bluuebunny/crossref_metadata_2025 huggingface dataset:
Local Structure and Vibrational Properties of α-Pu, α-U, and the α-U Charge Density Wave
Authors: Nelson Erik J. , Allen Patrick , Blobaum Kerri J. , Wall Mark A. , Booth Corwin H.
Published: April 2011

The local atomic environment and vibrational properties of monoclinic α-Pu, orthorhombic α-U, and the α-U charge-density-wave (CDW) modulation are examined by extended x-ray absorption fine structure spectroscopy (EXAFS). Debye-Waller factors from temperature-dependent EXAFS measurements are fit to a correlated Debye model. The observed Pu-Pu bond Debye temperature is θcD(α-Pu) = 162 ± 5 K for the pure α-Pu phase. The temperature dependence of the U-U nearest neighbor and second nearest neighbor Debye-Waller factors exhibits a sharp discontinuity in slope near TCDW = 43 K, the transition temperature at which the charge-density wave (CDW) in α-U occurs. Our measurement of the CDW using EXAFS is the first observation of the structure of the CDW in polycrystalline α-U.
Evidence of Embryo Formation as a Precursor to the Delta to Alpha-Prime Transformation in a Pu-Ga Alloy
Authors: Blobaum Kerri J.M. , Krenn C. R. , Wall M. A. , Massalski T. B. , Schwartz A. J.
Published: April 2011

It was experimentally observed that a single Pu-2.0 at% Ga sample can be thermally cycled many times, with nearly the same amount of transformation and reversion during each cycle, provided that the sample is annealed at 375°C for 8 hours and then conditioned at 25°C for at least 6 hours. The ambient temperature conditioning period is crucial for obtaining the same amount of transformation to alpha-prime in each thermal cycle. Here, we present results from a series of experiments that investigate the effects of conditioning time and temperature on alpha-prime_formation. When the sample is conditioned at 25°C for times between 0 and 6 hours, the amount of alpha-prime formed is a function of conditioning time. For conditioning treatments between 6 and 70 hours, however, the amount of alpha-prime_formed is nearly constant. Conditioning treatments at –50°C, 150°C, and 370°C all resulted in less alpha-prime_formation than the 25°C treatments. We hypothesize that embryos of the thermodynamically stable alpha phase form during the conditioning treatments, and these embryos form alpha-prime upon subsequent cooling. This result is an indirect confirmation of the Russian Pu-Ga equilibrium phase diagram.
Gas generation from water adsorbed onto pure plutonium dioxide powder
Authors: Veirs Kirk
Published: April 2011

The production of H2 from alpha-particle radiolysis of water adsorbed onto plutonium dioxide powders has been studied. Plutonium dioxide powders with specific surface areas of 1.0 and 21 m2/g were used. The specific surface area strongly affects the amount of water adsorbed. At water coverage between 1 and 2 monolayers the H2 yield per unit of energy deposited into the water is found to be between 0.05 and 0.13 molecules of H2 per 100 eV adsorbed dose (5 to 12 nmols/s W). The H2 yield increases to between 0.29 and 0.58 molecules per 100 eV adsorbed dose (28 to 56 nmol/s W) when the number of adsorbed monolayers of water is between 10 and 20. The latter H2 yield is similar to that of liquid water of 0.45 molecules per 100 eV adsorbed dose
Binary HfO2: SiO2 used as High-k Gate Oxide Material in Combinatorial Material Library Method
Authors: Chao Wen-Hsuan , Wang Lih-Ping , Wang Shu-Huei , Huang Tien-Heng , Wu Ren-Jen , Cheng Hung-Chiao
Published: April 2011

Hafnium silicates (HfO2:SiO2, HSO) have recently attracted much interest in the fields of fundamental science and technology because they have high dielectric constant and low leakage current. The structure and properties of HSO gate oxides were studied using a combinatorial continuous-compositional-spread method. HSO material libraries were synthesized on a 4-inch wafer at room temperature and at 200°C using a custom-built radio-frequency (RF) sputtering system. The electrical properties of HSO material libraries were measured using metal-oxide-semiconductor structure. X-ray diffraction (XRD) was utilized to characterize the structure and compositions of HSO material libraries. The effects of sputtering conditions on the properties of the HSO gate oxides were investigated. The dielectrics constants (εr) of HSO material libraries treated with rapid thermal annealing (600°C/1min/N2) were in the range 5∼23, as determined by C-V measurement, and the dielectric constant was observed to increase with HfO2 content. The I-V relations of the HSO material libraries indicate that the leakage current decreases as the amount of Si in the HSO films increases. The structural characteristics of HSO films with RTA treatment (1000°C/10sec/N2) varied from the amorphous to the crystalline state (tetragonal and monoclinic phase), according to the composition of material libraries. The correlation among the electrical properties, the composition and the crystal structure of the HSO films is discussed.
Fabrication of Nanoparticles and Microspheres with Uniform Magnetic Half-Shells
Authors: McNaughton Brandon H. , Stoica Vladimir A. , Anker Jeffrey N. , Tyner Katherine M. , Clarke Roy , Kopelman Raoul
Published: April 2011

We report a method for fabricating, anisotropically designed, multiphasic nano-particles with uniform magnetic half-shells. Cobalt layers were deposited onto commercially made non-magnetic polystyrene nanospheres and microspheres, using ultrahigh vacuum vapor deposition, which produced particles with a half-shell of uniform size, shape and magnetic content. Iron was also deposited onto commercially made silica nanospheres and microspheres and was characterized using transmission electron microscopy and scanning electron microscopy. The coercivity of the magnetic material layers, on the substrate-supported spheres, was enhanced compared to the bulk values of such films without spheres. The particles, once removed from the substrate, were amenable to being rotated in solution, which could allow for more accurate physical and chemical measurements in a variety of fluidic environments. Applications for imaging local mechanical, magnetic and electrical environments are also delineated.
Small Molecule Diffusion in Polymer Ultra-Thin Films
Authors: Ordaz Ivan , Singh Lovejeet , Ludovice Peter J. , Henderson Cliffod L.
Published: April 2011

