bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effects of the Precursor Solutions on the Structure and the Properties of Sol-Gel Derived Bst Thin Films
Authors: Ryoo Jeong Seon , Kang Seong Jun , Yoon Yung Sup 
Published: April 2011

AbstractWe have studied the effects of solvents and additives in the precursor solutions on the characteristics of barium strontium titanate (BST) thin films. The solution having two solvents, ie. acetic acid for barium acetate and strontium acetate and 2-methoxyethanol for titanium isopropoxide and also having an additive of ethylene glycol shows good stability and remains homogeneous even after a month of ageing. It produces excellent BST thin film without cracks. Dielectric constant, loss tangent at 10kHz and leakage current density at 3V of the BST(70/30) thin film made from this solution are 339, 0.052 and 13.3μA/cm2, respectively. We have also found that a Ta layer is a better diffusion barrier against Si than a Ti layer and is functional up to 750°C.
Mechanics of Metal Matrix Laminates
Authors: Teply J. L. 
Published: April 2011

AbstractThe mechanics of fracture and fatigue crack propagation of ARALL Laminates and Discontinuously Reinforced SiC Aluminum (DRA) laminates is studied. In these two, supposedly different, material systems the fracture and fatigue performance is closely related to their capability to delaminate. The delamination shape, length, rate of growth, effect on fatigue and fracture toughness are analyzed in the both lamination systems. The similarities between these two lamination systems fatigue and fracture failure modes are determined and summarized. Design for compression is also mantioned.
Fracture of Laminated and In Situ Niobium Silicide-Niobium Composites
Authors: Rigney J. D. 
Published: April 2011

AbstractThe mechanisms contributing to the fracture resistance of refractory metal intermetallic composites containing a BCC metallic phase (niobium) were investigated using model Nb-Si laminates and in situ composites. The controlling influence of ductile phase yield strength and fracture behavior were investigated by varying laminate processing parameters, and/or altering temperatures and applied strain rates during fracture experiments on all materials. The fracture behavior of “ductile” constituents were found to be influenced by phase grain size, solid solution content, constraint (as influenced by interfacial bond strengths), and the testing condition (high strain rates and low temperatures). The measured fracture resistance, when compared to theoretical models, was shown to be controlled by the “toughness” of the “ductile” phase and independent of the fracture behavior promoted (cleavage and ductile). The loss in ductility due to cleavage by high constraint, high strain rates and/or low temperatures was compensated by high yield and cleavage fracture stresses in order to provide a level of toughening similar to that contributed by ligaments which failed with lower yield stresses and greater strains.
Fatigue Crack Growth in Aluminum Laminate Composites
Authors: Hoffman P. B. , Carpenter R. D. , Gibeling J. C. 
Published: April 2011

AbstractFatigue crack growth has been measured in a laminated metal composite (LMC) consisting of alternating layers of AA6090/SiC/25p metal matrix composite (MMC) and AA5182 alloy. This material was tested in both as-pressed (F temper) and aged (T6 temper) conditions. Corresponding crack growth measurements were made in self-laminates of both the MMC and AA5182 materials to examine the role of the interfaces.The LMC-T6 material has a significantly higher fracture toughness than its MMC constituent but exhibits only modest improvements in nominal fatigue crack growth resistance and a lower nominal threshold. The LMC-T6 shows high levels of crack closure which reveal poor intrinsic crack growth resistance. Self-laminated AA6090/SiC/25p MMC in the F temper has lower microhardness, lower strength and superior intrinsic crack growth resistance compared to this material in the T6 condition. The fatigue fracture surface of T6 temper MMC remains macroscopically smooth despite the development of a large amount of crack closure. The selflaminated AA5182 exhibits a significant improvement in fatigue crack growth resistance after heat treatment and a corresponding change in crack morphology from smooth to very rough. This change leads to a large increase in roughness-induced closure. The effects of heat treatment are attributed to differences in interfacial strength.
Evaluation of Impact Damage Resistance in Laminated Composites Using Resins with Different Crosslink Densities
Authors: Lesser A. J. 
Published: April 2011

