bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron-Beam Assisted CVD of Silicon Homoepitaxial Films
Authors: West J. P. , Fleddermann C. B.
Published: March 2011

The use of a wide-area electron beam to aid the deposition of epitaxial silicon films has been studied. The electron beam used in this study is generated using a cold cathode, abnormal-glow discharge which allows a wide variation of electron energy and beam current. Depositions are performed on single crystal silicon substrates which are prepared using standard wet chemical silicon cleaning techniques and an in situ plasma etch using nitrogen tri-fluoride diluted in hydrogen. The beam diameter is approximately 10 cm and can readily be scaled up to accommodate larger diameters, allowing great potential for large area single wafer deposition. Using electron beams generated in this system, we have demonstrated enhanced growth rates and improved crystalline quality for films grown withelectronbeam enhancement.
The Initial Stages of Plasma Synthesis of Diamond Films
Authors: Meilunas R. , Wong M.S. , Sheng K. , Ong T.P. , Chang R.P.H.
Published: March 2011

The effects of plasma starting conditions on the initial stages of diamond nucleation and growth in a microwave plasma have been studied as a function of important deposition parameters. The influence of the substrate temperature on the diamond nucleation rate, quality, and final film morphology has been elucidated through various analytical measurements. The diamond films are characterized with Raman spectroscopy, X-ray diffraction, and scanning electron microscopy. Finally, methods are described for reproducibly controlling the grain size and morphology of the diamond films for tribological and abrasive applications.
Thermal and Photolytic Decomposition of Adsorbed Cadmium and Tellurium Alkyls
Authors: Stinespring C.D. , Freedman A.
Published: March 2011

Studies of the thermal and photon-induced surface chemistry of dimethyl cadmium (DMCd) and dimethyl tellurium (DMTe) under ultrahigh vacuum conditions have been performed for substrate temperatures in the range of 133 K to 295 K. Results on GaAs(100) and Si(100) surfaces indicate that for DMTe, the predominant adspecies, dimethyl tellurium, can be photodissociated to a metal adspecies at both 193 and 248 nm. For DHCd, the major adspecies, monomethyl cadmium, is unreactive to photon stimulation.
Epitaxial Silicon Layers Made by Reduced Pressure/Temperature CVD
Authors: Regolini J.L. , Bensahel D. , Mercier J. , D'Anterroches C. , Perio A.
Published: March 2011

In a rapid thermal processing system working at a total pressure of a few Torr, we have obtained selective epitaxial growth of silicon at temperatures as low as 650°C. When using SiH2Cl2 (DCS) as the reactive gas, no addition of HCl is needed. Nevertheless, using SiH4 below 950°C a small amount of HCl should be added.

Some kinetic aspects of the two systems, DCS/HCI/H2 and SiH4/HCl/H2, are presented and discussed. For the DCS system, we show that the rate-limiting reactions are slightly different from those commonly accepted in the literature, where the results are from systems working at atmospheric pressure or in the 20-100 Torr range.

Our model is based on the main decomposition of DCS, SiH2Cl→SiHCl + HCl, instead of the widely accepted reaction SiH2Cl2→SiCl2 + H2. This is the main reason why no extra HCl is required in the DCS/H2 system to obtain full selectivity from above 1000°C down to 650°C.
X-Ray Lithography Studies of Polysilane using a Laser Plasma X-Ray Source
Authors: Kubiak Glenn D. , Outka Duane A. , Zeigler John M.
Published: March 2011

A laser-generated plasma source of monochromatized soft x-rays has been used to study the x-ray lithographic resist properties of poly(cyclohexylmethylsilane-co-dimethylsilane). X-ray absorption spectra near the SiL2,3 edge of unexposed samples were measured to guide the choice of exposure photon energy. We find that poly(cyclohexyl-methylsilane-co-dimethylsilane) exhibits positive tone at x-ray energies near 105 eV (Si 2p resonance), a sensitivity of 1000 mJ/cm2 and a contrast of 1.5. Sensitivity is found to increase markedly when exposed samples are held in air before development. Using simple wire mesh masks, estimates of the minimum achievable linewidth have been made.
Arf Laser-Induced Chemical-Vapor Deposition of Tungsten for Gate Electrodes
Authors: Matsuhashi H. , Nishikawa S. , Ohno S.
Published: March 2011

The deposition of W films by ArF laser-induced chemical-vapor deposition (LCVD) was investigated as a function of incident laser power, WF6 and H2 partial pressures, and substrate temperature. The deposition of W films by LCVD is discussed dividing that into two parts, thermal CVD (TCVD) and photon assisted CVD (PhCVD). The rate of PhCVD has been defined as the difference between the rates with and without laser irradiation. The reaction orders for PhCVD are 1, 0 with respect to WF6 and H2 partial pressures, respectively, and the rate linearly increases with increase in laser repetition rate. The activation energy in PhCVD is 0.17 eV. These facts indicate that, in LCVD, PhCVD takes place independently of TCVD and that the deposition rate in PhCVD is determined by the formation of F radicals in the dissociation of WF6 molecules by laser irradiation.

