bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective Growth of Al Nanowhiskers on the Patterned Substrate by Glancing Angle Deposition at High Temperature
Authors: Suzuki Motofumi , Kita Ryo , Hamachi Kenji , Nagai Koji , Nakajima Kaoru , Kimura Kenji
Published: April 2011

We demonstrated high temperature glancing deposition (HT-GLAD) of Al on the heated substrate with trench patterns. When Al was deposited under the condition, where the Al vapor is incident at very glancing on the sidewall but on the surface, Al nano-whiskers grew only on the sidewall of the trenches since HT-GLAD condition is achieved only for the sidewall. On the other, Al was deposited at glancing angle both on the surface and the sidewalls, nano-whiskers grow both on the surface and the sidewalls of the trenches. The selective growth of the nano-whisker is successfully achieved by controlling the geometrical deposition conditions. Remarkably, moreover, the nano-whiskers grow not only on the illuminated sidewalls but also on the shadow sidewall. In addition, few nano-whiskers grow on the shadow region of the bottom of the trenches. In order to understand the peculiar growth of Al nano-whiskers, novel transport processes of Al atoms other than the surface diffusion have to be clarified. The reevaporation or reflective scattering on the sidewalls of the trenches is likely to play an important role in the growth of nano-whiskers.
Fabrication and Characterization of Spectroscopically Encoded Core-shell Nanoparticle-polymer Nanocomposite
Authors: Dai Sheng , Farah Abdiaziz A. , Alvarez-Puebla Ramon A , Bravo-Vasquez Juan P , Fenniri Hicham
Published: April 2011

Metal nanoparticles are of great importance in the fabrication of new nanocomposite materials. One area of increasing interest is the application of metal nanoparticles (NP) as substrates for surface enhanced Raman scattering (SERS). In this regard, self-assembled monolayers (SAMs) of sulfur containing organic compounds are ideal target for SERS studies due to the strong affinity of sulfur for noble metals. Two types of molecules were synthesized for this study, an organic-soluble and a water-soluble styrene derivative. Self-assembling behaviors of these monomers on gold or silver nanostructured surfaces at room temperature were studied by UV-Vis spectroscopy, dynamic light scattering (DLS), SERS spectroscopy, and scanning electron microscopy (SEM). It was found that the interaction between sulfur compounds and metal NPs is strongly dependent on the NP size and the monomer environment. The hydrophilic NP surface switches to hydrophobic upon binding of sulfur-containing monomers, which leads to the formation of aggregates in aqueous solution for both water-soluble and oil-soluble monomers. The self-assembling behavior of these monomers on the metallic surface was compared with that of the corresponding homopolymers. Due to macromolecular and steric effects, the binding interaction between homopolymer and metal NP is weaker than that between NP and monomers. Surface polymerization of these monomers on metallic surfaces was observed as supported by SERS. Core-shell nanoparticles could also be obtained through seeded emulsion polymerization, but a decrease in SERS activity was observed.
Raman Characterization of Silicon Nanoclusters Embedded in Fused Silica
Authors: Barba David , Clavel Milene , Martin Francois , Ross Guy
Published: April 2011

Silicon nanocrystals (Si-nc) and amorphous silicon (a–Si) aggregates either produced by silicon implantation in fused silica have been studied by micro-Raman spectroscopy. Under certain experimental conditions, relevant information regarding both the dimension and the size distribution of Si-nc can be extracted from the energy shifts and the spectral distortion of the phonon excitation observed near 520 cm−1. Results are presented for different sample annealing times and ion fluences. These data agree with the direct observation by TEM of non-uniformly depth-distributed silicon nanocrystals. Moreover, measurements recorded for different Raman probing depths give evidence of chemical composition changes within the fused silica matrix. The depth evolution of the phonon peak associated with the Raman signature of a-Si near 470 cm−1 shows the presence of amorphous silicon, whose concentration is higher in the region where the large Si-nc are located.
Radiological Control of Gold Octahedral and Prism Nanoparticles
Authors: Nenoff Tina M. , Jones Jason C. , Provencio Paula P. , Berry Donald T.
Published: April 2011

We report on a fundamental morphology growth of gold-based nanoparticles by solution radiolysis. Radiolysis of pure gold-polymer solutions of different dose rates and aging time is examined. A detailed description will be presented of the experimentation, testing and analysis. In particular, we will present data on the formation of gold nano-octahedra and -prism particles. The γ-irradiations were carried out with a 60Co source of 1.345 × 105 Ci (Sandia National Laboratories Gamma Irradiation Facility (GIF). Nanoparticle characterization techniques included are UV-vis and TEM. Similar to what has been seen in earlier silver nanoparticle studies, dose rate dictates the size of nanoparticles formed. At high dose rate, all reducing species are produced and scavenged within a short time, and then coalesce into separate nanoparticles. At low dose rate, the coalescence process is faster than the production rate of the reducing radicals. The reduction of radicals occurs mainly on clusters already formed. The differences in the morphologies result from a combination of dose rate, aging and lack of radical scavengers (e.g. isopropyl alcohol), resulting in either gold nano-spheres, octahedral or prism nanoparticles. The progressive evolution with dose rate of the UV-visible absorption spectra of radiation-induced metal clusters is discussed.
Electronic and Magnetic Characterization of in vivo Produced vs. in vitro Reconstituted Horse Spleen Ferritin
Authors: Papaefthymiou Georgia C. , Viescas Arthur J. , Devlin Eamonn , Simopoulos Athanassios
Published: April 2011

