bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleation and Growth of the First Phase in Sputter-Deposited Nb/Al Multilayer Thin Films
Authors: Barmak K. , Vivekanand S. , Ma F. , Michaelsen C.
Published: April 2011

The formation of the first phase in the reaction of sputter-deposited Nb/Al multilayer thin films has been studied by power-compensated and heat-flux differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. The modulation periods of the films are in the range of 10-500 nm. Both types of calorimetrie measurements, performed at a constant heating rate, show the presence of two peaks (A and B) for the formation of the single product phase, NbAl3. Isothermal calorimetrie scans show that peak A is associated with a nucleation and growth type transformation. The formation of NbAl3 is thus interpreted as a two-stage process of nucleation and lateral growth to coalescence (peak A) followed by normal growth until the consumption of one or both reactants (peak B). Transmission electron microscopy investigations of samples annealed into the first stage of NbAl3 formation show the presence of this phase at the Nb/Al interface and its preferential growth along the grain boundaries of the Al layer. The latter highlights the role of reactant phase grain structure in product phase formation.
Interaction of Silicate Liquid with Sapphire Surfaces
Authors: Ramamurthy Sundar , Hebert Brian C. , Carter C. Barry , Schmalzried Hermann
Published: April 2011

The wetting behavior of a calcium aluminosilicate liquid in contact with sapphire of four crystallographically different orientations has been investigated using scanning electron microscopy and atomic force microscopy. Continuous layers of glass films heat-treated at 1600°C and 1700°C result in dewet pockets of glass on the surface. The heat treatment also causes the alumina surfaces to facet which presents interesting shapes to the glass pockets. The morphology of the pockets with respect to the orientation of the facets is useful in understanding qualitatively the liquid-solid interfacial energies relative to the orientation of the facets. This approach enables a sequential study of the interaction between the facets and the silicate liquid. Based on temperature, the equilibrium composition of the silicate changes by solution-precipitation and evaporation processes which affects the facet and step morphology. This experiment directly emphasizes the relevance of anisotropy in the α-Al2O3 crystal structure which may ultimately control some of the key issues of materials’ processing.
Kinetic Competition During Duplex Partitionless Solidification in Ni-V Alloys
Authors: Allen D.R. , Perepezko J.H.
Published: April 2011

A structure composed of both partitionless face-centered cubic (α-fcc) and body-centered cubic (β-bcc) phases has been observed following high undercooling solidification of nickel-vanadium (Ni-V) alloys in the composition range 47-51.7 at.% V. Containerless processing and rapid solidification suppresses the formation of the equilibrium σ phase and results in the simultaneous formation of partitionless fcc and bec phases. Transmission electron microscopy analysis has identified regions in which 0.1-1 μηι a and β grains co-exist in a duplex structure. A nucleation and growth kinetics analysis has been developed to describe the conditions under which this structure may form. Thermodynamic and kinetic arguments have been used to provide bounds on various kinetic parameters. These bounds indicate that the nucleation rates for a and β must be larger than about 1027 m−3 s−3 to account for the number of grains observed in the time available for nucleation, and the growth rates are constrained to be larger than about 1 m/s to account for complete solute trapping.
Model Evaluations of Phase Diagrams of the Systems SrO - (Mn, Fe, Co, Ni)O
Authors: Revzin B. , Pelleg J.
Published: April 2011

A model of substitutional ionic solid solution is applied for prediction of excess energy and the construction of binary phase diagrams of the systems SrO-MnO, SrO-FeO, SrO-CoO and SrO-NiO.
A Mechanism for Supercooling in Organic Liquids
Authors: Thoma Paul E.
Published: April 2011

In this investigation, a mechanism for supercooling in organic liquids is formulated. By comparing the melting temperature and spontaneous freezing temperature of the chemicals evaluated with their molecular characteristics, the factors promoting supercooling are developed. The results obtained indicate that the following molecular characteristics promote supercooling in organic liquids:

sharing of electrons between the atoms of a molecule;

A three-dimensional chemical structure;

A permanent, three-dimensional, and partially charged pocket within the chemical structure;

A partially charged projection having a charge opposite that of the pocket and located on the side of the molecule opposite that of the pocket.
A New Experimental Method for Investigating the Nucleation Kinetics of Solids in Supercooled Liquid Si
Authors: Jin Song H. , Im James S.
Published: April 2011

In this paper, we first describe and then demonstrate the soundness of a new experimental method that is designed to deliver a wide range of accurately measured nucleation rates of solids in supercooled liquid Si. The method utilizes thin-film processes, as well as laser-quenching and detection techniques, in order to first induce isothermal transformation and then extract the corresponding solid nucleation rates over a frequency range potentially greater than ten orders of magnitude. The technological and scientific gains that can result from acquiring such information are discussed.
Morphology of Ag Islands Grown on GaAs (110) at Low Coverage: Monte Carlo Simulations
Authors: Challa A. , Drucker J. , Cale T.S.
Published: April 2011

The growth morphology of Ag on GaAs (110) surfaces, at low coverages, is investigated with Monte Carlo simulations using a solid-on-solid model. Experimentally Ag deposited at room temperature forms 3D isotropic islands and forms needle-like islands elongated along the <110> direction when deposited at 250°C. Preliminary simulation results using 2D island growth model indicated that the elongation of islands at 250°C deposition is due to anisotropic surface diffusion and nearest-neighbor interactions along the <100> and <110> directions. The island morphologies obtained using a 3D island growth model are in good agreement with experimentally observed morphologies.
Structural Decomposition at Sn/GaAs(001) Interface
Authors: Nasr S. A. , Zinke-Allmang M.
Published: April 2011

Morphological studies of the system Sn/GaAs(001) are required to interpret electronic anomalies of devices which include doped III-V MBE grown thin films. Previous studies focused on the dynamics of Sn on As terminated surfaces. The current study complements those studies on a Ga terminated surface, i.e., conditions which may occur locally for short periods during MBE growth.