MOS capacitors with LCVD-W gates were fabricated and their characteristics were compared with those with sputtered-W gates. It was shown that the level of contamination due to mobile ions in the capacitor with the LCVD-W gate was extremely low.
A Study of Defects in Ordered Ternary Semiconductor Epilayers
Authors: McKernan S. , Carter C. B. , Bour D. P. , Shealy J. R.
Published: March 2011

Ordered GaxIn1-xP epilayers grown on GaAs substrates have been studied in the electron microscope. Dark-field images and high-resolution micrographs have directly revealed the presence of an ordering of the Ga and In (111) planes. Several different planar defects have been identified in the ordered structure. There is a very high density of faults parallel to the (001) growth surface. Models for these faults have been constructed in terms of stacking faults and twin boundaries in the ordered structure. Other flat planar defects which occur approximately parallel to (111) and (111) planes can also be described in these terms.
Gold-Nickel Multilayer Films: Structure-Property Correlations
Authors: Nutt S. R. , Green K A. , Baker S. P. , Nix W. D. , Jankowski A.
Published: March 2011

Gold-nickel multilayer films with periods of 1.2 - 4.6 nm were deposited on silicon substrates by magnetron sputtering, and plan and cross-sectional specimens were examined by transmission electron microscopy. The cross-sectional specimens revealed well-defined layering and columnar growth features that extended through the film thickness. Dark striations extending normal to the layers were attributed to diffraction contrast from defect strain fields. Diffraction patterns showed that the films were highly textured and that short-period films had a single fcc structure, while long-period films separated into three fcc structures. High-resolution images of the layer interfaces showed local regions of epitaxy partitioned by regions of disorder.

Indentation tests using a Nanoindenter, a depth-sensing indentation device, were performed to measure the elastic modulus and hardness of the films. No modulus enhancement was detected, and a small variation in hardness was measured.
Stress Gradients and Anisotropy in Thin Films
Authors: Fisher Robert M. , Duan J. Z. , Fox Alan G.
Published: March 2011

Indications that steep through-thickness strain gradients occur in vapour-deposited chromium films stemming from previous observations of film curling during spontaneous delamination from substrates, have been substantiated by analysis and simulation of Bragg X-Ray diffraction peaks. The presence of large through-thickness compressive strains, that increase quadratically with distance from the substrate from about zero at the interface to around 0.8% at the film surface, was deduced by empirical computer matching of diffraction peak shapes.
Residual Stress Analysis of Al Alloy Thin Films by X-Ray Diffraction as a Function of Film Thickness
Authors: Shute Carla J. , Cohen J. B. , Jeannottea D. A.
Published: March 2011

Residual stress has been measured as a function of layer thickness in thin films of an Al alloy on oxidized Si by the x-ray “d” versus sin2ψ technique. Samples with and without a passivation layer were examined. The results show an increase in residual stress with decreasing film thickness for the passivated samples and indicates that the interface between the metal film and SiO2 may be a region of high stress.
Thin HgCdTe LPE Layers Grown on CdTe and CdZnTe Substrates
Authors: Yamamoto Kosaku , Maekawa Tohru , Takigawa Hiroshi
Published: March 2011

The dependence of the growth pattern of thin HgCdTe LPE layers on lattice mismatch was investigated. Epilayers grown on substrates with a lattice mismatch of more than 0.2% show island-like growth, which are aligned with the network of misfit dislocation lines. Thin epilayers grown on substrates with a lattice mismatch of less than 0.05% have mirror-like flat surfaces. It was found that the surface defects for thick epilayers also have a lattice-mismatch dependency.
Viscoelastic Stress Relief in Patterned Silicon-on-Insulator Structures
Authors: Letavic Theodore J. , Maby Edward W. , Gutmann Ronald J.
Published: March 2011

A high-temperature viscoelastic stress relief technique has been investigated as a means for reducing in-plane stress encountered during zone-melt recrystallization of patterned silicon-on-insulator structures. This technique incorporates a phosphosilicate glass layer between the silicon film and the insulating substrate to provide a viscous flow mechanism for stress relief within the composite structure. The stress relaxation can bequalitatively described by a mechanical model which couples thermal expansion and viscoelastic flow. The model predicts the time constant for stress relief at high temperatures as a function of pattern size, and the results are useful as a design aid for zone-melt recrystallization experiments.
The Relationship between Intrinsic Stress of Silicon Nitride Films and Ion Generation in A 50 KHz RF Discharge
Authors: Aite K. , Holleman J. , Middelhoek J. , Koekoek R.
Published: March 2011

Silicon nitride films prepared by the Plasma Enhanced Chemical Vapor Deposition technique (PECVD) are widely used in microelectronics. The intrinsic stress value of the silicon nitride films is a key factor which determines their reliability. A low frequency (50 kHz) RF discharge and a N2/NH3 /SiH4 gas mixture were used to deposit silicon nitride films on 4-inch silicon wafers in a horizontal hot-wall reactor at a temperature of 350 °C.

The compressive stresses in the deposited films were found to increase linearly with the nitrogen ionization created in the glow discharge. The nitrogen ion bombardment at the film surface induces ion implantation into the deposited film which results in film expansion. The stresses were deduced by the interference fringes technique and from surface profiler measurements. Optical Emission Spectroscopy of the N2/NH3/SiH4 discharge was used for measuring the N+2 peak intensity variation with the partial pressure of the nitrogen gas.

