bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth of Laser Ablated YBa2Cu3O7−δ Films as Examined by Rheed and Scanning Tunneling Microscopy
Authors: Russek Stephen E. , Roshko Alexana , Sanders Steven C. , Rudman David A. , Ekin J. W. , Moreland John 
Published: March 2011

ABSTRACTUsing scanning tunneling microscopy (STM) and reflection high energy electron diffraction (RHEED) we have examined the growth morphology, surface structure, and surface degradation of laser ablated YBa2Cu3O7−δ thin films. Films from 5 nm to ltm thick were studied. The films were deposited on MgO and LaAlO3 substrates using two different excimer laser ablation systems. Both island nucleated and spiral growth morphologies were observed depending on the substrate material and deposition rate used. The initial growth mechanism observed for a 5–10 nm thick film is replicated through different growth layers up to thicknesses of 200 run. Beyond 200 rnm, the films show some a-axis grains and other outgrowths. The thinnest films (5–10 nm) show considerable surface roughness on the order of 3–4 nm. For both growth mechanisms the ledge width remains approximately constant (∼ 30 nm) and the surface roughness increases as the film thickness increases. The films with spiral growth have streaked RHEED patterns despite having considerable surface roughness, while the films with island growth have more of a three dimensional diffraction pattern. RHEED patterns were obtained after the film surfaces were degraded by exposure to air, KOH developer, a Br-methanol etch, and a shallow ion mill. Exposure to air and KOH developer caused only moderate degradation of the RHEED pattern whereas a shallow (I nm deep) 300 V ion mill completely destroyed the RHEED pattern.
In-Situ Laser Processing and Microstructural Characteristics of YBa2Cu3O7−δ Thin Films on Si with TiN Buffer Layer
Authors: Tiwari P. , Zheleva T. , Narayan J. 
Published: March 2011

ABSTRACTWe have prepared high-quality superconducting YBa2Cu3O7−δ (YBCO) thin films on Si(100) with TiN as a buffer layer using in-situ multitarget deposition system. Both TiN and YBCO thin films were deposited sequentially by KrF excitner laser ( λ = 248 nm ) at substrate temperature of 650°C. Thin films were characterized using X-ray diffraction (XRD), four-point-probe ac resistivity, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Rutherford backscattering (RBS). The TiN buffer layer was epitaxial and the epitaxial relationship was found to be cube on cube with <100> TiN // <100> Si. YBCO thin films on Si with TiN buffer layer showed the transition temperature of 90–92K with Tco (zero resistance temperature) of ∼84K. We have found that the quality of the buffer layer is very important in determining the superconducting transition temperature of the thin film. The effects of processing parameters and the correlation of microstructural features with superconducting properties are discussed indetail.
Epitaxial Growth of TiN Films on (100) Silicon Substrates by Laser Physical Vapor Deposition
Authors: Tiwari P. , Zheleva T. , Narayan J. 
Published: March 2011

ABSTRACTWe have synthesized epitaxial TiN films having low resistivity on (100) silicon substrates using pulsed laser deposition method. The TiN films were characterized using X-ray diffraction, Rutherford back-scattering, four-point-probe ac resistivity, high resolution transmission electron microscopy techniques and epitaxial relationship was found to be <100> TiN // <100> Si. TiN films showed 10–20% channeling yield. In the plane, four unit cells of TiN match with three unit cells of silicon with less than 4.0% misfit. This domain matching epitaxy provides a new mechanism of epitaxial growth in systems with large lattice misfits. Room-temperature resistivity of these films was found to be about 15 μΩ-cm. Implications of low-resistivity epitaxial TiN in silicon device fabrication are discussed.
Phase Composition and Microstructure as a Function of Deposition Conditions for Potassium Tantalate Niobate Thin Films Grown by Pulsed Laser Deposition
Authors: Cotell C.M. , Leuchtner R.E. 
Published: March 2011

