bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Characterization of Lithiated Nickel Based Metal Oxides as Positive Electrode Materials for Lithium Ion Batteries
Authors: Fujitani S. , Fujimoto H. , Nohma T. , Nishio K.
Published: April 2011

LiNi1−xCoxO2(x=0.2, 0.3, 0.4) was synthesized through a sintering process from two different types of source materials of nickel and cobalt, namely each respective hydroxide and oxide, and composite hydroxide. Influence of the difference on charge-discharge characteristics, crystal structure and distribution of the metal elements was investigated.

The composite hydroxides formulated in Ni1−xCox(OH)2 as the source material brought better homogenized composite lithiated nickel based metal oxides exhibiting the larger specific discharge capacity. Further modification of LiNi0.6Co0.4)2 by manganese through sintering from the composite hydroxide including manganese brought a good charge-discharge cycle performance as well as a high discharge capacity of 160mAh/g level.

A cylindrical test cell of 18mm in diameter and 65mm in height using the LiNi0.6Co0.3Mn0.1O2 exhibited discharge capacity of 1700mAh which is larger than that using LiCoO2, and also exhibited a competitive charge-discharge cycle performance to commercialized lithium ion batteries.
Characterization of Creep Behavior of SrCoo.8 Feo.203-x
Authors: Ajkic G. , Eeler L. , Alama K.
Published: April 2011

In order to achieve commercial utilization, oxygen separation membranes and solid oxide fuel cells must be able to maintain their mechanical integrity over acceptable life-time periods. This imposes a need for characterization of mechanical behavior of the materials used under operating conditions (high temperature and low stress), in order to identify mechanisms that lead to mechanical degradation during operation. In this study, a series of compressive creep tests on rectangular specimens of SrCO0.8Feo.2O3-x of different grain sizes (2.4 to 6.8 microns) is performed in air, covering a temperature range of 850 to 975 °C and stress range of 10–20 and 40–50 MPa. In the high stress range the material has been found to render temperature dependent stress exponents (2.2 to 2.9) and high steady-state strain rates. In the low stress range the stress exponent has been found to be dose to unity (1.1 to 1.3) indicating diffusion controlled creep. The activation energy appears to assume two different values depending on operating temperature region, 457 kJ/mole below 925 OC and 268 kJ/mole above 925 OC. These values, being much higher than that for oxygen diffusion (<100 kJ/mole) indicate cation diffusion controlled creep. The shift in the value of activation energy indicates a shift in the slowest moving (rate-controlling) species between A and B cation sites. The inverse grain size exponent has been found to be dose to unity.
Porosity in Polysilsesquioxane Xerogels
Authors: Baugher Brigitta M. , Schneider Duane A. , Loy Douglas A. , Rahimian Kamyar
Published: April 2011

Polymerization of organotrialkoxysilanes is a convenient method for introducing organic functionality into hybrid organic-inorganic materials. However, not much is known about the effects of the organic substituent on the porosity of the resulting xerogels. In this study, we prepared a series of polysilsesquioxane xerogels from organotrialkoxysilanes, RSi(OR′)3, with different organic groups (R = H, Me, Et, dodecyl, hexadecyl, octadecyl, vinyl, chloromethyl, cyanoethyl). Polymerizations of the monomers were carried out under a variety of conditions, varying monomer concentration, type of catalyst, and alkoxide substituent. The effect of the organic substituent on the sol-gel process was often dramatic. In many cases, gels were formed only at very high monomer concentration and/or with only one type of catalyst. All of the gels were processed as xerogels and characterized by scanning electron microscopy and nitrogen sorption porosimetry to evaluate their pore structure.
A New Route to Prepare Hard and Anti-Scratching Coatings at Room Temperature
Authors: Liu Yanjing , Claus Richard O. , Rosidian Aprillya , Zeng Tingying
Published: April 2011

Nanocomposites of transparent, multilayer structures of different thin-films have been fabricated on single crystal silicon and quartz substrates by the new deposition technique called electrostatic self-assembly (ESA) method. The method is based on the alternating adsorption of anionic and cationic polyelectrolytes in the aqueous forms. The films were then characterized by UV/Vis spectroscopy, ellipsometry, and nano-indenter. A linear behavior of both optical absorption and film thickness as the number of bilayers increases was observed, which indicated the formation of homogeneous and uniform thin-films on both substrates. The study also observed that the films prepared by this novel method have some improved mechanical properties.
Materials With Improved Properties From Polymer-Ceramic Nanocomposites
Authors: Kuchta Frank-Dieter , Lemstra Piet J. , Keller Andrew , Batenburg Lawrence F. , Fischer Hartmut R.
Published: April 2011

In order to link the fundamental research field of polymer crystallization with the technical important field of composite materials polymer-layered silicate nanocomposites from polyethylene (PE) are prepared and their morphology and properties are investigated. The effect of an external confinement introduced by highly anisotropic silicate layers of organically modified clay minerals on crystal growth and nanocomposite properties has been studied. The prepared nanocomposites of organically modified clay minerals and PE exhibit not only a homogeneous distribution of individual silicate layers but also of tactoids. The isothermal crystallization rate of PE in the corresponding nanocomposite at 120 °C is increased in the composite material due to the action of the silicate layers. A significant effect on crystal phase has not been observed so far but from X-ray experiments, however the crystal size seems to be influenced. The thermal stability of the nanocomposites is significantly enhanced and the decomposition mechanism has been changed due to the presence of the layered silicates within the host polymer acting as a barrier for the diffusion of small molecules like oxygen. Due to the none permanent attachment of the polymer chains to the silicate surface the thermal-mechanical properties are only moderately enhanced at low temperature while the glass transition temperature remains unaffected.
Praseodymium and Neodymium-Based Nanocrystalline Hard Magnetic Alloys
Authors: Davies H.A. , Harland C.L. , Betancour R.J.I. , Mendoza S.G.
Published: April 2011

