bluuebunny/crossref_metadata_2025 huggingface dataset:
Issues in the Energetics of Metastable Oxides and Oxyhydroxides
Authors: Navrotsky Alexandra
Published: April 2011

In both low temperature materials synthesis (sol gel processing, chimie douce) and low temperature geochemistry (weathering, geothermal and hydrothermal reactions, diagenesis) metastable and/or poorly crystalline materials are encountered. Despite the lack of equilibrium, energetic considerations play a major role in the formation and transformation of such phases. Recent calorimetric studies on heats of formation of zeolites and related metastable frameworks, on nanophase alpha and gamma alumina, and on manganese oxides and hydroxides are summarized. These studies illustrate the effects of framework topology, cation content, hydration and surface energy on the formation, persistence, and eventual transformation to more stable phase assemblages of these environmentally important materials.
Interaction of Organic Additives With Ceramic Surfaces In Colloidal Slurries
Authors: Sigmund W. M. , Wang L. , Sindel J. , Rotov M. , Aldinger F.
Published: April 2011

Three different dispersants, a low molecular weight compound (aminoalkanol), a polymer (polyelectrolyte) and a block-co-polymer (block polyethylenoxide-polyacrylic acid) were investigated with AFM and rheology in an aqueous system in order to elucidate the influence of the size and structure of the molecule on the dispersion stabilization. The AFM studies indicate that the aminoalkanol gives repulsive forces due to electrostatic repulsion only. The polyelectrolyte seems to stabilize the dispersion with both steric and electrostatic repulsive forces. A new compound that was designed for pure steric stabilization in aqueous media a block-co-polymer consisting of a polar anchor block and a stabilizing neutral chain was investigated for its behavior. The AFM measurements show that it is likely that this compound causes repulsion of silicon nitride surfaces due to steric repulsion only. Rheological measurements of aqueous powder slurries show that the adsorption of the organic additives is of great importance. Due to a more silicon dioxide like acidic surface of the investigated Si3N4 - powder the carboxylate anions of the block-co-polymer adsorb badly. Therefore, no sterically repulsive forces can be built up. This then causes an increase in the slurry's viscosity.
Monosized Aggregates - A New Model
Authors: Gopal Mani
Published: April 2011

For applications requiring colloidal particles, it is desirable that they be monosized to better control the structure and the properties. In a number of systems, the monosized particles come together to form aggregates that are also monosized. A model is presented here to explain the formation of these monosized aggregates.
Electrode Materials for Ferroelectric Capacitors: Properties of Reactive DC Sputtered IrO2 Thin Films
Authors: Balu Venkatasubramani , Chen Tung-Sheng , Jiang Bo , Kuah Shao-Hong , Lee Jack C. , Chu Peir , Jones Robert E. , Zurcher Peter , Taylor Deborah J. , Gillespie Sherry
Published: April 2011

Due to its low resistivity and excellent thermal stability, IrO2 has attracted attention as an alternative for electrode material in ferroelectric integrated circuit applications. In this work, IrO2 films deposited using reactive DC magnetron sputtering were studied. Film properties such as resistivity, crystallinity and morphology were examined as a function of deposition condition. Optimum process parameters to obtain high quality IrO2 thin films are suggested.
Voltage Shifts and Defect-Dipoles in Ferroelectric Capacitors
Authors: Warren W. L. , Pike G. E. , Dimos D. , Vanheusden K. , Al-Shareef H.N. , Tuttle B. A. , Ramesh R. , Evans J. T.
Published: April 2011

We review the processes and mechanisms by which voltage offsets occur in the hysteresis loop of ferroelectric materials. Simply stated, voltage shifts arise from nearinterfacial charge trapping in the ferroelectric. We show that the impetus behind voltage shifts in ferroelectric capacitors is the net polarization, with the net polarization being determined by the perovskite and the aligned defect-dipole components. Some common defect-dipoles in the PZT system are lead vacancy-oxygen vacancy complexes. One way to change the net polarization in the ferroelectric is to subject the PZT capacitor to a dc bias at elevated temperature; this process is spectroscopically shown to align defect-dipoles along the direction of the applied electric field. The alignment of defect-dipoles can strongly impact several material properties. One such impact is that it can lead to enhanced voltage shifts (imprint). It is proposed that the net polarization determines the spatial location of the asymmetrically trapped charge that are the cause for the voltage shifts. An enhanced polarization at one electrode interface can lead to larger voltage shifts since it lowers the electrostatic potential well for electron trapping, i.e., more electron trapping can occur. Defect-dipole alignment is also shown to increase the UV sensitivity of the ferroelectric.
Retentivity Studies on Lead Zirconate Titanate Thin Film Capacitors
Authors: Yoo In K. , Kim Chang J. , Desu Seshu B.
Published: April 2011

Retention characteristics of various ferroelectric memory cell structures, based on lead zirconate titanate (PZT) capacitors, were investigated under different test conditions. Test of retentivity without any pre-treatment, revealed very high rates of polarization loss with time for partially polarized PZT capacitors. However, when different structures were subjected to a thermal cycle before retentivity study, they indicated significant polarization loss or polarization reversal in FRAM and MFMIS(metal-ferroelectric-metal-insulatorsemiconductor) structures. This thermal cycle dependent retentivity problem was attribute to pyroelectric charges that are developed during the temperature cycle.

