bluuebunny/crossref_metadata_2025 huggingface dataset:
Variation of Local Mechanical Stress During the Different Processing Steps of Ic-Isolation: a Micro-Raman Spectroscopy Study
Authors: De Wolf Ingrid , Maes Herman E. , Norström Hans
Published: March 2011

Local mechanical stress introduced in the silicon substrate during the successive steps of poly-buffered local isolation of MOS integrated circuits is studied with micro-Raman spectroscopy. It is shown that the magnitude and the local variation of the stress is highly affected by the different processing steps. After deposition of the nitride mask, the stress can be described as caused by an edge-force. Field oxidation reduces the mask-induced stress but introduces thermal stress from the field oxide. Also the formation of the bird's beak gives rise to additional local tensile stress, especially at the tip of the bird's beak. Removal of the nitride mask results in a partial relaxation: the stress caused by the bird's beak relaxes. In this last stage of the isolation process, the stress image is mostly determined by the field oxide.
Mechanical Stress Measurements in Window-Plated Permalloy Thin Film Strips
Authors: Ross C. A.
Published: March 2011

Mechanical stress measurements in long window-plated strips of permalloy have been made and show an anisotropy in the in-plane stresses. The stress parallel to the strip length is independent of the strip width and thickness, and exceeds the in-plane stress perpendicular to the strip length. The difference between the two stresses depends on the ratio of strip width to thickness, and is in agreement with finite element simulations of stress distributions in similar thin film strips which are etched out of a sheet film of the same material. This result allows calculations of intrinsic stress distributions in more complex window-plated structures. The effect of annealing on the strips is to increase the in-plane stress anisotropy as well as the overall level of stress, by an amount which increases with the annealing temperature.
Growth of Strain-Free GaAs on Si/Sapphire
Authors: Sohn Hyunchul , Weber E.R. , Tu Jay , Smith J.S.
Published: March 2011

GaAs epitaxial layers were successfully grown on Si/Sapphire substrates using Molecular Beam Epitaxy(MBE). Residual compressive strain was found in GaAs films on Si/Sapphire. By Photoluminescence, the magnitude of residual strain in GaAs on Si/Sapphire was estimated to be 5×10-4 which is about one order smaller than that of GaAs on Si.

As an effort to achieve further reduction in the residual strain, Indium- doped GaAs films were used as buffer layers in order to compensate compressive thermal strain by tensile misfit strain in the GaAs layer. Using this method, strain- free GaAs layers could be grown with thickness up to 0.4 μm on Si/Sapphire.
Barriers to Strain Relaxation in Epitaxial Fluorides on Si(111)
Authors: Li Weidan , Hymes Steve , Murarka Shyam P. , Schowalter Leo J.
Published: March 2011

The mechanical stress of epitaxial SrF2 and CaF2 films on Si(111) substrates has been measured as a function of temperature by the substrate curvature technique. The temperature dependence of the stress in the SrF2 film is interpreted in terms of an energy barrier to dislocation motion. When the strain energy is smaller than the value needed to overcome the barrier, the change in stress is due mainly to elastic deformation. As the temperature change increases, the strain energy becomes large enough to overcome the barrier, at which point plastic deformation initiates. Unlike SrF2, the stress behavior of the CaF2 film for increasing temperature is quite different from its behavior for decreasing temperature. This unusual behavior is not understood at this time.
Electronic structure of short-period ZnSe/ZnTe superlattices grown by MOVPE at 300ºC
Authors: Briot N. , Cloitre T. , Briot O. , Boring P. , Ponga B.E. , Gil B. , Aulombard R.L. , Gailhanou M. , Sallese J.M. , Jones A.C.
Published: March 2011

The ZnSe-ZnTe combination is a potential candidate for the realisation of visible light-emitting devices. The lattice mismatch between bulk ZnSe and bulk ZnTe is important (∼ 8%). Therefore, their hetero-structures are strained and high quality superlattices will only be grown if having small periods. This prescription can be fulfilled in the case of metal organic vapour phase epitaxy (MOVPE) growth by combining triethylamine dimethyl zinc adduct with di-isopropyl telluride as precursors for the growth of the ZnTe layers. The growth of high quality ZnTe can then be performed at a temperature of 300ºC , close to the best MOVPE-growth temperature for ZnSe (280ºC). Lowering the growth temperature of ZnTe to this value, we could thus obtain sharp interfaces. This work reports on ZnSe-ZnTe superlattices grown on ZnSe and ZnTe buffers deposited on GaAs substrates. We demonstrate that the stokes-shift between the reflectance and photoluminescence features ( ∼ 40 meV ) measured when the thickness of ZnSe layers does not exceed 20 Å, drastically increases for layer thicknesses beyond this critical value. This, we interpret in terms of the onset of plastic relaxation which favours tellurium diffusion in the ZnSe slices. Then photoluminescence spectra broaden ( contributions of trapped-excitons dominate), and observation of free excitons in reflectance become impossible. We have studied in detail the optical properties of the superlattices and compared our findings with the predictions of a multiband envelope function calculation. We show that both zone centre excitons as well as excitons associated with the miniband dispersions (saddle-point excitons) are observed in these superlattices.
Stability of the Fullerenes Thin Film Deposited on the SI(100) Surface
Authors: Rafii-Tabar H. , Kawazoe Y. , Kamiyama H.
Published: March 2011