The magnetic properties of nanophase exchange enhanced RE-Fe-B based alloys ribbons prepared by melt spinning are presented and discussed. The alloy systems investigated include NdyFe94−yB6 and PryFe94−yB6, for y within the range 6-20 at%, and the data are compared in the context of the larger anisotropy field for the Pr2Fe14B phase in comparison with Nd2Fe14B. Experimental studies are also reported for nanophase (Nd-Pr)- Fe-B alloys with various proportions of Nd:Pr, to investigate the increase in coercivity of NdFeB by partial substitution of Nd by Pr, and for (Nd, Pr)-(Fe-Co)-B-based systems, to study the degree to which the remanence enhancement can be maintained for alloys in which Co substitutes for Fe to increase the thermal stability.
Structure And Magnetic Properties Of Fe-N Thin Films Grown By Ecr Deposition
Authors: Németh S. , Akinaga H. , Boeve H. , Bender H. , Boeck J. De , Borghs G.
Published: April 2011

The growth of FexNy thin films on GaAs, In0.2Ga0.8As, and Si02/Si substrates using an ultra high-vacuum (UHV) deposition chamber equipped with electron cyclotron resonance (ECR) microwave plasma source is presented. The structural properties of the deposited films have been measured using various techniques as x-ray diffraction (XRD), Auger electron spectroscopy (AES), and transmission electron microscopy (TEM). The results of XRD measurements show that the films consist of a combination of α-Fe, α'-Fe, γ-Fe4N, and α”- Fe16N2 phases. The depth profiles, calculated from the Auger peak intensities, show a uniform nitrogen concentration through the films. The TEM reveals a columnar structure of these films. The properties of the different Fe-N layers have been exploited in the fabrication of Fe(N) / FexNy / Fe trilayer structures, where Fe(N) means a slightly nitrogen doped Fe film. The magneto-transport properties of this trilayer structure grown on In0.2Ga0.8As substrates are presented.
Mechanical Loss Associated with Stress Anomaly in Ni3Al and Ni3(Al, Ta) Single Crystals
Authors: Carreno-Morelli E. , Cheng B.L. , Demura M. , Schaller R. , Baluc N. , Bonneville J.
Published: April 2011

The mechanical loss and shear modulus behaviors of Ni3Al and Ni3(Al, Ta) single crystals have been investigated in the temperature range 100 K – 1300 K. The mechanical loss spectra exhibit two temperature regimes, which are separated by a relaxation peak at nearly 950 K for a frequency of 1 Hz. This relaxation peak has been interpreted by the stress re-orientation of Al-Al elastic dipoles in the (111) octahedral plane [1, 2]. In the low temperature regime, corresponding to the anomaly domain of the flow stress, the mechanical loss of pre-deformed specimens exhibit a strong positive dependence on both the oscillation amplitude and the amount of pre-strain.

Pre-deformations, which were performed either at room temperature or at 100 K, yield a broad maximum in the mechanical loss that extends from nearly 100 K up to 550 K. This maximum is observable for only strain amplitudes larger than 10−4 and entirely vanishes after heating the specimens above 550 K. The increase in mechanical loss has been attributed to the bowing of the superkinks under the action of the applied stress. The gradual and irreversible decrease in damping above 300 K is interpreted in terms of pinning of the screw dislocation segments by a thermally activated process leading to the formation of Kear-Wilsdorf locks.
Crystallization Behaviour of Amorphous Si0.5Ge0.5 Films Observed by Positron Annihilation
Authors: Edelman F. , Börner F. , Krause-Rehrberg R. , Werner P. , Weil R. , Beyer W. , Butz R.
Published: April 2011

The crystallization behavior (ordering) of undoped and boron-doped Si0.5Ge0.5 films, deposited on SiO2/Si(001) substrate by molecular beam epitaxy in hish vacuum at room temperature, were studied by XRD, HRTEM and in situ by Doppler broadening spectroscopy using monoenergetic positrons. Some decomposition features of SiGe solid solutions were demonstrated via splitting the XRD peaks at high temperatures. The SiGe decomposition was detected in the precrystalline state of the SiGe undoped and doped films in the temperature range from 450 to 600 K by compaering S- and W-parameters of SiGe with that of amorphous silicon and germanium. In conclusion, we discuss model of internim ordering states before crystallization.
ARC Discharge for the Synthesis of Monoclinic Ga2O3 Nanowires
Authors: Choi Young Chul , Bae Dong Jae , Lee Seung Mi , Park Young Soo , Lee Young Hee , Park Gyeong-Su , Choi Won Bong , Lee Nae Sung , Kim Jong Min
Published: April 2011

Monoclinic gallium oxide (β-Ga2O3) nanowires were catalytically synthesized by electric arc discharge of GaN powders mixed with a small amount (less than 5 %) of transition metals under a pressure of 500 Torr (80 %-Ar + 20 %-O2). Scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM) images showed that the average diameter of the wires were about 30 nm and their lengths were as long as up to one hundred micrometer, resulting in extremely large aspect ratio. Fourier diffractogram was indicative of single crystalline nature of the β-Ga2O3 wire. HRTEM image also showed β-Ga2O3 with twin defects at the center of the wire which might play as nucleation seeds. Both X-ray diffraction (XRD) patterns and FT-Raman spectra of the wires identified the observed nanowires as monoclinic crystalline gallium oxides.
Preparation of Highly Ordered Mesoporous Thin Film with Alkyltrimethylammonium(CnTMA+)
Authors: Goto Y. , Sugimoto N. , Fukushima Y , Imada Y. , Kubota Y. , Sugi Y
Published: April 2011

