bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical properties of charging effect in Au nanoparticle memory device
Authors: Jung Sung-Mok , Kim Hyung-Jun , Kim Bong-Jin , Seo Il , Yoon Tae-Sik , Kim Yong-Sang , Lee Hyun Ho
Published: August 2010

Semiconductors or metal nanoparticles (NPs) using their monolayer bindings with self-assembly chemicals are an attractive topic for device researchers. Electrical performance of such structures can be investigated for a particular application, such as memory device. Currently, Au NPs has been reported to show a substantial potential in the memory applications. In this study, Au NP and gluing layer were fabricated through a new method of monolayer formation of a chemical bonding or gluing.
In this study, a new NPs memory system was fabricated by using organic semiconductor, i.e., pentacene as the active layer, evaporated Au as electrode, SiO2 as the gate insulator layer on silicon wafer. In addition, Au NPs coated with binding chemicals were used as charge storage elements on an APTES (3-amino-propyltriethoxysilane) as a gluing layer. In order to investigate chemical binding of Au NP to the gate insulator layer, GPTMS (3-glycidoxy-propyltrimethoxysilane) were coated on the Au NPs. As a result of that, a layer of gold nanoparticles has been incorporated into a metal-pentacene-insulator-semiconductor (MPIS) structure. The MPIS device with the Au NP exhibited a hysteresis in its capacitance versus voltage analysis. Charge storage in the layer of nanoparticles is thought to be responsible for this effect.
Commercial Production of Silicon Solar Cell Feedstock by Upgrade of Metallurgical Grade Silicon
Authors: Mott John R , Bragagnolo Julio A , Hayes Michael P.
Published: August 2010

The relation between impurity content in Solar Grade Silicon (SGS) and solar cell quality is the subject of intensive research. The PV industry has developed around the use of silicon made by the Siemens process for the semiconductor industry, with impurity levels typically in the parts per billion by weight (ppbw) range. There is a growing consensus that SGS with impurities in the parts per million range (ppmw) can be obtained cost effectively from Metallurgical Grade Silicon (MGS) and used to yield solar cells with comparable performance (see for example ‘Beneficial Effects of Dopant Compensation on Carrier Lifetime in Upgraded Metallurgical Silicon’ by S. Dubois et al. in the 23rd European Photovoltaic Solar Energy Conference, Valencia, September, 2008). This provides insight on the success encountered by Timminco, an early SGS market entrant, in commercializing silicon material with [P] levels of the order of 2 ppmw.
Current Work
We have successfully reduced P to about 2 ppmw, a level that appears acceptable for solar cell fabrication, by application of a novel unidirectional solidification (UDS) technique at a 50% material yield. This is important as UDS, by its nature, implies a loss of silicon, while little or no silicon is lost in B reduction, partially achieved in this furnace using a glass slagging process. Figure 1 shows [P] data from 16 UDS runs on samples taken from the melt, before and after UDS, and a solid sample taken from the silicon frozen on the cold silicon collection surface. The error bars represent a standard 20% error value. We note that the average values of [P] in the molten silicon samples increase from 11.9 ppmw before UDS to 15.9 ppmw after UDS. The average value of [P] in the solid silicon sample is 4.9 ppmw.
The average value of the solid silicon, 4.9 ppmw P, taken with the average value of the starting silicon, 11.9 ppmw P, demonstrates an effective refining ratio of 0.41, even at a 50% solid fraction. Performing a second UDS on silicon obtained from runs in Figure 1, yields [P] around 2 ppmw (Figure 2).In addition to P and B reduction, in this paper we also discuss the hardware designed to implement this process in commercial production in volumes exceeding 4,000 MT per year. MB Scientific, the original process developer, and NC Consulting, an engineering company, have developed a plant design that can produce SGS at an estimated cost that will allow for profitable large scale production, and have joined in a new company, Silicon Forge, to commercialize the large-scale production technology.
Improving the Conversion Efficiency and Decreasing the Thickness of the HIT Solar Cell
Authors: Inoue Hirotada , Tsunomura Yasufumi , Fujishima Daisuke , Yano Ayumu , Taira Shigeharu , Ishikawa Yasuko , Nishiwaki Takeshi , Nakashima Takeshi , Asaumi Toshio , Taguchi Mikio , Sakata Hitoshi , Maruyama Eiji
Published: August 2010

In order to reduce the power-generating cost of silicon solar cells, it is necessary to achieve a high conversion efficiency using a thinner crystalline silicon (c-Si) substrate. The HIT (Heterojunction with Intrinsic Thin-layer) solar cell is an amorphous silicon (a-Si) / c-Si heterojunction solar cell that exhibits the potential to make this possible. Our recent R&D activities have achieved the world’s highest conversion efficiency of 23.0% with a practical sized (100.4 cm2) HIT solar cell, by improving the quality of the surface passivation, reducing the optical absorption loss and reducing the resistance loss. We have also developed a HIT solar cell with a thickness of only 98 mm, which has a very high conversion efficiency of 22.8%. This value is comparable to that of the conventional HIT solar cell, which has a thickness of more than 200 mm. Moreover, we have fabricated HIT solar cells using thinner c-Si substrates (96 to 58 μm), and found that the Voc increased with decreases in the substrate thickness, and reached an extremely high value of 0.745 V with a thickness of only 58 μm. This indicates that the surface recombination velocity of the HIT structure is extremely low due to the excellent passivation of the c-Si surface.
PV Metamaterial Based on the Nanostructured Si
Authors: Kuznicki Zbigniew T. , Meyrueis Patrick
Published: August 2010