We have performed a constant temperature classical molecular dynamics simulation of the epitaxial growth of a C60 monolayer film deposited on the dimerized Si(100) surface. Our simulation, based on non-central many-body inter-atomic potentials, is capable of predicting the structural stability of the C60 film and the Si substrate and provides a theoretical basis for the results of a recently-performed STM- based experiment for this system.

Three-dimensional geometries have been generated on computer and used for the animation of the simulation runs.
Planarization with Cyclotene™ 3022 (BCB) Polymer Coatings
Authors: Stokich T.M. , Fulks C.C. , Bernius M.T. , Burdeaux D.C. , Garrou P.E. , Heistand R.H.
Published: March 2011

This work examines the planarization of polymer thin film coatings derived from Cyclotene™ 3022 prepolymer resins. Cyclotene™ 3022 is a divinyl siloxane bis-benzocyclobutene prepolymer (DVS-BCB, CAS 117732-87-3). It is used primarily as a dielectric in microelectronics applications.

Using profilometry, planarization measurements have been made on thin films spun over features consisting of lines and trenches. Feature widths have been varied from 2 to 1000 μm and the feature depths and film thickness have been varied from 1 to 16 μm. Effects of the processing procedure, resin concentration and resin additives have been explored. Local (versus global) planarization will be discussed.

Planarization has been found to depend on all feature dimensions and the polymer film thickness. Lines or other structures having a width of 100 μm or less can be planarized to 90% or better with standard commercial formulations of Cyclotene™ 3022, provided that the mean film thickness is twice the line-height or feature-depth. Metals such as Al, Cu, Cr and Ti can all be planarized to this degree; however, surface preparations may influence the result.
Modeling Stresses in Polyimide Films
Authors: Pottiger Michael T. , Coburn John C.
Published: March 2011

The trend towards higher density and smaller feature sizes in today's devices, and the increasing costs associated with designing and manufacturing these devices, has placed a greater emphasis on obtaining an a priori understanding of how various materials will perform in a device. A number of manufacturers have turned to computer modeling, utilizing finite element analysis to aid in the design of new devices and reduce the costs associated with preparing prototypes. The use of computer modeling requires a constitutive equation relating the response of a material to an applied load. Polymer behavior is complex and writing an equation or a series of equations that describe the behavior of the polymer over the entire range of possible temperatures and deformations is nontrivial. Instead, series of equations that describe ideal material behavior are used in an attempt to describe the behavior of real materials over a narrow range of temperatures and deformations. For solids, the ideal material response that is generally used to describe real polymer behavior is linear elasticity.
Mechanical Properties of Excimer Laser Modified Titanium Surfaces
Authors: Jervis T. R. , Zocco T. G. , Hubbard K. M. , Nastasi M.
Published: March 2011

Excimer laser processing enables both thermally-driven transformations and the incorporation of solutes into the surface of materials through melting and diffusional mixing. We have examined the effect of excimer laser processing on the microstructure and surface mechanical properties of titanium alloys. Changes in the surface hardness due to laser processing were studied using a Nanoindenter™. Alloying experiments using both mixing of evaporated surface layers of boron and laser gas alloying in air and in nitrogen all result in changes in the surface hardness of the material. Alloying with boron results in an amorphous surface which is somewhat harder than the as polished surface. Laser processing in air and pure nitrogen results in incorporation of oxygen and nitrogen and the development of fine precipitates of TiO and TiN respectively. Substantial increases in surface hardness result due to solution and precipitation mechanisms. Nanoindenter™ data from several depths in the material are correlated with microstructure and solute concentration to illuminate the strengthening mechanisms involved.
Hrem Study of Fracture and Deformation Behavior of Nanostructured Thin Films
Authors: Ke Ming , Milligan Walter W. , Hackney Stephen A. , Carsley John E. , Aifantis Elias C.
Published: March 2011

