bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and Surface Morphology of Epitaxial Ni Films on MgO(111) and (001) Substrates: Growth of High Quality Single Domain Films
Authors: Sandström Per , Svedberg Erik B. , Birch Jens , Sundgren Jan-Eric
Published: April 2011

Ni films were deposited by ultra high vacuum magnetron sputtering onto MgO(111) and (001) substrates kept at temperatures Ts between 20°C and 600°C. The structure and the morphology of the 100 nm thick films were analyzed using X-ray diffraction (XRD) and atomic force microscopy (AFM). On MgO(111), all Ni films have a strong [111] oriented texture with high out-of-plane as well as high in-plane orientations with an increased crystalline quality with temperature. At 300°C the Ni 111 peak width is ∼0.25° in the ω direction, showing a high crystal quality for a heteroepitaxial metal film. Pole-figure analysis shows that the films are built up of two domains for temperatures ≤200°C and at 600°C, while at 300°C and 400°C only one domain is formed. The RMS roughness, as measured with AFM, of the film increases with temperature with a local maximum between 150° to 200°C and a local minimum at 300°C which corresponds to the transition from two domains to one. On MgO(001), Ni shows three completely different textures depending on the deposition temperature. At ambient temperature a mixed (1 −4 1) and (022) texture with traces of (002) is formed. Between 100°C and 200°C Ni grows with a single domain (001) texture. At higher temperatures a highly oriented 8-fold (75-1) texture is formed. The highest crystalline quality is obtained at 100°C where the FWHM of the Ni 002 peak at 100°C is 0.24° in the ω−2θ direction and 0.18 in the ω direction which shows the good crystalline quality also in this case. Both the RMS surface rougness and the surface feature size increases with the deposition temperature but with local miminas at 100°C corresponding to the film with highest crystalline quality.

The weak Ni-O interaction together with a strong metal-metal bonding between the Ni atoms results in an in plane supercell matching between the Ni film and the MgO substrates at 300-400°C for the MgO(111) substrate and 100-200°C for the MgO(001) substrate.

The (7 5 −1) texture formed by Ni on MgO(001) substrates at deposition temperatures ≥300°C, places each interfacial Ni atom in the preferred position on top of an O atom on the MgO surface, and in addition, also better accommodates the mismatch between the two crystal lattices.
Reliability Assurance for Thermo-Optic Solid State Optical Switches
Authors: Dobbelaere P. M. C. De , Van Der Wel P. J. , Hendriksen B. , Flipse M. C. , Thackara J. , Zhu N. , Freeman J.
Published: April 2011

The reliability assurance program for the BeamBoxTM thermo-optic solid state optical switches is presented. The different phases of the program are discussed, and some of the results are described.
Strength and Fatigue of Modified Sol-Gel Clad Optical Fibers
Authors: Skutnik Bolesh J. , Trumbull M. R
Published: April 2011

Dynamic and static fatigue results are presented for the first time for a new type of optical fiber, whose modified sol-gel cladding is a fenestrated (micro porous) form of silica. Unjacketed fibers have mean Weibull strengths in bending of 6.5 to 7.6 GPa with Weibull slopes in the 40 to 60 range. The strength decrease with decreasing strain rate is similar for both jacketed and unjacketed fibers. Even the unjacketed fibers tested in ambient water or in boiling water retain a majority of their mean strength, 7.6 GPa (ambient air) versus 6.5 GPa (ambient water) versus 5.5 GPa (boiling water). Exposure to boiling water for 1 hour has no measurable affect on the strength of these fibers. Exposure to boiling water for 8 hours, however, does significantly broaden the low strength end for the unjacketed fiber. The dynamic fatigue and static fatigue parameters in ambient water are substantially the same, ND = 22±2 and Ns 21±4, for the jacketed and unjacketed fibers. Possible mechanisms are discussed to explain the strength and fatigue behavior of these fibers in light of their unique structure.
Optical-Fiber and Entry-Cone Contact Stresses
Authors: Anderson J. M. , Malluck J. F. , Tabaddo M. M. , Sidbury C. K. , McNeil T. E.
Published: April 2011

Many of the broken fibers in optical connectors, especially those that seem to occur over time without apparent provocation are found in the ferrule at the transition from entry cone to alignment capillary. This paper contends that many such breaks are due to local stresses caused by debris or some other relatively rigid imperfection in the transition neighborhood. Stress estimates from beam theory and from a finite-element model are presented along with some indirect experimental observations supporting the contention.
The Dimensional Stability of Adhesives, Zirconia, and Silica in Optical Connector Ferrules and their Impact on Optical Performance
Authors: Reith L.A. , Ebizlioglu O.S. , Koza M. , Mann J. , Ozgur M. , Bowmer T.
Published: April 2011

In order to achieve the optimum optical performance of fiber optic connectors, it is critical that there be good physical contact at the fiber-to-fiber interface. Loss of physical contact results in increased insertion loss and reflectance. Today's connectors are designed to have mating surfaces with tightly controlled endface geometries to ensure physical contact during temperature variations and repeated matings. However, material degradation of the fiber, ferrule, or the adhesive which holds the fiber into the ferrule, can change the endface geometry and cause eventual failure of the connector. Tests have been developed or are under development to quantify mechanical changes in these materials, including adhesive creep, fiber pistoning, ferrule deformation and roughening, and fiber deterioration. This paper will describe the latest test results acquired from applying these procedures.
Damage-Free Photo-Assisted Cryogenic Etching of GaN as Evidenced by Reduction of Yellow Luminescence
Authors: Hsieh J. T. , Hwang J. M. , Hwang H. L. , Hung W. H.
Published: April 2011

