bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Properties of Carbon Nanotube Reinforced Polycarbonate at Cryogenic Temperature
Authors: Oliver Anita , Mbaruku Abdallah L. , Schwartz Justin
Published: April 2011

Carbon nanotube (CNT) reinforced polymers are of high interest for various industries due to their unique mechanical and electrical properties. Most research has been done at room temperature (RT), but little is known about properties at cryogenic temperature. This paper presents results on CNT-polycarbonate (PC) composites with respect to mechanical properties at 77 K in comparison with RT. CNT-PC composites with 0wt% (neat), 0.1wt%, and 1.0wt% CNTs have been studied. Results imply that the CNT effects are more obvious at low temperature and are seen in the form of serrations in the stress-strain plot. No significant difference has been noticed between the neat and reinforced samples at either temperature. However, it was determined that the strength increases drastically while the elongation decreases at low temperature as compared to RT. SEM images confirm that the samples at low temperature exhibit brittle failure. Additionally, it can be seen that at low temperature the nanotubes align with the direction of tensile force while the nanotubes at RT align with the sample surface.
Gas Pressure Sensor Based on PECVD Grown Carbon Nanotubes
Authors: Ficek Richard , Elias Marek , Zajickova Lenka , Jasek Ondrej , Vrba Radimir
Published: April 2011

In present paper we describe development and manufacturing of the pressure sensor based on electron field emission from carbon nanotubes (CNTs). The sensor consisted of two parts, silicon membrane as an anode and multiwalled CNTs on a silicon cathode, creating a vacuum micro-chamber. Both electrodes were fabricated from the silicon single crystal (Si) wafer of the orientation (<100>) doped by phosphorus. The CNTs were grown by plasma enhanced CVD using iron catalyst in atmospheric pressure microwave torch. The catalyst was patterned into the area corresponding to the membrane dimensions. The thin CNTs with the diameter about 80 nm were straight standing perpendicularly to the substrate due to a crowding effect. In order to find the threshold current the emission characteristics of prepared sensors were measured.
Carbon Felt/Carbon Nanotubes/Pani as pH Sensor
Authors: Silva Glaucio Ribeiro , Matsubara Elaine Yoshiko , Corio Paola , Rosolen Jose Mauricio , Mulato Marcelo
Published: April 2011

This work proposes the use of the composite carbon felt/carbon nanotube/Polyaniline as an alternative for applications as a pH sensor device. The carbon felt/carbon nanotube is an electronic conductivity material that was obtained from polymer felt (poliacrilonitrile felt) using oxidation and carbonization processes. The cup-stacked and bamboo-like tubes were grown on the fibers of carbon felt by chemical vapor decomposition method. The sensor was obtained by incorporating polyaniline (Pani) on the nanotubes present on the fibers of carbon felt/carbon nanotubes composite. The measuring process uses an EGFET (Extended Gate Field Effect Transistors) configuration, which is a derivation of the ISFET (Ion Sensitive Field Effect Transistor) - that is basically a chemical semiconductor sensor. The drain-current versus source-drain voltage is presented for varying pH concentrations from 2 up to 12.
High-Aspect-Ratio Micromachining of Fluoropolymers Using Focused Ion Beam
Authors: Matsui Yoshinori , Miyoshi Nozomi , Oshima Akihiro , Seki Shu , Washio Masakazu , Tagawa Seiichi
Published: April 2011

Poly(tetrafluoroethylene) (PTFE) microstructure with high aspect ratio (> 200) and without solid debris along the edge was fabricated with high etch rate by using FIB. Gasification of PTFE by FIB is responsible for the high aspect ratio, the high etch rate, and the no solid debris. Roughness of etched surface of the PTFE increases with fluence, although edge of the etched area has good profiles. The etch mechanism seems to be complicated.
Ion Beam-induced Quantum Dot Synthesis in Glass
Authors: Bernas Harry , Espiau de Lamaëstre Roch
Published: April 2011

Irradiation-induced processes are often considered only in their nonequilibrium aspects. The purpose of this brief review is to show that chemistry, and particularly redox properties, play a major role in the thermal evolution of such systems and generally cannot, therefore, be neglected. This is exemplified by the synthesis of Ag nanoclusters in glasses and silica, under both low (gamma-ray) and high (MeV ion) deposited energy density irradiation conditions. The nanocluster formation mechanism is shown to be similar to the latent image formation process in photography. The corresponding information was used to control nucleation and growth of PbS clusters in glasses, leading to promising optical properties. In the course of these studies, we also showed that lognormal size distributions characterize the absence of information on the nanocluster formation process.
Ion Bombardment Improvement on Thermoelectric Properties of Multilayered Bi2Te3/Sb2Te3 Deposited by Magnetron Sputtering
Authors: Zheng Bangke , Budak S. , Chhay B. , Zimmerman R. L. , ILA D.
Published: April 2011

