bluuebunny/crossref_metadata_2025 huggingface dataset:
Ulm-12 and Ulm-19: The Hydrated and Anhydrous Forms of the First Synthetic Oxyfluorinated Iron Phosphate with an Open Structure
Authors: Cavellec Myriam , Riou Didier , Grenèche Jean Marc , Férey Gérard
Published: April 2011

ULM-19 or [Fe4(PO4)4F2], [C6H14N2], was obtained in a monocrystalline form from the dehydration of single crystals of ULM-12, or [Fe4(PO4)4F2(H2O)3], [C6H14N2] at 260°C. It is monoclinic (S.G. P21/n) with a = 10.009(7), b = 12.235(8), c = 17.28(2) Å, β = 106.04(5)°, V = 2034(3) Å3, Z = 4. Its structure, which can be described from the corner sharing of hexameric Fe3P3 and dimeric FeP units, directly derives from that of ULM- 12 by the loss, on three of the four Fe(III) polyhedral sites of the structure of ULM-12, of the terminal water molecules. This induces drastic changes in the coordination polyhedra of Fe(III): three octahedra and one square pyramid in ULM-12, and one octahedron, one square pyramid, one trigonal bipyramid and one tetrahedron in ULM-19. These evolutions were confirmed and characterized by in situ Mössbauer spectrometry measurements using a cryofurnace. The loss of water opens 6-ring channels beside the 12-ring tunnels already existing in ULM-12.
Precipitation of Spinel Iron Oxide : Nanoparticle Size Control
Authors: Jolivet J. P. , Vayssieres L. , Chaneac C. , Tronc E.
Published: April 2011

The mean particle size of magnetite precipitated in aqueous solution can be adjusted and stabilized against ripening over a large nanometric range (1.5 to 12.5 nm) by controlling the pH and the ionic strength imposed by a non-complexing salt in the precipitation medium. The higher the pH and the ionic strength are, the smaller the particle size is. An explanation for this phenomenon is based on the lowering of the oxide-solution interracial tension due to the surface electrostatic charge increase. A critical pH value corresponding to the saturation of the interface is defined and calculated. When the precipitation is effected above this critical pH value, the spontaneous decrease in surface area by ripening is avoided and, for a given ionic strength, the particle size depends only on the acidity. This model correlates well with the experimental results. This provides the first experimental example of thermodynamic stabilization of oxide nanoparticles.
Low Temperature Hydrothermal Processing (<100°C) of Stoichiometric BaxSr1-xTiO3 Thin Films and Powders
Authors: Roeder Ryan K. , Slamovich Elliott B.
Published: April 2011

BaxSr1-xTiO3 (BST) thin films and powders were processed below 100°C by hydrolyzing Ti metal-organic precursors and TiO2 powder in alkaline Ba/Sr containing aqueous solutions. Film and powder stoichiometries were examined by x-ray diffraction (XRD), and powder stoichiometries were measured by wavelength dispersive spectroscopy (WDS). Both XRD and WDS results showed that Sr cations were more readily incorporated in BST than Ba cations. A thermodynamic model is introduced to predict BST stoichiometry for pH and solution composition. The model is demonstrated for carbonates that also form hydrothermally with Ba and Sr in solid solution, showing good agreement with experimentally measured stoichiometries and confirming a higher reactivity of the Sr cation.
Mixed-Metal Templated Phosphate Phases
Authors: Nenoff Tina M. , Jackson Nancy B. , Harrison William T. A. , Thoma Steven G. , Kohler Steven D.
Published: April 2011

In an effort to direct the structure formation and subsequently the catalytic properties of novel materials, both organic molecules and transition metals have been systematically incorporated into zinc phosphate materials, and various transition metals into zirconium phosphate materials. The resultant phases in the Zn/P experiments are determined not by the organic template, but by the type and stoichiometric amount of metal incorporated and by the organic template's anion. Furthermore, only one of the phases, a Ni/Zn/P, shows any acidic catalytic behavior. Similarly, the transition metals incorporated in stoichiometric amounts into the catalytically active novel zirconium phosphate are highly structure directing. Their presence inhibits the formation of the phosphate phase, instead promoting the formation of tetragonal ZrO2. The catalytic activity of the products are greatly diminished from the baseline material.

The synthesis and characterization methods for each phase will be presented. Characterization techniques employed include single-crystal and powder X-ray diffraction, magnetic susceptibility, thermal analysis, DCP and FTIR.
Colloidal Chemistry of Mineral Coagulants as Influenced by Organic Ligands
Authors: Molis E. , Thomas F. , Bottero JY.
Published: April 2011

In the present work, we examine the transformations of aggregated Al13 polycations interacting in suspension with low-molecular-weight organic acids at near neutral pH. The consequences of the interaction strongly depend on the complexing power and concentration of ligands. The most striking feature is the existence of two domains separated by a characteristic adsorbed ligand concentration, corresponding to charge neutralisation by ligands. In the lower concentration domain, ligands interact with the surface aluminum atoms by forming complexes, decreasing the surface charge. In this domain, no soluble aluminum is released from the aggregates. At higher concentration, ligands are adsorbed in excess by ligand exchange and hydrogen bonding, which results in charge reversal. Simultaneously, ligand promoted dissolution of the aggregates occurs, in the form of soluble complexes. It is assumed that dissolution originates from the initially neutral sites. In aquatic media, such radical insitu changes are able to strongly influence the transport and sedimentation of colloids and associated species.
17O NMR Studies of Titanate Repolymerization in Water
Authors: Bunker B. C. , Peden C. H. F. , Kirkpatrick R. J. , Turner G. L.
Published: April 2011