The influence of film thickness and polymer molecular weight on the diffusion coefficient of water in poly(methyl methacrylate) thin films supported on gold coated surfaces has been studied using vapor sorption experiments via quartz crystal microbalance (QCM) methods. Diffusion coefficients for films ranging in thickness from approximately 1 μm to 50 nm were determined. It is observed that the diffusion coefficient of water in PMMA on weakly interacting substrates is a strong function of film thickness, and that the diffusion coefficient decreases drastically as film thickness is reduced below a critical thickness value. Furthermore, it is found that polymer molecular weight also appears to play an important role in determining the diffusion behavior of such polymer thin film systems.
Simulation Study of Confinement Effects on the Melting Transition in Hexane and Decane Monolayers Between Two Graphite Slabs
Authors: Pint Cary , Roth Michael
Published: April 2011

The melting transition in hexane and decane monolayers are studied through use of a canonical ensemble molecular dynamics (MD) simulation method, where the monolayer is physisorbed onto a single, infinite graphite slab, with another confining graphite slab some varying vertical distance from the monolayer. Using a simple united-atom model to depict the alkanes, simulations suggest that the monolayer melting transition is largely dependent upon the average density of the physisorbed monolayer in addition to the spacing between the two graphite slabs. In particular, hexane is studied at two distinct coverages: (i) a fully commensurate (FC) monolayer, and (ii) a uniaxially incommensurate (UI) monolayer with an average density 0.9 times that of the FC monolayer. In the case of no confinement, both the FC hexane and decane monolayers exhibit a power law relation between the melting temperature of the monolayer and the graphite slab separation. In contrast, the UI hexane monolayer deviates from this behavior, suggesting that the power law behavior is an effect of the in-plane space, and how the monolayer melting transition depends upon this in-plane space. Finally, the role of the top (confining) layer corrugation in the power-law relationship, and the importance of this study toward future applications are briefly discussed.
Evidence of re-entrant behavior in laponite-PEO systems
Authors: Baghdadi Hossein , Bhatia Surita R. , Jensen Elizabeth E. C. , Easwar Nalini
Published: April 2011

Rheology and dynamic light scattering capture re-entrant behavior of laponite-polymer systems. Neat laponite under basics conditions and concentrations of 2wt% or greater forms a viscoelastic soft glass due to electrostatic repulsions. We show that that addition of low molecular weight poly(ethylene oxide) (PEO) melts the glass due to a depletion force. The depletion force speeds up dynamics in the system resulting in a low viscosity solution. A re-entrant viscoelastic solid is formed with the addition of high molecular weight PEO due to the polymer chains bridging between laponite particles. As expected the transition from a low to high viscosity solution scales with the polymer mean square end-to-end distance and gap between laponite particles.
Silica-Supported Au and Pt Nanoparticles and CO Adsorption
Authors: Mott Derrick , Luo Jin , Smith Andrew , Chan Wai-Pan , Bozza William , Sarkhel Anjana , Park Sara , Zhong Chuan-Jian
Published: April 2011

The understanding of the surface properties of metal nanoparticles is essential for exploiting their unique catalytic properties. This paper reports findings of the preparation of silica-supported Pt and Au nanoparticles and the FTIR characterization of CO adsorption on the supported nanoparticles. The nanoparticles were prepared by both a traditional impregnation method and molecular-capping based synthesis method. By comparing the spectroscopic characteristics of CO adsorption on these catalysts, similarities and differences in CO stretching bands have been identified. The findings are significant because important insights have been gained into the surface binding properties of Au and Pt nanoparticle catalysts.
Fabrication and Characterization of Molybdenum Oxide Nanofibers by Electrospinning
Authors: Wang Guan , Huang Xianrong , Dudley Michael , Gouma Pelagia-Irene , Yang Xiaoqing
Published: April 2011

Molybdenum oxide/ Poly (ethylene oxide) composite nanofibers were prepared by combining the sol-gel process and electrspinning technique. An ethanol solution of Poly(ethylene oxide) (PEO) was mixed with molybdenum isopropoxide to form a precursor solution. Composite nanofibers were obtained by electrspinning this viscous solution. By calcination of the composite fibers, pure molybdenum oxide nanofibers and nano-rods were obtained with diameters of 100-nanometer scale. Morphology of the fibers has been characterized by scanning electric microscopy. Components and structures of the final products have been identified by EDAX and grazing incidence XRD. Calcination process has been studied by DSC and TG analysis. The real time dynamics of the structural evolution from composite fibers to nanocrystalline metal oxide fibers has been investigated by synchrotron-based in-situ x-ray diffraction.
Synthesis of Au Nano-particles under Energetic Irradiation Fields
Authors: Maeda Nobuhiro , Hiroki Taiei , Hori Fuminobu , Okuda Shuichi , Taniguchi Ryoichi , Kojima Takao , Kambara Tadashi , Abe Tomoko , Iwase Akihiro
Published: April 2011