In order to keep the stoichemistry of Bi2Te3 and Sb2Te3 so as to keep the electrical and thermal conductivity advantage of the layered structure of bulk Bi2Te3 and Sb2Te3 in each period of the superlattice, magnetron sputtering, which is operated at relatively low temperature, was used to deposit multiplayer Bi2Te3/Sb2Te3 thermoelectric superlattice device. The two guns in our magnetron sputtering device is oriented at a certain angle to get off-axis plasma plume, which will form lattice with preferential orientation for electrical conductivity in each layer. The super lattice was then bombarded by MeV Si ions with different fluence in order to form nanoscale cluster quantum dot-like structures. In addition to the effect of quantum well confinement of the phonon transmission, the nanoscale clusters produced by the bombardment of ion beam further adversely affect the thermal conductivity. The defect and disorder in the lattice caused by bombardment and the grain boundary of these nanoscale clusters increase the scattering of phonon and increase the chance of the inelastic interaction of phonon and the annihilation of phonon, this limits phonon mean free path. Phonons are chiefly absorbed and dissipated along the lattice, therefore reduces the cross plane thermal conductivity, The increases of the electron density of state in the miniband of nanoscale cluster quantum dot-like structure formed by bombardment also increases Seebeck coefficient, and the electrical conductivity. Eventually, the thermo-electric figure of merit of superlattice films increases.
Nanoscale Surface Modification of UltraHigh Molecular Weight Polyethylene (UHMWPE) Samples with the W + C Ion Implantation
Authors: Urkac E. Sokullu , Oztarhan A. , Tihminlioglu F. , Kaya N. , Budak S. , Chhay B. , Muntele C. , OKs E. , Nikolaev A. , ILA D.
Published: April 2011

In this work, Ultra High Molecular Weight Poly Ethylene (UHMWPE) samples were implanted with W + C ion by using Metal-Vapour Vacuum Arc (MEVVA) ion implantation technique. Samples were implanted with W and C atoms with a fluence of 1017ion/cm2 and extraction voltage of 30 kV. Mechanism underlies this modification characterized with ATR-FTIR, UV-VIS-NIR Spectrum and Rutherford Backscattering Spectrometry (RBS). Surface morphology of implanted and unimplanted samples were examined in nanoscale with AFM.
MeV Ion-Beam Bombardment Effects on The Thermoelectric Figures of Merit of Zn4Sb3 and ZrNiSn-Based half-heusler compounds
Authors: Budak S. , Guner S. , Muntele C. , Smith C. C. , Zheng B. , Zimmerman R. L. , ILA D.
Published: April 2011

Semiconducting â-Zn4Sb3and ZrNiSn-based half-heusler compound thin films were prepared by co-evaporation for the application of thermoelectric (TE) materials. High-purity solid zinc and antimony were evaporated by electron beam to grow the â-Zn4Sb3thin film while high-purity zirconium powder and nickel tin powders were evaporated by electron beam to grow the ZrNiSn-based half-heusler compound thin film. Rutherford backscattering spectrometry (RBS) was used to analyze the composition of the thin films. The grown thin films were subjected to 5 MeV Si ions bombardments for generation of nanostructures in the films. We measured the thermal conductivity, Seebeck coefficient, and electrical conductivity of these two systems before and after 5 MeV Si ions beam bombardments. The two material systems have been identified as promising TE materials for the application of thermal-to-electrical energy conversion, but the efficiency still limits their applications. The electronic energy deposited due to ionization in the track of MeV ion beam can cause localized crystallization. The nanostructures produced by MeV ion beam can cause significant change in both the electrical and the thermal conductivity of thin films, thereby improving the efficiency. We used the 3ù-method measurement system to measure the cross-plane thermal conductivity ,the Van der Pauw measurement system to measure the cross-plane electrical conductivity, and the Seebeck-coefficient measurement system to measure the cross-plane Seebeck coefficient. The thermoelectric figures of merit of the two material systems were then derived by calculations using the measurement results. The MeV ion-beam bombardment was found to decrease the thermal conductivity of thin films and increase the efficiency of thermal-to-electrical energy conversion.
High Resolution Thermal Imaging of Integrated Circuits
Authors: Tessier Gilles , Bardoux Mathieu , Filloy Céline , Fournier Danièle
Published: April 2011

Thermoreflectance is an non contact optical method using the local reflectivity variations induced by heating to infer temperature mappings, and can be conducted at virtually any wavelength. In the visible, the technique is now well established. It can probe temperatures through several micrometers of transparent encapsulation layers, with sub-micron spatial resolution and 100 mK thermal resolution. In the ultraviolet range, dielectric encapsulation layers are opaque and thermoreflectance gives access to the surface temperature. In the near infrared, thermoreflectance is an interesting solution to examine chips turned upside down, since these wavelengths can penetrate through silicon substrates and give access to the temperature of the active layers themselves. Here, we explore the possibilities of each wavelength range and detail the CCD-based thermal imaging tools dedicated to the high resolution inspection of integrated circuits.
Nanofiber Based Er(III) Metal Pyrochlore Oxides: Synthesis and Characterization
Authors: Wang Ruofeng , Bender Edward T. , Aljarrah Mohannad T. , Evans Edward A. , Ramsier Rex D.
Published: April 2011

Erbium(III) doped TiO2 nanofibers (Er2Ti2O7) have been synthesized by electrospinning mixtures of polymers, metal-containing materials, and erbium acetate. These electrospun nanofibers were subsequently annealed at temperatures of 550, 750, 950, and 1150 oC to remove the organics and leave behind the metal oxides. The crystal structure and optical properties of the nanofiber pyrochlores were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transformation IR (FTIR) spectroscopy. Different crystal structures were formed by controlling the annealing conditions. XRD data are compared with near-IR spectra to better understand the effects of annealing temperature on the Er (III) thermally-excited selective optical emission process.
Nanocrystalline Eu3+ Doped M3Al2O6 (M: Ba, Ca and Sr) Red Phosphors Prepared by Sucrose-PVA-Metal Ion Complex Route
Authors: Manavbasi Alp , Zed Palkin , LaCombe Jeffrey C.
Published: April 2011