Local structures of high surface area sodium titanate materials have been examined as a function of pH using solid state 17O nuclear magnetic resonance (NMR) spectroscopy. Using 17O NMR, it is possible to determine the relative populations of nonbridging oxygens as well as oxygens bridging between two, three, and four titanium atoms. Results show that protonation of ion exchange sites in titanate materials is not a simple ion exchange process but involves a repolymerization and restructuring of the titanate network. The observed structural changes are consistent with reported phase stabilities of titanates in water as well as with known hydrolysis and condensation reactions.
Effects of Sputter-Deposited LaNiO3 Electrode on the Deposition and Properties of Ferroelectric Thin Films
Authors: Wu T. B. , Wu J. M. , Wu C. M. , Shyu M. J. , Chen M. S. , Doing J. S. , Yang C. C.
Published: April 2011

Highly (100)-textured thin film of metallic LaNiO3 (LNO) was grown on the Pt/Ti/SiO2/Si substrates by rf magnetron sputtering at ˜300°C, which was used as a bottom electrode to prepare highly (100)-textured ferroelectric films. Examples on the deposition of PbTiO3, (Pbl−xLax)TiO3, Pb(Zr0.53Ti0.47)O3, Pb[(Mg1/3Nb2/3)1−xTix]O3, and (Ba1−xSrx)TiO3 thin films by rf magnetron sputtering or sol-gel method are shown. A reduction of temperature for perovskite phase formation can be achieved, especially for those difficult to crystallize. The surface roughness of the ferroelectric films is also improved as compared to that of films deposited on conventional Pt electrode. Although the electrical properties of the ferroelectric films are affected by the out-diffusion of LNO when a higher temperature was used in the preparation of the films, under an appropriate processing condition, the highly (100)-textured films can have satisfactory electrical characteristics for application. Moreover, the polarization-fatigue property can be also improved by the use of LNO electrode.
Preparation of PbZrxTi1−xO3 Thin Films by KrF Excimer Laser Ablation Technique
Authors: Kurogi Hiromitsu , Yamagata Yukihiko , Ikegami Tomoaki , Ebihara Kenji , Tong Bok Yin
Published: April 2011

Pb(ZrxTi1−x)O3(PZT) thin films have excellent ferroelectric, optical, piezoelectric and pyroelectric properties. We prepared PZT thin films using the excimer laser ablation technique. A pulsed KrF excimer laser was used to ablate PZT bulk targets. We have studied optimum preparation conditions such as an oxygen pressure, a laser energy fluence and a substrate temperature.

In this paper, we investigated the composition, crystallization and ferroelectric properties of the PZT films prepared under various deposition conditions.

The X-ray diffraction (XRD) patterns showed that the PZT films prepared on MgO(100) substrates at 600°C and with a laser fluence of 2J/cm2 had a perovskite - pyrochlore mixed structure. The condition of 100 mTorr oxygen pressure provided high quality perovskite films. It is found that the stoichiometric composition of the deposited films is obtained in ambient oxygen of 100˜400 mTorr. The ferroelectric properties of the Pt/PZT/Pt/MgO structure were studied. The capacitance-voltage characteristics and the corresponding hysteresis loop of the dielectric-electric field curve were discussed.

We also studied optical emission of the PZT plasma plume to understand quantitative relation between the PZT film quality and the ablation plume plasma. We identified spectral lines originated in Pb, Pb+, Zr, Zr+, Ti, Ti+, PbO and TiO. These spectral intensities have remarkable dependence on the ambient O2 pressure.
Photoelectric Properties of PbTiO3/Si Heterostructures
Authors: Alexe M. , Pintilie L. , Pintilie I. , Pignolet A. , Senz S. , Hesse D.
Published: April 2011

Photoelectric properties of PbTiO3/Si heterostructures were investigated over a broad range of wavelengths. The spectral distribution of the a.c. open-circuit voltage was measured for wavelengths ranging from 0.35 μm to 4 μm. Two local peaks are observed at 0.38 μm and 0.9 μm which can be attributed to band-to-band excitations in PbTiO3 and Si respectively. The shape of the a.c. signal depends both on the light intensity and on the wavelength. When the heterojunction is reverse-biased, a d.c. photocurrent was observed which has a similar spectral distribution as the a.c. open-circuit voltage.
Preparation of Self-Patterned SrBi2Ta2O9 Thin Films from Photo-Sensitive Solutions
Authors: Soyama Nobuyuki , Uchida Hiroto , Kageyama Kensuke , Ogi Katsumi , Scotit Michael C. , Cuchiaro J. D. , Derbenwick G. F. , Mcmillan Larry D. , Araujo Carlos A. Paz De
Published: April 2011

Photo-sensitive SrBi2Ta2O9 (SBT) solutions were evaluated and the patterning process flow for SBT films using the solutions was optimized. By adding a soft-bake process before UVirradiation, self-patterned SBT films were successfully prepared from the solutions and the cross sectional shape of the patterned films was improved. The photo-sensitivity of the solutions was estimated to be 900 mJ/cm2. The photo-reaction in the precursor gel film formed from the solution was traced by measuring IR absorption spectra. The obtained films had excellent ferroelectric properties comparable to conventional SBT films.
Mechanical and Thermal Stability of Heavily Drawn Pearlitic Steel Wire
Authors: Aernoudt Etienne , Sevillano Javier Gil , Delrue Hilde , Humbeeck Jan Van , Watté Piet , Lefever Ignace
Published: April 2011

Having interlamellar spacings on the nanometer scale, there is no doubt about considering heavily drawn pearlitic steel wire as a nano-layered material. This extremely fine structure is of great technical importance: indeed, as the interlamellar distance determines the onset of plastic flow, the wire can be brought to a tensile strength beyond 4000 MPa and is therefore one of the strongest materials on the market nowadays.