We synthesized the highly ordered mesoporous thin films with alkyltrimethyl-ammonium (CnTMA+). The arrangement of mesopores was depend on the Si/surfactant ratio. The hexagonal(P6mm) arrangement was observed, when Surfactant/Si ratio was 1/10. Increasing the Surfactant/Si ratio to 1.6/10, the cubic (Pm3n) arrangements were observed. A steel vessel for the measurement of the nitrogen adsorption isotherms of thin film on the substrate was designed. It was found that mesopore arrangements in the film is more regular than that in the powder samples prepared by the same acidic synthesis conditions.
Sintering Behavior of Nano-Ceramic Coatings
Authors: De Hosson J.Th.M. , Popma R. , Hooijmans J.
Published: April 2011

This paper concentrates on the densification of sol gel derived thin nano-ceramic coatings by laser radiation and by furnace treatment. Deposition of the film is done by means of spin coating of Zirconia. The sintering of the layer is observed using a number of different measuring techniques. Especially, attention is paid to the densification behavior and the grain growth in the layer, investigated by scanning electron microscopy and ellipsometry. Also the different crystal phases observed are addressed. During sintering at a constant temperature a change in the sintering behavior with time is observed. This change is observed for most temperatures. Both the initial fast sintering of the process (for all sintering temperatures), and the final slow sintering (only at the higher sintering temperatures) are explained.
CuPt Ordering Signatures of Phonons in GaInP2
Authors: Alsina F. , Cheong H. M. , Mestres N. , Pascual J. , Mascarenhas A.
Published: April 2011

We present a comprehensive overview of the large spectroscopic evidence on the influence of ordering on the Raman and infrared spectra of partially ordered GaInP2. Our phonon mode calculation within the adiabatic bond charge model describes the appearance of new phonons and also the optical anisotropy.
Evolution of the Shape and Size of Ingaas Selforganized Quantum Dots
Authors: Xie Qianghua , Brown J. L. , Jones R. L. , Nostrand J. E. Van
Published: April 2011

We have found a shape transformation of InGaAs quantum dots formed via a fractional monolayer deposition technique on GaAs (001) surfaces. This is evidenced by the bimodal quantum dot height (peaked at 8.5 nm and 14.5 nm) and aspect ratio (peaked at 0.18 and 0.26) distributions. The lateral size, height, and aspect ratio all become convergent, suggesting a simultaneous quantum dot size equalization and shape stabilization. Photoluminescence peaks red shift as a consequence of dot growth, and their line-widths become smaller due to dot shape stabilization and size equalization. A record low inhomogeneous broadening of 18.4 meV at a wavelength of 1180 nm (4 K) is obtained for vertically-aligned, shape-stabilized, and size-equalized InGaAs dots.
Real-Time Observation of Pt-Si Micro-Droplet Migration by Photo-Electron Emission Microscopy
Authors: Yang W. , Ade H. , Nemanich R. J.
Published: April 2011

The formation and dynamics of Pt-Si liquid droplets on Si (001) substrates have been investigated by Photo-electron Emission Microscopy (PEEM). After ambient deposition of a 10nm Pt film, a uniform PtSi layer was transformed into an island structure at ∼ 800°C. The PtSi islands of micrometer size began to melt and were transformed into molten Pt-Si alloy islands below the melting point of PtSi. At ∼1100°C surface migration of the micro-droplets was observed. The moving droplets coalesced with nearby islands and grew in size. The motion was related to the temperature difference across the substrate, and droplet migration was observed from the cold to the hot regions of the surface. The migration velocity was measured as a function of temperature and droplet size. The driving force for migration is related to material diffusion, equilibrium at the solid-liquid interfaces, and surface energetics.
Computer Simulation of Nucleation on Patterned Surfaces
Authors: Kuronen A. , Nurminen L. , Kaski K.
Published: April 2011

We have studied qualitatively the effect of patterned substrate surface on adatom nucleation using Kinetic Monte Carlo simulations and solid-on-solid model. The inhomogeneity in the activation energies of adatom diffusion was incorporated into the simulations using two models: a) periodic variation of the adatom–substrate interaction energy as a function of the adatom lateral position and b) adding a direction dependent and periodically varying diffusion barrier energy to the adatom diffusion activation energy. The effect of the patterned surface was clearly manifested as a confinement of nucleated islands and, consequently, narrowing the island size distribution. The effect was strong in a narrow temperature range.
Structural Evolution During the Initial Epitaxial Growth of Moon on Sapphire
Authors: Ryan P. A. , Tsui F.
Published: April 2011

Structural evolution during initial epitaxial growth of Mo (111) and (110) on Al2O3 substrates has been studied using real-time reflection high energy electron diffraction and in-situ scanning tunneling microscopy. The Mo (111) growth on sapphire (0001) is initiated by the formation of small mound-like 3-dimensional (3D) islands that are correlated with unique length scales. The observed surface length scales depend on growth temperature and rate, and they coarsen as the thickness increases. The initial growth of Mo (110) on sapphire (1120) begins with layer-by-layer growth for the first monolayer, and subsequently the growth is 3D with mound-like features that are larger than those corresponding (111) counterparts. In both orientations lattice relaxation occurs within the first 2 – 3 monolayers.
Enhancement of the Adhesion of Cordierite Glass-Ceramic Coatings on Molybdenum by the Deposition of Metallic Interlayers on the Substrate
Authors: Calata Jesus Noel , Lu Guo-Quan , Kuhr Thomas A.
Published: April 2011