ABSTRACTPotassium tantalate niobate [K(Ta1−xNbx)O3 or KTNJ films were deposited by pulsed laser deposition (PLD) on (100)MgO substrates from targets of KTN with x=0.45. The effects of substrate temperature (300–700°C) and ambient oxygen pressure (50 and 300 mTorr) on the characteristics of films were investigated. At 500°C and 300 mTorr, films were amorphous with a few isolated, randomly-oriented crystalline grains of perovskite and pyrochlore. At 600°C and 300 mTorr, the films comprised a columnar microstructure consisting of a mixture of amorphous phase with (100) perovskite. At 650°C, films were almost entirely (100) perovskite. At 700°C, the films were predominantly (100) perovskite, but contained a much higher fraction of pyrochlore. At 50 mTorr, pyrochlore was found in significant fractions up to 650°C. At 700°C, films were predominantly (100) perovskite. Rutherford Backscattering analysis of the chemical composition showed that all the films were potassium-deficient and the tantalum to niobimn ratio exceeded that found in the targets for all deposition conditions. There appeared to be a relationship between oxygen pressure during deposition and the amount of potassium retained in the films.
Interfacial Reactions During Processing of Thin Nickel Oxide Films Grown by Pulsed-Laser Ablation
Authors: Kotula Paul G. , Carter C. Barry 
Published: March 2011

ABSTRACTThe study of oxide solid-state reactions is a natural application for pulsed-laser ablation (PLA) because high quality films of virtually any oxide composition can be fabricated. In this study, the effect of interfacial morphology on reaction kinetics in the model oxide system of nickel oxide (NiO) and alumina (α-Al2O3) is investigated. Thin films of NiO have been grown on single-crystal substrates of basal (0001) α-Al2O3 by PLA in order to study the initial stages of the nickel-aluminate spinel (NiAl2O4) phase transformation. The initial state, a 100 nm NiO film on (0001) α-Al2O3, is characterized with both plan-view and cross-section transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The final state of the spinel reaction layer between the NiO and α-Al2O3 after various heat-treatments is also characterized by the same techniques.
Species Temporal and Spatial Distributions in Laser Ablation Plumes
Authors: Hastie John W. , Bonnell David W. , Paul Albert J. , Schenck Peter K. 
Published: March 2011

ABSTRACTThe intermediate species present in laser ablation plumes, particularly those formed during pulsed laser deposition (PLD) of thin films, have been identified for a variety of advanced materials systems. Optical multichannel analysis spectroscopy has been used to monitor the atomic and ionic species present, via their spectral emissions. Molecular beam-sampling mass spectrometry has been used to monitor the molecular species present, in addition to atoms and ions. With both monitoring approaches, temporal and spatial species distribution information has been obtained. Velocity distributions, obtained from the time-dependent mass spectral studies, show the effects of isentropic expansion to be predominant when compared with gasdynamic models of the plume evolution process. Also, the plume structure was found to be particularly sensitive to target elemental distribution. Examples of systems studied include high temperature superconductors, refractory compounds, ferroelectrics and nanostructured magnetic films.
Unique Features of Laser Ablation
Authors: Hanabusa Mitsugu 
Published: March 2011

ABSTRACTThe advantage and disadvantage of laser ablation as a thin Film deposition technique are discussed on the basis of my own experiences. High instantaneous growth rate is useful to produce amorphous films, and reactive deposition can be achieved by gases introduced in the deposition chamber. Combining these two features, hydrogenated amorphous silicon films were produced. Laser ablation is characterized by the presence of energetic neutrals and ions in beams, which helped to deposit diamond-like carbon films. Also selective-area deposition is made possible by placing a mask between the target and substrate. In pulsed laser ablation the mask must be placed close to the substrate to avoid the spreading of deposits. The thickness profilr can bc controlled by residual gas pressure, and using this technique microlenses were fabricated, in addition to ridge-type optical waveguides. The particle problem which plagues laser ablation is more serious for targets with low fractional ionic character. The usefulness of a molten target as the means to eliminate particles was confirmed for aluminum.
Ion-Assisted Pulsed Laser Deposition of Cubic Boron Nitride on Si (100) Substrates
Authors: Friedmann T. A. , Mccarty K. F. , Klaus E. J. , Johnsen H. A. , Medlin D. L. , Mills M. J. , Ottesen D. K. , Stulen R. H. 
Published: March 2011

ABSTRACTWe are studying the boron nitride system by using a pulsed excimer laser to ablate from hexagonal BN (hBN) targets to form cubic BN (cBN) films. We are depositing BN films on heated (400°C) Si (100) surfaces and are using a broad beam ion source operated with Ar and N2source gasses to produce BN films with a high percentage of sp3-bonded cBN. The best films to date show ∼85% sp3-bonded BN as determined from infrared (IR) reflection spectroscopy. High resolution transmission electron microscopy (TEM) and selected area electron diffraction (SAD) confirm the presence of cBN in these samples. The films are polycrystalline and show grain sizes up to 500 Å.
The Optimization of Niobium Diselenide Thin Films Through Control of Pulsed Laser Deposition Parameters
Authors: Day Allan E. , Laube Samuel J.P. , Donley M.S. , Zabinski J.S. 
Published: March 2011