Nanocrystalline gold and nickel thin films were prepared by both ion beam sputter deposition and electron beam evaporation techniques. The grain sizes were between 8–60 nm, depending on the processing. The deformation and fracture behavior of these nanostructural thin films were then investigated in a high resolution electron microscope (HREM) with atomic resolution. The behavior was a strong function of grain size. During slow strain rate deformation of small grain size materials (< 25 nm), nanopores formed and grew at grain boundary triple junctions in the front of crack and eventually linked with the main crack. The coalescence of the main crack with the growing nanopore, along with the elimination of the ligament between the two by a diffusive process, both indicated that diffusion played a role in deformation and fracture of these nanocrystalline thin films. In nickel films with larger grain sizes (> 25 nm), the cracks propagated in a mixed mode which was partially intergranular and partially transgranular. The transgranular propagation was crystallographic in nature, showing very fine, distinct crystallographic facets on the crack faces. It is suggested that a transition from intergranular propagation to a “cleavage-like” mechanism of propagation occurs with the increase of grain size.
The Role of Indentation Depth on the Measured Hardness of Materials
Authors: Shell De Guzman Melissa , Neubauer Gabi , Flinn Paul , Nix William D.
Published: March 2011

Ultra micro-indentation tests on Ni and Cu samples showed increasing hardness with decreasing penetration depth over a range from 200 to 2000 nm. The results suggest increased strain hardening with decreased indentation depth. To establish that this is a real material effect, a series of tests were conducted on amorphous materials, for which strain hardening is not expected. The hardness of Metglas® was found to be independent of depth. A simple model of the dislocation densities produced under the indenter tip describes the data well. The model is based on the fact that the high density of dislocations expected under a shallow indentation would cause an increase in measured hardness. At large depths, the density of geometrically necessary dislocations is sufficiently small to have little effect on hardness, and the measured hardness approaches the intrinsic hardness of the material.
Adhesion Properties of Metallic and Oxide Thin Films Produced by Several Methods
Authors: Ottermann C. , Tadokoro N. , Tomita Y. , Bange K.
Published: March 2011

Adhesion of Cr, SiO2, TiO2 and Ta2O5 films with thicknesses between 40 nm and 380 nm has been investigated using a new scratch-test method based on a vibrating diamond micro-indenter. The oxide films are produced on different substrates by sol-gel technique (SG), reactive evaporation (RE), reactive ion plating (IP) and plasma impulse chemical vapor deposition (PICVD); Cr-layers are deposited by sputtering (SP) on quartz. Large variations in adhesion are found for different coating techniques and deposition conditions, especially the substrate temperature. The adhesion can be correlated with microscopic properties in the film-substrate interface where differences are analyzed in term of hydrogen content, film growth and density. The adhesion is also connected with other macroscopic film quantities.
Stress-Corrosion Cracking and Blistering of Thin Polycrystalline Silicon Films in Hydrofluoric Acid
Authors: Monk D.J. , Krulevitch P. , Howe R.T. , Johnson G.C.
Published: March 2011

Thin (0.1 μm) LPCVD polycrystalline silicon (poly-Si) films are shown to exhibit permeability and suffer structural degradation when exposed to concentrated hydrofluoric acid. Analysis by TEM and SEM reveals two attack mechanisms. (1) Poly-Si films deposited onto phosphosilicate glass (PSG) at 605ºC exhibit tensile residual stress and degrade immediately upon exposure to HF, a phenomenon which we attribute to stress-corrosion cracking. Phosphorus from the PSG layer enters the poly-Si during the deposition, resulting in a microstructural gradient which contributes to the cracking mechanism. (2) As-deposited tensile poly-Si films on phosphorus-free LPCVD SiO2 (LTO) and annealed films on LTO and PSG blister at different rates in HF due to penetration at foreign particle inclusion sites and other film defects. Unannealed compressive films deposited at 650ºC onto PSG do not show any evidence of attack.
Fracture Toughness of Silicon and Thin Film Micro-structures by Wedge Indentation
Authors: de Boer M.P. , Huang He , Nelson J.C. , Jiang Z.P. , Gerberich W.W.
Published: March 2011

Silicon rooftop structures 30 µm high and of 1 µm linewidth were fabricated in a microelectronics facility using anistropic KOH etching. Aluminum-1% silicon was sputter-deposited to investigate the effects of a ductile thin film on the fracture toughness of a brittle material. The rooftop structures were indented by a Knoop indenter purposely placed off-center so that the indenter was wedge-shaped. Deformation and cracks were photographed by SEM. Crack threshold load per unit width are reported for normal cracks, running perpendicular to the roofline. Fracture toughness is calculated by first order approximation and finite element modeling using SEM measurements of the length of normal cracks. Without a thin film, values for silicon are in reasonable agreement with the literature. With a thin film of only 600 Å, fracture toughness is increased by 45%. Cracks nearly parallel to the roofline also appeared at higher load values. Characteristics of both types of cracks are discussed.
Mechanical Characterization of Diamond-Like Carbon (DLC) Coated Polycarbonates
Authors: Hsieh Alex J. , Huang Paul , Venkataraman Shankar K. , Kohlstedt David L.
Published: March 2011