Sintered coatings of cordierite-base glass-ceramic do not adhere readily on bare molybdenum substrates. This is due to the absence of a stable metal oxide film on the substrate that serves as a suitable transition layer between the glass-ceramic and the substrate. To address this problem, dual layers of either chromium/nickel or chromium/copper were deposited by electroplating on the molybdenum substrates. Glass powder in slurry form was then cast on the substrates using a doctor blade and sintered in a helium-hydrogen atmosphere at 950°C. The metallic interlayer structure was found to produce an excellent bond between the coating and the substrate. The adhesion of the coatings was observed to be sensitive to the thickness of the deposited metal layers. Quantitative chemical analysis of the interface region was performed to explain the difference in adhesion quality. In all instances, the fracture surface was found to occur at the chromium oxide/chromium boundary providing a clear indication that the chromium oxide layer plays an important role in enhancing the adhesion. The superior adhesion in samples with the Cr-Cu interface was attributed to Cu acting as an effective diffusion barrier to Mo. Cr however, was able to diffuse through the Cu layer enhancing the bond between Mo and Cu by alloying with the Mo. Ni was not as effective as Cu in preventing the diffusion of Mo towards the glass-ceramic coating but a thicker Cr layer still produced a strong bond. In samples where the distinct Cr layer was either too thin or non-existent, adhesion was poor possibly because the Cr oxide does not bond well to the Ni-Cr alloy layer that formed after firing.
Near-Interface Crack Initiation in Thermal Barrier Coatings
Authors: Zhang Z. , Bloomer T. E. , Kameda J. , Sakurai S.
Published: April 2011

The delamination behavior of thermal barrier coatings (TBC) in transition ducts of inservice used combusters has been characterized using a protruded four-point bending testing technique recently developed by the authors. A reinforced protruded TBC specimen allowed the formation of TBC cracks adjacent to the TBC/alumina interface in a similar mode to inservice TBC failure. Finite element stress analysis showed that a peak transverse stress appeared in a protruded TBC part away from the interface and a large principal tensile stress operated on planes inclined to the interface. It was found that the onset of near-interface TBC cracks in the protruded TBC specimen did not occur under the high transverse and principal tensile stresses. The critical local tensile stress for the onset of TBC cracks near the interface, estimated to be 127 MPa, was lower than that of the near-center TBC. The near-interface TBC cracking behavior in the protruded TBC tests is discussed in light of the residual stress distribution and stressed volume effect.
Modelling the Effect of Composition on the Stability of Equilibrium Intergranular Films with Diffuse Interfaces
Authors: Bishop C. M. , Carter W. C.
Published: April 2011

Current understanding of the equilibrium thickness of interfacial films derives from models which balance a steric repulsion against an attractive force between abutting crystals such as the van der Waals forces [1]. Recent experimental observations indicate that, a) film thickness is a non-monotonic function of additions of impurities and b) impurities are non-uniformly distributed in the interfacial phases and triple junctions [2]. We have developed a model which couples the steric terms which affect the equilibrium thickness with composition for a semi-infinite film in equilibrium with a chemical reservoir at a fixed composition.
Dewetting of Reactive CaMgSiO4 Glass Films on Single-Crystal MgO(001) Substrate
Authors: Yanina S. V. , Carter C. B.
Published: April 2011

The early stages of dewetting of a reactive silicate (CaMgSiO4) film on a ceramic (MgO) substrate were studied by scanning probe microscopy. Subsequent interactions between the glass phase and an underlying single-crystal substrate, such as dissolution/re-precipitation of substrate material at the glass-ceramic interface and evaporation of silicate phase, were investigated by observing selected areas of the specimens through a series of annealing-quenching cycles. Implications deduced from the CaMgSiO4-MgO equilibrium phase diagram on the process of dissolution/re-precipitation of MgO are briefly discussed.
Solid Phase Epitaxial Recrystallization of AlN Films on Sapphire (0001): A Novel Substrate Approach for GaN Epitaxy
Authors: Vispute R. D. , Patel A. , Sharma R. P. , Venkatesan T. , Zheleva T. , Jones K. A.
Published: April 2011

High quality and lattice matched buffer layers are needed for the growth of device quality GaN thin films on sapphire for optoelectronic applications. In this context, we report the fabrication of AlN thin films having low defect densities through a novel process called solid phase epitaxial recrystallization (SPER). In this process, as-grown crystalline AlN thin films, having a large defect concentration (such as threading dislocations due to a large lattice mismatch between AlN and sapphire and low angle grain boundaries), were thermally annealed in an inert atmosphere at various temperatures ranging from 1200-1600° for 30 min. The as-grown and annealed samples were characterized using x-ray diffraction, transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and UV-visible spectroscopy. The ion channeling/RBS and TEM results clearly indicate a substantial reduction in the defect density for the recrystallized AlN films. The surface morphology of the SPER AlN films was smooth with a surface roughness close to the unit cell height. The optical bandgap was sharp as compared to as-grown films, with a bandgap of 6.2 eV. The recrystallized films having smooth surface morphology and low defect densities may be useful for the growth of device quality GaN films on sapphire.
Characterization of Si, SiGe and SOI Structures Using Photoluminescence
Authors: Higgs V.
Published: April 2011

