bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Intrinsic In-Plane Stress on the Local Atomic Structure of Thermally Grown SiO2
Authors: Fitch J. T. , Bjorkman C. H. , Sumakeris J J , Lucovsky G.
Published: March 2011

The effect of thermal history on the local atomic structure of thermally grown and annealed SiO2 films is discussed. Thin films of SiO2 were prepared for study by (1) thermal oxidation of silicon at 850°C and 1050°C in a dry oxygen ambient and, (2) by subsequent rapid thermal annealing at temperatures between 850°C and 1200°C. After thermal processing, the film thickness was reduced incrementally by a wet chemical etchback technique to within 50 Å of the growth interface. Relief of intrinsic growth stress by viscous flow was investigated, at each thickness increment, on a local atomic scale by infrared spectroscopy and on a macroscopic scale by beam-bending type stress measurements. Results were analyzed in terms of a Maxwell model. Changes in film thickness and refractive index resulting from viscous flow during annealing were shown to obey a Clausius-Mossotti relationship. Local atomic strain values, calculated from shifts in the IR bond-stretching frequency, showed a linear correlation with measured stress values giving a value for a plane-strain Young's modulus of 4.7 × 1011 dynes/cm2. This compares favorably with the literature value of 8.8 × 1011 dynes/cm2.
X-Ray Diffraction Determination of Stresses in Thin Films
Authors: Vreeland T. , Dommann A. , Tsai C.-J. , Nicolet M.-A.
Published: March 2011

This paper presents the methodology employed in the determination of the stress tensor for thin crystalline films using x-ray rocking curves. Use of the same equipment for the determination of the average stress in poly- or non-crystalline thin films attached to a crystalline substrate is also discussed. In this case the lattice curvature of the substrate is determined by measurement of the shift In the Bragg peak with lateral position in the substrate.

Strains in single crystal layers may be measured using Bragg diffraction from the layers and from the substrate or a reference crystal, with the highest strain sensitivity of any known technique. The difference in Bragg angles for a strained and an unstrained crystal is related to the change in d spacing of the Bragg planes, and the elastic strain is related to'this angular difference. The separation of two peaks on an x-ray rocking curve is generally not equal to the difference in Bragg angles of two diffracting crystals, so diffractometer measurements must be carefully Interpreted in order to obtain x-ray strains in crystalline films (x-ray strains are strains relative to the reference crystal). The unstrained d spacings of the film and the d spacings of the reference crystal must be known to obtain the elastic strains in the film, from which the stress tensor is determined.
Intrinsic Stress in a-Germanium Films Deposited by RF-Magnetron Sputtering
Authors: Fahnline D. , Yang B. , Vedam K. , Messier R. , Pilione L.
Published: March 2011

Thin a-Ge films deposited by rf-magnetron sputtering undergo a change from compressive to tensile stress as the argon gas pressure is increased. Spectroscopic ellipsometry, neutron activation analysis, and a dual laser beam reflection technique were used to determine the film's void fraction content, Ar/Ge atomic percent, and stress, respectively. The results of these three measurements indicate that as the film's Ar/Ge content increases, the void fraction decreases and the intrinsic stress becomes compressive. These findings are consistent with currently accepted bombardment mechanisms.
Behavior of Defects Related to Interface-Stresses in Model Submicron Soi Structures
Authors: Theodore N. D. , Carter C. B. , Arney S. C. , MacDonald N. C.
Published: March 2011

The origin and propagation of defects in novel submicron SOI structures have been investigated by transmission electron microscopy. The majority of the defect configurations observed could be explained in terms of dislocations generated as a result of stresses induced by the oxidation process. Dislocations were found to propagate into the silicon along particular {111} planes in conformity with stress-modelling. The examination of particular dislocation configurations allowed an estimation of the stresses at the silicon/ silicon dioxide interface. Defect densities were observed to depend on the geometry of the structures.
The Influence of Thickness and Wavelength on the Mechanical Properties of a Compositionally Modulated Ceramic Thin Film
Authors: Oliver W. C. , List F. A. , McKee R. A.
Published: March 2011

The hardness and modulus of thin (<1 μm) ceramic films have been investigated using the differential mechanical properties microprobe (DMPM). The DMPM consists of a computer controlled ultra-low load indentation system with a special system that allows the elastic stiffness of the contact to be determined continuously during the indentation process. The films were deposited in a molecular beam epitaxy (MBE) system utilizing unique high temperature effusion cells. Two specimens have been studied. The first is a wedge shaped layer of amorphous Al2O3 on a silicon substrate. The thickness of the layer varies from 0 to 990 nm at the two extreme sides of a 3 in. silicon wafer. The effect of layer thickness on the hardness and modulus as measured with the DMPM has been quantified for this system. The second specimen is made up of 38 repetitions of alternating layers of crystalline TiO2 and amorphous Al2O3. The wavelength of the composition modulation and the thickness of the film varies uniformly from 0 to 38 nm and from 0 to 1460 nm respectively across the 3 in. diameter of the silicon substrate.
Studies of Si Surface Chemistry and Epitaxy Using Scanning Tunneling Microscopy and Spectroscopy
Authors: Avouris Phaedon , Wolkow Robert
Published: March 2011

We apply scanning tunneling microscopy (STM) and spectroscopy (STS) to study the reaction of NH3 with Si(111)-(7×7), and the epitaxial growth of CaF2 on Si(11). By a combination of topographs and atom-resolved spectra we can follow the spatial distribution of the reaction and changes in electronic structure with atomic resolution. We find that there are strong site-selectivities for the NH3 reaction on the 7×7 surface. We also observe the initial stages of the CaF2 deposition and even are able to image insulating multi-layer CaF2 films.
Silane Adsorption and Decomposition on Si(111)-(7×17)
Authors: Gates S. M. , Greenlief C. M. , Beach D. B.
Published: March 2011

