bluuebunny/crossref_metadata_2025 huggingface dataset:
Proton Irradiation Enhancement of Implanted Layers on Ceramic YBCO Bulk
Authors: Andreone D. , Cherubini R. , Colombo S. , Gerbaldo R. , Mezzetti E. , Minetti B. , Periale F.
Published: March 2011

In this work the possibility of enhancing the critical current density in proton implanted surface layers on YBCO bulk is discussed. A complete transport characterization shows that, for what concerns two samples from different irradiation runs, the critical current density has been enhanced. Increases of other meaningful parameters, such as average pinning energy and vortex-antivortex coupling strength, have also been found, although the relative effect of the implanted layer on the whole specimen cannot be evaluated in a fully quantitative way.
High Tc YBa2Cu3O7−x Thin Films on GaAs-Based Substrate Using MgO Buffer Layers with Sb Passivation Technique 1
Authors: Tseng M. Z. , Jiang W. N. , Hu E. L. , Mishra U. K.
Published: March 2011

High quality YBCO films have been grown on GaAs-based substrates via depositing MgO epitaxial buffer layers prior to YBCO growth. The critical temperature of the best YBCO film, Tc(0) was 87K and Jc>6.7×104 A/cm2 at 77K. The MgO buffer layers are usually [100] oriented along the normal of GaAs (100) substrates with full-width-half-maximum (FWHM) of rocking curve varying from 1–3 degree. We found that the uniformity and quality of MgO buffer layers are very sensitive to the pre-deposition preparation of GaAs-based substrates. Nonuniform MgO buffer layers are often obtained on those substrates prepared by wet chemical processing. Reproducible, controlled formation of the MgO buffer layer was achieved using an antimony passivation scheme, after molecular beam epitaxial (MBE) growth of the desired structure of the substrate.
On the Determination of Intrinsic Properties of Ceramic High-Tc Superconductors by Ac Susceptibility Measurements
Authors: Ludwig F.
Published: March 2011

Various models have been proposed to interpret ac susceptibility curves measured on sintered high-To superconductors (HTSC) and to deduce parameters like critical current densities and critical fields. To get more clearness, systematic studies of position and height of the intergranular maximum in χ'' have been performed on several ceramic HTSC samples in dependence of both ac field amplitude and sample size. In the present paper, the data are used to discuss the various models proposed in the literature. It is shown that modifications of the critical state model using incorrect jc(Hi) functions as well as other interpretations of the χ'' peak yield not actually intrinsic but sample size and geometry dependent parameters. The dependence of both position and height of the intergranular maximum in χ '' on ac field amplitude and sample size can be explained in the framework of a modified critical state model using a power law for the jc(Hi) dependence.
Synthesis, Microstructure, Critical Current Density, Magnetization and Relaxation of Hot-Pressed YBa2Cu3O6+δ Through Partial Melting Post-Oxygenation
Authors: Kunga P. J. , Maleya M. P. , Mchenry M. E.
Published: March 2011

Hot-pressed YBa2Cu3O6+δ superconductor with plate-like grains annealed at the partial melting temperature ( ∼ 1,000 C) followed by slow cooling in oxygen atmosphere has resulted in enhanced magnetization hysteresis loops which show weak dependence on magnetic field. The X-ray diffraction pattern exhibits the significant features associated with the reflection (003) and (006), and a higher compaction density in hot-pressed samples compared with cold-pressed samples was observed from the SEM micrographs. Morphology study and microstructural analysis by SEM and TEM, respectively, indicate that grains were well aligned during hot-pressing mostly with their c-axes parallel to the pressing axis, and many intersecting twins were actually formed during post-oxygenation. Local oxygen-deficient regions likely existing in these hot-pressed and oxygenated samples are believed to act as effective flux pinning centers at high temperatures (∼ 50 K and above). The measurement of magnetic relaxation was employed to interpret the observed pinning behavior. The critical magnetization current density (Jc) calculated using the Bean model and the average grain dimension is in the order of 104 Amp/cm2 at 75 K up to 1 T. Because of a shorter period of oxygenation and a weak field dependence of Jc values, the process of hot-pressing combined with partial melting post-oxygenation is technologically practical in forming various shapes as desired from oxide superconductors.
Oxygen Deficiencies at Defects in YBa2CU3O7-δ as Determined by High Resolution Parallel Electron Energy Loss
Authors: Kramer M. J. , McCallum R. W.
Published: March 2011

There has been considerable discussion on the exact nature of the pinning defects in the high temperature ceramic superconductors, and the YBa2Cu3O7-δ (Y123) structure in particular. High resolution parallel electron energy loss spectrometry (PEELS) allows for fine spatial resolution (< 17 nm) and fast acquisition times to probe the oxygen content of defects (i.e., dislocations, stacking faults, twin boundaries and grain boundaries), all which have been proposed as potential pinning sites or weak-links. Oxygen deficiencies up to 13% were measured at twin boundaries, and 20% at grain boundaries while stacking faults showed an increase in oxygen and copper content. Regions of low oxygen (0.5 < δ < 1) were usually confined to an area within approximately 50 nm of the defect, which is within the spatial resolution of the measurements. Examination of the fine structure of the oxygen K-edge suggests that the oxygen holes are absent at the twin and grain boundaries.
Superconducting behavior of YBa2Cu3O6–8/Bi2Sr2CanCun-1Ox multilayers
Authors: Narumi E. , Lee J. , Li C. , Patel S. , Shaw D. T.
Published: March 2011

