling technology for a future “Green” economy which will rely, in part, on hydrogen as an energy currency. The traditional semiconductor-based PEC material systems studied to date, however, have been unable to meet all the performance, durability and cost requirements for practical hydrogen production. Technology-enabling breakthroughs are needed in the development of new, advanced materials systems, and toward this end, the U.S. Department of Energy’s Working Group on PEC Hydrogen Production is bringing together experts in analysis, theory, synthesis and characterization from the academic, industry and national-laboratory research sectors. Key Working Group activities, as described in this paper, include performing techno-economic analyses of large-scale PEC production systems and establishing standardized testing and screening protocols for candidate PEC materials systems. In addition, a number of Working Group “Task Forces” are focused on advancing critical PEC materials theory, synthesis and characterization capabilities for application in the research and development of broad-ranging materials systems of promise, including complex metal-oxide and -nitride compounds, amorphous silicon alloys, III-V semiconductors and the copper chalcopyrites. The current status of Working Group activities and progress is summarized.
Electronic Structure Properties of the Photo-Catalysts YVO4 and InVO4 Slab Systems with Water Molecules Adsorbed on the Surfaces
Authors: Oshikiri Mitsutake , Boero Mauro , Matsushita Akiyuki , Ye Jinhua
Published: August 2010

Electronic structure properties of a photo-catalyst slab system based on a material YVO4 or InVO4 which is sandwiched by water molecular layers have been investigated by first-principles calculation. As a result, we found the tendency that the band gap of the InVO4 slab system sandwiched by water molecular layers was smaller than that of YVO4 system while the band gap values of the bulk crystals of YVO4 and InVO4 are almost same. This result may provide us a good clue to understand the reason why the InVO4 system can indicate a visible light response in photo-catalysis and the YVO4 system can not.
Morphologic, Compositional and Magnetic Characterization of Sputtered CoCr Thin Films for Applications in MTJs as Hard Spin Injectors
Authors: Martino Paola , Chiolerio Alessandro , Pandolfi Paolo , Tiberto Paola , Allia Paolo
Published: August 2010

Spin-polarized currents across an insulating tunnel barrier, needed for the development of efficient magnetic tunneling junctions (MTJs), may be obtained using hard spin injector electrodes. Thin films of CoCr solid solutions have been fabricated involving two main steps: 1) deposition of Co/Cr alternated layers via RF magnetron sputtering both onto silicon (100) substrates and thermally oxidized wafers and 2) thermal annealing in a partial Ar pressure of 1 mTorr at 450°C for 1 hour and cooling treatment in a uniform magnetic field (600 Oe). The deposition of stacks of pure elements and subsequent diffusion treatment has been preferred instead of the direct deposition of the native alloy because in the former case the right composition and magnetic bias may be tuned more easily playing on the layer thicknesses and number of repetitions.

A detailed numerical correlation of field effect SEM images and EDX micro-maps was used to evaluate the oxygen diffusion on the magnetic film, while an alternating gradient force magnetometer (AGFM) allowed us to evaluate at room temperature both coercivity and magnetic bias obtained after the field cooling treatment. The effect of standard thermal treatment on the homogeneity of the films is discussed, and a possible alternative heating technique is proposed.
Could Life Originate between Mica Sheets?: Mechanochemical Biomolecular Synthesis and the Origins of Life
Authors: Hansma Helen Greenwood
Published: August 2010

The materials properties of mica have surprising similarities to those of living systems. The mica hypothesis is that life could have originated between mica sheets, which provide stable compartments, mechanical energy for bond formation, and the isolation needed for Darwinian evolution. Mechanical energy is produced by the movement of mica sheets, in response to forces such as ocean currents or temperature changes. The energy of a carbon-carbon bond at room temperature is comparable to a mechanical force of 6 nanoNewtons (nN) moving a distance of 100 picometers. Mica's movements may have facilitated mechanochemistry, resulting in the synthesis of prebiotic organic molecules. Furthermore, mica's movements may have facilitated the earliest cell divisions, at a later stage of life's origins. Mica's movements, pressing on lipid vesicles containing proto-cellular macromolecules, might have facilitated the blebbing off of ‘daughter’ protocells. This blebbing-off process has been observed recently in wall-less L-form bacteria and is proposed to be a remnant of the earliest cell divisions (Leaver, et al. Nature457, 849 (2009).
Measuring Elastic Properties of Highly Metastatic Cells using Nano-Capillary Wrinkling
Authors: Iyer Nan , Cooper Katelyn , Yang Jianing , Zenhausern Frederic
Published: August 2010