ABSTRACTNiobium diselenide has potential for use as a conductive lubricant, but to achieve the optimal properties of low friction coefficient, high conductivity and oxidation resistance, the SeJNb ratio and crystallinity must be carefully controlled. It has been shown that Pulsed Laser Deposition (PLD) permits the required degree of control, even over films with complex stoichiometries. (4–8). In this study, PLD was used to grow stoichiometric, crystalline thin films of niobium diselenide and to study the effects of laser deposition parameters on film properties. Film chemistry and crystallinity were evaluated using XPS, RBS, and glancingangle XRD. Friction and wear measurements were taken on a ball-on-flat tribometer. The deposition apparatus incorporates a fully computerized data acquisition and control system that facilitated the correlation of the laser deposition parameters to film properties. This study has shown that film chemistry could be changed from substoichiometric to superstoichiometric and crystallinity varied between amorphous to highly crystalline by appropriate choice of PLD parameters. The property correlations and acquisition system that permitted the identification of the optimal growth conditions will be described.
Structural Analysis of Carbon Thin Films Deposited by Pulsed Laser Deposition
Authors: Capano M.A. , Qian F. , Singh R.K. , Mcdevitt N.T. 
Published: March 2011

ABSTRACTThe objective of the current study is to gain a greater understanding of the atomic structure of carbon films deposited by UV-pulsed-laser ablation. Films deposited onto Si substrates at 293 K, 473 K, 673 K, and 873 K are characterized using X-ray reflectometry and Raman spectroscopy. Film densities are shown to initially decrease from a maximum density of 2.39 g/cm3 as temperature increases. Above 673 K the density remains constant. When compared with Raman spectroscopy data, the reflectometry data are shown to be sensitive to microstructural changes within the films. The possibility of using density measurements as a boundary condition for more quantitative analysis is discussed. Also, Raman spectroscopy indicates that the graphitic domain size initially decreases, passes through a minimum, and then increases as temperature increases. The amount of bond-angle disorder is shown to decrease with increasing substrate temperature. However, an upward shift in frequency of the Raman D peak is not observed with the presumed decrease in sp3 bonding as the deposition temperature increases. These and other experimental results are presented and discussed.
Synthesis of Sic Fine Particles by Gas-Phase Reaction Under Short-Time Microgravity
Authors: Okutani Takeshi , Nakata Yoshinori , Suzuki Masaakt , Maniette Yves , Goto Nobuyoshi , Odawara Osamu , Mori Kiyoshi 
Published: March 2011

ABSTRACTSiC fine particles were synthesized by the gas-phase thermal decomposition of tetramethylsilane (Si(CH3)4) in hydrogen under microgravity of 10−4G for 10 sec. Rapid heating to the temperature over 800°C which is required for thermal decomposition of Si(CH3)4) under short-time microgravity was attained using a chemical oven where the heat of exothermic reaction of combustion synthesis of Ti-A1-4B composites was used as the heat source. Monodisperse and spherical SiC fine particles were synthesized under microgravity, whereas aggregates of SiC fine particles were synthesized under 1 G gravity. The SiC particles synthesized under microgravity (150-200 nm) were bigger in size and narrower in size distribution than those under 1 G gravity (100-150 nm).
Synthesis of Nanocrystalline Fe-based Particles by CO2 Laser Pyrolysis
Authors: Bi Xiang-Xin , Eklund Peter C. 
Published: March 2011

ABSTRACTNanocrystalline Fe (α and γ phases), Fe-carbide (Fe3C, Fe7C3 ), Fe-sulfide (Fel-xS), Fe-nitride (Fe3N and Fe4N) particles with narrow size distributions have been produced using a CO2 laser pyrolysis of vapor mixtures of Fe(CO)5 with C2H4, H2S or NH3. Typical production rates of ∼ 1 - 3 g/hr were observed. The chemical phase and size of these nanoscale particles can be controlled by reaction parameters such as laser intensity and gas composition. Pyrolytic carbon coatings were found to be present on the Fe-carbide particles, but absent in the Fe-sulfide and -nitride particles.
Synthesis of Nanocrystalline Co-W Alloys
Authors: Osmola D. , Renaud E. , Erb U. , Wong L. , Palumbo G. , Aust K.T. 
Published: March 2011