Damage-free etching of GaN by Cl2, assisted by an ArF (193 nrm) excimer laser, is demonstrated. At low temperatures, photo-assisted etching can provide a better etch rate and largely improve the surface morphology and quality. AFM results show that the etched GaN surface is obtained with a root-mean-square roughness of 1.7 nm. As compared with the photoluminescence spectra of photoelectrochemical wet etched GaN, the photo-assisted cryogenic etching is proved to be a damage-free dry etching technique.
Mechanism for Radiative Recombination in In0.15Ga0.85N/GaN Multiple Quantum Well Structures
Authors: Monemar B , Bergman J P , Dalfors J , Pozina G , Sernelius B E , Holtz P O , Amano H , Akasaki I
Published: April 2011

We present a study of the radiative recombination in In0.15Ga0.85N/GaN multiple quantum well samples, where the conditions of growth of the InGaN quantum layers were varied. The piezoelectric field as well as short range potential fluctuations are screened via different mechanisms by donor electrons and excited electron-hole pairs. These effects account for a large part of the spectral shift with donor doping (an upward shift of the photoluminescence (PL) peak up to 0.2 eV is observed for a Si donor density of 2 × 1018 cm-3 in the well), with excitation intensity and with delay time after pulsed excitation (also shifts up to 0.2 eV). It appears like 2-dimensional screening of short range potential fluctuations is needed to fully explain the data. We suggest that excitons as well as shallow donors are at least partly impact ionized by electrons in the rather strong lateral potential fluctuations.
Optical Absorption, Raman, and Photoluminescence Excitation Spectroscopy of Inhomogeneous InGaN Films
Authors: Robins L.H. , Paul A.J. , Parker C.A. , Roberts J.C. , Bedair S.M. , Piner E.L. , El-Masry N.A.
Published: April 2011

InGal-xN films with x=0.06 to x=0.49 were characterized by optical transmittance, Raman, and photoluminescence excitation spectroscopies. Previous microstructural characterizations detected phase separation only in films with x>0.2. The transmittance data suggest that compositional inhomogeneity is also present in the lower-x films (x<0.2). Both Raman and photoluminescence excitation spectra show features that correlate with compositional inhomogeneity and phase separation in the films with x>0.2. The composition dependence of the Raman spectra, from x=0.28 to x=0.49, is consistent with an increase in the size of the phase-separated regions with increasing x.
Synthesis of Nitrogen-Rich GaNAs Semiconductor Alloys and Arsenic-Doped GaN by Metalorganic Chemical Vapor Deposition
Authors: Gherasimova M. , Gaffey B. , Mitev P. , Guido L. J. , Chang K. L. , Hsieh K. C. , Mitha S. , Spear J.
Published: April 2011

Arsenic-doped GaN films and GaNAs films have been synthesized by MOCVD. Samples were grown on sapphire, GaN-coated sapphire, and GaAs substrates. Composition, structure, and phase distribution were characterized by EPMA, SIMS, XRD, and TEM. The arsenic content increases demonstrably as the growth temperature descreases from 1030 to 700°C. In the high temperature limit, high quality arsenic-doped GaN forms on GaN-coated sapphire. In the low temperature regime, nitrogen-rich GaNAs forms under some growth conditions, with a maximum arsenic mole fraction of 3%, and phase segregation in the form of GaAs precipitates occurs with an increase in arsine pressure, Preferential formation of the nitrogen-rich phase on GaN-coated sapphire suggests the presence of substrate-induced “composition pulling”.
Defect States in SiC/GaN-and SiC/AlGaN/GaN-Heterostructures Characterized by Admittance and Photocurrent Spectroscopy
Authors: Witte H. , Krtschil A. , Lisker M. , Christen J. , Scholz F. , Off J.
Published: April 2011

Deep defect levels in n-type GaN/AlN/6H-SiC- and GaN/AlGaN/6H-SiC- heterostructures grown by Metallorganic Vapor Phase Epitaxy were analyzed by Thermal and Optical Admittance and Photocurrent Spectroscopy. The various thermal and optical transitions in the spectra originating from both the Schottky contact as well as the GaN/SiC- and AlGaN/GaNheterojunctions were separated. This was achieved by variation of the modulation frequency, the use of different contact arrangements and by comparison with reference spectra from GaN/Sapphir samples and SiC substrates. In the GaN/AlGaN/SiC structures a bias voltage dependent peak shift was found which is correlated to an interface related defect distribution. In additionally to, SIC related defects, defect-band-transitions involving defects with transition energies at 2.2eV, 1.85eV, EG-(470±40) meV and EG-(65-95) meV were found for the GaN layer.
Microstructure of GaN Grown on (111) Si by MOCVD
Authors: Follstaedt D. M. , Han J. , Provencio P. , Fleming J. G.
Published: April 2011

Gallium nitride was grown on (111) Si by MOCVD by depositing an AlN buffer at 1080°C followed by GaN at 1060°C. The 2.2 μm layer cracked along {1-100} planes upon cooling to room temperature, but remained adherent. We were nonetheless able to examine the material between cracks with TEM. The character and arrangement of dislocations are much like those of GaN grown on Al2O3: ∼2/3 pure edge and ∼1/3 mixed (edge + screw), arranged in boundaries around domains of GaN that are slightly misoriented with respect to neighboring material. The 30 nm AlN buffer is continuous, indicating that AIN wets the Si, in contrast to GaN on Al2O3.
Epitaxial Growth of III-Nitride Layers on Aluminum Nitride Substrates
Authors: Schowalter L.J. , Shusterman Y. , Wang R. , Bhat I. , Arunmozhi G. , Slack G.A.
Published: April 2011