At extremely large strains (well beyond ε = 4) and/or at moderate temperatures, the pearlitic steel loses its strength. Several possible failure mechanisms, like fragmentation of the cementite or thermal and strain-induced cementite dissolution, are put forward, but until now, there is no definite understanding of the really active mechanism.

In the present work, the calorimetric differential scanning technique, in combination with thermopower measurements and the high-resolution atomic force microscopy, have turned out to be most promising tools to reveal some of the mechanisms that are responsible for the degradation of the lamellar aggregate.
Orowan-Based Deformation Model for Layered Metallic Materials
Authors: Kreidler Eric R. , Anderson Peter M.
Published: April 2011

An Orowan-based deformation model for layered metallic materials is presented and used to calculate the stress-strain behavior for two deformation modes. This model assumes that layer thicknesses are sufficiently small so that single rather than multiple dislocation pileups form. Deformation then proceeds by increasing the density of single dislocation pileups. Furthermore, it is assumed that the controlling stress for plastic deformation is that to propagate a tunneling dislocation loop inside an embedded elastic-plastic layer. Initially, the resolved stress required to propagate an isolated tunneling loop does not depend on whether the loop shears the layer perpendicular to an interface or stretches it parallel to an interface. At larger strains, the tunneling arrays become sufficiently dense such that local dislocation interaction changes the line energy of a tunneling dislocation. As a result, the elastic-plastic layers may exhibit modest softening when sheared or substantial hardening when stretched. When the elastic-plastic layers are embedded into a multilayered specimen with alternating elastic-only layers, no macroscopic strain softening is observed. However, the predicted macroscopic stress-strain curves for stretching and shearing are significantly different in their dependence on layer thickness.
Effects of Ductile Phase Additions on the Fracture Behavior and Toughness of DRA Composites
Authors: Ellis L. Yost , Lewandowski J. J. , Hunt W. H.
Published: April 2011

Discontinuously reinforced aluminum (DRA) composites have been processed to contain discrete regions of unreinforced aluminum with the objective of enhancing the damage tolerance. The effects of changes in the ductile phase size, shape and strength as well as the SiCp reinforcement distribution on the toughness were studied. The incorporation of the ductile phase can increase the crack growth resistance of the DRA composite. In such cases, stable crack propagation (i.e. R curve behavior) is observed in contrast to the behavior of the conventional DRA composite which fails catastrophically under the conditions tested. The level of toughening is affected by the size and mechanical properties of the ductile phase as well as the orientation and shape of the ductile regions with respect to the test geometry (i.e. crack arrestor vs crack divider).
Mechanical Property Data for Coated Systems-The Prospects for Measuring “Coating Only” Properties using Nanoindentation
Authors: Hainsworth S. V. , Page T. F.
Published: April 2011

One of the critical aspects of assessing the properties of coated systems is the prospect of being able to measure the properties of the coating in isolation of the substrate. This has led to an increase in the use of continuously-recording indentation techniques (or nanoindentation techniques) for assessing the mechanical properties of coated systems since they can be used to measure the materials response to contact deformation at a scale relevant to the coating thickness. This paper presents the results of a new method for analysing the nanoindentation loading curves for coated systems. The analysis of the loading curve uses the relationship P = Kmδ2 which describes the indenter displacement, δ, in terms of the applied load P. For each material, Km can be predicted from its modulus E and hardness H. One result is that if either of E or H is known, then the other may be calculated from the experimental loading curve. Further, the method has the potential to differentiate between the responses of the coating only, the coating and substrate in combination, and that dominated by the substrate once the load has become sufficient for cracking of the coating such that it no longer plays a significant role in supporting the applied load. In many cases, careful analysis of the loading curves allows the displacement ranges associated with these regimes to be identified. This is shown to be a powerful experimental tool for the interpretation of the mechanical properties of coated systems.
Probing Silicate/Sapphire Interfaces with AFM and Nanoindentation
Authors: Lilleodden E. T. , Zagrebelny A. V. , Ramamurthy S. , Carter C. B.
Published: April 2011

A nanoindentation study of a calcium-aluminosilicate/α-alumina system is described. Thinfilms of CaAl2Si2O8 glass were deposited on α-alumina single crystals of {1120} and {1102} orientations by pulsed-laser deposition. These samples were then subjected to a heat treatment causing the glass to crystallize and to dewet the sapphire surface. A nanoindentation device retrofitted on an atomic force microscope was employed to probe the mechanical properties of the samples. It uniquely enables the characterization of sub-micron features such as the dewet crystallites which necessitate small displacements and exact positioning of the indenter. Strong dependencies on the crystallographic anisotropy were observed in the morphology, but less so on the mechanical properties. In addition, displacement-excursions were observed and are explained in terms of yielding in the substrate.
The Influence of Strengthening Mechanisms on Stress Relaxation in Thin Aluminum Metallization
Authors: Gorrell Jonathan , Holloway Paul , Jerman Hal
Published: April 2011