Dilute aqueous solutions with Au3+ ions and Polyethylene Glycol Monostearate are irradiated with ∼1 MeV γ-ray from 60Co source, 10 MeV pulsed electrons or 1.6 GeV carbon ions. After the irradiation, the color of solutions changes from buff yellow to reddish color. The UV-vis absorption spectra show that after the irradiation, light absorption around 530 nm appears, which corresponds to the excitation of the surface plasmon due to Au nano-particles. The result confirms that the irradiation reduces Au3+ ions in the aqueous solutions and synthesizes Au nano-particles. Size and shape of the nano-particles are examined by using 200kV transmission electron microscope. Effects of irradiation parameters (total dose and dose rate) on Au nano-particle synthesis are discussed.
Mechanochemical Synthesis, Structural Characterization and Visible Light Photocatalysis of TiO2/ZnFe2O4 Nnanocomposites
Authors: Srinivasan Sesha S. , Kislov Nikolai , Wade Jeremy , Smith Matthew , Stefanakos Elias , Goswami Yogi
Published: April 2011

Nanocomposite heterogeneous semiconductors with suitable energy levels (gaps) are exhibiting excellent photocatalytic properties under visible light irradiation. TiO2/ZnFe2O4 has been selected among different alloys because of (i) its low band gap ∼1.9 eV (ii) the nontoxicity of ZnFe2O4 (iii) visible light absorption characteristics of ZnFe2O4 due to its narrow band gap and (iv) not being susceptible to photoanodic corrosion. A mechanochemical synthesis approach using high energy milling is employed to prepare TiO2/ZnFe2O4 under different experimental parameters and conditions. The effects of ball milling and calcination on the photocatalytic behavior of TiO2 and TiO2/ZnFe2O4 have been determined. The as-milled nanocomposite materials are characterized with PXD, SEM and EDS procedures. The photocatalytic activity of TiO2/ZnFe2O4 nanocomposites for the photodegradation of phenol under visible light irradiation has been studied systematically by UV-Vis spectrometer. It is interesting to note a red shift of 0.25 eV in the absorption edge of the ball-milled TiO2 sample when compared to the non ball milled TiO2 photocatalyst.
Practical Nanomaterials and Nanostructures in Electronics
Authors: Rae Alan
Published: April 2011

A quiet revolution is occurring in electronics where nanometals have the ability to revolutionize adhesives and solders, nano oxides are revolutionizing fuel cell efficiency, and nanowires as well as nanotubes have the potential both to enhance short term evolutionary and long term revolutionary improvement.

This paper outlines some roadmap predictions and picks three areas with concrete examples- nano metals for ink jet formation of circuits, nano oxides in fuel cells, and lithographically developed nanowires for sensor application and details technical and commercial progress.
Fabrication of Highly-ordered and Densely-spaced Silicon Nano-needle Arrays for Bio-sensing Applications
Authors: Yin Aijun , Xu Jimmy
Published: April 2011

In this work, we report a success in fabricating highly-ordered and densely-packed array of silicon nano-needles that are vertically aligned, straight and long, meeting many of the requirements for biomolecular sensing and integration with silicon electronics. Yet, we show that they can be fabricated with a relatively simple and non-lithographic method.

In this approach the array of nano-needles of high uniformity in length and diameter are made out of silicon by reactive ion etching (RIE) through either an anodic aluminum oxide (AAO) membrane or an array of metallic nano-dot caps that are evaporated on a silicon wafer using an AAO membrane as mask. The AAO membrane itself is formed non-lithographically via anodization of pure aluminum foil and contains an array of highly-ordered and highly-uniform nano-pores. By using the AAO membrane either directly as an etching mask or as an evaporation mask to deposit metallic nanodots which in turn serve as an etching mask, deep and high aspect-ratio etching is possible to allow the formation of the nanoneedles in a Si substrate.
Characteristic Comparison Of Epitaxial PZT And PMN-PT Films Grown On (100)cSrRuO3//(100)SrTiO3 Substrates By Metalorganic Chemical Vapor Deposition
Authors: Yokoyama Shintaro , Okamoto Satoshi , Saito Keisuke , Iijima Takashi , Okino Hirotake , Yamamoto Takashi , Nishida Ken , Katoda Takashi , Sakai Joe , Funakubo Hiroshi
Published: April 2011

We grew the epitaxial Pb(Zr1-xTix)O3 [PZT] and (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 [PMN-PT] films, above 2 μm in thickness, on (100)cSrRuO3//(100)SrTiO3 substrates by metalorganic chemical vapor deposition (MOCVD). PbTiO3 content (x) dependencies of the crystal structure, dielectric and piezoelectric properties were systematically investigated for these films. The constituent phase changed from a rhombohedral (pseudocubic) single phase, a mixture phase of rhombohedral (pseudocubic) and tetragonal phases, and a tetragonal single phase with increasing x for both of PZT and PMN-PT films. The mixture phase region was observed when x=0.40−0.60 for PZT films and x=0.40−0.55 for PMN-PT films, which became wider than that reported ones for PZT sintered bodies and PMN-PT single crystals. In addition, x value moves to the higher one than that reported for the single crystal and/or the sintered body in case of PMN-PT films, while was almost the same in case of PZT films. The dependence of relative dielectric constant εr was maximum at the mixed phase region for both films, which were similar to the case of their bulk materials. The higher value of εr was ascertained for the PMN-PT films compared with PZT films, however, the magnitude was lower than the reported one for bulk materials. The longitudinal electric-field-induced strain Δx33 and transverse piezoelectric coefficient e31,f for PZT films were also maximum at the mixed phase region, on the other hand, that for PMN-PT films were maximum at larger x edge of rhombohedral (pseudocubic) region. Almost the same order of Δx33 was observed under applied electric fields up to 100 kV/cm, while larger e31,f was observed in PMN-PT films compared with the case of PZT films. e31,f coefficients of ∼−8.9 C/m2 and ∼−11.0 C/m2 were calculated for the PZT film with x=0.46 and for the PMN-PT film with x=0.39, respectively.
Iridium Electrodes for Ferroelectric Capacitors Deposited by Liquid-Delivery MOCVD
Authors: Ritterhaus Yves , Hur'yeva Tetyana , Lisker Marco , Burte Edmund Paul
Published: April 2011

