bluuebunny/crossref_metadata_2025_split huggingface dataset:
Resorcinol-Formaldehyde and Carbon Aerogel Microspheres
Authors: Alviso C. T. , Pekala R. W. , Gross J. , Lu X. , Caps R. , Fricke J. 
Published: April 2011

AbstractAerogels are a unique class of materials possessing an open-cell structure with ultrafine cells/pores (<100nm), high surface area (400–1100 m2/g), and a solid matrix composed of interconnected particles, fibers, or platelets with characteristic dimensions of 10nm. Although monolithic aerogels are ideal candidates for many applications (e.g. transparent window insulation), current processing methods have limited their introduction into the commercial marketplace. Our research focuses on the formation of resorcinol-formaldehyde (RF) aerogel microspheres which offer an attractive alternative to monolith production. An inverse emulsion polymerization is used to produce these spherical gel particles which undergo solvent exchange followed by supercritical drying with carbon dioxide. This process yields aerogel microspheres (10–80μ diameter) which can be used as loosely packed powders, compression molded into nearnet shapes using a polymer binder, or used as additives in conventional foaming operations to produce new aerogel composites with superior thermal properties. The emulsification procedure, thermal characterization, mechanical properties, and potential applications of RF aerogel microspheres will be discussed.
Direct Synthesis of Acidic Aluminosilicate Mesoporous Molecular Sieves
Authors: Mokaya Robert , Jones William 
Published: April 2011

AbstractA simple and versatile synthetic route, whereby primary amine surfactants are the template in the assembly of aluminosilicate inorganic species, is used to prepare aluminosilicate mesoporous molecular sieves in which Brønsted acidity is generated by simply calcining the as-synthesised material. Al incorporation is accompanied by charge-balancing protonated amine molecules. Si and Al are incorporated into the mesoporous framework to yield materials with textural properties similar to those of MCM-41 but with substantially higher Brønsted acidity.
Periodic Mesoporous Silica Gels
Authors: Anderson M. T. , Martin J. E. , Odinek J. G. , Newcomer P. , Wilcoxon J. P. 
Published: April 2011

AbstractWe have synthesized monolithic particulate gels of periodic mesoporous silica by adding tetramethoxysilane to a homogeneous alkaline micellar precursor solution. The gels exhibit 5 characteristic length scales over 4 orders of magnitude: fractal domains larger than the particle size (>500 nm), particles that are ˜150 to 500 nm in diameter, interparticle pores that are on the order of the particle size, a feature in the gas adsorption measurements that indicates pores ˜10–50 nm, and periodic hexagonal arrays of ˜3 nm channels within each particle. The wet gel monoliths exhibit calculated densities as low as ˜0.02 g/cc; the dried and calcined gels have bulk densities that range from ˜0.3–0.5 g/cc. The materials possess large interparticle (˜1.0–2.3 cc/g) and intraparticle (˜0.6 cc/g) porosities.
The Effect of Heat Generation on the Development of Vermicular α-Al 2O3 in Alumina Films
Authors: Bagwell R.B. , Messing G.L. 
Published: April 2011

AbstractThe transformation of transition aluminas (i.e. θ-A12O3) to α-A12O3 results in an interconnected, porous microstructure that is commonly described as ‘wormy’ or‘vermicular’. The effect of heat generated during the exothermic transformation at the θ-Al2O3/α-Al2O3 interface on the development of the vermicular α-A12O3 morphology was analyzed in boehmite-derived thin films. The vermicular structure may arise in an analogous manner to the thermal dendrites formed in metals during solidification. However, the analysis shows that heat generation and transfer at the interface does not play a significant role in the development of α-A12O3 dendrites.
Boehmite and Yttrium Oxide Coatings on Silicon Nitride From Aqueous Sols
Authors: Buchta Michael , Shih Wei-Heng 
Published: April 2011

AbstractTo improve the processing of silicon nitride, boehmite and yttrium oxide were coated on silicon nitride particles by an aqueous sol-gel method. It is shown that boehmite and Y2O3 can be coated on Si3N4 particles from aqueous solutions. However, the Y2O3 coating is not as complete as boehmite coating. The coating of a yttria coating followed by a boehmite coating was attempted and the TEM showed a coating twice as thick as the Y2O3 or AlOOH coating. Hydrothermal treatment of yttrium nitrate hydrous hydroxide results in the formation and growth of Y(OH)3 fibers which can be calcined and transformed into Y2O3 fibers at 500°C.
Dielectric and Ferroelectric Properties of Pulsed Laser Deposited Strontium Barium Niobate Thin Films
Authors: Liu Y. , Ong C.W. , Choy C.L. , Chan P.W. 
Published: April 2011