For each memory cell structure, the underlying mechanisms for the rapid polarization. loss were discussed. Furthermore, guidelines for improving the memory retention were proposed based on the theoretical interpretation of the phenomena.
Electronic Structure of the Layered Ferroelectric Perovskite SrBi2Ta2O9
Authors: Robertson J , Chen C W , Warren W L
Published: April 2011

The band structure of the Bi layered perovskite SrBi2Ta2O9 (SBT) has been calculated by the tight binding method. We find both the valence and conduction band edges to consist of states primarily derived from the Bi-O layer rather than the perovskite Sr-Ta-O blocks. The valence band maximum arises from 0 p and some Bi s states, while the conduction band minimum consists of Bi p states, with a band gap of 5.1 eV. It is argued that the Bi-O layers largely control the electronic response of SBT while the ferroelectric response originates from the perovskite Sr-Ta-O block. Bi and Ta centered traps are calculated to be shallow, which may account in part for the excellent fatigue properties of SBT.
Preparation and Characterization of (Sr1−xTix)O3 and (Ba1−xSrx)TiO3 Thin Films using ECR Plasma Assisted MOCVD
Authors: No Kwangsoo , Lee Joon Sung , Song Han Wook , Lee Won Jong , Yu Byoung Gon , Jiang Zhong-Tao
Published: April 2011

Ba(TMHD)2, Sr(TMHD)2 and Ti-isopropoxide were used to fabricate the (SrxTi1 x)O3 and (Ba1 x Srx)TiO3 thin films. The decomposition and degradation characteristics of Ba(TMHD)2 and Sr(TMHD)2 with storage time were analyzed using a differential scanning calorimeter (DSC). The thin films were fabricated on Si(p-type 100) and Pt/SiO2/Si substrates with Ar carrier gas using ECR plasma (or without ECR plasma) assisted MOCVD. Experimental results showed that the ECR oxygen plasma increased the deposition rate, the ratio of Sr/Ti, the dielectric constant and the leakage current density of the film. The dependency of the crystallinity and the electrical properties on the Sr/Ti ratio of films were investigated. However, almost of the films deposited with Ar carrier gas had slightly high dielectric loss and high leakage current density and showed non-uniform compositional depth profiles. NH3 gas was also used to decrease the degradation of the MO-sources. Mass spectra in-situ monitoring of source vapors in ECR-PAMOCVD system were obtained. By introducing NH3 as a carrier gas, a significant improvement was achieved in the volatility and the thermal stability of the precursors, and the vaporization temperatures of the precursors were reduced compared to Ar carrier gas. The uniform compositional depth profile, less hydrogen and carbon content and the good electrical properties of (SrxTi1−x)O3 thin films were obtained with NH3 carrier gas. The (Ba1−xSrx)TiO3 thin film were fabricated to have very fine and uniform microstructure, the dielectric constant of 456, the dielectric loss of 0.0128, the leakage current density of 5.01 × 10−8A/cm2 at 1V and the breakdown field of 3.65MV/cm.
Synthesis of Carbon Nitride Composite Thin Films Prepared by Pulsed Laser Deposition Method
Authors: Kumar Ashok , Inturi R. B. , Ekanayake U. , Chan H. L. , You Q. , Watiuhewa G. , Barnard J. A.
Published: April 2011

Carbon nitride/titanium nitride composite coatings have been deposited on Si (100) and 7059 coming glass by in-situ pulsed laser deposition technique. A pulsed laser (λ = 248 nm) has been used to ablate the both pyrolytic graphite and TiN targets. It has been shown that TiN provides a lattice-matched structural template to seed the growth of carbon nitride crystallites (W. D. Sproul et. al., Appl. Phys. Lett. Vol. 67, 203–205; 1995). This paper describes the same approach to grow carbon nitride composite coatings with varying thicknesses of buffer layer and carbon nitride films at different temperatures and pressures. Our preliminary results show the superior mechanical properties (hardness and modulli). The films have been characterized by Xray diffractometer, SEM, FTIR and Raman spectroscopic techniques.
Toughening Mechanisms in Al/Al-SiC Laminated Metal Composites
Authors: Lesuer D. R. , Wadsworth J. , Riddle R. A. , Syn C. K. , Lewandowski J. J. , Hunt W. H.
Published: April 2011

The fracture toughness of laminated metal composites consisting of alternating layers of a metal matrix composite (Al6090/SiC/25p) and a monolithic aluminum alloy (Al5182) has been studied as a function of the volume fraction of the component materials. Finite element simulations of the fracture toughness tests have been used to study the mechanisms of crack growth and extrinsic toughening. The mechanisms responsible for toughening in laminated metal composites are described.
Toughness and Subcritical Crack Growth in Nb/Nb3Al Layered Materials
Authors: Bloyer D. R. , Rao K. T. Venkateswara , Ritchie R. O.
Published: April 2011

A brittle intermetallic, Nb3Al, reinforced with a ductile metal, Nb, has been used to investigate the resistance curve and cyclic fatigue behavior of a relatively coarse laminated composite. With this system, the toughness of Nb3Al was found to increase from ∼1 MPa√m to well over 20 MPa√m after several millimeters of stable crack growth; this was attributed to extensive crack bridging and plastic deformation within the Nb layers in the crack wake. Cyclic fatigue-crack growth resistance was also improved in the laminate microstructures compared to pure Nb3Al and Nb-particulate reinforced Nb3Al composites with crack arrester orientations in the laminate providing better fatigue resistance than either the matrix or pure Nb.
Fabrication, Structure and Properties of Aluminum-Aluminide Layered Composites
Authors: Alman D. E.
Published: April 2011