With the development of microelectromechanical systems there is a need for stronger aluminum thin films that resist stress relaxation. A number of strengthening mechanisms are used extensively for bulk aluminum alloys, but very few have been used to improve the performance of thin films. Pure aluminum, standard microelectronicsmetallization (A1-.04Cu-.017Si), alloy T201 (Al-.046Cu-.006Ag-.004Mn-.003Mg-.003Ti), and alloy 2090 (Al-.026Cu-.021Li-.001Zr) were electron beam evaporated or sputter deposited onto (100) silicon substrates.. Stress versus temperature and stress relaxation were measured in the films. Pure aluminum and AlSiCu alloy films exhibited plastic deformation at low stresses and low temperatures. The T201 and 2090 films exhibited residual elastic stresses at room temperature of 350 MPa and 500 MPa, and did not plastically deform until 240°C at 100 MPa stress, or 270°C at 200 MPa stress, respectively. The T201 film also showed a low stress relaxation rate. We speculate that solid solution strengthening caused the increase in strength of the T201 film, and that age hardening caused the increase in strength of the 2090 film.
Thermal Properties of Magnetron Sputtered TiN And TiAlN Thin Films on HSS
Authors: Lugscheider E. , Knotek O. , Barimani C. , Zimmermann H. , Lake M.
Published: April 2011

Increasing demands on production processes in terms of performance, reliability and environmental compatibility shape the specification profile for modem wear resistant coating systems. The specification of PVD coated cutting tools by the parameters hardness, wear and frictional behavior, chemical structure or chemical resistance are already known and inspected by small scale tests, e.g. pin on disc or taber abraser test. Hitherto the thermophysical properties of thin film PVD coatings were not characterized completely although the investigation of the thermal diffusivity of coated substrates give information about the thermal barrier function of the deposited coating.

To determine the thermophysical properties of PVD coatings the Jenoptik Thermal Wave Inspection (TWIN) can be used. This nondestructive and contactless measuring system is based on the photothermal spectroscopy. In this paper fundamentals of the TWIN measuring technique are presented as well as first TWIN results of investigated MSIP TiN and TiAlN coated and oxidized high speed steels.
The Study of Tribological Performance and Surface Film Characterization of Bismuth Dioctyldithiocarbamate
Authors: Ligeong Chen , Junxiu Dong , Guoxu Chen
Published: April 2011

In this study, bismuth dioctyldithiocarbamate has been synthesized, and Its tribological behaviors, such as friction-reducing ability, antiwear property and extreme pressure performance have been respectively evaluated with a ring-on-block test rig and a fourball machine. In addition to correlate its tribological behaviors with the film formed on the metallic rubbing surface under boundary lubrication conditions, surface analyses have been conducted to characterize the surface film by means of Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy(XPS) and energy dispersion of X-ray (EDX).

Test results show the additive compound can effectively improve the friction and wear of the rubbing couples. On the other hand, EDX confirmed the presence of carbon, oxygen, sulfur, nitrogen, bismuth and iron on the surface; AES revealed their depth distribution of atomic concentration percentages. Whereas XPS further disclosed that the composition of the surface film was composed of organic and inorganic species including iron sulfide and sulfate, metallic bismuth, bismuth oxide and sulfide etc. which are conducive to the reduction of friction and wear.
The Mechanics of a Free-Standing Strained Film / Compliant Substrate System
Authors: Freund L. B.
Published: April 2011

The deformation of film/substrate systems due to a through-the-thickness distribution of mismatch strain is discussed for cases when the layers are thin, compliant and freestanding. The connection between substrate curvature and mismatch strain is reviewed within the framework of small strains and small deflections. These results are applied to determine the second-order correction to the Stoney formula and to note the connection between mismatch strain distribution and curvature history. Then, for small strains but large deflections, it is observed that a symmetric system with equi-biaxial mismatch strain can undergo a bifurcation in deformation mode. It is also shown that the bifurcation response is sensitive to system imperfections. Finally, the critical condition for introduction of an interface misfit dislocation in an epitaxial system is established, thereby extending the Matthews-Blakeslee criterion to the case of free-standing compliant systems.
Stress Determination in Thermally Grown Alumina Scales Using Ruby Luminescence
Authors: Renusch D. , Veal B. W. , Koshelev I. , Natesan K. , Grimsditch M. , Hou P. Y.
Published: April 2011

By exploiting the strain dependence of the ruby luminescence line, we have measured the strain in alumina scales thermally grown on Fe-Cr-Al alloys. Results are compared, and found to be reasonably consistent with strains determined using x-rays. Oxidation studies were carried out on alloys with compositions Fe - 5 Cr - 28 Al and Fe - 18 Cr - 10 Al (at. %, bal. Fe). Significantly different levels of strain buildup were observed in scales on these alloys. Results on similar alloys containing a “reactive element” (Zr or Hf) in dilute quantity are also presented. Scales on alloys containing a reactive element (RE) can support significantly higher strains than scales on RE-free alloys. With the luminescence technique, strain relief associated with spallation thresholds is readily observed.
Investigation of The Elastic Modulus of Sol-Gel Derived Titania Using Three-Point Bending Tests
Authors: Jämting Å. K. , Bell J. M. , Swain M. V.
Published: April 2011

There is increasing interest in the use of sol-gel derived films in tribological applications, and this necessitates an understanding of the mechanical properties of these films. Few investigations into the mechanical properties of sol-gel films have been undertaken, and in this study we have concentrated on measurement of the elastic modulus of sol-gel derived titania films as a preliminary stage in a full investigation of stress in sol-gel deposited thin films. Sol-gel films are often very thin and in order to understand the influence of the substrate on the measured elastic modulus, we have used a multiple coating technique to deposit titania films of increasing thickness on various substrates. A three point bending apparatus is used to measure the elastic modulus. The three-point bending apparatus has very low load and displacement measuring capabilities as is required for the very thin sol-gel films. Measurements of the compositional uniformity of the films have been performed using RBS, and this has been combined with film thickness measurements to determine the film porosity. This information ensures that the measured properties relate to intrinsic film properties. The results of all these measurements will be presented.
A Model of Cleavage Fracture along Metal/Ceramic Interfaces
Authors: Lipkin D. M. , Beltz G. E. , Clarke D. R.
Published: April 2011