There are several ways to nanostructure Si. Some of them, e.g. nanoscale Si-layerd systems buried within the n+ layer of a crystalline Si can provide an initial material with unpredicted optoelectronic behavior. Such a transformation leads to a PV Si metamaterial, whose optoelectronic properties arise from qualitatively new response functions that are (i) not observed in the constituent materials and (ii) result from the inclusion of artificially fabricated, intrinsic and extrinsic, low-dimensional components. We show that an extremely strong c-Si:P absorptance, is larger than can result from conventional conversion because the surface population increases by injection of additional carriers from a nanostratum (transformed up to a Si-metamaterial) lying just behind the top c-Si:P-layer.
Possible Formation of H-type Aggregates in H2TPyP/PMMA Guest Host Films
Authors: Mota Wesley da Silva , Melo Wanessa Canedo , Nunes Luiz Antônio de Oliveira , Machado Antônio Eduardo da Hora , Batista Alzir Azevedo , Guedes Ilde , Barbosa Newton Martins
Published: August 2010

In this work we have employed UV-Vis absorbance and excitation techniques in addition to quantum chemical calculations to investigate the probable formation of H-type aggregates of zero charged aryl substituted porphyrin in a guest- host solid state structure. The films were factored via casting technique mixing free-base tetrapyridyl porphyrins (H2TPyP) and polymethilmethacrilate polymer (PMMA) chlorophorm solutions. A pathway for the possible formation of H-type aggregate is suggested.
Neutron Diffraction Study of the Structural Changes Occurring During the Low Temperature Oxidation of UO2
Authors: Baldinozzi Gianguido , Desgranges Lionel , Rousseau Gurvan
Published: August 2010

The oxidation of uranium dioxide has been studied for more than 50 years. It was first studied for fuel fabrication purposes and then later on for safety reasons to design a dry storage facility for spent nuclear fuel that could last several hundred years. Therefore, understanding the changes occurring during the oxidation process is essential, and a sound prediction of the behavior of uranium oxides requires the accurate description of the elementary mechanisms on an atomic scale. Only the models based on elementary mechanisms should provide a reliable extrapolation of laboratory results over timeframes spanning several centuries. The oxidation mechanism of uranium oxides requires understanding the structural parameters of all the phases observed during the process. Uranium dioxide crystal structure undergoes several modifications during the low temperature oxidation that transforms UO2 into U3O8. The symmetries and the structural parameters of UO2, β-U4O9, β-U3O7 and U3O8 were determined by refining neutron diffraction patterns on pure single-phase samples. Neutron diffraction patterns, collected during the in situ oxidation of powder samples at 483 K were also analyzed performing Rietveld refinements. The lattice parameters and relative ratios of the four pure phases were measured during the progression of the isothermal oxidation. The transformation of UO2 into U3O8 involves a complex modification of the oxygen sublattice and the onset of complex superstructures for U4O9 and U3O7, associated with regular stacks of complex defects known as cuboctahedra which consist of 13 oxygen interstitial atoms. The structural modifications during the oxidation process are discussed.
Radiation Tolerance and Disorder – Can They Be Linked?
Authors: Whittle Karl , Blackford Mark , Smith Katherine L. , Lumpkin Gregory , Zaluzec Nestor J.
Published: August 2010

The future expansion of nuclear power provides materials challenges that are not easily overcome, for example the safe immobilisation of nuclear waste is an important component in any future expansion of nuclear power. The use of ceramic-based materials, as opposed to borosilicate glasses, is now being investigated widely. The ability of ceramics to be tailored to a specific waste stream is now understood and obtainable quickly and with minimal cost. A second component that limits the expansion of fission-based technologies is the development of materials that are not only tolerant of radiation damage, but are also capable of retaining mechanical strength at high temperatures. One concern for any material however, is the effect of radiation damage, primarily from alpha-decay damage, which in many systems can transform the material from crystalline to amorphous. The effects of such radiation damage on both the structural and chemical properties can range from trivial to critical, for example volume expansion and are the primary focus of much research. As part of a long-term research programme the effects on radiation tolerance of a range of ordered and disordered materials are discused.
Quantification of Trace and Ultra-trace Elements in Nuclear Grade Manufactured Graphites by Fast-Flow Glow Discharge Mass Spectrometry and by Inductively Coupled Plasma – Mass Spectrometry after Microwave – Induced Combustion Digestions
Authors: Wang Xinwei , Bhagat Gaurav , O'Brien Kevin Michael , Putyera Karol
Published: August 2010

FF-GDMS and MIC-ICP-MS methods were developed for the determination of mg/kg- and μg/kg-level B, Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, Sb, W and Pb in nuclear-grade graphite. Consistent results have been achieved in determining trace elements like B, Ti, Cr, Mn, Zr, Sb and Pb by both methods, which vary mostly less than ±30%, and are in line with the manufacturer reference values. On Mg, Al, Fe, Co, Zn, Mo and W, FF-GDMS analyses also show good agreement with the manufacturer's data. Continuing efforts in identifying source of interference, which has limited the MIC-ICP-MS analysis of these elements, is currently underway.
In situ Characterization of UO2 Microstructure Changes During an Annealing Test in an Environmental Scanning Electron Microscope
Authors: Marcet Mathieu , Pontillon Yves , Desgranges Lionel , Simeone David , Aubrun Isabelle , Felines Isabelle , Brunaud Laurent
Published: August 2010

