bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and Luminescence of Ce-doped Lu2SiO5 Nanophosphor
Authors: Blair Michael Wayne , Jacobsohn Luiz G , Bennett Bryan L , Muenchausen Ross E , Sitarz Stephanie C , Smith James F , Cooke D Wayne , Crozier Peter A , Wang Ruigang
Published: April 2011

Nanophosphors correspond to nanostructured inorganic insulator materials that emit light under particle or electromagnetic radiation excitation. In this work we investigate the structure and luminescent properties of Ce-doped Lu2SiO5 (LSO) nanophosphors prepared by solution combustion synthesis with the Ce content 0.1 to 12 at. %. Samples were characterized by transmission electron microscopy (TEM), line scan electron energy-loss spectroscopy (EELS), x-ray diffraction (XRD), and electron paramagnetic resonance (EPR) spectroscopy. Photoluminescence excitation and emission spectra are composed of two major bands centered at 360 and 430 nm, respectively. These results reveal a red-shift and enhanced Stokes shift for the nanophosphors when compared to bulk. Ce content was also found to affect photoluminescence emission intensity and fluorescent lifetime. The nanophosphor concentration quenching curve presents a broad maximum centered at 1 at.%. Lifetime measurements show a continuous decrease from 34 to 21 ns as Ce content is increased.
Investigation of Nano-thin β-SiC Layers for Chemical Sensors
Authors: Rahimi Ronak , Raghavan Srikanth , Shelton N.P. , Penigalapati Dinesh , Balling Andrew , Woodworth Andrew A. , Denig Tobias , Stinespring Charter D. , Korakakis D.
Published: April 2011

Silicon Carbide possesses a combination of properties that make it ideal for use in electronics. Its high values of electric breakdown field, melting point and saturated electron drift velocity have attracted the attention of the semiconductor community. Although the interest in β-SiC/Si devices has intensified in recent years [1-2], little focus has been given to the study of nano-thin film devices. Monocrystalline nano-thin β-SiC films have been reproducibly grown on Si (100) by Gas Source Molecular Beam Epitaxy (GSMBE). Auger Electron Spectroscopy and Reflection High Energy Electron Diffraction characterization have confirmed a growth consistent of β-SiC/Si. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) characterization has determined film thicknesses of 30nm. These nano-films have been used in the fabrication of Metal-Semiconductor-Metal (MSM) devices formed from aluminum Schottky contacts. Under electrical characterization, these MSM devices have exhibited unique properties in that the dominant conduction path does not occur at the β-SiC/Si interface [3] as previously reported, but within the entire β-SiC layer. It is proposed that the device is isolated from the Silicon substrate and due to the nano-thin β-SiC films used in this work the differentiation between surface and ‘bulk’ is not clear. Results obtained through chemical experimentation have indicated that conduction is largely dependent on the surface condition of the device. This suggests the possibility for nano-thin, surface-like, β-SiC films to be used in chemical agent sensors.
In-situ synthesis of Si3N4/TiN nanocomposite powders in cryogenic solution
Authors: Yang Mei , Lü Mingli , Zhu Hongmin
Published: April 2011

A new method of Si3N4/TiN nanocomposite powders through reaction at low temperatures was proposed and tested. The reduction of titanium chloride and silicon chloride by sodium was conducted in liquid ammonia at the temperature range of −40°C∼−50°C, and titanium nitride and silicon nitride nanopowders were obtained. Based on these reactions, in-situ coating and co-precipitation were conducted. The TiN nano-particles deposited on the surface of Si3N4 particles as the nuclei in the in-situ coating and in the co-precipitation two or more source of ions were reduced uniformly in the liquid ammonia. Si3N4/TiN nanocomposite powders were prepared by the both routes and were characterized with X-ray diffraction, transmission electron microscopy. The effects of in-situ and the particle size on the morphology of the composite were discussed.
Dielectric and Thermomechanical Properties of Polypropylene/Multi-Walled Carbon Nanotubes Nanocomposites
Authors: Kanapitsas A. , Logakis E. , Pandis C. , Zuburtikudis I. , Pissis P. , Delides C. G , Vatalis A. S.
Published: April 2011

The purpose of this work is to examine the dielectric, electrical and thermo-mechanical properties of multi-walled carbon nanotubes (MWCNT) filled polypropylene nanocomposites formed by melt-mixing. To that aim dielectric relaxation spectroscopy (DRS) and dymamic mechanical analysis (DTMA) were employed. The results are discussed in terms of nucleating action of MWCNT and interfacial polymer-filler interactions. Special attention is paid to percolation aspects by both ac conductivity measurements for the samples which are above the percolation threshold and permittivity measurements for the samples which are below percolation threshold.
Phase Separation in Silica Sol-gel System Containing Anionic Surfactant
Authors: Matsui Taisuke , Nakanishi Kazuki , Kanamori Kazuyoshi , Hanada Teiichi
Published: April 2011