High quality, epitaxial growth of AlN and AlxGal-xN by OMVPE has been demonstrated on single-crystal AIN substrates. Here we report characterization of epitaxial layers on an a-face AlN substrate using Rutherford Backscattering/ion channeling, atomic force microscopy (AFM), x-ray rocking curves, and preliminary electrical characterization. Ion channeling along the [1010] axis gives a channeling minimum yield of 1.5% indicating a very high quality epitaxial layer.
Growth and Characterization of BxGal-xN on 6H-SiC (0001) by MOVPE
Authors: Wei C. H. , Xie Z. Y. , Edgar J. H. , Zeng K. C. , Lin J. Y. , Jiang H. X. , Ignatiev C. , Chaudhuri J. , Braski D. N.
Published: April 2011

Boron was incorporated into GaN in order to determine its limits of solubility, its ability of reducing the lattice constant mismatch with 6H-SiC, as well as its effects on the structural and optical properties of GaN epilayers. BxGal-xN films were deposited on 6H-SiC (0001) substrates at 950 °C by low pressure MOVPE using diborane, trimethylgallium, and ammonia as precursors. A single phase alloy with x=0.015 was successfully produced at a gas reactant B/Ga ratio of 0.005. Phase separation into pure GaN and BxGal-xN alloy with x=0.30 was deposited for a B/Ga reactant ratio of 0.01. This is the highest B fraction of the wurtzite structure alloy ever reported. For B/Ga ratio ≥ 0.02, no BxGal-xN was formed, and the solid solution contained two phases: wurtzite GaN and BN based on the results of Auger and x-ray diffraction. The band edge emission of BxGal-xN varied from 3.451 eV for x=0 with FWHM of 39.2 meV to 3.465 eV for x=0.015 with FWHM of 35.1 meV. The narrower FWHM indicated that the quality of GaN epilayer was improved with small amount of boron incorporation.
GaN: From Selective Area to Epitaxial Lateral Overgrowth
Authors: Li X. , Bishop S. G. , Coleman J. J.
Published: April 2011

The evolution of the topography of GaN stripes as a function of stripe width (2 - 120 μm), fill factor and substrate smoothness has been explored. The spatially resolved optical properties of these structures have been characterized by cathodoluminescence imaging and line scans. Implications from the optical study have been discussed.
A Critical Comparison Between Movpe and MBE Growth of III-V Nitride Semiconductor Materials for Opto-Electronic Device Applications
Authors: Johnson M.A.L. , Yu Zhonghai , Brown J.D. , Koeck F.A. , El-Masry N.A. , Kong H.S. , Edmond J.A. , Cook J.W. , Schetzina J.F.
Published: April 2011

A systematic study of the growth and doping of GaN, AlGaN, and InGaN by both molecular beam epitaxy (MBE) and metal-organic vapor phase epitaxy (MOVPE) has been performed. Critical differences between the resulting epitaxy are observed in the p-type doping using magnesium as the acceptor species. MBE growth, using rf-plasma sources to generate the active nitrogen species for growth, has been used for III-Nitride compounds doped either n-type with silicon or p-type with magnesium. Blue and violet light emitting diode (LED) test structures were fabricated. These vertical devices required a relatively high forward current and exhibited high leakage currents. This behavior was attributed to parallel shorting mechanisms along the dislocations in MBE grown layers. For comparison, similar devices were fabricated using a single wafer vertical flow MOVPE reactor and ammonia as the active nitrogen species. MOVPE grown blue LEDs exhibited excellent forward device characteristics and a high reverse breakdown voltage. We feel that the excess hydrogen, which is present on the GaN surface due to the dissociation of ammonia in MOVPE, acts to passivate the dislocations and eliminate parallel shorting for vertical device structures. These findings support the widespread acceptance of MOVPE, rather than MBE, as the epitaxial growth technique of choice for III-V nitride materials used in vertical transport bipolar devices for optoelectronic applications.
Gan Nanotubes
Authors: Lee Seung Mi , Lee Young Hee , Hwang Yong Gyoo , Eisner J. , Porezag Dirk , Frauenheim Thomas
Published: April 2011

We perform parametrized density-functional calculations to predict the stability and formation mechanism of GaN nanotubes. Strain energies of GaN nanotubes are comparable to those of carbon nanotubes, suggesting the possibility for the formation of GaN nanotubes. We note that an intermediate phase with [4,6,10] polygons exist at armchair tube edge, which may play as a nucleation seed of further tube growth.
Crystal Structure and Defects in Nitrogen-Deficient GaN
Authors: Oktyabrsky S. , Dovidenko K. , Sharma A. K. , Joshkin V. , Narayan J.
Published: April 2011

We have studied crystal structure and associated defects in GaN films grown on sapphire under nitrogen-deficient conditions by metalorganic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD). The structural quality of the PLD films grown at 750 °C was comparable with those grown by MOCVD at 1050 °C having threading dislocations density of about 1010 cm-2 at a film thickness 150-200 nm. Microstructure of the PLD films grown at temperatures above 780°C was found to be similar to that of nitrogen-deficient MOCVD films indicating the loss of nitrogen due to thermal decomposition of the nitride layers. Nitrogen-deficient MOCVD and PLD films exhibit polycrystalline structure with a mixture of cubic zinc-blende and wurtzite hexagonal GaN grains retaining tetragonal bonding across the boundaries and hence the epitaxial orientations and polarity. Renucleation of the wurtzite phase at different {111} planes of cubic GaN results in a rough and faceted surface of the film. Most of the stoichiometric films displayed (0001) Ga-face polarity, but the renucleated inclined wurtzite grains grew in the opposite N-face polarity. The major defects related to the cubic structural metastability are stacking faults and microtwins which being nuclei of the metastable cubic phase have an extremely low energy. We elucidate that the cubic phase is more stable under the nitrogen deficiency and, therefore, can exist without decomposition at higher nitrogen vacancy concentrations in the material.
NIIN As an Ohmic Contact to P-GAN
Authors: Ingerly D. B. , Chang Y. A. , Chen Y.
Published: April 2011