The reactive sticking coefficient, SR, of SiH4 on the Si(111)-(7×7) surface has been studied as a function of hydrogen coverage (ΘH) in the surface temperature (TS) range 80–500°C. At 400°C, evidence is seen for two adsorption regimes which are proposed to correspond to minority and majority surface sites. On the minority sites (ΘH = 0 to 0.08), SR is approximately independent of TS. On the majority sites (ΘH > 0.08), SR is a complicated function of TS and ΘH. After SiH4 exposure, surface SiH is the dominant stable decomposition intermediate from 80 to 500°C, with detectable populations of SiH2 and SiH3 present at the lowest temperatures.
Chemisorption of HF on Silicon Surfaces
Authors: Joycea S. A. , Yarmoff J. A. , Johnson A. L. , Madey T. E.
Published: March 2011

We have investigated the interaction of gaseous hydrofluoric acid (HF) with single crystal silicon surfaces using soft x-ray photoemission spectroscopy and Electron Stimulated Desorption Ion Angular Distributions (ESDIAD). Examination of the Si(2p) core level for surfaces saturated with HF shows the formation of silicon-fluoride bonds indicating the dissociative chemisorption of HF on both Si(111) and Si(100) surfaces. Inspection of the F(2s) and F(2p) valence levels at saturation coverage indicate that only one-half monolayer of fluorine bonds to the silicon. The primary ion desorbed by electron bombardment of these surfaces is F+ with only a minor contribution from H+. ESDIAD images from a saturation coverage of HF on stepped Si(100) surfaces reveal F+ desorption primarily along the direction of the terrace dimers. The ESDIAD patterns from HF adsorbed on Si(111) are characterized by strong normal F+ emission with a weak background component of off-normal emission. These results are consistent with the dissociative chemisorption of HF where the ion emission direction is determined by the Si-F bond directions.
Effects of Potassium on the Adsorption and Reactions of Nitric Oxide on Silicon Surface
Authors: Ying Z. C. , Ho W.
Published: March 2011

The adsorption, thermoreactions, and photoreactions of NO coadsorbed with K on Si(111)7×7 at 90 K have been studied and compared with the results obtained from the Kfree surface. The experiments were performed under ultra-high vacuum conditions using high resolution electron energy loss spectroscopy, work function change measurements, and mass spectrometry. NO adsorbs both molecularly and dissociatively on the K-free surface. Two molecular N–O stretching modes are observed at 188 and 225 meV. The concentration of these NO molecules on the surface decreases as the K exposure increases and vanishes at high K exposures. A new N–O stretching mode, attributed to adsorption of NO molecules on K clusters, is observed at 157 meV. After thermal heating or photon irradiation, the surface is covered with atomic O and N. The surface is more oxidized in the presence of K. A steady decrease in the photodesorption cross section is observed as the K exposure increases and is attributed to K-induced band structure changes.
Metal Atom Routes to Metal-Based Clusters in Polymers
Authors: Andrews Mark P. , Galvin Mary E. , Heffner Sharon A.
Published: March 2011

Past syntheses of polymer composites have largely evolved from chemical reduction or thermal decomposition of organometallic or inorganic precursor molecules in polymers, or plasma and thermal co-deposition of metal vapors and carbonaceous free radicals. Our approach involves the site-specific capture of metal atoms deposited in vacuum to give isolated, high energy mononuclear organometallic centers within a polymer film. These centers can be converted at ambient or sub-ambient temperatures (ie, below the polymer glass transition temperature) to, for example, metal oxide microclusters.

We describe the results of our studies of a prototypical system involving chromium atoms and their conversion to corundum-type oxide microclusters in arene-functionalized polymer films. Thus Cr was deposited into 150 K liquid tetrahydrofuran solutions of polystyrene or poly(styrene-isoprene-styrene) triblock, spun in vacuo as thin films on the surface of a rotating glass cryostat. Evidence from epr spectrscopy shows that the resulting polymer-anchored (inter/intra-chain) bis(arene)Cr sandwich complex is locally mobile in the macroscopically rigid film at room temperature. The Cr atom is discharged from the rings by subsequent reaction with oxygen diffused into the film. Although α Cr2O3is a classic twosublevel antiferromagnet that is not epr active above 308 K, we observe an intense signal even at 77 K in these films. Cr2O3microclusters are indicated, and these are confirmed by in situ measurements of the oxidation and aggregation process.

The metal atom methodology has also been used to synthesize silver microsphere/polymer composites. With quadratic electrooptic phase modulation, these composites were found to show a third order susceptibility enhanced by coupling the dipolar surface plasmon mode of the particles with incident light.
Interaction of in Atom Spin-Orbit States with Si(100) Surfaces
Authors: Oostra Doeke J. , Smilgys Russell V. , Leone Stephen R.
Published: March 2011