By inducing phase separation parallel to the sol-gel transition of alkoxy-derived silica systems, silica monoliths with well-defined co-continuous macropores were obtained from the systems containing anionic surfactants. We adopted three kinds of anionic surfactants which differ from each other in the length of alkyl chain (CH3(CH2)17SO3Na, CH3(CH2)15SO3Na, CH3(CH2)13SO3Na). Mesopores were also found in the silica skeletons presumably by the supramolecular templating. Characterization of the dried or heat-treated samples was carried out by a scanning electron microscope (SEM) and nitrogen adsorption measurements. Experimental results showed that due to the moderate interaction between silica oligomers and surfactants, most of the surfactants are distributed to the solvent phase which determines the macropore volume. The median size and volume of the macropores could be controlled independently by the starting composition. In the absence of any additive to enhance templating by the surfactant, the samples exhibited only amorphous mesopores.
Examination of Mesopore Structure of Hierarchically Macro/mesoporous Silica by Thermoporometry
Authors: Fukui Etsuji , Shinohara Keiske , Nakanishi Kazuki , Kanamori Kazuyoshi , Hanada Teiichi
Published: April 2011

Thermoporometry was employed to monitor the mesopore evolution in wet, drying and heat-treatment stages of monolithic macro/mesoporous silica with SBA-15 like structure. Direct comparison of mesopores in wet state was only possible with the samples extracted with sulfuric acid. In good agreement with the preceding study, the sulfuric acid not only removed the surfactant but also modified the silica gel network into that with reduced amount of micropores and increased stability against the drying stress. Thermoporometry revealed that the structural evolution takes place completely in the wet condition, which accompanies a decrease in the thickness of non-freezable water.
Chemical Data Writing into Metal/oxide Interface: Characterization of Low Dimensional Interface Reactions by I-V Measurements
Authors: Ishii Masashi , Nakao Aiko , Sakurai Kenji
Published: April 2011

We investigated electric and chemical properties of metal/Y2O3 interfaces. The Pt/Y2O3 interface can be chemically activated by bias voltage, resulting in a microscopic oxidation-reduction center at interface. The oxidation-reduction of the center alternatively changed resistance of the Pt/Y2O3 system, and the alternation yield hysteresis with respect to the bias voltage, i.e. a memory effect. On the other hand, in Au/Y2O3 system, non-oxidization of Au induced ejection of O2 gas from the interface, so that there was no memory effect. Possible reactions of these metal/Y2O3 systems were proposed, and the balance between oxidation and reduction at microscopic center was concluded to be essential for the memory effect.
Engineered Nanocomposites for Solid Oxide Fuel Cells By Colloidal Crystal Templating
Authors: McLachlan Martyn A , Ying An , Kilner John A , McComb David W , Skinner Stephen J
Published: April 2011

Colloidal crystal templating has been used to prepare three-dimensionally ordered macroporous (3DOM) films of La1-xSrxMnO3-d (LSM), yttria stabilized zirconia (YSZ) and porous composites of LSM and YSZ. These materials have direct applications as cathodes in solid oxide fuel cells (SOFCs). The 3DOM materials have been prepared by low temperature processing, which is a major step towards overcoming electrode sintering, interdiffusion and deleterious phase formation associated with conventional high temperature processing. The preparation of porous composites and the elimination of high temperature densification presents an opportunity to create SOFCs with a large number of triple phase boundaries which should be accompanied by an corresponding improvement in device performance. The microstructure of the 3DOM films was assessed using scanning electron microscopy and the crystal structure and phase purity assessed by x-ray diffraction.
Failure and Formation of Axial Nanowire Heterostructures in Vapor-Liquid-Solid Growth
Authors: Paladugu Mohanchand , Zou Jin , Guo Ya-Nan , Auchterlonie Graeme J. , Joyce Hannah J. , Gao Qiang , Tan H. Hoe , Jagadish Chennupati , Kim Yong
Published: April 2011

To observe the axial growth behavior of InAs on GaAs nanowires, InAs was grown for different growth durations on GaAs nanowires using Au nanoparticles. Through transmission electron microscopy, we have observed the following evolution steps for the InAs growth. (1) In the initial stages of the InAs growth, InAs cluster into a wedge shape preferentially at an edge of the Au/GaAs interface by minimizing Au/InAs interfacial area; (2) with further growth of InAs, the Au particles move sidewards and then downwards by preserving an interface with GaAs nanowire sidewalls. The lower interfacial energy of Au/GaAs than that of Au/InAs is attributed to be the reason for such Au movement. This downward movement of Au nanoparticle later terminates when the nanoparticle encounters InAs growing radially on the GaAs nanowire sidewalls, and with further supply of In and As vapor reactants, the Au nanoparticles assist the formation of InAs branches. These observations give some insights of vapor-liquid-solid growth and the kinks formation in nanowire heterostructures.
Engineering Morphology of Surfaces by Oblique Angle Etching
Authors: Cansizoglu Mehmet F. , Karabacak Tansel
Published: April 2011

During a typical chemical etching process growth front morphology generally generates an isotropic rough surface. In this work, we show that it is possible to form a rippled surface morphology through a geometrical self-assembly process using a chemical oblique angle etching technique. We observe in our Monte Carlo simulations that obliquely incident reactive species preferentially etch the hills that are exposed to the beam direction due to the shadowing effect. In addition, species with non-unity sticking (etching) coefficients can be re-emitted from the side walls of the hills and etch the valleys, which at the end can lead to the formation of ripples along the direction of the beam. This mechanism is quite different than the previously reported ripple formation during ion-beam bombarded surfaces where the particles have much higher energies, lower incidence angle and ripple formation is mainly due to physical deformation of the surface. We investigate the ripple formation process in our simulated surfaces for a wide range of etching angle and sticking coefficient values.
Strain-assisted Formation of Nano-scaled Lamellar Structure in Ti-39at%Al Single Crystals
Authors: Koizumi Yuchiro , Tanaka Takayuki , Takeshi Fujita , Yoritoshi Minamino
Published: April 2011