Nanocrystalline (<100 nm) red emitting Eu3+- doped M3Al2O6 (M = Ba, Ca and Sr) phosphors were prepared by an aqueous sucrose-PVA-metal ion complex route. The aqueous sucrose-PVA solution includes 20 mol% PVA, and the method is based on the dehydration of a transparent metal ion-sucrose-PVA solution to a highly viscous liquid and then precursor formation by heating at 250°C. The phase formation and the crystallite size measurements were made by x-ray diffraction techniques. Photon correlation analysis revealed that all synthesized phosphor particles range in size from 400 nm to a few microns. The photoluminescence (PL) and PL excitation characteristics have been investigated. All samples have broad CT bands centered at around 269 nm and only the Ca3Al2O6:Eu3+ exhibited the characteristic f-f transitions of Eu3+ ions mainly located at 396 and 465 nm in comparable levels with the CT band. The emission spectrum of Ca3Al2O6:Eu3+ is dominated by the red (5D0 ¡æ 7F2) transition band located at 614 nm, however the Eu3+ doped Sr3Al2O6 and Ba3Al2O6 phosphors have comparable emission intensity in the red (5D0 ¡æ 7F2 ) and orange (5D0 ¡æ 7F1 ) transition bands. The highest intensity of the red emission was obtained when the Ca3Al2O6:Eu3+ phosphor was excited at 396 nm.
Slow Crack Growth Analyses of Oxygen Transport Ceramic Membranes
Authors: Nagabhushana Nagendra , Zhang Jing , Nithyanantham Thangamani , Bandopadhyay Sukumar
Published: April 2011

Perovskite-type oxides are promising materials with potential use as dense membranes for oxygen separations. We herein report slow crack growth (SCG) studies of La0.2Sr0.8Fe0.8Cr0.2O3-δ (LSFCO) perovskite membranes as Oxygen Transport Membranes (OTM). Two sample batches of perovskite were tested to investigate the effect of temperature, specific chemical environments, and loading rate on flexure strengths, using four-point bending tests. The first batch was examined at room temperature in air. The second batch was soaked in a N2/air atmosphere at 1000°C for 1 hour prior to application of load. Loading rates varied from 0.00005 mm/s to 0.01 mm/s. Flexural strength data indicate that the examined OTM material showed little susceptibility to SCG at room temperature in air. However, the sample is susceptible to SCG in a N2/air environment at 1000°C. Also, the experiments demonstrate flexural-strength rate dependency, with strength increasing with the loading rate. The observed phenomena are explained by the decomposition and microstructural transitions in the perovskite. The results provide important information about OTM mechanical degradation, which is valuable for future OTM design applications.
Synthesis and Optical Properties of SERS-active Nanocomposite Microspheres
Authors: Farah Abdiaziz , Dai Sheng , Jawabrah Al-Hourani Baker , Bravo-Vasquez Juan P. , Cho Jae-Young , Fenniri Hicham
Published: April 2011

An approach to prepare metal nanoparticle-polymer microbeads with integrated Raman tags using SERS as reliable diagnostic tool is reported. In essence, spectroscopically encoded (4-thioacetyl)styrenes were assembled on well-characterized 50 nm Au NPs and subjected to suspension polymerization conditions using styrene and methacrylic acid as comonomers and divinylbenzene as crosslinker. The resulting metal embedded nanocomposites were characterized by SEM, TEM, DSC, TGA, Raman and SERS to determine their morphology, particle size, composition, thermal stability and their optical and electronic properties.
Deconvolution of Self-encoded Polymer Beads in Random Microarrays for Antigen Biosensing by Raman Spectroscopy
Authors: Bravo-Vasquez Juan P , Alvarez-Puebla Ramon A , Blais David , Zhang Ying , Raez Jose , Pezacki John P , Fenniri Hicham
Published: April 2011

Random bead microarray in which each bead has been functionalized with different biomolecules are of great interest. The process by which one would identify the location of each bead is referred to as decoding. The decoding step has played a challenging role in microarray technologies due to the increase in complexity with the increase in array size. Here we report a novel, fast and reliable method of decoding randomly assembled arrays based on polymer beads with unique spectroscopic signatures. Beads were synthesized by dispersion polymerization of a family of styrene monomers and methacrylic acid to generate a spectroscopically encoded bead library. In addition to identifying the self-encoded beads through their unique spectrum in a tetraplex experiment, Raman spectroscopy was used to monitor antibody-antigen binding events on the barcoded beads. The simplicity, versatility and rapid analysis enabled by this self-encoded bead array platform technology demonstrates its potential in high-throughput biomolecular multiplex screening.
The Effect of Surface States on Secondary Electron (SE) Dopant Contrast from Silicon p-n Junctions
Authors: Chee Augustus K. W. , Rodenburg Conny , Humphreys Colin John
Published: April 2011

Detailed computer modelling using finite-element analysis was performed for Si p-n junctions to investigate the effects of surface states and doping concentrations on surface band-bending, surface junction potentials and external patch fields. The density of surface states was determined for our Si specimens with a native oxide layer. Our calculations show that for a typical density of surface states for a Si specimen with a native oxide layer, the effects of external patch fields are negligible and the SE doping contrast is due to the built-in voltage across the p-n junction modified by surface band-bending. There is a good agreement between the experimental doping contrast and the calculated junction potential just below the surface, taking into account surface states, for a wide range of doping concentrations.
Three Dimensional Observation of Flux Pinning Centers in Dy-doped YBa2Cu3O7-x Coated Superconductors by STEM Tomography
Authors: Ortalan Volkan , Herrera Miriam , Morgan David G. , Rupich Martin W. , Browning Nigel D.
Published: April 2011