We propose a mechanism by which cleavage-type crack growth along a metal/ceramic interface could proceed concomitantly with significant plastic dissipation in the metal. The large strain gradients in the immediate vicinity of the crack tip are postulated to lead to extensive local hardening. A simple, continuum-based model is used to identify a characteristic length scale ahead of the crack tip, within which the material can not plastically deform subject to the cracktip stress field. An analytical expression is derived for the crack-tip shielding afforded by the plastic zone. The coupling between the plastic dissipation and the ideal work of fracture is found to be synergistic, with slight variations in Griffith energy affecting order-of-magnitude changes in toughness. These results suggest a possible mechanism for a number of interfacial fracture phenomena observed in thick- and thin-film metal/ceramic systems, including segregation-induced interfacial embrittlement, the ductile-to-brittle transition, and stress corrosion cracking.
Determination of Burgers Vector of Screw Dislocations in 6H-SiC Single Crystals by Synchrotron White Beam X-Ray Topography
Authors: Si W. , Dudley M. , Carter C. , Glass R. , Tsvetkov V.
Published: April 2011

Individual screw dislocations along the [0001] axis in 6H-SiC single crystals have been characterized by means of Synchrotron White Beam X-ray Topography (SWBXT). The magnitude of the Burgers vector was determined from: (1) the diameter of circular diffraction-contrast images of dislocations in back-reflection topographs, (2) the width of bi-modal images associated with screw dislocations in transmission topographs, (3) the magnitude of the tilt of the lattice planes on both sides of dislocation core in projection topographs, and (4) also the magnitude of the tilt of the lattice planes in section topographs. All of the four methods showed reasonable consistency. The sense of the Burgers vector can also be deduced from the abovementioned tilt of the lattice planes. Results revealed that in 6H-SiC a variety of screw dislocations can be found with Burgers vector magnitude ranging from 1c to 7c (c is the lattice constant along [0001] axis). This work demonstrates that SWBXT can be used as a quantitative technique for detailed analyses of line defect configurations.
Applications of Soft X-Ray Fluorescence Spectroscopy in Materials Science
Authors: Callcotit T.A. , Jia J.J. , Zhou L. , Ederer D.L. , Terminello L.J. , CARLISLE J.A. , Perera R.C.C. , Samant M.G. , Himpsel F.J. , Arakawa E.T.
Published: April 2011

Soft x-ray fluorescence spectroscopy provides an element and angular momentum selective measure of the valence band density of states in complex materials. Results are presented demonstrating the use of SXF both as a means of solving materials problems and as a means of increasing our fundamental understanding of low energy excitation processes in various types of materials. As examples of materials applications, we discuss the L2,3 spectra of Si in various environments, and describe radiation damage studies in Beryl. Fundamental new insights are provided by the study of SXF spectra excited near an x-ray threshold. For such excitation, recent work demonstrates that an electronic Raman scattering process can greatly modify the normal fluorescence spectrum. We discuss near threshold studies of graphite, h-BN and NiS to demonstrate that the nature of the electronic excitation processes differs dramatically in various classes of materials and provides important new insights into their properties.
Photoelectron Angular Distributions Of Ultrathin NI/CU(001) Films
Authors: Mankey G.J. , Subramanian K. , Stockbauer R.L. , Kurtz R.L.
Published: April 2011

We present measurements of the evolution with film thickness of the 3d electronic states at the Fermi energy of ultrathin Ni films. The morphology and thickness of the films is determined from x-ray photoelectron spectroscopy. x-ray photoelectron diffraction and x-ray magnetic linear dichroism using synchrotron radiation. Photoelectron angular distributions were measured using an ellipsoidal mirror analyzer. Even at submonolayer Ni coverages, the 3d electronic states exhibit bulk-like properties. This is attributed to the short screening length of electrons in metals, the localization of the 3d electrons, the similarity of the Ni and Cu ion cores, and finally the interaction with the underlying fcc periodic potential.
Correlation Of Magnetic Dichroism in X-Ray Absorption and Photoelectron Emission using Ultrathin Magnetic Alloy Films
Authors: Tobin J.G. , Goodman K.W. , Mankey G.J. , Willis R.F. , Denlinger J.D. , Rotenberg E. , Warwick A.
Published: April 2011

We have begun a program to characterize magnetic alloy overlayers using both magnetic x-ray circular dichroism (MXCD) and magnetic x-ray linear dichroism (MXLD). This will allow a direct comparison of MXCD-absorption and MXLD-photoelectron emission. First results from the Advanced Light Source will be presented.
Domain Structure and Transient Photoconductivity in Ordered Ga0.47In0.53As Epitaxial Films
Authors: Ahrenkiel S. P. , Ahrenkiel R. K. , Arent D. J.
Published: April 2011