Evaluations of DLC coated polycarbonates have been carried out via high speed projectile impact, three point bend, and continuous microscratch tests. Radial and circumferential microcracks appeared on the back surfaces and near the regions of impact as a result of the high speed impact stresses. Despite the impact, the adhesion of the DLC coating in the area between the cracks remained, except in the immediate vicinity of impact. In the three point bend tests, transverse cracks developed and propagated in the DLC coating when the applied strain reached the fracture limit of the coating. No delamination occurred in the continuous microscratch tests; instead, cracking of the coating was observed in DLC coated polycarbonates. Microcracking was the dominant mode of failure which was consistent in these three diversed mechanical tests. Results of the SEM studies further confirmed microcracking prior to delamination as observed in the high speed impact tested coupons.
Internal Stress Measurement on CVD diamond Coatings by X-ray Diffraction and Raman Spectroscopy
Authors: Van Acker K. , Mohrbacher H. , Blanpain B. , Van Houtte P. , Celis J.P.
Published: March 2011

Internal stresses are measured in CVD diamond coatings deposited on a variety of substrate materials by low incident beam angle X-ray diffraction and by micro-Raman spectroscopy. The X-ray diffraction technique gives an integral stress value over a comparably large coating area whereas the Raman technique results in localized stress information with a lateral resolution of down to 1 µm. The stress values obtained from both methods compare well for diamond coatings of 6 μm thickness whereas a difference is observed for thicker coatings.
Mechanical Properties and Residual Stresses in Oxide/Metal Multilayer Films Synthesized by Ion Beam Assisted Deposition
Authors: Kalnas C. E. , Parfitt L. J. , Goldiner M. G. , Was G. S. , Jones J. W.
Published: March 2011

Films of Al, Al2O3 and Al/Al2O3 microlaminates were formed by ion beam assisted deposition (IBAD) at R ratios from 0.0025 to 0.5 and film thicknesses between 150 and 2600 nm. Oxide films were amorphous while metal layers were crystalline with small grains and texture for both PVD and IBAD conditions. The average stress in the oxide film is tensile at R=0 and becomes compressive, saturating at approximately 15 eV/atom. The residual stress in the Al films is tensile over all R ratios and the stress in the microlaminate roughly follows a rule of mixtures. Deformation of ductile substrates on which films had been deposited revealed that the critical strain to fracture was strongly dependent on residual stress. Large compressive stresses in monolithic films produced by ion beam assisted deposition delayed the onset of crack initiation while the presence of multiple layers, in general, lowered the crack density at saturation, suggesting a possible ductilizing effect.
Thermomechanical Behaviour of AgNi Multilayers and Magnetoelastic Effects
Authors: Pelosin V. , Rodmacq B. , Teixeira S.R. , Hillairet J. , Carlotti G.
Published: March 2011

The elastic and anelastic properties of AgNi multilayers prepared by sputtering were investigated during the course of anneal cycles. The respective temperature variations of some of the elastic constants and moduli were followed by Brillouin scattering and dynamical methods based on use of a torsion pendulum and a vibrating-reed system. The last two enabled to investigate the internal damping associated with the presence of two-dimensional defects. It appears that the motion of interfaces and grain boundaries is inhibited by the high defect density. In contrast, substantial effects associated with the motion of the magnetic domain walls were evidenced. Concurrently, internal stresses were studied by in situ deflection measurements. Flow stress values on the order of 1 GPa were observed. Dilatometry experiments showed that a large part of the non-recoverable modifications in the state of stress induced by thermal cycling originates in the densification of the material.
X-ray Analysis of Ni/Ti Multilayers
Authors: Chaudhuri J. , Alyan S.M. , Jankowski A.F.
Published: March 2011

The structure, composition and strain in Ni/Ti multilayers are analyzed using x-ray diffraction theories. The repeat period of the multilayers used in this study ranges from 1.3 to 12.8 nm. The composition modulation is obtained by using a kinematical theory of x-ray diffraction. A sine wave for the shorter repeat period and a rectangular wave for the longer repeat period are predicted for the composition modulation. The strain within each atomic layer is found by iteratively fitting the experimental x-ray diffraction pattern with the simulated one from a dynamical theory of x-ray diffraction. The strain at the interface is tensile in Ni and compressive in Ti with a complete relaxation of the strain at a distance away from the interface.
The Structure and Mechanical Properties of Ru-Cu and Ru-Ti Nanolayer Composites
Authors: Kung H. , Nastasi M. , Jervis T. R. , Hubbard K.M. , Messner R.M. , Mitchell T.E. , Embury J.D.
Published: March 2011

Multilayers of Ru-Cu and Ru-Ti have been prepared by electron beam evaporation technique. One set of composites has Ru thickness varying from 250 to 2500Å alternating with Cu or Ti of 15Å. The other set has 250Å of Ru and the Cu or Ti layer varies between 15 and 200Å. Nanoindentation measurements show that there is no significant change in hardness as either Ru or Cu/Ti thickness varies. However, the Ru-Cu multilayer has twice the hardness of the Ru-Ti system. High resolution transmission electron microscopy discloses that there is an epitaxial orientation relationship between Ru and Ti in Ru-Ti while no such relationship exists in Ru-Cu.