The fabrication of aluminum-aluminide layered composites by reactive bonding of elemental Al and Ni foils was investigated. It was observed that after hot-pressing, thin Ni foils were converted to NiAl. The as-processed Al-NiAl layered structure could be heat-treated to produce an equilibrium Al-Al3Ni layered composite. Tensile tests revealed that composites could be produced that failed in a “tough” manner and were stronger and stiffer than aluminum.
FGMs by Sedimentation
Authors: He Y. , Subramanian V. , Lannutti J.
Published: April 2011

Simple sedimentation in organic solvents followed by hot-pressing is used to produce alumina-NiAI functionally graded materials (FGMs). Varying degrees of agglomeration influenced the phase arrangement in the mixed layer(s) producing microstructural variation. We discovered a pronounced structural dependence on NiAl stoichiometry. Slight variations in Al content are known to influence Tdb and these apparently lead to large increases in residual stress. Zirconia - NiA1 FGMs were better able to accorrunodate these levels of residual stress possibly due to accommodation by enhanced tetragonal phase retention. However, these FGMs undergo transformation of the tetragonal phase to the monoclinic fonn, starting from the surface. Finally, variable microstructures result in detectable changes in the stress-strain behavior of alumina-NiAl FGMs.
Finite Element Studies of the Influence of Pile-up on the Analysis of Nanoindentation Data
Authors: Bolshakov A. , Oliver W. C. , Pharr G. M.
Published: April 2011

Methods currently used for analyzing nanoindentation load-displacement data give good predictions of the contact area in the case of hard materials, but can underestimate the contact area by as much as 40% for soft materials which do not work harden. This underestimation results from the pile-up which forms around the hardness impression and leads to potentially significant errors in the measurement of hardness and elastic modulus. Finite element simulations of conical indentation for a wide range of elastic-plastic materials are presented which define the conditions under which pile-up is significant and determine the magnitude of the errors in hardness and modulus which may occur if pile-up is ignored. It is shown that the materials in which pile-up is not an important factor can be experimentally identified from the ratio of the final depth after unloading to the depth of the indentation at peak load, a parameter which also correlates with the hardness-to-modulus ratio.
Stress Reduction in PACVD Amorphous Diamond Coatings by Boron Addition
Authors: Wagner V. , Dekempeneer E. H. A. , Geurts J. , IJzendoorn L. J. van , Sporken R. , Caudano R.
Published: April 2011

The applications of super hard coatings of diamond-like carbon (DLC) films are often limited by adhesion problems caused by intrinsic stress in the deposited layer due to the PACVD growth process. One approach to reduce the stress are less optimal process parameters. However, they also affect the desired high hardness of the films. Our approach in this study is to add B2H6 to the gas mixture, which shifts the composition towards another very hard compound (B4C). A sequence of amorphous BxC1-x:H films with a thickness of 0.5μm and a boron content between 0 and 50 at.-% were deposited on silicon substrates using a capacitively coupled r.f PACVD reactor. The tribological film properties and the internal stress were determined by depth-sensing indentation and laser reflection measurements. For an addition of x ≥5 at.-% boron the decrease of the internal film stress is found to be clearly larger than the effect on the hardness value. For boron contents x > 18% the internal stress is reduced by a factor of 5 while the reduction of hardness is only a factor of 2.3. For microscopic structure analysis Raman and infrared spectroscopy are applied. They reveal an increasing hydrogenation of the carbon network. Therefore, the softening is attributed to a boron induced modification to a more polymeric-like material.
Nanoindentation of Soft Films on Hard Substrates:The Importance of Pile-Up
Authors: Tsui T. Y. , Oliver W. C. , Pharr G. M.
Published: April 2011

Nanoindentation is a common technique for measuring the mechanical properties of thin films. Here, we address the potential measurement errors caused by pile-up when soft films deposited on hard substrates are tested by nanoindentation methods. Pile-up is exacerbated in soft film / hard substrate systems because of the constraint the substrate exerts on plastic deformation of the film. To experimentally examine pile-up effects, aluminum films with thicknesses of 240 and 1700 nm were deposited on hard glass substrates and tested by standard nanoindentation techniques. The aluminum/glass system is interesting because the film and substrate have similar elastic moduli; thus, any unusual behavior in the nanoindentation results may be attributed to differences in the plastic flow characteristics alone. A detailed scanning electron microscopy examination of nanoindentation hardness impressions in the film revealed that common methods for analyzing nanoindentation data underestimate the true contact areas by as much as 80%, which results in overestimations of the hardness and modulus by as much as 80% and 35%, respectively. The sources of these errors and their influence on the measurement of hardness and elastic modulus are discussed, and a simple model for the composite hardness of the film/substrate system is developed. The model could prove useful in measuring the hardness and elastic modulus of soft-film / hard substrate systems when it is not possible to make indentations shallow enough to avoid the substrate influences.
Mechanical Properties of CaF2Single Crystal Substrates Determined from Nanoindentation Techniques
Authors: Aruga A. , Inturi R. B. , Barnard J. A. , Bradt R. C.
Published: April 2011

CaF2single crystals are interesting substrate materials for deposition of thin films. Its structure is cubic and it cleaves on {111} planes. CaF2, whose hardness has been reported to be 4 on the Moh's scale, is plastic and soft. In this study, the mechanical properties such as hardness(H) and Young's modulus(E) of single crystal CaF2mineral were measured by using a nanoindenter with a Berkovich indenter normal to (100) and (111) planes. A normal indentation size effect (ISE) in accordance with the traditional power law and the proportional specimen resistance model (PSR) of Li and Bradt [1] was observed. The values of E and H on (100) plane are larger than those on (111) plane and these values on both planes decrease with increase in time during the hold segment. The effect of displacement rate on mechanical properties of (100) and (111) surfaces is also studied.
Effect of Film Thickness and Substrate Surface Treatment on Substrate Deformation: DLC on MgO
Authors: Strojny A. , Lilleodden E. T. , Wang G. , Sivertsen J. V. , Gerberich W. W.
Published: April 2011