When the nitrogen ionization was increased, a shift of the main infrared transmission peak corresponding to the Si-N bond in the silicon nitride films was observed using Fourier Transform Infrared Spectroscopy (FTIR). The Si-H and N-H infrared peaks in the films were not affected by the ion bombardment. A linear relationship was found between the wavenumber of the main infrared Si-N peak νM (835–875 cm−1) and the intrinsic stress σi of the deposited nitride films with the slope dνM/dσi −4.85×10−8 cm−1 /Pa.
Thermal Strain Measurements in Epitaxial CoSi2/Si by Double Crystal X-Ray Diffraction
Authors: Bai Gang , Nicolet Marc-A. , Vreeland Thad , Ye Q. , Kao Y. C. , Wang K. L.
Published: March 2011

The perpendicular x-ray strain of epitaxial CoSi2 films grown on Si(111) substrates at ∼ 600°C by MBE was measured at various temperatures. Within experimental error margins, the strain decreases linearly with rising temperature at a rate of (1.3±0.1) × 10-5/°C from room temperature up to 600°C. Over that temperature range and the duration of a complete measurement (∼5h to ∼ 2h), these strain values remain reversible. At 593°C, the x-ray strain is -0.85%, which is about the strain that a stress-free CoSi2 film on Si(111) would have at that temperature. This results show that the stress in the epitaxial CoSi2 film is fully relaxed at the growth temperature. Strains below the growth temperature are induced in the film by the difference in the linear coefficient of thermal expansion of CoSi2 and Si. They were calculated by assuming that the density of misfit dislocations formed at the growth temperature remains constant. The slope of the strain-temperature dependence obtained that way agrees with the measured slope if the unknown Possion ratio of CoSi2 is assumed to be VcoSi2 = 0.35. A film stress of ∼ 0.8 GPa at room temperature was calculated using the above value for the Possion ratio, 130 GPa for the Young modulus, and the measured x-ray strain.
Stresses in Films Deposited by Planar Magnetron Sputtering on Glass Substrates of Different Thickness
Authors: Zhou Zhi-Feng , Fan Yu-Dian
Published: March 2011

Stresses affect the structure and properties of the films significantly. In this paper, Co-Cr films were deposited by D.C. planar magnetron sputtering on rectangular glass plates of thickness varied from 0.18 to 2.00mam. The measurement of stress was performed by the bending plate technique with the detection of capacitance change. The temperature of the bending plate was measured by an Fe-Ni thin film thermocouple on the back side of the substrate. The experimental results showed that the stresses were all tensile, but in the films on the thicker substrates were smaller than that on the thinner ones. And apparently the temperature rise of the thicker substrates during deposition was lower than that of the thinner ones. The magnetic characteristics of the Co-Cr films related to the substrate thickness may be attributed to both stress and temperature difference in the films deposited on the substrates of different thickness.
Mechanical Stress as a Function of Temperature in Thin Aluminum Films and its Alloys
Authors: Gardner Donald S. , Flinn Paul A.
Published: March 2011

Aluminum alloys have virtually replaced aluminum for interconnections in VLSI because of their improved reliability. Mechanical stress is a problem of growing importance in these interconnections. Stress as a function of temperature was measured for thin aluminum films and several aluminum alloys and layered films consisting of silicon, copper, titanium, tungsten, tantalum, vanadium, and TiSi2. Solid-state reactions of the aluminum with the additives and with the ambient during thermal cycling will occur and depending on what compounds have formed and at what temperature, this will determine the morphology and reliability of the metallization. The measurement technique, based on determination of wafer curvature with a laser scanning device, directly measures the total film stress and reflectivity in situ during thermal cycling. Changes in stress were detected when film composition and structure varied and were correlated using x-ray diffraction with the formation of aluminides. Other phenomena that contribute to stress changes including elastic behavior, recrystallization, grain growth, plastic behavior, yield strength, and film hardening from precipitates.
Adsorption of Silicon Tetrachloride on Si(111) 7×7
Authors: Gupta P. , Coon P. A. , Koehler B. G. , George S. M.
Published: March 2011

The kinetics of SiCl4 adsorption on Si(lll) 7×7 were studied using laser induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. The initial reactive sticking coefficient of SiCl4 on Si(lll) 7×7 was observed to decrease with increasing surface temperature. This decrease was consistent with a precursor-mediated adsorption model. Both LITD and TPD experiments monitored SiCl2 as the main desorption product. These results suggest that SiC12 may be the stable chlorine species on the Si(lll) 7×7 surface.
Silicon Suboxides: The “Co-Deposition” of a-Si:H and SiO2
Authors: Tsu D. V. , Lucovsky G. , Watkins M. W.
Published: March 2011

The deposition mechanism of silicon suboxides (SiOx, x<2) prepared by remote plasma enhanced chemical vapor deposition (Remote PECVD) is investigated. These films were deposited in a Deposition/Analysis chamber designed to investigate the gas phase chemistry. In this technique, an O2/He mixture is plasma excited, and the silane reactant is injected into the deposition chamber down-stream from the plasma tube. We show that if the plasma after-glow is prevented from extending into the deposition region by an electrical grid placed between the plasma tube and the deposition region, silicon dioxide is then deposited for all O2/He mixtures investigated (0.1 to 1.0 %). In contrast, hydrogenated suboxides of silicon are deposited when the plasma after-glow is allowed to extend past the grid into the deposition region.
Surface Chemistry on Microclusters: Recent Results from Silicon and Germanium Cluster Beams
Authors: Alford J. M. , Smalley R. E.
Published: March 2011

Supersonic cluster beam techniques have recently produced some fascinating new information as to the surface chemistry and physics of small (2–100 atom) clusters of various semiconductors. For example, it appears that silicon clusters exhibit a remarkably pronounced alternation in reactivity as a function of cluster size. For ammonia chemisorption certain clusters such as Si33+, Si39+, and Si45+ have been found to be almost completely inert, while neighboring clusters such as Si36 and Si45+ chemisorb ammonia readily. Such sharply patterned reactivity results may provide significant clues as to the detailed nature of semiconductor surface restructuring and the consequent effects of this restructuring upon the surface chemistry.
Contributions of Gas Phase Reactions to CVD Processes
Authors: Desu S. B. , Kalidindi Surya R.
Published: March 2011

An analytical model to account for the effects of gas phase reactions in CVD processes is presented. In this model a system with only two reactions, gas phase production of an intermediate and reaction of the intermediate on the surface of the substrate to form the film is considered. The reaction kinetics, convective and diffusive transport mechanisms are coupled to analyse the thickness distribution over the length of the reactor.