The strengthening mechanism proposed by Koehler [1] predicts that Ru-Ti composites should have a higher strength than Ru-Cu due to the larger modulus difference between Ru and Ti. The discrepancy between the prediction and the experimental results suggests that other strengthening mechanism(s) may be operating. We have proposed two models based on a "shear" mechanism to explain the differences observed between these two systems. The effects of these mechanisms in controlling the deformation process in nanolayer composites are discussed.
Use of Magneto-Optic Kerr Effect Measurements to Study Strain and Misfit Accommodation in Thin Films of Ni/Cu (100)
Authors: Inglefield H.E. , Ballentine C.A. , Bochi G. , Bogomolov S.S. , O'Handley R.C. , Thompson C.V.
Published: March 2011

We have detected magnetic transitions in Ni/Cu (100) films as a function of Ni thickness through in situ measurements of the magneto-optic Kerr effect (MOKE). Crystalline quality was monitored using in situ RHEED and Auger electron spectroscopy. Films were deposited by molecular beam epitaxy on silicon wafers and cleaved sodium chloride with varying epitaxial Ni layer thicknesses between 10 and 200 A. High-resolution TEM images of these films indicate decreasing misfit dislocation spacing and decreasing strain as measured by moiré fringe analysis with increasing Ni thickness. These observations have been correlated with changes in magnetic anisotropy as measured by MOKE. MOKE, therefore, may provide a tool for in situ monitoring of the kinetics of misfit accommodation in magnetic thin films.
Stress-Temperature Behavior of O3-TEOS Sub-Atmospheric CVD (SACVD) Oxide Films Deposited on Various Oxide Underlayers
Authors: Robles Stuardo A. , Yieh Ellie , Galiano Maria , kwok Kurt , Nguyen Bang C.
Published: March 2011

A systematic evaluation of the stress-temperature behavior of O3-TEOS Sub-Atmospheric CVD (SACVD) oxide films used in IMD applications was performed in order to elucidate the surface dependence and mechanical stability of these films when deposited on different oxide underlayers such as PECVD TEOS-based, Silane-based, and thermally grown oxides. SACVD films were deposited at 360°C using different O3:TEOS molar flow ratios. The results obtained in this study indicate that the stress-temperature behavior of SACVD films deposited on PECVD Silane-based and TEOS-based oxides using N2O as the oxidizing agent is similar to that of the SACVD films deposited on silicon. However, a large stress hysteresis is obtained when SACVD films are deposited on PECVD TEOS-O2 and thermally grown oxide underlayers. This large stress hysteresis results from the surface dependence effects of the SACVD oxides on thermally grown and PECVD TEOS-O2 oxide underlayers. Also, this stress hysteresis can be reduced or eliminated by treating the oxide underlayer surface with an in-situ Ar, He, or N2 plasma. Furthermore, it was also found that the SACVD oxides deposited using higher O3:TEOS molar flow ratios are chemically and mechanically more stable.
Elastic Properties of Sputtered Thin Films: Influence of Different Preparation Conditions
Authors: Bottani C.E. , Elena M. , Beghi M. , Ghislotti G. , Guzman L. , Miotello A. , Ossi P.M.
Published: March 2011

This work presents the first results of a study aimed at better understanding the elastic behaviour of hard coatings produced by various techniques. This is important also in view of the need to be able to control the level of internal stresses, particularly in PVD coatings. It is well known that in extreme cases excessive internal stress can lead to complete film destruction. We devote this paper to reactively magnetron sputtered TiN, one of the most widely used compounds. Thin TiN films of different compositions were deposited on Si substrates and characterized by SEM, AES, XRD and Brillouin light scattering.
TEM Investigation of Microwave Joined Si-SiC/Al/Si-SiC and α-SiC/Al/α-SiC.
Authors: Arunajatesan S. , Carim A. H. , Yiin T. Y. , Varadan V. K.
Published: March 2011

Electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) have been used to examine the SiC/Al interfaces in microwave joined Si-SiC/Al/Si-SiC and α-SiC/Al/α-SiC. Both the SiC/Al interfaces display intimate contact between the ceramic and metal and are free of porosity. EPMA of the α-SiC/Al/α-SiC joints reveals that no Al has diffused into the bulk α-SiC, unlike the reported diffusion of Al in Si-SiC/Al/Si-SiC. The TEM investigations show that while the Si-SiC/Al/Si-SiC interface is reaction-free, the α-SiC/Al/α-SiC joint contains Si at the interface. The TEM findings are correlated to the strength data available on these joints and the possible reasons for the presence of Si in the absence of Al4C3 in the α-SiC/Al/α-SiC joint are discussed.
Rapid Infrared Joining of Titanium Alloys and Titanium Matrix Composites
Authors: Blue Craig A. , Lin Ray Y.
Published: March 2011