A new Photoluminescence (PL) method has been developed to detect defects in the near surface region of Si wafers and Si-on-insulator (SOI) structures. Wafer maps (up to 300 min diameter) can be readily acquired and areas of interest can be scanned at high resolution (≈1 μm). The excitation laser beam is modulated to confine the photogenerated carriers; defects are observed due to the localised reduction of the carrier lifetime. Si p-type (10 Ohm.cm) wafers were intentionally contaminated with various levels of Ni and Fe (1×109−5×1010atoms/cm2) and annealed. The PL intensity was observed to decrease due to the metal related non-radiative defects. Whereas in contrast, for Cu, (1×109−5×1010atoms/cm2) the PL intensity actually increased initially and reached a maximum value at 5×109atoms/cm2. It is suggested that during contamination the Cu related defects have complexed with existing defects (that have stronger recombination properties) and increased the PL. Further Cu contamination (1×1010−5×1010atoms/cm2) produced a reduction in the PL intensity. PL mapping of strained SiGe epilayers showed that misfit dislocations can be detected and PL can be used to evaluate material quality.

PL maps of SOI bonded wafers revealed that the non-bonded areas, voids or gas bubbles could be detected. This was confirmed using defect etching and polishing, voids as small as ≈30 μm in diameter could be detected. SOI wafers fabricated using the separation by implanted oxygen (SIMOX) technique were also analysed, variations in the recombination properties of the layer could be observed. Further inspection using transmission electron microscopy (TEM) revealed that the defects were non-uniformities of the buried oxide covering several microns and containing tetrahedral stacking faults. Focused ion beam (FIB) milling and secondary ion mass spectrometry (SIMS) showed that these defects were at the Si/SiO2interface and were chemically different to the surrounding area.
High real-space resolution structure of materials by high-energy x-ray diffraction
Authors: Petkov V. , Billinge S. J. L. , Heising J. , Kanatzidis M. G. , Shastri S. D. , Kycia S.
Published: April 2011

Results of high-energy synchrotron radiation experiments are presented demonstrating the advantages of the high-resolution atomic Pair Distribution Function technique in determining the structure of materials with intrinsic disorder.
Charge Transfer and Local Structure in Thermoelectric Germanium Clathrates
Authors: Palmqvist A.E.C. , Iversen B.B. , Furenlid L.R. , Nolas G.S. , Bryan D. , Latturner S. , Stucky G.D.
Published: April 2011

Germanium clathrates have recently received attention as potential highly efficient thermoelectric materials based on the phonon glass electron crystal (PGEC) concept [1-4]. A combined EXAFS and XANES study has been performed in order to investigate the local structure and the degree of charge transfer between the guest atoms and the framework atoms. Analysis of the Sr, Ga, and Ge K-edge XANES spectra of a Sr8Ga16Ge30 clathrate reveals that the atoms are close to neutrally charged and that the degree of charge transfer is low in agreement with recent theoretical predictions and charge density distribution measurements [3,5].
Nonlinear Ultrasonic Parameter in Precipitate-Hardened Steels
Authors: Hurley D. C. , Balzar D. , Purtscher P. T.
Published: April 2011

We have investigated several specimens of ASTM A710 steel containing copper-rich precipitates with variations in the final aging treatment. X-ray diffraction line-broadening and small-angle neutron-scattering experiments revealed the existence of the precipitates and associated coherency strain. We determined the nonlinear ultrasonic parameter β for each specimen by harmonic-generation experiments and measured the ultrasonic longitudinal velocity νL and attenuation αL. Although νL and αL showed no consistent trends, β increased with increasing strain. This correlation is compared to a microstructural model for harmonic generation that includes a contribution from precipitate-pinned dislocations.
Scanning Acoustic Microscopy and x-ray Diffraction Investigation of Near Crack Tip Stresses
Authors: Sathish S. , Martin R. W.
Published: April 2011

Scanning Acoustic Microscopy has been used to measure and map the Rayleigh wave velocity and the Surface Skimming Longitudinal wave velocities near a crack tip in a sample of Ti-6AI-4V. X-ray diffraction measurements have been performed to map the stress in the same region of the sample. The differences in the contrast between the two acoustic velocity images and their sensitivity to stress are examined. Similarities between x-ray stress images and acoustic velocity images are discussed.
Nondestructive Characterization of Corrosion Protective Coatings on Aluminum Alloy Substrates
Authors: Hoffmann J. , Sathish S. , Khobaib M. , Meyendorf N. , Netzelmann U. , Matikas T.E.
Published: April 2011

This paper describes the initial phase of the development of a nondestructive, multisensor approach for detecting, quantifying and monitoring degradation of organic coatings applied to aluminum surfaces. Descriptions of the purposes and chemical compositions of layered coatings used on aircraft structures are provided. The discussion then concentrates on ultrasonic thickness measurements. One is the well-established pulse/echo scanning acoustic microscopy and, as a proposed alternative, continuous acoustic waves measurements with a probe in contact to the sample. Advantages and disadvantages of the two methods and their potential as in field applications are discussed.
Photoluminescence Characterization of Defects in Thermal Oxide
Authors: Nishikawa Hiroyuki , Stathis James H.
Published: April 2011

Defects in thermal oxides were investigated by a photoluminescence technique. Thermal oxides with a thickness of 100 nm grown either by dry or wet oxidation were studied. A broad PL band at 2-4 eV was observed for both dry and wet oxides. Effects of annealing under vacuum or in atmospheres of Ar or N2 on the PL were also examined. The PL intensity was enhanced for the case of wet oxide by vacuum annealing at 700 °C. High-temperature anneal above 750 °C without O2 further generated PL centers for both dry and wet oxides. The formation mechanism of the PL centers will be discussed in terms of the decomposition of oxide at Si/SiO2 interface.
Microstructural Evolution in Copper Films Undergoing Laser Pulsing at High Pressures
Authors: Jakkaraju R. , Dobson C. D. , Greer A. L.
Published: April 2011