Measuring elastic properties of cells has gained importance in the study of malignant transformations. The stiffness of a cell, which is technically referred to as the modulus of elasticity or Young's Modulus, E, is the measure of the amount of cell deformation caused by an applied known force. In vitro studies have shown that cancer cells have much lower elastic stiffness than normal cells. These stiffness measurements and their differences can be used to study the behavioral mechanics of how cancer cells grow, profligate, and die in a patient. Another important use of this difference in elasticity is in cancer detection.

In this study, we explore the viability of measuring the elastic modulus of cancer cells by using a method that only requires the use of a low magnification microscope and a digital camera. In particular we are interested in applying the previously reported relationship between the wrinkling of thin films and the elastic properties of freely floating polystyrene (PS) films. Our work extends the scope of previous thin film studies by evaluating wrinkle formation in floating polystyrene films coated with biological cells. Our results show that the wrinkle formation is modified, both in morphology and in size, by the presence of a cellular monolayer on top of the PS film.
Sucker Rings from the Humboldt Squid Dosidicus gigas: The Role of Nanotubule Architecture on the Mechanical Properties
Authors: Miserez Ali , Weaver James , Kisailus David , Birkedal Henrik
Published: August 2010

The suckers that line the arms and tentacles of squid are equipped with rigid toothed ring-like elements that increase the gripping power during prey capture and handling. The sucker rings of the Humboldt squid Dosidicus gigas, are fully proteinaceous and contain nanotubules with diameters ranging from 100 to 250 nm. It has been shown previously that the ensuing porosity is a prime determinant of the local elastic modulus [A. Miserez et al., Adv. Mater. 21, 401 (2009)]. Here additional nanoindentation data are presented together with structural analyses. The nanomechanical data support our model that the measured modulus is determined by the local porosity. The dry moduli reach ca. 8 GPa and are reduced about two-fold in the hydrated state. This surprisingly small reduction is discussed in relation to possible chemistries responsible for assembly of these structures.
Design of Nano-Composites for Ultra-High Strengths and Radiation Damage Tolerance
Authors: Misra Amit , Zhang X. , Demkowicz M. J. , Hoagland R. G. , Nastasi M.
Published: August 2010

The combination of high strength and high radiation damage tolerance in nanolaminate composites can be achieved when the individual layers in these composites are only a few nanometers thick and therefore these materials contain a large volume fraction associated with interfaces. These interfaces act both as obstacles to slip, as well as sinks for radiation-induced defects. The morphological and phase stabilities of these nano-composites under ion irradiation are explored as a function of layer thickness, temperature and interface structure. Using results on model systems such as Cu-Nb, we highlight the critical role of the atomic structure of the incoherent interfaces that exhibit multiple states with nearly degenerate energies in acting as sinks for radiation-induced point defects. Reduced radiation damage also leads to a reduction in the irradiation hardening, particularly at layer thickness of approximately 5 nm and below. The strategies for design of radiation-tolerant structural materials based on the knowledge gained from this work will be discussed.
Deposition of Ordered Arrays of Metal Sulfide Nanoparticles in Nanostructures Using Supercritical Carbon Dioxide
Authors: Wang Joanna , Smetana Alexander B. , Boeckl John J. , Brown Gail J. , Wai Chien M.
Published: August 2010