ABSTRACTElectroplating is one of the most technologically advanced methods to synthesize nanophase materials both as coatings and in bulk form. This paper demonstrates the formulation of a processing “window” for nanocrystalline Co-W alloys using factorial design. The microstructural evolution from polycrystalline to nanocrystalline to amorphous Co-W microstructures is shown for electrodeposits produced from a bath containing cobalt sulphate, sodium tungstate, Rochelle salt and ammonium chloride. The effect of operating variables such as temperature and current density is discussed.
Transformations and Hydrogen Storage in Ball-Milled Iron-Titanium
Authors: Tessier P. , Zaluski L. , Yan Z.-H. , Trudeau M.L. , Bormann R. , Schulz R. , Ström-Olsen J.O. 
Published: March 2011

ABSTRACTNanocrystalline and amorphous Fe-Ti at or close to the equiatomic composition have been prepared by ball milling, starting either from the elemental components or from the pre-melted intermetallic. The final structure, whose evolution has been monitored by Xray diffraction and transmission electron microscopy, is found to be critically dependent on milling conditions and contamination level.Hydrogen absorption properties of both the amorphous and nanocrystalline alloys have been investigated. These properties are substantially modified by the reduction in grain size. We will also discuss the influence of the activation process and repeated hydrogen charging on substitutional disorder and grain size.
Luminescence of Rare Earth Metalorganic Complexes in Sol-Gel Derived Host Materials
Authors: Matthews Lowell R. , Knobbe E. T. 
Published: March 2011

ABSTRACTThe narrow, intense emission bands of europium(III) make its compounds of interest for various optical source applications. Previous studies have shown that europium thenoyltrifluoroacetonate complexes, e.g. Eu(TTFA)3, have superior fluorescence properties in select media with respect to inorganic salts like EuCl3. It has been shown that such complexes may be incorporated into solid-state matrices via the sol-gel process. The present research examines the luminescence behavior of a metalorganic complex (Eu(TTFA)3) doped into a sol-gel derived silica-acrylate ORMOSIL host and extends our earlier work on doped silica gel materials. The present study focuses on the effects of dopant concentration and dopant-matrix interaction, and seeks to compare the behavior of Eu(ITFA)3 in silica and ORMOSIL gel host materials.
SOL-GEL DERIVED SENSOR MATERIALS FOR USE IN AQUEOUS TRANSITION METAL ION DETECTION
Authors: Yates L. M. , Arbuthnot D. , Harmon H.J. , Knobbe E. T. 
Published: March 2011

ABSTRACTOpto-chemical transducers, which exhibit changes in luminescence and/or absorption characteristics as a function of local conditions, are currently of great interest for use in performing quantitative chemical analyses. Present research is focused on the preparation and characterization of novel optrode materials which may be remotely interrogated via optical fiber carriers. The approach under investigation involves preparation of sol-gel derived films which are sensitized by the entrapment of analyte-complexing organic probe molecules. Zn(II)aq induced perturbations to the luminescence behavior of a porphyrin derivative entrapped within a porous sol-gel derived host matrix are detailed.
Nanocomposite Dielectric Material: Au/SiO2-gel
Authors: Vezzoli G.C. , Chen M.F. 
Published: March 2011

ABSTRACTA nanocomposite of clusters of gold atoms in a silica gel matrix has been prepared by the sol-gel technique through reduction of gold chloride. This composite was fabricated to explore novel techniques for materialsengineering new high dielectric strength substances for capacitor applications. The gold islands amidst the silica gel sea are materials-designed to utilize the percolation threshhold phenomenon to create a peak in the dielectricconstant as a function of optimal topology. Experimental results indicate an average dielectric constant of the order of 5000 at 1 kHz, and a maximum versus temperature at ∼ −100°C. Electron microscope and microprobe analysis indicate ellipsoidal Au particles or clusters of a dimension ranging from a hundred angstroms to several thousand angstroms.
Lessons From Biology for Materials Scientists
Authors: Birchall J. Derek 
Published: March 2011