Theoretical deposition rate profiles in the direction of gas flow are shown with varying deposition temperatures and gas flow velocities for both surface and gas phase reaction controlled mechanisms. It has been shown that by analyzing the nature of the deposition rate profiles, the rate limiting step in a CVD process can be identified.
Electronic Structure of Adsorbed Trimethylaluminum on Clean Si(100) Surfaces
Authors: Motooka T. , Fons P. , Greene J. E.
Published: March 2011

The electronic structure of dimerized trimethylaluminum (TMA), Al2(CH3)6. adsorbed on Si(100) surfaces has been investigated using molecular orbital (MO) calculations based on a cluster description of TMA/Si(100). The calculated results suggest that the interactions between TMA and the Si(100) surface are described by overlap of the TMA electron-deficient bond and Si surface dangling-bond orbitals. The electron-deficient bond orbital is the highest occupied MO of TMA and acts as an electron acceptor for charge transfer from a surface Si atom to TMA consistent with observed core-level and valence photoelectron spectra.
Purposeful Chemical Design of Mocvd Precursors for Silicon-Based Systems
Authors: Aylett Bernard J.
Published: March 2011

It is shown that volatile molecular compounds with silicon-metal bonds can act as effective MOCVD precursors to metal silicides, which aredeposited as thin films under relatively mild conditions. Strategies for the design and synthesis of such “prevenient” precursors are explored, and possible extensions of this approach are considered.
Chemical Vapor Deposition of Silicon Carbide Using a Novel Organometallic Precursor
Authors: Lee Wei , Interrante Leonard V. , Czekaj Corrina , Hudson John , Lenz Klaus , Sun Bing-Xi
Published: March 2011

Dense silicon carbide films have been prepared by low pressure chemical vapor deposition (LPCVD) using a volatile, heterocyclic, carbosilane precursor, MeHSiCH2SiCH2Me(CH2SiMeH2). At deposition temperatures between 700 and 800° C, polycrystalline, stoichiometric SiC films have been deposited on single crystal silicon and fused silica substrates. Optical microscopy and SEM analyses indicated formation of a transparent yellow film with a uniform, featureless surface and good adherence to the Si(lll) substrate. The results of preliminary studies of the nature of the gaseous by-products of the CVD processes and ultrahigh vacuum physisorption and decomposition of the precursor on Si(100) substrates are discussed.
Chemical Vapor Deposition of Chromium Carbide from Organometallic Precursors
Authors: Rutherford N. M. , Larson C. E. , Jackson R. L.
Published: March 2011

Chemical vapor deposition from CpCr(CO)3H, Cr(CH2CMe3)4, and Cr(NPri2)3at low pressures yields chromium carbide films at temperatures as low as 330 °C. The films are mirror-bright and extremely smooth with no significant features observable by SEM. In general, films prepared at higher temperatures had lower resistivities, and were more likely to be crystalline than those prepared at lower temperatures. However, amorphous films deposited at 330 °C were much harder than the crystalline films. Chemical vapor deposition from Cr(NPri2)3resulted in carbide films with the most desirable properties.
Surface Processes in CVD: Laser- and Low Energy Electron-Induced Decomposition of W(CO)6 on Si(111)-(7×7)
Authors: Friend Cynthia M. , Swanson J. R. , Flitsch F. A.
Published: March 2011

The decomposition of W(CO)6 adsorbed on Si(111)-(7×7) using low energy electrons and ultraviolet photons has been investigated under ultrahigh vacuum conditions. This work is motivated by a desire to understand the mechanism for laser- and electron-assisted chemical vapor deposition (CVD) of tungsten using volatile coordination complexes and to specifically understand the role of the surface in these processes. Both electron stimulated and photo-assisted decomposition of the adsorbed W(CO)6 are observed. No thermal decomposition of the W(CO)6 occurs under the conditions of these experiments, based on independent temperature programmed reaction experiments, ruling out the possibility of laser- or electron-induced heating as the cause of decomposition. Furthermore, the interaction of the W(CO)6 with the Si(111)-(7×7) surface is shown to be exceedingly weak based on the fact that the desorption energy is 9.46 ± 0.77 kcal/mol. Desorption of CO is induced during both ultraviolet photolysis and electron bombardment. Carbon monoxide is exclusively evolved during ultraviolet photolysis: no W-containing fragments are desorbed. During electron bombardment, a small amount of the W(CO)6 is desorbed, accounting for ∼10% of the desorption. In both cases, CO-containing W fragments remain on the surface after decomposition at low surface temperature. The remaining surface fragments do not undergo further photolysis at 308 nm but do react thermally. Competing desorption and dissociation of CO are thermally induced resulting in carbide and oxide impurities in the deposited material. The fact that strongly bound W(CO)x fragments are trapped on the surface is proposed as a limiting factor in the purity of tungsten deposits using the decomposition of W(CO)6.
Excimer Laser Photodissociation Studies of Disilane AT 193 nm
Authors: Jasinski J. M. , Chu J. O. , Begemann M. H.
Published: March 2011