A rapid infrared joining (RIJ) technique has been developed at the University of Cincinnati for high temperature materials. This technique takes only a few seconds to a few minutes to join parts up to 1.8 cm in thickness. The advantages of the RIJ technique are quick, simple, inexpensive, no vacuum or pressure needed, no effect on the microstructure of the base material, flexible and feasible for portable operation. For titanium joining, both Ti-6AI-4V and β21S/SCS-6 composite have been successfully joined with infrared at about 1000 °C for 30 seconds in argon with a TiNiCu brazing alloy. The maximum joint shear strength is up to 554 MPa, which is higher than that of any bond joined with conventional brazing techniques. Our study has shown that the longer the joining time, the wider the joining affected zone. Prolonged joining cycles allow for attack of the titanium alloy by the molten brazing alloy. Results from the titanium matrix composite (TMC) joining show that the joining strength for the infrared bonded parts is superior to those processed with the conventional techniques.
Capacitor Discharge and Flash Welding of Sic-Reinforced High Temperature Al Alloys
Authors: Schwartz D. S. , Devletian J. H. , Chen S. J. , Gould J.
Published: March 2011

Discontinuously reinforced Al alloys (DRAs) are difficult to join using conventional fusion welding techniques due to inhomogeneous redistribution of the reinforcements and reaction between molten Al and SiC. Two specialized welding techniques, capacitor discharge welding and flash welding, were assessed as possible ways to avoid these problems. Using these techniques, welds were made with two DRAs: 8009/SiC/llp and 2009/SiC/15w. Capacitor discharge welding resulted in the formation of Al-carbides in the weld zones, but flash welding produced satisfactory joints in both DRAs.
Direct Bonding Method of Aluminum to Stainless Steel by Pressure Casting of Aluminum
Authors: Suganuma Katsuaki
Published: March 2011

A new process for joining Al to stainless steel has been established by using pressure casting of Al in air. Blocks of AISI type 304 austenitic stainless steel to be joined were placed in a mold and were preheated at 450 °C – 600 °C in air. Molten Al was poured into the mold and a pressure of 50 MPa was applied immediately. Stainless steel was tightly bonded to Al by the present process. At the optimum preheating condition, the interface strength was higher than that of Al and fracture did not occur at the interface. At the interface, an intermetallic compound layer was formed, and it was analyzed by TEM. Because this process can be carried out in air by casting of Al, the process has a potential for the mass-production of Al/stainless steel joints or clads.
Wafer Bonding for Hybrid Circuit Technology Using Solid-State Reactions
Authors: Ma Z. , Zhou G. L. , Shen T. C. , Lin M. E. , Hsieh K. C. , Allen L. H. , Morkoç H.
Published: March 2011

In this study, we report a new wafer bonding technique for the integration of GaAs- and InP-based optical devices with prefabricated Si electronic devices in hybrid circuit technology. This technique uses a Au-Ge eutectic alloy as the bonding materials between GaAs and Si wafers, and between InP and Si wafers. This process takes advantage of the low temperature solid-state reactions at GaAs/Au-Ge, InP/Au-Ge, and Si/Au-Ge interfaces. The bonding was carried out by annealing the samples at 280–300°C in an alloying furnace. The reliability of the joined wafers was evaluated by both cleavage test and standard thermal cycling test. The joining interfaces were characterized by scanning electron microscopy and transmission electron microscopy. The results reveal that the bonding is achieved by low temperature reactions at the GaAs/Au-Ge and InP/Au-Ge interfaces as well as solid-phase epitaxial regrowth at the Si interfaces. The joined structure has very good integrity.
Microstructural Investigation of κ-Modification Layers in CVD α-Al2 O3/K-Al2 O 3 Multilayer Coatings
Authors: Halvarsson Mats , Vuorinen Sakari , Nordén Hans
Published: March 2011

Multi layer alumina coatings consisting of layers of either pure α-A12 O3 or κ-Al2O3, were deposited in a hot wall CVD reactor. In order to nucleate and grow a desired alumina polymorph (α/κ) in each layer, thin α- and κ-modification layers were deposited between the alumina layers. This investigation examines the interfacial structure of the κ-modification and the alumina layers. The materials were examined using a combination of XRD, SEM, TEM and EDX.