We have studied the effects of straining prior to annealing for lamellar structure formation in a Ti-39at%Al single crystal intending to accelerate the lamellar structure formation and decrease the resultant lamellar spacing via preferential nucleation of γ-TiAl phase at dislocations in α2-Ti3Al phase. In a crystal cold-rolled to 10% reduction before annealing, a fine lamellar structure with 88 nm average spacing was formed by annealing at 1073 K for 1×104 s whereas no lamella were observed in the crystal subjected to the same annealing without cold-rolling. In addition, it was also demonstrated that when the crystal is locally strained by indentation and annealed at 1073 K for 1×104 s, a lamellar structure with 43 nm average lamellar spacing is formed in areas near the indentation and there were no lamella beyond these areas. This means that distributions of lamellae can be controlled by controlling the distribution of strain before annealing.
Development of Oil/Water/Surfactant Microemulsions as Templates for Micro and Nanostructured Metal Foams
Authors: Cock Catherine , Renee Woo , O'Neil Brenda , Leigh McKenzie , Manning Jason , Bakker Martin Gerard
Published: April 2011

There are a range of applications for bicontinuous metal micro and nanostructures including as porous electrodes for supercapacitors, in fuel cells and in advanced batteries. We have previously demonstrated a number of methods of generating metal nanostructures by electrodeposition into various templates including hexagonal surfactant phases and mesoporous silica. More recently we have been exploring the application of oil-in-water microemulsions as templates. We have found empirically that the formation of microstructure is strongly effected by the viscosity of the oil phase, the rate of metal electroreduction and the surface roughness of the substrate. We interpret these observations as reflecting a competition between growth of the metal around the oil droplet and the redistribution of the oil in front of the growing metal film. We are currently exploring bicontinuous and water-in-oil phases with the expectation that such templates will yield bicontinuous metal films with larger accessible surface areas. Preliminary results with water-in-oil phases appear to show the formation of bicontinuous nanostructured films on the 20 nm length scale.
Modified Microparticles of Calcium Alginate Gel for Controlled Release of Anesthetics
Authors: Batyrbekov Erkesh E. , Akylbekova Turar N. , Iskakov Rinat M.
Published: April 2011

The aim of this work is the development of controlled delivery system immobilized by local anesthetics on the basis of modified microparticles of calcium alginate gels. The kazkain, rikhlokain, lidokain and novokain were used as local anesthetics. Modified microparticles were obtained by syringed dropwise a solution of ansthetics in sodium alginate into solution of polymers such as chitosan or polyethyleneimine in calcium chloride. The obtained modified alginate microparticles were contained immobilized anesthetics in core of particles and a surface layer of polymer. Effects of polymer concentration and exposure duration on the thickness of polymer coating were determined. The release of anesthetics from the modified alginate gel particles into a physiological solution with different thickness of coating were studied. All the release data show the typical pattern for a matrix controlled mechanism. The cumulative amount of drug released from alginate gels was linearly related to the square root of the time and the release rate decreased this time. The process is controlled by the diffusion of anesthetics through the polymeric coating. The data shown a possibility of the regulation of the rate of anesthetics release from the modified alginate particles by way of alternation of thickness of the polymer coating. The anesthetic effect of the alginate microparticles containing drugs was tested on rats by method “tail flick” according two criteria: full analgesia – the absence of reaction on pain and sufficient analgesia – exceeding of pain threshold sensibility two and more times. Medical-biological tests show that the duration of anesthetic activity for the drug-containing alginate beads increases at 5-8 times in comparison of free drugs.
Protein-Based Hydrogels for Cell Transplantation under Constant Physiological Conditions
Authors: Foo Cheryl T Wong Po , Heilshorn Sarah
Published: April 2011

A promising treatment for multiple neurological disorders including stroke, Huntington's, and Parkinson's is the transplantation of stem cells into the diseased site to promote regeneration of the neural tissue. However, viability of transplanted cells is often low (15-35%) and unpredictable. Cell viability has been directly correlated with functional outcome of the treatment, motivating the development of more reliable cell transplantation procedures. To protect transplanted cells from shear stress during injection and from the hostile, inflammatory environment of the diseased brain tissue, many research groups are exploring physical hydrogels as a protective, growth-permissive matrix to enhance cell viability. However, physical hydrogels require an environmental trigger to induce gelation. These environmental triggers include sudden changes in temperature, pH, or salt concentration - all of which are detrimental to encapsulated cells and proteins and complicate their use in a clinical environment. To address this need, we have designed a two-component, protein-based hydrogel system that can self-assemble under constant physiological conditions.