Diamond-Like Carbon films with thicknesses controlled in the 10 to 100 nm range were sputter-deposited on single crystals of MgO. The substrates were prepared with varying roughness from 5 to 50 nm and varying surface dislocation densities from 100 to 2000 disl./μ2. Mechanical properties of the film and film-substrate interactions were investigated with an atomic force microscope retrofitted with a diamond indenter.

The load bearing capacity of the substrate increased with increasing film thickness. As the indenter approached the film-substrate interface, load excursions occurred for the thinner films. No excursion was found for the thick film. Load excursions may be attributed to dislocations nucleating at the interface and/or film delamination.
Characterization of the Mechanical and Tribological Properties of Sputtered a:SiC Thin Films
Authors: Scharf T. W. , Inturi R. B. , Barnard J. A.
Published: April 2011

D.C. magnetron sputtering from a CVD β-SiC target has been utilized to deposit amorphous SiC thin films on various substrates (Coming 7059 glass, unoxidized Si (111), and sapphire). The approximately 1 μm thick films were grown under various Ar sputtering pressures and flow rates. In situ annealing during deposition in vacuum and ex situ post-deposition annealing in air, both at 500°C for two hours, were implemented to determine their effects on the properties of the films. The mechanical properties were assessed via nanoindentation. An accelerated sphere-on-flat(tape) wear tester was administered to measure the wear volume losses and resultant wear rates under 0.1 and 0.2N loads, a 0.024m/s tape speed, and a 1mm ruby sphere diameter. An atomic force microscope (AFM) established the wear scar volume losses as well as the surface arithmetic roughness (RA) and root mean square roughness (RMS) of the films. The amorphous microstructure was verified by X-ray diffractometry. There was a decreasing trend in the plastic contact damage resistance, hardness, elastic modulus, and wear resistance of the films with increased amounts of Ar gas pressure; on the other hand, annealing of the lower Ar content films generated an increase in these properties compared to the as-deposited films. Atomic force microscopy revealed a more pronounced change in surface features and roughness for the in situ annealed films.
Isothermal Stress Relaxation in Al, Alcu and A1vpd Films
Authors: Lokker J. P. , Jongste J. F. , Janssen G. C. A. M. , Radelaar S.
Published: April 2011

Mechanical stress and its relaxation in aluminum metallization in integrated circuits (IC) are a major concern for the reliability of the material. It is known that adding Cu improves the reliability but complicates plasma etching and increases corrosion sensitivity. The mechanical behavior of AlVPd, AlCu and Al blanket films is investigated by wafer curvature measurements. During thermal cycling between 50°C and 400°C the highest tensile stress is found in AlVPd. In a subsequent experiment, the cooling was interrupted at several temperatures to investigate the stress behavior during an eight hour isothermal treatment. Isothermal stress relaxation has been observed in the three types of films and is discussed.
Strain, Structure and Electronic States in MBE Grown (Nb, Ti)O2 Mixed Rutile
Authors: Chambers S. A. , Gao Y. , Thevuthasan S. , Wen S. , Merkle K. L. , Shivaparan N. , Smith R. J.
Published: April 2011

We have grown and characterized epitaxial NbxTi1-xO2 on TiO2(110) and (100) for the purpose of investigating the role of chemically-inequivalent metal atoms on the thermal and photocatalytic properties of TiO2. Our goal is to introduce, in a highly controlled fashion, a Group VA transition metal into the lattice of a Group IVA transition metal oxide without altering the crystallographic structure. So doing would alter the electronic structure in interesting and potentially useful ways by the addition of one valence electron per substituted metal atom. However, strain builds in the film as more Nb is added at a rate which depends on the crystallographic orientation of the growth direction. Films grown along (110) can accommodate Nb mole fractions as high as ˜0.3 without forming misfit dislocations, whereas those grown along (100) are limited to ˜10 at. % Nb. Nb-O bond lengths in NbxTil−xO2 are the same as Ti-O bond lengths in pure TiO2 prior to the onset of dislocation formation. The extra 4d valence electron per Nb atom forms a nonbonding band which is degenerate with bonding states in the valence band region.
Growth, Structure, and Mechanical Properties of Pulsed Laser Deposited TiN/TiB2 Microlaminates
Authors: Kumar Ashok , Inturi R. B. , Ekanayake U. , Chan H. L. , Barnard J. A.
Published: April 2011

Hard coatings of TiN and TiB2 have many interesting properties such as high thermal and electrical conductivity, high melting point, good thermodynamic stability and combination of these properties make them an interesting prospect for a wide range of tribological and electronic applications. It is understood that artificial multilayer structures have shown anamolously high hardness and modulii making them likely candidate for future protective coatings. Single layer of TiN, TiB2, and TiB2/TiN microlaminates coatings with varying thickness have been deposited on Si (100) and oxidized Si(111) substrates by in-situ pulsed laser deposition method. These films are deposited at 10 Hz repetition rate of excimer laser (λ = 248 nm). Our preliminary results show that elastic modulii and hardness values of multilayered coatings are superior than monolithic coatings of either of the two constituent materials. The coatings have been characterized by X-ray diffiractometer and AFM techniques. Detailed results have been presented to correlate the effect of microlaminate thickness on the mechanical properties.
Fracture of Thin Synthetic Diamond Films
Authors: Drory M. D.
Published: April 2011