AbstractIt is generally recognized that fiber-reinforced laminated composites are susceptible to damage resulting from low-velocity impacts. Over recent years, many strategies have been devised to increase the fracture toughness of resin matrix materials with the aim of improving the composites overall resistance to impact damage. One popular strategy for enhancing the fracture toughness of thermosets involves increasing its molecular weight between crosslinks which, in turn, enhances the resins ductility. In this paper, we investigate the efficiency of this toughening approach with regard to resisting damage in composite laminates subjected to lowvelocity impacts. Generic damage characteristics and mechanisms are reviewed and it is shown that two different events occur during the impact process. First, the laminate experiences a local failure which resembles a Hertzian fracture process followed by subsequent delamination between the plies. Results are presented illustrating the effects that systematically increasing the molecular weight between crosslinks of the resin has on each of these mechanisms. Also, the residual compressive strength (Compression After Impact) of the laminates made with these resins is presented.
Brick Structure Improved by Using Cement Mortar Containing Short Carbon Fibers
Authors: Zhu Mingguang , Chung D. D. L. 
Published: April 2011

AbstractThe addition of short carbon fibers in the optimum amount of 0.5% of the cement weight to mortar increased the brick-to-mortar bond strength by 150% under tension and 110% under shear when the gap between the adjoining bricks was fixed, and by 50% under tension and 44% under shear when the gap between the adjoining bricks was allowed to freely decrease due to the weight of the brick above the joint. This effect is attributed to the decrease of the drying shrinkage by the fiber addition. The drying shrinkage decrease was particularly large at 2 to 24 h of curing. At 24 h, the shrinkage was decreased by 50% by the addition of fibers in the amount of 0.5% of the cement weight. Fibers in excess of the optimum amount gave less bond strengthening due to increased porosity in the mortar.
Young's Modulus and Density of thin TiO2 Films Produced by Different Methods
Authors: Ottermann C. R. , Kuschnereit R. , Anderson O. , Hess P. , Bange K. 
Published: April 2011

AbstractThe Young's modulus and density are analyzed for 280 and 500 nm thick TiO2 layers deposited by reactive evaporation (RE) and ion plating (IP) by means of surface acoustic wave spectroscopy (SAWS) and grazing incidence X-ray reflection spectroscopy (GIXR). The layers are amorphous or polycrystalline, and have densities between 2.9 g/cm3 and 3.8 g/cm3, depending on the deposition conditions. The measured Young's moduli vary between 65 GPa for RE films and 147 GPa for IP layers. They are independent of film thickness, but correlate with the density. A change of the Young's modulus due to the phase transition from amorphous to anatase is described, which occurs at temperatures above 210°C.
Tribological Properties of Nitrogen Implanted and Boron Implanted Steels
Authors: Kern K. T. , Walter K. C. , Fayeulle S. , Griffin A. J. , Kung H. , Lu Y. , Nastasi M. , Tesmer J. R. 
Published: April 2011

AbstractSamples of steel with high chrome content were implanted separately with 75 keV nitrogen ions and with 75 keV boron ions. Implanted doses of each ion species were 2-,4- and 8 × 1017 /cm2. Retained doses were measured using resonant non-Rutherford Backscattering Spectrometry. Tribological properties were determined using a pin-ondisk test with a 6-mm diameter ruby pin with a velocity of 0.94 m/min. Testing was done at 10% humidity with a load of 377g. Wear rate and coefficient of friction were determined from these tests. While reduction in the wear rate for nitrogen implanted materials was observed, greater reduction (more than an order of magnitude) was observed for boron implanted materials. In addition, reduction in the coefficient of friction for high-dose boron implanted materials was observed. Nano-indentation revealed a hardened layer near the surface of the material. Results from grazing incidence x-ray diffraction suggest the formation of Fe2N and Fe3N in the nitrogen implanted materials and Fe3B in the boron implanted materials. Results from transmission electron microscopy will be presented.
Copper Grown Diamond Films
Authors: Pereira E. , Fan Qi Hua , Gracio J. 
Published: April 2011

AbstractDiamond has been synthesised on copper using Microwave Plasma Chemical Vapour Deposition (MPCVD). The effect of substrate pre-treatment including different polishing and cleaning on diamond nucleation was investigated. It has been found that the residues from the polishing process played an important role in the diamond nucleation. Diamond films synthesised under optimised conditions presented a narrow 1332cm-1 Raman peak. During the ramp down procedure, diamond films usually cracked due to the large thermal mismatch between copper and diamond. To avoid this problem, the effect of growth temperature and deposition time was investigated and a two-step-growth method for stress relief is proposed.
Reversible Force-Resistivity Behavior of Thin Films of the TTF-Tcnq Family
Authors: Vollmann W. , Sonntag H.-U. 
Published: April 2011