Sn is deposited on in-situ cleaned Ga rich GaAs(001) surfaces and the evolution of morphological structures is presented as a function of annealing temperature and Sn supersaturation. Three distinct regimes were observed, (i) a low temperature range (T ≤ 500°C) where Sn shows a propensity toward three-dimensional clustering, (ii) an intermediate temperature range (500°C ≤ T ≤ 625°C) where a transition in the morphology occurs due to strong interactions with the substrate resulting in the formation of characteristic etch-patterns and (iii) a high temperature regime (T ≥ 650°C) where the thermal decomposition of GaAs dominates while the deposited Sn desorbs fast.
Step-Edge Barriers on GaAs(001)
Authors: Šmilauer P. , Vvedensky D.D.
Published: April 2011

We investigate growth of GaAs(001) using kinetic Monte Carlo simulations of a very simple atomistic solid-on-solid model. The key features of this model are a short-range incorporation process of freshly deposited atoms and additional activation barriers to interlayer transport. Both are required to obtain close agreement between measured electron-diffraction intensities and simulated surface step densities during growth and post-growth equilibration on vicinal surfaces. This model is used to study long-time evolution of the surface morphology. Large pyramid-like features develop during growth on a singular surface which coarsen in time while maintaining an approximately constant slope. Growth on a vicinal surface is also found to be unstable. Simulated surface morphologies are compared with recent work using atomic-force microscopy. Finally, we show how a suitably modified version of this model helps to explain the recently observed phenomenon of re-entrant layer-by-layer chemical-beam etching of a singular GaAs(001) surface. The central features responsible for this behavior are the site selectivity of the etching process combined with step-edge barriers to interlayer adatom migration.
Heteroepitaxial Layer Morphology and Misfit Defect Formation
Authors: Cullis A.G.
Published: April 2011

The manner in which misfit strain can influence the morphology of heteroepitaxial layers is reviewed. Following a brief consideration of theoretical modelling, examples of experimental observations for two important materials systems, SiGe/Si and InGaAs/GaAs, are given. It is demonstrated that the formation of undulations of specific types is driven by partial elastic stress-relief and a lowering of the system free energy. Under these conditions, islands of deposit can be formed during initial growth and ripples can be produced upon continuous layers. Furthermore, the presence of surface morphological distortions and the accompanying strain fluctuations also can have a significant impact upon misfit dislocation introduction. Relationships between these fluctuations and dislocation source behaviour are described.
Si1-xGex Critical Thickness for Surface Wave Generation During UHV-CVD Growth at 525°C
Authors: Lafontaine H. , Houghton D.C. , Bahierathan B. , Perovic D.D. , Baribeau J.-M.
Published: April 2011

Several Si1-xGex/Si heterostructures were grown at 525°C using a commercially available UHV-CVD reactor. Layers with a germanium fraction ranging from 0.15 to 0.5 were examined by means of cross-sectional transmission electron microscopy and atomic force microscopy. Surface waves were found in layers with a thickness above a critical value which decreases rapidly as the Ge fraction is increased. Both experimental and modeling results show that surface waves are generated before misfit dislocations for Ge fractions above 0.3.
Control of Defect Structures in CuGaSe2 Epitaxial Films
Authors: Chen Wei , Gu Gin-Lern , Tseng Bae-Heng
Published: April 2011

An in-situ annealing process, which is conducted in the growth chamber by exposing the film to a Se beam immediately after film deposition, is developed to control defect structures in CuGaSe2 epitaxial films. TEM observations showed that the films annealed at a temperature above 450°C could completely remove anti-phase domain boundaries and effectively annihilate threading dislocations. The annealing process also changes the distributions of intrinsic point defects in the film. Photoluminescence (PL) may reflect the microstructure improvement in the films. A suppress of the donor-to-acceptor transitions caused by antisite defects and an enhancement in the PL intensity were found in a annealed film.
Mechanical Crystallization of Metglas Fe78B13Si9 by Cryogenic High Energy Ball Milling
Authors: Huang B. , Perez R.J. , Crawford P.J. , Nutt S.R. , Lavernia E.J.
Published: April 2011

A nanocrystalline material was synthesized by cryogenic ball milling of Metglas Fe78B13Si9 ribbons. The nanocrystalline structure consisted of α-Fe(Si) and Fe2B grains of 2-13 nm in diameter. In the early stages of milling, bending-induced shear bands were formed, followed by the initial stages of crystallization. As the milling proceeded, predominantly wearlike mechanisms caused further crystallization. The crystallization process was slowed considerably by the addition of 17 at.% Ni during cryogenic milling. The results indicate that the 17 at.% Ni did not form a supersaturated solid solution in the metallic glass, but impeded crystallization by reducing the efficiency of bending and wear-like mechanisms during milling.
0.35 μm Technologies in Japan
Authors: Kikkawa Takamaro , Sakai Isami
Published: April 2011