Large residual stresses in diamond coatings may result in film failure through splitting, delamination and substrate failure. In addition, the CVD diamond growth environment may degrade the substrate mechanical properties. These issues are examined for diamond-coating of a tool steel alloy. Diamond growth was achieved on the steel substrate with the use of a titanium interlayer. Embrittlement of the Ti interlayer was not evident, however the substrate hardness was severely degraded.
High Resolution Synchrotron X-Ray Diffraction Tomography Of Large-Grained Samples
Authors: Piotrowski D.P. , Stock S.R. , Guvenilir A. , Haase J.D. , Rek Z.U.
Published: April 2011

In order to understand the macroscopic response of polycrystalline structural materials to loading, it is frequently essential to know the spatial distribution of strain as well as the variation of micro-texture on the scale of 100 μm. The methods must be nondestructive, however, if the three-dimensional evolution of strain is to be studied. This paper describes an approach to high resolution synchrotron x-ray diffraction tomography of polycrystalline materials. Results from model samples of randomly-packed, millimeter-sized pieces of Si wafers and of similarly sized single-crystal Al blocks have been obtained which indicate that polychromatic beams collimated to 30 μm diameter can be used to determine the depth of diffracting volume elements within ± 70 μm. The variation in the two-dimensional distribution of diffracted intensity with changing sample to detector separation is recorded on image storage plates and used to infer the depth of diffracting volume elements.
Pb Induced Layer-by-Layer Growth and the Dependence on an Amount of Surfactant in the Growth of Ni on Ni(100) Surface
Authors: Iwanami M. , Kamiko M. , Matsumoto T. , Yamamoto R.
Published: April 2011

Surfactant epitaxy has been expected to be a powerful method to improve thin film growth from three dimensional island mode to layer-by-layer growth one. Supposing that Pb is the surfactant and Ni is the substrate and deposition metal, we have investigated how the surfactant atoms segregate on surface by computer simulations using the modified embedded atom method. To verify the effect of Pb on the homoepitaxial growth of Ni, we have performed a series of experiments on the growth of Ni on Ni(100) surface with and without Pb using reflection high energy electron diffraction (RHEED). It was clearly found that Pb induced layer-by-layer growth of Ni metal film. The result of the dependence of the growth behavior on the thickness of Pb layer suggests that there is the most suitable thickness of a surfactant layer which is not always the monolayer.
Changes in Structure and Composition of Silicon Oxide Thin Films Induced by Ultraviolet Illumination
Authors: Parada E. G. , González P. , León B. , Pérez-Amor M. , Silva M. F. DA , Soares J. C. , Fernández A. , González-Elipe A. R.
Published: April 2011

The transformation of silicon oxide thin films at room-temperature by UV-photons provided by a Xe2* incoherent excimer lamp (λ = 172 nm, Δλ = 14 nm) was studied. Films were produced at low-temperature (T = 260 °C) by ArF laser-induced CVD (LCVD) in parallel configuration from a silane/nitrous oxide/argon gas mixture. The silicon oxide films were irradiated in several consecutive steps to follow-up the modifications with the illumination time. Rutherford backscattering (RBS), infrared (IR) and X-ray photoelectron (XPS) spectroscopies, ellipsometry, and elastic recoil detection analysis (ERDA) were used to characterize the effects of the irradiation on the structure, composition, density, and hydrogen content.

Under the UV illumination the as-deposited film evolves from a suboxide film (SiO1.6) to a stoichiometric silicon dioxide (SiO2), and its originally strained structure changes towards a relaxed tetrahedral configuration. The UV irradiation is able to anneal at room temperature the silicon oxide films breaking the Si-H bonds and incorporating new SiO and hydroxyl groups in a relaxed network. The hydrogen does not effuse out, but remains in the film as molecular hydrogen and/or forming silanol or water groups.
Structure and Magnetic Properties of Epitaxial Ordered FePd (001) Thin Films
Authors: Gehanno V. , Marty A. , Gilles B.
Published: April 2011

Equiatomic FePd (001) thin films have been deposited by Molecular Beam Epitaxy on a Pd (001) surface. We show that the degree of chemical order in the epitaxial layer is highly dependant on the temperature of deposition thus leading to a drastic change in the magnetic properties. At 25°C, while the RHEED oscillations reveal a layer by layer growth, the structural study demonstrates that the disordered phase has grown. In that case, the easy magnetization axis lies in the plane of the layer. At 350°C, the RHEED oscillations show that the growth proceeds bilayer by bilayer. We find that the tetragonal L10 ordered phase is stabilized with its 4-fold symmetry axis along the growth direction and this results in a perpendicularly magnetized thin film. The Transmission Electron Microscopy study reveals the presence of twins and antiphase boundaries in the ordered film.
Tem Study of Strain Compensated InP/GaAs/GaP/GaAs Superlattice Structures
Authors: Rusakova I. , Bensaoula A. H. , Bensaoula A.
Published: April 2011