AbstractThe electrical properties of vacuum sublimed thin films of TTF-TCNQ and its derivatives mainly are determined by electron barriers at grain boundaries. The electrical conductivity is thermal activated and exhibits a significant dependence on a force acting perpenticularly to the film plane. The sample resistance R decreases continiously with increasing force F. TCNQ thin films on steel show a similar R-F relation. The effect has been observed already at forces of 1 N, but also up to about 60 kN. An explanation of these phenomena is given by a grain boundary limited hopping mechanism with pressure dependent potential barrier width and height. Morphology investigations by SEM support the model.
The Nucleation of Crystalline TiSi2 Phases from Amorphous TiSix Layers and Interfacial Layers
Authors: Tung R. T. , Fujii K. , Kikuta K. , Chikaki S. , Kikkawa T. 
Published: April 2011

AbstractSilicide reaction between co-deposited TiSix layers and Si was studied. It was shown that an amorphous TiSix layer, with x − 0.5–1, deposited between amorphous Si and the Ti film led to a significant reduction in the observed C49→C54 TiSis transformation temperature. Amorphous TiSix layers generated by the pre-deposition of Ti and pre-annealing also enhanced the nucleation of the C54-TiSi2 phase. The efficacy of the interfacial TiSix layer was demonstrated on undoped and heavily doped n- and p-type α-Si, but was found to be absent on single crystal Si. Possible mechanisms of these phenomena are discussed.
Structural Transformations Due to Intermixing During Deposition oF Fe/Pt(001) Epitaxial Multilayers
Authors: Hufnagel T. C. , Kautzky M. C. , Ramaswamy V. , Leming A. , Clemens B. M. 
Published: April 2011

AbstractPrevious studies of the structure of epitaxial Fe/Pt(001) multilayers have shown that the structure of the Fe layers depends on the Fe layer thickness. For small thicknesses (< 12 Å) the Fe is fcc, while for greater thicknesses (> 22 Å) the Fe has a bcc structure. We speculated that this transition of the Fe structure is a result of intermixing with subsequently deposited Pt. We explore this transition further by examining superlattice satellite peaks around the (111) fundamental reflection, and by using grazing incidence x-ray scattering (GIXS) to examine the structure of epitaxial Fe/Pt(001) multilayers during sputter deposition. The GIXS observations show that the initial growth of Fe is in the bcc structure; thin bcc Fe layers are partially transformed to fcc by subsequent deposition of Pt. The transformation is thermodynamically favorable because the intermixed fcc phase has lower epitaxial mismatch and bulk chemical free energy than the bcc phase.
A Study on the Growth of a Ferroelectric Thin Film Using Ionized Cluster Beam Epitaxy Technique and the Application for Ulsi Fabrication
Authors: Lee Hyun Seok , Sung Man Young 
Published: April 2011

AbstractThe dielectric properties of Ba0.65Sr0.35TiO3(BST) films deposited by an electron beam assisted ionized cluster beam epitaxy (ICBE) technique were investigated. Highly (110) oriented BST films having a thickness up to 1, um have been successfully grown on a Si (100) substrate at 400°C using the electron beam assisted ICBE system with a plasma O2 source. It was found that the dielectric constant increases from 475 to 1191 with different process conditions. A BST film with a thickness of 500Å deposited at a substrate temperature of 400°C has a dielectric constant of 1191 and a leakage current of about 2.37×10-9 A/cm2. This shows the BST film can be applied to dielectrics of ULSI capacitors.
Grafted Metallized Particle Interconnect (G. M. P. I.)
Authors: Crotzer David R. , Wolf Thomas A. , IPD Augat 
Published: April 2011

AbstractAn electrical contact surface is described which combines the flexibility of a low resistance elastic interface with bonded conductive particles for penetration during compressive mating to metallic oxide layers. The processes for applying both technologies is described including the types of interfacial bonds provided. Both technologies permit high conductivity across the layers. Such technologies offer advantages for connectors requiring low normal forces, superior oxidative resistance to the environment, elastic conductors with the same resistance as bare copper, and high volume processing capabilities.The first layer of conductive coating includes grafting an elastomeric bridge from the primary surface to the outer layer of metal particles and flakes. The secondary outer coating involves deposition of sharp, hard, conductive particles onto the grafted surface. Each coating bonds to the other forming several layers outward from the primary elastomeric substrate.Product applications include a conductive elastic interface for interconnecting a BGA to a PCB via a socketed solution. The elastomeric interface overcomes co‐planarity issues associated with mating the BGA chip to a PCB. Compressive forces are reduced as compared to metal connectors providing lower total force for high I/O counts. Environmental constraints are reduced due to the durability of the elastomeric system.
Investigation of the Flow Behavior of Participate Filled Fluids
Authors: Driscoll T. E. , Li P. C. , Lehmann G. L. , Cotts E. J. 
Published: April 2011