A 1 μg High Burn Up Structure (HBS) fragment was extracted from a UO2 fuel pellet irradiated for 7 cycles in a EDF Pressurised Water Reactor (PWR). In situ examinations were performed with an Environmental Scanning Electron Microscope (ESEM) in order to characterize UO2 microstructure evolution during a temperature ramp up to 1,600K. The results are compared to previously published data on HBS annealing tests performed in a Knudsen cell where observed burst releases are explained as sample cracking during the experimental sequence.
Effect of Oversized Alloying Elements on Damage Rates and Recovery in Zirconium
Authors: Borysenko Valeriy , Petrusenko Yuri , Barankov Dmitro
Published: August 2010

Studies were made into the influence of oversized rare-earth atoms on the processes of radiation defect accumulation and annealing in two-component zirconium alloys. Zr and Zr-X alloys (where X = Sc, Dy, Y, Gd and La) have been irradiated with 2 MeV electrons at 82 K. The radiation-induced resistivity has been measured in situ as a function of dose. As compared to unalloyed zirconium, the alloys have exhibited a decrease in the resistivity gain, this decrease being proportional to both the concentration and the size of dopant atoms. A possible explanation for the effect is offered. The difference between the recovery processes in zirconium and in its alloys has been studied. To this end, the irradiated specimens were subjected to isochronal annealing at temperatures between 82 and 350 K. It is shown that Dy, Y, Gd and La atoms trap interstitial atoms at stage I of the recovery. The dissociation of interstitial-impurity complexes takes place at stage II. In zirconium alloys with Dy, Y and Gd, splitting of recovery stage III into two substages has been revealed. The Zr-La alloy has not shown this splitting. Isothermal annealing data were used to determine the activation energies of recovery stages, and also to calculate the activation energy spectra for zirconium and its alloys. The oversized atoms of rare-earth metals are shown to interact effectively with both the interstitials and the vacancies in the zirconium matrix. This effect must be taken into account when developing new radiation-resistant Zr-base alloys or modifying the ones already existing.
Enhanced Hydrogen Storage Properties of Magnesium Nanotrees with Nanoleaves
Authors: Cansizoglu Mehmet , Karabacak Tansel
Published: August 2010

Hydrogen storage in advanced solid state materials has been an intense area of research due to many drawbacks in conventional high pressure or cryogenic liquid hydrogen storage methods. A practical hydrogen storing material is required to have high storage capacity and fast dehydrogenation kinetics. Among many solid state materials for hydrogen storage, magnesium hydride (MgH2) combines a hydrogen capacity of 7.6 wt % with the benefit of the low cost of production and abundance. The main difficulties for implementing MgH2 are slow absorption/desorption kinetics and high reactivity towards air and oxygen, which are also common issues in most lightweight metal hydrides. Previously, improvements in hydrogen storage and release properties have been reported by using nanostructured magnesium that can be obtained through various fabrication methods including ball-milling, mechanical alloying, and vapor transport. In this study, we investigate the hydrogen absorption and desorption properties of magnesium “nanotrees” fabricated by glancing angle deposition (GLAD) technique, and also conventional Mg thin films deposited at normal incidence. Mg nanotrees are about 15 μm long, 10 μm wide, and incorporate “nanoleaves” of about 20 nm in thickness and 1,2 μm in lateral width. A quartz crystal microbalance (QCM) gas absorption/desorption measurement system has been used for our hydrogen storage studies. Nanostructured and thin film Mg have been deposited directly on the surface of the gold coated unpolished quartz crystal samples. QCM hydrogen storage experiments have been performed at temperatures ranging between 100-300 °C, and at H2 pressures of 10 and 30 bars. Our QCM measurements revealed that Mg nanotrees can absorb hydrogen at lower temperatures and also at a faster rate compared to Mg thin film. In addition, Mg nanotrees can reach hydrogen storage values of about 4.80 wt% at 100 °C, and up to about 6.71 wt% (which is close to the theoretical maximum storage value of Mg) at temperatures lower than 150 °C. The significant enhancement in hydrogen absorption properties of our Mg nanotrees is believed to originate from novel physical properties of their nanoleaves. These nanoleaves are very thin (∼20 nm) and both surfaces are exposed to hydrogen enhancing the diffusion rate of hydrogen together with a decreased diffusion length. Based on X-ray diffraction measurements, individual nanoleaves have non-close-packed crystal planes that can further enhance the hydrogen absorption kinetics. In addition, our nanostructured Mg have been observed to quite resistant to surface oxidation, which is believed to due to the single crystal property of the Mg nanoleaves, which further improves the absorption kinetics of hydrogen.
Synthesis of Pt-TM(transition metals) Catalysts and Their Hydrogenation Ability of Methyl Acrylate
Authors: Amari Miki , Okada Satoshi , Demura Masahiko , Nishio Keishi , Shibata Hirobumi , Kineri Tohru , Gunji Takahiro , Tamura Ryuji
Published: August 2010