Based on the criteria for the solid state exchange reaction with p-GaN, we have investigated the intermetallic compound Niln as a possible ohmic contact. The contacts were fabricated by depositing Niln on p-GaN films (p ∼ 2 × 1017 cm-3) using RF sputtering from a compound target. The as-deposited, Niun contacts were found to be rectifying and using I-V characterization a Schottky barrier height of 0.82 eV was measured. Rapid thermal annealing of the contacts was shown to significantly decrease their resistance, with contacts annealed at 800°C for I min yielding the lowest resistance. When annealed at 800°C for 1 min Niln contacts exhibited a specific contact resistance of 8-9 × 10-3 Ωcm2, as measured by the circular transmission line model. To allow a more universal comparison the more traditional Ni/Au contacts, processed under the same conditions, were used as a standard. Their measured specific contact resistance (ρc = 1.2 - 2.1 x 10-2 Ωcm2) was significantly higher than that of the Niln contacts. Demonstrating that Niln has promise as an ohmic contact to p-GaN and should be studied in greater detail.
Temperature-Dependent Onset of Yielding in Dislocation-Free Silicon: Evidence of a Brittle-To-Ductile Transition
Authors: Folk R. H. , Khantha M. , Pope D. P. , Vitek V.
Published: April 2011

An investigation of the brittle-to-ductile transition (BDT) in silicon has been conducted on essentially dislocation-free silicon test specimens made by photolithography. No pre-cracks or additional dislocation sources were introduced into the samples. Three-point bending tests of the samples reveals a well defined transition from brittle fracture of the specimens to complete yielding near 732°C at a crosshead displacement rate of 0.1 mm/min. Limited plasticity is observed below 732°C but is insufficient to prevent crack propagation suggesting that yielding is not dislocation mobility limited. Instead the transition may be controlled by the nucleation of a sufficient density of dislocations. Further support comes from the results of experiments conducted at temperatures below 732°C in which samples were rapidly pre-loaded within the linearly elastic regime, then immediately retested. This rapid pre-loading results in a lower transition temperature. This would not be expected if dislocation mobility controlled the BDT. Instead, it is believed that the transition only occurs when a sufficient density of dislocations has nucleated within the sample. In these experiments, the pre-loading event may increase the dislocation nucleation rate. The source of the dislocations in these defect free samples is still under investigation.
Molecular Dynamics Studies of Interfacial Crack Propagation in Heterogeneous Media
Authors: Corbett John M. , Selinger Robin L. B.
Published: April 2011

We use molecular dynamics simulation to investigate the evolution of a crack front in interfacial fracture in three dimensions. We find that when a crack passes through a localized region of heterogeneous toughness, crack front waves are initiated and propagate laterally. We also investigate the development of roughness of the crack front when the crack propagates in a region of heterogeneous toughness. We find that in steady state the mean square width W of the front scales with system size L as W∼L0.35, in agreement with recent theoretical predictions.
Dry Etching of PZT Films with CF4/Ar High Density Plasma
Authors: Park Chanro , Cho Jun Hee , Choi Chang Ju , Seol Yeo Song , Choi Il Hyun
Published: April 2011

Lead-Zirconate-Titanate (PZT) films were etched with CF4/Ar mixed gases in high-density plasmas. Etch characteristics of the PZT film were investigated by using in-situ plasma diagnostic tools in conjunction with the surface analysis after etching. Densities of ionic species such as F+ and CFx+(x=1∼3) and their ion energy distributions within the plasma were measured by a mass spectrometer. Characteristics of the CF4/Ar plasma were obtained by using Langmuir probe measurements. Etch rate of the PZT film was sharply increased up to a peak at 30 % CF4 as the gas ratio of CF4/(Ar+CF4) increased, and then was gradually decreased. After etching, the surface of PZT film was covered with fluorine that was bonded chemically with underlying PZT film. Ion assisted etching mechanism for the PZT was proposed and its validity was confirmed by using the results of the plasma diagnostics.
In Situ Mass Spectroscopy of Recoiled Ion Studies of Degradation Processes in SrBi2Ta2O9 Thin Films During Hydrogen Gas Annealing
Authors: Im J. , Auciello O. , Krauss A.R. , Gruen D.M. , Chang R.P.H. , Kim S.H. , Kingon A.I.
Published: April 2011

It is known that the forming gas (N2-H2 mixture) annealing process required for microcircuit fabrication results in an unacceptable electrical degradation of SrBi2Ta2O9 (SBT) ferroelectric capacitors due mainly to the interaction of H2 with the ferroelectric layer of the capacitor. We have found a strong relationship between changes in the surface composition of the ferroelectric layer and the electrical properties of SBT capacitors as a result of hydrogen annealing. Mass spectroscopy of recoiled ions (MSRI) analysis revealed a strong reduction in the Bi signal as a function of exposure to hydrogen at high temperatures (∼500°C). The Bi signal reduction correlates with Bi depletion in the SBT surface region. Subsequent annealing in oxygen at temperatures in the range of 700–800°C resulted in the recovery of the MSRI Bi signal, corresponding to the replenishment of Bi in the previously Bi-depleted surface region. XRD analysis (probing the whole SBT film thickness) showed little difference in the XRD spectra of the SBT films before and after hydrogen and oxygen-recovery annealing. The combined results of the MSRI and XRD analyses can be interpreted as an indication that the degradation of the electrical properties of the SBT capacitors, after hydrogen annealing, is mainly due to the degradation of the near surface region of the SBT layer.
Micro-Raman Study of Pb(Zr,Ti)O3 Thin Films in Feram
Authors: Kimura Takahiro , Horii Yoshimasa , Nakamura Tomoji , Honda Koichiro
Published: April 2011

We examined the Raman spectra of the tetragonal Pb(Zr, Ti)O3 (PZT) films between FeRAM cells with a micro-Raman apparatus. We found that a Raman light peaked at 600cm−1 polarized linearly perpendicular to the polarization of the exciting light had a different intensity for each of the film.