Thin iridium films are required as electrode material for ferroelectric capacitors. SBT or PZT are often used as ferroelectric material in such capacitors. The PZT based non-volatile ferroelectric random access memories show better fatigue characteristics if platinum is replaced by iridium as electrode material. Metalorganic chemical vapor deposition (MOCVD) was used for the deposition because of the superior step coverage on three-dimensional structures compared to the conventional physical vapor deposition processes of metal layers. Particularly, in memory fabrication, good step coverage is essential. The iridium films were deposited on different substrates at temperatures of 300 – 500 °C by liquid-delivery MOCVD. The precursor Ir(EtCp)(1,5COD) [iridium(ethylcyclopentadienyl)(1,5-cyclooctadiene)] was diluted in toluene (0.1 M concentration) for the deposition experiments. The iridium films were deposited onto TiO2/SiO2/Si-, SiO2/Si-, and Si-substrates to compare the iridium film properties on different substrates. The growth conditions like oxygen flow, growth temperature, and reactor pressure were varied. The growth rates were in a range between 0.05 and 4.6 nm per minute. We found that the growth rates were highly influenced by the oxygen flow and the substrate material. Oxygen assisted the decomposition of the precursor, and carbon and hydrogen of the organic source were oxidized, which suppressed its incorporation into the iridium layer. Annealing in an oxidizing ambient at temperatures above 700 °C resulted in an increased oxidation of the films as proved by XRD analyses. The resistivity of the films was determined by the Van-der-Pauw method. Low resistivities of 7 – 70 µΩcm were obtained for the as-deposited iridium films.
Strain Relaxation and Dislocation Confinement in Epitaxial SrTiO3 by Two-Step Growth Technique and the Resulting Dielectric Response
Authors: Yamada Tomoaki , Sherman Vladimir O. , Tagantsev Alexander K. , Su Dong , Muralt Paul , Setter Nava
Published: April 2011

A two-step growth technique was used to achieve effective strain relaxation and dislocation confinement of epitaxial SrTiO3(STO) films and through this to improve their microwave dielectric properties. The crystallization of a very thin quasi-amorphous STO layer deposited at a low temperature in the initial growth step enhanced the strain relaxation from the lattice mismatch at the expense of the formation of high density of misfit dislocations. By varying the thickness of the first layer, different strain states of the films were systematically achieved while keeping the total film thickness unchanged. This allowed the study of the effect of strain on permittivity, and showed good agreement with theoretical predictions. Further more, the two-step growth technique suppressed significantly the threading dislocation density in the film, the dislocations being confined to the first layer. This in turn caused reduction in the extrinsic dielectric loss at microwave frequency. The loss reduction was analyzed and explained based on a dielectric composite model.
10 Tbit/inch2 Ferroelectric Data Storage with Offset Voltage Application Method
Authors: Hashimoto Sunao , CHO Yasuo
Published: April 2011

Ferroelectrics are expected to become one of the next generation ultra-high density data storage media. The requirements for pulse amplitude and the duration to switch the domain were both markedly decreased by using a new domain stabilizing method; offset voltage application method. Additionally, with this method it became possible to invert a smaller domain with a diameter of less than 10 nm. Finally, significant progress was made regarding the memory density for ferroelectric data storage, and an area density of 10.1 Tera-bit/inch2 was successfully achieved. This represents the highest memory density for rewritable data storage reported to date.
Molecular volume and polarizability in the amorphous dielectric Zr0.2Sn0.2Ti0.6O2
Authors: Barron S. C. , van Dover R. B.
Published: April 2011

The dielectric constant of a material is strongly dependent on both the polarizability and the density of the material through the Clausius Mossotti equation. While the atomic polarizability depends on the stoichiometry of the constituent atoms, the molecular polarizability is a function of the atoms’ short range bonding structure and hence can be strongly dependent on processing conditions. Since the density of the material also depends on the thermally activated diffusivity of atoms during processing, varying the processing temperatures has an effect on both the molecular polarizability and the density. The dielectric constant of Zr0.2Sn0.2Ti0.6O2 is shown to be a strong function of the substrate temperature during sputter deposition with the highest value ∼55 at 200 °C and lower values at both higher and lower process temperatures. We have investigated the bonding structure and density of the oxide dielectric deposited at a variety of substrate temperatures in order to elucidate the relative effects of each.
Dislocation-Related Etch Protrusions Formed on 4H-SiC (000-1) Surfaces by Molten KOH Etching
Authors: Gotoh Masahide , Tawara Takeshi , Nakamura Shun-ichi , Tamori Tae , Kuboki Yoshiyuki , Yonezawa Yoshiyuki , Nishiura Masaharu
Published: April 2011

In this study, we investigated surface features formed by molten KOH etching of (000-1) substrates and epilayers, using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (TEM). We found the surface features formed on (000-1) are protrusions, in contrast to well-known dimples on (0001).
Deep Levels and Compensation in High Purity Semi-Insulating 4H-SiC
Authors: Mitchel William C , Mitchell W. D. , Smith H. E. , Carlos W. E. , Glaser E. R.
Published: April 2011