The spatial distribution of flux pinning centers in YBa2Cu3O7 (YBCO) coated conductors significantly affects the conductive properties. Nanoparticles acting as pinning centers can be intentionally introduced into the structure by chemical doping. In this study, a Dy-doped YBa2Cu3O7-x coated superconductor was investigated and the particle composition was found to be as (YsDy1-s)2Cu2O5 with s ∼0.6. A tomographic tilt series was acquired using a scanning transmission electron microscope (STEM) to determine the 3-D distribution of nanoparticles. In the investigated sample area, 71 particles were located with a particle size distribution ranging between 13 and 135 nm. The distribution uniformity and size of the particles appeared to be dependent on the grain boundary network structure. Large particles were observed to be located on grain boundaries indicating that fast grain boundary diffusion may determine the particle size.
Quantitative STEM and HRTEM Studies on Au Metallic Nano-Catalysts
Authors: Li Long , Menard Laurent D. , Xu Fengting , Nuzzo Ralph G. , Yang Judith C.
Published: April 2011

Nano-catalysts, Au nano-particles on TiO2 (anatase), were studied by means of quantitative scanning transmission electron microcopy (Q-STEM) and high-resolution transmission electron microcopy (HRTEM). All the Au nano-catalysts were produced from an Au13 precursor, Au13[PPh3]4[S(CH2)11CH3]4, TiO2 supports, with three treatments: (1) thermal heating in the air at 400°C for 2 hours, (2) exposure to ozone (O3) at room temperature, and (3) exposure to atomic oxygen (AO, or O) with a AO dose of 7.3 ×1018 atom/cm2 at room temperature. Both reactive oxygen species O3 and AO produced significantly small sizes of Au particles as compared to those from the heating treatment in the air (2.7 ± 0.6 nm, 324 b 264 atoms). Ozone produced the smallest (1.2 ± 0.5 nm, 40 ± 49 atoms), whereas AO produced smaller (2.1 ± 0.7 nm, 72 ± 98 atoms), with a broad size distribution and a variety of shapes. HRTEM studies on the AO treated Au/TiO2 samples found that there could exist relationship between the particles size and their shapes which also affected by the interaction with TiO2 supports. The support effect of TiO2 to the shapes of Au particles was also studied.
Plasticity Mechanism of Indium Antimony (InSb) in the Brittle Regime: Combined Study with Conventional TEM and LACBED
Authors: Kedjar Bouzid , Thilly Ludovic , Demenet Jean-Luc , Rabier Jacques
Published: April 2011

Indium antimony (InSb) has been deformed in compression under gaseous confining pressure (Paterson apparatus) above and below the brittle to ductile transition occurring around 150°C. Thin foils have been prepared from the deformed samples and dislocations were characterized with conventional TEM as well as LACBED. This paper focuses on the room temperature deformation microstructures which appeared to be extremely complex with the observation of very well arranged network of perfect and partial dislocations. In such case, the traditional dislocation extinction conditions were extremely difficult to apply and only the use of the LACBED technique uncovered the nature of the observed dislocations and gave further insight to their interactions, revealing in particular the presence of partial dislocation dipoles. These original observations suggest a change of deformation mechanism at the brittle to ductile transition temperature.
Reduction of Contrast in ADF-STEM Images Due To Amorphous Layer
Authors: Maccagnano-Zacher Sara , Mkhoyan Andre , Silcox John
Published: April 2011

A study of high-resolution ADF imaging in uncorrected and aberration-corrected STEMs was carried out by multislice simulation. The presence of amorphous layers at the surface of a crystalline specimen is shown to significantly alter the visibility of the atomic columns in ADF images. After propagating through an amorphous layer a portion of the beam passes without any alteration while scattered electrons introduce a Gaussian background. An amorphous layer at the beam entry surface appears to have slightly more of an effect on the ADF image contrast than that of an amorphous layer at the exit surface, and this difference increases with increasing atomic number. With constant crystal layer thickness, the reduction of contrast as a function of increasing amorphous layer is found to have the same behavior, regardless of the thickness of the initial crystal layer thickness.
The Atomic, Electronic and Defect Structure of the Dynamically Formed Cu2O/Cu Interfaces
Authors: Han Xuetian , Yang Judith C.
Published: April 2011

To gain fundamental insights into metal oxidation, the dynamically formed Cu/Cu2O interface was investigated by cross-sectional TEM (Transmission Electron Microscopy) methods. Copper (001) films were oxidized in oxygen within a UHV chamber to create Cu2O islands that formed epitaxially with respect to the Cu film. The cross-sectional Cu2O/Cu TEM sample was prepared by dual beam (DB) focused ion beam (FIB) instrument and the interface was probed by high-resolution TEM (HREM) and electron energy loss spectrum (EELS). It is found that Cu2O {110} layer distance significantly decreases from the interface area to the bulk Cu2O region, which is about 3∼4 unit cell thickness in Cu2O side; while the {100Cu2O layer distance increases with increasing distance from the interface region. The chemical Cu/Cu2O interface thickness has been measured with EELS analysis, which is about 2nm where the oxidation state of Cu gradually changes from Cu0 to Cu+1. This transition region indicates the area where Cu/Cu2O interface exists and suggests the existence of metastable Cu oxides. The Cu2O island growth mechanism of predominantly anion interfacial diffusion at the initial stage oxidation has been proposed.
Off-Axis Electron Holography of Self-Assembled Co Nanoparticle Rings
Authors: Kasama Takeshi , Dunin-Borkowski Rafal E. , Scheinfein Michael R. , Tripp Steven L. , Liu Jie , Wei Alexander
Published: April 2011