This paper describes silicide and salicide technologies in Japan for 0.35 μm CMOS ULSIs and beyond. Polycide gate electrodes have been developed for CMOS devices from 1.0 μm to 0.35 μm design rule regime, in which Wsi2 has been used dominantly as a silicide gate material. On the other hand, silicide films are formed selectively on source/drain diffusion layers by salicide techniques, in which TiSi2 is used as a salicide material. TiSi2 is also used as a salicide material of both gate electrodes and source/drain diffusion layers for dual gate (n+/p+) CMOS. The TiSi2 thin film is formed by Ti sputtering and subsequent rapid thermal annealing. A preamorphization technique before Ti sputtering has been developed to obtain equal silicide properties on p+ and n+ diffusion layers. A high-temperature Ti sputtering technique has been developed in conjunction with pre-amorphization. CoSi2 and NiSi have also been developed as salicide materials for quartermicron CMOS and beyond.
Stress in Silicon Due to the Formation of Self Aligned Poly-CoSi2 Lines Studied by Micro-Raman Spectroscopy
Authors: Howard D. J. , Wolf I. De , Bender H. , Maex K.
Published: April 2011

The application of CoSi2 in ever shrinking Si CMOS source-drain technologies demands a better knowledge of the states of stress caused by the formation of cobalt-silicides in Si. In this study the variation in local mechanical stress in the silicon substrate near arrays of polycrystalline cobalt-silicide lines was investigated by micro-Raman spectroscopy. The lines were formed by annealing Co sputtered in windows in lithographically patterned, thermal oxide coated Si wafers. The CoSi2 lines varied in width from ˜0.25 to 5.0μ, in number from 2 to 7, and in thickness from ˜ 10 to 230nm. The spacing between lines was 1 and 3 times the line width.

Trends in the Si stress between CoSi2 lines are described as a function of line width and line thickness. From the stress measured in the Si, information is obtained about the stress in the CoSi2 lines. In addition, the Si stress due to lines of primarily CoSi phase (monosilicide) is compared with the Si stress due to polycrystalline-CoSi2 (disilicide) lines.

Cross section TEM and SEM micrographs of the CoSix line morphologies are used to aid the description of the resulting stress profiles. Some theoretical modeling of the stress in the Si due to the CoSix lines is presented for comparison with the micro-Raman spectroscopy results.
Electrical Characteristics of CoSi2 Layers Formed by Mevva Implantation of Co into Si
Authors: Peng Qicai , WONG S. P.
Published: April 2011

High dose Co implantation into Si has been performed with a metal vapor vacuum arc (MEVVA) ion source at an extraction voltage of 70 kV to doses from 8×1016 to 6×1017 ions cm−2 at substrate temperatures (Ts) in the range of 210°C to 700°C. Annealing was performed in nitrogen at various temperatures for various time intervals by either furnace annealing (FA) or rapid thermal annealing (RTA). The electrical properties of the CoSi2 layers formed were studied using resistivity and Hall effect measurements from 10 to 300K. We found that for all the samples prepared by MEVVA implantation, as long as a continuous CoSi2 layer was formed after annealing, a strong temperature dependence of the Hall coefficient was observed with a large peak at around 90 to 110K. The magnitude of the peak also varies depending on the substrate parameters and processing conditions. However, the temperature dependence of the resistivity for these CoSi2 layers follows the atthiessen's rule. We also found that it does not require high substrate temperature nor very high temperature annealing in order to form a CoSi2 layers with low resistivity by MEVVA implantation. Such low resistivity CoSi2 layers can be formed with a substrate temperature as low as 210°C after either RTA at high temperature for a few seconds or FA at a relatively low temperature of 750°C for one hour. The dependence of the electrical properties on Ts is also presented and discussed.
Epitaxial Films of Cobalt Disilicide (100) Evaporated onto Si (100) from a Mixed Source
Authors: Goeller P. T. , Wang Z. , Sayers D. E. , Glass J. T. , Nemanich R. J.
Published: April 2011

Thin films of (100) oriented CoSi2 have been electron beam evaporated onto Si(100)substrates from a mixed Co-Si target. A sharp c(2×2) low energy electron diffraction (LEED)pattern resulted after annealing the films to 800°C. Extended x-ray absorption fine structure (EXAFS) of the film indicated the phase to be CoSi2. Quantitative x-ray photoelectron spectroscopy (XPS) analysis revealed the surface of the film to be slightly Si rich, indicating the Si terminated CoSi2 variant. Analysis of transmission electron microscope (TEM) diffraction patterns also provided evidence of the (100) orientation of the film.
Patterning of Silicide Layers by Local Oxidation
Authors: Dolle M. , Mantl S. , Hacke M. , Mesters S. T. , Bay H. L.
Published: April 2011

A novel method for patterning of silicide layers based on local oxidation is presented. We investigated unifom and local oxidation of epitaxial CoSi2 layers on Si(100). During thermal oxidation of CoSi2 a SiO2 surface layer forms and the silicide layer moves deeper into the substrate. Single crystalline CoSi2 layers on Si(100) remain single crystalline even if they are shifted into the substrate several hundred nm. Local oxidation of such a silicide layer allows lateral patterning of the silicide. The oxidized regions of the silicide layer are pushed inwards and separate from the surface layer at a critical oxidation time. This allows the formation of buried patterned silicides or metallized mesa structures. The technique seems to be also applicable for polycrystalline silicides.
Laser Crystallized Polysilicon Thin Films and Applications
Authors: Boyce J. B. , Mei P. , Fork D. K. , Anderson G. B. , Johnson R. I.
Published: April 2011