A study of temperature dependent Hall effect (TDH), electron paramagnetic resonance (EPR), photoluminescence (PL) and secondary ion mass spectrometry (SIMS) measurements has been made on high purity semi-insulating (HPSI) 4H-SiC crystals grown by the physical vapor transport technique. Thermal activation energies from TDH varied from a low of 0.55 eV to a high of 1.5 eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Carrier concentration measurements indicated the deep levels had to be present in concentrations in the low 1015 cm-3 range. Several defects were detected by EPR including the carbon vacancy and the carbon-silicon divacancy. PL measurements in the near IR showed the presence of the UD-1, UD-2 and UD-3 emission lines that have been found in HPSI material. No correlation between the relative intensities of the PL lines and the TDH activation energies was seen. SIMS measurements on nitrogen, boron and other common impurities indicate nitrogen and boron concentrations higher than those of individual deep levels as determined by TDH or of intrinsic defects as determined by EPR such as the carbon vacancy or the divacancy. It is determined that several different defects with concentrations greater than or equal to 1x1015 cm-3 are required to compensate the residual nitrogen and boron.
Top-down and bottom-up nanofabrication for multipurpose applications.
Authors: Di Fabrizio Enzo , Romanato Filippo , Cabrini Stefano , Deangelis Francesco , Yu Arum Amy , Barsotti Rober , Dealla Giustina Gioia , Brusatin Giovanna , Stellacci Fracesco
Published: April 2011

In this article we will show three recent examples of combined strategies aiming at merging top-down and bottom-up approach for nanofabrication at nanoscale level. The first example shows the fabrication of nanogaps performed by Focus Ion Beam technique that have been used to measure the conductivity of few gold nanoparticles aggregates deposited by Dip Pen lithography. The second example deals with the parallel replica of high resolution master generated by Electron Beam lithography by means of an innovative lithographic process based on DNA supramolecular nano-stamping. The latter example proposes the possibility to generate, through radiation exposure, direct patterning of hybrid sol gel material doped with fluorescent molecules. The outline of the fabrication approaches and their scientific and technical perspective are discussed.
Influence of Low Molecular Weight PDMS Chains in PDMS-based Non-Photolithography
Authors: Kim Jinook , Lee C. H. , Park Mikyung , Chae G. S. , Chung In-Jae
Published: April 2011

We describe that an elastomeric stamp of poly(dimethylsiloxane) (PDMS) can modify the surface energy of some surfaces when brought into conformal contact with the number of stamping. We focus on an increase of the hydrophobicity of the patterned surface due to diffusion of low molecular weight (LMW) silicone polymer chains. The transfer of PDMS to the surface during patterning is relevant to and calls for attention by those who are using this method in applications where control of the surface chemistry is of importance for the application.
Using Self-assembly and Selective Chemical Vapor Deposition for Precise Positioning of Individual Germanium Nanoparticles on Hafnia
Authors: Coffee Shawn S , Winkenwerder Wyatt A , Stanley Scott K , Davood Shahrjerdi , Banerjee Sanjay K , Ekerdt John G
Published: April 2011

Germanium nanoparticle nucleation was studied in organized arrays on HfO2 using a SiO2 thin film mask with ~20-24 nm pores and a 6×1010 cm-2 pore density. Poly(styrene-b-methyl methacrylate) diblock copolymer was employed to pattern the SiO2 film. Hot wire chemical vapor deposition produced Ge nanoparticles using 4-19 monolayer Ge exposures. By seeding adatoms on HfO2 at room temperature before growth and varying growth temperatures between 725-800 K, nanoparticle size was demonstrated to be limited by Ge etching of SiO2 pore walls.
Radiation Shielding Analysis for Various Materials in the Extreme Jovian Environment
Authors: Atwell William
Published: April 2011

Earlier particle experiments in the 1970s on Pioneer-10 and -11 and Voyager-1 and -2 provided Jupiter flyby particle data, which were used by Divine and Garrett to develop the first Jupiter trapped radiation environment model. This model was used to establish a baseline radiation effects design limit for the Galileo onboard electronics. Recently, Garrett et al. have developed an updated Galileo Interim Radiation Environment (GIRE) model based on Galileo electron data. In this paper, the GIRE model was utilized to generate trapped proton and electron spectra as a function of Rj (Rj = radius of Jupiter = ∼71,400 km). Using these spectra and a high-energy particle transport codes (MCNPX and HZETRN), radiation exposures and dose effects for a variety of shielding materials (Al, polyethylene [PE], and Ta plus several other elemental materials for “Graded-Z” portion of the paper) and thicknesses are presented for the Icy Moon, Europa, Ganymede, and Callisto for several orbital inclinations. In addition, an in-depth discussion and absorbed dose calculations are presented for “Graded-Z” materials and several computer codes were utilized for comparison purposes. We find overall there is generally quite good agreement between the various computer codes utilized in the study: MCNPX (Monte Carlo) vs. HZETRN (deterministic) for slab shielding and the comparison of “Graded-Z” shielding using the CEPXS, NOVICE, and NASA JPL codes. Finally, we conclude that the merits of using “Graded-Z” materials that include PE, due to cost and weight, should aid future Jupiter mission planners and spacecraft designers.
Sol-Gel Synthesis of Thick Ta2O5 Films for Photonic Band Gap Materials
Authors: Ndiege Nicholas , Wilhoite Tabitha , Subramanian Vaidyanathan , Shannon Mark , Masel Rich
Published: April 2011

Advances in microelectromechanical systems has generated an ever growing demand for novel insulating material applicable to high temperature systems. Photonic bandgap materials are appealing for such applications, specifically Ta2O5 due to its high index of refraction, refractory nature and negligible absorbance in the infrared region. The challenge faced in the realization of such materials is the synthesis of crack free Ta2O5 films whose thickness is in the order of a quarter wavelength of the incident infrared radiation.