A novel process of pulse-heating copper films under high pressure has been developed for filling high-aspect-ratio vias and contact holes with copper. A copper film is sputter-deposited on to an oxidised silicon substrate containing an array of via holes with varied aspect ratios. The film, which is thick enough to bridge over the via holes, is then subjected to laser pulse heating under selected pressures of inert gas. Via filling has been achieved, up to an aspect ratio of 6 for 0.35 μm diameter holes. The microstructure of the pulse-heated copper films has been investigated by X-ray diffraction, and by focused ion beam microscopy (FIB) including sectioning. The FIB images of the film over a via pattern show a ‘chequer-board’ pattern of grains corresponding to the square pattern of via holes underneath. This pattern can be explained by transient melting of the film under pulse-heating and subsequent solidification in which each via hole acts as a nucleation site and has a crystal associated with it. Even though the as-deposited films are fine-grained and have (111) texture, the treated films can show (111) or (100) texture, depending on processing conditions. The origins of the final film texture and the possibilities for microstructural control are discussed.
Computing Thin Film Mechanical Properties with the Oliver and Pharr Method
Authors: Wolff P. J. , Lucas B. N. , Herbert E. G.
Published: April 2011

A commonly used technique to compute mechanical properties from indentation tests is the Oliver and Pharr method. Using dimensional analysis and finite element modeling, this paper investigates errors when the Oliver and Pharr method is used to compute thin film properties.
Measuring Thin Film Fracture Toughness Using the Indentation Sinking-in Effect and Focused Ion Beam
Authors: Tsui Ting Y. , Joo Young-Chang
Published: April 2011

A new experimental technique is developed to measure the fracture toughness of a hard metal thin film deposited on a soft substrate. A pre-crack was fabricated in the thin film by using the advanced focused ion beam (FIB) milling techniques. The crack extension force was generated by means of the indentation sinking-in effect. The effect creates a bending moment and tensile stress on the hard thin film near the indentation, which promotes crack growth. The amount of crack tip blunting prior to the critical failure was measured from the FIB cross-sectioned micrographs. By using the crack tip opening displacement model (CTOD), the fracture toughness of the thin film was calculated. The results show the nickel phosphorus (NiP) thin film fracture toughness is at least 15.0MPa√m. The finite element method (FEM) was used to understand the modes of mixity near the crack tip. The results indicate the crack tip modes of mixity are dominated by the Mode I opening, provided the indentation is sufficiently far from the pre-crack or the indentation depths is small when compared with the film thickness.
Anisotropic Plasma Etching of Barium-Strontium-Titanate Thin Films for 4 Gbit DRAM Devices
Authors: Schneider Stefan , Kennard Mark A. , Waser Raine
Published: April 2011

Reactive Ion Etching of Ba0.7Sr0.3TiO3 (BST) thin films was studied using a Lam Research Corporation TCP™ 9400SE high density, low pressure plasma reactor. The BST thin films were etched with a variety of reactive gas combinations in a transformer coupled plasma (TCP) by varying etching parameters such as plasma density, DC bias to wafer susceptor, gas pressure, and -flow. The etch process was characterized by measuring the etch rate, etch selectivity to photo resist and SiO2 etch profiles, side wall deposition (fence), and etch product residues. Plasma etching of BST was found to be dominated by physical sputtering. With the chemistries used, the etch products have little or no volatility. Such a process regime is expected to contaminate the wafer with sidewall deposition (fences) and residues, which are both detrimental for further processing and may cause a possible particle problem and a low mean time between cleaning the process tool. The photoresist mask thickness and slope were varied to characterize the relationship between profile and residue. The photoresist mask was sloped using in situ plasma processing. Through optimization of mask and etch parameters, an etch process suitable for integration of BST capacitors into ULSI structures was achieved.
Low Temperature Preparation of Sr2(Ta1-x, Nbx)2O7 Ferroelectric Thin Film by Pulsed Laser Deposition
Authors: Noda Minoru , Nakaiso Toshiyuki , Sugiyama Hideki , Okuyama Masanori
Published: April 2011

Preferentially (151)-oriented Sr2(Ta1-x, Nbx)2O7 (STN) thin films on Pt have been prepared at temperatures as low as 550 and 600°C, in O2 and N2O atmospheres, respectively, by pulsed laser deposition (PLD). The temperatures are significantly lower than those prepared by sol-gel methods, where 950°C was reported. These are the lowest growth temperatures of crystalline STN thin films. Composition ratio (x) in the target material was determined to be around 0.3 from measurement of the Curie temperature and ferroelectric properties. Active oxygen generated by laser irradiation in ambient O2 or N2O atmosphere is found to be very effective for chemical reaction, and decreases the growth temperature of crystalline STN films. It is also confirmed by surface AFM and cross-sectional SEM observations that the film has a columnar-shaped structure with grain size ranging from 50 to 100 nm. Remanent polarization (Pr) and coercive field (Ec) are 0.4μ C/cm2 and 30 kV/cm, respectively. Finally, we expect the low temperature STN film prepared by PLD to be a promising ferroelectric for the application in ferroelectric memory FETs.
Frequency Dependence of the Coercive Voltage of Ferroelectric Thin Films
Authors: Waser R. , Lohse O. , Grossmann M. , Boettger U. , Bolten D. , Tiedke S.
Published: April 2011