Magnetic nanophases nucleated within horse spleen apoferritin nanotemplates underin vivophysiological conditions andin vitroreconstitution were characterized by Mössbauer spectroscopy in lyophilized form. Mössbauer spectra recorded at 80 K indicate that for thein vivoproduced ferritin the presence of phosphates within the ferritin biomineral core results in larger quadrupole splittings, both at interior and surface sites, 0.62 mm/s and 1.06 mm/s, respectively, as compared to 0.56 mm/s and 0.75 mm/s for the reconstituted ferritin. Data collected at lower temperatures give blocking temperatures of 55 and 40 K forin vitroandin vivosamples. At 4.2 K, both samples give similar saturation hyperfine field values for the interior (495 kOe) and surface (450 kOe) iron sites. The temperature dependence of the reduced hyperfine magnetic fields at the interior iron sites is consistent with the collective magnetic excitations model, due to the particle's magnetization precession about the anisotropy axis. In contrast, a marked decrease in the reduced hyperfine field at surface sites with increasing temperature indicates a more complex spin excitation energy landscape at the surface.
Reaction Dynamics for Gold Nanoparticles Synthesis in Solution Plasma
Authors: Hieda Junko , Saito Nagahiro , Takai Osamu
Published: April 2011

We describe the dynamics of the synthesis of gold nanoparticles by glow discharge in aqueous solutions. Initial [AuCl4]− concentration and the voltage applied between the electrodes were varied. Reduction rates were calculated from changes in concentration of [AuCl4]− vs. discharge time. A pulsed power supply was used to generate discharges in the aqueous solutions. The morphology of the nanoparticles obtained was observed by transmission electron microscopy (TEM). [AuCl4]− was reduced by H radicals or electrons generated by the discharge. Dendrite-shaped nanoparticles ∼150 nm in size were formed after discharge for 1 min. The pH of the solution decreased gradually with increasing discharge time. The decrease in pH led to dissolution of gold nanoparticles. The reduction and dissolution rates increased proportionately with the applied voltage. The size of gold nanoparticles decreased during discharge and was 20 nm after discharge for 45 min. When the reduction rate lowered as a result of dissolution, anisotropic nanoparticles were formed and continued to grow in the solution.
Synthesis and Structural Transformation of Luminescent Nanostructured Gd2O3:Eu Produced by Solution Combustion Synthesis
Authors: Jacobsohn Luiz G. , Bennett Bryan L. , Sitarz Stephanie C. , Ugurlu Ozan , Sharma Ana L. Lima , Cooke D. Wayne , Muenchuasen Ross E.
Published: April 2011

In this work we explore the uniqueness of solution combustion synthesis (SCS) technique to produce luminescent nanostructured materials with metastable phases. We synthesized Gd2O3:Eu with the high-temperature phase and induced phase transformation toward the room temperature phase to investigate the effects of structural transformation on the luminescent properties. SCS is based on exothermic redox reactions that undergo self-sustaining combustion, yielding powders composed of agglomerates of nanocrystals with typical dimensions of tens of nanometers. Synthesis of materials through SCS occurs in conditions far from thermodynamic equilibrium and, due to the high temperatures achieved during combustion, metastable crystallographic phases can be formed. Eu-doped Gd2O3 was obtained with base-centered monoclinic structure and average nanocrystal size of 35 nm as determined by Debye-Scherre analysis. Phase transformation to the cubic structure was induced by isothermal annealing at 1000 oC for up to 152 hrs and followed by x-ray diffraction (XRD). Luminescence excitation and emission spectra were obtained as a function of annealing time. The transformation from monoclinic to cubic structure was followed by the behavior of the (111) monoclinic/(222) cubic intensity ratio. The ratio value for the as-prepared material is 6, decreasing fast to 3 after 5 hrs. annealing, and reaching a value of 0.1 after 152 hrs. Concomitant to the structural transformation, nanocrystal size was followed for both crystalline phases. The average nanocrystal size for the cubic phase increases from 27 to 47 nm from 1 to 152 hrs., respectively. On the other hand, nanocrystals with the monoclinic phase remained with a constant size around 38 nm. Overall, variation in size is small due to the low connectivity among nanocrystals resulting from the low isostatic pressure employed to prepare the pellets, together with the non-uniform shape of the agglomerates. Photoluminescence excitation spectra are dominated by a broad centered near 278 nm and assigned to the O2-Eu3+ charge transfer band. Photoluminescence emission results present the 5D0-7FJ (with J = 0-4) transitions of Eu3+ ions. The behavior of these bands was investigated as a function of annealing time and subsequently related to the structural changes.
Influence of the Time-Temperatur-Profile on Powder Characteristics of Nanocrystalline Anatase (TiO2) produced by Chemical Vapor Synthesis
Authors: Djenadic Ruzica , Chowdhury Sankhanilay Roy , Spasova Marina , Gondorf Andreas , Akyildiz Erdal , Winterer Markus
Published: April 2011