Optical emission, laser spectroscopic and mass spectrometric techniques have been used to study the ArF excimer laser induced photochemistry of disilane at 193 nm. Evidence is found for the formation of a number of photofragments from single and multiphoton dissociation. Effects due to secondary photolysis are observed at high excimer laser repetition rates.
Uv Excimer Laser Induced Prenucleation of Surfaces from Spin-on Films Followed by Electroless Metallization
Authors: Esrom Hilmar , Wahl Georg , Stuke Michael
Published: March 2011

UV excimer laser light-induced prenucleation of various surfaces from spin-on films in air is described. Good results were obtained using palladium acetate on substrate materials ranging from ceramics to polymers and even paper. Virtually any surface material can be prenucleated in this way. The Pd-prenucleated planar and curved surfaces can be metallized by a vast variety of metals using electroless plating solutions (Cu, Ni, Au, Pt, Co, Sn, and even alloys). Results are described in detail for copper from a standard electroless solution (Doduco or Shipley). Contact metallization through via holes using this process was aachieved with excellent contact properties.
Preparation of Ultrafine Copper Particles in Poly (2-Vinylpyridine)
Authors: Lyons Alan M. , Nakahara S. , Pearce E. M.
Published: March 2011

Ultrafine copper particles were prepared by the thermal decomposition of a copper formate-poly(2-vinylpyridine) complex. At temperatures above 125°C, a redox reaction occurs where Cu+2 is reduced to copper metal and formate is oxidized to CO2 and H2. The decomposition reaction was studied by thermogravimetric analysis, differential scanning calorimetry and mass spectrometry. Copper concentrations up to 23 wt% have been incorporated into the polymer by this technique. The presence of the polymeric ligand induces the redox reaction to occur at a temperature 80°C lower than in uncomplexed copper formate. Incorporation of the reducing agent (formate anion) into the polymer precursor enables the redox reaction to occur in the solid state. Films of the polymer precursor were prepared and the formation of metallic copper particles were studied by visible and infrared spectroscopy, x-ray diffraction techniques, and transmission electron microscopy. Results from these measurements indicate that spherical copper particles with an average diameter of 35angstrom are isolated within the polymer matrix. The particles are thermodynamically stable at temperatures up to the decomposition of the polymer matrix (≈350 °C), but oxidize rapidly upon exposure air.
Small Angle Scattering from Nanocrystalline Pd
Authors: Wallner G. , Jorra E. , Franz H. , Peisl J. , Birringer R. , Gleiter H. , Haubold T. , Petry W.
Published: March 2011

The microstructure of nanocrystalline Pd was investigated by small angle scattering of neutrons and X-rays. The samples were prepared by compacting small crystallites produced by evaporation and condensation in an inert gas atmosphere. The strong scattering signal is interpreted to arise from crystallites embedded in a matrix of incoherent interfaces. Size distributions were deduced from the scattering curves. They consist of two parts: the crystallite size distribution dictated by the production process, and a structureless contribution due to the correlation in the spatial arrangement of the crystallites. The crystallite size distribution may be described by a log-normal distribution centred at R=2nm. The characteristic form of the correlation contribution arises from the dense packing of non-spherical crystallites. From the scattering cross-section in absolute units the volume fraction vc of crystallites was obtained as vc≈0.3, and the mean atomic density ρi in the interfaces as ρi≈0.52. The change of structural parameters during thermal annealing of the samples was studied. Up to high temperatures an appreciable volume fraction of crystallites with nearly unchanged size remains along with large particles.
Sintering of Nanophase TiO2 At 550°C
Authors: Epperson J. E. , Siegel R. W. , White J. W. , Klippert T. E. , Narayanasamy A. , Eastman J. A. , Trouw F.
Published: March 2011

Samples of nanophase TiO2 were prepared by the condensation of Ti vapors into clusters, their in situ oxidation to TiO2, and their consolidation into thin disks. Small angle neutron scattering was measured in the as-consolidated condition and after selected isothermal sintering anneals of up to 23 h at 550°C. The maximum entropy analysis method was used to obtain the size distributions of the scattering centers from the scattering curves. The results are interpreted in terms of a microstructural model consisting of nanometer sized grains of TiO2 separated by about 0.5 nm wide boundary regions, which contain voids and TiO2 of ≤60–70% of bulk density.
Characterisation of Ultrafine Microstructures Using a Position-Sensitive Atom Probe (POSAP)
Authors: Cerezo Alfred , Grovenor Chris R. M. , Hetherington Mark G. , Shollock Barbara A. , Smith George D. W.
Published: March 2011

A new development in the experimental techniques of atom probe microanalysis is described, which involves the use of a position sensitive detector system. This detector subtends a large solid angle (∼20°) at the specimen, and therefore permits the collection of ions from a substantial fraction of the whole surface area of the emitter. Progressive pulsed field evaporation leads to the construction of a three-dimensional map of the atomic chemistry of the specimen. The new instrument is ideally suited to the investigation of complex, ultrafine microstructures. Applications to the study of age-hardened aluminium alloys and Alnico permanent magnet materials are described.
Study of Multicomponent Magnetic Nanostructures with Digital Image Processing Technique.
Authors: Valanju A. P. , Jeong I. S. , Kim D. Y. , Walser R. M.
Published: March 2011

Previously, we used Digital Image Processing (DIP) to explore the relationships between the growth morphologies of sputtered two-phase nanostructures and their soft magnetic properties [1]. In this work we extended the application of DIP to analyse the effects of deposition parameters and annealing conditions on their soft magnetic properties including disaccommodation.