We showed that the difference in the intensities can be explained by the differing distributions of grain orientations in the films. Based on this knowledge, we estimated the volume fraction of 90° domains as well as the average spontaneous polarization of the grains.
Size Effect of Ferroelectric and Ferromagnetic Properties of Bi-based Perovskite Type Materials
Authors: Tabata H. , Ueda K. , Kawai T
Published: April 2011

Bismuth-based-layer-structured ferroelectric films have been formed epitaxially on Nb-doped SrTiO3 substrates by pulsed laser deposition (PLD). These films show an atomically smooth surface with a wide terrace of 100 nm∼200 nm, as observed by atomic force microscopy (AFM) which is ideal for measuring such properties. Thin films of (Bi0.7, Ba0.) (Fe0.7, Ti0.3)O3 exhibit both ferroelectric and ferromagnetic (weak ferromagnetism) properties at room temperature. In these samples, a size effect is discussed at the same time.
SrTiO3/BaTiO3 Artificial Superlattices Obtained by Injection MOCVD
Authors: Lindner J. , Weiss F. , Haessler W. , Kobernik G. , Senateur J.-P. , Oswald S. , Santiso J. , Figueras A.
Published: April 2011

SrTiO3/BaTiO3 superlattices were deposited using injection MOCVD. The films obtained on LaAlO3(LAO), Al2O3, SrTiO3(STO) and SrTiO3:Nb(STO:Nb) were charcterized using X-ray diffraction. While the films on LaAlO3 (012), SrTiO3(100) and SrTiO3:Nb (100) were epitaxial, the multilayers deposited on Al2O3(0001)were highly oriented, but displaying two different in-plane orientations. To our knowledge, this is the first time that BTO/STO superlattices were deposited by MOCVD.
Effect of Cerium Silicate Formation on the Structural and Electrical Properties of Pt/SrBi2Ta2O9/CeO2/Si Capacitors
Authors: Lee Ho Nyung , Shin Dong Suk , Kim Yong Tae , Chow Sung Ho
Published: April 2011

We have fabricated metal/ferroelectric/insulator/semiconductor (MEFIS) capacitors of Pt/SrBi2Ta2O9(SBT)/CeO2/Si and Pt/SBT/Ce-Si-O/Si. The cerium silicate (Ce-Si-O) layer is formed by reaction between CeO2 thin film and SiO2/Si substrate at 1100 °C. The SBT film on the cerium silicate layer is smoother than the SBT/CeO2. The memory window of the SBT/Ce-Si-O increases to 1.4 V at a sweep voltage of ±5 V, whereas the memory window of the SBT/CeO2 is 0.8 V at the same sweep voltage.
Improved properties of TaOx films doped with Al and N
Authors: van Dover R. B. , Schneemeyer L. F. , Fleming R. M. , Werder D. J.
Published: April 2011

Simultaneous addition of Al and N to Ta-O thin films is found to significantly improve the dielectric properties of the films. Specifically, substitution of 10-40 at. % Al for Ta along with ∼2 at. % N for O is found to decrease the density of catastrophic defects in the films, resulting in high and statistically more uniform breakdown voltages. This conclusion is based on evaluation of ∼750 individual capacitors in each experiment.
Ferroelectric C-Axis Oriented Pb5Ge3O11 Thin Films for One Transistor Memory Application
Authors: Li Tingkai , Zhang Fengyan , Hsu Sheng Teng
Published: April 2011

One transistor memory devices have been proposed recently. To meet the needs of one transistor memory applications, C-axis oriented Pb5Ge3O11 (PGO) thin films were prepared using metalorganic chemical vapor deposition (MOCVD) and rapid thermal processing (RTP). It was found that the nucleation of C-axis Pb5Ge3O11 phase started at a deposition temperature below 400°C and grain growth dominated at 500°C or above. With increasing annealing temperature, the remanent polarization (Pr) and coercive field (Ec) values increased, and the hysteresis loops of the Pb5Ge3O11 films were well saturated and symmetrical after the post-annealing. The C-axis PGO thin film showed good ferroelectric properties at 5V: 2Pr and 2Ec values were 2.0 - 4.0 µC/cm2 and 90 - 110 kV/cm, respectively. The films also showed excellent fatigue characteristics: no fatigue was observed up to 1 × 109 switching cycles. The retention and imprint properties have also been studied. The leakage currents of the PGO films were 2 - 5 × 10−7 A/cm2 at 100 kV/cm and dielectric constants were 40 - 70. The high quality MOCVD Pb5Ge3O11 films can be used for single transistor ferroelectric memory devices.
Molecular Dynamics Simulations of Hexadecane/Silicalite Interfaces
Authors: Webb Edmund B. , Grest Gary S.
Published: April 2011