Chemical Vapor Synthesis (CVS) is the conversion of molecular species into nanocrystalline particles by chemical reactions in a gas flow reactor. Pure anatase nanoparticles are generated in a hot wall reactor from titanium isopropoxide using different time-temperature-profiles. The time-temperature-profile (T(t)-profile) in the gas phase of the reactor has a profound influence on the particle characteristics such as particle microstructure and surface chemistry and, therefore, on the quality of the powder consisting of nanocrystalline particles. In this study a simple reaction-coagulation-sintering model (CVSSIN) was used to predict influence of the T(t)-profile on the powder characteristics. The as-synthesized anatase powders show a very high degree of crystallinity, primary particle of about 10 nm sizes and a low degree of agglomeration.
Synthesis and Characterization of Spectroscopically Encoded Nanocomposites
Authors: Jawabrah Al-Hourani Baker , Dai Sheng , Alvarez-Puebla Ramon A. , Bravo-Vasquez Juan P. , Fenniri Hicham
Published: April 2011

Three sulfur-containing styrene monomers with different leaving groups, 4-vinylphenyl ethanethioate, 1,2-bis(4-vinylphenyl)disulfane, and butyl(4-vinylphenyl)sulfane, were synthesized through nucleophilic substitution/addition reactions and purified through column chromatography. In aqueous solution, these monomers could bind to the surface of gold nanoparticles and form self-assembled monolayers (SAMs). SAMs were analyzed by Raman spectroscopy and showed SERS activity with enhancement factors of more than 105. In addition, SAMs were also formed on the surface of gold/silver nano-island films. The bulk Raman and SERS spectra of monomers on different gold nanostructured materials were very similar. The enhancement factors and the formation of SAMs depended on monomer structure and fabrication method. Also depending on the deposition conditions, laser induced polymerization of the mercaptostyrene monomers SAMs was observed.
Development of Micro- and Nanocellular Polymers
Authors: Ruckdaeschel Holger , Gutmann Peter , Altstaedt Volker , Schmalz Holger , Mueller Axel H.E.
Published: April 2011

The batch-foaming behavior of multiphase polymer blends and block copolymers was systematically investigated using carbon dioxide as a blowing agent. Three different polymer systems were evaluated: (i) nanostructured triblock terpolymers, (ii) microstructured polymer blends, and (iii) nanostructured polymer blends. In order to obtain nanostructured blends, immis-cible blends of poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene-co-acrylonitrile) (PPE/SAN) were melt-compatibilised via polystyrene-b-polybutadiene-b-poly(methyl methacry-late) triblock terpolymers. Due to the specific interaction between the respective components, a nanostructured interphase between PPE and SAN was observed. With regard to neat block co-polymers, the self-assembly of solvent-cast SBM triblock terpolymers was exploited in order to produce nanostructured morphologies. In each case, the resulting foam morphology was charac-terized by evaluating the foam density as well as the cell size. Combined with the multiphase structure of the non-foamed material and its thermal as well as physical behavior, relationships between the foaming characteristics and the cellular morphology were established. As an exam-ple for the foaming results, submicro-cellular structures were observed by foaming nanostruc-tured polymer blends, while the cell walls still revealed the nanostructured morphology. In con-trast, batch-foaming of neat triblock terpolymers led to the formation of microcellular foams; however, as highlighted by scanning electron microscopy, the cell walls did undergo some fur-ther expansion and formed additional nano-sized cells. In the light of these results, new routes for preparing cellular polymers are derived by systematically exploiting the multiphase charac-teristics of polymer blends and block copolymers.
Novel Planer Microwave Circuit Applications and Characterization of Ni Nanowires
Authors: Marson Ryan , Kuanr Bijoy K , Mishra Sanjay R , Camley Robert E , Celinski Zbigniew
Published: April 2011

Arrays of Ni nanorods were electrodeposited into alumina oxide templates with various lengths (11-50 micro meter) and fixed pore diameter (150 nm). The magnetization behavior of these rods were investigated with ferromagnetic resonance (FMR) techniques; fixed frequency (conventional FMR) and swept frequency (Network Analyzer FMR). Both resonance spectra indicate the presence of strong dipolar interaction between the nanorods. The fundamental magnetic parameters like spontaneous magnetization, gyromagnetic ratio, and magnetic anisotropies of the nanorods were derived from the angular variation of resonance field data. Further, the use of nanorods as a tunable stop-band notch-filter in a coplanar waveguide geometry has been assessed. The stop-band frequency (fr) is observed to be tunable up to 24 GHz with an applied field (H) of up to 6 kOe. The theoretical fitting of fr(H)data to resonance relation yield values of effective field (Heff) and gyromagnetic ratio, which are a little higher than the conventional FMR results.
Electric Field Directed Growth of Molecular Wires of Charge Transfer Molecules on Prefabricated Metal Electrodes
Authors: Sai T Phanindra , Raychaudhuri A K
Published: April 2011

Molecular wires of charge transfer molecules were formed by co-evaporating the 7 7 8 8-Tetracyanoquinodimethane [TCNQ] (acceptor) and Tetrathiafulvalene [TTF] (donor) molecules across prefabricated metal electrodes. Molecular wires of TTF TCNQ were also formed by evaporating single complex of TTF:TCNQ across prefabricated metal electrodes The prefabricated metal electrodes were made using electron beam lithography on SiO2 and glass cover slip substrates. Even though TTF: TCNQ wires grown from both co-evaporation and evaporation techniques show semiconductor like behavior in temperature dependence of resistance they show different activation energies due the difference in stoichiometry of TTF and TCNQ.
Pseudo-wetting Behaviour of Nanostructures Induced by STM
Authors: Campbell Paul , Walmsley George
Published: April 2011