ABSTRACTLiving organisms make use of inorganic materials such as calcium carbonate and phosphate, silica, iron oxide etc. to construct support structures, protective armour, magnetic devices gravity devices and so on. The structures are remarkably adapted for the duties they have to perform, the adaptation being at all levels from the nanometer to the macroscopic. Microscopic detail is controlled in order that the macroscopic structure forms an efficient functional component of a machine and the structure develops in response to signals from the local environment. The study of these biogenic minerals and the mechanism of their formation can inspire new approaches to the synthesis and design of new materials and to the advantageous modification of old materials. Examples are given in this paper.
Oxide and Metal Intercalated Clay Nanocomposites
Authors: Malla P. B. , Komarneni S. 
Published: March 2011

ABSTRACTTruly nanocomposite materials that are stable to about 400 to 700°C can be prepared by intercalating oxides or metal clusters of about 0.4 to 2.0 nm in between ∼1.0 nm layers of smectite clays. Both the chemistry and size of intercalates (pillars) can be varied to introduce unique catalytic, molecular sieving, dehumidifying and adsorption properties in these materials. The intercalated clays also provide opportunities to prepare compositionally and stoichiometrically diverse nanocomposite precursors to high temperature structural and electronic ceramics. Although montmorillonite is the most widely used host, further designing in properties can be achieved by using other members of smectite family having subtle crystal chemical and compositional variations, such as beidellite, nontronite, saponite or hectorite. The sol-gel chemistry involving the preparation of positively charged mono- or multiphasic solution-sol or colloidal-sol particles is a viable approach to introduce chemically diverse oxide particles in the interlayers of smectite. Reduction of transition metal ions or complexes in the interlayers of smectite to zerovalent metal clusters/particles using polar liquids is another novel approach to develop catalytically active, high surface area materials.
Preparation of Nanophase SiC/Si3N4, SiC/B4C and Stoichiometric Sic From Mixtures of A Vinylic Polysilane and Metal Powders
Authors: Jrang Zhiping , Rhine Wendell E. 
Published: March 2011

ABSTRACTPyrolysis of a vinylic polysilane (VPS, Union Carbide Y12044) under argon at 1600 °C resulted in the formation of SiC with 20% residual carbon. The excess carbon was transformed to B4C or SiC by mixing B or Si powder with VPS and pyrolyzing the mixture under a flow of argon. When excess Si was added and the mixture was pyrolysed under N2 at 1395 °C, a SiC/ Si3N4 composite was obtained. All the products showed a fine-grained microstructure and excellent homogeneity. The precursors and the pyrolysis products were characterized by means of FIIR, TGA, XRD, SEM, STEM, BET, and elemental analysis.
Effect of the Matrix on the Oxidation of Nanostructured Ge Granular Films
Authors: Waite M.M. , Shah S. Ismat , Doele B.A. 
Published: March 2011

ABSTRACTNanostructured Ge granular thin films were prepared by magnetron sputtering of composite targets pressed from mixtures of Ge and ceramic powders. The ceramics used were Al2O3, MgO and SiO2. Films in the Gex(Al2O3)l-x system were composed of Ge particles 10-60 nm in size uniformly embedded in the ceramic matrix, particularly for low Ge concentration films. X-ray photoelectron spectroscopy (XPS) was used to characterize these films. Samples were identified according to the coordination of Ge with the oxygen as (i) Ge-Ge4, (ii) Ge-Ge3O, (iii)Ge-Ge2O2, (iv) Ge-GeO3 and (v) Ge-O4. Using the modified Sanderson model1 and its modifications2, we found Ge oxidation to be largely composition dependent. Similar results were obtained for Ge granular films in MgO and SiO2 matrices.
Microstructural Development in Nano-Crystalline Zinc Sulfide Powders
Authors: Han Y. , Voiles E.T. , Chumbley L.S. , Akinc M. 
Published: March 2011

ABSTRACTMonodispersed, spherical, submicron size zinc sulfide powders were previously prepared in our laboratory utilizing homogeneous precipitation by thermal decomposition of thioacetamide in acidic aqueous solutions. Electron microscopic investigations of these powders indicated that the individual particles were agglomerates of 8∼14 nm size crystallites. It has been known that zinc sulfide does not sinter under ambient pressure due to the covalent nature of its bonding, high melting point, and relatively high vapor pressures at elevated temperatures. The heat treatment of these nano-crystalline zinc sulfide powders, however, showed some degree of sintering at temperatures as low as 600°C under vacuum.