In this work, we investigate the effects that alternating stress has on the structural quality of chemical beam epitaxy grown InP/GaAs/GaP/GaAS superlattices. Grown on GaAs (100), InP has a lattice mismatch of +3.9% whereas that of GaP grown under the same conditions is -3.7%. We have shown in previous work [1] that it is possible to use the principle of strain balancing to achieve highly coherent, electronically active, structures. We use TEM to first evaluate the critical thickness of GaP/GaAs and InP/GaAs heterolayers, then proceed with an extensive structural study of strain compensated structures. Misoriented substrates were also chosen to intentionally induce dislocations, allowing us to observe their structure without changing the overall strain conditions.
Characterization of Co-Cr-Mo Alloys Used in HIP Implant Articulating Surfaces
Authors: Varano R. , Bobyn J. D. , Yue S.
Published: April 2011

The microstructure, crystallography and mechanical properties of a wrought (ASTM F-1537) Co-Cr- Mo hip implant alloy were studied in this work. The effects of carbon content, heat treatment and room temperature compression on the above characteristics were also analyzed. Metallography of the asreceived material revealed the presence of ‘twins’ in a relatively fine microstructure with some randomly distributed grain boundary carbides. Heat treatment of the specimens produced a coarser microstructure, more uniformly distributed grain boundary carbides and annealing twins. Neutron diffraction of the specimens, which were deformed at room temperature, exhibited an increase in the volume fraction of the more stable Co-hexagonal closed-packed (HCP) crystal structure, due to a strain-induced transformation (SIT) from the metastable Co-face-centered cubic (FCC) crystal structure. It was also seen that the higher C specimens, as well as the heat treated specimens, possessed a lower volume fraction of the HCP phase. It was found, through shear punch testing, that the deformed specimens exhibited higher mechanical properties without any significant losses to the ductility of the material.
The Synthesis and Superconducting Behavior of Crystalline Superlattices: (TiSe2)m(NbSe2)n
Authors: Noh Myungkeun , Johnson David C.
Published: April 2011

A series of kinetically stable, crystalline superlattices containing an integral number of intergrown TiSe2 and NbSe2 layers have been synthesized by controlled crystallization of elementally modulated reactants. Theta-theta and rocking curve data were collected to study the evolution of the initially layered reactants into the crystalline superlattices as a function of temperature. Nucleation of the dichalcogenide structure occurs upon annealing at temperatures above 200°C with the c-axis oriented perpendicular to the substrate surface. The [00l] diffraction linewidths decrease with increased annealing time and temperature suggesting growth of the c-axis domain size. High quality c-axis oriented dichalcogenide crystalline superlattices result from extended annealing at the relatively low annealing temperature of 500°C. The large number of well resolved [00l] Bragg diffraction peaks confirm the well developed crystal structure of the product superlattices in this direction. Four probe electrical conductivity measurements were used to determine the variation of the superconducting critical temperature as a function of the number of TiSe2 and NbSe2 layers in the superlattice.
Mixed Mode Fracture in Electronic Packages
Authors: Soboyejo W. O. , Sinha V. , Kenner V.
Published: April 2011

In this paper, mixedmode (mode I + mode II) fracture toughness data are presented for the prediction of molding compound (silica filled epoxy resin) failure. The stresses necessary to cause the package cracking under mixed mode loading are experimentally determined. Measured toughness values are presented as a function of modemixity and temperature
Microstructure and Reliability of Sputter Deposited
Cr-Crcu-Cu thin Films for Flip-Chip Applications
Authors: Zhang Na , Mcnicholas Mark , Colvin Neil
Published: April 2011

The Cr‐CrCu‐Cu metal scheme, as a terminal multistructure metallization for flip chip applications, has been investigated utilizing PVD sputter deposition varying the conditions of deposition power and temperature, and film thickness. A modified Controlled Collapse Chip Connection (C4) process was utilized in order to evaluate the aforementioned deposition of the Cr‐CrCu‐Cu multilayers and the effect of film microstructure on the parameters of shear strength and thermal cycle reliability. Thermal cycle reliability results proved to be a function of both the CrCu alloy and the Cu overlayer thickness. Transmission electron microscopy (TEM) cross‐sections of the Cr‐CrCu‐Cu multilayers suggests that the columnar grain structure of the CrCu layer may provide a sacrificial thermal diffusion barrier between the PbSn alloy solder balls and the Al bond pads during the thermal‐cycle tests.
Selective Growth of GaN and Al0.2Ga0.8N on GaN/AlN/6H-SiC (0001) Multilayer Substrates Via Organometallic Vapor-Phase Epitaxy
Authors: Nam O. H. , Bremser M. D. , Ward B. L. , Nemanich R. J. , Davis R. F.
Published: April 2011

The selective growth of GaN and Al0.2Ga0.8N has been conducted on stripe and circular patterned GaN/A1N/6H-SiC(0001) multilayer substrates. Growth morphologies on stripe patterns changed with the widths of stripes and the flow rate of TEG. No ridge growth was observed along the edges of the stripe patterns, and the (0001) top facets were very smooth. Uniform hexagonal pyramid arrays of undoped GaN and Si-doped GaN were successfully grown on 5μm circular patterns. Field emission measurement of a Si-doped GaN hexagonal pyramid array exhibited a turn-on field of 25V/μm for an emission current of 10.8nA at an anode-to-sample distance of 27μm.
The Effect of Hydrogen on the Molecular-Beam-Epitaxy Growth of GaN on Sapphire Under Ga-Rich Conditions
Authors: Buczkowski S. L. , Yu Zhonghai , Richards-Babb M. , Giles N. C. , Romano L. T. , Myers T. H.
Published: April 2011