Silver sulfide (Ag2S) and cadmium sulfide (CdS) nanoparticles of adjustable sizes are synthesized using a water-in-hexane microemulsion method and stabilized by dodecanethiol. The stabilized metal sulfide nanoparticles can be deposited homogenously on flat substrates forming ordered 2D arrays in supercritical fluid carbon dioxide (Sc-CO2). The use of Sc-CO2 leaves the particles unaffected by de-wetting effects and surface tension caused by traditional solvents and produces uniform arrays. The Sc-CO2 deposition technique can effectively fill the metal sulfide nanoparticles into nanoscale features, which is difficult to achieve by conventional solvent evaporation methods.
Effect of Sintering Atmosphere on the Microstructure of Gold Nanoparticulate Film
Authors: Jang Seonhee , Cho Hyejin , Kang Sungkoo , Choi Joonrak , Oh Sungil , Joung Jaewoo , Kim Donghoon
Published: August 2010

Over the past few decades, metallic nanoparticles (NPs) have been of great interest due to their unique properties which distinguish them from those of bulk metals. Many attempts have been conducted to investigate the characteristics of NPs and their applications. However, the sintering process which converts metallic NPs to conductive film was not established yet. In this study, the microstructure evolution of Au NPs after sintering under different thermal condition was examined and the film quality was studied based on densification, organic residues and electrical resistivity. Au NP ink dispersed in a toluene were spin coated on Ni-plated FCCL or Si substrates and thermally treated in a furnace under different sintering profiles under various types of flows such as air, nitrogen (N2), or reducing atmosphere of formic acid (FA). The Au ink was consisted of Au NPs coated with an organic capping molecule. The capping molecules not only help NPs to disperse but prevent aggregation and precipitation of NPs out of solution. When the NPs are treated by thermal process, the surface ligands from capping molecule start to decompose and necking and melting of NPs occur producing the film with the electrical conductivity. The diameter of Au NPs was approximately between 5-7 nm with spherical shape. The Au film sintered under air showed only necking between neighboring Au NPs without further grain growth. When Au NPs films were sintered under N2 atmosphere, NPs fused together in clusters. Under sintering with flows of FA, a larger area of pores due to the volume shrinkage of the film was observed since an agglomeration and melting of NPs were considerably progressed compared to the film sintered under N2. Sintering with a flow of a single gas such as air or N2 showed organic residues in the film indicated by C-H or C-O stretch peaks. However, when mixed flows of FA and N2 were applied, there was no IR peaks from organic substances observed in the film. It is assumed that the organic capping molecules surrounding the Au NPs were removed significantly with sintering with two flows of FA and N2. The microstructure showed less pore distribution and lower level of organic residues compared to those sintered under air, N2, or FA atmospheres. The electrical resistivity was about twice of bulk value of 2.44 μΩ -cm. Overall Au NPs film sintered under FA and N2 resulted in a better sintering effect based on densification of the film and level of residual organics, translating into a relatively high electrical conductivity.
Three-dimensional Organic Field-effect Transistors on Plastic Substrates: Flexible Transistors with Very High Output Current
Authors: Takeya Jun , Uno M. , Nakayama Kengo
Published: August 2010

Attractiveness of organic field-effect transistors are in their low-cost and easy fabrication processes as well as their mechanical flexibility, while a significant drawback has been their poorer transistor performances than those of silicon and oxide semiconductors because of lower carrier mobility in organic semiconductors. We have developed an easy MEMS-based process to fabricate three-dimensional organic transistors with metal-insulator-semiconductor structures of multiple vertical channels on plastic platforms. The design maximizes the space availability and the output current per area. The flexible three-dimensional organic transistors indeed present outstanding current of ∼ 0.5 A/cm2, which is more than sufficient for driving pixels of typical organic light-emitting diodes. High on-off ratio up to 107 is also demonstrated.
Leakage Current Reduction and Ferroelectric Property of BiFe1-xCoxO3 Thin Films Prepared by Chemical Solution Deposition Using Rapid Thermal Annealing
Authors: Nguyen TruongTho , Kanashima Takeshi , Okuyama Masanori
Published: August 2010