Composite YBCO/BSCCO films on MgO(lOO) substrates were fabricated by using laser deposition. The structures and transport properties of these composite films were studied. The model of 3D percolating network in YBCO thin films will be discussed.
In-Situ Surface Observation of C-Axis Oriented YBa2Cu3O7−x Thin Films by Leed, XPS and ISS
Authors: Tanaka S. , Nakamura T. , Tokuda H. , Iiyama M.
Published: March 2011

1. Abstract

In an ultra-high vacuum equipment, YBa2CU3O7−x (YBCO) thin films were deposited by the ozone-assisted co-evaporation method and their surfaces were investigated by LEED, XPS and ISS without breaking the vacuum. A LEED pattern was observed for the first time at an as-deposited surface. A clean, crystalline and superconducting surface was preserved to the top of the film. Only Cu atoms were detected at the first monolayer by ISS, suggesting that clean surfaces are stabilized by Cu-O layers.
Microstructure of In-Situ Grown YBa2Cu4O8 Thin Films Deposited by MOCVD
Authors: Uehara K. , Sakai H. , Hayashi H. , Shiohara Y. , Tanaka S.
Published: March 2011

High-resolution transmission electron microscopy (HREM) has been used to study the microstructures of Y-Ba-Cu-0 superconducting thin films in which the YBa2Cu4O8 phase was the main phase. From cross-sectional observations, the c-normal 123 phase predominated in the film near the substrate surface, while the c-normal 124 phase occupied the region near the film surface. Another remarkable microstructure was that a-normal 123 variants overcame the c-normal 123 region, but the c-normal 124 phase surpassed the a-normal 123 phase in the upper part of the film.
Growth of Cerium Oxide Buffer Layers and Superconducting thin films on Silicon
Authors: Amirhaghi S , Beech F , Craciun V , Sajjadi A , Vickers M , Tarling S , Barnes P , Andboydi W
Published: March 2011

Films of CeO2 have been grown on Si and glass substrates using the laser ablation deposition technique. X-ray diffraction measurements for the films deposited on glass indicated that they are the same as films grown on Si covered with the native oxide. This evidence supports a picture in which chemical rather than crystal-lographic effects constrain the film growth. The crystal quality for films grown on Si was shown to improve with increasing film thickness away from the amorphous layer. Low cooling rates as well as reduced film thickness were effective in avoiding the formation of micro-cracks. The surface morphology was shown to be dependent on the laser wave-length as well as the oxygen partial pressure. Thin films of YBa2Cu3O7δ could easily be grown on CeO2/Si showing c-axis orientation, whereas the growth of BiSrCaCuO (2212) on CeO2/Si resulted in the two films mixing with each other.
Tl-Based Films: A Comparison of Processing Procedures
Authors: Morosin B. , Venturini E. L. , Tigges C. P. , Ginley D. S. , Volk S. R.
Published: March 2011

The structural, electrical and magnetic properties are compared for three superconducting Tl-Ca-Ba-Cu-O thin films prepared by different deposition and sintering protocols. One film containing a mixture of Tl2Ca2Ba2Cu3Ox and Tl2Ca2Ba2Cu3Oy structural phases has the best superconducting properties. Deposition of a Tl-free Ca-Ba-Cu-O precursor film followed by sintering in Tl-O vapor may be the preferred protocol to obtain a single structural phase.
Reflection High Energy Electron Diffraction Studies of the Growth of DyBa2Cu3O7−x Films and Structures Grown on SrTiO3 Substrates
Authors: Achutharaman V. S. , Chandrasekhar N. , Goldman A. M.
Published: March 2011

Intensity oscillations of the specular reflection high energy electron diffraction (RHEED) beam contain useful information on the mode of growth and the evolving structure of thin films. We present RHEED studies of the growth of DyBa2Cu3O7−x films and DyBa2Cu3O7−x/DY2O3/DyBa2Cu3O7−x structures on SrTiO3; substrates deposited by ozone-assisted molecular beam epitaxy. The effect of substrate temperature, ozone flux and surface step densities on the epitaxial relationship and evolving microstructure will be discussed. The strong damping of the oscillations and identical time periods under different nuoleation and growth conditions suggest that the intensity oscillations are a consequence of to diffuse scattering from step edges rather than a layer-by-layer growth mode. It was also found that Dy2O3 can be used to fabricatee tri-layer type structures but not superlattice structures.
Ultrafast Electrical Superconducting to Normal States Switching in Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O Microstrips
Authors: Balevičius S. , Bičūnas A. , Butkute R. , Jasutis V. , Lisauskas V. , Vailionis A. , Flodström A. , Vengalis B.
Published: March 2011

Switching from superconducting (S) to normal (N) state was investigated using short rise time (∼ 10−10 s) electric pulses in MBE grown Bi-Sr-Ca-Cu-O and rf magnetron sputtered Y-Ba-Cu-O submicron thickness microstrips. It was found that two reversible processes: fast electronic (τ∼10∼−12 s) and slow thermal (τ∼10∼−8s) one take place during switching. At high current densities (∼107 A/cm2) irreversible changes in strip material induced by thermal runaway occurred. The use of a superconducting element as fast fault-current limiter or pulse sharpening device is pointed out.
Multifilamentary Bismuth(2223) Multilayer-Wound Conductors for Power Transmission Lines
Authors: Mukai H. , Shibuta N. , Sato K. , Hara T. , Ishii H. , Yamamoto T.
Published: March 2011

The fundamental problems of applying high-Tc superconductors to power transmission lines were studied, and prototypes of multilayer-wound conductors were fabricated and evaluated.