Recent progress in the measuring techniques based on a combination of a quasistatic P-V analysis, conventional dynamic hysteresis measurements, and fast pulse characterization allows to determine the coercive voltage as a function of the frequency over a range of more than seven orders of magnitude. In this review, we explain the experimental techniques and present the results for the thin film systems of SrBi2Ta2O9 (SBT) and Pb(ZrTi)O3 (PZT). Theoretical models of the correlation between the ferroelectric relaxation and the coercive voltage are discussed in the light of the new data.
Magnetooptic Waveguide Material Structures and Devices
Authors: Tsai Chen S. , Su Jun
Published: April 2011

Recent advances in the techniques for preparation of Ce-doped yttrium iron garnet (YIG) films on gadolinium gallium garnet (GGG) and semiconductor substrates, hybrid material structures of YIG/GGG- gallium arsenide (GaAs) combination, and the resulting microwave and guided-wave magnetooptic (MO) devices are presented. For example, high-efficiency MO Bragg cell modulators using the YIG/GGG-alumina material structure have been realized using a non-uniform bias magnetic field as well as an electronic feedback. Such MO modulators are being used to construct integrated optic devices such as optical scanners, switches, and frequency shifters. Also, a wideband microwave bandstop filter with a carrier frequency tuning range as high as 2.5 to 23.0 GHz using the YIG/GGG-GaAs material structure has been realized. The same material structure can be employed to perform MO Bragg diffraction experiment at ultrahigh carrier frequencies.
BaTiO3 Waveguides on MgO Buffered-Sapphire Single Crystals
Authors: Lisoni Judit G. , Siegert M. , Lei C. H. , Jia C. L. , Schubert J. , Zander W. , Buchal Ch.
Published: April 2011

Within our program to develop ferroelectric thin film optical waveguides, we have studied the growth of epitaxial waveguides BaTiO3 on r-plane sapphire substrates with a MgO buffer layer. The films were prepared by pulsed laser deposition (PLD). Their structural properties were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Rutherford backscattering (RBS) in random and channeling (RBS-c) configuration and atomic force microscopy (AFM). They displayed good crystalline quality, characterized by an RBS-c minimum yield of about 4–6%, a full width at half maximum (FWHM) of the XRD rocking curve measurement of the BaTiO3(200) reflection of 0.32° and a rms roughness of 1.2 nm in a film of ∼ 1.0 μm thickness. The epitaxial relationship was found to be BaTiO3(100) // MgO(100) // A12O3(1102). The refractive index, the birefringence and the optical losses have been measured.
Excited State Absorption in Dendrimers Incorporating Diphenylaminodiphenylpolyene Moieties Via Photo-Induced Electron Transfer
Authors: Sonnenberg W. , Hyfield A , Short K , Spangler L. , Spangler C.
Published: April 2011

During the past decade there has been considerable progress in the design of new organic materials for optical power limiting (OPL) applications. Among the more promising of the new material approaches are reverse saturable absorbers (RSAs) which derive their optical limiting capability from the photogeneration of highly absorbing transient excited states. Most of the previous research in this field has focused on excited state absorption from singlet or triplet states whose cross-sections are greater than the original S0 – S1 transition- However, other transient states, such as polaronic radical ions or bipolaronic diions, formed by photo-induced electron transfer, are attractive alternatives. We have initiated studies to determine if these transient charge states can be photo-generated efficiently, and if their excited states absorption and lifetimes are acceptable for current optical power limiting requirements.
Phosphorescence Studies of Reverse Saturable Absorption Materials
Authors: Pooler E. S. , Clark C. M. , Kirkpatrick S. M.
Published: April 2011

Phosphorescence studies of reverse saturable absorption materials (RSA) are discussed. Absorption and emission measurements of an RSA material, specifically Zinc 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin (ZnOBP), are performed in a proprietary host polymer. Spectra are analyzed to estimate the relative energy level of the first triplet state of ZnOBP with respect to the ground state.
Strain Analysis in Thin La1−xCaxMnO3 Films by Grazing Incidence X-ray Scattering
Authors: Petit M. , Martinez-Miranda L. J. , Rajeswari M. , Biswas A. , Kang D. J. , Venkatesan T.
Published: April 2011

We have performed depth profile analyses of the lattice parameters in epitaxial thin films of La1−xCaxMno3 (LCMO), where x = 0.33 or 0.3, to understand the evolution of strain relaxation processes in these materials. The analyses were done using Grazing Incidence X-ray Scattering (GIXS) on films of different thicnesses on two different substrates, (100) oriented LaAlO3 (LAO), with a lattice mismatch of ∼2% and (110) oriented NGO, with a lattice mismatch of less than 0.1%. Films grown on LAO can exhibit up to three in-plane strained lattice constants, corresponding to a slight orthorhombic distortion of the crystal, as well as near-surface and columnar lattice relaxation. As a function of film thickness, a crossover from a strained film to a mixture of strained and relaxed regions in the film occurs in the range of 700 Å. The structural evolution at this thickness coincides with a change in the resistivity curve near the metalinsulator transition. The in-plane compressive strain has a range of 0.2 – 1.5%, depending on the film thickness for filsm in the range of 400 - 1500 A.
Colossal Magnetoresistance in New Manganites
Authors: Shen C. H. , Liu R. S. , Hu S. F. , Lin J. G. , Huang C. Y.
Published: April 2011