AbstractThe dielectric and ferroelectric properties of pulsed laser deposited strontium barium niobate (SBN) thin films were investigated. The samples were prepared using a Q-switched Nd:YAG laser with a wavelength of 355 nm and a fluence of 8 J cm−2. The oxygen ambient pressure and substrate temperature were set at 50 mTorr and 700 °C, respectively. The measurements of x-ray diffraction show that the films have tungsten-bronze- type structure. Pt/SBN/Pt capacitor structure was made on (111) silicon wafer to perform the ferroelectric and dielectric measurements. From the observations of the P-E loops, the saturation polarization, remanent polarization and coercive field at 25°C are equal to 40.7 μC cm−2, 32.5 μC cm−2 and 3.8 kV cm−1. The shape of the P-E loop becomes slimmer at temperatures above 150 °C, indicating that a ferroelectric-to-paraelectric transition occurs. The dielectric constant and loss tangent of the films at 10 kHz were found to be equal to 240 and 0.4, respectively. The saturation and remanent polarization remain almost unchanged after 109 switching cycles, indicating that pulsed laser deposited SBN films have good fatigue endurance.
Multilayer Lead Zirconate Titanate and Barium Titanate Ferroelectric Capacitors
Authors: Chang L.H. , Anderson W.A. 
Published: April 2011

AbstractFerroelectric PbZrxT1−xO3 (PZT) thin films have been deposited on Pt coated Si substrates by if magnetron sputtering. The optimized processing condition to obtain proper stoichiometric PZT, the desired ferroelectric perovskite phase, and better dielectric properties was demonstrated using a PZT target with Pb(Zr+Ti) ratio of 1.2 and depositing at 350°C, followed by thermal treatment at 620°C for 30 min. The structural and electrical properties of the PZT layer were further improved by fabricating a novel multilayer structure which combined the PZT with the nanolayer BaTiO3. The leakage current density was reduced from 2×10−7 A/cm2 for the single layer structure to 2×10−9 A/cm2 for the multilayer structure at a field of 4×105 V/cm, while maintaining a high relative effective dielectric constant of 442. The relative dielectric constant of the PZT film in the multilayer structure was calculated to be about 880.
Influence of Strontium Concentration on the Microstructure and Electrical Properties of Sol-Gel Derived Barium Strontium Titanate Thin Films
Authors: Gust M.C. , Momoda L.A. , Mecartney M.L. 
Published: April 2011

AbstractBaxSrl−xTiO3 thin films with varying Sr concentration were prepared on Pt coated Si substrates using methoxypropoxide based alkoxide precursors. Films were crystallized by heat treating at 700°C for 30 minutes in an oxygen atmosphere after deposition of each layer. Film thickness ranged from 230 to 260 nm. No evidence of tetragonality was observed in any of the compositions. Films with higher Sr concentrations had a larger average grain size, larger grain size distribution, and increased (111) orientation on (111) oriented Pt. The highest dielectric constant of ˜400 was found for Ba 0.5Sr0.5TiO3, although no direct correlation could be made between the composition and dielectric properties.
Influence of PbTiO3 Buffer Layers on Microstructural Properties of Pb(Zr,Ti)O3 Films Deposited by Sputtering
Authors: Cattan E. , Roma R. , Velu G. , Jaber B. , Remiens D. , Thierry B. 
Published: April 2011

AbstractPb(Zr,Ti)O3 (PZT) films with very thin PbTiO3 (PT) buffer layers inserted between the film and the Si/SiO2/Ti/Pt substrate were grown by a rf magnetron sputtering technique. The Xray diffraction patterns and the surface morphology of PT as a function of the thickness, in the range of 20 to 400 Å, were first investigated. Such a marked contrast in morphological features was not observed when the thickness was above 400 Å. The films were grown in-situ at 500°C. We found modification of the PT orientation when its thickness varied between 20 Å and 400 Å. This implies a gradual evolution of the lattice parameters in the nucleation stage of PT films. Insertion of these buffer layers was found to exert marked effects. Up to 400 Å the PT was grown with a [100] preferred orientation. The orientation of PZT could be controlled by changing the thickness and then the orientation of PT. The results will be discussed in terms of the effects of the buffer layer on the crystalline structure and the surface morphology of PZ
Characterization of Mis Capacitor of Bst Thin Films Deposited on Si by Rf Magnetron Sputtering
Authors: Paek S.H. , Park C.S. , Won J.H. , Lee K.S. 
Published: April 2011