Multifilamentary silver sheathed wires have good anti-strain. properties. A 61-filament bismuth(2223) wire proved to maintain 90% of initial transport current property after 150 cycles of bending (bent-straightened-bent reversely-straightened) with 0.18% strain. A 61-filament wire of 114m unit-length was produced and proved to have a Jc of 9,700 A/cm2 with an Ic of 9.34A for the whole length at 77.3K.

Using these multifilamentary wires, prototypes of multilayer-wound conductors were produced by the react-and-wind technique. A 1.4m long three layer-wound conductor could carry 590A (Jc=7.020A/cm2) in liquid nitrogen.

These results indicate that the basic problems of high-Tc superconductor application to power transmission lines will be overcome using this technology.
Solidification Mechanism of YBa2Cu3Ox Superconductors
Authors: Nakamura Yuichi , Izumi Teruo , Shiohara Yuh , Tanaka Shoji
Published: March 2011

Directional solidification of the zone melting method was performed in order to clarify the growth mechanism on YBa2Cu3Ox (123) superconductors from the partial molten state. The effect of a platinum addition for crystal growth was also investigated. Results indicate that a higher G/R ratio was preferable for the continuous growth of 123 crystals, and lead to the idea that the necessary solute for the peritectic reaction is provided from dispersed Y2BaCuO5 (211) particles in liquid to 123 interface through the liquid. Based on this idea, we developed a solidification model which is in good agreement with the experimental results. In the case of a platinum addition, the coarsening rate of 211 particles decreased, and the cell spacing of 123 crystals also decreased. It is tentatively suggested that the platinum addition decreases the products of the diffusivity in liquid and the Gibbs-Thomson coefficients, which include the surface energy between 211 or 123 phase and liquid,(DLΓ211 and DLΓ123).
On Extrinsic Effects in the Surface Impedance of Cuprate Superconductors
Authors: Halbritter J.
Published: March 2011

Presently, the rf surface impedance Z of cuprate superconductors is still shrinking with material improvements, which is shown clearly by Z = Z1+Zres still dominated by extrinsic properties summarized in Zres. We present evidence that Zres is due to the large leakage current jbi and the small critical current jcj of weak links. The latter destroys the intrinsic shielding from a λ1 -thin seam λJ deep into the bulk. This causes rf residual losses Rres ≈ (ΩμO)2λJ3 σb1/2. Rres stays finite at T≃O by σb1(T→O)≈σb1(αjb1) being amplified by (λj/λ1>103 as a weighting factor. An appropriate measure of weak links is the grain boundary resistance Rbn(∝ρ(O)) enhancing λj ∝ Rbn and Rres ∝ Rbn2. Thus, Zres is minimal for minimal extrapolated normal conducting resistivity ρ(T→O).

To identify the weak links as new entity the H-field dependence is most helpful, because at very low fields Hc1J∝ 1/λJ Josephson fluxons penetrate into the weak links. These Josephson fluxons show negligible flux flow or flux creep, and enhance Zres by λJ(H, T) ∝ l/√Jjc (H, T). The measured JcJ (H, T) - and Jbl - values explain Zres quantitatively as well as in temperature ∝ ( a+ Tn) (n ≈ 1, THc1J) dependence being thus a unique method to obtain the different Hc1-values. The strength of the field dependence d Zres/dH ∝ Zres (Hc1J*)/Hc2J(T) is not only a measure of Zres and HC2j(T) but is crucial for nonlinear effects and (fluxon) noise also, which limits the performance of rf devices.
Processing Effects on the Contact Resistance of Ion Beam Sputtered Silver on Highly Oriented C-Axis and A-Axis YBCO Films
Authors: Narbutovskih M. , Rosner J. , Merchant P. , Jacowitz R. D.
Published: March 2011

This paper reports on the processes used to achieve low resistance silver contacts to YBCO thin films that have either c-axis or a-axis orientation. Characterization by x-ray diffraction and TEM verified that these films are highly oriented with either the a or the c axis oriented perpendicular to the substrate surface. TEM examination of some of the Ag/YBCO interfaces reveals the presence of an amorphous layer. We will describe the effects of ion beam etching and RTA alloying on the contact resistivity for both orientations.
Flux Pinning Defects Induced by Electron Irradiation in Y1Ba2Cu3O7–8 Single Crystals
Authors: Giapintzakis J. , Kirk M. A. , Lee W. C. , Rice J. P. , Ginsberg D. M. , Robertson I. M. , Wheeler R.
Published: March 2011

Single crystals of R1Ba2Cu3O7–8, (R=Y, Eu and Gd), have been irradiated with 0.4–1.0 MeV electrons in directions near the c-axis. An incident threshold electron energy for producing flux pinning defects has been found. In-situ TME studies found no visible defects induced by electron irradiation. This means that point defects or small clusters ( ≤ 20 Å) are responsible for the extra pinning. A consistent interpretation of the data suggests that the most likely pinning defect is the displacement of a Cu atom from the CuO2 planes.
Epitaxial Superconductor Film Growth on Ultratffln Silicon Wafers for Infrared Detection
Authors: Li Q. , Fenner D. B. , Johansson M. E. , Hamblen D. G. , Hamblen W. D. , Lynds L. , Karrai K. , Liu S. , Dunmore F. , Drew H. D. , Zhang H. , Xu P.
Published: March 2011