We examine the influences of spontaneous atomic ordering and the associated subvariant domain structure on the transient photoconductivity in epitaxial Ga0.47In0.53As films grown by MOCVD on InP 2°-<110>. Ultra-high frequency photoconductivity decay is used to measure carrier lifetimes in ordered and disordered material following excitation with a YAG laser. Ordered material shows an extended lifetime of 18–186 gis that decreases with incident power. Strongly ordered material showed two CuPt-B subvariants in TEM diffraction patterns and images. Ordering in the first 0.5 μm of growth consists of a fine, interwoven structure with the subvariants closely associated. The subvariants then segregate into imperfectly ordered columnar superdomains that form a mosaic in the film plane with numerous order/order interfaces. In addition, order/disorder interfaces form within and adjacent to the partially ordered superdomains. We attribute the extended transient photoconductivity lifetime in ordered samples to trapping effects that result from the subvariant domain structure.
Depth-Sensitive Strain Analysis of a W/Ta/W Trilayer
Authors: Malhotra S. G. , Rek Z. U. , Yalisove S. M. , Bilello J. C.
Published: April 2011

The high-resolution x-ray diffraction technique was used to determine the entire strain tensor as a function of x-ray penetration depth in a 400 nm W/Ta/W trilayer, which consisted of 150 nm W, 100 nm Ta, and 150 nm W. The strain tensor was calculated in a laboratory reference frame to determine the variation of in-plane strains, εxx, and εyy, and the normal strain εzz as a function of x-ray penetration depth. Two different methods were then used to determine the strains εxx, εyy, and εzz in each layer of trilayer, and both indicated that the strain states in the W layers were fe same, and that the strains εxx and εyy. in the W and Ta layer were the same magnitude. The difference between the Ta and W arose witK the normal strain, εzz, and was due to a Poisson contraction effect. The average residual stresses in the trilayer were determined with the HRXRD data, and also with sin2ψ and a substrate curvature technique, double-crystal diffraction topography. All three techniques indicated that the average biaxial stress in the trilayer was ∼1.0 GPa.
Thin-Film Deposition Via Pulsed Laser Ablation
Authors: Panayotov V. G. , Kelly M. C. , Gomlak G. G. , Birdwhistell T. L. T. , Koplitz B. D.
Published: April 2011

We report on a novel experimental approach for thin-film deposition via pulsed laser ablation. A combination of design features including the incorporation of original sample manipulation methods as well as enhanced analytical capabilities allow for experimental control and flexibility for thin-film deposition studies of a variety of materials. Here, the application is illustrated with a study of 532 nm pulsed laser ablation and subsequent deposition of CdTe.Conditions have been found that produce a mildly energetic ablation plume, and the average kinetic energies for the neutral and ionic ablation species in the plume have been determined to be approximately 2 and 11 eV, respectively. It has been shown that in the presence of an electric field the ionic species can be diverted away from the detector (and subsequently from the eventual deposit). Thin film deposits clearly reveal an increase in the number of sub-micron particles when direct ablation ions contribute to the deposition. The possibility for extraction of ablation ions and preparation of ablation plumes of neutrals only has been clearly demonstrated.
Structural and Surface Morphology Changes in CuInSe2 Thin Films as a Function of Cu/In Ratio
Authors: Fons P. , Niki S. , Yamada A. , Tweet D. J.
Published: April 2011

Due to its high near bandedge absorption, CuInSe2 is considered to be one of the most promising solar cell materials. As CuInSe2 films are usually grown by metastable processes, the Cu/In ratio often deviates from the ideal ratio of unity. To investigate the structural and morphological changes induced by such stoichiometric variations we have grown a series of epitaxial CuInSe2 epitaxial thin films with varying Cu/In ratios by molecular beam epitaxy on GaAs(001) substrates from elemental sources at a growth temperature of 450° C. Overall structural, microstructural and surface morphological changes were observed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy, respectively. It was observed that as films deviated from stoichiometry, twinning occurred preferentially on the anion {1 · 1 · 2} planes.
Process Development and Reliability Study Of Gfpdni Finish For Sc Packaging
Authors: Boguslavsky I. , Abys J. A.
Published: April 2011

GFPdNi was tested for Frame-Lid Assemblies (FLAs) utilized in the sealing SC packages. Plating conditions were adjusted to enhance corrosion resistance with concurrent control over hydrogen content and thickness distribution of the deposit. GFPdNi-plated lids exhibit excellent corrosion resistance, most notably when compared standard Au-plated and GFPdNi-plated lids after a heat-treatment used to simulate sealing process (Fig. 1). This is most likely due to PdNi layer being known as a good interdiffusion barrier.

The reliability of lidded packages was tested by standard methods. It has been revealed that the thickness of the PdNi layer affects the yield in thermal cycling and thermal shock experiments. Auger studies implemented for failure analysis showed the correlation between intermetallic diffusion during the sealing process (due to insufficient thickness of PdNi deposit) and the reliability of the solder joint. A successful field evaluation trial has proven the capability of this new plating process.
Patterning of LiGaO2 and LiAlO2 by Wet and Dry Etching
Authors: Lee J. W. , Pearton S. J. , Abernathy C. R. , Wilson R. G. , Chai B. L. , Ren F. , Zavada J. M.
Published: April 2011

LiGaO2 and LiAlO2 have similar lattice constants to GaN, and may prove useful as substrates for III-nitride epitaxy. We have found that these materials may be wet chemically etched in a number of acid solutions, including HF, at rates between 150–40,000 Å/min. Dry etching with SF6/Ar plasmas provides faster rates than Cl2/Ar or CH4/H2/Ar under Electron Cyclotron Resonance conditions, indicating the fluoride etch products are more volatile that their chloride or metalorganic/hydride counterparts. Dry etch rates are low ( < 2, 000 Å/min), providing high selectivity (>5) over the nitrides. The incorporation of hydrogen in these materials is also of interest because this could provide a reservoir of hydrogen that may passivate dopants in overlying nitride films. In 2H implanted samples, 50 % of the deuterium is lost by evolution from the surface by annealing at 400 °C for 20 min and all of the deuterium is gone at 700°C. The diffusivity of 2H is ∼10-13 cm2/s at 250°C in LiA1O2, approximately two orders of magnitude higher than in LiGaO2.
Ohmic Contact to n-GaN with TiN Diffusion Barrier
Authors: Kamińska E. , Piotrowska A. , Guziewicz M. , Kasjaniuk S. , Barcz A. , Dynowska E. , Bremser M. D. , Nam O. H. , Davis R. F.
Published: April 2011