Ferroelectric Bi1.1Fe0.9Co0.1O3 (BFCO) thin films were prepared on Pt/TiO2/SiO2/Si substrates by chemical solution deposition method using rapid thermal annealing (RTA). The thickness of all BFCO thin films is about 100 nm. Although the BFCO prepared at 545°C has a large value of difference of polarization at zero field, 88 C/cm2, the P-E hysteresis loop of the BFCO thin film prepared at 520°C looks like more saturated and shows 47 C/cm2 of difference of polarization at zero field in the applied electric field of 2 MV/cm. The leakage current of the BFCO film annealed at 520°C, is about 2 × 10-2 A/cm2 at room temperature (RT). Moreover, it is also shown that the saturated possibility of P-E hysteresis loops and in 2 MV/cm their apparent difference of polarization at zero field depend on not only the leakage current but also scanning frequency used to measure BFCO thin films. Accordingly, the P-E hysteresis loops of BFCO thin films prepared from 520°C to 545°C seem to be saturated at high frequency from 10 KHz to 20 KHz when these samples are measured at RT.
Isothermal Martensitic Transformation Kinetics in Ni-Mn-Sn Ferromagnetic Shape Memory Alloys
Authors: Shamberger Patrick , Pakhomov Alexandre , Ohuchi Fumio
Published: August 2010

This study examines the kinetics of the martensitic phase transformation in a representative Ni-Mn-Sn Heusler alloy. Here, we present data on isothermal and continuous cooling/warming transformations in both bulk polycrystalline and individual small particle samples. We demonstrate that while the martensite to austenite transformation proceeds very rapidly (faster than the time-scale of our observations), the austenite to martensite transformation has a significant isothermal component. A similar asymmetry is also noted in transformation behavior of individual martensite plates. We conclude that the observed time dependence is due primarily to nucleation-limited kinetics.
Polyoctenamer - Single Walled Carbon Nanotube Composites: Spectroscopic Investigations
Authors: Chipara Alin Cristian , Mion Thomas , Villegas Rafael , Lozano Karen , Chipara Dorina Magdalena , Tidrow Steven C. , Chipara Mircea
Published: August 2010

Composites of single walled carbon nanotube dispersed within polymeric matrices have been investigated by spectroscopic techniques (Raman and Wide Angle X-Ray Spectroscopy). Raman investigations included an in depth analysis of the radial breathing mode (for single wall carbon nanotubes) and a brief analysis of the lines originating from the polymeric matrix. Raman spectra were successfully simulated by computer assuming that the as recorded spectrum is a convolution of lines whose line shape is well described by a modified Breit-Wigner-Fano equation. The dependence of the position of the lines belonging to the radial breathing mode on the concentration of single walled carbon nanotube has been investigated, with emphasis on information pertinent to the stress transfer from the macromolecular matrix to the filler and to the coating of single walled carbon nanotube by polymeric chains. Complementary Wide Angle X-Ray Spectroscopy measurements provided information about the effect of the loading with single walled carbon nanotube on the crystal structure of the polymeric matrix. The research aims to a better understanding of the interactions between polymeric matrices and nanofillers.
The Effect of Carbon Nanotube Surface Energy on the Adhesion of Macrophages
Authors: Chun Young Wook , Webster Thomas J.
Published: August 2010

Purified carbon nanotubes (with removed toxic catalytic particles) have been considered as novel materials for drug delivery and for generating artificial organs more efficiently than traditional tissue engineering materials due to their unique surface features. The surface chemistry of carbon nanotubes has been modified through various functionalization strategies to increase biocompatibility. Importantly, modulating the intrinsic material surface energy of carbon nanotubes (without functionalization, thus, establishing permanent, non degradable chemical, and physical surface properties) can potentially reduce an immune response mediated by macrophages. Herein, we report macrophage responses on different surface energy carbon nanotubes while keeping their nanoscale surface roughness. Specifically, interactions of ultra hydrophobic (bare or unmodified) and hydrophilic carbon nanotubes (due to the formation of oxide layers) with macrophages were investigated. It was observed that macrophage density on both carbon nanotube scaffolds were lower than on traditional materials. In particular, the amount of released cytokine (TNF-α) from macrophages cultured on hydrophilic carbon nanotube scaffolds was much smaller than on hydrophobic carbon nanotube scaffolds. All results clearly supported that tailoring the surface energy of carbon nanotubes mediates a macrophage immune response.
Generation and Capture of CO2and CO in Graphite Oxide Stacks during Thermal Reduction
Authors: Acik Muge , Guzman Rodolfo , Chabal Yves J
Published: August 2010