Both components of the hydrogel system are created using recombinant protein technology, which allows synthesis of exact monomer sequences within monodisperse polymers. The first hydrogel component is a block copolymer made of several repeats of a peptide sequence encoding the WW domain-fold, a short triple-stranded, anti-parallel, beta-sheet. The WW domains are interspersed with a random-coil, hydrophilic spacer to enhance polymer flexibility and solubility. The second hydrogel component is made of several repeats of a polyproline rich peptide sequence interspersed with a random-coil, hydrophilic spacer. Upon mixing the two hydrogel components together, the WW-domains in component 1 and the polyproline rich peptides in component 2 bind together with 1:1 stoichiometry. This binding has an apparent association constant of 2.2×105 M, as measured by isothermal titration calorimetry. This peptide-binding event serves as the physical crosslinks to form a polymeric network composed of the two components. Because gelation is initiated by simply mixing the two components together at physiological pH, temperature, and ionic strength, this system is highly biocompatible and easy to use. Furthermore, the precision of protein engineering allows both components to be easily modified. For example, increasing the length of the hydrophilic spacers will increase the resulting network pore size. Additionally, bioactive peptide sequences, such as the RGD cell-binding domain, have been introduced into the hydrophilic spacers to modify cell-scaffold interactions. Our long-term objective is to design a self-assembling hydrogel system for cell delivery that will both improve cell viability and mimic many of the essential cues in the developmental niche to encourage cell differentiation and outgrowth.
Live-cell Imaging at Low Interaction Forces
Authors: Campbell Paul
Published: April 2011

Imaging live cells using atomic force microscopy (AFM) is perhaps the most challenging role within which the tool can be deployed. The procedure requires that the target cells be maintained under thermostated physiological fluids in order that viability is retained. Furthermore, once the imaging probe has engaged with the target cells, the use of appropriate imaging forces that guarantee reasonable spatial resolution must be weighed against the need to maintain a ‘light touch’ so that the integrity of this most delicate structure is not compromised. The purpose of the present study was ostensibly to image live cells (PtK2 epithelial cells)in-vitroand to examine those force regimes and tip properties that lead to best imaging. Interestingly, by employing ultra low imaging forces (FL< 100pN) whilst operating in contact mode, as opposed to ‘tapping’ mode, it was possible to achieve spatial resolutions in the range of about 25nm, which was sufficient to resolve the constituent fibres of the cytoskeletal network and other subcellular detail. Emipircally, certain tips were found to generate better resolution images than others, and we characterized those tips by imaging a commercial ion-beam etched spike array to determine not only the radius of curvature at the active imaging tip, but also the general morphology of the apex region. Force distance curves could be obtained which allowed a Hertzian analysis of the cellular elasticity. In this instance a value for the Young's modulus, EC, was determined to be 75kPa. Time-lapse imaging in this low force regime allowed the non-intrusive observation of cytoskeletal reorganisation during motility over extended periods of up to 7 hours.
Spontaneous Self-Assembly, Functionalization, and Meso-Scale Host-Guest Science of Organic Nanotubes
Authors: Kameta Naohiro , Masuda Mitsutoshi , Shimizu Toshimi
Published: April 2011

Self-assembly in water at pH 6 and 10 of a wedge-shaped bolaamphiphile (1), bearing amino and glucose hydrophilic headgroups, was found to give two types of nanotubes with different inner diameters of 20 and 80 nm, respectively. X-ray diffraction and IR measurement revealed that the nanotubes have distinct inner and outer surfaces covered with amino and glucose headgroups, respectively. The nanotubes were able to effectively encapsulate an anionic spherical protein, ferritin, and DNA into the hollow cylinder under neutral pH conditions. Positively charged amino groups in the nanotube hollow cylinder proved to accelerate the encapsulation of the anionic biomacromolecules via electrostatic interaction. Covalent modification of the amino groups with a fluorescent donor dye on the inner surface of the nanotube allowed us to achieve the construction of an optical recognition system for encapsulation of guest molecules. Fluorescence resonance energy transfer (FRET) from the fluorescent donor located on the inner surface to the ferritin labeled with fluorescent acceptor enabled us to visualize the encapsulation and transportation features of the ferritin in the nanochannel shaped by the hollow cylinder structure.
Sol-gel Encapsulated Gold-Silica Nanoshell-based SERS Sensors
Authors: Lin Yu-Jen , Gala Pankti , Bishnoi Sandra Whaley
Published: April 2011

We have used sol-gel methods to immobilize gold-silica nanoshells to create robust SERS based sensors. Using a protocol commonly used to immobilize proteins, biologically friendly SERS sensors for the study of gold binding peptides and proteins have been created. Specifically, by combining tetramethyl orthosilicate (TMOS), methyltrimethoxysilicate (MTMS), phosphate buffer, and gold nanoparticles we have created sol-gels with reduced fluorescence and Raman backgrounds. The resulting substrates have been tested using the Raman scattering response of 4-mercaptonbenzoic acid (4-MBA) to determine porosity and long-term stability of this SERS substrate. Multiple rinse cycles using phosphate buffer showed no significant decline in the SERS response of the substrate up to ten rinse cycles. Future studies will test the feasibility of using such substrates for the detection of biomolecules on the surface of gold.
Functionalized Porous Silicon in a Simulated Gastrointestinal Tract: Modeling the Biocompatibility of a Monolayer Protected Nanostructured Material
Authors: Albrecht Daniel S. , Lee Jacob T. , Molby Nick , Rhodes Steven D. , Dam Hieu Minh , Siegel Jason L. , Porter Lon A.
Published: April 2011