Scattering and desorption of In from Si(100) is investigated. Laser induced fluorescence is used to probe the desorbing and or scattered species. Auger Electron Spectroscopy is used to study the composition on the surface. The results show that at surface temperatures below 820 K a two dimensional layer of In desorbs by a half order mechanism. This is explained by assuming two dimensional In islands on the surface. Above 820 K, desorption takes place by a first order mechanism. The desorption para-meters appear to be spin-orbit state specific. The desorption energy for In 2P3/2 is 2.8 ± 0.4 eV and for In 2P½ 2.5 ± 0.2 eV. The difference is equal to the difference in the spin-orbit energy. So far no specular scattering of In is observed, suggesting that the sticking coefficients are unity.
Reactive Atom-Surface Scattering the Adsorption and Reaction of Atomic Oxygen on the Si(100) Surface
Authors: Engstrom J. R. , Nelson M. M. , Engel T.
Published: March 2011

The adsorption and reaction of atomic oxygen on the Si(100) surface has been examined by employing supersonic beam techniques, X-ray photoelectron spectroscopy and mass spectrometry. Atomic oxygen adsorbs with a unit probability of adsorption on the clean Si(100) surface. The probability of adsorption decreases monotonically with increasing coverage. At surface temperatures above approximately 1000 K. the adsorption of atomic oxygen results in the gasification of the substrate, producing SiO(g). In comparison to molecular oxygen for this reaction, where two surface intermediates were implicated, only one surface intermediate is formed from the reaction of atomic oxygen with the Si surface.
Atom- and Radical-Surface Sticking Coefficients Measured Using Resonance Enhanced Multiphoton Ionization (REMPI)
Authors: Robertson Robert M. , Rossi Michel J.
Published: March 2011

Sticking coefficients γ of neutral transient species at ambient temperature were measured using in situ Resonance Enhanced Multiphoton Ionization (REMPI) of the transients in a Knudsen cell. γ for I and CF3I‡ on a stainless steel surface were 0.16 and >0.5, respectively, whereas γ for CF3 on the same surface was measured to <0.01; γof SiH2 on a growing carbon containing amorphous silicon surface was 0.11; this value increased to 0.15 for interaction of SiH2 with a “pure” growing silicon-hydrogen surface, and γ of SiH2‡ on both types of surfaces was found to be >0.5.
Amorphous to Crystalline Structural Transition during Growth of Silicon by Plasma Enhanced Chemical vapor Deposition
Authors: Varhue W. J. , Krause S. , Dea J. , Jung C. O.
Published: March 2011

The growth of thin Si films by RF glow discharge undergoes a transition from amorphous to microcrystalline as power density is increased. This results in a substantial change in the film's electrical conductivity and activation energy for electrical conduction. The RF glow discharge has been characterized in terms of plasma density, plasma potential and electron temperature with emissive Langmuir Probe measurements. The structural transition has been observed with a transmission electron microscope.
In Situ Characterization of thin film Growth by Ftir Irras
Authors: Butler J. E. , Koller K. B. , Schmidt W. A.
Published: March 2011

In-situ analysis of low temperature Plasma Enhanced Chemical Vapor Deposition (PECVD) SiO2 films deposited on HgCdTe, Silicon, and Aluminum substrates was performed by double modulation Fourier Transform Infrared Reflection Absorption spectroscopy (FT-IRRAS). The sensitivity and selectivity of this technique are sufficient for an in-situ assessment of the film quality and reaction conditions at any stage of film growth. An oblique angle of incidence of ca. 557deg; was chosen to yield maximum sensitivity for the 1260 cm−1 LO mode of SiO2 on Si. The peak frequency and shape of the LO mode absorption band varied with the quality of the SiO2 films. This diagnostic technique can be applied readily to in-situ analysis of dielectric thin films formed under a variety of reaction conditions as long as the gaseous ambient is partially transmissive to the IR radiation.
Surface Reaction Mechanisms in the Metallisation and Etching of Semiconductor Materials.
Authors: Wee A , Murrell A J , French C L , Price R J , Jackman R B , Foord J S
Published: March 2011

Surface spectroscopic techniques have been used to investigate aluminium deposition form tri-methyl aluminium (TMA) on Si(100), and the etching of InP by chlorine. Thermal reactions and processes stimulated by UV lamps and ion beams are examined. The results are interpreted in the light of the adsorption states which are formed and the surface transformations of chemical states which are observed to occur.
Nucleation Barriers in Chemical Vapor Deposition of Triisobutylaluminum on Silicon
Authors: Mantell D. A.
Published: March 2011

The nucleation of chemical vapor deposition (CVD) using triisobutylaluminum (TIBA) on Si (100) surfaces is observed in situ with x-ray photoelectron spectroscopy (XPS). Oxygen from oxide on the silicon inhibits the rate of nucleation by reacting with adsorbed TIBA and forming a thin layer of oxidized organometallic. This layer blocks active adsorption sites and prevents further deposition. On a surface without oxide, the TIBA molecules decompose liberating aluminum that can migrate and nucleate into islands opening sites for further adsorption and film growth. By removing the oxide (native or thermal) in selected areas of the surface, the barrier to nucleation is removed and aluminum deposition can occur in a predetermined pattern.
Mixed Metal Organometallic Clusters: Precursors for Intermetallic Powders
Authors: Gonsalves K. E. , Kembaiyan K. T.
Published: March 2011

ntial catalytic applications [1]. Also, in non-catalytic areas, there is a move to build alloy powders from large metal clusters [2]. Therefore, we have initiated a program to develop intermetallic powders from mixedmetal organometallic precursors [3]. Here we report the synthesis and characterization of iron-cobalt intermetallic powders obtained from heteroorganometallic clusters [4]. Our objective therefore is to (1) provide a simple and effective means of synthesizing iron-cobalt intermetallics (2) vary the ratio of iron to cobalt in such intermetallics, and (3) provide a method to produce homogeneous products from iron-cobalt metalorganic precursors specifically synthesized for this purpose. The resulting intermetallics may have unique magnetic characteristics.
Excimer Laser Induced Photochemistry of Silane-Ammonia Mixtures
Authors: Jasinski J. M. , Beach D. B. , Estes R. D.
Published: March 2011