We use off-axis electron holography in the transmission electron microscope (TEM) to study magnetic flux closure (FC) states in self-assembled nanoparticle rings that each contain between five and eleven 25-nm-diameter Co crystals. Electron holograms are acquired at room temperature in zero-field conditions after applying chosen magnetic fields to the samples in situ in the TEM by partially exciting the conventional microscope objective lens. Mean inner potential contributions to the phase shift are determined by turning the samples over, and subsequently subtracted from each recorded phase image to obtain magnetic induction maps. Our results show that most nanoparticle rings form FC remanent magnetic states, and occasionally onion-like states. Although the chiralities (the directions of magnetization) of the FC states are determined by the shapes, sizes and positions of the constituent nanoparticles, reproducible magnetization reversal of each ring can be achieved by using an out-of-plane magnetic field of between 1600 and 2500 Oe.
Synchrotron Characterization of Texture and Stress Evolution in Ag Films
Authors: Vodnick Aaron , Lawrence Michael , Little Bethany , Worden Derek , Baker Shefford
Published: April 2011

Real-time in-situ synchrotron x-ray diffraction measurements were performed at the Cornell High Energy Synchrotron Source to characterize both the texture evolution and stresses within the individual texture components of Ag films during recrystallization. As deposited films had a nearly perfect (111) fiber texture. During isothermal anneals, stress and texture were characterized in real-time as the texture evolved into a strong (001) fiber. An Avrami analysis of the evolving texture fractions yielded very different activation energies for films on different barrier layers, suggesting different governing mechanisms were responsible for secondary grain growth. The strains were used to test a common model for texture prediction that assumes the same strain within each texture component. It was found that secondary (001) grains were able to grow primarily strain free. Selection for this strain energy minimizing orientation occurred during the nucleation process during which texture interactions play an important role. By using these real time measurements, we are able to show that driving forces for texture transformations in metal films may not be as simple previously described.
In-Situ Neutron Diffraction Study of the Behavior of AL6XN Stainless Steel Under Biaxial Loading
Authors: Gharghouri Michael , Marin Tito , Rogge Ronald B , Dawson Paul R
Published: April 2011

In–situ neutron diffraction has been used to measure lattice strains parallel to two principal stress directions in biaxially-loaded AL6XN stainless steel. A new fixture was developed for loading thin-walled tubular specimens through combinations of internal pressure and axial loading. Under these conditions, the principal directions (σzz and σθθ in a cylindrical r, θ, z coordinate system) remain constant with respect to the initial crystallographic texture regardless of the level of biaxiality, a distinct advantage for diffraction experiments over the traditional tension/torsion tests for which this condition does not hold. Specimens were first pressurized to the level required to obtain a chosen value of σθθ. The axial load was then increased to reach the yield surface at different σθθ/σzz ratios, ranging from uniaxial to balanced biaxial loading (0, 0.4, 0.7, 1 according to Tresca). The {200}, {220}, {222}, and {311} reflections were measured in the axial and hoop directions as a function of axial load. A sequence of axial loading/unloading episodes was applied for different levels of plastic deformation. Under uniaxial tension, the {200} reflection showed the highest axial strains, followed by the {311}, and {220}/{222} reflections. With increasing internal pressure (biaxiality), the axial lattice strains corresponding to a given axial stress tended to decrease, and the responses of the various reflections tended to merge.
Modeling of Charge Transport in a Hybrid Metal / Organic / Inorganic Device
Authors: Mendez Henry Alberto
Published: April 2011

A Metal / Organic / Inorganic semiconductor heterostructure was built and characterized in situ under ultra-high vacuum conditions (UHV). The aim was to investigate the influence of a perylene-derivative organic thin film on the transport electronic properties of Schottky Ag / GaAs diodes. The device was studied using a combination of photoemission spectroscopy (PES) and electrical measurements. The obtained results were discussed using the analytical expressions of a trapped charge limited current (TCLC) model.
Specialty High Performance Coatings for Optical Fiber Applications via Perfluorocyclobutyl (PFCB) Aryl Ether Polymers
Authors: Budy Stephen M. , Iacono Scott T. , Hawkins Wade , Foy Paul , Ballato John , Smith Dennis W.
Published: April 2011

There is a growing need for optical fiber coatings that can sustain higher temperatures than present materials permit. To date, polyimides are used predominantly but they generally are difficult to process and usually require multiple depositions to achieve the desired film thickness. Perfluorocyclobutyl (PFCB) aryl ether polymers have demonstrated much success as processable and amorphous fluoropolymers,[1] with particular emphasis on high performance optical applications.[2] This work discusses recent efforts into perfluorocyclobutyl aryl ether polymer-based optical fiber coatings.[3] A series of silica-based optical fibers were drawn with differing PFCB polymer coatings compositions and molecular weights on a Heathway draw tower. Results include a more than doubled usage temperature of coating (decomposition temperatures (Td) in nitrogen and air were above 450 °C) without affecting fiber mechanical properties and comparable isothermal stability to conventional coatings, except with a >150 °C higher temperature. Preliminary results of the first successful coating of optical fibers by PFCB polymers will be presented herein, as well as future endeavors.
Poly and Nano-crystalline High Electron Mobility Thin Film Transistors on Plastic Substrates for Large Area Applications
Authors: Paydavosi Sara , Tamaddon Amir-Hossein , Mohajerzadeh Shams , Robertson Michael D
Published: April 2011