Owing to its photoluminescent properties and high surface area, porous silicon (por-Si) has shown great potential toward a myriad of applications including optoelectronics, chemical sensors, biocomposite materials, and medical implants. However, the native hydride-termination is only metastable with respect to surface oxidation under ambient conditions. Por-Si samples oxidize and degrade even more quickly when exposed to saline aqueous environments. Borrowing from solution phase synthetic methods, a selection of hydrosilylation reactions has been recently reported for functionalizing organic groups onto oxide-free, hydride-terminated porous silicon surfaces. Monolayers, bound through direct silicon-carbon bonds, are produced via thermal, microwave, Lewis acid, and carbocation mediated pathways. All of these wet, benchtop methods result in the formation of stable monolayers which protect the underlying silicon surface from ambient oxidation and chemical attack. However, no direct comparison of monolayer stability resulting from these diverse mechanisms has been reported. A variety of alkyl monolayers were prepared on porous silicon using the diverse hydrosilylation routes describe above and then immersed into a sequence of simulated gastric and intestinal fluids to replicate the conditions of potential por-Si biosensors or medicinal delivery systems in the human gastrointestinal tract. Degradation of the organic monolayers and oxidation of the underlying por-Si surfaces were monitored using both qualitative and semiquantitative transmission mode Fourier transform infrared spectroscopy (FTIR). Our initial results indicate that methods employing chemical catalysts often incorporate these species within the monolayer as defects, producing less robust surfaces compared to catalyst-free reactions. Regardless, monolayer protected por-Si samples demonstrated superior durability as opposed to the unfunctionalized controls.
Light Emission Properties and Biological Applications of Lanthanide Doped Oxide Nanoparticles
Authors: Mialon Genevieve , Giaume Domitille , Moreau Melanie , Casanova Didier , Nguyen Thanh-Liem , Popoff Michel-Robert , Alexandrou Antigoni , Gacoin Thierry , Boilot Jean-Pierre
Published: April 2011

Rare-earth doped oxides as bulk materials are well known for their numerous applications in light emitting devices. Emission properties of nanoparticles, in association with their small size, open the way to new applications such as the elaboration of transparent luminescent devices or new biological labels. The key issue for such applications is the control of the surface state of the particles in order to preserve their dispersion state, to guarantee a strong emission and/or ensure strong interactions with specific target sites. Our work in this field mainly concerns yttrium vanadate particles (YVO4:Ln with Ln=Eu, Dy and Yb/Er) that are obtained as aqueous suspensions through a simple reaction of coprecipitation [1]. As compared to the bulk material, these particles (10-40 nm in diameter) exhibit the characteristic emission from the lanthanide dopant but with a lower efficiency (quantum yield of 15% and emission lifetime of 0.7 ms). The first part of our work is devoted to the improvement of the emission properties of particles. Our results show that the emission process is altered either by surface hydroxyl groups or by the poor cristallinity of the particles. We show that large improvement can be obtained following an original process which allows recovering the particles as colloidal dispersions after their thermal treatment at 1000°C. In the case of Eu3+ doped particles, quantum yield and emission lifetime were increased up to 40% and 0.8 ms respectively without notable increase of particle size. Moreover, the emission spectrum, either from colloidal suspensions or from single particles fits almost perfectly to the one from the bulk material. The second part of our work is devoted to the surface derivatization of the particles for applications as biological probes [2]. We chose a general scheme involving the coating of the nanoparticles with a thin layer of amino-silane. This process was chosen in order to allow further versatile grafting reactions trough the surface amino groups. This strategy will be detailed in the case of the coupling between our particles and a protein through the use of a homo-bifunctional cross-linker. The quantification of the number of attached proteins was achieved using dual-color microscopy and fluorescently-tagged proteins, by observing the step-like photobleaching of the organic fluorescent tag. The observation of labelled toxins interacting with living cells shows the high potentiality of rare-earth-doped oxide particles as new biological probes.
Fluorescent Hydrogel Sensor Particles for Detection of Protease Activity
Authors: Patrick Alison , Ulijn Rein V
Published: April 2011

We demonstrate the design of novel sensor particles that display fluorescence in the presence of elastase, an enzyme that is present at elevated levels in chronic (non-healing) wounds. Poly(ethyleneglycol acrylamide) hydrogel particles, approximately 200μm in diameter are used as a polymeric matrix, to which a peptide based sensing element is attached. This sensing element consists of a Förster resonance energy transfer (FRET) pair separated by an enzyme cleavable linker. In addition, negatively charged Glutamic acid (Glu) residues are incorporated into the hydrogel structure to facilitate diffusion of the positively charged enzyme into the hydrogel matrix. Enzymatic hydrolysis of the enzyme cleavable linker results in fluorescence of the donor molecule being switched on. We have shown that these particles can detect elastase to a concentration of 100ng/ml, a concentration found in chronic wound fluids. These particles simultaneously detect and address balances in elastase levels and may therefore find applications as smart wound dressings.
Biocatalysis for Material Science and Drug Discoveries
Authors: Bruno Ferdinando Francesco , Samuelson Lynne A , Nagarajan Subhalakshmi , Nagarajan Ramaswamy , Kumar Jayant
Published: April 2011