Pulsed excimer-laser crystallization of amorphous silicon on non-crystalline substrates is an important processing technique for large-area polycrystalline silicon films and devices. Interest stems, in large part, from proposals to use polycrystalline silicon on glass in large-area electronic applications, such as flat-panel active matrix displays and two-dimensional imaging systems. The polycrystalline silicon is envisioned to increase the functionality and reduce costs over the current circuits that use amorphous silicon. Also, it is found that laser-crystallized polycrystalline silicon exhibits some interesting materials properties, such as a sharp peak in the average grain size with large lateral grain growth as a function of excimer laser energy density. The average grain size increases with increasing laser fluence and peaks on the order of several microns or two orders of magnitude larger than the film thickness. The grain size then decreases with further increases in laser fluence. This peak in grain size is accompanied by a similar peak in the Hall electron mobility. This is a significant relationship for devices since the grain structure has a substantial influence on electrical properties. But to the detriment of device parameters, this large lateral grain growth occurs over a very arrow range of laser fluences and is accompanied by a corresponding peak in the surface roughness of the films. These relationships between laser processing conditions, materials properties, and device parameters force a compromise between large grain size for high mobility and homogeneity of material for uniformity of device characteristics. A window does exist in process parameter space where good-quality devices with uniform characteristics have been obtained. In addition, these attributes have been achieved under conditions that yield good polycrystalline silicon and good amorphous silicon devices on the same wafer within a mm of one another, allowing for hybrid polycrystalline and amorphous silicon circuits.
Silicon Recrystallization in Sipos Material Obtained by Disilane
Authors: Pedroviejo J. J. , Garrido B. , Ferrer J. C. , Cornet A. , Scheid E. , Morante J. R.
Published: April 2011

Conventional and Rapid Thermal Annealing of Semi-Insulating Polycrystalline Silicon layers obtained by Low Pressure Chemical Vapor Deposition (LPCVD) from disilane Si2H6 have been performed in order to determine the structural modifications induced on the layers by these thermal treatments. The study of these modifications has been carried out by several analysis methods like FTIR, XPS, TEM, RAMAN and ellipsometry. The results obtained are presented, contrasted and discussed in this work.
Mechanical Properties of Thermally Crystallized Boron-Doped Silicon Thin Films
Authors: Scafidi P. , Cali J. , Bustarret E.
Published: April 2011

P-type polycrystalline silicon films on silicon wafers were obtained by annealing at 575 °C boron-doped amorphous hydrogenated silicon (a-Si:H) films. During the anneal, the internal stress of the film changed from compression to tension. The crystallization kinetics became faster when increasing the boron concentration. The hardness and elastic modulus of each film were determined by nanoindentation. The elastic modulus increased systematically upon crystallization. Wafer curvature monitoring during the thermal cycle allowed us to derive the thermal expansion coefficient of a-Si:H for different boron doping levels. Above a critical temperature of 320°C, the internal stress of the a-Si:H films rapidly changed toward a tensile state, independent of the boron concentration. Analysis of the hydrogen-bonding configurations by Fourier transform infrared spectroscopy indicated that this rapid stress change was due to hydrogen out-diffusion. The evolution of the internal stress with time was followed during the 575°C crystallization isothermal plateau. The circular blistering and spalling observed upon annealing in some cases of low doping levels was correlated with the presence of microvoids and with the internal stress of the a-Si:H film.
High Performances of Low Temperature (≤ 600°C) Unhydrogenated Polysilicon Thin Film Transistors
Authors: Pichon L. , Raoult F. , Mourgues K. , Bonnaud O.
Published: April 2011

Low temperature unhydrogenated polysilicon thin film transistors are elaborated through a fourmask gate aluminium process. Temperature process does not exceed 600°C. Active layer is made of undoped polysilicon layer, an in-situ phosphorus polysilicon layer constitutes source and drain windows and a SiO2 APCVD layer ensures gate insulation. The transistors exhibit electrical properties as good as in the case of hydrogenated ones: a low threshold voltage (VT = 4–5 V), an acceptable optimum field effect mobility (≅ 42 cm2/Vs), a high On/Off state switching, and a high On/Off state current ratio (≅ 107) for a drain voltage equal to 1 V.
Thin Ti/TiN Barriers for Ulsi Application
Authors: Huang C. K. , Wang Shi-Qing
Published: April 2011

In advanced ULSI devices, Ti (titanium)/TiN (titanium nitride) film stack is commonly used as liner materials. Ti is used to reduce contact/via resistance while TiN is utilized as an adhesion/diffusion barrier layer. Ti/TiN liner with optimized thickness combinations should be used for progressively advanced ULSI devices with features of reduced dimensions and increased aspect ratios in order to effectively reduce contact/via resistance, ensure barrier quality, and maximize cross section of metal conductors with low electrical resistivities. This study evaluates the film properties such as sheet resistance, density, stress, grain structures, and reflectance of individual Ti and TiN, and composite Ti/TiN films manufactured by collimated physical vapor deposition (PVD). The film thickness ranges from 5 to 60nm. The dependence of these properties on the film thickness will be discussed.
Strain Measurement and Calculation in Passivated Cu Lines Deposited by Three Different Methods
Authors: Marieb T. , Mack A. S. , Cox N. , Gardner D. , Mu X. C.
Published: April 2011