This work seeks to investigate the effect of addition of polyvinyl pyrollidone (PVP) as a binder material in the sol gel synthesis of thick, uniform and crack free Ta2O5 films. Incorporation of PVP into the sol precursor has enabled uniform and crack free films with thicknesses of up to 2.4 microns to be realized. Chemical probing of the precursor was conducted via TGA, FTIR, and NMR analysis of the sol to elucidate the processes behind this film formation. The calcined oxide films were characterized via SEM, XRD and XPS.
Direct immobilization of DNA on partially functionalized diamond surface
Authors: Yang Jung-Hoon , Song Kwang-Soup , Kuga Shouma , Kawarada Hiroshi
Published: April 2011

Amino groups were functionalized directly on the diamond surface after treating oxidation and fluorination for detection of DNAs, respectively. For simple process, immobilization of probe DNAs was carried out directly on the partially aminated diamond without linker molecules. After fabricating micropatterned diamond, specific hybridization with Cy-5 labeled target DNA at a concentration of 100 nM could be clearly detected on H-terminated, partially O-terminated, and partially F-terminated diamonds, respectively. The hybridization intensities determined by epifluorescence microscopy were compared and analyzed.
Photochemical Micro-pattern Substitution of Functional Groups for Protein Attachment Control
Authors: Murahara Masataka , Sato Yuji
Published: April 2011

Hydrophilic and hydrophobic groups were selectively incorporated on the poly(methyl methacrylate) [PMMA] surface using a Xe2 excimer lamp and ArF excimer laser. With this new technique, a protein adsorption on the PMMA surface can be controlled.

PMMA was firstly irradiated with a Xe2 excimer lamp in the presence of perfluoropolyether [PFPE] liquid layer to incorporate CF3 groups, and secondly, the PMMA surface was irradiated by an ArF excimer laser through a patterned reticle in the presence of water to incorporate OH groups or NH2 groups in an ammonia gas ambience. The area ratio of hydrophilic and hydrophobic of the modifying sample was made to 1:3, 1:1, and 3:1. The results showed that the fibrin absorption on the sample with hydrophilic and hydrophobic micro domains depended on the area ratio of the hydrophilic and hydrophobic. The absorption coefficient of the amide band remarkably decreased with increase in water contact angle. Furthermore, it was confirmed that the absorption coefficient of fibrin decreased as the interval of CF3 and OH or NH2 groups was narrowed from 250 to 20 μm, and the fibrin sticking on the modified surface with the 20 μm hydrophilic and hydrophobic micro domains was reduced to one-twenty of that on the untreated sample.
Creating conjugated hydrogel encapsulated membranes
Authors: Jeon Tae-Joon , Malmstadt Noah , Schmidt Jacob
Published: April 2011

Device engineering for ion channel proteins requires developing systems that incorporate mechanically stable, long-lived lipid bilayer membranes. Building on our previous work, we have further increased lipid bilayer longevity through covalent conjugation of lipid molecules in the bilayer to an encapsulating hydrogel. This is accomplished by polymerizing the hydrogel in situ around a gigaohm-seal membrane containing vinyl-modified lipid head groups, forming a conjugated hydrogel encapsulated membrane (cgHEM). Membranes formed in this manner show remarkable stability, maintaining gigaohm-level resistance for over 270 hours, better than an order-of-magnitude improvement over the previous state of the art. They also demonstrate the capacity to support the incorporation and measurement of ion channel proteins at the single-molecule level.
Effect of Substrate Surface Modification on Biomineralization of Osteoblasts
Authors: Meng Yizhi , Ba Xiaolan , Kwak Seo-Young , DiMasi Elaine , Ruppel Meghan , Miller Lisa , Ge Shouren , Pernodet Nadine , Rafailovich Miriam , Qin Yi-Xian
Published: April 2011

Understanding how biomineralization occurs in the extracellular matrix (ECM) of bone cells is crucial to the development of a successfully engineered bone tissue scaffold, and to date there has not been a well-established method for the quantitative examination of bone mineralization in situ. We investigated the mechanical properties of MC3T3-E1 osteoblast-like cells and the crystalline properties of their biomineralized ECM in vitro using shear modulation force microscopy (SMFM), confocal laser scanning microscopy (CLSM), synchrotron X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The elastic modulus of the mineralizing cells increased at time points corresponding to mineral production, whereas that of the non-mineralizing cells did not vary significantly over time. CLSM showed a restructuring of the F-actin fiber network of mineralizing cells with time, which indicates remodeling activities in the cytoskeleton and was not seen in the non-mineralizing cells. Both XRD and FTIR showed that the mineralizing subclone produced hydroxyapatite in situ and that the non-mineralizing subclone was in fact weakly biomineralizing.
Control of Enzymatic Activities by Magnetite Nanoparticles
Authors: Zhou Hui , Aubin-Tam Marie-Eve , Hamad-Schifferli Kimberly
Published: April 2011

Enzymes are proteins that catalyze chemical reactions, participating in almost all processes in the cell to achieve significant reaction rates and serving a wide variety of functions inside living organisms. Here, we intended to control enzymatic activities by applying external radio frequency magnetic field (RFMF) through nanosized antenna. Ribonuclease A (RNase A), which is a relative small protein that cleave single-stranded RNA, was conjugated to magnetite nanoparticles (NP) by non-covalent interaction. The diameters of Fe3O4 nanoparticles are less than 10nm. External RFMF was applied, and the enzymatic activities of RNase A were tuned at different levels by varying the frequencies and incubation times. Comparison results by using water bath were also presented.
Strained Si-based Nanomembrane Materials
Authors: Scott Shelley A. , Roberts Michelle M. , Savage Donald E. , Lagally Max G.
Published: April 2011