The interface between liquid hexadecane and the (010) surface of silicalite was studied by molecular dynamics. The structure of molecules in the interfacial region is influenced by the presence of pore mouths on the silicalite surface. For this surface, whose pores are the entrances to straight channels, the concentration profile for partially absorbed molecules is peaked around 10 monomers inside the zeolite. No preference to enter or exit the zeolite based on absorption length is observed except for very small or very large absorption lengths. We also found no preferential conformation of the unabsorbed tails for partially absorbed molecules.
Recent Advances in Plasma Deposition of Functional Coatings on Polymers
Authors: Martinu L. , Wertheimer M. R. , Klemberg-Sapieha J. E.
Published: April 2011

Plasma enhanced chemical vapor deposition (PECVD) is increasingly being applied for the fabrication of functional coatings on polymeric substrates. This presentation briefly reviews the energetics of plasma-surface interactions leading to the deposition of films for different applications such as optical coatings, barriers against gas and vapor permeation, and protective coatings for space. Particular emphasis is placed on the formation and characterization of a relatively wide (tens of nm) interfacial region (“interphase”) between the coating and the polymer, its role in adhesion, and in optical, mechanical and other functional porperties of thin film systems on plastic substrates.
Plasma Treatment of Polymers for Improving Al Adhesion
Authors: Lamendola R. , Matarrese E. , Creatore M. , Favia P. , d'Agostino R.
Published: April 2011

PET and Kapton thin films have been plasma processed in order to increase sputtered aluminum adhesion. The effect of different plasma feedings, such as NH3, O2, and He, has been evaluated on polymer/metal adhesion and on chemical modifications of polymer surface at different plasma power and treatment time. The chemistry at polymer/metal interface has been studied in order to find the suitable experimental conditions for transferring the plasma process to industrial scale.

The role of acid-base reactions in promoting Polymer/Aluminum adhesion has been investigated. Surface composition has been investigated by X-ray Photoelectron Spectroscopy; adhesion measurements have been accomplished by 180° Peel Test.
Inner Pore of Porous Fluoropolymer to Hydrophilic by using UV Light and H20 Vapor
Authors: Ito Shinsuke , Murahara Masataka
Published: April 2011

Inner pores of porous PTFE was modified photochemically by using ArF excimer laser for improvement of water permeability. In this study, two modification methods are described. One is using ethanol solution, and another is H20 vapor as a reaction gas. These reaction sources were employed for modification of inner pores. In the case of using ethanol solution, the modified sample indicates both hydrophilication and oleophilication. On the contrary, the hydrophilic groups are substituted into the inner pore with H20 vapor. The hydrophilication of modified samples were evaluated by the measurement of contact angle with water and water permeability. The substituted OH radicals were inspected by ATR-FTIR measurement.
Gravitational Effects on Mercuric Iodide Crystal Growth
Authors: Steiner Bruce , Berg Lodewijk Van Den , Laor Uri
Published: April 2011

Gravity can affect the physical vapor growth of mercuric iodide in two distinct ways. First, gravity will induce convection during growth, which strongly mixes residual impurities and any elementary gases resulting from imperfect stoichiometry, either of which can then form precipitates in the growing crystal. Second, gravity loads the resulting crystal, which is particularly soft while still hot, especially in the absence of precipitates. We have investigated the effects of these processes on the resulting crystalline regularity and the effects of various types of irregularity, in turn, on performance.

High resolution synchrotron x-radiation diffraction imaging of three generations of crystals, grown both in microgravity and in full gravity, provide graphic evidence of the influence of gravity on mercuric iodide crystal growth. These images tie together the results of other characterization studies, identifying the crystallographic sources of the observed property enhancement in microgravity. The first process, convection, is found to be particularly important, both in its influence on observed crystalline regularity and in the resulting electronic performance of detectors made from these crystals.

As a result of these investigations, the crystalline regularity and performance of terrestrial crystals has been substantially improved, although the resulting crystals have not yet achieved parity with the performance of crystals grown in microgravity. We propose new experiments in microgravity for property optimization.
Zeolite Crystal Growth in Space
Authors: Sacco A. , Bac N. , Warzywoda J. , Rossetti G. , Valcheva-Traykova M.
Published: April 2011

The extensive use of zeolites and their impact on the world's economy has resulted in many efforts to characterize their structure and improve the knowledge base for nucleation and growth of these crystals. Zeolite crystal growth (ZCG) experiments have been conducted in space by many researchers. The results have been varied with little overall constancy with respect to the types of zeolites grown, the procedures used, and methodologies employed for comparison of terrestrial and microgravity processed crystals. Results from this laboratory have indicated that solutions must be mixed in space, and that the nucleation mechanism as well as the growth mechanism is affected by the “suppression” of fluid motion. Earlier flight experiments (STS-43, STS-50 and STS- 57) indicated that by controlling the nucleation event, the size of the crystals could be increased with improved structural quality compared to the ground-based controls. This was hypothesized to be the result of hindrance of the solution/dissolution mechanism caused by reduced fluid motion. USML-2 (STS-73) zeolite experiments were designed to further enhance the understanding of nucleation and growth of zeolite crystals, while attempting to provide a means of controlling the defect concentration in microgravity. Zeolites A, X, and Silicalte were grown during the 16-day United States Microgravity Laboratory number 2 (USML-2) mission. All zeolites were successfully grown in the 16 day mission. The zeolite A and X crystals were in general larger in dimension (10-50%), but not substantially different in crystal perfection as measured by their lattice parameters. However, They were significantly smoother as indicated by AFM. Zeolite β as well as Silicalite were only slightly larger in size but, appear to have different distributions of Aluminum atoms as determined by selective catalytic reactions.
A Testbed for Testing Materials Properties in Space
Authors: Landis Geoffrey A. , Bailey Sheila G. , Sextont Andrew
Published: April 2011