The behavior of nano-scale liquid metal droplets has recently received renewed research interest following the exciting new observations of Sutter and Sutter [1]. In the present paper, we consider whether similar conditions can be generated for observing liquid metal droplet phenomena in a scanning probe architecture. Strong interactions between tip and sample in tunnelling microscopies can be deliberately invoked by lowering the tunnel gap impedance. Indeed, nanoscale features may be created this may, often exhibiting temporal stability suggestive of applications for ultra high density data storage. Alternatively, unstable features may form, and their decay characteristics can be related to local dynamics and kinetics. In real liquids, one such evolutionary mode involves the phenomenon of wetting, and the formation of thin precursor films. Here, it is demonstrated that a similar process may occur for the decay of a nanoscale mound of [presumed] Au atoms onto an Au(111) substrate. The mound is thought to be created by a ‘jump-to-contact’ process when the gap impedance, Zg, is deliberately lowered by reducing the tip-surface displacement. Resultant features have a diameter of circa 30nm, and heights of up to l0nm. They appear stable when scanned repeatedly at gap impedances higher than 10MΩ, however if Zg is lowered below 500kΩ, then morphology can alter dynamically, and a thin layer of material, only two atomic widths thick, is seen to emanate from the periphery. Relaxation in the nanostructure is observed. Interestingly, the observations agree qualitatively with wetting phenomena observed on microscale droplets of involatile liquids on solid surfaces. Favourable comparisons may also be drawn in the light of recent results using molecular-dynamics simulations and Monte-Carlo methods.
Elasticity Models for the Spherical Indentation of Gels and Soft Biological Tissues
Authors: Lin David C. , Dimitriadis Emilios K. , Horkay Ferenc
Published: April 2011

AFM micro- or nanoindentation is a powerful technique for mapping the elasticity of materials at high resolution. When applied to soft matter, however, its accuracy is equivocal. The sources of the uncertainty can be methodological or analytical in nature. In this paper, we address the lack of practicable nonlinear elastic contact models, which frequently compels the use of Hertzian models in analyzing force curves. We derive and compare approximate force-indentation relations based on a number of hyperelastic general strain energy functions. These models were applied to existing data from the spherical indentation of native mouse cartilage tissue as well as chemically crosslinked poly(vinyl alcohol) gels. For the biological tissue, the Fung and single-term Ogden models were found to provide the best fit of the data while the Mooney-Rivlin and van der Waals models were most suitable for the synthetic gels. The other models (neo-Hookean, two-term reduced polynomial, Fung, van der Waals, and Hertz) were effective to varying degrees. The Hertz model proved to be acceptable for the synthetic gels at small strains (<20% for the samples tested). Although this finding supports the generally accepted view that many soft elastic materials can be assumed to be linear elastic at small strains, we propose the use of the nonlinear models when evaluating the large-strain indentation response of gels and tissues.
Highly Efficient Silver Nanoparticle Formation on Dialdehyde-Modified DNA
Authors: Wirges Christian Thomas , Timper Jan , Simon Ulrich , Carell Thomas
Published: April 2011

We investigated the efficient nucleation of silver nanoparticles on aldehyde-modified DNA strands. The aldehyde-bearing DNA was prepared by PCR incorporation of diol-modified synthetic deoxyuridine derivatives and subsequent cleavage of the diol groups to aldehyde functions using sodium periodate. Formerly unavailable dialdehyde-bearing DNA could be prepared by this mild and selective method. Both dialdehyde-DNA and monoaldehyde-DNA are capable of inducing silver nanoparticle formation without the addition of any external reductant. Interestingly, dialdehyde-DNA shows a different kinetic behavior and is about four times as efficient in silver nanoparticle formation as monoaldehyde-DNA. These data suggest a potentially unique mechanism of silver nanocluster formation induced by the dialdehyde groups. SEM measurements of fully metallized DNA strands show homogeneous metal coverage and selective metal deposition exclusively on the DNA template.
Failure Characteristics of Bilayer Lipid Membranes (BLMs) Formed over a Single Pore
Authors: Hopkinson David , Leo Donald J.
Published: April 2011

A new methodology has been developed to measure the maximum pressure that can be withstood by a bilayer lipid membrane (BLM) formed over porous substrates. A custom test fixture was fabricated to pressurize BLMs in very fine increasing increments until they fail. This experiment was performed on 1-Stearoyl-2-Oleoyl-sn-Glycero-3-Phosphatidylocholine (SOPC) BLMs formed over polycarbonate substrates with a single pore ranging from 5 to 20 microns in diameter. Failure pressure was found to be inversely proportional to pore diameter. The same set of experiments was repeated for BLMs that were formed from a mixture of SOPC and 50 mol% cholesterol (CHOL). The presence of cholesterol was found to increase the failure pressure of the BLMs by 56% on average. A model of the characteristic pressure curve from this experiment was developed based on the pressurization and flow of fluid through a porous substrate. The model was found to accurately fit the experimental pressure curves.
Toxicity of BSA-stabilized Silver Nanoparticles on Immune Circulating Cells
Authors: Hayman Imani , Mehl Patrick , Kapoor Veena , Wilson Otto
Published: April 2011