Passivated Cu lines deposited by CVD, electroplating, and sputter-reflow were investigated using x-ray diffraction. Blanket films of the three types were measured for strain and texture post-deposition and after an anneal step to mimic the passivation temperature step. Texture in the CVD films was random, while the electroplated and sputtered films showed a strong {111} texture. Lines were then measured of each type. The measured strain was modeled using finite element calculations. While the strain in Cu was high compared to Al lines of similar geometry, no stress voiding was observed using high voltage scanning electron microscopy.
Dynamic Simulation of Crack Propagation with Dislocation Emission and Migration
Authors: Zacharopoulos N. , Rolovitz D. J. , Lesar R. A.
Published: April 2011

We present a simulation procedure for fracture that self-consistently accounts for dislocation emission, dislocation migration and crack growth. We find that the dislocation microstructure in front of the crack tip is highly organized and shows a complex temporal-spatial evolution. The final dislocation microstructure and the number of emitted dislocations immediately proceeding fracture varies rapidly with the loading rate. For high loading rates, fracture occurs at smaller loads with increasing loading rate. However, the load at fracture shows a maximum with respect to loading rates.
Effect of Crack Blunting on Subsequent Crack Propagation
Authors: Schiøtz J. , Carlsson A. E. , Canel L. M. , Thomson Robb
Published: April 2011

Theories of toughness of materials depend on an understanding of the characteristic instabilities of the crack tip, and their possible interactions. In this paper we examine the effect of dislocation emission on subsequent cleavage of a crack and on further dislocation emission. The work is an extension of the previously published Lattice Greens Function methodology[l, 2, 3]. We have developed a Cavity Greens Function describing a blunt crack and used it to study the effect of crack blunting under a range of different force laws. As the crack is blunted, we find a small but noticeable increase in the crack loading needed to propagate the crack. This effect may be of importance in materials where a dislocation source near the crack tip in a brittle material causes the crack to absorb anti-shielding dislocations, and thus cause a blunting of the crack. It is obviously also relevant to cracks in more ductile materials where the crack itself may emit dislocations.
Hydrogen Diffusion in Quartz: A Molecular Dynamics Investigation
Authors: Bongiorno A. , Colombo L.
Published: April 2011

We present a molecular dynamics investigation on hydrogen diffusivity in crystalline quartz by computing the diffusion coefficient over a wide range of temperatures (700K < T < 1500K) and by characterizing the diffusion path and mechanism. Our main findings are: (i) hydrogen diffusion is anisotropically confined along the c-axis in α- and β-quartz; (ii) hydrogen diffuses through a jump-like mechanism; (iii) the temperature-dependent diffusivity follows an Arrhenius law with activation energy of 0.56 eV and 0.27 eV for α-and β-quartz, respectively.
Calculation of Electromagnetic Constitutive Parameters of Insulating Magnetic Materials with Conducting Inclusions
Authors: Kuster Drs. Eric , Moore Rick , Lust Lisa , Kemper Paul
Published: April 2011

A Method of Moments (MoM) electromagnetic model of percolating conducting films was applied to calculate the effective parameters of the composite formed by conducting inclusions placed within a dispersive magnetic but nondispersive dielectric matrix. The MoM calculations demonstrate a coupling between the magnetic properties of the matrix and the effective composite permittivity and frequency dispersion of the composite. The coupling of permittivity and permeability is observed near the percolation threshold of the composite and for high conductivity inclusions. The prediction agrees with physical expectations since near percolation the conduction correlation length dominates the effective permittivity of the composite and this correlation length is determined by both the permittivity and permeability of the composite.
Mechanism Of Thermally Assisted Creep Crack Growth
Authors: Golubović Leonardo , Moldovan Dorel
Published: April 2011

We use atomistic Monte-Carlo simulations to investigate the dynamics of cracks which sizes are smaller than the Griffith length. We demonstrate that such cracks can irreversibly grow proviso their size is larger than a certain critical length which is smaller than the Griffith length, as recently suggested [ L. Golubović and A. Peredera, Phys. Rev. E51, 2799 (1995)]. We show here that this thermally assisted creep crack growth is dominated by irreversible changes in the region of the crack tip, primarily in the form of dislocation emissions and nucleation of microcavities and voids. These processes act together during the crack growth: the crack tip region acts as a source for emissions of dislocations which subsequently serve as seeds for creation of vacancy clusters in a region away but still close to the crack tip. Eventually, passages between these vacancy clusters and the mother crack are formed and the crack thus increases in size. As this process repeats, the crack grows.
Mechanism Of Ductile Rupture In The AL/Sapphire System Elucidated Using X-Ray Tomographic Microscopy
Authors: King Wayne E. , Campbell Geoffrey H. , Haupt David L. , Kinney John H. , Riddle Robert A. , Wien Walter L.
Published: April 2011

The fracture of a thin metal foil constrained between alumina or sapphire blocks has been studied by a number of investigators. The systems that have been investigated include Al [1,2], Au [3], Nb [4], and Cu [5]. Except for Al/ Al2O3interfaces, these systems exhibit a common fracture mechanism: pores form at the metal/ceramic interface several foil thicknesses ahead of the crack which, under increasing load, grow and link with the initial crack. This mechanism leaves metal on one side of the fracture surface and clean ceramic on the other. This has not been the observation in Al/ A12O3 bonds where at appropriate thicknesses of Al, the fracture appears to proceed as a ductile rupture through the metal.