The evolution of structural, electrical and magnetic properties with the isovalent chemical substitution of Ca2+ into the Sr2+ sites in new series of two-dimensional La1.2(Srl.8−XCax)Mn2O7 compounds (x = 0 ∼ 1.8) and three-dimensional La0.6(Sr0.4−xCax)MnO3 compounds (x = 0 ∼ 0.4) are investigated. The highest magnetoresistance (MR) ratios [ρ(0) - ρ(H) / ρ(0)] of 52 % (H = 1.5 T) at 102 K and 13 % (H = 1.5 T) at 210 K were observed for the x = 0.4 samples in La1.2(Sr1.8−xCax Mn2O7 and La0.6(Sr0.4−xCax)MnO3, respectively. The Curie temperatures (Tc) decreased from 135 K to 102 K and 370 K to 270 K for x = 0 to 0.4 in La1.2(Sr1.8−xCax)Mn2O7 and La0.6(Sr0.4−xCax)MnO3, respectively. The compositional dependence of the structural variation has been found in La0.6(Sr0.4−xCax)MnO3. Our results confirm that the dimensionality as well as ionic size plays an important role in controlling the colossal magnetoresistance in manganites.
B-Site Doped Lanthanum Strontium Manganites by the DAAS Technique
Authors: Yang S. , Kolody M.R. , Lin C.-T. , Adams P.M. , Speckman D.M.
Published: April 2011

Magnetic perovskites of the general form La0.7Sr0.3Mn1−yFeyO3 (y = 0, 0.05, 0.10, and 0.15) have successfully been synthesized using deposition by aqueous acetate solution (DAAS). Crystalline, iron-doped, lanthanum strontium manganite (Fe-doped LSMO) powders are obtained by preparing an aqueous solution of metal acetate precursors in the proper stoichiometry, drying the solution to generate a glassy gel, consolidating the gel, and then firing the gel for short periods of time (<2hrs). This novel technique has the potential for depositing large area thin films with high throughput and low cost. Powder samples of La0.7Sr0.3Mn1−yFeyO3 prepared by DAAS and annealed for 100 minutes at 1200°C are of high purity, are single phase, and exhibit excellent electrical and magnetic characteristics. Powders annealed at 1200°C or greater exhibit sharp metalinsulator transitions. Increasing the iron dopant concentration in these powders from 0% to 15% decreases the metal-insulator transition temperature of these samples from ∼360K to about 140K. The resistivity of these powders also increases with increasing substitution of the lattice B-site with iron, as does the unit cell volume of the lattice. Preparation of an iron doped LSMO powder that exhibits a maximum magnetoresistance at 305K was successfully carried out via a careful selection of iron content and anneal temperature. This compound, La0.7Sr0.3Mn0.93Fe0.07O3, exhibits a magnetoresistance of 40% at 305K and an applied field of 5 Tesla.
Two Peak Effect in GMR: A Chemical Effect?
Authors: Vertruyen B. , Rulmont A. , Dorbolo S. , Bougrine H. , Vanderbemden Ph. , Ausloos M. , Cloots R.
Published: April 2011

We show that the synthesis conditions have a dramatic influence on the resistivity behavior of calcium and sodium doped LaMnO3. Several samples prepared by lowtemperature techniques exhibit a double-peaked curve of resistance versus temperature. The model of spin-polarized intergranular tunneling provides a good approach to discuss our experimental results. Grain size and crystallinity are proved to be essential parameters, which are strongly influenced by the preparation process (e.g. the precursors nature and the thermal treatment).
Growth of “colossal” magnetoresistance heterostructures by molecular beam epitaxy
Authors: O'Donnell J. , Andrus A. E. , Oh S. , Colla E. , Warusawithana M. , Davidson B. A. , Eckstein J. N.
Published: April 2011

We discuss the heteroepitaxial growth of La1−xSrxMnO3 films and CaTiO3 insulating barriers by molecular beam epitaxy. We find that the surface morphology and residual resistivity of the manganite electrodes is critically dependent on the film stoichiometry. The most important parameter is the concentration of La+Sr (cubic perovskite A-site cations) to that of Mn (B-site cation). If La+Sr is supplied in slight excess, the films grow with atomically flat surfaces, but the residual resistivity at 4.2K is high (as high as 6500 µΩ-cm), and Curie temperature (Tc) low (<300 K). If Mn is supplied in slight excess, the films have high Tc (370 K) and residual resistivity (35 µΩ-cm) better than bulk single crystal values, but the surface is no longer atomically flat. There appears to be a very narrow region of phase space where it is possible to have low resistivity, high Tc films with atomically flat surfaces. This is precisely where one would like to place heterostructure devices.
Electrodynamic Properties of Single-Crystal and Thin-Film Strontium Titanate, and Thin-Film Barium Strontium Titanate
Authors: Findikoglu A.T. , Jia Q.X. , Kwon C. , Gibbons B.J. , Rasmussen K.Ø. , Fan Y. , Reagor D.W. , Bishop A.R.
Published: April 2011

We have used a coplanar waveguide structure to study broadband electrodynamic properties of single-crystal and thin-film strontium titanate (STO), and thin-film barium strontium titanate (BSTO). We have implemented low-frequency capacitance (100 Hz - 1 MHz), swept-frequency transmittance (45 MHz - 4 GHz), and time-domain transmittance (dc - several GHz) measurements to determine effective refractive index (or, dielectric constant), and dissipation factor (or, loss tangent) as a function of dc bias (up to 4×106 V/m) and temperature (20 - 300 K). The STO samples used superconducting electrodes and were designed to operate at cryogenic temperatures, whereas BSTO samples used normal conducting electrodes and exhibited optimal performance around room temperature. By using nearly identical electrode geometries for all devices, we were able to conduct a direct comparative study among them, and investigate not only single-crystal vs thin-film, but also cryogenic vs room-temperature applications.