Infrared spectroscopy is used to monitor the evolution of CO2(2330-2350 cm-1) and CO (2050-2200 cm-1) generated during thermal reduction of graphite oxide. The appearance of CO2at low temperatures (≤200°C) is associated with oxygen removal in species such as anhydrides, esters, lactols, carboxylic acids and lactones either at the edges or in the distorted basal plane of the GO sheets. At higher temperatures (250°C-750°C), release of CO is observed and may be due to decomposition of CO2or oxygen-containing species like ethers, carbonyls, phenols or quinones. Observation of these gases is possible in multilayer GO because they are trapped in between the interlayer spacing of GO stacks for a time sufficient for detection.
Amino Terminated Polyethylene Glycol Functionalized Graphene and Its Water Solubility
Authors: Hou Shifeng , Cuellari Robert D. , Hakimi Najeeb Hoshang H. , Patel Krutika , Shah Pratik , Gorring Matthew , Brachfeld Stefanie
Published: August 2010

A chemical modification process was developed to functionalize graphene with specific groups. Graphene oxide (GO) was successfully functionalized with thionyl bromide which can be used as precursors for further functionalization. Amino terminated-polyethylene glycol (PEG-NH2) molecules were linked to single-layer graphene sheets through covalent bond. FT-IR, SEM and UV-vis spectroscopy techniques were used to characterize PEG modified graphene oxide and PEG modified reduced graphene oxide (PEG-RG). PEG-RG could disperse in water, tetrahydrofuran and ethylene glycol, with individual, single-layer graphene sheets spontaneously. The dispersion behavior of PEG-RG in an aqueous solvent has been investigated. A series of solutions of PEG-RG with concentrations of 0.001% to 1.5% were prepared and the PEG-RG dispersions exhibited long-term stability. In addition, a PEG-RG film with layered structure and high conductivity has been successfully prepared by filtration.
Suppression of Edge Recombination in InAs/InGaAs DWELL Solar Cells
Authors: Gu Tingyi , El-Emawy Mohamed A , Yang Kai , Atintz Andreas , Lester Luke F
Published: August 2010

The InAs/InGaAs DWELL solar cell grown by MBE is a standard pin diode structure with six layers of InAs QDs embedded in InGaAs quantum wells placed within a 200-nm intrinsic GaAs region. The GaAs control wafer consists of the same pin configuration but without the DWELL structure. The typical DWELL solar cell exhibits higher short current density while maintaining nearly the same open-circuit voltage for different scales, and the advantage of higher short current density is more obvious in the smaller cells. In contrast, the smaller size cells, which have a higher perimeter to area ratio, make edge recombination current dominant in the GaAs control cells, and thus their open circuit voltage and efficiency severely degrade. The open-circuit voltage and efficiency under AM1.5G of the GaAs control cell decrease from 0.914V and 8.85% to 0.834V and 7.41%, respectively, as the size shrinks from 5*5mm2 to 2*2mm2, compared to the increase from 0.665V and 7.04% to 0.675V and 8.17%, respectively, in the DWELL solar cells.
The lower open-circuit voltage in the smaller GaAs control cells is caused by strong Shockley-Read-Hall (SRH) recombination on the perimeter, which leads to a shoulder in the semi-logarithmic dark IV curve. However, despite the fact that the DWELL and GaAs control cells were processed simultaneously, the shoulders on the dark IV curve disappear in all the DWELL cells over the whole processed wafer. As has been discussed in previous research on transport in QDs, it is believed that the DWELL cells inhibit lateral diffusion current and thus edge recombination by collection first in the InGaAs quantum well and then trapping in the embedded InAs dots. This conclusion is further supported by the almost constant current densities of the different area DWELL devices as a function of voltage.
Electron Reflector Strategy for Thin CdTe Solar Cells
Authors: Hsiao Kuo-Jui , Sites James R.
Published: August 2010