AbstractUnderfill encapsulants, used in direct‐chip‐attachment (DCA) packaging of electronics, consist of an epoxy resin in which a high concentration of solid particles are suspended. As a fluid mixture key features of these encapsulants are their relatively large particle sizes and large particle‐to‐liquid density ratios (ρs/ρ0 ?2.4). Experiments have been conducted to characterize the flow behavior of model mixtures of negatively buoyant, spherical particles suspended in Newtonian liquids. Capillary flow in a parallel surface channel is used to simulate the underfill flow process. The effects of varying the channel spacing, particle size and liquid carrier are reported here. The flow behavior is contrasted with a linear fluid, effective viscosity model. Particle settling appears to be linked to the more complex behavior observed in both our model suspensions and measurements using an actual commercial encapsulant.
MOVPE GaN Gas-Phase Chemistry for Reactor Design and Optimization
Authors: Safvi S. A. , Redwing J. M. , Thon A. , Flynn J. S. , Tischler M. A. , Kuech T. F. 
Published: April 2011

ABSTRACTThe results of gas phase decomposition studies are used to construct a chemistry model which is compared to data obtained from an experimental MOVPE reactor. A flow tube reactor is used to study gas phase reactions between trimethylgallium (TMG) and ammonia at high temperatures, characteristic to the metalorganic vapor phase epitaxy (MOVPE) of GaN. Experiments were performed to determine the effect of the mixing of the Group III precursors and Group V precursors on the growth rate, growth uniformity and film properties. Growth rates are predicted for simple reaction mechanisms and compared to those obtained experimentally. Quantification of the loss of reacting species due to oligmerization is made based on experimentally observed growth rates. The model is used to obtain trends in growth rate and uniformity with the purpose of moving towards better operating conditions.
Reactive ION Beam Etching of GaN Grown By Movpe
Authors: Saotome K. , Matsutani A. , Shirasawa T. , Mori M. , Honda T. , Sakaguchi T. , Koyama F. , Iga K. 
Published: April 2011

ABSTRACTA dry etch technique using Cl2 based reactive ion beam etching (RIBE) has been developd for GaN-based semiconductor lasers. The etching rate of 350 − 1000 Å/min was obtained. This is applicable for micro fabrication of GaN based materials in the same way as used for other III-V group semiconductors. Furthermore, it is found that the surface damage of GaN layers induced by the RIBE-etch can be removed using ultra-violet assisted wet-etching using alkali solution. The PL intensity of damaged GaN layers is increased after the post-process wet-etching.
Comparison of Ni/Au, Pd/Au, and Cr/Au Metallizations for Ohmic Contacts to p-GaN
Authors: Trexler J. T. , Pearton S. J. , Holloway P. H. , Mier M. G. , Evans K. R. , Karlicek R. F. 
Published: April 2011

ABSTRACTReactions between electron beam evaporated thin films of Ni/Au, Pd/Au, and Cr/Au on p-GaN with a carrier concentration of 9.8 × 1016 cm−3 were investigated in terms of their structural and electronic properties both as-deposited and following heat treatments up to 600°C (furnace anneals) and 900°C (RTA) in a flowing N2 ambient. Auger electron spectroscopy (AES) depth profiles were used to study the interfacial reactions between the contact metals and the p-GaN. The electrical properties were studied using room temperature current-voltage (1-V) measurements and the predominant conduction mechanisms in each contact scheme were determined from temperature dependent I-V measurements. The metallization schemes consisted of a 500 Å interfacial layer of Ni, Pd, or Cr followed by a 1000 Å capping layer of Au. All schemes were shown to be rectifying as-deposited with increased ohmic character upon heat treatment. The Cr/Au contacts became ohmic upon heating to 900°C for 15 seconds while the other schemes remained rectifying with lower breakdown voltages following heat treatment. The specific contact resistance of the Cr/Au contact was measured to be 4.3×10−1 Ωcm2. Both Ni and Cr have been shown to react with the underlying GaN above 400 °C while no evidence of a Pd:GaN reaction was seen. Pd forms a solid solution with the Au capping layer while both Ni and Cr tend to diffuse through the capping layer to the surface. All contacts were shown to have a combination of thermionic emission and thermionic field emission as their dominant conduction mechanism, depending on the magnitude of the applied reverse bias.
Evolution of Ti Schottky Barrier Heights on n-Type GaN with Annealing
Authors: Hirsch Michèle T. , Duxstad Kristin J. , Haller E. E. 
Published: April 2011