AbstractThe application of high dielectric (Ba, Sr)TiO3 [BST] thin films for Metal-Insulator- Semiconductor(MIS) capacitors was investigated. BST thin films were deposited on p-Si(100) substrates by the RF magnetron sputtering with temperature range of 500–600 °C. We examined the characteristics of MIS capacitor with various oxygen pressure, substrate temperature and (Ba+Sr)/Ti ratio. The dielectric properties of MIS capacitors consisting of AI/BST/SiO2/Si sandwich structure were measured for various conditions. The charge state densities of the MIS capacitors were determined by high frequency (1 MHz) C-V measurement. Also, current-voltage characteristics of the MIS capacitor were investigated. In order to reduce the leakage current in MIS capacitor, high quality SiO2 layer was grown on bare p-Si substrate by thermal oxidation. By applying SiO2 layer between BST thin films and Si substrate, low leakage current of 10−10 order was observed. Futhermore, the leakage current showed the dependence on the oxygen concentration in plasma gas and the (Ba+Sr)/Ti ratio. Also, the BST MIS structure showed relatively high capacitance even though it is the combination of high-dielectric BST thin films and SiO2 layer. By C-V measurement, the polarity of effective oxide charge changed with the oxygen concentration in plasma gas and (Ba+Sr)/Ti ratio of sputtering target.
Synthesis and Mechanical Properties of Niobium Films by Ion Beam Assisted Deposition
Authors: Ji H. , Was G. S. , Jones J. W. 
Published: April 2011

AbstractMechanical properties of niobium thin films are studied by controlling the microstructure, texture and residual stress of the films using ion beam assisted deposition (IBAD). Niobium films were deposited onto (100) Si substrates and their microstructure, texture and residual stress were measured as a function of ion energy and R ratio (ion to atom arrival rate ratio). The grain sizes of these films ranged from 20 nm to 40 nm and no effect of ion bombardment was observed. All the films have strong (110) fiber texture, but the in-plane texture is a strong function of the incident angle, energy and flux of the ion beam. Results show that while the degree of the texture increases with increasing ion energy and flux, it is also a strong linear function of the product of the two. The residual stress of the films was measured by a scanninglaser reflection technique. As a function of normalized energy, the stress is tensile for En < 30 eV/atom with a maximum of 400 MPa at about 15 eV/atom. It becomes compressive with increasing normalized energy and saturates at - 400 MPa for En > 50 eV/atom. Both PVD (physical vapor deposition) and IBAD films have a hardness of about 6 GPa at shallow depth measured by nanoindentation. The different stress state may be responsible for the 15%difference on hardness observed between the PVD and IBAD films.
Time Dependent Stress Fields Ahead of the Interface Cracks in Creep Regime
Authors: Biner S. B. 
Published: April 2011

AbstractIn this study the behavior of stationary interface cracks in layered materials at creep regime in plane-strain condition and pure opening dominated mode-I load state was studied numerically. The results indicate that the introduction of a transitional layer to the interface of the elastic-creeping bimaterials significantly elevates the stress values ahead of the interface cracks under identically applied load levels at creep regime.
Multi-Phase Functionally Graded Materials for Thermal Barrier Systems
Authors: Jackson M. R. , Ritter A. M. , Gigliotti M. F. , Kaya A. C. , Gallo J. P. 
Published: April 2011

AbstractMetallic candidates for functionally graded material (FGM) coatings have been evaluated for potential use in bonding zirconia to a single crystal superalloy. Properties for four materials were studied for the low-expansion layer adjacent to the ceramic. Ingots were produced for these materials, and oxidation, expansion and modulus were determined. A finite element model was used to study effects of varying the FGM layers. Elastic modulus dominated stress generation, and a 20–25% reduction in thermal stress generated within the zirconia layer may be possible.
Hardness and Deformation Mechanisms of Highly Elastic Carbon Nitride Thin Films as Studied By Nanoindentation
Authors: Hainsworth S. V. , Sjöström H. , Page T. F. , Sundgren J-E. 
Published: April 2011