A novel biomimetic route for the synthesis of conducting homopolymers and copolymers from aniline, phenol, pyrrole and 3,4-ethylenedioxy-thiophene in the presence of a polyelectrolyte, such as polystyrene sulfonate (SPS) is presented. A poly(ethylene glycol) modified hematin (PEG-Hematin) and the enzyme horseradish peroxidase (HRP) were used to catalyze the copolymerization of different monomers. UV-vis, FTIR, XPS, TGA and electrical conductivity studies for all complexes indicated the presence of a stable and electrically conductive form of these polymers. Furthermore, the presence of a polyelectrolyte, such as SPS, in this complex provides a unique combination of properties such as processability and water-solubility. Additionally catechins, the active compounds found in green tea, were polymerized and found to exhibit very interesting anti-carcinogenic properties. Here we report a unique enzymatic approach for the synthesis of water-soluble poly(catechins) with enhanced stability and potent anti-proliferative effects on human cancer cells in vitro. Various stereoisomers of catechin [(+), (-), (±)] and (-)-epicatechin have been biocatalytically polymerized using HRP in ethanol/buffer mixtures. This one-pot biocatalytic polymerization is carried out in ambient conditions yielding water-soluble poly(catechins). These synthesized poly(catechins) were tested for their growth inhibitory properties using a variety of normal and cancerous human epithelial cell lines. The poly(catechins) exhibit statistically significant greater growth inhibitory effects when compared to the monomers and exhibited specificity, inhibiting the growth of breast, colorectal and esophageal cancer cells while having little effect on normal epithelial cell growththus achieving a high therapeutic ratio. The synthesis, characterization and the growth inhibitory effects of these novel water-soluble poly(catechins) will also be presented.
Optical Properties of Carbon Nanotubes: Near-Infrared Induced Hyperthermia as Therapy for Brain Tumors
Authors: Gomez-De Arco Lewis , Chen Meng-Tse , Wang Weijun , Vernier Thomas , Pagnini Paul , Chen Thomas , Gundersen Martin , Zhou Chongwu
Published: April 2011

In this work chemical functionalization of carbon nanotubes was conducted with the aim of improving their ability to be integrated into biological systems. Functionalized SWNT demonstrated to be an excellent vehicle to translocate a highly conjugated organic fluorophore across the cell membrane while causing little toxicity to the cells. Functionalized SWNT were introduced into different lines of the primary brain tumor cells Glioblastoma Multiforme (GBM). Once within the cell interior, the optical properties of the SWNT were used for both fluorescent imaging characterization and selective killing of tumor cells that had exhibited high SWNT uptake levels upon exposure to NIR radiation. Propidium iodide (PI) was employed as an indicator to determine the number of cells with compromised plasma membrane. Cell surviving ratio of as little as 10-20 percent were found in samples with intracellular nanotubes exposed to NIR radiation while a cell surviving ratio of about 95 percent was typical in irradiated samples without intracellular nanotubes. Control samples showed cell surviving ratios comparable to exposed samples without intracellular nanotubes. This study reveals new insights upon the influence of SWNT optical properties in the physicochemical processes within cells and how they can be used to develope therapy for cancerous brain tumors.
Understanding of Passivation Mechanism in Heterojunction c-Si Solar Cells
Authors: Kondo Michio , De Wolf Stefaan , Fujiwara Hiroyuki
Published: April 2011

Intrinsic hydrogenated amorphous silicon (a-Si:H) films can yield in outstanding electronic surface passivation of crystalline silicon (c-Si) wafers as utilized in the HIT (heterojunction with intrinsic thin layer) solar cells. We have studied the correlation between the passivation quality and the interface nature between thin amorphous layers and an underlying c-Si substrate for understanding the passivation mechanism. We found that a thin (∼5nm) intrinsic layer is inhomogeneous along the growth direction with the presence of a hydrogen rich layer at the interface and that completely amorphous films result in better passivation quality and device performance than an epitaxial layer. Post annealing improves carrier lifetime for the amorphous layer, whereas the annealing is detrimental for the epitaxial layer. We have also found that the passivation quality of intrinsic a Si:H(i) film deteriorates severely by the presence of a boron-doped a-Si:H(p+) overlayer due to Si-H rupture in the a-Si:H(i) film. Finally, for a passivation layer in the hetero-junction structure, a-Si1−xOx will be demonstrated in comparison with a-Si:H.
MW plasma enhanced CVD of intrinsic Si for thin film solar cells
Authors: Van Aken Bas B. , Leegwater Hans , Dorenkamper Maarten , Devilee Camile , Loffler Jochen , Heijna Maurits C.R. , Soppe Wim J.
Published: April 2011

Our aim is the development of high-throughput production technology for high efficiency, amorphous and microcrystalline thin film silicon photovoltaics (PV) on flexible substrates. A roll-to-roll system is developed, with three deposition chambers for the continuous deposition of n-type, intrinsic and p-type Si. Novel MW sources for plasma enhanced chemical vapour deposition (PECVD) are introduced in the roll-to-roll coater as MW-PECVD combines good quality with large area, high rate deposition of intrinsic Si. A comparison is made between Raman and UV-reflection spectroscopy.
Low Temperature Synthesis of Nanocrystalline Silicon and Silicon Oxide Films by Plasma Chemical Vapor Deposition
Authors: Tomyo Atsushi , Kaki Hirokazu , Takahashi Eiji , Hayashi Tsukasa , Ogata Kiyoshi , Uraoka Yukiharu
Published: April 2011