The failure of sandwich geometry samples has been considered in several published models, e.g., [6,71. The predictions of these models depend on the micromechanic mechanism of crack extension. For example, Varias et al. proposed four possible fracture mechanisms: (i) near-tip void growth at second phase particles or interfacial pores and coalescence with the main crack, (ii) high-triaxiality cavitation, i.e., nucleation and rapid void growth at highly stressed sites at distances of several layer thicknesses from the crack tip, (iii) interfacial debonding at the site of highest normal interfacial traction, and (iv) cleavage fracture of the ceramic. Competition among the operative mechanisms determines which path will be favored.

This paper addresses the question of why the fracture of the A1/A12O3 system appears to be different from other systems by probing the fracture mechanism using X-ray tomographic microscopy (XTM). We have experimentally duplicated the simplified geometry of the micromechanics models and subjected the specimens to a well defined stress state in bending. The bend tests were interrupted and XTM was performed to reveal the mechanism of crack extension.
Simulation Of Thermal Stresses, Voids And Fracture At The GaAs/Ceramic Interface
Authors: Strifas Nickolaos , Christou Aris
Published: April 2011

Stresses induced at the GaAs-Al2O3 interface by large ΔT excursions have been investigated by finite element simulation and have been correlated with experimental results. The effects of power and temperature cycling on crack propagation at the die attach are investigated. The FEA (finite element analysis) method is used to simulate the effect of die attach voids on the peak surface temperature and on the die stresses. These voids in the die attach are identified to be the major cause of die cracking. It was found that stresses developed on the die because of the environmental temperature changes and their dissipation as part of an effective thermal management is necessary to ensure reliable performance.
Stress-assisted Kosterlitz-Thouless Dislocation Nucleation: the Statistical Physics of Plastic Flow
Authors: Selinger Robin L. Blumberg
Published: April 2011

The stress-assisted Kosterlitz- Thouless (K-T) transition was proposed by Khantha, Pope and Vitek [1] as a possible mechanism for the abrupt transition from brittle to ductile behavior of single crystals as a function of temperature. We argue that in a two-dimensional crystal under elevated temperature and applied shear stress, the microscopic mechanism of the stressassisted K- T transition is the nucleation of dislocation dipole pairs with a preferred Burgers vector orientation. This defect population gives rise to an anisotropic hexatic phase with quasi-long range order along one axis and short-range order along the orthogonal axis. The laboratory signature of such a phase is scattering peaks that are “streaked,” i.e. strongly broadened along a single direction. We discuss experimental data for an analogous twodimensional system which displays order of this type. Potential implications for the brittleductile transition in three dimensions are outlined.
Molecular Statics Simulation Of Crack Propagation In A-Fe Using Eam Potentials
Authors: Shastry Vijay , Farkas Diana
Published: April 2011

The behavior of mode I cracks in α-Fe is investigated using molecular statics methods with EAM potentials. A double ended crack of finite size embedded in a cylindrical simulation cell and fixed boundary conditions are prescribed along the periphery of the cell, whereas periodic boundary conditions are imposed parallel to the crack front. The displacement field of the finite crack is represented by that of an equivalent pileup of opening dislocations distributed in a manner consistent with the anisotropy of the crystal and traction free conditions of the crack faces. The crack lies on the {110} plane and the crack front is located either along á100ñ, á110ñ or á111ñ directions. The crack tip response is rationalized in terms of the surface energy (γs) of the cleavage plane and the unstable stacking energies (γus) of the slip planes emanating from the crack front.
Surface Stress Effects On Fracture
Authors: Cammarata R.C. , Sieradzki K.
Published: April 2011

The effects of surface stress on fracture are reviewed. Calculations by Thomson et al. seem to suggest that surface stresses do not affect cleavage fracture when the crack propagates in a self similar manner even though the surface stress can lead to large stresses near the crack tip. However, surface stresses may have an important effect on dislocation emission near the crack tip. A simple analysis is offered to show how these effects may be incorporated into a modified Rice ductile-brittle fracture criterion by adding a term to the unstable stacking energy that takes into account the energy to form an incipient ledge.
Mechanical and Thermal Properties of SiC-SiC Composites Made With CVR SiC Fibers
Authors: Kowbel W. , Tsou H. T. , Bruce C. A. , Withers J. C.
Published: April 2011

Nicalon fiber is the primary reinforcement in SiC-SiC composites currently produced by a variety of techniques including CVI and polymer infiltration. Low strength retention and dimensional change at high temperatures of the Nicalon fibers limits the choice of manufacturing processes which can be employed to produce low cost SiC-SiC composites. MER has developed a SiC reinforcement based upon the conversion of low cost carbon fabric to SiC via a Chemical Vapor Reaction (CVR) process. These new SiC filaments exhibit excellent creep resistance at temperatures up to 1600°C. SiC-SiC composites were fabricated using different types of graphite fabric converted to SiC fabric utilizing the CVR process combined with a polycarbosilane (PCS) infiltration and CVI densification. In addition, enhancement of the composite through-the-thickness thermal conductivity was accomplished via boron doping of the matrix. A correlation between processing conditions, microstructure and properties of the SiC-SiC composites will be presented.
The Effect of Source Microstructure on the Close-Space Sublimation of CdTe Thin Films for Solar Cell Applications
Authors: Albin D. , Rose D. , Swartzlander A. , Moutinho H. , Hasoon F. , Asher S. , Matson R. , Sheldon P.
Published: April 2011