AbstractCarbon nitride (CNx) thin films (0.18<x<0.43), deposited by magnetron sputtering of C in a N2 discharge, have been observed to be extremely resistant to plastic deformation during surface contact (i.e. exhibit a purely elastic response over large strains). Elastic recoveries as high as 90% have been measured by nanoindentation. This paper addresses the problems of estimating Young's modulus (E) and hardness (H) in such cases and shows how different strategies involving analysis of both loading and unloading curves and measuring the work of indentation each present their own problems. The results of some cyclic contact experiments are also presented and possible deformation mechanisms in the fullerene-like CNx structures discussed.
Viscoelastic Properties of Healthy Human Artery Measured in Saline Solution by AFM-Based Indentation Technique
Authors: Lundkvist A. , Lilleodden E. , Siekhaus W. , Kinney J. , Pruitt L. , Balooch M. 
Published: April 2011

AbstractUsing an Atomic Force Microscope with an attachment for indentation, we have measured local, in vitro mechanical properties of healthy femoral artery tissue held in saline solution. The elastic modulus (34.3 kPa) and viscoelastic response (τɛ = 16.9 s and τσ = 29.3 s) of the unstretched, intimal vessel wall have been determined using Sneddon theory and a three element model (standard linear solid) for viscoelastic materials. The procedures necessary to employ the indenting attachment to detect elastic moduli in the kPa range in liquid are described.
Micro-Indentation using Strain Rate Sensitivity to Examine Deformation of Polymeric and Metallic Surface Layers
Authors: Newson W. R. , Diak B. J. , Saimoto S. 
Published: April 2011

AbstractA sensitive method to characterize the inelastic deformation of solids is to measure the thermodynamic response of the deforming volume by applying an inelastic strain rate change. Using the step ramp technique on a displacement controlled micro-indentor with Berkovich tip, the apparent activation volumes were determined for linear low density polyethylene, and eutectic Pb-Sn solder for depths less than 10 μm. The results show that the activation volume is a unique measure of a given microstructure.
Low Pressure OMVPE Grown Compressive Strained Ingaas QWS Surrounded by Tensile Strained Ingaas Spacers
Authors: Laboutine O. A. , Choo A. G. , Kim S. H. , Kim N. H. , Park H. S. , Park Y. J. , Kim T. I. 
Published: April 2011

AbstractThe photoluminescence (PL) measurement of unstrained and compressive strained InxGa1−xAs quantum wells (QWs) demonstrated that the interfaces had a roughness of 1 to 2.5 monolayers (ML). The spacer layers of tensile strained InyGa1−yAs were inserted between a compressive strained In0.7Ga0.3As QW and the InP barrier layers. PL spectra of the In0.7Ga0.3As/InyGa1−yAs/InP structures grown at 605°C became significantly narrower with increasing Ga content in the spacer layers above (1−y)=0.6. The PL line width of the In0.7Ga0.3As/In0.3Ga0.7As alternatingly strained multiple quantum well (MQW) structures gradually decreased when the number of periods and the deposition temperature increased. The structure, consisting of 4 periods grown at 635°C, exhibited a PL line width of about 4 meV which corresponded to the QW thickness fluctuation of 0.5 ML. The superlattice satellites of X-ray rocking curves of MQW structures were better defined under an envelope corresponding to the tensile strained layers.
Epitaxial Growth and Structure of Highly Mismatched Oxide Films with Rock-salt Structure on MgO
Authors: Langjahr P. A. , Wagner T. , Lange F. F. , Ruole M. 
Published: April 2011

AbstractCaO thin films were grown on (001) MgO single crystal substrates by a chemical solution deposition method to study the influence of a relatively high lattice mismatch (14%) on the epitaxial growth. In order to minimize an influence of a different crystal structure and chemistry between film and substrate, film and substrate were chosen to have the same structure (NaCl) and a similar chemistry. The films were heat treated until they broke up into single crystal islands on the MgO substrate. X-ray pole figure analysis and TEM observations of the CaO-films showed that most of the grains had a single out-of-plane orientation (111)CaO || (001)MgO, corresponding to two non-redundant, symmetry related in-plane variants [1 10](111)CaO || [110](001)MgO and [110](111)CaO || [110](001)MgO. A near coincidence site lattice (NCSL) model could be constructed for the interface, suggesting good lattice and charge matching for the observed orientation relations. The mechanisms and energetics leading to the experimentally observed orientation relations are discussed.
Effect of Boron Doping on the C49 TO C54 Phase Transformation in Ti/Si (100) Bilayers
Authors: Libera M. , Quintero A. 
Published: April 2011