Nanocrystalline silicon (nc-Si) and SiO2 films have been synthesized at a low substrate temperature using inductively coupled plasma chemical vapor deposition (ICP-CVD) methods with internal low-inductance antenna (LIA) units. The synthesis of these materials was performed in the separate vacuum containers where LIA units were installed so that the induced electric field from an antenna could be used effectively. Radio frequency (13.56 MHz) power was supplied through the matching circuit units. H2 and SiH4 gases were used for nc-Si synthesis, and O2 and SiH4 gases were used for SiO2 deposition. The gas flow ratios were 15 for H2/SiH4 and 4.0 for O2/SiH4. A substrate temperature, gas pressure, RF power and process time were varied in order to investigate optimum conditions for nc-Si synthesis. Silicon oxide films were deposited under conditions of 300°C, 0.2 Pa and 24 mW/cm3. A sample was prepared by SiO2 deposition and subsequent nc-Si synthesis after removing the natural oxide on silicon substrate by buffered 1%-HF (BHF) solution. In some cases, plasma treatments were inserted before or after nc-Si synthesis. The diameter and number density of nc-Si were determined by a high-resolution transmission electron microscopy (HR-TEM). Plan-view TEM images of nc-Si showed that spatially isolated nc-Si was synthesized and that the diameter and the standard deviation of nc-Si could be controlled not only with a substrate temperature, gas pressure, RF power and process time but also with pre/post plasma treatments. The resultant trend suggests that radical precursors and reactive nucleation sites on the SiO2 surface have an important role in the synthesis of nc-Si. The diameter of almost all nc-Si under the present conditions was less than 10 nm. In particular, under conditions of the substrate temperature of 200°C and 4.0 Pa with oxygen plasma pretreatment and hydrogen plasma posttreatment, the mean diameter and number density of nc-Si were 2.7 ± 0.5 nm and 6.5 × 1011 cm−2, respectively. This result is suitable for quantum effect device applications. In addition, electronic properties of a single SiO2 film were examined with the fabricated metal oxide semiconductor (MOS) capacitor. Breakdown voltage was 7.5 MV/cm at 1.0 × 10−6 A/cm2 and leakage current was 1.0 × 10−9 A/cm2 at 2.0 MV/cm for a SiO2 film with a thickness of 12 nm. This result clearly supports the present SiO2 film is capable of the thin dielectric layer of nc-Si devices.
Cyclically Varying Hydrogen Dilution for the Growth of Very Thin and Doped Nanocrystalline Silicon Films by Hot-Wire CVD
Authors: Lopez Fernando Villar , Antony Aldrin , Muñoz Delfina , Rojas Fredy , Escarré Jordi , Stella Marco , Asensi José Miguel , Bertomeu Joan , Andreu Jordi
Published: April 2011

An important issue for the massive implementation of thin silicon technology in photovoltaic is the use of plastic substrates, which allow the use of roll-to-roll deposition systems and planar monolithic interconnection between the cells. However, the use of plastic substrates require a fully low temperature process; especially critical in the deposition of the thin amorphous (a-Si:H) or nanocrystalline (nc-Si:H) layers. Hot-Wire Chemical Vapour Deposition (HW-CVD) technique has demonstrated to be a good alternative to deposit quality thin films at low temperature. In this paper we focus our study on very thin (50 nm) n- and p-doped nc-Si:H films deposited at low substrate temperature around 100°C. We have observed that, in this low temperature deposition conditions, the promotion of an a Si:H incubation layer leads to a poor doping efficiency and poor electrical properties of the films. Hence, in addition to the optimization of the deposition conditions, we deposited doped layers by cyclically varying the hydrogen dilution (CVH) during deposition process. This CVH method promotes a layer-by-layer growth and inhibits the formation of the incubation layer. Several doped nc-Si:H layers have been deposited with and without this CVH method. The structural, electrical and optical properties of these films and advantage of CVH in improving the device quality of the thin doped layers are reported.
Analysis of Compositionally and Structurally Graded Si:H and Si1−xGex:H Thin Films by Real Time Spectroscopic Ellipsometry
Authors: Podraza Nikolas , Li Jing , Wronski Christopher R. , Horn Mark W. , Dickey Elizabeth C. , Collins Robert W.
Published: April 2011

Silicon-germanium (Si1−xGex:H) thin films have been prepared by plasma enhanced chemical vapor deposition of SiH4 and GeH4 and measured during growth using real time spectroscopic ellipsometry. A two-layer virtual interface analysis has been applied to study the structural evolution of Si:H films prepared in multistep processes utilizing alternating intermediate and low H2-dilution material layers, which have been designed to produce predominately amorphous films with a controlled distribution of microcrystalline particles. The compositional evolution of alloy-graded a-Si1−xGex:H has been studied as well using similar methods. In each case, depth profiles of microcrystalline content, fμc, or Ge content, x, have been extracted. Additionally, real time spectroscopic ellipsometry has been used to monitor post-deposition exposure of a-Si:H, a-Si1−xGex:H, and a-Ge:H films to a hydrogen plasma in situ in order to determine sub-surface amorphous film modification similar to that which would occur when a highly H2-diluted layer is deposited on a layer prepared with lower dilution. These analyses provide guidance for enhanced performance of Si:H based solar cells, through controlled bandgap grading using compositionally graded amorphous binary alloys (a-Si1−xGex:H) or the incorporation of controlled fractions of microcrystallites into bulk amorphous i-layer materials, and by providing a fundamental understanding of the modification of component layers during the deposition of subsequent layers in multilayer stacks.
Two-Step Capacitance Transients From an Oxygen Impurity Defect
Authors: Datta Shouvik , Cohen J. David , Xu Yueqin , Branz Howard M.
Published: April 2011