The microstructure of CdTe sources grown on bare 7059 and SnO2-coated 7059 glass substrates used in the close-space sublimation (CSS) growth of CdTe films, is affected by nucleation conditions during their fabrication. For CdTe sources grown on bare glass substrates, denser source microstructures with smaller grains are promoted by low-temperature nucleation conditions. Growth rates of CdTe films deposited using these source plates are inversely proportional to the packing density of the grains. CdTe sources grown on glass undergo significant texture changes during their use in subsequent CSS deposition. CdTe sources grown on SnO2-coated glass substrates exhibit dense structures both with and without low-temperature nucleation and increased grain size with low-temperature nucleation. These source plates show less texture change associated with thermal annealing than their bare-glass counterparts, however, they are much more susceptible to CdO formation during subsequent CSS deposition processes in which oxygen is present. Source oxidation results in a decrease of the (111)/(220) x-ray diffraction intensity. Analysis of the (111)/(220) intensity ratio with and without source oxidation suggests the preferential formation of CdO on the (111) planes. In general, source oxidation appears to be a inversely proportional to the grain size of the source material.
A Model of the Gas-Phase Chemistry of Boron Nitride CVD From BCl3 and NH 3*
Authors: Allendorf Mark D. , Melius Carl F. , Osterheld Thomas H.
Published: April 2011

The kinetics of gas-phase reactions occurring during the CVD of boron nitride (BN) from BCl3 and NH3 are investigated using an elementary reaction mechanism whose rate constants were obtained from theoretical predictions and literature sources. Plug-flow calculations using this mechanism predict that unimolecular decomposition of BCl3 is not significant under typical CVD conditions, but that some NH3 decomposition may occur, especially for deposition occurring at atmospheric pressure. Reaction of BCl3 with NH3 is rapid under CVD conditions and yields species containing both boron and nitrogen. One of these compounds, Cl2BNH2, is predicted to be a key gas-phase precursor to BN.
The Chemistry of Boron and Titanium Diboride Formation: Decomposition of TiCl4 and BCl3 in Hydrogen and Helium*
Authors: Osterheld Thomas H. , Allendorf Mark D.
Published: April 2011

Measurements of the decomposition of mixtures of boron trichloride (BCl3), titanium tetrachloride (TiCl4), and hydrogen at elevated temperatures are presented. The decomposition of BCl3 with hydrogen appears to drive the chemistry in this system. The species depositing boron on the surface contains at least 2 chlorine atoms. Once deposited, the surface chlorine is removed by reaction with hydrogen to form HCl and, presumably, surface B-H bonds.
XPS Studies of the Interactions of Biocells with Various Silicon Based Surfaces
Authors: Seal S. , Krezoski S. , Barr T. L. , Petering D. H.
Published: April 2011

Siliceous materials are the principal components of Earth's crust and also have become key ingredients of modem technology. Recently, we have expanded our chemical characterization of complex silicates (e.g., framework [1] and sheet types [2]) to include studies of their interaction with select biocells [3,4]. It is becoming apparent that the surface chemistry of these silicates, and perhaps that of silica itself, plays a key role in the oft resulting cell pathogenesis, thus enhancing the value of further investigations with X-ray photoelectron spectroscopy. The present research describes the unique growth of Ehrlich (murine or rat tumor) cells on Sio and SiO2 wafers, and also on select seaentine silicates (such as chrysotile asbestos). Tbese growth studies were followed by both cell/silicate separations and unique freeze drying [3,4]. XPS examination at select stages discovered cell induced alterations in the Si, O, Mg and particularly Fe chemistry of the silicon based systems as well as corresponding changes in the cell chemistry. Many of these features were confirmed by atomic absorption spectroscopy.
Surface Induced Calcium Phosphate Nucleation and Growth
Authors: Song L. , Campbell A. A. , Li X. S. , Bunker B. C.
Published: April 2011

Calcium phosphate nucleation on colloidal oxide surfaces, such as TiO2, SiO2 and Al2MO3, has been studied as a model system to understand the role of surface chemistry on crystal nucleation kinetics and phase formation. The nucleation induction times have been measured using Constant Composition (CC) technique and calcium phosphate phases formation have been determined mainly by X-ray diffraction. The results indicated TiO2 not only significantly reduces the nucleation induction time and interfacial energy but also stimulates octacalcium phosphate formation over dicalcium phosphate dihydrate. SiO2 and Al2O3 have little effect on both nucleation kinetics and phase formation.
Growth Dynamics and Exciton Localization in Strained CdSe Quantum Structures
Authors: Flack F. S. , Hunt A. , Hennessey H. , Samarth N. , Levy J. , Nikitin V. , Crooker S. A. , Awschalom D. D. , Jassim M. Al
Published: April 2011

Coherently strained CdSe quantum structures are fabricated under varying dynamical growth conditions during the epitaxy of cubic CdSe on (100) ZnSe. Reflection high energy electron diffraction (RHEED) is employed to monitor the growth mode (2D vs. 3D). Conventional photoluminescence (PL) shows that both growth modes yield quantum structures with high PL efficiencies in which excitons are strongly localized by interface fluctuations at varying length scales. Spatially-resolved, near-field PL from quantum structures formed during 3D growth reveals reproducible fine structure in the PL spectrum attributed to emission from excitons laterally confined to quantum dot-like regions. Transmission electron microscopy (TEM) studies suggest that these observations result from a combination of island growth and strain-driven interdiffusion.
Effects of Birefringence in Ordered GaInP/AlGaInP Lasers
Authors: Moritz A. , Wirth R. , Geng C. , Scholz F. , Hangleiter A.
Published: April 2011