The Photovoltaic Engineering Testbed (PET) is a facility to fly on the International Space Station to test advanced solar cell types in the space environment. The purpose is to reduce the cost of validating new technologies and bringing them to spaceflight readiness by measuring them in the in-space environment. The facility is scheduled to be launched in 2002.
High-Temperature Deformation of Uniaxially Aligned Lamellar TiAl/Ti3Al
Authors: Heinrich H. , Abbächerdi V. , J. D. , Kostorz G.
Published: April 2011

Uniaxially aligned polysynthetically twinned two-phase TiAl/Ti3Al material is produced by induction zone melting and deformed in uniaxial compression. Above 1000 K the strain rate sensitivity is independent of the lamellar orientation and increases strongly with increasing deformation temperature. Results for the strain rate sensitivity parameters are somewhat lower than those obtained for γ-TiAl single- and polycrystals. If the lamellae are oriented parallel or perpendicular to the deformation axis, the flow stress decreases with increasing strain. After plastic deformation the dislocation density in the lamellae is remarkably low indicating recovery processes. At the lamellar interfaces misfit dislocations and periodic arrangements of dislocations with Burgers vectors inclined to the lamellar boundaries are found. In contrast to deformation at lower temperatures, deformation twinning is rare.
Elastic and Plastic Properties of Gamma + Laves Phase In-situ Composite Alloys Using Nanoindentation Techniques
Authors: Weaver M. L , Stevenson M. E , Shamsuzzoha M. , Ott R. D. , Brady M. P
Published: April 2011

In the present study, the local elastic and plastic properties of the γ- TiAl and the Laves phases have been investigated in a series of γ + Laves alloys using room-temperature compression, Vickers microhardness, and nanoindentation with an emphasis on elucidating the local property changes in γ + Laves alloys deformed at room temperature. This study shows that nanoindentation can be used to provide useful information on plastic flow in multiphase intermetallic alloys.
The Character of Steps on Gamma/Alpha-2 Interfaces in a Low Misfit Lamellar TiAl-Based Alloy
Authors: Shang P. , Cheng T.T. , Aindow M.
Published: April 2011

The defect character of steps on lamellar γ/α2 interfaces in a quinternary TiAl-based alloy has been studied using high resolution transmission electron microscopy. The interfaces consisted of atomically flat coherent terraces separated by interfacial steps across equal even numbers of {111}γ and (0002)α2 planes. Circuit mapping was used to identify the Burgers vectors of these steps from lattice images obtained at [101]γ and [110]γ zone axes. It was found that the Burgers vectors exhibited by the two-layer steps are different from those reported previously and are consistent with those expected for perfect disconnections as described by Pond's topological theory of interfacial defects, and not with the usual partial dislocation model.
The Mechanical Properties of FeAl
Authors: Baker I. , George E. P.
Published: April 2011

In the last few years, considerable progress been made in obtaining reproducible mechanical properties data for binary FeAl alloys. Two sets of observations are the foundation of this progress. The first is that the large equilibrium vacancy concentrations that exist in FeAl at high temperature are easily retained during cooling, and that these strongly affect the low-temperature mechanical properties. The second is that room-temperature ductility is adversely affected by water vapor. The purpose of this paper is to highlight our understanding of key phenomena and to show how an understanding of the factors which control the yield strength and fracture behavior has followed from the discovery of the above two effects.
High Temperature Corrosion of Spray-Atomized FeAl (40at.%) Based Alloys:Immersed in a Molten Salt Mixture of V2O5-Na2SO4
Authors: Amaya M. , Lavernia E. J. , Martinez L.
Published: April 2011

We studied the high temperature corrosion of spray atomized and deposited FeAl40at% based intermetallic alloys immersed in a molten salt mixture of 80%V2O 5+20%Na2SO4 (wt%) over the temperature range of 600–900°C. Experiments were realized by the weight loss method and the potentiodynamic polarization electrochemical technique in three different samples: FeA140at%, FeA140+0.lat%B and FeA140+0.lat%B+10at%A12O3. Measurements of weight loss and corrosion current density as a function of the molten salts temperature were obtained and discussed in terms of the passive layer morphology and corrosion products formed during the tests. It was found that the iron aluminide doped with boron and reinforced with alumina particulate was more corrosion resistant in the test temperature range. The weight loss experiments revealed that at 700°C all alloys developed maximum corrosion rate. This behavior was related with the dissolution of protective oxide layer on metal base due the formation of vanadate phases which are highly corrosive at this temperature.
Direct Measurement of Dislocation Exhaustion Rates During Plastic Deformation of Ni3Al Compounds
Authors: Matterstock B. , Martin J. L. , Bonneville J. , Kruml T.
Published: April 2011

Two methods of repeated transients (stress relaxation and creep) which can be performed during straining at a constant strain rate are recalled together with the way the results are interpreted. The repeated creep method has been adapted to Ni3A1 compounds for which the amount of creep strain during the second creep could not be detected so far. Because of a small stress increase between creeps, it is possible to measure microscopic activation volumes, dislocation exhaustion rates and strain hardening coefficients. Results in Ni3A1 polycrystals and Ni3(AI,Hf) single crystals are presented. Orders of magnitude of dislocation exhaustion rates are given. They are particularly high in Ni3A1 as compared with other materials. They compare well with the work hardening coefficient and with total dislocation densities measured by electron microscopy.
Constitutional and Thermal Defects in Nickel Aluminides
Authors: Korzhavyi P. A. , Abrikosov I. A. , Johansson B.
Published: April 2011