Silver nanoparticles have shown immense potential in many biomedical applications, specifically wound healing. These nanoparticles reduce the degree of inflammation in wounds and increase the rate of wound healing overall in a dose-dependent manner. Moreover, silver nanoparticles exhibit antibacterial and antimicrobial properties. While the mechanism of action for silver nanoparticles is not clear, current studies focus on the effect of silver nanoparticles on recipient cells and tissues. It is shown that silver nanoparticles are more toxic to these recipient cells in comparison to other metal nanoparticles. This suggests that the bactericidal properties of the silver nanoparticles are size dependent. Our present work investigates the toxicity level of silver nanoparticles on specific immune circulating cells. The approach is to report the LD50 level as a function of the ratio of the nanoparticles concentration (ppm) to the cell concentration (cell number/ml) used in the assays. This method allows a normalization of the LD50 capable to compare the toxicity of the nanoparticle on different types of cells. Next, the localization of the silver nanoparticles within the cells will be determined, and the toxic mode of action of the nanoparticles will be modulated by the modification of the synthesis method.
Cell-Adaptable Protein Scaffolds for Spinal Cord Nerve Regeneration
Authors: Straley Karin , Po Foo Cheryl Wong , Heilshorn Sarah
Published: April 2011

A key attribute missing from current state-of-the-art biomaterials is the ability to be remodeled by the host after implantation. In contrast, the natural extracellular matrix (ECM) is constantly being remodeled by proteases secreted from cells in response to local environmental changes. Mimicking this strategy, we have designed a new protein-based scaffold that can be degraded and remodeled on demand by the growth cones of regenerating neurites. Using recombinant protein techniques, we synthesized a family of biodegradable and biologically active scaffold materials. The scaffolds include peptide sequences derived from natural ECM proteins. Interspersed with these ECM domains are proteolytic sequences readily degraded by tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA), two proteases secreted by the growth cones of extending neurites. By altering the primary amino acid sequences of the protease cleavage domains, we can tune the degradation rates of otherwise identical engineered proteins in a controlled and predictable manner over approximately two orders of magnitude. These recombinant proteins are crosslinked to form bulk, protein-based scaffolds with mechanical properties that can be tuned to match that of the spinal cord. Initial cell experiments have shown that the proteins support growth and differentiation of the model PC-12 neuronal-like cell line. By tailoring the scaffold degradation rate to the tPA and uPA secretion levels of specific neuronal populations, we aim to fabricate a scaffold that will promote neurite extension through the matrix by allowing local degradation to occur specifically around the neuronal growth cone while maintaining the bulk integrity of the overall scaffold.
Buckling of Microtubules in Living Cells Modulated by Surrounding Cytoplasm and Filament Network
Authors: Li Teng
Published: April 2011

The mechanics of living cells is largely determined by their cytoskeleton, a dynamic network of microtubules and protein filaments in the cytoplasm. Microtubules are the most rigid cytoskeletal filaments and bear compressive forces in cells. Microtubules in vivo often severely buckle into short wavelengths. By contrast, isolated microtubules in vitro buckle into single long-wavelength arcs. To explain this discrepancy, we describe a mechanics model of microtubule buckling in living cells. The model shows that, while the buckling wavelength is set by the interplay between the microtubules and the elastic surrounding filament network, the buckling growth rate is set by the viscous cytoplasm. The quantitative results from the model shed light on developing new and robust methods to measure various in vivo mechanical properties of subcellular structures, e.g., bending rigidity of microtubules, elastic modulus of filament network, and viscosity of cytoplasm. The model can also be readily generalized to study the deformation of hard engineering materials at soft bio-interfaces.
Mechanical Properties of Nanoparticle Hydroxyapatite/gelatin Constructs
Authors: Fox Steven , Stanishevskaya Inessa , Chowdhury Shafiul , Catledge Shane , Stanishevsky Andrei
Published: April 2011

Bone consists of up to 70% mostly nanocrystalline hydroxyapatite (HA), and the rest is mostly collagen. One can suggest that synthetic nanoHA/collagen composites could potentially be the closest materials to resemble the bone microarchitecture and prepare resorbable bone substitutes and scaffolds. However, the data on the mechanical properties and property/structure relationships of HA/collagen composites are still scarce. It can be explained, in part, by the high cost of collagen and substantial amounts of materials needed for many tests. However, gelatin is cheap, has many properties similar to collagen, and can be used as a model material for the mechanical testing of HA-based composites. In this study, we report the results of an investigation of some mechanical properties of HA/gelatin composites with 0 to 80% HA nanoparticle (size 15-60 nm) loading by weight. The HA nanoparticle dispersions were mixed with gelatin in trifluoroethanol or in water in different ratios and placed in Teflon molds to produce the sheets with the thickness in the range of 0.4 – 1.0 mm. Nanoindentation technique was used to determine the Young's modulus and hardness. Bending tests were performed using dynamic mechanical analysis with the amplitudes in the 1 – 50 micron range at 1 Hz. The values of Young's modulus (1 – 20 GPa), hardness (70 – 500 MPa) and bending modulus (0.3 – 2.4 GPa) were obtained. The highest values of the Young's modulus and hardness of these composite materials were achieved for 40% – 60% HA content by weight, which was close to the values for similar HA/collagen composites. However, the maximum bending strength was observed for 20 – 35% HA content. We discuss further the observed trends of the mechanical properties and their dependence on other factors such as the test conditions, sample geometry, and HA particle size.
Drug Delivery Systems Based on Hydroxyapaptite-coated Poly(lactic-co-glycolic acid) Microspheres
Authors: Xu Qingguo , Czernuszka Jan T
Published: April 2011