We have prepared a number of Pt-TM(transition metals) alloys with various TM elements and evaluated their catalytic abilities by means of hydrogenation of methyl acrylate. High catalytic activities are obtained when the crystalline structures are similar, i.e., fcc structure, indicating that the crystal structure of a catalyst plays an important role in hydrogenation of methyl acrylate. Furthermore, for a certain TM element, i.e., Mo, the catalytic activity is found to surpass that of Pt metal.
Could Porosity Induce Gaps in the Vibrational Density of States of Nanoporous Silicon?
Authors: Noyola Juan Carlos , Valladares Alexander , Valladares R. M. , Valladares Ariel A.
Published: August 2010

As in our previous work [1] nanoporous silicon periodic supercells with 1000 atoms but now with 80 % porosity were constructed using the Tersoff potential and our novel approach [2]. The approach consists first in constructing a crystalline diamond-like supercell with a density (volume) close to the real value, and then lowering the density by increasing the volume, subjecting the resulting periodic supercell to Tersoff-based molecular dynamics processes at a temperature of 300 K, followed by geometry relaxation [1]. As in the ab initio approach [2] the resulting samples are also essentially amorphous and display pores along some of the crystallographic directions. We report the radial (pair) distribution function (RDF), g(r), the bond angle distribution, the pore structure where prominent and a computational prediction for the vibrational density of states for this structure. We then compare it to the 50 % porous sample presented in Ref [1]. The soft acoustic phonons are displaced towards lower energy in the 80 % porosity sample whereas the optical modes are displaced towards higher energies. The pseudo gap, existing in the 50 % porous sample, is depleted even more in the 80 % sample indicating a tendency towards the creation of a phonon gap for higher porosity materials. Some conjectures that point to the possible engineering of porous materials to produce predetermined phonon properties are discussed.
Stress-controlled phonon-impurity resonances in terahertz silicon lasers
Authors: Pavlov Sergey G.
Published: August 2010

Optically pumped terahertz silicon lasers utilize transitions between shallow donor states at low lattice temperatures. Population inversion in these lasers is built-up due to selective relaxation routes of optically excited electrons into impurity ground state. Each relaxation step of the electron occurs under assistance of intervalley and intravalley phonons with energies approaching the particular energy gaps between interacting excited donor states. These impurity phonon interactions determine, at the end, the lifetimes of the laser levels, and, therefore, efficiency of intracenter silicon lasers. Deformation of silicon crystal is a classical example of controllable influence on energy spectrum of shallow donor levels due to specific splitting and shifts of conduction band valleys. Using moderate (up to 400 MPa) external uniaxial deformation of a crystal, one can radically modify the impurity spectra while the phononic spectra remain almost unchanged. We have demonstrated significant improvement of efficiency for intracenter silicon lasers followed by changes of lifetime for the upper and the lower laser levels due to moving the impurity levels either into or out of resonance with corresponding intervalley phonon frequencies.
Effect of Alloying Elements on the Elastic Properties of γ-Ni and γ'-Ni3Al from First-principles Calculations
Authors: Wang Yunjiang , Wang Chongyu
Published: August 2010

The effect of alloying elements Ta, Mo, W, Cr, Re, Ru, Co, and Ir on the elastic properties of both γ-Ni and γ′-Ni3Al is studied by first-principles method. Results for lattice properties, elastic moduli and the ductile/brittle behaviors are all presented. Our calculated values agree well with the existing experimental observations. Results show all the additions decrease the lattice misfit between and γ′ phases. Different alloying elements are found to have different effect on the elastic moduli of γ-Ni. Whereas all the alloying elements slightly increase the moduli of γ′-Ni3Al expect Co. Both of the two phases are becoming more brittle with alloying elements, but Co is excepted. The electronic structures of γ′ phase alloyed with different elements are provided as example to elucidate the different strengthening mechanisms.
On Effective Indenters Used in Nanoindentation Data Analysis
Authors: Fu Guanghui , Cao Ling , Cao Tiesheng
Published: August 2010

Effective indenter concept was introduced by Pharr and Bolshakov to explain nanoindentation unloading curves. This paper shows that the contact stiffness under a uniform pressure distribution is 57% higher than what is given by the fundamental relation. This is due to the fact that there is no physical indenter that gives a uniform pressure distribution during elastic contact, and the fundamental relation used in nanoindentation data analysis does not apply.
The Micromechanisms of Deformation in Nanoporous Gold
Authors: Dou Rui , Derby Brian
Published: August 2010

We have carried out a TEM investigation of the micromechanisms of deformation in these nanoporous gold specimens after compression testing. We find that the nanoporous specimens show deformation localised to the nodes between the ligaments of the foamed structure, with very high densities of microtwins and Shockley partial dislocations in these regions. These deformation structures are very different from those seen after solid nanowires are tested in compression, which show very low dislocation densities and a few sparsely distributed twins. However, similar dislocation structures to those found in the nanoporous specimens are observed in the larger nanowires when they are deformed in bending. The currently accepted model for the deformation of nanoporous gold, implicitly assumes that the deformation of these structures is by bending near the nodes where ligaments intersect. We hypothesis that the much higher dislocation densities seen in both the nanoporous gold and the nanowires deformed in bending are evidence for the presence of geometrically necessary dislocations in these deformed structures.
Electrospun Polymer/MWCNTs Nanofiber Reinforced Composites “Improvement of Interfacial Bonding by Surface Modified Nanofibers”
Authors: Ozden Elif , Menceloglu Yusuf Ziya , Papila Melih
Published: August 2010