Steady-state and time resolved molecular beam sampling mass spectrometry have been used to study the ArF excimer laser induced photochemistry of silaneammonia mixtures at 193 nm. Under both steady state and single laser shot conditions, products as complicated as tetraaminosilane are formed promptly. A mechanism which accounts for the formation of all observed products is proposed and evaluated.
Defects and Their Control in SiO2 Films Prepared by D2 –Lamp Photochemical Vapor Deposition
Authors: Nonaka Hidehiko , Arai Kazuo , Ichimura Shingo
Published: March 2011

Amorphous silica films deposited from the mixture of gases (Si2 H6 and Si2F6) by deutrium-lamp CVD were studied by IR, vacuum UV, EPR and Auger electron (AE) spectrometries. The F-doping enhanced the film growth and removed defects in the film such as -H, -OH, and E' centers. A model on deposition and defect formation mechanisms was proposed based on the thermodynamic Stabilities of resultant HF in the reactions. The AES study showed that the film surface modified by activated oxygen had an increased hardness against electron beams.
Organometallic Chemical Vapor Deposition of Gaas Using Novel Organometallic Precursors
Authors: Jones R. A. , Cowley A. H. , Benac B. L. , Kidd K. B. , Ekerdt J. G. , Miller J. E.
Published: March 2011

The goals of the research are the design and synthesis of a new class of precursor compounds for III/V compound semiconductor materials, growth of films with these precursors and developoment of an understanding of the relationships between precursor structure, film growth reactions and film properties. Conventional OMCVD of III/V compound materials has a number of inherent safety and processing problems associated with the group III alkyl and group V hydride sources. Our approach to these problems is the synthesis of a single precursor with a fixed III:V stoichiometry and a direct two center, two electron sigma III V bond., These, compounds have the general formula,[R2M(R 2 E)] 2 and R2M(R 2 E) 2M R2 (MM = Al, Ga, In; E=P, As; R, R = alkyl, aryl). The III V bond in these compounds is stronger than the other bonds and the minium deposition temperature can be controlled by employing subsituents that undergo facile hydrocarbon elimination.

A typical example is the use of [Me 2Ga(µ t Bu 2 As)] 2 as the single source for GaAs films. The organometallic precursor is a solid crystalline powder which is maintained at 130°C to generate enough vapor for OMCVD. Typical film growth conditions involve the use of H2 or He as the carrier gas, substrate temperatures of 500 to 700°C, and a total system pressure of 0.0002 Torr. GaAs(100), Si(100) (As doped 30 off toward (011) and quartz have been used as substrates. Film composition has been established with XPS. The Ga 3d, As 3d, and C ls signals at 18.8, 40.9, and 284.6 eV, respectively, reveal the films to be 1:1 Ga:As and void of carbon. The carbon levels are less than 1000 ppm. X ray diffraction and SEM results suggest polycrystalline GaAs on quartz and epitaxial GaAs on GaAs(100) and Si(100). (2 K) photoluminescence measurements on GaAs, grown on semi insulating GaAs(100) and Si doped GaAs(0 100) at 570 C. produce PL signals indicating that crystalline domains are present, the measurements indicate degeneratively n doped material and show that good Ga:As ratios and low levels (ca. 1 ppm) of impurities are present. Growth rates:∼ 1.0 mm/hour.
Ion Beam Assisted Deposition of Metal Films
Authors: Gamo Kenji , Namba Susumu
Published: March 2011

The chtaracteristics of ion beam assisted deposition are discussed and compared with those of photon beam assisted deposition. Effects of various deposition parameters including ion species, beam energy and substrate temperature are discussed. Deposited films usually include impurities such as C and O. Inclusion of oxygen takes place by enhanced oxidation by background oxygen and may be reduced by depositing in a clean vacuum. Promising applications of maskless ion beam assisted deposition are also discussed.
Focused Ion Beam-Induced Carbon Deposition
Authors: Harriott L. R. , Vasile M. J.
Published: March 2011

A process for repair of micron and submicron sized transparent defects on photomasks is described. Opaque films are deposited at the intersection of the flux of organic monomers from a gas jet and a 20 keV Ga ion beam. Focused ion beam-induced deposition differs from other ion-induced, electron beam and laser processes due to the very high ion current density and the sputtering of the material as it is being deposited. We have explored the deposition-sputtering rate competition for several precursor materials as a function of monomer flux and ion beam dose rate. Our results suggest a model for deposition which requires polymerization of the precursor through carbon-carbon double bonds to favor deposition over sputtering by creating high molecular weight material at the target.
Spin-on Silicon Oxide (Sox): Deposition and Properties
Authors: Smolinsky Gerald , Ryan Vivian
Published: March 2011