This paper describes the study of an electron-trapping defect which underwent significant configurational relaxation in oxygen contaminated hydrogenated amorphous silicon-germanium (a-Si,Ge:H) alloys grown by hot-wire chemical vapor deposition. An unusual two-step electron emission from this relaxed defect is studied using junction-capacitance-based measurements. In this work, we monitor the recovery of the relaxed defect after filling it by photoexcited electrons and also by electrons injected with a voltage filling pulse. The dependence of the transient shape on filling pulse time is described. We have also performed experiments which clearly demonstrate that this is a bulk defect and exclude contributions from any additional blocking junctions.
Production Technology of Large-Area, Light-Weight, Flexible Solar Cell and Module
Authors: Shimosawa Makoto , Kawano Shinichi , Ishikawa Takamasa , Nakamura Tetsuro , Sakakibara Yasushi , Kiyofuji Shinji , Enomoto Hirofumi , Nishihara Hironori , Kamoshita Tomoyoshi , Miyagi Masahide , Saito Junichiro , Takano Akihiro
Published: April 2011

Production technologies of a-Si/a-SiGe flexible film solar cells have been established. The film solar cells having a unique monolithic device structure using through-hole contacts are continuously fabricated on flexible plastic films. Production technologies, such as (1) low temperature and high speed textured electrode deposition method, (2) high speed amorphous silicon deposition method, (3) modified roll-to-roll deposition apparatus technology, (4) large-area high quality transparent electrode deposition method, and (5) very high speed laser patterning method were developed. Increasing deposition rate of textured metal electrode was developed for improving production capacity. We developed and proposed low-temperature textured electrode deposition technique named “selective reactive sputtering”. In the deposition method, Ag-based electrode is deposited using small amount of Al containing Ag alloy targets. Ar/O2 mixed gas is used for reactive sputtering. In the deposition conditions, Ag is not oxidized and maintains low resistivity, whereas Al is oxidized selectively and changes the surface morphology drastically. The oxide incorporation affects on the surface reaction and enhances surface roughness formation. We also developed an amorphous silicon deposition control method which can increase deposition rate without deteriorating film properties. We found peak-to-peak voltage at the cathode (Vpp) had information of the plasma and could be used for optimizing the deposition conditions. Vpp has a strong relationship with stabilized efficiency of solar cells. Very high laser patterning method was also developed. The laser patterning method using a galvano scanner improves the pattering speed remarkably. Our new factory in Kumamoto started commercial production in the last year. We can produce 12MW/Y of solar cells using the new production line that can apply 1m-wide and 2000m-long film substrates at this time. We are planning to install more production lines and have 40MW/Y production capacity in FY 2008.
High Fill Factor a-Si:H Sensor Arrays with Reduced Pixel Crosstalk
Authors: Vygranenko Yuriy , Sazonov A. , Striakhilev D. , Chang J. H. , Heiler G. , Lai J. , Tredwell T. , Nathan A.
Published: April 2011

In this paper, we report on low noise, high fill factor amorphous silicon (a-Si:H) image sensor structures for indirect radiography. Two types of the sensor arrays comprising n-i-p photodiodes and m-i-s photosensors have been fabricated. The device prototypes contain 100 × 100 pixels, with a pixel pitch of 139 μm. The active-matrix addressing is provided by low off-current TFTs. The sensors are vertically integrated onto the TFT-backplane, by implementing a 3-μm-thick low-k interlayer dielectric. This dielectric layer serves to reduce the data line capacitance and to planarize underlying topography. The detector was designed for reduced data-line resistance and parasitic coupling. Details of the device design and fabrication, along with sensor performance characteristics, are presented and discussed.
Theoretical Investigation of New Quantum-Cross-Structure Device as a Candidate beyond CMOS
Authors: Kondo Kenji , Kaiju Hideo , Ishibashi Akira
Published: April 2011

We propose a new quantum cross structure (QCS) device as a candidate beyond CMOS. The QCS consists of two metal nano-ribbons having edge-to-edge configuration like crossed fins. The QCS has potential application in both switching devices and high-density memories by sandwiching a few molecules and atoms. The QCS can also have electrodes with different dimensional electron systems because we can change the widths, the lengths, and the heights of two metal nano-ribbons, respectively. Changing the dimensions of electron systems in both electrodes, we have calculated the current-voltage characteristics depending on the coupling constants between a molecule and the electrode. We find that the conductance peak is much sharper in case of weak coupling regardless of dimensions of electron systems in electrodes, compared to strong coupling case. We also find that the conductance peak of QCS having electrodes with two-dimensional electron systems (2DES) is much sharper than that of QCS having electrodes with three-dimensional electron systems (3DES) in case of strong coupling because of quantum size effect of 2DES. These results imply that the QCS with the very sharp conductance peak can serve as the devices to switch on and off by very small voltage change.
Bulk Growth of SiC
Authors: Wellmann Peter , Müller Ralf P. , Sakwe Sakwe A. , Künecke Ulrike , Hens Philip , Stockmeier Mathias , Konias Katja , Hock Rainer , Magerl Andreas , Pons Michel
Published: April 2011

The paper reviews the basics of SiC bulk growth by the physical vapor transport (PVT) method and discuss current and possible future concepts to improve crystalline quality. In-situ process visualization using x-rays, numerical modeling and advanced doping techniques will be briefly presented which support growth process optimization. The “pure” PVT technique will be compared with related developments like the so called Modified-PVT, Continuous-Feeding-PVT, High-Temperature-CVD and Halide-CVD concepts. Special emphasis will be put on dislocation generation and annihilation and concepts to reduce dislocation density during SiC bulk crystal growth. The dislocation study is based on a statistical approach. Rather than following the evolu-tion of a single defect, statistic data which reflect a more global dislocation density evolution are interpreted. In this context a new approach will be presented which relates thermally induced strain during growth and dislocation patterning in networks.