Incorporation of an electron reflector is a proposed strategy to improve the open-circuit voltage of CdTe thin-film solar cells. An electron reflector is basically a conduction-band barrier at the back surface, which can reduce the recombination resulting from the electron flow to the back surface. It should be particularly beneficial for cells with thicknesses below two microns when the CdTe absorber layer is fully depleted at its typical carrier density, because back-surface recombination is a primary limitation to the performance of fully depleted cells. Cells with thickness below two microns can also benefit from optical reflection at the back interface.
One-dimension numerical simulation is used to investigate the electron reflector strategy and optical back reflection for thin CdTe cells. Theoretically, about a 200-mV increase in voltage and 3% in efficiency are achievable for a thin CdTe solar cell with 2×1014-cm-3 hole density, 1-ns lifetime, and a 0.2-eV electron reflector barrier. Furthermore, with the electron reflector, good CdTe cell performance at thicknesses as thin as 0.4 μm should be possible.
Textured substrate based organic solar cell for higher absorption and improved performance
Authors: Nalwa Kanwar Singh , Park Joong Mok , Leung Wai , Constant Kristen , Ho Kai Ming , Chaudhary Sumit
Published: August 2010

The performance of polymer-based photovoltaic devices is limited by several factors like high band-gap and low charge-carrier mobility, to name a few. Thicker active-layers have high optical absorption but the transport of carriers in them is inefficient. Thus the optimal thickness of the active-layers has to be determined carefully. This conflict can be resolved using a three-dimensional (3D) microscale textured grating shaped solar cell geometry. The solar cells in this study were fabricated on photoresist gratings to give them 3D texture required for enhanced light absorption. Introduction of texturing has a significant effect on over all power conversion efficiency of the devices. Grating based solar cell having 2 micron pitch showed improved power conversion efficiency over the flat solar cell. In addition to favorable guiding of optical modes, the improvement in efficiency is accomplished by homogenous coverage of the spin-coated active layer, which is a challenging process for non-flat surfaces. Uniform thickness in this study was facilitated by the sufficiently high pitch and low height of the underlying photoresist gratings.
Screen-Printed Al Back Contacts on Si Solar Cells: Issues and Some Solutions
Authors: Mehta Vishal , Sopori Bhushan , Reedy Robert , To Bobby , Moutinho Helio , Ravindra Nuggehalli M.
Published: August 2010

This paper identifies some mechanisms that lead to problems in back Al contact formation. Major issues are related to a basic problem that the Al melt has a large surface tension and tries to ball up during the firing step. Other issues arise from dissolution of the Si-Al interface and entrapment of glass within the Si-Al alloy. Si diffusion into Al can be applied to control the melt, while cooling rate can help improve the structure of various regions of the back contact for a favorable series resistance. We also discuss a modified time-temperature profile that can lead to a deep and uniform back-surface field.
Investigation of Fired and Non-fired Si-SiNx Interface Properties by Deep-level Transient Spectroscopy measurements
Authors: Gong Chun , Simoen Eddy , Yang Rui , Posthuma Niels , Van Kerschaver Emmanuel , Poortmans Jef , Mertens Robert
Published: August 2010

In this paper, fired and non-fired direct PECVD deposited Si-SiNx interface properties with and without NH3 pretreatment on both n- and p-type mono-crystalline silicon samples were investigated with deep-level transient spectroscopy (DLTS) measurements. A and B defect states are identified at the Si-SiNx interface. Energy-dependent electron and hole capture cross sections were measured by small-pulse DLTS. Fired samples with NH3 pretreatment show the lowest DLTS signals, which suggests the lowest overall Dit. The combination of NH3 pretreatment and firing is also suggested for application in the solar cell fabrication.
CENTESIL: A Pilot Plant for R&D in Polysilicon
Authors: Cañizo Carlos del , Rodríguez Araceli , Ovejero Gabriel , Luque Antonio
Published: August 2010