High quality SiO2 films are obtained by spin-coating wafers with a sol/gel of silicic acid in either a 2, 3, or 4-carbon linear-aliphatic alcohol. Some properties of the deposited film depend upon the solvent: such as density, tensile stress, and infrared spectrum. However, Rutherford-back-scattering analysis indicates the O:Si ratio (2.00±05) to be independent of the solvent. The infrared spectrum of the oxide exhibits Si-OSi absorption in the range 1070–1080 cm.−1 depending on the curing temperature and solvent system. (The weaker Si-OSi band is found at 804–810 cm.−1) In addition, low-temperature-cured (<500 °C) films show Si–OH absorption. Films hot-plate baked at 150–350 °C are stable but not fully cured. Films from propanol baked at 400 °C have a refractive index of 1.41–1.42 and a wet-etching rate in 30:1 BOE of ˜1250 Å/min. Films cured at 900 °C have a refractive index of 1.42–1.43, a wet-etching rate of ˜430 A/min, and are more dense by a factor of ˜1.25. Dry-etching with CHF3/O2 occurs at rates comparable to those of CVD oxides. Multiple applications lead to crack-free films as thick as 0.6–0.8 μ m. Deposition over aluminum-patterned topography results in a smoothing of the surface and suppression of hillock growth in the aluminum even after a 450 °C cure. SOX adheres to silicon, aluminum, and silicon dioxide. A boron-doped SOX is readily prepared.
Organometallic Precursors for III-V Semiconductors
Authors: Byrne Erin K. , Douglas Trevor , Theopold Klaus H.
Published: March 2011

Organometallic molecules containing covalently linked gallium and arsenic or indium and phosphorus have been synthesized and characterized spectroscopically and by X-ray diffraction. These precursors can be transformed into the corresponding III-V materials in a chemical reaction proceeding at ambient temperature. The compound semiconductors prepared in this way are obtained as amorphous powders. During the reaction, quantum size effects may be observed by UV-VIS spectroscopy as the particles grow.
Electrical Properties of Hard Carbon Films
Authors: Varhue Walter , Pandelisev Kiril , Shinseki Brian
Published: March 2011

The electrical resistivity, optical band gap and activation energy for electrical conduction have been determined as a function of preparation conditions. The operating conditions for the glow discharge reactor have been interpreted in terms of ion energy and reactive species production. The change in the electrical properties could not be explained as a percentage of [SP3] versus [SP2] bonding ratio. Rather, these two species are embedded in an amorphous medium which determines the materials electrical properties.
Deposition of Thin Alumina Films from Supercritical Water Jets
Authors: Brand J. I. , Miller D. R.
Published: March 2011

Thin alumina films are grown on a silicon substrate, in vacuum, at a rate of about 10 Å per second, and at substrate temperatures below 1500C. Alumina is dissolved in supercritical water and the resulting solution expanded in a supersonic free jet, which is directed at the substrate. The films are characterized by ESCA and FTIR.
An Antimony Planar Diffusion Source
Authors: Wilson Jack , Gustaferro Robert , Bonny Alan , Maddox Ed
Published: March 2011

Antimony is a useful n-type dopant for buried layers, due to its low rate of lateral diffusion in subsequent processing steps. To date, no solid planar diffusion source has been available. Reported here is the development of such a source.

The source is made by high temperature synthesis in a hot press. A mixture of antimony trioxide and silicon powders is placed in the press, and heated under pressure. The reaction

results in a solidified product. Wafers are sliced from this product to form the actual planar diffusion sources.

The sources are used in a two-step doping process: a predeposition followed by a drive-in. Oxygen is required in both steps, due to the chemistry involved. Typical properties of the doped silicon are: sheet resistance, 10 Ω/square, junction depth, 4–6 microns, and antimony surface concentration. 3–8 × 1019/cm3.
Optical Properties of Finely-Structured Particulates
Authors: Sheng Ping , Zhou Min-Yao , Chen Zhe , Chui S. T.
Published: March 2011

We show that rod-like particulates structured from interleaving layers of metal and insulator (or semiconductor) can exhibit novel infrared and far-infrared characteristics that are tunable through the variation of their geometric parameters. In particular, a dispersion of these particles can be made to absorb strongly at any prescribed far-infrared frequency by controlling their transverse dimensions and insulator fractions.
Fabrication and Properties of Granular Fe-Ni Alloys
Authors: Gavrin A. , Chien C. L.
Published: March 2011

Granular alloys of the form (Fe50Ni50)x(Al2O3)1−x, where x is the volume percent, have been produced by sputtering from a single composite target. The microstructure has been verified by X-ray diffraction and by transmission electron microscopy (TEM). The grains are single phase FeNi alloys with the fcc structure and range in size from 15 Å to 50 Å. Superparamagnetism has been observed, and the coercivity has been found to decrease with increasing grain size. The results are compared to previous work on granular Fex(SiO2)1−x.
Study of the Lattice Dynamics of Iron Nanocrystals by Mossbauer Spectroscopy
Authors: Childress J. , Levy A. , Chien C. L.
Published: March 2011

The vibrational properties of iron particles with nanometer sizes in Fe-SiO2 and Fe-A12O3 granular materials are studied by Mössbauer spectroscopy. The spectra include contributions from metallic Fe atoms at the core of the particles and apparently from surface and oxidized Fe atoms, which are analyzed separately. The temperature dependences of the recoilless fractions are analyzed using the Debye model. The Mossbauer Debye temperature ΘM for metallic Fe is found to decrease dramatically with smaller grain sizes, indicative of a “softening” of the phonon spectrum.
Coercivity in Granular Fe - Al2O3
Authors: Streitz F. H. , Chien C. L.
Published: March 2011

We present the results of a comparison between the magnetic properties of granular Fe–Al2O3 and Fe–SiO2. Granular Fe-SiO2 was found earlier to display an anomalous increase in coercivity which appears to scale with the Fe grain size. The Fe-Al2O3 samples were prepared under similar conditions and their magnetic properties determined. The coercivity in granular Fe-Al2O3 is also seen to increase with increasing grain size, showing that the effect is not unique to the Fe-SiO2 system. A major difference between granular Fe–Al2O3 and Fe–SiO2 is the size of the Fe grains, which are smaller in Al2O3.
Microstructure and Magnetic Behavior of Fe/Ti Multilayered Films
Authors: Ono Satoshi , Nitta Michio , Naoe Masahiko
Published: March 2011

Fe/Ti multilayered films composed of Fe and Ti layers with various thickness ( dFe of 10 ∼ 1000 A and dTi of 10 ∼ 200 A ) have been prepared at Ar gas pressure of 2 mTorr by two pairs of Facing Targets Sputtering apparatus which can deposit very thin and continuous films on plasma-free substrates. The total thickness of Fe layers was 1000 A in all of the specimen films.