The κ-modification layers exhibited an FCC structure and were composed of (Ti,AI)(C,O). Orientation relationships were frequently found at the (i) α-A12O3/κ-modification/κ-A12O3 layer interfaces and (ii) κ- A12O3/κ-modification/κ- A12O3 layer interfaces:
Synthesis and Characterization of Metal Silicide/Silicon Carbide Composites by Low Temperature Solid-State Reactions
Authors: Zeng D. , Hampden-Smith M. J. , Wang L.-M.
Published: March 2011

Co-reduction of mixtures of MoCl3(THF)3 and SiCls4 in THF using Li/C10H8 or both Li/C10Hs8 and LiBEt3H resulted in formation and separation of black powders which upon thermal annealing at temperatures ranging from 750°C to 1 100°C produced crystalline molybdenum silicide and silicon carbide composite. Co-reduction of mixtures of WCI4 and GeBr4 with LiBEt3H in THF formed W2C and elemental Ge which upon thermal treatment at 750°C for 4 hours generated a small amount of crystalline W5Ge3.
Plasticity of MoSi2 Below 900°C
Authors: Chang H. , Gibala R.
Published: March 2011

The mechanical behavior of polycrystalline MoSi2 tested in compression at temperatures from 750°C to 950°C has been investigated. This material can be deformed to several percent strain without fracture at temperatures as low as 900°C. This same material prestrained at 1300°C and subsequently tested at lower temperatures can be deformed to substantial strain at 800°C, and even exhibits modest plasticity at 750°C. Both prestrained and unprestrained materials exhibit microcracking combined with dislocation substructures containing high densities of dislocations. Unprestrained MoSi2 exhibits a yield point in this temperature range which does not exist when it is prestrained. The stress-strain curves of the prestrained material in this temperature range are similar qualitatively to those of the unprestrained material at 1100°C and above. These observations suggest that at these temperatures MoSi2 is a dislocation density limited material which can deform by dislocation plasticity processes if a sufficient dislocation density is available.
Microstructure and Mechanical Properties of Nitrided Molybdenum Silicide Coatings
Authors: Hirvonen J-P. , Suni I. , Kattelus H. , Lappalainen R. , Torri P. , Kung H. , Jervis T.R. , Nastasi M.
Published: March 2011

Mo-Si-N films with a high nitrogen concentration were produced by sputter-deposition in the presence of nitrogen plasma. The chemical composition was determined with Rutherford backscattering and nuclear reaction analysis. The ratio of Mo to Si was 1:2 in the coatings with a nitrogen concentration of 50 %. The microstructure of the as-deposited coatings on a silicon substrate was amorphous and no crystallization was found after annealing up to 1000 °C, although some relaxation was observed in X-ray diffraction. This was confirmed in highresolution transmission electron microscope examination. The hardness of the Mo-Si-N films was 18.8 GPa as determined with a nanoindenter. This is significantly higher than that of MoSi2 films, 11.2 GPa. The hardness of the Mo-Si-N films increased to 24.4 GPa after annealing at 800 °C, which is approximately the same as the hardness of the high-temperature tetragonal phase of MoSi2, 25.5 GPa. Similarly, the modulus of the as-deposited Mo-Si-N film was higher (257 GPa) than that of the MOSi2 film (222 GPa). However, only a slight increase in the modulus of the Mo-Si-N film was found after annealing at 800 °C, whereas the modulus of the crystallized tetragonal MoSi2 was 382 GPa. No cracking was found in the Mo-Si-N films even after annealing at 1000 °C.
High Temperature Silicide Thin-Film Thermocouples
Authors: Kreider Kenneth G.
Published: March 2011

High-temperature silicides have been used in mechanical structures, heating elements, and electronic, CMOS applications. Their stability in high temperature oxidizing environments and excellent electrical conductivity may also make them useful as high temperature thin-film sensors in harsh environments. We have investigated sputter deposited MoSi2, ReSi2, TaSi2, TiSi2, and WSi2 thin films and characterized their performance as thermoelements and stability up to 1200 °C. A multilayer technique was developed to ensure constant silicide stoichiometry during oxidation thereby maintaining a constant Seebeck coefficient. In addition techniques were developed to suppress the formation of metal oxides from the silicides. The results indicated excellent stability of Seebeck coefficient up to 1200 °C. These results are compared with the problems of thin film instability in the Seebeck coefficient found in noble metal thermocouples. Potential applications for temperature and heat transfer measurements will be discussed.
Overview of High Temperature Structural Silicides
Authors: Petrovic J.J. , Vasudevan A.K.
Published: March 2011

High temperature structural silicides represent an important new class of structural materials, with significant potential applications in the range of 1200-1600 °C under oxidizing and aggressive environments. Silicides, particularly those based on MoSi2, are considered to be promising due to their combination of high melting point, elevated temperature oxidation resistance, brittle-to-ductile transition, and electrical conductivity. Possible structural uses for silicides include their application as matrices in structural silicide composites, as reinforcements for structural ceramic matrix composites, as high temperature joining materials for structural ceramic components, and as oxidation-resistant coatings for refractory metals and carbon-based materials. The historical development of structural silicides, their potential applications, and important issues related to their use are discussed.
The Properties and Uses of Refractory Metals and Their Alloys
Authors: Briant C.L.
Published: March 2011