In-house synthesized copolymers Polystyrene-co-glycidyl methacrylate (PSt-co-GMA) are electrospun as mat of surface modified nanofibers with and without multi walled carbon nanotubes (MWCNTs). Composites are then formed by embedding layers of the nanofiber mats into epoxy resin. Interfacial bonding between polymer matrix and the nanofibers, and surface modification driven enhancement in mechanical response is assessed under flexural loads. Results indicate that at elevated temperture storage modulus of epoxy reinforced by PSt-co-GMA nanofibers and PSt-co-GMA/ MWCNTs composite nanofibers is about 10 and 20 times higher than the neat epoxy, respectively, despite weight fraction of the nanofibers being as low as 2%. Interfacial interaction is revealed by the storage modulus comparison of unmodified Polystyrene (PSt) and modified PSt-co-GMA nanofiber reinforced composite. To enhance further the resulting “crosslinked” structure, crosslinking agent ethylenediamine is also sprayed on the nanofibrous mats. Increased crosslinking density improves mechanical response of sprayed-over PSt-co-GMA nanofibers reinforced composites which is about 4 times higher than plain PSt-co-GMA nanofibers.
Silicide Film Formation in the Ta/Ti/Si System by RF Induction Heating
Authors: Pelleg Joshua , Rosenberg Shmuel , Sinder Misha
Published: August 2010

Silicidation of Ta-Ti-Si film on Si (111) and Si (100) substrates was investigated by a new radio frequency (RF) heating in order to evaluate the progress of reaction and establish whether the substrate orientation influence on the rate of reaction prevails. Substrate orientation was observed notwithstanding the high temperatures applied and the very short duration of RF. It was observed that while the reaction on Si (111) goes to completion, on Si (100) substrates under the same conditions intermediate phases remained.
A qualitative analysis of the RF treatment of a conductor film on the silicon substrate is presented. It is done for the first time using the mathematical approach of the heat explosion theory. According to the analysis the specimens might experience either heating at constant temperature or by a sudden temperature increase. The relation between the parameters for the heat explosion regime is presented in simple analytical form. Measurable quantities such as sheet resistance and the magnetic field applied determine the stage of the process. The value of the resulting sheet resistance indicates whether the progress of the RF occurred by heating in the slow growth temperature regime or in the heat explosion stage where reactions of a conductor film occur within a fraction of a second.
Controlling Neuronal Growth on Au Surfaces by Directed Assembly of Proteins
Authors: Staii Cristian , Viesselman Chris , Ballweg Jason , Hart Steven , Williams Justin C , Dent Erik W , Coppersmith Susan N , Eriksson Mark
Published: August 2010

Studying how individual neuronal cells grow and interact with each other is of fundamental importance for understanding the functions of the nervous system. However, the mechanism of axonal navigation to their target region and their specific interactions with guidance factors such as membrane-bound proteins, chemical and temperature gradients, mechanical guidance cues, etc. are not well understood. Here we describe a new approach for controlling the adhesion, growth and interconnectivity of cortical neurons on Au surfaces. Specifically, we use Atomic Force Microscopy (AFM) nanolithography to immobilize growth-factor proteins at well-defined locations on Au surfaces. These surface-immobilized proteins act as a) adhesion proteins for neuronal cells (i.e. well-defined locations where the cells “stick” to the surface), and b) promoters/inhibitors for the growth of neurites. Our results show that protein patterns can be used to confine neuronal cells and to control their growth and interconnectivity on Au surfaces. We also show that AFM nanolithography presents unique advantages for this type of work, such as high degree of control over location and shape of the protein patterns, and application of proteins in aqueous solutions (protein buffers), such that the proteins are very likely to retain their folding conformation/bioactivity.
Oligonuleotide Delivery with Dendritic Poly(L-lysine) for Treatments of the Liver Disorders
Authors: Watanabe Kazuto , Harada-Shiba Mriko , Suzuki Akira , Higuchi Yuriko , Kawakami Shigeru , Hashida Mitsuru , Gokuden Risa , Kurihara Ryohsuke , Sugao Yusuke , Mori Takeshi , Katayama Yoshiki , Niidome Takuro
Published: August 2010

A cationic peptide dendrier, dendritic poly(L-lysine), forms complexes with oligonucleotides and can deliver them to liver after intravenous injection. Here, we tried to deliver apolipoprotein B-specific siRNA for the treatment of hypercholesterolemia and NFκB decoy for the hepatitis treatment. Significant therapeutic effects in those disease model mice were observed after intravenous injection of the oligonucleotides complexes with dendritic poly(L-lysine).
Nano- and Micro-Scale Adhesion in Drug-eluting Stents
Authors: Tan Ting , Meng Juan , Rahbar Nima , Li Hannah , Papandreou George , Maryanoff Cynthia , Soboyejo Winston oluwole
Published: August 2010