The formation of n-GaN/Ti ohmic contacts with TiN diffusion barriers has been investigated by electrical measurements, x-ray diffraction and SIMS. It has been shown that the onset of the ohmic behaviour is associated with the thermally induced phase transformation of Ti into TiN at the GaN/Ti interface. It is suggested that the process is accompanied by an increase in the doping level in the semiconductor subcontact region. The presence of a TiN barrier is found to inhibit excessive decomposition of GaN and to confine the reaction between n-GaN and Ti.
PtIn2 ohmic contacts to n-GaN
Authors: Ingerly D. B. , Chang Y. A. , Perkins N. R. , Kuech T. F.
Published: April 2011

A new metallization scheme has been developed to form ohmic contacts to n-GaN. Contacts were fabricated by sputtering the intermetallic compound, PtIn2 on n-GaN (n ∼ 5 ×l017 cm−3) grown by metalorganic vapor phase epitaxy (MOVPE) with some of the contacts subjected to rapid thermal annealing. Contacts in the as-deposited state exhibited nearly ohmic behavior with a specific contact resistance of 1.2 × 10−2 Ω cm2. Contacts subjected to rapid thermal annealing at 800 °C for 1 minute exhibited linear current-voltage characteristics and a decrease in contact resistance. To rationalize the reaction at the contact interface the phase diagram of the PtIn2-PtGa2-InN-GaN reciprocal system at 800 °C was calculated based on known and estimated thermodynamic values. This phase diagram suggests that there will be a solid state exchange of In and Ga atoms at the Ptln2/GaN contact interface producing (InxGa1-x)N and Pt(In,Ga)2. Results from Auger depth profiling used to examine the Ptln2/n-GaN contacts are consistent with this estimated phase diagram information. It is proposed that the formation of (InxGa1-x)N at the contact interface is responsible for the ohmic behavior of Ptln2 contacts.
Stacked InGaN/AlGaN Double Heterostructures
Authors: Roberts J. C. , McIntosh F. G. , Aumer M. E. , Piner E. L. , Joshkin V. A. , Liu S. , El-Masry N. A. , Bedair S. M.
Published: April 2011

InGaN ternary alloys can be the basis for light emission from the near UV to the red region of the electromagnetic spectrum. When InGaN/AIGaN double heterostructures emitting different colors are stacked in a single structure, simultaneous emission of different wavelengths will be achieved. If the color and the intensity of emission for each well are adjusted properly, tailored emission spectra, including white light, will be feasible. We demonstrate this concept with two wells emitting at different wavelengths that are stacked between AIGaN barrier layers. The emitted PL spectra for the stacked structure is found to be the superposition of the emission from the individual double heterostructures that were grown separately.
Carrier Recombination Dynamics of InGaN/GaN LEDs and Its Applications to the Optimization of uv Generation Efficiency
Authors: Basrur J. P. , Choa F. S. , Liu P-L. , Sipior J. , Rao G. , Carter G. M. , Chen Y. J.
Published: April 2011

To obtain small size high speed ultraviolet sources, we studied the UV generation process and efficiency of GaN Blue LEDs. The blue and UV emissions follow a 4-level recombination model. Depending on a given pump pulse amplitude the UV to blue generation ratio increases and saturates with the increasing of pump pulse duration. High efficiency, upto 450 μ W UV power at 380 nm, can be obtained from a 1.2 mW blue LED.
Surface Reconstructions and III-V Stoichiometry: The Case of Cubic and Hexagonal GaN
Authors: Feuillet G. , Hacke P. , Okumura H. , Hamaguchi H. , Ohta K. , Balakrishnan K. , Yoshida S.
Published: April 2011

Surface reconstructions for MBE grown GaN are identified. Different cases are considered according to the type of substrate or crystal symmetry and surface phase diagrams are obtained. Through different examples, it is shown how growth monitoring can be efficiently achieved through the use of surface reconstructions. Finally, from the observation that a residual arsenic overpressure in the MBE chamber changes the surface reconstructions of cubic (001) GaN grown onto 3C-SiC (001) substrates to that commonly observed for GaN growth on (001) GaAs, it is proposed that arsenic might be a surfactant for nitride growth.
Low-Temperature Deposition and Characterization of AlxIn1-xN Thin Films
Authors: Qiu Guohua , Olowolafe J. O. , Peng Tao , Unruh K. M. , Swann C. P. , Piprek J.
Published: April 2011

Thin III-V nitride semiconductors fidms are commonly prepared using metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). These methods often require high temperatures (800–1000°C) for the films to grow epitaxially. In the present work, we deposited AlxIn1-xN films on Si substrates by reactive magnetron sputttering method at low substrate temperature. The properties of the films have been studied by RBS, x-ray diffraction, and optical measurements. The AlxIn1-xN films deposited at room temperature were confirmed to be crystalline by x-ray diffraction. Band gap energies of our AlxIn1-xN alloys varies from 1.9 ev to 4.2 ev The bandgap energy vs. lattice constant curve was constructed and confirmed to bow downwards.
Growth of Bulk AlN and GaN Single Crystals by Sublimation
Authors: Balkas C. M. , Sitar Z. , Zheleva T. , Bergman L. , Shmagin I. K. , Muth J. F. , Kolbas R. , Nemanich R. , Davis R. F.
Published: April 2011