Epitaxial YBCO/YSZ thin films have been successfully grown on ultrathin Si(100) wafers as part of an effort to fabricate infrared detectors which are both fast and highly responsive. Single crystal Si wafers with thicknesses ranging from 400 μm to 3μm are used as growth substrates. Detectors are fabricated by patterning the YBCO films into meanderline structures and their IR response is evaluated as a function of substrate thickness. So far, we have achieved a responsivity of 1750 V/W with a 10 Hz chopping rate on the 25 μm substrate, and rise/fall times as fast as 3 msec on the 3 μm substrate. We have also measured the low temperature IR transmission from 15 μm to 300 μm of both the YSZ buffered Si substrate, and the complete YBCO/YSZ/Si sample. This study indicates that silicon is a superior substrate for the fabrication of high performance infrared focal plane detector arrays.
High Tc Tri-Layers for Josephson Junctions
Authors: Eckstein J. N. , Bozovic I. , Klausmeier-Brown M. E. , Virshup G. F.
Published: March 2011

Atomic Layer-by-Layer Molecular Beam Epitaxy (ALL-MBE) of high Tc superconducting films can be used to grow defect-free and flat multi-layer structures in which superconducting molecular layers are stacked with molecular layers having other electronic properties. In particular, tri-layers consisting of c-axis Bi2Sr2CaCu2O8 base and counter electrode layers, each several hundred angstroms thick, have been grown separated by single molecular layers of metastable compounds such as Bi2Sr2Can-1CunO2+4 where n ranged from 5 to 11. Furthermore, the electronic properties of such barrier layers have been modified by doping with trivalent cations. Using such structures, tri-layer Josephson junctions have been fabricated which exhibit hysteretic I - V characteristics. Other doping schemes have given insulating layers which dominate c-axis transport, demonstrating the ability of this technique to grow thin, 25 Å, single molecular layers that are free of pinholes.
Transmission Electron Microscopy and X-Ray Diffraction Studies of a,b-Axis Oriented YBa2Cu3O7-δ Films
Authors: Streiffer S. K. , Lairson B. M. , Zielinski E. M. , Bravman J. C.
Published: March 2011

Quantitative high resolution transmission electron microscopy and x-ray diffraction have been used to study films of YBa2Cu3O7-δ grown on LaAlO3 substrates at low substrate temperatures. Based on analysis of high-resolution micrographs, it is asserted that the films are b-axis oriented near the film-substrate interface, and switch to a-axis oriented at some distance away from the interface, in a manner which varies from sample to sample. Thus, the films undergo a change in orientation as a function of distance from the substrate. X-ray diffraction confirms that these films contain both a-axis oriented and b-axis oriented components normal to the plane of the substrate, consistent with the high-resolution microscopy data.
Effects of Controlled Defects on the Vortex-Solid Melting Transition of Y-Ba-Cu-O Single Crystals
Authors: Jiang W. , Yeh N. -C. , Reed D. S. , Kotlani U. , Tombrello T. A. , Rice A. P. , Holtzberg F.
Published: March 2011

We report systematic studies of the dc transport properties in proton-irradiated Y-Ba-Cu-O single crystals. We find that the onset of vortex dissipation in moderately irradiated samples is associated with the occurrence of a second-order vortex-solid melting transition. In addition, the decreasing zero-field transition temperature and increasing critical current density with the increasing defects reveal the effects of disorder on reducing the electron mean-free-path and on increasing the pinning density.
Microwave Impedance Studies on High Temperature Superconductors Using a Dielectric Sapphire Resonator in High Magnetic Fields
Authors: Kriplani Ushma , Yeh N.-C. , Jiang W. , Reed D. , Strayer D. M. , Gupta A. , Holtzberg F. , Kussmaul A.
Published: March 2011

The vortex dissipation in an Nd-Ce-Cu-Ol epitaxial film is measured at microwave frequencies using the high-Q modes of a sapphire ring resonator, over a large range of temperatures and external DC magnetic fields. The results are qualitatively consistent with a generalized thermally-activated flux-flow (TAFF) model.
Simulation of vortex-line pinning by defects in the Y-Ba-Cu-O system
Authors: Jamison R. , Burmester C. P. , Wille L. T. , Gronsky R.
Published: March 2011

The finite temperature properties of a two-dimensional flux lattice are studied by Monte Carlo simulation, with particular attention to the effects of twin-boundaries. The parameters selected are appropriate for the YBa2Cu3O7 high-temperature superconducting system. The intrinsic properties of the vortex state are investigated by monitoring system evolution at fixed temperature and applied magnetic field. By varying the temperature, the loss of type-II superconductivity via fluxoid lattice melting is also examined. The introduction of model defects induces the creation of metastable and glassy states which reduce overall hexatic order but are found to enhance system resistance to flux-lattice melting.
Thin Film Ag/YBCO Multistructures for Metal Contact Applications
Authors: Powers M. , Gronsky R. , Washburn J.
Published: March 2011

A technique is presented where Ag is initially sputter deposited on a single crystal ceramic substrate followed by in situ deposition of YBa2Cu3O7δ The resulting microstructure shows Ag islands amidst a c-axis oriented YBCO film, apparently with intimate contact between the YBCO and substrate. This morphology appears ideal for electrical contact to the {hko} surfaces of the superconductor with current carrying CuO planes in maximum contact with the Ag.
Environmental Testing of High Tc Superconductive Thermal Isolators for Space-Borne Cryogenic Detector Systems
Authors: Wise Stephanie A. , Buckley John D. , Randolf Henry W. , Verbelyi Darren , Haertling Gene H. , Hooker Matthew W. , Selim Raouf , Caton Randall
Published: March 2011

NASA's requirements for space-based cryogenic detector systems include the long-term storage of the liquid helium cryogen necessary for the optimized performance of far-infrared (IR) detectors. Significant heat loads on the liquid helium dewars exist due to the numerous electrical connections to the detectors, accounting for approximately 20 percent of the total heat load for some systems. High temperature superconductor lead assemblies are under development to replace the existing manganin wires connecting instruments at 80 K to the detector array at 4.2 K. These superconductive elements provide adequate current transport properties, while decreasing the thermal load on the liquid helium dewar. As a result, mission lifetimes can be extended by 10 percent or more.