This paper presents a combined experimental and theoretical/computational study of adhesion and interfacial fracture between multilayers in a CYPHER®model drug eluting stents (DES). Atomic Force Microscopy (AFM) is used to obtain pull-off forces between coated AFM tips and substrates that simulate the bimaterial surfaces in the DES. Adhesion theories and fracture mechanics concepts are then applied to obtain estimates of the fracture toughness over a range of mode mixities between pure mode I and pure mode II. The trends in the estimates are shown to be in good agreement with experimental measurements of interfacial fracture toughness obtained from Brazil disk specimens over the same range of mode mixities.
Microfabrication of Asymmetric, Homogeneous Cell-laden Hydrogel Microcapsules
Authors: Dang Tram T. , Xu Qiaobing , Bratlie Kaitlin M , O'Sullivan Esther S , Chen Xiao Y , Langer Robert , Anderson Daniel G.
Published: August 2010

Cell encapsulation has been broadly investigated as a technology to provide immunoprotection for transplanted endocrine cells. Here we develop a new fabrication method that allows for rapid, homogenous microencapsulation of insulin-secreting cells with varying microscale geometries and asymmetrically modified surfaces. Micromolding systems were developed using polypropylene mesh, and the mesh material/surface properties associated with efficient encapsulation were identified. Cells encapsulated using these methods maintain desirable viability and preserve their ability to proliferate and secrete insulin in a glucose-responsive manner. This new cell encapsulation approach enables a practical route to an inexpensive and convenient process for the generation of cell-laden microcapsules without requiring any specialized equipment or microfabrication process.
Biomaterials Nano Geometry for Control of Stem Cell Differentiation
Authors: Brammer Karla , Oh Seunghan , Jin Sungho
Published: August 2010

Two important goals in stem cell research are to control the cell proliferation without differentiation, and also to direct the differentiation into a specific cell lineage when desired. Recent studies indicate that the nanostructures substantially influence the stem cell behavior. It is well known that mesenchymal stem cells (MSCs) are multipotent stem cells that can differentiate into stromal lineages such as adipocyte, chondrocyte, fibroblast, myocyte, and osteoblast cell types. By examining the cellular behavior of MSCs cultured in vitro on nanostructures, some understanding of the effects that the nanostructures have on the stem cell’s response has been obtained. Here we demonstrate that TiO2 nanotubes produced by anodization on Ti implant surface can regulate human mesenchymal stem cell (hMSC) differentiation towards an osteoblast lineage in the absence of osteogenic inducing factors. Altering the dimensions of nanotubular-shaped titanium oxide surface structures independently allowed either augmented human mesenchymal stem cell (hMSC) adhesion at smaller diameter levels or a specific differentiation of hMSCs into osteoblasts using only the geometric cues. Small (˜30 nm diameter) nanotubes promoted adhesion without noticeable differentiation, while larger (˜70 - 100 nm diameter) nanotubes elicited a dramatic, ˜10 fold stem cell elongation, which induced cytoskeletal stress and selective differentiation into osteoblast-like cells, offering a promising nanotechnology-based route for novel orthopaedics-related hMSC treatments. The fact that a guided and preferential osteogenic differentiation of stem cells can be achieved using substrate nanotopography alone without using potentially toxic, differentiation-inducing chemical agents is significant, which can be useful for future development of novel and enhanced stem cell control and therapeutic implant development.
Fabrication of (Ti-O-N-Si)/Ti Composite Coating on NiTi Shape Memory Alloy Using PIIID and Coating Evaluation
Authors: Sun Tao , Wang Langping , Wang Min
Published: August 2010

A compact and uniform (Ti, Si, O, N)/Ti composite coating was fabricated on the surface of a NiTi shape memory alloy (SMA) (containing 50.8 at.% Ni) using plasma immersion ion implantation and deposition (PIIID) with radio-frequency (RF) magnetron sputtering. The coating and coated NiTi SMA were studied using various techniques. Analysis showed that the Ni content was drastically reduced on the surface of coated samples due to coating formation. This could greatly improve the biocompatibility of NiTi SMA. There was no TiO2 or TiN formation in the coating. The shape memory ability of NiTi SMA samples was no deteriorated by the coating process. The coating significantly improved the corrosion resistance and wear resistance of NiTi SMA and also rendered the material bioactive.
Electrochemical Deposition of Apatite/Collagen Composite Coating on NiTi Shape Memory Alloy and Coating Properties
Authors: Wang Min , Sun Tao
Published: August 2010

In this investigation, an apatite/collagen composite coating was formed at 37C on a NiTi shape memory alloy (SMA) through electrochemical deposition using double-strength simulated body fluid (2SBF) which contained dissolved collagen. Surface characteristics, wettability and stability of the composite coating were subsequently studied. Scanning electron microscope (SEM) examination of the surface of composite coatings revealed that many collagen fibers were embedded in apatite with flake-like structure and apatite nanocrystals nucleated and grew on collagen fibrils. Energy dispersive X-ray (EDX) spectroscopy analysis showed that the Ca : P ratio of the composite coating was about 1.35, which is close to that of octocalcium phosphate. Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) analysis were also conducted for the composite coating. Compared to bare NiTi SMA samples, the potentiodynamic polarization curves of NiTi SMA samples with the composite coating displayed lower corrosion current density, more positive corrosion and breakdown potential, suggesting that the composite coating was chemically stable and provided corrosion resistance for NiTi SMA.
Syntheses of Hydroxyapatite Nanospheres Through a Facile Sol-gel Method
Authors: Li Kai , Tjong Sie Chin
Published: August 2010