The periodic microstructure due to compositional modulation was clearly observed not only in the low angle region of X-ray diffraction diagrams but also in the Auger electron spectroscopic depth profile.

With decreasing dFe from 1000 to 20 A, the diffraction intensity of (110) plane in the Fe bcc phase lowered for dTi of 10∼200 A and its interplanar spacing ( d-spacing ) increased for dTi above 50A. This diffraction peak disappeared with further decreasing d below 15 A. At dFe around 25 A, a different peak appeared at the angle slightly lower than that of Fe(110) peak. The diffraction intensity of (002) plane in the Ti hcp phase increased with decreasing dFe. However, its d-spacing depended little on the dFe and took the same value as that of bulk Ti except for very small dTi.

The net saturation magnetization of Fe layers in all of the specimen films decreased gradually with decreasing dFe from 1000 to 50 A, decreased abruptly with further decreasing dFe and became nearly zero at dFe below 15A.

The films annealed at 200 and 400 °C showed obscure periodic microstructure and had larger d-spacing of ∝ −Fe(110) and smaller saturation magnetization than those of the as-deposited ones.
X-Ray Diffraction analysis of Au/Ni Multilayers
Authors: Chaudhuri J. , Shah S. , Jankowski A. F.
Published: March 2011

X-ray diffraction is a useful method to measure the microscopic strain profile in multilayered materials. Depth profiles of strain in the modulation direction are obtained by an iterative fitting of the experimental diffraction pattern with a kinematic model. This approach was used to characterize the coherency strain profile in Au/Ni superlattices.

The accommodation of coherency strain through the superlattice is dependent upon the atomic misfit between the component materials and the thickness of each layer. The depth profile of strain was determined for multilayers with repeat periodicities of 2.92 nm and 4.26 nm. A significant volume fraction of interfaces is present in these nanometric dimensioned laminates.
Microstructure of Nanocrystalline Ceramics
Authors: Hahn H. , Logas J. , Höfler H. J. , Bier Th. , Averback R. S.
Published: March 2011

The microstructure of nanocrystalline (n-) TiO2 was studied as a function of sintering temperature up to 1273 K. Grain growth was monitored using x-ray diffraction and scanning electron microscopy. Measurements of density and permeability of He and Ar were also conducted. The specific surface area and the total pore volume were determined quantitatively using the nitrogen adsorption method. These measurements revealed that highly compacted n-TiO2 had green body densities as high as 75 % of bulk density and that sintering occurred at much lower temperatures than in conventional powder. Densification proceeded by loss of the small pores first. The possibilities of achieving high densities with limited grain growth will be discussed.
Chemical Vapor Deposition of Ultrafine Ceramic Structures
Authors: Gallois B. M. , Mathur R. , Lee S. R. , Yoo J. Y.
Published: March 2011

Ultrafine ceramic structures based on the nitrides and carbides of titanium and silicon have been synthesized in a computer-controlled hot-wall CVD reactor. Layered deposits have been produced by pulsing the reactant gases judiciously under software control. The development of a columnar structure which is endemic to most CVD materials has been suppressed. Skeletal structures of filaments have also been grown with appropriate catalysts by the vapor-liquid-solid mechanism and immediately infiltrated in situ with different materials to produce filament-reinforced composite coatings.

Ultrafine-grained carbon films and filaments have been grown from methane-hydrogen mixtures by RF plasma-assisted CVD. The microstructural features of these materials are of the order of 20 to 100 nm. The subgrain structure determined by Raman spectroscopy varies from 2 to 3 nm.
Cryomilling of Nano-Phase Dispersion Strengthened Aluminum
Authors: Luton M. J. , Jayanth C. S. , Disko M. M. , Matras S. , Vallone J.
Published: March 2011

In recent years considerable effort has been expended on the development of dispersion strengthened alloys by mechanical alloying. Our research has shown that considerable improvement in microstructure control and properties can be gained by carrying out milling at cryogenic temperatures. We have found that aluminum and dilute aluminum alloys can be dispersion strengthened with aluminum oxy-nitride particles by the use of a slurry milling technique where the fluid medium is liquid nitrogen. The alloyed powders produced by this technique are strengthened by aluminum oxy-nitride particles which are typically 2–10 nm in diameter and with a mean spacing of 50–100 nm. The dispersoids are generated during the milling process by adsorption and reaction with components of the liquid nitrogen bath. On thermal treatment prior to consolidation, the alloyed powders recrystallize to a grain size which is typically in the range 0.05 to 0.3 μm. The alloys exhibit a yield stress in excess of 325 MPa at room temperature and a virtually temperature independent yield stress of about 130 MPa at temperatures greater than 375° C. The paper describes the preparation of dispersion strengthened aluminum by cryomilling, the characteristics of the microstructure and discusses some aspects of the mechanical properties.
Statics and Dynamics of Grain Boundaries in Ni3Al
Authors: Farkas Diana
Published: March 2011