The formation energies of intrinsic point defects and the interaction energies of possible defect pairs in NiA1 are calculated from first principles within an order-N, locally self-consistent Green's function method in conjunction with the multipole electrostatic corrections to the atomic sphere approximation. The theory correctly reproduces the ground-state properties of the off-stoichiometric NiAl alloys. The constitutional defects (antisite Ni atoms in Ni-rich and Ni vacancies in Al-rich NiAl) are shown to form ordered structures in the ground state, in which the defects of the same kind tend to avoid each other at the shortest separation distance on their sublattice. A mean-field theory is applied to calculate the equilibrium concentrations of thermal defects. The statistics of thermal defects is interpreted in terms of dominant composition-conserving complex defects which are shown to be triple defects in Ni-rich and nearly stoichiometric NiAl. In the Al-rich region a novel thermal excitation dominates where two constitutional Ni vacancies are replaced by one antisite Al atom. The number of vacancies, as well as the total number of point defects decrease with temperature in Al-rich NiAl. The boundary between the two regions is treated analytically. The vacancy concentration exhibits a minimum in its temperature dependence at the boundary. Similar analysis is applied to study constitutional and thermal defects in Ni3Al. The calculated effective vacancy formation energy in Ni3Al as a function of concentration is in excellent agreement with recent experimental data.
Ideal Cleavage Fracture of Transition-Metal Silicides: A Comparison Analysis
Authors: Yoo M. H. , Yoshimi K.
Published: April 2011

A simple empirical model for the ideal cleavage energy, resulting from a rigid-body separation, is proposed in terms of four variables, viz., the elastic stiffness constant, the interplanar spacing, and two adjustable length parameters. The ratio of these parameters is assessed based on the available results of ab-initio slab-supercell calculations. Ideal cleavage energies and stress intensity factors of transition-metal silicides are estimated, and the available fracture toughness data are discussed.
Microsample Testing of Single Crystalline Ti-52 at%Al and Ti-55.5 at%Al
Authors: Zupan Marc , Dimiduk D. M. , Hemker K. J.
Published: April 2011

Dislocation activity in two-phase commercial TiAl alloys occurs most readily in the γ-TiAl phase, and measurements of the CRSS of single crystalline γ-TiAl provides a solid foundation for understanding the mechanical performance of these alloys. Single crystals of γ-TiAl with greater than 54.5 at%Al have been grown using the optical float zone crystal growing technique, but single crystals with lower Al content, closer to that of commercial alloys, have not. In the present study, polycrystalline ingots of Ti-52 at%Al have been heat treated to form very large grains, and microsample tensile specimens, which have a nominal gage cross-section of 250μm × 300μm, a gage length of 250μm and an overall length of 3 mm, have been machined from within single grains. Microsample high-temperature stress-strain curves for Ti-55.5 at%Al single crystals oriented along the [001] and [010] are presented. Tensile tests results for Ti-52 at%Al tested at 1073K along the [237], [173] and [344] orientations will also be discussed.
Changes in the Degree of LRO in B2-Ordered Intermetallic FeAl
Authors: Rohrhofer K. , Lang H. , Rosenkranz P. , Kozubski R. , Püschl W. , Pfeiler W.
Published: April 2011

Changes in the degree of long-range order (LRO) have been investigated in B2-ordered intermetallicFe-44.8at%Al by electrical resistivity measurement (resistometry). Order variations were observed during isochronal annealing for different states of initial thermal treatment. A complicated behaviour of resistivity changes with temperature is observed when starting with a small degree of disorder. Very slight re-ordering is found already at about 470K and is surprisingly followed by a slight disordering above 530K. Only for very long annealing times the expected ordering tendency is observed in this temperature range. Above 710K re-ordering is continued and reversible equilibrium changes of order with temperature are observed above 830K.
Point Defect Characterization in CoAl Using Positron Annihilation
Authors: Puff Werner , Logar Bernd , Balogh Adam G.
Published: April 2011

Vacancy-like defects in CoAl in the composition range 48.5 at.-% <Cco, < 53 at.-% are investigated by means of positron lifetime spectroscopy and Doppler-broadening measurements. The observed lifetimes in the annealed samples confirm that defects are quenched-in during the production of the samples. The values of the positron lifetime and the S-parameter decrease with increasing Co concentration. After quenching from 1400°C or 1600°C an increase in the positron parameters isobserved. Long-time annealing of the Co-rich sample shows a dramatic decrease of the positron lifetime to the expected bulk lifetime.
High-Temperature Creep of Nb-Al-V Alloys
Authors: Rong Tie-Sheng , Aindow Mark
Published: April 2011

Nb-15A1-20V alloys with about 45% by volume of an A15 phase in a B2 matrix have been subjected to creep deformation at temperatures between 1000°C and 1200°C and stresses from 80 MPa to 240 MPa in vacuum. The creep curves show a rapid transition from primary to steady-state creep with a well-defined activation energy. Microstructural observations show that the creep deformation occurs mainly in the B2 matrix and is controlled by dislocation mechanisms. Samples which had been coldrolled and annealed to reduce the size of A 15 precipitates and increase the yield strength were found to have lower creep resistance than those with unrefined microstructures. The significance of these observations for the creep mechanisms is discussed.
An Investigation of Point Defects in NiAl Using Positron Annihilation Techniques
Authors: Puff Werner , Logar Bernd , Balogh Adam G.
Published: April 2011

Vacancy-like defects in NiAl in the composition range 47 at.-% < CNi < 53 at.-% are investigated by means of positron lifetime spectroscopy and Doppler-broadening measurements. The observed lifetimes in the annealed samples confirm that defects are quenched-in during the production of the samples. Isochronal annealing of samples quenched at 1600°C and after proton irradiation show that the induced defects are quite different.