Hydroxyapatite (HA) nanospheres were synthesized via the sol-gel route in the presence of poly(vinyl alcohol) (PVA). The HA nanospheres were formed from the reaction between (NH4)2HPO4 and CaCl2 in ethanol/PVA sol-gel system, in which ammonia solution (NH3•H2O) was added to adjust the pH of solution. The as-synthesized products were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDAX). XRD patterns and FTIR spectra showed that the HA nanospheres exhibit the crystalline structure and vibration bands of HA. The Ca/P molar ratio of HA nanospheres (50˜70nm) approached the stoichiometric value of 1.67, on the basis of EDAX results. Simulated Body Fluid (SBF) immersion test for three weeks demonstrated that the apatite layer can be formed on the HA nanospheres sintered at 550°C.
Quantitative Investigations of Nanoscale Elasticity of Nanofibrillar Matrices
Authors: Tiryaki Volkan M , Khan Adeel Ahmed , Pastor Alicia , Alduhaileb Raed A , Delgado-Rivera Roberto , Ahmed Ijaz , Meiners Sally A , Ayres Virginia M
Published: August 2010

Recent research indicates that nanophysical properties as well as biochemical cues can influence cellular re-colonization of a tissue scaffold. It has also been shown nanoscale elasticity can strongly influence cellular responses. In the present work, quantitative investigations of the elasticity of a nanofibrillar matrix scaffold that has demonstrated promise for spinal cord injury repair are compared with complementary transmission electron microscopy investigations, performed to assess nanofiber internal structures. Interpretive model improvements are identified and discussed.
Optical Properties of Electrospun Nanofiber Substrates
Authors: Davis Lynn , Walls Howard J , Mills Karmann C. , Guzan Kim , Yaga Robert , Ensor David S
Published: August 2010

Light impinging upon electrospun nanofiber substrates encounters a complex media where a multitude of factors controls the transmittance and reflectance of light through the structure. The chemical composition of the nanofiber plays a significant role in that it determines the index of refraction of individual fibers. However, the surrounding media (e.g., air, encapsulating polymer, etc.) also plays an equally important role. In addition, physical effects such as fiber diameter, fiber morphology, fiber packing density (i.e., structure void volume), and substrate thickness play a large role in determining the light management properties of nanofibers. Our research has demonstrated that the transmittance and reflectance of undoped nanofibers can be adjusted through proper manipulation of these factors. For example, similar electrospinning formulations can produce either highly transmitting or highly reflecting light structures depending upon fabrication parameters that impact the final properties of the nanofiber substrates. In addition, a degree of wavelength dependent reflectance and transmittance can be imparted simply by adjusting the physical properties of the nanofibers to promote preferential light scattering below selected frequencies. This paper provides an overview of various factors impacting the light management properties of nanofiber substrates and the importance of controlling these factors to meet end-use applications.
Nontoxic Silicon Nanocrystals and Nanodiamonds as Substitution for Harmful Quantum Dots
Authors: Fucikova Anna , Valenta Jan , Pelant Ivan , Brezina Vitezslav
Published: August 2010

The commercially available semiconductor quantum dots have been proven to be slightly to significantly toxic by recent publications depending on the chemical composition. We are developing new non-toxic fluorescent labels based on (i) nanocrystalline silicon, suitable for in vivo studies due to their biodegrability, and on (ii) nanodiamonds, intended mainly for in vitro use due to their long-term stability and nondegradilibity.
P-layer Optimization in High Performance a-Si:H Solar Cells
Authors: Xu Yueqin , Nemeth Bill , Hasoon Falah , Hong Lusheng , Duda Anna , Wang Qi
Published: August 2010

We report our progress toward high-performance hydrogenated amorphous silicon (a-Si:H) solar cells fabricated in NREL's newly installed multi-chamber film Si deposition system. The a-Si:H layers are made by standard radio frequency plasma-enhanced chemical vapor deposition. This system produces a-Si:H p-i-n single-junction devices on Asahi U-type transparent conducting oxide glass with >10% initial efficiency. The importance of the p-layer to the cell is identified: it plays a critical role in further improving cell performance. Our optimization process involves changing p-layer parameters such as dopant levels, bandgap, and thickness in cells as well as applying a double p-layer. With the optimized p-layer, we are able to increase the fill factor of our cells to as high as 72% while maintaining high open-circuit voltage.
Silicon Germanium Oxide (SixGeyO1-x-y) Infrared Sensitive Material for Uncooled Detectors
Authors: Anvari Reza , Cheng Qi , Hai Muhammad Lutful , Bui Truc Phan , Syllaios A. J. , Ajmera S. K. , Almasri Mahmoud F.
Published: August 2010