Thick films of the superconductive material on low thermal conductivity substrates (e.g. yttria stabilized zirconia and fused silica) have been proposed to replace the existing lead assemblies. This work describes some of the design constraints on such a device as well as preliminary analyses of the effects of vibration, gamma irradiation, and long term exposure to high vacuum and liquid nitrogen encountered in operating such a device in space.
Temperature and Frequency Dependence of the Infrared Absorption in Three Kinds of Bi-Based Compounds
Authors: Hayashi Y. , Harada Y. , Sasakura H. , Nagayama M.
Published: March 2011

Infrared absorption measurements have been made in three kinds of Bi compounds of a high-Tc family mainly by making use of powdered samples. Two of them are superconductors with Tc's of 108 K and 82 K, respectively, and the remaining one is a semiconductor. In each of the superconducting compounds, there appears Mid-Infrared absorption band: No such absorption band is found in the semiconducting compound. At Far-Infrared region, many absorption peaks due to phonons are clearly detected in all of these samples. Some of the phonon modes have been identified. At very low energy region, free carrier absorption appears in superconductors. Only this part of the absorption shows a temperature dependence. Absorption intensity decreases as the temperature decreases.
Evidence for Weak Link Effects in Epitaxial Thin Films of YBCO on LaAlO3
Authors: Bohandy J. , Kim B. F. , Moorjani K. , Adrian F. J.
Published: March 2011

Evidence of weak link effects in epitaxial thin films of YBa2Cu3O7-yon LaAlO3 is obtained from magnetically modulated resistance (MMR) measurements. This result suggests that weak links could provide a mechanism for the residual microwave loss in high quality superconducting thin films which contain predominantly low angle grain boundaries.
Multilayers and Multiturn Coils of YBaCuO/MgO/YBaCuO Layers Prepared by Multitarget Sputtering
Authors: Wunderlich R. , Kleinitzke J. , Meyer B. , Müller J.
Published: March 2011

The deposition of large area multilayers with smooth surfaces is an important topic for the realisation of high quality multiturn coils for flux transformers. We have developed a co-sputtering process from two metallic targets for the deposition of large areas of extremely smooth YBaCuO thin films. Conditions for epitaxial growth of MgO layers on YBaCuO have been investigated. Epitaxial multilayers with good electrical properties (Tc,o > 82 K) have been fabricated.
Plasma Impulse CVD Deposited TiO2 Waveguiding Films: Properties and Potential Applications in Integrated Optical Sensor Systems
Authors: Heming M. , Danielzik B. , Otto J. , Paquet V. , Fattinger Ch.
Published: March 2011

Plasma impulse CVD deposited titania thin films, deposited at low substrate temperatures, exhibit low volume losses of < 0.2 dB/cm and high environmental stability. Their use in novel concepts for integrated optical immunosensors is discussed.
Sol-Gel Coatings for Electrochromic Devices
Authors: Macedo M. A. , Dall'Antonia L. H. , Aegerter M. A.
Published: March 2011

All solid state electrochromic smart windows with the configuration glass/ITO/WO3/electrolyte/TiO2-CeO2/ITO/glass have been realized. These devices have potential applications in architectural and automotive fields to regulate the transmission and reflection of the radiant energy. The ion storage electrode TiO2–CeO2 have been realized by sol-gel process and its electrochemical properties are studied as a function of various parameters (thickness, heat treatment, etc.). The electrochemical and optical performances of two cells are reported.
Alignable Deposition of Thin Film Semiconductor Materials for Integrated Micro-Opto-Electronic Systems
Authors: Camperi-Ginestet C. , Jokerst N. M. , Augustine G. , Hargis M. , Allen M.
Published: March 2011

The selective and alienable deposition of patterned thin film epitaxial GaAs/GaAlAs and InP/InGaAsP devices onto host substrates such as silicon for low cost hybrid integrated micro-opto-electronic systems is reported. Using a combination of semiconductor etch layers and selective etches, the epilayers can be separated from the growth substrate. We use a thin polyimide diaphragm as the transparent transfer medium for these epitaxial materials and devices. Each of these thin film devices or a group of these devices on the polyimide is optically aligned and selectively deposited onto the host substrate. Using this technique, GaAs and InP-based light emitting diodes and optical detectors which are microns thick were grown on lattice matched GaAs and InP substrates, lifted off, aligned and selectively deposited onto a silicon host substrate. The devices were then electrically contacted and tested using standard microelectronic fabrication and testing techniques. This method also enables the manufacturable, sparse distribution of costly photonic devices or the deposition of aligned arrays of devices to fabricate larger arrays. The integration of these light weight devices with microsensors and microactuators will foster micro-opto-electro-mechanical integration.
Characterization of Thin Films using Micromechanical Structures
Authors: Pratt R. I. , Johnson G. C. , Howe R. T. , Nikkel D. J.
Published: March 2011

Micromechanical structures designed for material characterization through analysis of their nonlinear dynamic response are presented. The structures consist of a rigid movable mass supported by beams which are attached to the wafer substrate. The structures are designed so that they are geometrically constrained, which is the source of their nonlinearity. The nonlinearity is shown to be well modeled by Duffing's equation for a stiffening spring and it is this model which is used to fit the test data to the desired mechanical properties, namely Young's modulus, intrinsic stress and damping.
Determination of Eigenstresses from Curvature Data
Authors: Ferrari Mauro , Weber Marie
Published: March 2011