The tremendous expansion and the relative avidity for silicon of the solar cell technology has resulted in a dramatic change of the polysilicon industry structure. While in the past the polysilicon was manufactured almost exclusively for the semiconductor industry, in 2008 around 67% of the total production was consumed by the solar industry. The consequence is that while in 2000 virtually only 7 companies supplied all the polysilicon consumed worldwide, in 2008 there were 11 major suppliers and numerous new ventures entering this market. Based on this in 2006 CENTESIL was founded as a new private-public partnership venture to deal with the polysilicon research. For it, a pilot plant is in advanced state of construction that has been preceded of some laboratory-size implementations. The pilot plant is designed for a production capacity of 60 kmol of trichlorosilane per day and 2 t of purified silicon per batch at the CVD reactor. The purpose is to allow the photovoltaic companies worldwide to count with an independent research centre to help them to establish their own polysilicon plant. The R&D activities already carried out by CENTESIL and the present status of the project are discussed in the paper.
Optical and Physical Characterization of Cu2-xSe Thin Films for Real Time Spectroscopic Ellipsometry on Cu(In,Ga)Se2-based Photovoltaic Devices
Authors: Walker James D , Khatri Himal , Little Scott , Ranjan Vikash , Collins Robert , Marsillac Sylvain
Published: August 2010

In situ, real time spectroscopic ellipsometry (RTSE) has been used to study the growth processes and optical properties of Cu2-xSe - an important binary compound in the fabrication of high efficiency copper indium gallium diselenide (CIGS) photovoltaic devices. It was found that the high surface roughness of the Cu2-xSe layers necessitated a “graded” optical model in order to extract meaningful dielectric functions at both 550 °C and room temperature. The optical model was verified at room temperature against SEM micrographs and reflectance measurements carried out ex situ. The growth temperature dielectric functions presented in this study are expected to allow for a greater level of control and understanding of the so-called 2- and 3-stage processes for CIGS fabrication in which a Cu2-xSe phase, present at the CIGS grain boundaries, acts as a fluxing agent for the growth of photovoltaic quality CIGS. Real time optical feedback via RTSE combined with the growth temperature dielectric functions presented here could play an important role in improving material fabrication on both the laboratory and industrial scales.
Deactivation Treatments of Silicon Solar Cells for Efficiency Recovery after Illumination Degradation
Authors: Wang Teng-Yu , Wang Terry , Chen Yen-Ju , Kou Chwung-Shan , Chen Chien-Hsun , Chang Wei-Lun , Chen Sung-Yu , Du Chen-Hsun , Sun Wen-Ching , Lan Chung-Wen
Published: August 2010

We applied the deactivation treatments to p-type single crystalline silicon solar cells for deactivating the recombination-active boron-oxygen complex. The methods we used include thermal annealing treatment, capacitively couple plasma (CCP) treatment, and plasma immersion ion implantation (PIII) treatment. The results showed that all the deactivation treatments were working and the energy transfer efficiency (Eff) was thereby increased by more than 1% absolute compared to the degraded state base on the increasing of the open-circular voltage (Voc) and short-current density (Jsc). The CCP deactivated treatment got better efficiencies than PIII treatment because the PIII treatment damaged the surface of solar cells. After the forming gas treatment, the samples could be improved to close to the PIII samples due to the surface damage repairing. However, the increased efficiency could not be kept and would be degraded again after illumination.
Can We Describe phase Transition in Insulators within the Landau PT theory Framework?
Authors: Simeone David , Baldinozzi Gianguido , Gosset Dominique , Luneville Laurence , Mazerolles Léo
Published: August 2010