AbstractWe have demonstrated that the formation of C54 TiSi2 on Boron-doped single crystal silicon substrates, under RTA annealing conditions in a Nitrogen ambient, leads to a thicker TiN capping surface layer, thinner silicide layer, higher C49 to C54 transformation temperature and greater interface roughness compared to C54 TiSi 2 formation on undoped single crystal silicon substrates. Titanium films 32 nm thick were deposited on undoped and boron-doped single crystal silicon substrates. The films were annealed at 3 /C/isn nitrogen to final quenching temperatures between 500 °C and 900 TC. Ex-situ four point probe sheet resistance, cross sectional transmission electron microscopy (XTEM), high resolution transmission electron microscopy (HRTEM) and x-ray diffraction (XRD) were used to analyze the resulting TiN on TiSi2 bilayer. The C49 to C54 transformation occurs circa 760 TC and 810 TC for the undoped and boron-doped cases respectively. HRTEM observations reveal a thick 20 nm TIN layer on the C54 TiSi2 film in the boron-doped case but only fine dispersed TiN particles embedded on the top of the silicide in the undoped case. It was observed that the resultant silicide in the boron-doped case was thinner and the TiSi2 /Si(100) interface is rougher. XRD and TEM analysis show that in the boron doped case, there is a preferred C54 (040) orientation compared to a random orientation for the undoped case.
In-Situ Tem Characterization of Whiskers on Al Electrodes for Thin-Film Transistors
Authors: Tsujimoto K. , Tsuji S. , Saka H. , Kuroda K. , Takatsuji H. , Suzukip Y. 
Published: April 2011

AbstractThe recent attention paid to stress migration of aluminum (Al) electrodes in thin-film transistor liquid crystal display (TFT-LCD) applications indicates that wiring materials with low electrical resistivities are of considerable interest for their potential use in higher-resolution displays. In this paper, we firstly describe how as-grown Al whiskers on Al electrodes fabricated on a LCD-grade glass substrate can be characterized by means of a high-voltage transmission electron microscope (HV-TEM) operated at 1 MV. The whiskers ranging from 300 to 400 nm in diameter are sufficient to be transparent to high-voltage electrons. This allows detailed observation of whisker characteristics such as its morphology and crystallography. In most cases, the as-grown Al whiskers in our study had straight rod shapes, and could be regarded as single crystals. Secondly, we report on the in-situ fabrication and observation of Al whiskers at elevated temperature with the HV-TEM. Since relatively thick TEM samples (up to about 1 mm) can be set on a sample holder in the HV-TEM, various growth stages of Al whiskers can be investigated under various heating conditions. Finally, we demonstrate a TEM sample preparation method for the cross-section of an individual Al whisker, using focused ion beam (FIB) etching. This technique makes it possible to reduce the thickness of an Al whisker close to the root. Both bright- and dark-field TEM images provide nanostructural information on the whisker/Al thin-film interface.
Correlation Between Structural and Electronical Properties Of Strained V2O3 Thin Films
Authors: Schuler H. , Klimm S. , Horn S. 
Published: April 2011

AbstractEpitaxial thin films of V2O3 were grown on c-axis oriented sapphire substrates by reactive e-beam evaporation. The high orientation and epitaxy is shown by low energy electron and x-ray diffraction. The microstucture of the films was investigated by AFM imaging. The measurements show an island growth mode with a temperature dependent increase of the grain size. At a growth temperature of above 700°C a change of the surface structure is observed, which produces much more structured and irregular shaped crystallites. High temperature growth also causes changes in the electronical properties, due to an increased stress in the films as measured by XRD. The metal-insulator transition (MIT) and the properties of the metallic phase of the films were determined mainly by temperature dependent electrical resistivity measurements. The metallic properties are distorted in films grown at low temperature (T<500°C) probably due to defects, dislocations and grain boundaries. Favorable growth conditions for films showing a single crystal like MIT were found in a narrow temperature range around 550°C. For higher growth temperatures (T>650°C) metallic behavior at high temperatures is suppressed by an in plane tensile stress. The electronic properties of such films are similar to those of chromium doped V2O3. The relation between growth conditions, structural properties and resulting electronic properties is discussed.