Thin-film transistors (TFT) of poly and nano crystalline silicon have been made at temperature as low as 170°C on flexible PET (polyethylene terephthalate) substrates.The crystallization of the silicon film has been achieved using external mechanical stress assisted by a plasma hydrogenation technique. The formation of TFT is possible by means of a lateral crystallization of amorphous silicon under the channel region. High mobility TFTs with an electron mobility of 25cm2/Vs and an on/off ratio of 2000 have been obtained. Scanning electron microscopy, X-ray diffraction analysis and optical microscopy have been used to examine the crystallinity of the layer. In addition we report the deposition of high quality low-temperature silicon-oxide layers on PET substrates using an RF-plasma enhanced chemical vapor deposition unit with direct introduction of oxygen gas into the chamber and its reaction with Silane. Infrared spectroscopy was used to examine the quality of the oxide layer.
Rigid-Rod Sensitizers bound to Semiconductor Nanoparticles
Authors: Taratula Olena , Galoppini Elena
Published: April 2011

A series of “rigid-rod” dyes with an organic chromophore (pyrene or coumarin) attached through an oligophenylenethynylene (OPE) rigid bridge, linear or branched, to an anchoring isopthalic acid unit (Ipa) were synthesized and studied for solar cells (DSSCs) applications. The new dyes were attached to metal oxide (MOn = TiO2, ZrO2 and ZnO) nanoparticles films via the two COOH binding groups on the Ipa unit to investigate their binding and photophysical properties at the semiconductor surface. FTIR-ATR spectra show that all dyes did bind to the metal oxide films through carboxylate bonds. Fluorescence emission on insulating ZrO2 films was employed to study aggregation of the organic rigid-rods. Studies of the pyrene rigid-rods in solar cells showed near quantitative conversation of absorbed photons into electricity.
Energy Band Engineering for Improved Vertical Transport in Quantum Structured III-V p-i-n Solar Cells
Authors: Alemu Andenet , Freundlich Alex
Published: April 2011

The use of InGaAsN and GaBiAsN quantum structures in the intrinsic region of conventional III-V p-i-n solar cells, lattice matched to GaAs, presents several advantages for photovoltaic (PV) application. First they allow for very shallow to zero valence band offsets thus permitting the free movement of holes. Second, a wide range of band-gap values are made possible due to the large band gap decrease upon the introduction of minute amounts of N and Bi. Using band structure calculations that include the strain effects, conduction and valence band anti-crossing models describing the large band gap bowing and the transfer matrix method, we present the theoretical investigation of optimum design conditions for enhanced vertical transport. The direct quantum mechanical resonant tunneling of electrons out of the quantum structures and into the continuum of the conduction band of the host semiconductor material can be facilitated provided that an adequate choice of material parameters is made. The high electron transmission probability together with the free movement of quasi-3 D holes is predicted to result in enhanced PV device performance. Furthermore, the increase in electron effective mass due to the incorporation of N translates in enhanced absorptive properties, ideal for PV application.
Factors Affecting Exchange Bias in Polycrystalline Metallic Thin Films
Authors: Fernandez-Outon Luis Eugenio , Vallejo-Fernandez Gonzalo , O'Grady Kevin
Published: April 2011

We describe the factors which control the measured value of exchange bias (HEX) in bilayers consisting of sputtered metallic thin films of an antiferromagnet (AF) in contact with a ferromagnetic (F) layer. Experimental measurements show that the value of HEX is determined by the grain volume distribution which limits the exchange bias via small grains which are thermally unstable, and large grains which cannot be set when the system is field annealed to set the AF at temperatures below TN. All the results are interpreted in terms of a granular model where the energy barrier to reversal within the AF is grain volume dependent. We show how this affects setting in metallic AFs at T<TN. We have also found that exchange bias is moderated by disordered spins at the F/AF interface. These spins can be ordered at low temperatures and by field annealing. Ordering of interfacial spins leads to an increase in HEX of up to 30%.
Experimental Tests of Possible Mechanisms for the Organic Magnetoresistive Effect
Authors: Nguyen Tho Duc , Rybicki James , Sheng Yugang , Wohlgenannt Markus
Published: April 2011

We experimentally test three existing models of organic magnetoresistance (OMAR) which are all based on carrier spin dynamics. We first prove that hyperfine field originating from the hydrogen nuclei in organic materials is necessary for observing OMAR by studying C60 sandwich devices using several different electrode materials. We show that C60, unlike many other organic semiconductors, does not exhibit any intrinsic OMAR effect. However, we find that as soon as the carriers in C60 are brought in proximity with hydrogen-containing compounds, either in the form of a polymeric electrode, or side-chain substituents, a weak OMAR effect is observed. Next, we perform charge-induced absorption and electroluminescence spectroscopy in a polyfluorene organic magnetoresistive device. Our experiments allow us to measure the singlet exciton, triplet exciton and polaron densities in a live device under an applied magnetic field, and to distinguish between three models of OMAR. These models are based on different spin-dependent interactions, namely exciton formation, triplet exciton-polaron quenching and bipolaron formation. We show that the singlet exciton, triplet exciton and polaron densities and conductivity all increase with increasing magnetic field. Our data are inconsistent with the exciton formation and triplet-exciton polaron quenching models.
Magnetism and Recoilless Fraction of Cerium-Doped Hematite Nanoparticles System
Authors: Sorescu Monica , Diamandescu Lucian
Published: April 2011