Based on studies of simple oxides, this paper demonstrates that the specific energy deposition modes under irradiation induce modifications of materials over different length scales. On the other hand, we show the Landau phase transition theory, widely used to explain the structural stability of materials out of irradiation, can give a general framework to describe the behavior of these oxides under irradiation. The use of X-ray diffraction techniques coupled with the Raman spectroscopy allows defining in a quantitative way the phenomenological parameters leading to predictive results. This paper clearly shows that in two model systems, pure zirconia and spinels, no unexpected new phases are produced in these oxides irradiated at room temperature and with different fluxes. Such a phenomenological approach may be useful to study the radiation tolerance of many crystalline ceramics (e.g. the zirconium based americium ceramics).
Microstructure and Thermophysical Characterization of Mixed Oxide Fuels
Authors: Freibert Franz J. , Saleh Tarik A. , Hampel Fred G. , Schwartz Daniel S. , Mitchell Jeremy N. , Davis Charles C. , Neuman Angelique D. , Willson Stephen P. , Dunwoody John T.
Published: August 2010

Pre-irradiated thermodynamic and microstructural properties of nuclear fuels form the necessary set of data against which to gauge fuel performance and irradiation damage evolution. This paper summarizes recent efforts in mixed-oxide and minor actinide-bearing mixed-oxide ceramic fuels fabrication and characterization at Los Alamos National Laboratory. Ceramic fuels (U1-x-y-zPuxAmyNpz)O2 fabricated in the compositional ranges of 0.19≤x≤0.3 Pu, 0≤y≤0.05 Am, and 0≤z≤0.03 Np exhibited a uniform crystalline face-centered cubic phase with an average grain size of 14μm; however, electron microprobe analysis revealed segregation of NpO2 in minor actinide-bearing fuels. Immersion density and porosity analysis demonstrated an average density of 92.4% theoretical for mixed-oxide fuels and an average density of 89.5% theoretical density for minor actinide-bearing mixed-oxide fuels. Examined fuels exhibited mean thermal expansion value of 12.56×10−6/°C-1 for temperature range (100°C<T<1500°C) and ambient temperature Young's modulus and Poisson's ratio of 169 GPa and of 0.327, respectively. Internal dissipation as determined from mechanical resonances of these ceramic fuels has shown promise as a tool to gauge microstructural integrity and to interrogate fundamental properties.
Low Temperature Synthesis of Silicon Carbide Inert Matrix Fuel (IMF)
Authors: Shih Chunghao , Tulenko James , Baney Ronald
Published: August 2010

A process for the synthesis of silicon carbide (SiC) inert matrix fuels at a low temperature (1050 °C) is reported which utilized a liquid polymer precursor. As the polymer content increased, the theoretical density of the pellet at first increased and then reached a plateau. From the onset of the plateau, the packing of the one micron SiC particles in the green body was determined to be 64-68% at 600 MPa pressing pressure. As expected, mixing coarse and fine SiC particles gave a higher pellet density. The maximum density achieved was 80% of the theoretical density. Mercury porosimetry showed that the largest pore size was around 10% of the largest particle sizes present in the green body. SEM images showed that ceria, which was selected as a surrogate for PuO2 in the present study, was well distributed.
Thermal Stability of Microstructure in Grain Boundary Character Distribution-Optimized and Cold-Worked Austenitic Stainless Steel Developed for Nuclear Reactor Application
Authors: Yamashita Shinichiro , Yano Yasuhide , Tanikawa Ryusuke , Sakaguchi Norihito , Watanabe Seiichi , Miyagi Masanori , Sato Shinya , Kokawa Hiroyuki
Published: August 2010

Grain boundary character distribution-optimized (GBCD) Type 316 corresponding austenitic stainless steel and its cold-worked ones (GBCD+CW) are one of prospective nuclear materials to be considered for next generation energy systems. These steels were thermally-aged at 973 K for 1 and 100 h and were examined by transmission electron microscopy (TEM) to evaluate microstructural stability during high temperature exposure. TEM results revealed that microstructures of both specimens prior to ageing contained step-wise boundaries which is composed of coincidence site lattice (CSL) and random grain boundaries and also that the GBCD+CW specimens had dislocation cells and networks as well as deformation twins whereas as the GBCD one possessed few dislocations. After thermal ageing, the precipitates formed on not only random grain boundaries but also dislocations, contributing to prevent significant microstructural change occurring such as recrystallization and dislocation recovery.