Various modeling techniques have been used to study the structure of grain boundaries in ordered compounds, particularly Ni3Al. The techniques include computer simulation, group theoretical analysis and the cluster variation method for high temperature effects. A multiplicity of possible grain boundary structures was analyzed for different misorientations and grain boundary plane location. 1The influence of several alloy properties like atomic size differences and deviation from stochiometry on the occurrence of these different structures is analyzed. The implications of these results for grain boundary misorientation distribution, grain boundary plane location and faceting behavior are discussed and compared to experimental findings. The possibility of orderdisorder transitions in the grain boundary region is also discussed.
The Microchemistry of Grain Boundaries in Ni3Al
Authors: Sieloff D. N. , Brenner S. S. , Ming-Jian Hua
Published: March 2011

Grain boundary regions in B-doped as well as B-free Ni3AI were studied by field-ion microscopy and atom probe microanalysis. In the ductile, recrystallized, Ni-rich alloys the segregation of boron was often accompanied by an enrichment of nickel. Such an enrichment was not observed at boundaries in B-free alloys. Boron was also observed to segregate to the boundaries in a 25.2A1 - IB alloy which was reported to contain boron clusters. Such clusters were not observed, instead a high concentration of boron pairs were found.
On Microstrucitural Evolution in Gas Atomized Ti-50 at.% Al-2 at.% Nb Powder
Authors: Shih Donald S. , Scarr Gary K. , Chesnutt James C.
Published: March 2011

Microstructural development in helium gas atomized Ti-50A1-2Nb (at.%) powder has been characterized using x-ray diffractometry and transmission electron microscopy. The structure of the as-atomized powder was a mixture of two phases: an ordered fct (L10)γ TiAl phase and an hcp α Ti phase containing fine (≈ 10–20 nm) D019 α2 domains. Large powder (≈ 250 μm) contained ≈ 14 volume % hcp phase, while fine powder (≈37 μm) contained ≈ 72 volume % hcp phase. However, this α+α2 constituent was metastable and transformed to the γ phase during annealing.
Slip System Modification in NiAl
Authors: Miracle D. B. , Russell S. , Law C. C.
Published: March 2011

An effort to modify the slip vector in the B2 compound NiAl was undertaken to overcome the brittle failure associated with the <100> slip vector which typically operates in this compound. Alloying additions were made to reduce the ordering energy of NiAl, and hence to promote <111> slip. Preliminary indications showed that Cr and Mn were effective in producing <111> slip in polycrystalline NiAl tested at room temperature. Two-surface slip trace analyses and TEM g·b analyses performed on aligned crystals of NiAl showed that <111> dislocations operate on either { 110} or {112} slip planes. However, the slip vector at 660°C was seen to revert to <100>, which operates on both {100} and {110} planes.
Stacking Sequence Changes in A3B-Type Close-Packed Structures: a One-Dimensional Stacking Model
Authors: Pei Shiyou , Massalski T. B.
Published: March 2011

Structural modifications resulting from changes in the sequence of stacking of close-packed layers are very common in A3B-type transition-metal alloys. In the present work, a one-dimensional model of stacking has been explored. We found that the stacking changes observed in these alloys can be interpreted in terms of interactions between a few adjacent layers.
Deformation and Defects in Laves Phases
Authors: Livingston J. D. , Hall E. L. , Koch E. F.
Published: March 2011

Prototype Laves Phases MgCu2 and MgZn2 have been deformed in compression at various temperatures and strain rates, and dislocations produced by deformation have been characterized by TEM. Ternary cubic Laves phases Mg(Cu,M)2, where M-Al, Ni, Si, and Zn, have also been deformed, and substantial solution hardening was observed
Ab Initio Calculations of Ordered Intermetallic Phase Equilibria
Authors: Sluiter M. , Fontaine D. De , Guo X. Q. , Podloucky R. , Freeman A. J.
Published: March 2011

General procedures for computing alloy phase equilibria from ab initio electronic structure calculations are reviewed and applied to the Al-Li phase diagram. Free energies were calculated by the cluster variationm.method (CVM) in the tetrahedron approximation for the fcc and bcc lattices and ordered superstructures. Input was provided by first principles FLAPW calculations. The computed phase diagram for both stable and metastable structures agrees remarkably well with the experimental one.
Microstructure and Elevated Temperature Flow Properties of Rapidly Solidified TiAl-Base Alloys
Authors: Graves J. A. , Ghosh A. K.
Published: March 2011

Rapid solidification processing (RSP) of TiAl-base alloys often results in the formation of metastable crystalline products (e.g., Ti3Al) A key parameter controlling both the solidification pathway and the stability of the metastable structure is alloy chemistry. This study focuses upon the influence of minor alloy additions on the microstructure and properties of Ti52Al48 alloys produced by RSP. While alloys having minor Ta addi ions (<1 at.%) maintain near-equilibrium solidification structures similar to the binary alloy, the addition of Cr at a level of 5 at.% results in a nearly 100 vol.% metastable Ti3Al structure containing a fine dispersion of TiCr2 grain boundary precipitates. These precipitates limit grain growth during elevated temperature exposure, maintaining the fine (TiAl) grain size created during decomposition of the metastable product structure. Mechanical property evaluation of the consolidated RSP material indicates a greatly reduced flow stress for the fine grained Cr modified alloys. A preliminary analysis attributes this to the reduction in grain size and enhanced elevated temperature diffusion rates for the Cr containing TiAl-base alloys.
On the Macroscopic Flow Behavior of the Phases Present in Ti-24Al-llNb
Authors: Giths S. J. , Koss D. A.
Published: March 2011