Cerium-doped hematite particles of the type xCeO2-(1-x)α-Fe2O3 (x=0.1, 0.5) were synthesized using mechanochemical activation and characterized by X-ray diffraction (XRD) and Mössbauer spectroscopy. XRD patterns yielded the dependence of lattice parameters and particle size as a function of ball milling time for each value of the molar concentration x. For x=0.1, the Mössbauer spectra were fitted with one or alternatively, two sextets, corresponding to Ce ions substituting Fe ions in the hematite structure. For x=0.5, Mössbauer spectra fitting required the addition of a quadrupole-split doublet, representing Fe substituting Ce in the CeO2 lattice. We evidenced this transition using our recently developed method for precise determination of the recoilless fraction in a single room-temperature transmission Mössbauer measurement of a two-absorber sample. We observed the occurrence of a minimum in the values of the recoilless fraction for t=4 hours of milling, followed by a further decrease of the f factor due to the appearance of nanoparticles in the system.
Magnetization and Magnetotransport Properties of Thermally Evaporated Co-Sn-Co Trilayer
Authors: Chiolerio Alessandro , Allia Paolo , Coisson Marco , Tiberto Paola
Published: April 2011

We report on growth, morphology and magnetic behavior of the pseudo spin-valve (PSV) Si/Co(15 nm)/Sn(50 nm)/Co(15 nm). Thermal evaporation was chosen as experimental deposition technique for its versatility and cost effectiveness. Magnetisation and magnetotransport measurements performed at low temperature showed that the sample has a complex behaviour related to the different morphology and thickness of the outer Co layers. Combining magnetic and magnetotransport data, a model based on three magnetic phases has been developed, associating them to the Co underlayer, to the Co cap layer and to possible nanometre-sized Co islands embedded in the Sn layer, respectively. A three-phase model coherently explains both magnetisation and magnetoresistance datasets.
Development of Strategies to Improvement Ordering and Perpendicular Alignment of Cylinder Phase Block Copolymers Used as Templates for Bit Patterned Media
Authors: Garrett Seth , Franco Vincent , Snowden Timothy , Redden Chris , Warke Vishal , Bakker Martin Gerard
Published: April 2011

Bit patterned media, including media fabricated with a gradient in composition, is being developed as a potential path to higher information storage density. The noise level in such media is significantly impacted by the precision of the ordering of the individual bits and by the narrowness of their size distribution. Block copolymers that phase separate on the appropriate length scale are one method of pattern generation that is receiving considerable attention. For cylinder forming block copolymer phases the ordering and degree of perpendicular alignment is largely determined by the matching of the substrate surface to the block copolymer. If the chemical properties of the substrate surface match the average for the block copolymer, then thin films of the block copolymer align perpendicularly on annealing. Although there are a number of examples where the substrate surface fortuitously matches the block copolymer, in general an orienting layer is necessary to provide the appropriate match. The most popular approach has been to synthesize a random copolymer with the same average composition as the block copolymer. In order to produce suitably thin orienting layers it has been necessary to chemically tether the random copolymer to the substrate. Previously used chemistry has not been suitable for noble metal substrates such as platinum. We have been developing an alternate approach using thiol functional groups which we anticipate will be more suitable for Pt capped substrates.
Stress Dependence of Crystal Structure of Polycrystalline BiFeO3 Thin Films on Membrane Structure Prepared by Pulsed Laser Deposition
Authors: Nakashima Seiji , Ricinschi Dan , Nakamura Yoshitaka , Okuyama Masanori , Fujisawa Hironori , Shimizu Masaru
Published: April 2011

An Influence of stress of crystal structure of polycrystalline BiFeO3 (BFO) thin film on membrane structure has been investigated. To confirm the stress dependence of the crystal structure, reciprocal space mapping measurement of polycrystalline BFO thin films on Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (625 μm) plate substrate and Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (15 μm) membrane substrate have been performed. These BFO thin films have been prepared by pulsed laser deposition (PLD). The obtained BFO thin films were polycrystalline and mainly oriented to (001) and (110) plane. From reciprocal space mapping measurement, (110) oriented BFO grains on Pt/TiO2/SiO2/Si (15 μm) membrane substrate were expanded perpendicularly to the film plane about 0.15% and compressed in parallel to the film plane about 0.7% comparing to that on Pt/TiO2/SiO2/Si (625 μm) plate substrate. And (001) oriented BFO grains on the Pt/TiO2/SiO2/Si membrane substrate were expanded about 0.20% perpendicularly to the film plane and compressed about 1.3% in parallel to the film plane comparing to that on Pt/TiO2/SiO2/Si (625 μm) plate substrat
Microscopic Mechanism and Domain Formation in the Paraelectric to Ferroelectric Phase Transitions in BaTiO3
Authors: Pasciak Marek , Leoni Stefano
Published: April 2011

A design approach to ferroelectric materials critically depends on an accurate description of the microscopic features associated with paraelectric-to-ferroelectric phase transitions. The fine structures of domains, domain walls, and domain boundary dynamics as well as a precise understanding of local atomic displacements can be accessed using adequate potential models based on ab initio calculations and advanced molecular dynamics simulations. For BaTiO3 a complex scenario of microscopic domains in the paraelectric (cubic) phase and in the ferroelectric (tetragonal) phase is obtained. Therein, the static and dynamic role of domain/antidomain features, as well as their dependence on Ti displacements around the <111> manifold is clearly emerging.
Characteristics of BST Capacitors with Aluminum Electrode and Iridium Oxide Barrier Layers
Authors: Kalkur Thottam , Troung Troung
Published: April 2011