Ternary semiconductors like GaInP under certain growth conditions exhibit a (partial) chemical ordering in form of a superlattice of alternate Ga-rich and In-rich planes in (111) direction. We have performed measurements of the polarization properties of light propagating in ordered GaInP/AlGaInP quantum well waveguide structures with various amounts of strain and observed a mode conversion between transverse electric (TE) and transverse magnetic (TM) modes for light propagating along (110). Lasers built of ordered material with the cavity in this direction show a distorted polarization of the laser light which depends on ordering and strain. We show that these effects are caused by an optical birefringence due to the reduced symmetry of the ordered material which leads to a coupling of the TE and TM modes. Only a new linear combination of TE and TM modes, the “super-modes”, can propagate in the waveguide without change. Within this simple model the polarization behavior of the light in the waveguide and in lasers can be explained very well.
Modeling of Temperature Increase Due to Joule Heating During Electromigration Measurements
Authors: Liu H. C. Louie , Murarka S. P.
Published: April 2011

Electromigration (EM), the mass transport phenomenon under applied electrical field, is known to cause degradation in interconnections and thus to compromise the devices' reliability. High current density and high temperature conditions are usually adopted to evaluate the EM lifetime. Such high current density will raise the temperature at the test sites because of Joule heating. Thus the actual temperature on the test surface, not the ambient temperature, is an important parameter affecting the lifetime of the metallization. A simple model is proposed here to predict the temperature rise in such interconnections and the calculated values agree well with the experimentally measured rise in temperature. Only heat conduction and convection are considered and illustrative equivalent electrical analogy technique is used to solve the problem. This model, using a commercially available spreadsheet and its iteration functions, is shown to match closely with experimental results.
Electromigration in Submicron Wide Copper Lines
Authors: Kononenko O. V. , Matveev V. N. , Koval Yu. I. , Dubonos S. V. , Volkov V. T.
Published: April 2011

Copper films were deposited onto oxidized silicon wafers by the self-ion assisted technique. A 0 and 6 kV bias was applied to the substrate during the deposition. The films were patterned into parallel line arrays of 20 lines 0.5 mm long, using electron lithography and dry etching. After patterning, the lines were covered by silicon oxide and annealed in vacuum for 1 hour at the temperature 450° C. Electromigration testing was performed in air in the temperature range from 280° to 350° C and at a current density 3.106 A/cm2.

It was found that the resistivities of the films deposited at 6 kV and without bias were 1.7 and 2.0 μΩcm, respectively. The median times to failure are 398.6 and 240 h and the deviations in the time to failure are 0.8 and 0.54 for 6 kV lines and 0 kV lines, respectively. An electromigration activation energy of 0.89 eV was found for 0 kV films.
Phase Formation in Cu(Sn) Alloy Thin Films
Authors: Clevenger L. A. , Arcot B. , Ziegler W. , Colgan E. G. , Hong Q. Z. , d'Heurle F. M. , Cabral C. , Gallo T. A. , Harper J. M. E.
Published: April 2011

The interdiffusion of Cu and Sn and the formation and dissolution of Cu-Sn precipitate phases have been examined for Cu(Sn) alloy thin films. Cu(Sn) films were deposited by electron beam evaporation in either a Sn/Cu bilayer or Cu/Sn/Cu trilayer film structure, with overall Sn concentrations from 0.1 to 5 atomic percent. Analysis by in situ resistivity, calorimetry, electron diffraction and x-ray diffraction measurements indicates that the bilayer and trilayer films form the intermetallic phase η-Cu6 Sn5 during film deposition. Upon heating, the ε-Cu3Sn phase forms at 170°C, then this phase dissolves into the Cu matrix at approximately 350°C. Finally, ζ- Cu10Sn3 phase forms and precipitates after heating to 500°C and cooling to room temperature. The final resistivity of Cu/Sn/Cu films with more than 2 atomic percent Sn was greater than 3.5 μΩ - cm. However, resistivities from 1.9 to 2.5 μΩ - cm after annealing were obtained with Cu/Sn/Cu films containing less than 2 atomic percent Sn.
Chemical Vapor Deposition of Copper Films: Influence Of The Seeding Layers
Authors: Yoon Kyoung-Ryul , Kim Seok , Choi Doo-Jin , Kim Ki-Hwan , Koh Seok-Keun
Published: April 2011

The low pressure chemical vapor deposition of Cu was investigated on TiN substrates that had been locally seeded with thin Cu layers. These Cu layers were 5Å, 40Å and 130Å thick and had been produced by PIB (Partially Ionized Beam) deposition. The growth rate and the XRD peak intensity ratio (I(111)/I(200)) of CVD-Cu increased somewhat in the case of Cu seeded TiN/Si substrates compared with as-received TiN/Si substrate. At the deposition temperature of 200°C, Cu film deposited on the 40Å seeded substrate had the lowest electrical resistivity value, 2.42 μ Ω cm that is as high as 1.5 times the bulk copper value. In adhesion test, as the seeding thickness increased from 0Å to 130Å, the adhesion strength increased from 21 N to 27 N.