ABSTRACTWe report the effect of mild annealing on Ti Schottky diodes on n-type GaN. The Ti films were deposited by electron beam evaporation on n-type GaN grown by metal organic vapor deposition. We determine the effective barrier height Ф60 by current-voltage measurements as a function of temperature. The as-deposited Ti contacts show rectifying behavior with low barrier heights Ф60 ≤ 200meV. At annealing temperatures as low as 60°C we observe an increase of the barrier height to values of 250meV. After annealing at 230°C and above a stable barrier height of 450meV is measured. The increase in barrier height is not due to any macroscopic interfacial reaction. The origin of the observed changes are discussed in terms of the Schottky-Mott model and possible microscopic interfacial reactions.
MBE Growth of (In)GaN for LED Applications
Authors: Riechert H. , Averbeck R. , Graber A. , Schienle M. , Strauβ U. , Tews H. 
Published: April 2011

ABSTRACTWe report on essential aspects of the growth of InGaN / GaN p-n junctions by gas-source molecular beam epitaxy (MBE) and present the first blue and green electroluminescence from such structures grown entirely by MBE.A study of the growth conditions for a GaN nucleation layer on sapphire and for the subsequent growth of undoped GaN points out the necessity for Ga-stabilized growth. Unintentionally doped GaN grown at 1 μm/h shows background doping levels below 1017 cm-3 and mobilities up to 320 cm2/Vsec (at 300K). Narrow photoluminescence with very low intensity in the yellow spectral range is observed. N- and p-type doping of GaN with Si and Mg yields layers with high mobilities (220 and 10 cm2/Vsec, respectively at 300K) at carrier densities typical for devices.Although incorporation of Indium is strongly temperature-dependent, InGaN-layers with In-contents of over 40% are obtained routinely. The optical properties of our InGaN layers typically exhibit the commonly observed, broad deep level luminescence. Finally, we present electroluminescence in the visible spectral range up to 540 nm from InGaN / GaN double-heterojunctions.
MBE Growth of III-V Nitride Films and Quantum-Well Structures Using Multiple RF Plasma Sources
Authors: Johnson M. A. L. , Yu Zhonghai , Boney C. , Rowland W. H. , Hughes W. C. , Cook J. W. , Schetzina J. F. , El-Masry N. A. , Leonard M. T. , Kong H. S. , Edmond J. A. 
Published: April 2011

ABSTRACTMBE growth of III-V nitrides is being studied at NCSU using MOVPE grown GaN buffer layers on SiC as substrates. Rf plasma sources are being used for the generation of active nitrogen during MBE deposition. Through the use of multiple rf plasma sources, sufficient active nitrogen is generated in order to examine the properties of III-V nitride layers grown at higher substrate temperatures and growth rates. The resulting MBE-grown GaN films exhibit remarkably intense photoluminescence (PL) dominated by a sharp band-edge peak at 3.409 eV having a FWHM of 36 meV at 300K. No deep level emission is observed. AlGaN and InGaN films and quantum well structures have also been prepared using multiple sources. A modulated beam MBE approach is used in conjunction with the multiple rf plasma sources to grow InGaN. RHEED and TEM studies reveal flat 2D InGaN quantum well structures. Depending on the indium content, GaN/InGaN single-quantum-well structures exhibit electroluminescence at 300K peaked in the blue-violet to the green spectral region.
Growth of (0001) ZnO Thin Films on Sapphire
Authors: Drehman A. J. , Yip P. W. 
Published: April 2011

ABSTRACTUsing reactive rf sputtering, we have grown (0001) oriented ZnO films in situ on heated c-axis sapphire substrates, that are promising, particularly in terms of surface roughness, as buffer layers for the subsequent epitaxial growth of III-V nitride films. We compare the effects of on-axis and off-axis sputter geometries on the film epitaxy and smoothness. We also examined the effect of substrate temperature on the growth and smoothness and quality of the film. X-ray diffraction was used to verify the hexagonal ZnO phase, its c-axis orientation and, qualitatively, the degree of its epitaxy. Atomic Force Microscopy (AFM) was used to determine the ZnO growth morphology and roughness. Our best films, obtained by off-axis sputter deposition, have a surface roughness of less than 1 nm.