The high frequency operation of BST capacitors necessitates the development of low series resistance electrodes. As an alternative to platinum, DC magnetron sputtered IrO2/Aluminum top electrode metallization for BST capacitors has been proposed. The capacitance voltage characteristics of BST capacitors did not change significantly due to the deposition of aluminum on iridium oxide. Post annealing in nitrogen environment shows that IrO2/Al metallization does not degrade annealing temperature up to 450 oC.
X-ray Analysis of Strain Relaxed Domain Structure in (100)/(001)-oriented epitaxial PbTiO3 thick films grown on (100)SrTiO3 substrates
Authors: Funakubo Hiroshi , Kim Yong Kwan , Yokoyama Shintaro , Ikariyama Rikyu , Funakubo Hiroshi , Streiffer S. K. , Nishida Ken , Saito Keisuke
Published: April 2011

Crystal structure of epitaxially grown (100)/(100)-oriented PbTiO3 films on (100)SrTiO3 substrates with 3.8 μm in thickness was investigated by the XRD reciprocal space mapping techniques. The observed poles of PbTiO3004, 400, 204, 402 and 420 scans can be successfully explained using the model consisting with the one type of (001) domain and three types of (100) domains in good agreement with the estimation from the scanning probe microscopy in conjunction with the in-plane and out-of plain XRD analysis.
Ferroelectric Thin Films Grown on Base-Metal Foils for Embedded Passives
Authors: Ma Beihai , Kwon Do-Kyun , Narayanan Manoj , Balachandran U.
Published: April 2011

Development of electronic devices with higher performance and smaller size requires the passive components to be embedded within a printed wire board (PWB). The “film-on-foil” approach is the most viable method to fabricate suitable passive components. We have deposited high-permittivity thin films of ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) on base metal foils by chemical solution deposition. These capacitors could be embedded into PWBs. However, formation of a parasitic low-permittivity interfacial layer of nickel oxide during thermal processing of the PLZT films considerably reduces the capacitance density. Two approaches were taken to overcome the problem. In the first, a conductive buffer layer of lanthanum nickel oxide (LNO) was inserted between the PLZT film and the nickel foil to hinder the formation of deleterious interfacial oxide. In the second, high temperature processing was done under low oxygen partial pressure such that no interfacial oxide was formed. By these approaches, we have grown high-quality ferroelectric PLZT films on nickel and copper foils. With samples of PLZT grown on LNO-buffered Ni, we measured a dielectric constant of 1300 (at 25°C) and 1800 (at 150°C), leakage current density of 6.6 × 10−9 A/cm2 (at 25°C) and 1.4 × 10−8 A/cm2 (at 150°C), and breakdown field strength >1.2 MV/cm. With samples of PLZT on Cu, we obtained encouraging initial results of dielectric constant >450 and dielectric loss tan(δ) ≈0.04.
Effect of Diamagnetic A2+ Substitution on the Magnetic and Ferroelectric Properties of the Bi1−xAxFeO3 Multiferroics
Authors: Khomchenko V. A. , Kiselev D. A. , Vieira J. M. , Jian Li , Lopes A. M. L. , Pogorelov Y. G. , Araujo J. P. , Kholkin A. L.
Published: April 2011

Investigation of crystal structure, magnetic and local ferroelectric properties of the diamagnetically-doped Bi1−xAxFeO3 (A= Ca, Sr, Pb, Ba; x= 0.2, 0.3) ceramic samples has been carried out. It has been shown that the solid solutions have a rhombohedrally distorted perovskite structure described by the space group R3c. Piezoresponse force microscopy data have revealed the existence of the spontaneous ferroelectric polarization in the samples at room temperature. Magnetization measurements have shown that the magnetic state of these compounds is determined by the ionic radius of the substituting elements. A-site substitution with the biggest ionic radius ions has been found to suppress the spiral spin structure of BiFeO3 and to result in the appearance of weak ferromagnetism. The magnetic properties have been discussed in terms of doping- induced changes in the magnetic anisotropy.
Energy Harvesting From PZT Nanofibers
Authors: Shi Yong , Shi Yong
Published: April 2011

In this paper, we demonstrated that Lead Zirconate Titanate (PZT) nanofibers can be used to harvest energy from dynamic loading and mechanical vibration. PZT nanofibers were fabricated by electrospinning process. SEM image of PZT nanofibers has shown that the average diameter of these fibers is about 150nm, which can be tuned from 50nm to 200 nm by varying the composition and viscosity of the precursor for electrospining. Titanium substrate with ZrO2 layer was used to collect the PZT nanofibers for the demonstration of energy harvesting from dynamic loading. The largest output voltage is 170mV under 0.5% strain; the frequency of the output voltage is the same as that of the input loading. Silicon substrate with trenches was used to collect the nanofibers for energy harvesting from vibration. The output voltage generated from 150Hz sinusoid vibration source has peak voltages of 64.9mV and -95.9mV. These experimental results suggest that PZT nanofibers have great potentials for energy harvesting from environments and being used as nanogenerators. Further study is under the way to optimize the design and improve the efficiency.
Microwave Growth of ZnO Bulk Crystals
Authors: Cheng Jiping , Zhang Yunjin , Guo Ruyan
Published: April 2011

A novel approach for fabricating ZnO crystals using self-encapsulated microwave melt growth technique is developed, which permits idealized temperature profile for the nucleation of the ZnO crystals and their growth in a contamination-free environment. This paper reports that both un-doped ZnO and p-type doped ZnO (by P or Li:N doping) single crystals were successfully fabricated by this technique. The as-grown ZnO crystals were of light brown to clear in color depending on processing conditions. Their transparency and colorless form were restored after post-growth annealing in oxygen.