Nucleation and growth of GaN under Ga-rich conditions by molecular beam epitaxy using a nitrogen rf plasma source is shown to result in both a smoother GaN surface and a reduced inversion domain content. In addition, preliminary results of the dramatic effect of atomic hydrogen on growth kinetics for Ga-rich growth are presented.
Impact of Growth Temperature, Pressure, and Strain on the Morphology of GaN Films
Authors: Fujii H. , Kisielowski C. , Krueger J. , Leung M. S. H. , Klockenbrink R. , Rubin M. , Weber E. R.
Published: April 2011

GaN films grown on sapphire at different temperatures are investigated. A Volmer-Weber growth mode is observed at temperatures below 1000K that leads to thin films composed of oriented grains with finite size. Their size is temperature dependent and can actively be influenced by strain. Largest grains are observed in compressed films. It is argued that diffusing Ga ad-atoms dominate the observed effects with an activation energy of 2.3 ± 0.5 eV. Comparably large grain sizes are observed in films grown on off-axes sapphire substrates and on bulk GaN. This assures that the observed size limitation is a consequence of the 3D growth mode and not dependent on the choice of the substrate. In addition, the grain size and the surface roughness of the films depend on the nitrogen partial pressure in the molecular beam epitaxy (MBE) chamber,most likely due to collisions between the reactive species and the background gas molecules. This effect is utilized to grow improved nucleation layers on sapphire.
Nano-Tubes in GaN
Authors: Liliental-Weber Z. , Chen Y. , Ruvimov S. , Swider W. , Washburn J.
Published: April 2011

Formation of vertical hollow nano-tubes in GaN grown on different substrates using different growth methods is described. These defects are shown to be of several different types, some related to threading dislocations, but others originating at tubular inversion domains, or crystal inhomogeneities. Kinetic mechanism based on slow growth rate on polar {0111} surfaces is proposed to explain the origin of these defects.
Inversion Domain Boundaries in GaN Grown on Sapphire
Authors: Romano L. T. , Northrup J.E.
Published: April 2011

Inversion domain boundaries (IDBs) in GaN grown on sapphire (0001) were studied by a combination of high resolution transmission electron microscopy, multiple dark field imaging, and convergent beam diffraction. Films grown by molecular beam epitaxy (MBE), metalorganic vapor deposition (MOCVD), and hydride vapor phase epitaxy (HVPE) were investigated and all found to contain IDBs. Inversion domains (IDs) that extended from the surface to the interface were found to be columnar with facets on the {10–10} and {11–20} planes. Other domains ended within the film that formed IDBs on the (0001) and {1–102} planes. The domains were found to grow in clusters and connect at points along the boundary.
High Resolution X-ray Diffraction Analysis of GaN-Based Heterostructures Grown by OMVPE
Authors: Goorsky M.S. , Polyakov A.Y. , Skowronski M. , Shin M. , Greve D.W.
Published: April 2011

We demonstrate the use of triple axis diffraction measurements, including Φ scans (in which the sample is rotated about an axis perpendicular to its surface) to assess the crystal perfection of wurtzite GaN layers on sapphire grown using different pre-nitridation growth treatments by or-ganometallic vapor phase epitaxy. The Φ scans determine the in-plane misorientation angles between the crystallites and hence provide information on the edge dislocation density. Using glancing incidence (1014) and (1015) reflections, we determined that the misorientation among the GaN crystallites decreases with increasing layer thickness and that the pre-nitridation conditions control the initial level of misorientation. Triple axis ω and ω-2θ scans around the (0002) reflection did not show a systematic trend with increasing layer thickness. However, layers grown without a pre-nitridation step tended to exhibit higher values of both mosaic spread and strain. The appropriate asymmetric reflections for GaN-based Φ scan measurements are determined using structure factor calculations, which are presented here.
Free and Bound Excitons in GaN Epitaxial Films
Authors: Meyer B.K.
Published: April 2011

We report on photoluminescence experiments on hexagonal GaN epitaxial films grown on 6H-SiC and sapphire substrates by organo-metallic and hydide vapor phase epitaxy. At low temperatures we observe free and neutral donor bound exciton transitions which allow to establish properties of the free excitons and localisation energies of the bound excitons involving different shallow donors. From temperature dependent luminescence experiments thermal activation energies are determined which measure the exciton localization and donor binding energies. The localization energies of the excitons scale with the respective donor binding energies (Haynes rule). The inter-impurity transitions of neutral donors are observed in fourier transform infra-red absorption. Three shallow donors with binding energies of 34.7 meV, 55 meV and 58 meV can be seen. We present evidence for the chemical nature of the shallow impurities.
Magnetic Resonance Studies of High-Resistivity GaN Films Grown on Al2O3
Authors: Glaser E. R. , Kennedy T. A. , Wickenden A. E. , Koleske D. D. , Freitas J. A.
Published: April 2011

We have made an attempt to obtain electronic and atomic structure information on the residual defects that exist in high-resitivity GaN epitaxial layers from optically-detected magnetic resonance (ODMR) experiments performed on the broad 3.0 and 2.2 eV photoluminescence (PL) bands observed from these films. The first observation of magnetic resonance on this 3.0 eV band reveals two ODMR signals. The first resonance is sharp (FWHM ∼ 3.5 mT) with g ∼ 1.950 and is assigned to effective-mass (EM) donors based on previous studies. The second feature is much broader (FWHM ∼18 mT) with a donor-like g-value of ∼ 1.977. This new resonance may be associated with partially EM-like donor states located ∼ 54 - 57 meV below the conduction band edge proposed recently to be involved in this 3.0 eV PL band.
Effects of X-ray and γ-ray Irradiation on GaN
Authors: Qiu C. H. , Leksono M. W. , Pankove J. I. , Rossington C. , Haller E. E.
Published: April 2011