Negatively charged poly(lactic-co-glycolic acid) (PLGA) microspheres were prepared by the solid-in-oil-in-water (s/o/w) method using the anionic surfactant, sodium dodecyl sulfate (SDS), and a hydrophilic antibiotic (amoxicillin) was encapsulated with an encapsulation efficiency of 40.6%. A layer of hydroxyapatite (HA) was coated on these negatively charged PLGA microspheres by a dual constant composition method in 3 - 6 hours. The HA-coated PLGA microspheres (HPLG) had a core-shell structure and were characterised by scanning electron microscopy, focused ion beam microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction and Fourier transform infrared spectroscopy. Sustained release of amoxicillin from HPLG for at least 31 days was shown from in-vitro drug release experiments. A typical triphasic drug release profile had been observed for PLGA and HPLG microspheres. This device exhibited two desirable properties: the sustained release from PLGA and osteoconductivity from HA. Hence, it could have potential applications in delivering drugs to treat bone disorders or infections.
The Effects of Chemical Functionalization vs. Biological Functionalization on Nanoparticle Binding Affinity
Authors: Benkoski Jason J , Patrone Julia J , Crookston James , Le Huong , Sample Jennifer
Published: April 2011

Due to their small size, high diffusivity, and chemically active surfaces, nanoparticles share much in common with water-soluble proteins. These similarities have generated great interest in using biofunctional nanoparticles as a route to deliver targeted therapeutics. Already nanoparticles have found applications in the hyperthermia of tumors, personal care lotions, and tissue scaffolding. Our study focuses on the targeting of such nanoparticles to specific biological sites. It therefore seeks to identify the factors that control the migration and capture of nanoparticles within living systems. In particular, we examine the affinity of anti-collagen coated magnetite nanoparticles for collagen IV-coated surfaces under flow stress. The studies are performed within microfluidic devices that are designed to mimic various fluid flow patterns within the body. We find, in this case, a large background signal due to nonspecific binding. Further examination shows a correlation between chemical functionality (e.g., surface charge, hydrophilicity) that suggests that a balanced approach between biological functionality and chemical functionality may reduce the background from nonspecific binding to acceptable levels.
Correlation of Hydrogen Dilution Profiling to Material Structure and Device Performance of Hydrogenated Nanocrystalline Silicon Solar Cells
Authors: Yan Baojie , Yue Guozhen , Yan Yanfa , Jiang Chun-Sheng , Teplin Charles W. , Yang Jeffrey , Guha Subhendu
Published: April 2011

We present a systematic study on the correlation of hydrogen dilution profiles to structural properties materials and solar cell performance in nc-Si:H solar cells. We deposited nc-Si:H single-junction solar cells using a modified very high frequency (VHF) glow discharge technique on stainless steel substrates with various profiles of hydrogen dilution in the gas mixture during deposition. The material properties were characterized using Raman spectroscopy, X-TEM, AFM, and C-AFM. The solar cell performance correlates well with the material structures. Three major conclusions are made based on the characterization results. First, the optimized nc-Si:H material does not show an incubation layer, indicating that the seeding layer is well optimized and works as per design. Second, the nanocrystalline evolution is well controlled by hydrogen dilution profiling in which the hydrogen dilution ratio is dynamically reduced during the intrinsic layer deposition. Third, the best nc-Si:H single-junction solar cell was made using a proper hydrogen dilution profile, which caused a nanocrystalline distribution close to uniform throughout the thickness, but with a slightly inverse nanocrystalline evolution. We have used the optimized hydrogen dilution profiling and improved the nc-Si:H solar cell performance significantly. As a result, we have achieved an initial active-area cell efficiency of 9.2% with a nc-Si:H single-junction structure, and 15.4% with an a-Si:H/a-SiGe:H/nc-Si:H triple-junction solar cell structure.
Polysilazane Precursor Used for Formation of Oxidized Insulator
Authors: Urabe Yuji , Sameshima Toshiyuki
Published: April 2011

We report on SiO2 film formation using Polysilazane precursor treated with remote oxygen plasma and high-pressure H2O vapor heating. Polysilazane precursor films with a thickness of 130 nm were formed on silicon substrates by spin coating method. They were annealed at 350°C in remote oxygen plasma at a pressure of 2.0×10−2 Pa and a 13.56×106 Hz radio frequency power of 300 W for 3h followed by 1.3×106-Pa-H2O vapor heating at 260°C for 3 h. Polysilazane precursor films were entirely oxidized by high-pressure H2O vapor heat treatment, and the density of Si-N bonding and Si-H bonding in Polysilazane precursor films were effectively dissociated by the combination of high-pressure H2O vapor heat treatment with remote oxygen plasma treatment. While MOS(Metal-Oxide-semiconductor) capacitors fabricated only by high-pressure H2O vapor heat treatment had a high specific dielectric constant of 6.1, a fixed oxide charge density of 1.3×1012 cm−2 and a density of interface trap of 5.4×1011 cm−2eV−1, the remote oxygen plasma treatment followed by high-pressure H2O vapor heat treatment allowed us to reduce them to 4.1 and 1.6×1011 cm−2, 4.2×1010 cm−2eV−1, respectively.
Electronic Properties Of Nanocrystalline Silicon Deposited With Different Crystallite Fractions And Growth Rates
Authors: Hugger Peter G. , Cohen J. David , Yan Baojie , Yue Guozhen , Xu Xixiang , Yang Jeffrey , Guha Subhendu
Published: April 2011