Curvature measurements are generally employed in conjunction with elementary structural analysis to estimate deposition stresses in miniaturized electro-mechanical systems. In this paper the validity of this procedure is discussed by presenting a closed form solution for a bilayer subject to nonuniform intrinsic straining, and comparing the exact stress-curvature relations with the oft-used formulae of Stoney and Brenner-Senderoff.
Theoretical Calculation for the Young's Modulus of Poly-Si and a-Si Films
Authors: Guo Shuwen , Zou Daowen , Wang Weiyuan
Published: March 2011

A newly theoretical calculation for the Young's modulus Eyof poly-Si and a-Si thin films based on the combination of grain and grain boundary effects as well as the dependance of crystalline orientations is presented. The calculated results are in agreement with the experimental results in a wide range of grain size and hydrogen concentrations published in the literatures. The reason for aberration among experimental data of poly-Si and a-Si films caused by different hydrogen concentrations, texture and grain size has been discussed. The results offer a better understanding of. the effects of film structures on elastic properties of poly-Si and a-Si films.
Ferroelectric Thin Films for Microelectromechanical Device Applications
Authors: Polla D. L. , Robbins W. P. , Tamagawa T. , Ye C.
Published: March 2011

Ferroelectric thin films of the lead zirconate titanate family have been integrated with silicon-based micromachined structures in the fabrication of microelectromechanical devices. Sol-gel deposition techniques have been applied in the formation of ferroelectric thin films with high piezoelectric and pyroelectric coefficients for physical forces sensors and infrared detectors, respectively. Knowledge of both electrical and mechanical properties is important in realizing microelectromechanical devices with predictable performance. This pape reports piezoelectric coefficient, pyroelectric coefficient, dielectric constant, and Young's modulus for lead zirconate titanate and lead titanate thin films.
Physical, Electrical, and Piezoelectric Properties of Hot-Forged Sr2(NbTa)2O7 Ceramics
Authors: Fuierer Paul A. , Shrout Tom R. , Newnham Robert E.
Published: March 2011

Solid solution compositions of Sr2(NbxTa1−x)2O7 ceramics with Tr ranging from 450°C to 1342°C were fabricated utilizing a hot-forging technique to achieve preffered grain orientation and thus enhance poling. Translucent samples with greater than 99% theoretical density were obtained using this process. Depending on composition, the degree of orientation as determined by x-ray diffraction was found to be 75% to 95%. The thermal expansion, resistivity, and dielectric constant were shown to be very anisotropic. The direction perpendicular to the forging axis proved to be the ferroelectric “easy” direction, exhibiting hysteresis behavior. Piezoactivity in PLS polycrystals was measured for the first time. Hot-forged samples were electrically poled and the electromechanical properties determined using the five different modes of vibration. For Sr2(Nb0.5Ta0.5)2O7: N24=1504 Hz-m, s44=18.2×10-12m2/N, k24=3.0%, d24=2.6 pC/N, g24=6.3×10-3 Vm/N, and Qm=1100. This material was also shown to resist depoling when exposed to temperatures as high as 650°C.
Stress and Microstructure in Phosphorus Doped Polycrystalline Silicon
Authors: Krulevitch P. , Johnson G. C. , Howe R. T.
Published: March 2011

The research presented here is an investigation of the effects of phosphorus doping on residual stresses and microstructure in polycrystalline silicon. Undoped polycrystalline silicon films were deposited on phosphosilicate glass layers and annealed at 1050 °C for 5 to 60 minutes. The stress gradient through the film thickness was measured from wafer curvature, and microstructure was examined with cross-sectional TEM. A 20 minute anneal is sufficient for stress relief in initially tensile films and produces a uniform microstructure consisting of 0.1-0.2 µm equi-axed grains.
Zeolates: A Coordination Chemistry View of Metal-Ligand Bonding in Intrazeolite MOCVD Type Precursors and Semiconductor Nanoclusters
Authors: Ozin Geoffrey A. , Bowes Carol L. , Steele Mark R.
Published: March 2011

Various MOCVD (metal-organic chemical vapour deposition) type precursors and their self-assembled semiconductor nanocluster products [1] have been investigated in zeolite Y hosts. From analysis of in situ observations (FTIR, UV-vis reflectance, Mössbauer, MAS-NMR) of the reaction sequences and structural features of the precursors and products (EXAFS and Rietveld refinement of powder XRD data) the zeolite is viewed as providing a macrospheroidal, multidendate coordination environment towards encapsulated guests. By thinking about the α- and β-cages of the zeolite Y host effectively as a zeolate ligand composed of interconnected aluminosilicate “crown ether-like” building blocks, the materials chemist is able to better understand and exploit the reactivity and coordination properties of the zeolite internal surface for the anchoring and self-assembly of a wide range of encapsulated guests. This approach helps with the design of synthetic strategies for creating novel guest-host inclusion compounds having possible applications in areas of materials science such as nonlinear optics, quantum electronics, and size/shape selective catalysis.
Double Rotation 23Na NMR Study of Guest-Host Interactions and Nanoscale Assemblies in Sodium Zeolite Y
Authors: Jelinek R. , Ozkar S. , Ozin G. A.
Published: March 2011

23Na double rotation NMR (DOR) provides information on site-specific adsorption of guest molecules within the porous framework of sodium zeolite Y. Anchoring of molybdenum-hexacarbonyl to extraframework Na+ cations in particular locations within the large α-cavities is detected. Changes of the chemical environments of the Na+ cations are observed upon loading trimethylphosphine molecules. Spin-lattice relaxation measurements yield insight on dynamic aspects of the anchoring sodium cations.
Charge Transport Mechanism in Molecularly Doped Polymers
Authors: Nishizawa H. , Sugiuchi M. , Uehara T.
Published: March 2011