Application of tensile strain to the Si(100) lattice is known to enhance carrier mobility in field effect transistors through modification of the Si band structure. Si is conventionally placed under tensile strain using methods such as Si3N4 capping for strained channel devices, and epitaxial growth of Si on a strain graded SiGe substrate for large area strain. The latter case preserves and propagates threading dislocations, and both cases require use of a bulk rigid substrate, which prohibits the use of strained Si in applications such as flexible electronics, or indeed in any application where strained Si is desirable on a non-epitaxial substrate. Elastically strained, single-crystal, Si-based nanomembranes, in which the release of a Si/SiGe/Si heterostructure from its growth substrate allows elastic strain sharing between the layers, circumvent these issues. These nanomembranes are extremely flexible, virtually dislocation-free, and transferable to almost any other surface.
Pronounced Photonic Effects of High-Pressure Water Vapor Annealing on Nanocrystalline Porous Silicon
Authors: Gelloz Bernard , Shibata Takayuki , Mentek Romain , Koshida Nobuyoshi
Published: April 2011

The effects of high-pressure water vapor annealing (HWA) on the refractive index of PS have been studied. HWA was conducted at 260 °C and 1.3 MPa, for 3 h. The refractive index (real partnand imaginary partk) was estimated by fitting reflectivity spectra. HWA considerably modifies the layers refractive index. It enhances the optical transparency of PS, particularly at short wavelengths down to below 400 nm. Both n and k are significantly reduced by HWA between 400 nm and 850 nm. These results are attributed to the high level of oxidation of PS after HWA. The high transparency of the treated layers enables Si-based photonics in the full visible range and also in the near UV range. Distributed Bragg reflectors (DBRs) have been fabricated. The central wavelengths appear blue-shifted compared to untreated samples due to the reduced refractive index. Almost no changes could be found in the reflectivity properties after one year storage in air for HWA-treated DBRs. Therefore, HWA is very useful for getting stable practical photonics devices in the visible and near UV range.
Mechanical properties of Ge/Si core-shell nanowires under a uniaxial tension
Authors: Yano Y. , Nakajima T. , Shintani K.
Published: April 2011

The mechanical properties of Si/Ge core-shell nanowires under a unixial tension are studied using molecular-dynamics simulation. The effects of anisotropy and the fraction of the core atoms on the Young's moduli of the core-shell nanowires are examined. The values of their Young's moduli deviate from those calculated using Vegard's law. Single atom chains are formed at the final stages of elongation of the nanowires.
Optical Properties of Si and Ge/Si Nanocrystals in Silicon Oxide Matrix
Authors: Uekusa Shin-ichiro , Kushida Atsuhiko
Published: April 2011

The contribution of oxide-related emission in Photoluminescence (PL) spectra from Ge and Si nanocrystals mixture embedded in silicon oxide (Ge/Si-SiO2) and Si nanocrystals embedded in silicon oxide (Si-SiO2) thin film prepared by RF-magnetron co-sputtering method is investigated. All as-deposited thin films were annealed for 1 hour in the temperature range from 300 to 1100 °C in an Ar atmosphere. The samples were evaluated by using PL, Energy dispersive spectroscopy (EDX), Raman scattering and X-ray photoelectron spectroscopy (XPS) measurements. All the measurements were performed at room temperature. The maximum PL intensity of Ge+Si-SiO2 mixture thin film has increased more than the Si-SiO2 thin film by approximately 10 times. From the results of Raman scattering and XPS measurements, it is consider that the oxygen defect centers in the host material SiO2 increased by the diffusion of Ge. An increase in the PL intensity of Ge+Si-SiO2 mixture thin film is systematically discussed.
Modeling the Capacitance-Voltage Characteristics of Organic Schottky Diode in the Forward Bias
Authors: Chiang Ko-Yu , Tseng Huai-Yuan , Lin Chang-Yu , Kung Chen-Pang , Hou Wei-Hsin
Published: April 2011

In this work, an accurate capacitance-voltage (C-V) model of organic Schottky diode is proposed. By taking the interface trap of the Schottky barrier into account, the capacitance model was derived from the junction and interface capacitance as a function of operation voltage. The model successfully describes the turn-around capacitance characteristic of Al/poly(3-hexylphiophene)(P3HT)/poly(3,4-ethylenedioxythiophene)poly(styrene sulfonate)(PEDOT:PSS)/IZO Schottky diode in the forward bias region. The simulated capacitances are in good agreement with our experimental data.
A Classic Molecular Semiconductor Revisited: New Aspects of Growth Mode and Conduction Characteristics in Thin Films of Phthalocyaninatozinc (PcZn)
Authors: Brinkmann Harry , Schlettwein Derck
Published: April 2011

PcZn as a well known organic semiconductor received new examination of its growth mode in thin films and reactions to oxygen exposure. PcZn thin films were grown on glass and polyimide substrates by physical vapor deposition. Ag electrodes had been deposited by a sputter process to allow electrical contact to the films. Conductivity measurements were performed in-situ during the growth of films under high vacuum conditions. Characteristic current peaks were observed and explained by a Stranski-Krastanov growth mode. Current voltage characteristics revealing space charge limitation could be obtained beginning in the monolayer range. For pristine films n-type conduction was observed. Following deposition an increase of the conductivity was measured, caused by changes of the film structure. Ripening under high vacuum conditions could be separately discussed from doping effects caused by oxygen exposure which led to the well- known p-type characteristics of PcZn.
Water-Soluble Conjugated Polyelectrolytes with Molecular Bumper for Efficient FRET Biosensor
Authors: Woo Han Young , Vak Doojin , Bazan Guillermo C
Published: April 2011