As part of the feasibility study of using III-V nitride semiconductors for x-ray and γ-ray detection, the irradiation effects on GaN were investigated. GaN films with very different electrical resistivity and electron concentration were used in the study. The electron mobility, photoconductivity spectra, and photo-luminescence spectra were measured before and after irradiation. An enhanced ημτ product for undoped GaN films and an enhanced blue luminescence for a Zn-doped sample were observed after irradiation.
Emission Mechanism of the InGaN MQW Grown by MOCVD
Authors: Narukawa Yukio , Kawakami Yoichi , Fujita Shizuo , Fujita Shigeo , Nakamura Shuji
Published: April 2011

Dynamical behavior of radiative recombination has been assessed in the In0.20Ga0.80N (3nm)/In0.05Ga0.95N (6 nm) multiple quantum well (MQW) structure by means of transmittance (TR), electroreflectance (ER), photoluminescence excitation (PLE) and time-resolved photoluminescence (TRPL) spectroscopy. The PL at 20 K was mainly composed of two emission bands whose peaks are located at 2.920 eV and 3.155 eV. The ER and PLE revealed that the transition at 3.155 eV is due to the excitons at quantized level between n=1 conduction and n=1 A(Γ9υ) valence bands, while the main PL peak at 2.920 eV is attributed to the excitons localized at the trap centers within the well. The TRPL features were well understood as the effect of localization where photo-generated excitons are transferred from the n=1 band to the localized centers, and then are localized further to the tail state. The origin of the localized centers were attributed to the In-rich region in the wells acting as quantum dots which could be observed by transmission electron microscopy (TEM) and energy-dispersive X-ray microanalysis (EDX).
Optical Dielectric Response of Gallium Nitride Studied by Variable Angle Spectroscopic Ellipsometry
Authors: Yao H. , Yan C. H. , Jenkinson H. A. , Zavada J. M. , Speck J. S. , Denbaars S. P.
Published: April 2011

Variable angle spectroscopic ellipsometry (VASE) and transmission measurements have been employed to study the dielectric response of gallium nitride (GaN) thin films — an important material for light emitting diodes (LEDs) and laser diodes applications. The GaN films were grown by atomsphere pressure metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates (α-AI2O3). Room temperature VASE measurements were made, in the range of 0.75 to 5.5eV, at the angle of incidence of 73, 75, and 77 degree, respectively. Evidence of anisotropy is observed especially in the spectral range under the band gap (∼3.4 eV), reflecting the nature of wurtzite crystal structure of GaN. The ordinary dielectric function ε⊥(ω) of GaN were obtained through the analysis of transmission and VASE data in the range below and above the band gap. The thickness of these GaN films is also determined via the analysis.
Growth of High Quality Poly-SiGe on Glass Substrates
Authors: Shiota Kunihiro , Inoue Daisuke , Minami Kouichirou , Yamamoto Masaji , Hanna Jun-ichi
Published: April 2011

The composition variation and strutural properties of poly-SiGe thin films were investigated by Reactive Thermal CVD with Si2H6 and GeF4. Deposition of the films was carried out at a low temperature of 450°C on oxidized silicon substrates using different growth parameters, i.e., the source gas flow ratio (Si2H6/ GeF4) and thegas flow rate. The structural profiles of as-deposited films were characterized by X-ray diffraction (XRD) and Raman scattering spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

All these films show (220) preferential orientation. The mole fractions of Si in poly-SixGe1−x films were estimated to be from 0.95 to 0.05 for x by using Vegard's law for the XRD peaks. TEM observation revealed that high crystallinity was well established even in poly-Si0.95Ge0.05 films owing to the direct nucleation on the substrate surface.
Comparative Optical Studies of Chemically Synthesized Silicon Nanocrystals
Authors: Delgado Gildardo R. , Lee Howard W.H. , Kauzlarich Susan M. , Bley Richard A.
Published: April 2011

We studied the optical and electronic properties of silicon nanocrystals derived from two distinct fabrication procedures. One technique uses a controlled chemical reaction. In the other case, silicon nanocrystals are produced by ultrasonic fracturing of porous silicon layers. We report on the photoluminescence, photoluminescence excitation, and absorption spectroscopy of various size distributions derived from these techniques. We compare the different optical properties of silicon nanocrystals made this way and contrast them with that observed in porous silicon. Our results emphasize the dominant role of surface states in these systems as manifested by the different surface passivation layers present in these different fabrication techniques. Experimental absorption measurements are compared to theoretical calculations with good agreement. Our results provide compelling evidence for quantum confinement in both types of Si nanocrystals. Our results also indicate that the blue emission from very small Si nanocrystals corresponds to the bandedge emission, while the red emission arises from traps.
Recent Progress in Microcrystalline Semiconductor Thin Films
Authors: Tanaka K.
Published: April 2011

Nanocrystalline/microcrystalline thin films prepared at relatively low temperatures by plasma-enhanced chemical vapor deposition (PECVD), in particular hydrogenated microcrystalline Si films (μc-Si:H), have attracted an increasing attention not only as potential materials for thin film solar cells, but also as active layers in thin film transistor arrays for flat panel displays. This paper reviews recent progress in the investigation of these materials; preparation methods, structural and optical properties, and electronic transports. Emphasis is placed on the understanding of the growth mechanism of μc-Si:H films as well as the microscopic characterization of the film structure.