Junction capacitance measurements were used to characterize the properties of nanocrystalline silicon (nc-Si:H) solar cells. These methods included drive-level capacitance profiling (DLCP) to obtain spatially-resolved defect densities, as well as transient photocapacitance (TPC) and transient photocurrent (TPI) spectra to reveal optically responsive states in the band-gap, and to estimate minority carrier behavior before and after lightsoaking. Crystalline volume fractions were estimated using Raman spectroscopy. Previously we had identified at least two types of distinct behaviors in such nc-Si:H materials that depended on the crystalline volume fraction. Here, in one case, we report results indicating that both types of behavior can occur in a single sample, possibly indicating that the structural properties of that sample have evolved during growth.
In-Situ Transmission Electron Microscopy Investigation of Aluminum Induced Crystallization of Amorphous Silicon
Authors: Kishore Ram , Sharma Renu , Hata Satoshi , Kuwano Noriyuki , Tomokiyo Yoshitsuga , Naseem Hameed , Brown W D
Published: April 2011

The interaction of amorphous silicon and aluminum films to achieve polycrystalline silicon has been investigated using transmission electron microscope equipped with in-situ heating holder. Carbon coated nickel grids were used for TEM studies. An ultra high vacuum cluster tool was used for the deposition of a ∼50nm a-Si films and a vacuum deposition system was used to deposit a ∼50nm Al films on a-Si film. The microstructural features and electron diffraction in the plain view mode were observed with increase in temperature starting from room temperature to 275 °C. The specimen was loaded inside TEM heating holder. The temperature was measured and kept constant for 5 minutes during which the microstructure at fixed magnification of X63K was recorded and the electron diffraction pattern of the same area was also recorded. The temperature was then increase and fixed at desired value and microstructure and EDP were again recorded. The temperatures used in this experiment were 30, 100, 150, 200, 225, 275°C. A sequential change in microstructural features and electron diffraction pattern due to interfacial diffusion of boundary between Al and amorphous Si was investigated. Evolution of polycrystalline silicon with randomly oriented grains as a result of a-Si and Al interaction was revealed. After the in-situ heating experiment the specimen was subjected to high resolution TEM and EDS investigations after removing the excess Al. The EDS analysis of the crystallized specimen was performed to locate the Al distribution in the crystallized silicon. These studies show that the Al induced crystallization process can be used to prepare polycrystalline as well as nanocrystalline silicon by controlling the in-situ annealing parameters. The investigations are very useful as the nanocrystalline silicon is being investigated for its use in developing high efficiency silicon solar structures.
Physically Based Compact Model for Segmented a-Si:H n-i-p Photodiodes
Authors: Chang Jeff Hsin , Tredwell Timothy , Heiler Gregory , Vygranenko Yuri , Striakhilev Denis , Kim Kyung Ho , Nathan Arokia
Published: April 2011

Hydrogenated amorphous silicon (a–Si:H) n–i–p photodiodes are used as pixel sensor elements in large-area flat-panel detectors for medical imaging diagnostics. Accurate model of the sensor plays an imperative role in determining the performances of the detector systems as well as ascertaining design issues prior to production. This work presents the formulation of a compact model for segmented a–Si:H n–i–p photodiodes suitable for circuit-level simulation. The underlining equations of the model are based on device physics where the parameters are extracted from pertinent measurement results of previously fabricated a–Si:H n–i–p photodiodes. Furthermore, the implemented model allows photoresponse simulation with the addition of an external current source. Results of the simulation demonstrated excellent matching with measurement data for different photodiode sizes at various temperatures. The model is implemented in Verilog-A and simulated under Cadence Virtuoso design environment using device geometry and extracted parameters as inputs. The model formulation and parameter extraction process, as well as measurements and simulation results are presented.
Self-aligned Amorphous Silicon Thin Film Transistors with Mobility above 1 cm2V−1s−1fabricated at 300°C on Clear Plastic Substrates
Authors: Cherenack Kunigunde H , Kattamis Alex Z , Hekmatshoar Bahman , Sturm James C , Wagner Sigurd
Published: April 2011

We have developed a fabrication process for amorphous-silicon thin-film transistors (a-Si:H TFTs) on free-standing clear plastic substrates at temperatures up to 300°C. The 300°C fabrication process is made possible by using a unique clear plastic substrate that has a very low coefficient of thermal expansion (CTE < 10ppm/°C) and a glass transition temperature higher than 300°C. Our TFTs have a conventional inverted-staggered gate back-channel passivated geometry, which we designed to achieve two goals: accurate overlay alignment and a high effective mobility. A requirement that becomes particularly difficult to meet in the making of TFT backplanes on plastic foil at 300°C is minimizing overlay misalignment. Even though we use a substrate that has a relatively low CTE, accurately aligning the TFTs on the free-standing, 70-micrometer thick substrate is challenging. To deal with this immediate challenge, and to continue developing processes for free-standing web substrates, we are introducing techniques for self-alignment to our TFT fabrication process. We have self-aligned the channel to the gate by exposing through the clear plastic substrate. To raise the effective mobility of our TFTs we reduced the series resistance by decreasing the thickness of the amorphous silicon layer between the source-drain contacts and the accumulation layer in the channel. The back-channel passivated structure allows us to decrease the thickness of the a-Si:H active layer down to around 20nm. These changes have enabled us to raise the effective field effect mobility on clear plastic to values above 1 cm2V−1s−1
Morphic Architectures: Atomic-Level Limits
Authors: Cavin Ralph , Zhirnov Victor
Published: April 2011