Single crystals of A1N to 1 mm thickness were grown in the range 1950-2250°C on 10×10 mm2 α(6H)-SiC(0001) substrates via sublimation-recondensation method. Hot pressed polycrystalline AlN was used as the source material. The color varied from transparent to dark green/blue. The crystal morphology varied with growth conditions. Most crystals were 0.3 mm -1 mm thick transparent layers which completely covered the substrates. Raman, optical and transmission electron microscopy (TEM) results are presented. Single crystals of gallium nitride (GaN) were also grown by subliming powders of this material under an ammonia (NH3) flow. Optical microscopy, Raman and photoluminescence results are shown.
Structural Analysis of GaN and GaN/InGaN/GaN DH Structures on Sapphire (0001) Substrate Grown by MOCVD
Authors: Sato Hisao , Naoi Yoshiki , Sakai Shiro
Published: April 2011

We have investigated lattice structures of GaN and InGaN/GaN single-heterostructures (SH) and double-heterostructures (DH) by the reciprocal space mapping using X-ray diffraction technique from (0002) plane. For a single GaN layers, the transition of the film structure from grains with relatively independent orientation at about 0.3 μm followed by the coalescence at about 1 μm, to a uniform film with mosaic structure at 1.4 μm was clearly observed. For DH structure, ω-mode FWHMs both from InGaN (In composition approximately 7 %) and capping-GaN layers increased with increasing film thickness from 20 nm to 110 nm indicating the increased mosaic structure in the thick InGaN. We also observed the dislocation related to this increasing mosaic structure.
Hexagonal Growth Hillocks in GaN Epilayers
Authors: Middleton P. G. , Trager-Cowan C. , Mohammed A. , O’Donnell K. P. , Van Der Stricht W. , Moerman I. , Demeester P.
Published: April 2011

We describe a study of the hexagonal growth hillocks commonly present in gallium nitride films. The MOVPE-grown epilayers of the present work exhibit a predominantly smooth morphology but small groups of hexagonal hillocks were found to populate the surface, particularly at the sample edges.

Scanning electron (SE) micrographs were taken of several groups of hillocks. At the maximum beam energy of 25 keV, two types of hexagonal hillock are visible. Hillocks in the first group are terminated by an apex (ie. they are pyramidal in form), while the other, flat-topped, hillocks terminate on (0001)-facets. As one lowers the electron beam energy, thereby reducing beam penetration, some of the flat-topped hillocks disappear from the image. From this we tentatively deduce that these hillocks are buried. The result of further investigations, using an atomic force microscope, are consistent with the presence of sub-surface features.

The relationship between the luminescence and morphological properties of a pyramidal hillock is studied via cathodoluminescence imaging. The band-edge emission originates from the full hexagonal structure, except for the central region, where only the defect-related yellow luminescence is apparent. We suggest this might be explained by defects associated with inversion domain boundaries at the hillock centre.
Recombination of Localized Excitons in InGaN Single- and Multiquantum-Well Structures
Authors: Chichibu S. , Azuhata T. , Sota T. , Nakamura S.
Published: April 2011

Spontaneous emission mechanisms of InGaN single quantum well (SQW) blue and green light emitting diodes (LEDs) and multiquantum well (MQW) laser diode (LD) structures were investigated. Their static electroluminescence (EL) peak was assigned to the recombination of excitons localized at certain potential minima in the quantum well (QW). The transmission electron micrographs (TEM) indicated fluctuation of In molar fraction in the QWs. The blueshift of the EL peak caused by the increase of the driving current was explained by combined effects of the quantum-confinement Stark effect and band filling of the localized states by excitons.
AlxGa1-xN-Based Materials and Heterostructures
Authors: Kung P. , Saxler A. , Walker D. , Zhang X. , Lavado R. , Kim K.S. , Razeghi M.
Published: April 2011

We present the metalorganic chemical vapor deposition growth, n-type and p-type doping and characterization of AlxGa1-xN alloys on sapphire substrates. We report the fabrication of Bragg reflectors and the demonstration of two dimensional electron gas structures using AlxGa1-xN high quality films. We report the structural characterization of the AlxGa1-xN / GaN multilayer structures and superlattices through X-ray diffraction and transmission electron microscopy. A density of screw and mixed threading dislocations as low as 107 cm-2 was estimated in AlxGa1-xN / GaN structures. The realization of AlxGa1-xN based UV photodetectors with tailored cut-off wavelengths from 365 to 200 nm are presented.
Changes in Optical Transmittance of Aluminum Nitride thin Films Exposed to Air
Authors: Sakuragi Yoshifumi , Watanabe Yoshihisa , Nakamura Yoshikazu , Amamoto Yoshiki
Published: April 2011

Aluminum nitride (AlN) thin films have been synthesized by ion-beam assisted deposition method and the influence of air-exposure on the optical transmittance has been studied. The kinetic energy of nitrogen ion beam was kept at 0.1 or 1.5 keV under the constant current density. Synthesized films have been exposed to controlled air (23 °C and RH; 50%) and optical transmission spectrum from 190 to 2200 nm has been measured by UV-visible spectrometer every week. Surface morphology of the films has been observed with an optical microscope (OM). The optical transmittance has not changed drastically up to one year. Observations by OM show that round features of some microns were produced on the surface after about 25 weeks exposure. These substances seem to be reaction products between AlN and water in air.