We report the design, synthesis and photophysical properties of two new water-soluble conjugated polyelectrolytes, poly(9,9'-bis(6-N,N,N-trimethylammoniumhexyl)fluorene-alt-1,4-(2,5-bis(6-N,N,N-trimethylammoniumhexyloxy))phenylene) tetrabromide (P1i) and poly((10,10'-bis(6-N,N,N-trimethylammoniumhexyl)-10H-spiro(anthracene-9,9'-fluorene))-alt-1,4-(2,5-bis(6-N,N,N-trimethylammoniumhexyloxy))phenylene) tetrabromide (P2i). They have same electronic conjugation but the main structural difference is the presence of the anthracenyl substituent orthogonal to the polymer main backbone in P2i. Fluorescence resonance energy transfer (FRET) from the two polymers as FRET donors to fluorescein-labeled single stranded DNA (ssDNA-Fl) was studied. It is observed the emission from ssDNA-Fl via FRET by excitation of P2i with a FRET efficiency of ∼60%. Fluorescein is not emissive within the ssDNA-Fl/P1i complex. We also observed clear PL quenching (Φ = 0.8 → Φ = 0.27) of fluorescein for P2i after electrostatic complexation with ssDNA-Fl. It suggests a quenching pathway of Fl emission through photo-induced charge transfer (PCT) in the electrostatic complex. Both P1i and P2i have same HOMO-LUMO electronic structures and a similar thermodynamic driving force for either FRET or PCT. It appears that PCT operates to a larger extent with P1i, proposing that the presence of the “molecular bumper” in P2i increases Fl emission by increasing the donor-acceptor distance, which decreases more acutely PCT quenching, relative to FRET.
Ultrahigh Vacuum Seebeck Effect and Conductivity Measurements on N-Doping of C60 Films
Authors: Hayashi Naoki , Kanai Kaname , Ouchi Yukio , Seki Kazuhiko
Published: April 2011

We constructed an ultrahigh vacuum (UHV) system with which in-situ conductivity and Seebeck coefficient measurements can be performed, including the detailed examination of the oxygen effect. It can also carry out the deposition of metal electrodes and organic films under UHV condition through measurements. The conductive characteristics of fullerene (C60) films were examined by the measurement at conductivity and Seebeck coefficient under UHV. We observed that the conductivity at room temperature was higher than 1×10−3 S cm−1. This value is two orders of magnitude in conductivity higher than the Hamed report. [A. Hamed et al., Phys. Rev. B 47, 10873 (1993).] Seebeck coefficient S was also measured. Its sign was negative, indicating electron conduction for C60 film. After the measurements under UHV, oxygen was introduced into the chamber by a variable leak valve. The conductivity decreased drastically by increasing the pressure of oxygen. It decreased more than five orders from under UHV to 1 atom oxygen. The temperature dependence of the conductivity was also examined. The conductivity was thermally activated. Activation energies of the conductivity increase by increase oxygen pressure. This means that the oxygen act as carrier traps. As an n-type dopant, acridine orange base (AOB) was co-deposited into C60 films. The magnitude in the conductivity increased but not drastic. The conductivity of doped film also decreased by increasing the pressure of oxygen. The conductivity even under 6.6×10−2 Pa, however, was high enough. Though AOB was not effective dopant against C60 film in UHV condition, AOB doped C60 film became resistant to oxygen.
Epitaxial Growth of C60 Thin Films using Continuous-wave Laser Molecular Beam Epitaxy
Authors: Yaginuma Seiichiro , Itaka Kenji , Haemori Masamitsu , Katayama Masao , Matsumoto Yuji , Koinuma Hideomi
Published: April 2011

We have fabricated C60 thin films on various substrates (mica, MoS2, HOPG, LiF, NaCl, KBr, KCl and CaF2) by using continuous-wave laser molecular beam epitaxy (CWL-MBE), which is very suitable technique to grow epitaxial organic thin films because of good controllability of evaporation as compared with Knudsen-cell method. The films were evaluated by reflection high-energy electron diffraction with micro channel imaging plate (MCP-RHEED) and atomic force microscopy (AFM). AFM images of the C60 films on mica, MoS2 and HOPG substrates show flat and homogeneous, morphology, and epitaxial growth of the films on mica and MoS2 substrates were observed by RHEED. This result shows mica, MoS2, HOPG substrates are good candidates for epitaxial growth of C60 thin films.
Assembly of Tailored Thiophene Oligomers on Gold Electrodes - Film Formation and Properties
Authors: Collier Peter Anthony , Deivaraj Theivanayagam Chairman , Kerk Wai Tat , Chin Wee Shong , Loh Kian Ping , Bai Ping , Li Er Ping
Published: April 2011

To examine the potential to apply chemically modified surfaces in organic thin film transistors (TFT), we report the synthesis and characterization of two tailored series of oligothiophene compounds. The oligomers have thiol end groups for coupling to gold electrodes and have regio-regular alkyl substitutions corresponding to Head-Head (HH-) and Head-Tail (HT-) molecular conformations. Variations in chain length, structures and end groups have enabled a detailed study of the deposition of films from solution and the films' properties.
Penetration of Tagged Organics into Caulked and Un-caulked Porous Dielectrics Measured by Rutherford Backscattering
Authors: Geil Robert D. , Senkevich Jay J. , Rogers Bridget R.
Published: April 2011

A novel method for studying the penetration of wet chemicals into caulked and uncaulked porous dielectrics was developed, and the barrier properties of parylene X were evaluated. Rutherford backscattering spectrometry (RBS) was used to study the penetration of chlorine-tagged organics, 3-chloro-1-propanol and a %5 HCl solution. After one minute of exposure time, eight times more 3-chloro-1-propanol diffused through uncaulked porous dielectric compared to caulked porous dielectric. Penetration from the side of the samples was found to be insignificant.