In this paper, we consider a thought problem intended to force consideration of fundamental limits for energy sources, sensors, computing elements, and communication systems as fundamental system dimensions are reduced to the few micron regime. Design of integrated systems at this level are shown to literally require the allocation of atoms for the various functions. We argue that although there are no fabrication technologies for systems on this scale and the tradeoffs between system functions are extreme, systems on this scale might be feasible; given end-of ITRS technologies.
Logic Devices with Spin Wave Buses - an Approach to Scalable Magneto-Electric Circuitry
Authors: Khitun Alexander , Bao Mingqiang , Wu Yina , Kim Ji-Young , Hong Augustin , Jacob Ajey P , Galatsis Kosmas , Wang Kang L
Published: April 2011

We analyze spin wave-based logic circuits as a possible route to building reconfigurable magnetic circuits compatible with conventional electron-based devices. A distinctive feature of the spin wave logic circuits is that a bit of information is encoded into the phase of the spin wave. It makes possible to transmit information as a magnetization signal through magnetic waveguides without the use of an electric current. By exploiting sin wave superposition, a set of logic gates such as AND, OR, and Majority gate can be realized in one circuit. We present experimental data illustrating the performance of a three-terminal micrometer scale spin wave-based logic device fabricated on a silicon platform. The device operates in the GHz frequency range and at room temperature. The output power modulation is achieved via the control of the relative phases of two input spin wave signals. The obtained data shows the possibility of using spin waves for achieving logic functionality. The scalability of the spin wave-based logic devices is defined by the wavelength of the spin wave, which depends on the magnetic material and waveguide geometry. Potentially, a multifunctional spin wave logic gate can be scaled down to 0.1μm2. Another potential advantage of the spin wave-based logic circuitry is the ability to implement logic gates with fewer elements as compared to CMOS-based circuits in achieving same functionality. The shortcomings and disadvantages of the spin wave-based devices are also discussed.
Studies of c-Axis Threading Screw Dislocations in Hexagonal SiC
Authors: Chen Yi , Huang Xianrong , Zhang Ning , Dhanaraj Govindhan , Sanchez Edward , MacMillan Michael F. , Dudley Michael
Published: April 2011

In our study, closed-core threading screw dislocations and micropipes were studied using synchrotron x-ray topography of various geometries. The Burgers vector magnitude of TSDs can be quantitatively determined from their dimensions in back-reflection x-ray topography, based on ray-tracing simulation and this has been verified by the images of elementary TSDs. Dislocation senses of closed-core threading screw dislocations and micropipes can be revealed by grazing-incidence x-ray topography. The threading screw dislocations can be converted into Frank partial dislocations on the basal planes and this has been confirmed by transmission synchrotron x-ray topography.
Observation of Asymmetric Wafer Bending for 3C-SiC Thin Films Grown on Misoriented Silicon Substrates
Authors: Zielinski Marcin , Portail Marc , Chassagne Thierry , Kret Slawomir , Nemoz Maud , Cordier Yvon
Published: April 2011

We present an experimental study of asymmetric wafer deformation for 3C-SiC layers grown on deliberately misorientated silicon substrates. An asymmetric curvature has been observed both on (100) and (111) oriented layers. In this work we focus on the (100) oriented samples. The curvature of the wafers is studied as a function of wafer thickness and offcut angle. We look for the correlations between the observed asymmetric strain relaxation and the layer morphology and microstructure. We claim that different defect pattern, measured along [110] and [1-10] direction can be at the origin of almost complete relaxation of mismatch strain along the offcut direction.
Epitaxial Growth on 2° Off-axis 4H SiC Substrates with Addition of HCl
Authors: Zhang Jie , Sunkari Swapna , Mazzola Janice , Tyrrell Becky , Stewart Gray , Stahlbush R , Caldwell J , Klein P , Mazzola Michael , Casady Janna
Published: April 2011

Epitaxial growth on 3-in, 2° off-axis 4H SiC substrates has been conducted in a horizontal hot-wall CVD reactor with HCl addition. The thickness of the epiwafers ranges from 3m to 11 m and the growth rate is 7 − 7.5 m/h. Although a rougher surface and a higher triangular defect density is observed using the standard process for 4° growth, an improved process has resulted in reduced triangular defect density down to around 4 cm−2and a smoother surface with the roughness of 1.1 nm for a 3.7 m thick epiwafer. Most interestingly, the basal plane dislocation density in the 2° off-axis epiwafers has been reduced to "negligible" levels, as confirmed by both the non-destructive UVPL mapping technique and the molten KOH etching on 2° epiwafers with thickness of around 10 m.