Magnetically soft, amorphous Co61B39 thin films, exhibiting a two-phase structure, were deposited by sequentially co-sputtering cobalt and boron. We digitized TEM micrographs of these thin films, prepared under different deposition conditions, and subjected to various post deposition processing. Digital Fourier transforms of the TEM micrographs were studied for evidence that the film anisotropy could be correlated with morphological order arising from long and short range interactions between particles over distances of ≈ 0.2 − 1.0 nm.

Our qualitative studies showed that important changes in soft magnetic properties were associated with changes in the two phase morphologies. We determined, for example, that specific morphological changes were associated with the reduction in the magnetic anisotropy produced by annealing. In general, decreases in anisotropy were associated with increased isotropy in Fourier space. The largest reductions and circular symmetric 2D Fourier transforms were produced by rotating field annealing.
Critical Phenomena in Nanoscale Multilayer Materials
Authors: Tsakalakos T. , Jankowski A.
Published: March 2011

We present a review of critical phenomena in a variety of nanoscale multilayer materials. Discontinuities of interdiffusitives at low temperatures, “the Supermodulus effect” and the “softening” of elastic constants of fcc-bcc structures, other mechanical properties at critical layer thickness are also presented. Some new calculations of elastic constants of (111) fcc and (110) bcc metallic superlattices show large changes as a function of homogeneous lattice strains. The effect of structural relaxations on a number of electronic and magnetic properties is discussed and a new analytical model is developed to explain the origin of interference effects when interfaces are apart by a few interplanar spacings. This model can predict relaxations at interfaces for a variety of materials including metals, semiconductors and ceramics.
Small Angle Neutron Scattering from Nanophase Titanium As A Function of Oxidation
Authors: Eastman J. A. , Epperson J. E. , Hahn H. , Klippert T. E. , Narayanasamy A. , Ramasamy S. , Siegel R. W. , White J. W. , Trouw F.
Published: March 2011

Nanophase titanium, prepared by the gas-condensation method both as aggregated powder and in lightly compacted discs, has been studied by conventional small angle neutron scattering, and by use of contrast variation methods. The contrast has been changed (a), isotopically, by means of deuterated/protonated solvents distilled into the specimen and (b) by progressive incremental oxidation of the Ti particles using fixed doses of low-pressure oxygen. It was shown that some evolution of the small angle pattern for lightly compacted nanophase Ti occurred over a period of several months at 300 K. Contrast matching by external solvent works well and has allowed the scattering lengths of oxidized and unoxidized specimens to be followed. The results imply that the scattering from metal and oxide can be separated under suitable conditions. The partial oxidation experiments indicate that there is both a fast and slow oxidation at 300 K. Also, during slow oxidation, high scattering length density scattering centers were formed whose number increased, but whose size remained the same at about 2 nm; these centers are tentatively assumed to be TiO2.
Electrodeposited Metallic Superlattices
Authors: Lashmore D. S. , Oberle Robert , Dariel Moshe P. , Bennettf L. H. , Swartzendruber Lydon
Published: March 2011

Electrochemical deposition of artificial compositionally modulated superlattices is described. It is shown that the quality of these alloys is comparable or superior to materials produced by vapor deposition or sputtering. The ambient temperature process described by Yahalom has been modified to include a feedback and control system in order to compensate for natural convective disturbances in the electrolyte. Data is presented for copper-nickel samples of varying wavelengths down to 2 nm which suggests that magnetic properties of thin nickel layers are comparable with bulk nickel. Alloys of other types whose properties can be tailored on a near atomic scale will also be discussed along with potential applications.
Phase Control in Nanophase Materials Formed from Ultrafine Ti Or Pd Powders
Authors: Eastman J. A.
Published: March 2011

The effect of He gas pressure during evaporation and post-evaporation O2 exposure on phase formation in nanophase materials has been examined. Ultrafine powders of Ti and Pd were prepared by the inert gas-condensation technique and bulk nanophase samples were formed by consolidation of these powders with or without prior exposure to O2. Evaporation of Ti in He pressures greater than 500 Pa followed by exposure to O2 results in the formation of ultrafine powders of crystalline rutile (TiO2) which are compacted to form nanocrystalline TiO2. Surprisingly, reducing the He pressure used during evaporation to less than approximately 500 Pa results in the formation of ultrafine powders of an amorphous phase. Room temperature consolidation of this powder under vacuum, however, results in nanocrystalline Ti being formed if the powder is not exposed to O2 prior to consolidation, and a mixture of rutile and an unidentified crystalline phase if the powder has been previously exposed to O2. Further reduction of the He pressure during evaporation of Ti to less than approximately 10 Pa results in the formation of crystalline Ti having a film-like morphology rather than than the desired ultrafine particles. Experiments on Pd evaporated in 10 to 6000 Pa of He have yielded ultrafine powders and consolidated samples of only the crystalline fcc phase, regardless of the He pressure
Metastable Nanocrystalline Carbides in Chemically Synthesized W-Co-C Ternary Alloys
Authors: McCandlish L. E. , Kear B. H. , Kim B. K. , wu L. W.
Published: March 2011