This paper presents the formation and the characterization of silicon germanium oxide (SixGeyO1-x-y) infrared sensitive material for uncooled microbolometers. RF magnetron sputtering was used to simultaneously deposit Si and Ge thin films in an Ar/O2 environment at room temperature. The effects of varying Si and O composition on the thin film's electrical properties which include temperature coefficient of resistance (TCR) and resistivity were investigated. The highest achieved TCR and the corresponding resistivity at room temperature were -5.41 %/K and 3.16×103 ohm cm using Si0.039Ge0.875O0.086 for films deposited at room temperature.
High Mobility a-Si:H TFT Fabricated by Hot Wire Chemical Vapor Deposition
Authors: Hsueh Chun-Yuan , Yang Chieh-Hung , Lee Si-Chen
Published: August 2010

The hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) having a very high field-effect mobility of 1.76 cm2/V-s and a low threshold voltage of 2.43 V have been fabricated successfully using the hot wire chemical vapor deposition (HWCVD).
Biaxial Texturing of Inorganic Photovoltaic Thin Films Using Low Energy Ion Beam Irradiation During Growth
Authors: Groves James , Hayes Garrett J , Li Joel B , DePaula Raymond F , Hammond Robert , Salleo Alberto , Clemens Bruce M
Published: August 2010

We describe our efforts to control the grain boundary alignment in polycrystalline thin films of silicon by using a biaxially textured template layer of CaF2 for photovoltaic device applications. We have chosen CaF2 as a candidate material due to its close lattice match with silicon and its suitability as an ion beam assisted deposition (IBAD) material. We show that the CaF2 aligns biaxially at a thickness of ~10 nm and, with the addition of an epitaxial CaF2 layer, has an in-plane texture of ~15°. Deposition of a subsequent layer of Si aligns on the template layer with an in-plane texture of 10.8°. The additional improvement of in-plane texture is similar to the behavior observed in more fully characterized IBAD materials systems. A germanium buffer layer is used to assist in the epitaxial deposition of Si on CaF2 template layers and single crystal substrates. These experiments confirm that an IBAD template can be used to biaxially orient polycrystalline Si.
Research Progresses on High Efficiency Amorphous and Microcrystalline Silicon-Based Thin Film Solar Cells
Authors: Geng Xinhua , Zhao Ying , Zhang Xiandan , Hou Guofu , Ren Huizhi , Ge Hong , Chen Xinliang
Published: August 2010

This paper reviews our research progresses of hydrogenated amorphous silicon (a-Si:H) and microcrystalline (μc-Si:H) based thin film solar cells. It coves the three areas of high efficiency, low cost process, and large-area proto-type multi-chamber system design and solar module deposition. With an innovative VHF power profiling technique, we have effectively controlled the crystalline evolution and made uniform μc-Si:H materials along the growth direction, which was used as the intrinsic layers of pin solar cells. We attained a 9.36% efficiency with a μc-Si:H single-junction cell structure. We have successfully resolved the cross-contamination issue in a single-chamber system and demonstrated the feasibility of using single-chamber process for manufacturing. We designed and built a large-area multi-chamber VHF system, which is used for depositing a-Si:H/μc-Si:H micromorph tandem modules on 0.79-m2 glass substrates. Preliminary module efficiency has exceeded 8%.
Boule Shape Dependence of Shear and von-Mises Stress Distributions in Bulk SiC during Sublimation Growth
Authors: Drachev Roman Victorovich , Hansen Darren , Loboda Mark J
Published: August 2010

An analytical study of the dependence of shear and von-Mises stress distributions, which develop during PVT (Physical Vapor Transport) growth of 4H-SiC, has been executed. The key parameters investigated include thermal conditions of the crystal growth and parameters of the growing boule geometry. The evaluation was conducted via a 24 full factorial DOE (Design of Experiments). Parameters of the growing boule geometry, i.e. seed diameter, growth front height, inclination angle and height of the side surface were set as the DOE factors, while responses were calculated using numerical simulations. It is found that unique SiC boule growth conditions, which simultaneously minimize both the shear stress and von Mises stress magnitudes, cannot be achieved. Optimization of the shear stress distribution favors longer SiC boules with small seed diameters, small expansion angles and flat growth fronts. Alternatively, optimization of von-Mises stress favors short crystals with small seed diameters and small expansion angles but with curved growth fronts. Consequently, optimization of stress components in SiC crystals involves careful investigation of the interaction and compromise of the reaction cell geometry and growth conditions.
Analysis of Dislocation Behavior in Low Dislocation Density, PVT-Grown, Four-Inch Silicon Carbide Single Crystals
Authors: Dudley Michael , Byrappa Shayan , Wang Huanhuan , Wu Fangzhen , Zhang Yu , Raghothamachar Balaji , Choi Gloria , Sanchez Edward , Hansen Darren , Drachev Roman , Loboda Mark
Published: August 2010

Synchrotron White Beam X-ray Topography studies are presented of dislocation behavior and interactions in a new generation of one hundred millimeter diameter, 4H-SiC wafers grown using Physical Vapor Transport (PVT) under specially designed low stress conditions. Such low stress growth conditions have, for example enabled reductions of basal plane dislocation (BPD) densities by two or three orders of magnitude compared to previous levels down to just a few hundred per square centimeter. This provides a unique opportunity to discern details of dislocation behavior which were previously precluded due to complications of image overlap at higher densities. Among the phenomena observed in these studies is the deflection of threading dislocations onto the basal plane producing various stacking fault configurations. Analysis of the contrast from these faults enables determination of their fault vectors which, in turn, provides insight into their possible formation mechanisms.