Charge-dipole interaction effects in molecularly doped polymers are discussed. The charge-dipole Coulomb interaction makes exponentially distributed traps. Calculating the mobility with their traps leads to mobility behavior like Gill's equation. The cancellation of a dipole corresponds to coincidence events of small-polaron hopping.
Ultrafast Excited-State Dynamics in a Fluoro-Aluminum Phthalocyanine Thin Film
Authors: Williams V. S. , Armstrong N. R. , Mazumdar S. , Sandalphon  , Peyghambarian N.
Published: March 2011

Using femtosecond pump-probe spectroscopy, bleaching of the π-π* absorption Q-band, and photo-induced absorption on the high energy side of the Q-band, have been observed and time-resolved in a nearly-amorphous thin film of fluoro-aluminum phthalocyanine. Following excitation, the induced absorption signal develops as the absorption saturation signal diminishes, suggesting exciton decay into a subgap state. The different bimolecular decay dynamics observed for the absorption saturation (τeff ≈700 fs) and induced absorption (τeff ≈ 2 ps) signals support this conclusion. Possible origins of the subgap state are discussed. In addition, polarization-dependent spectral hole burning is observed at very early times. These results suggest the need for exploration of thin phthalocyanine films which are ordered in three dimensions over distances of at least 200–300 Å. Initial femtosecond results for epitaxially-grown chloro-indium phthalocyanine structures, which meet these criteria, are similar to those for the nearly-amorphous film, but indicate an additional polarization-dependent photo-induced absorption within the Q-band.
Polyion Complexed Langmuir-Blodgeet (LB) Films for Optical Memory
Authors: Fujihira Masamichi
Published: March 2011

A stable monolayer was formed by spreading a chloroform solution of a photosensitive ionic amphiphilic compound on an aqueous subphase containing an ionic polymer with opposite charge. In addition to the increase in stability, the cross sectional area of the amphiphilic molecule usually increased on polyion complexation from that of the same amphiphilic molecule in the absence of the ionic polymer. Deposition of the monolayer onto the solid substrate as a very homogeneous LB film was possible. The increase in molecular area allows various photochemical reactions, which otherwise do not occur due to the steric hindrance, to proceed in the resulting LB films. A rapid decrease in emission of the polyion complexed pyrene LB films was observed upon UV irradiation in air. Application of this very sensitive quenching procedure to optical memory will be also presented.
Optical Properties of Lanthanide Metal Ion Polymer Complexes
Authors: Okamoto Yoshi , Kido Junji
Published: March 2011

The fluorescent characteristics of lanthanide chelates are of considerable interest in connection with electronic energy transfer processes and with their use in laser systems. We have synthesized various chelating groups, such as diketone and bypyridyl containing polymers and prepared their Tb3+ and Eu3+ complexes. Their fluorescent properties in connection with a possible laser action were investigated.

Electroluminscence (EL) in organic compounds has been investigated from fundamental as well as practical point of views. Various organic dyes were utilized as emitter materials in EL devices. In these examples, owing to the broad nature of the luminescence spectra of organic dyes, the luminescent colors are dull. We have utilized lanthanide metal ion complexes as a luminescent emitter.

Tb and Eu ion complexes emitted sharp green and red light, respectively. The configuration of the EL cell and experimental results are described.
A Study of the Structural Properties of Porous Silicon
Authors: Cafolla A A , Shen T-H , Matthai C C
Published: March 2011

We have implemented a modified diffusion limited aggregation model to simulate the porous silicon structure obtained by electro-chemical dissolution. The fractal structures thus obtained have been used as starting configurations from which a fully equilibrated structure was determined by the method of molecular dynamics.
Structural Efficiency of a Natural Composite
Authors: Saliba Joseph E. , Sawaya Georges E.
Published: March 2011

This study was initiated to investigate the structural efficiency of the “bessbeetle” (Odontotaenius Disjunctus) as compared to typical “man-made” or synthetic composites. This synthetic laminate is configured according to standard composites design practices. In fact, an orthotropic unidirectional T300 tape with circular fibers and 60% fiber volume fraction is used. The specific ply orientation of the symmetric man-made composite is [0/+45/-45/90]2S. The natural laminate studied is unsymmetric with the individual plies made of the same orthotropic unidirectional T300 tape but with different ply orientation. Contrary to previous beliefs the natural composite did not assume a balance of inplane and bending properties which in essence mimic the behavior of isotropic behavior. The results of the efficiency of the natural composite for tension did not show any noticeable advantages while the pure bending case resulted in higher values for the principal stresses in the unsymmetric laminate.
Theoretical Study of Polar and Non-Polar Interfaces in Compound Semiconductors: A Thermodynamic Analysis Based on Electronic Structure Calculations
Authors: Kohyama M. , Kose S. , Yamamoto R.
Published: March 2011

Polar and non-polar interfaces of grain boundaries in compound semiconductors can be defined by the stoichlometry in the interface region, and It Is possible to construct two polar and one non-polar Interfaces for a symmetrical tilt grain boundary In the zinc-blende structure of which the Interface Is polar surfaces. The atomic and electronic structures of polar and non-polar interfaces of the {122} Σ=9 grain boundary in SIC have been examined by using the SCTB method coupled with the supercell technique. By using the calculated binding energies, the relative stability of the polar and non-polar interfaces has been analyzed through calculations of the thermodynamic potentials as a function of the atomic chemical potentials. It has been shown that the wrong bonds and the stoichlometry much Influence the stability and properties of grain boundaries in SiC. The stability of polar Interfaces In heterovalent compound semiconductors has been discussed.
Density-Functional Thermodynamic Perturbation Theory of Lennard-Jones Solids
Authors: Kyrlidis Agathagelos , Brown Robert A.
Published: March 2011