Nanophase materials can be prepared either by physical methods or chemical methods. Physical methods include thermal evaporation, sputtering and melt quenching, whereas chemical methods include glow-discharge decomposition, chemical vapor deposition, sol-gel dehydration and gas-solid reaction. Recently, we have used controlled activity gassolid reactions to prepare nanophase WC-Co cermet powders at different WC loadings. In the process we have discovered some new metastable phases in the W-Co-C ternary system at temperatures below 1000 °C.
Effect of Ordering Energy on Grain Boundary Structure in L12 Alloys
Authors: Ackland G. J. , Vitek V.
Published: March 2011

Atomic structures of grain boundaries in two L12 ordered alloys with very different ordering energies have been calculated. The interatomic forces are represented by many-body empirical potentials based on the second moment approximation to the tight-binding density of states. Grain boundaries in strongly ordered alloys show very little relaxation. This results in the presence of columns of cavities in the boundaries. On the other hand boundaries in weakly ordered alloys, and also in pure f.c.c. materials, show extensive relaxations leading to much more homogeneous structures. We suggest that these structural features may be responsible for the intrinsic brittleness of grain boundaries in compounds such as Ni3Al in contrast with boundaries in pure f.c.c. metals or ordered alloys such as Cu3Au which are only embrittled by segregation.
Structural Energy Differences in Al3Ti: The Role of Tetragonal Distortion in APB and Twin Energies
Authors: Nicholson O. M. , Stocks G. M. , Temmerman W. M. , Sterne P. , Pettifor D. G.
Published: March 2011

At stoichiometry, DO22 is the observed ground state of Al2Ti and has a C/A ratio of 2.23, but as a function of both concentration and temperature other ordered arrangements of APB's are observed. These phase transitions have sparked many studies in which the energy has been treated as that of chemical rearrangement on an fcc lattice. We have found that at the ideal C/A ratio, the Ll2 structure is lower in energy, but as the tetragonal distortion increases the DO22 energy drops below that of Ll2. The critical role played by the tetragonal distortion in the balance between Ll2 and DO22 energies precludes the use of any model based on the undistorted lattice.

The major impediment to the development of Al3Ti as a high-temperature material is its lack of ductility. The standard approach is to make alloy additions which transform the structure to Ll2. An alternate approach is to work toward the enhancement of ductility in the DO22 phase. As a first step we have calculated the twinning energy in Al3Ti.
Slip Systems in Ni3(Al, Ti) At Temperatures Above the Peak in Flow Stress
Authors: Sun Y. Q. , Hazzledine P. M.
Published: March 2011

Dislocations in single crystals of Ni3(Al, Ti) deformed at temperatures above the peak in flow stress have been studied by the TEM “weak-beam” technique. <110> dislocations on the primary cube plane are mostly of edge character, and they have been observed to transform into “super” Lomer- Cottrell locks. <100> dislocations, by contrast, are principally of 45° character. They are believed also to become immobilized by dissociation on {111} planes. Properties of both dislocations on cube planes are discussed and are related to the deformation behaviour of L12ordered intermetallic alloys.
In-Situ Observation of Grain Boundary Behavior in Ni3 Al Alloys During Tensile Deformation in Sem
Authors: Lin Dongliang , Chen Da
Published: March 2011

The deformation behavior of Ni3Al alloys with various chemical compositions and subjected to different heat treatments were in-situ observed in SEN. Moreover, in-situ observations of slip trace are supplemented by the direct observation of dislocation arrangements by TEM. In boron-doped Ni3Al alloys it is shown that close to the grain boundary there exists a thin slip transition region, within which slip lines are reoriented or other slip systems are operated to produce a local strain accommodation and to relax the stress concentration at grain boundaries. However, boron-enhenced ductility is seriously affected by alloy stoichiometry, the addition of a tertiary alloy element and heat treatment, etc.
Deformation Behavior of High Temperature Intermetallic TiAl Alloyed with Gallium
Authors: Kad B. , Oliver B. F.
Published: March 2011

TiAl (γ) intermetallic has been investigated with ternary additions of up to 10 at% Ga. Optical microscopy reveals that gallium can be retained in solution to at least 7 at%. Microhardness data reveals that Ga substituted for Al such that Ti/(Al+Ga)=l causes solution softening. Deformation behavior of the single phase alloy in compression is reported. Perfect dislocations of the a/2[110] type and superdislocations of the a[011] type and a/2[112] type have been observed. TEM results indicate that primary deformation is contributed by a/2[110] type dislocations and twinning on (111) planes with wavy slip optically observed
WORKHA RDENING AND NON-OCTAHEDRAL SLIP SYSTEMS IN ORDERED Cu2NiZn
Authors: Morris D. G. , Morris M. A. , Biselli C.
Published: March 2011

The ordered Cu2NiZn alloy is virtually unique in showing a changing antiphase domain structure according to annealing temperature. At low annealing temperatures there are isotropic domains and at high annealing temperatures there are cube-oriented domains characteristic of highly anisotropic boundary energies. This property allows a comparison of dislocation behaviour for otherwise identical materials: the roles of cube crossslip and cube glide can then be distinguished from other mechanisms, for example elastic torque effects and dipole formation. Mechanical properties and dislocation structures are examined over a range of test temperatures. The material having cube-oriented domain boundaries shows a much higher work hardening rate over an intermediate temperature range. Strengthening at low temperatures is dominated by dipole and multipole formation, whilst deformation above ambient temperature leads to the appearance of non-octahedral glide, more frequently on planes near {110} than near {001}. For the material with cube-oriented domain boundaries there is some evidence to suggest point blockage by cross-slip onto cube planes, leading to the higher work hardening rate at the intermediate temperature. This study emphasizes the multiplicity of slip systems which may operate and discusses the relative importance of anisotropic antiphase boundary energies and anisotropic elasticity effects.
Creep-Fatigue Resistance of a Nickel-Aluminide
Authors: Tien J. K. , Bellows R. S.
Published: March 2011