The deformation behavior of two alloys whose compositions (Ti-25Al-9Nb and Ti-11Al-23Nb in at.%) correspond to alpha-two and beta phases in the Ti-24Al-11Nb alloy has been investigated. Results from both compression and tensile tests over a range of temperatures from 27° to 650°C indicate that the yield stress as well as the strain and strain-rate hardening characteristics of the Ti-24-11 alloy are controlled by the Ti3Al-base alpha-two phase. In contrast to the Alpha-two alloy, the Beta alloy has a flow stress which is very sensitive to temperature and strain rate at 650°C, suggesting the onset of high temperature creep processes.
Mechanical Alloying Behavior in the Nb-Si, Ta-Si, and Nb-Ta-Si Systems
Authors: Kumar K. S. , Mannan S. K.
Published: March 2011

The mechanical alloying behavior of elemental powders in the Nb-Si, Ta-Si, and Nb-Ta-Si systems was examined via X-ray diffraction. The line compounds NbSi2 and TaSi2 form as crystalline compounds rather than amorphous products, but Nb5Si3 and Ta5Si3, although chemically analogous, respond very differently to mechanical milling. The Ta5Si3 composition goes directly from elemental powders to an amorphous product, whereas Nb5Si3 forms as a crystalline compound. The Nb5Si3 compound consists of both the tetragonal room-temperature α phase (c/a = 1.8) and the tetragonal high-temperature β phase (c/a = 0.5). Substituting increasing amounts of Ta for Nb in Nb5Si3 initially stabilizes the α-Nb5Si3 structure preferentially, and subsequently inhibits the formation of a crystalline compound.
Pressure Casting of Ni3Al/Al2O3 Composites
Authors: Nourbakhsh Said , Liang Fei-Lin , Margolin Harold
Published: March 2011

A series of Du Pont PRD-166 and FP fiber reinforced Ni and nickel aluminide matrix composites, containing Ti or Y as a wetting agent, were produced by pressure casting. Modulus values determined under compression varied from 273 to 287 GPa in a direction parallel to the fibers and ranged from 148 to 159 in a direction normal to the fibers. Modulus values parallel to the fiber direction were approximately 5% lower than that predicted by the rule-of-mixtures. The much lower values of modulus normal to the fibers has been attributed to a number of sources which include fiber/matrix and fiber/fiber debonding and stress concentration resulting from voids existing at fiber/fiber bonds. It was observed, qualitatively, that good bonding between matrix and fiber occurred when Ti diffused from the matrix into fibers. The presence of Al in the matrix tended to inhibit Ti diffusion, increasingly as Al content increased. Thus fiber/matrix bond strength was poorer in the aluminides than in an alloy containing no Al. Y was not found to improve bonding, and an interface reaction zone was obserced in some areas where liquid metal initially entered the fiber preform.
Deformation Behavior of NiAl-Based Alloys Containing Iron, Cobalt, and Hafnium
Authors: Pank D. R. , Nathal M. V. , Koss D. A.
Published: March 2011

The effects of alloying additions on the mechanical properties of the B2 intermetallic NiAl have been investigated in both the melt-spun ribbon and consolidated, bulk form. The study is based on a matrix of NiAl-based alloys with up to 20 a/o Co and Fe additions and with reduced Al levels in the range of 30 – 40 a/o. Characterization of the melt-spun ribbon by optical and scanning electron microscopy indicates a range of microstructures: single phase β γ, necklace phase surrounding either martensitic or β grains, and a mixture of equiaxed martensitic and γ grains. Bend ductility is present in melt-spun and annealed ribbons exhibiting the γ necklace structure and in a single phase β material containing 20 a/o Fe.

The analysis of compressive flow behavior on consolidated, bulk specimens indicates that the single phase γ alloys exhibit a continuous decrease in yield stress with increasing temperature and profuse microcracking at grain boundaries. In contrast, multiphase (γ + either martensite or β) alloys tend to display a peak in flow stress between 600 and 800K with little or no signs of microcracking. In general, heat treatments which convert the martensitic grains to β + γ result in improved strength at temperatures above 600K and better resistance to crack initiation. These results are discussed in terms of the effects of β, martensite and γ on the yield stress and flow behavior of NiAl-based alloys.
Fabrication and Mechanical Properties of Ni3Al-Al2O3 Composites
Authors: McKamey C. G. , Povirk G. L. , Horton J. A. , Tiegs T. N. , Ohriner E. K.
Published: March 2011

The objective of this study is to develop a metal-matrix composite based on the intermetallic alloy Ni3Al reinforced with Al2O3 fibers, with improved high-temperature strength and lower density compared to the matrix material. This paper summarizes results of initial fabrication and mechanical tests on specimens produced using IC-15 [Ni-24% Al-0.24% B (at.%)] and IC-218 [Ni-16.5% Al-8% Cr-0.4% Zr-0.1% B (at.%)], with 20 vol. % Al2O3 fibers. Fabrication methods include both hot-pressing and hot-extrusion. Mechanical tests include four-point bending and tensile tests. The integrity of the fiber-matrix interface was studied and correlated with mechanical properties. Tensile ductilities of approximately 10% at room temperature were achieved for Ni3Al/Al2O3 composites with controlled material processing and interfacial structure. Fabrication of composites by hot-extrusion produced better tensile properties at room temperature, but superplastic behavior (i.e., low strengths, high ductilities) at 1000°C.