The thermodynamics of a fcc hard spheres solid is accurately described by recent density-functional approximations. This state is used as a reference in a thermodynamic perturbation analysis for a density-functional theory of Lennard-Jones solids. The free energy functional incorporates liquid state structural information and a density dependent potential decomposition for the Lennard-Jones interatomic potential. The computed free energies of the solids compare very well with the predictions of atonlistic simulations. Solid-liquid coexistence is predicted consistently to within 15% of results of Monte Carlo simulations, over the temperature range 0.75 ≤ kT/c ε ≤ 10.
Monte Carlo Study of Reconstruction of the Au (110) Surface Using Equivalent Crystal Theory
Authors: Good Brian S. , Banerjea Amitava
Published: March 2011

The (110) surface of gold is known experimentally to undergo a 1 × 2 reconstruction which is believed to be of the “missing row” type. There have been a number of theoretical studies of the energetics and geometry of this reconstruction. In this work, we present new results obtained using two versions of the Equivalent Crystal Theory (ECT). The ECT has proven to be quite accurate in providing predictions of surface energies and planar relaxations. The extended version of the ECT has been modified to better describe such quantities as elastic constants and shear energies. We have computed the energetics and geometry of the missing-row reconstructed surface, in both unrelaxed and relaxed form, using a Monte Carlo energy minimization technique, allowing relaxation of the positions of atoms up to three layers deep. We compare these results with previous theoretical work and with available experimental data.
A Study of the Dependence of the Structure of Σ = 3 Tilt Boundaries in Gold on the Inclination of the Boundary Plane
Authors: Wang Gui Jin , Vitek V.
Published: March 2011

The atomic structure of Σ = 3 tilt boundaries with variously inclined boundary planes has been studied using the many body potentials for gold. A chain unit model, analogous to the structural unit model, describes the relationship between different boundaries. The basic units in this model are units of the (111) and (112) twin boundaries and the model corresponds to atomic level faceting into these boundaries.
Sensitivity of Microsegregation Predictions to the Description of Phase Equilibria
Authors: Rettenmayr Markus
Published: March 2011

A numerical model has been developed to predict the element distribution and some microstructural features in dendritically solidified binary and ternary alloys. Phase diagrams calculated on the basis of thermodynamic functions are taken into account. Thus, a minimum of assumptions is needed to describe the equilibrium at the solid/liquid interface, the partition coefficient of an alloying element is allowed to change as a function of temperature and concentration of other alloying elements.

The description of the equilibrium at the interface appears to be highly significant. Assuming a constant partition coefficient may be justified for some binary alloys, but the assumption has to be verified for each system. Small additions, like dopants or impurities, influence the position of equilibria in phase diagrams, thus requiring the treatment of basically binary alloys as multicomponent systems. In ternary or higher order alloys the assumption of constant partition coefficients leads to erroneous results. For microsegregation predictions in technical alloys realistic phase diagrams have to be taken into account.
New Semi-Empirical Method for Alloys
Authors: Bozzolo Guillermo , Ferrante John
Published: March 2011

We introduce a new semi-empirical method for calculating alloy properties. The method Is based on the concepts of equivalent crystal theory of defect formation energies in elemental solids. With this new method we predict heats of formation, lattice parameters, surface energies, segregation senergies and other properties of several binary alloys of fcc (Cu, NI, Ag, Au, Al, Fe, Pd and Pt) and bcc (Cr, Mo, Fe, V) elements. The method is characterized for its extreme computational simplicity and good agreement with experimental results. Several applications of the method are discussed.
Continuous Displacement of “Lattice” Atoms
Authors: Kikuchi Ryoichi , Beldjenna Arezki
Published: March 2011

In the existing CVM (Cluster Variation Method) formulations, atoms are placed on lattice points. A modification is proposed in which an atom can be displaced from a lattice point. The displaced position is written by a vector r, which varies continuously. This model is treated in the CVM framework by regarding an atom at r as a species r. The probability of finding an atom displaced at r in dr is written as f(r)dr, and the corresponding pair probability is written as g(r1, r2)dr1dr2. We formulate using the pair approximation of the CVM in the present paper. The interatomic potential is assumed given, for example as the Lennard-Jones form. The entropy is written in terms of f(r) and g(r1, r2) using the CVM formula. The special feature of the present formulation which is different from the prevailing no-displacement cases of the CVM is that rotational symmetry of the lattice is to be satisfied by the f(r) and g(r1, r2) functions. After the general equations are written in the continuum vector form and in the integral equation formulation, an example of a single-component system is solved by changing integrals into summations over finite intervals. Further we construct simulations of displacement patters in such a way that the pattern satisfies the pair probability distribution which has been calculated as the output of the CVM analysis. The simulated pattern shows the wavy behavior of phonons. Future directions are discussed.
Molecular Dynamics Simulations of Hot Electrons and Lattice Relaxation in Realistic Cascade Volumes
Authors: Mazzone A.M.
Published: March 2011

This work presents a molecular dynamics simulation method designed to describe the processes of electron and lattice relaxation taking place in typical cascade volumes formed by high-energy implants. The simulation method is based on classical mechanics and includes the motions of electrons and nuclei. The results are in agreement with experiments.