A modified fatigue test matrix that provided both creep (high mean stress) and fatigue (alternating stress) damage was used to evaluate the creep-fatigue behavior of D.S. Ni3Al(B,Hf). The three generic regimes of below, at, and above peak yield strength temperature were investigated. It was found that the creep-fatigue resistance of this intermetallic remains high through the three temperature regimes, allowing it to be further considered as a monolith or as the matrix of high-temperature fiber reinforced composite.
Some Thermodynamic Properties of NiAl Calculated by Molecular Dynamics Simulations
Authors: Clapp P. C. , Rubins M. J. , Charpenay S. , Rifkin J. A. , Yu Z. Z. , Voter A. F.
Published: March 2011

Calculations of the surface free energy and anti-phase boundary energy as a function of low index orientations and temperature have been determined for equiatomic perfectly ordered bcc NiAl via molecular dynamics computer simulations. The simulations utilized an Embedded Atom Method calculation of the interatomic potentials and volume forces in the Ni-As alloy system. Values of about 0.95, 1.6, 1.9 and 2.0 J/m2 were found for surface energies of the {100}, {110}, {112} and {111} orientations:, respectively. APB energies of about 0.24 and 0.38 J/m2 were determined for {110} and {112} boundaries, respectively. In addition, we have examined the phase stability and relative energies of the ordered bcc, fcc and bct phases at low temperature, and find a bct phase with c/a = 1.32 slightly lower in energy than the bcc, presaging the martensitic transformation that occurs at finite temperatures in more nickel rich alloys.
Mechanical Properties of Diverse High-Temperature Compounds–Thermal Variation of Microhardness and Crack Formation
Authors: Fleischer Robert L.
Published: March 2011

Microhardness vs temperature and elastic moduli have been measured for a suite of intermetallic compounds that melt above 1400°C. Binary intermetallics were selected to represent a variety of crystal structures and yet have optimal combinations of high melting temperature (Tm) and low specific gravity. Some deliberately two-phase alloys were prepared in which one phase is a terminal-phase metal and the other an intermetallic compound.

Binary compounds can be described by two patterns. In those where plasticity is difficult, hardness decreased slowly with temperature up to Tm/2, the decrease being no more than that normally shown by the elastic moduli. In those compounds where single crystal plasticity is known (or at least plausible), microhardness decreases more rapidly than do elastic moduli, presumably due to thermally activated slip.
Parameters for Ductility Improvement in TiAl
Authors: Kawabata T. , Tamura Takashi , Izumi O.
Published: March 2011

The effect of the Ti/Al ratio and third elements (Cr, Hf and Nb) on the mechanical properties of TiAl has been studied. Solution hardening in these elements is so large that, e.g., the strength doubles by the addition of 3 at.% Cr. Ductility to fracture strain has been improved up to 2.7 % and 2.7 % by the Cr addition and the use of high purity base metals, respectively. Parameters relating to the improvement of ductility have been discussed. Namely, the improvement of ductility was caused by the decreases of the grain size, axial ratio and impurity. A hypothesis has been proposed that the ductility improvement was related with the excess shrinkage of volume of a unit cell due to the addition of the third element which implies the strengthening of chemical bonds and vice versa. The effect of twins and a lamellar structure with the plate-like Ti3Al and the matrix on the ductility have been discussed.
Microstructure and Mechanical Properties of Ll2-Structure Alloys Based on Al3Zr
Authors: Schneibel J. H. , Porter W. D.
Published: March 2011

The tetragonal compound Al3Zr can be transformed into the cubic Ll2 structure by additions of Cr, Fe, Ni or Cu. This result is interpreted in terms of Pettifor's structure map. The transformation is accompanied by substantial softening. The significant porosity of cast buttons which develops during the homogenization required to produce the Ll2 structure is attributed to the Kirkendall effect. Al-5.5Fe-25Zr (at. %) specimens with the Ll2 structure can be deformed at room temperature in compression, and their yield stress has been determined as a function of temperature. Al-Fe-Zr is nevertheless a brittle material. This is illustrated for Al-Fe-V-Zr Ll2-structure compound, the fracture toughness of which is only slightly higher than that of sintered SiC. Evidence is presented to suggest that Ll2 formation is accompanied by an increase in toughness. Significant improvements in the mechanical properties of Al3Zr-type alloys may possibly be achieved by improved processing.
Effect of Strain Rate on the Plastic Behaviour of Ll2Compounds Based on Ni3Al
Authors: Miura Seiji , Ochiai Shouichi , Oya Yoshihiro , Mishima Yoshinao , Suzuki Tomoo
Published: March 2011

In both single and polycrystalline Ni3Al, no strain rate dependence of 0.2% flow stress is observed in a temperature range where anomalous positive temperature dependence of strength is exhibited. A distinct strain rate dependence is observed, however, in single crystals when the test temperature is raised beyond the peak in flow stress. It is shown that (111) type slip involving diffusional process is responsible for the strain rate sensitivity at near [001] orientation, while (001) type slip which is governed by the Peierls mechanism at orientations away from [001]. In polycrystalline compound with a fine grain size an apparent loss of the positive temperature dependence of strength is observed at a slower strain rate due to grain boundary sliding.