This paper reviews the problems that have limited the applications of refractory metals and their alloys. It also presents examples from recent work that has been done to overcome these problems. The work discussed concerns the refractory metals niobium, tantalum, molybdenum, and tungsten and alloys based on these elements. Recent results on intermetallic compounds that contain a refractory metal and composites that are made of refractory metals and their intermetallics are also presented.
Recent Advances and Developments in Refractory Alloys
Authors: Nieh T.G. , Wadsworth J.
Published: March 2011

Refractory metal alloys based on Mo, W, Re, Ta, and Nb (Cb) find applications in a wide range of aerospace applications because of their high melting points and high-temperature strength. In this paper, we present recent progress in the understanding and applications of these alloys. Recent studies to improve the oxidation and mechanical behavior of refractory metal alloys, and particularly Nb alloys, will also be discussed. Some Re structures, for extremely high temperature applications (> 2000°C), made by CVD and P/M processes, are also illustrated. Interesting work on the development of new W alloys (W-HfC-X) and the characterization of some commercial refractory metals, e.g., K-doped W, TZM, and Nb-l%Zr, continues. Finally, recent developments in high temperature composites reinforced with refractory metal filaments, and refractory metal-based intermetallics, e.g., Nb3A1, Nb2Be17, and MoSi2, are briefly described.
Directional Solidification of Refractory Intermetallics: Single Crystals and Composites
Authors: Pope David P. , Shah Dilip M. , Romanow William , Huntley Mark
Published: March 2011

Directional solidification of intermetallic compounds using the optical imaging floating zone technique is discussed. The advantages and disadvantages of the technique are described, and the systems to which this technique has been applied are listed. Finally, application of the technique to growing in situ Cr2Nb/Nb composites is described. It is shown that well aligned, fine microstructures can be obtained using the technique. The aspect ratio of the Cr2Nb platelets is 200:1, or better, and are a few microns thick. The Cr2Nb has a strong <220> texture along the growth axis but the Nb is nearly random.
Investigation of B2 and Related Phases in Ti-Modified Nb-Al Alloys
Authors: Hou D.-H. , Yang S.S. , Shyue J. , Fraser H.L.
Published: March 2011

The B2 ordering and phase stability of three ordered intermetallic alloys with compositions (in at.%) of Nb-15Al-10Ti (10Ti alloy), Nb-15A1-40Ti (40Ti alloy), and Nb-15Al-25Ti (25Ti alloy) have been studied. All three alloys have the B2 crystal structure in the as-cast form. The Atom Location by Channeling Enhanced Microanalysis (ALCHEMI) technique has been employed to assess the site occupancy of these B2 alloys. The results of site occupancy are represented as Ordering Tie Lines on a ternary composition diagram. Various second phases were observed in heat treated samples. An ω-type phase was found in the 1OTi alloy in samples heat treated for 10 minutes and 4 hours at 900°C. At 800°C, orthorhombic phase was found in the 40Ti alloy while a three phase microstructure of o-phase/B2/A15 was observed in both the 10Ti and 25Ti alloys. Annealing at 1100°C leads to the dissolution of the o-phase and the presence of A15 phase in the 10Ti and 25Ti alloys, but no other phase in the 40Ti alloy. The observed phase equilibria in these alloys are compared with those in the literature.
Properties of Microlaminated Intermetallic-Refractory Metal Composites
Authors: Rowe R. G. , Skelly D. W. , Larsen M. , Heathcote J. , Lucas G. , Odette G. R.
Published: March 2011

Microlaminated composites of Nb3Al-Nb and Cr2Nb-Nb(Cr) were synthesized by high rate magnetron sputtering. Both composites were stable at elevated temperatures. A Cr2Nb-Nb(Cr) composite with 2 µm metal and intermetallic layers had room temperature tensile fracture strength over 725 MPa and a fracture toughness of about 20 MPa√m. Composites with 2 µm and 6 µm thick refractory metal and intermetallic laminations were compared and it was found that layer thickness did not affect fracture toughness. Microlaminates with the thicker 6 µm laminations had lower fracture strength, however. Good fracture strength and high fracture toughness indicated that microlaminated high temperature composites synthesized by vapor phase deposition exhibit the properties predicted by ductile toughening models.
Effects of Environmental Exposure on Ductile-Phase Toughening in Niobium Silicide-Niobium Composites
Authors: Rigney Joseph D. , Singh Preet M. , Lewandowski John J.
Published: March 2011

A variety of materials have been toughened by incorporating ductile phases. Brittle silicide intermetallics such as Nb5Si3 composited with niobium particles incorporated during in situ processing techniques have realized significant improvements in toughness and stable crack extension. In the present work, toughness tests conducted on Nb5Si3/Nb materials monitored in a scanning electron microscope were instrumental in viewing the role of the deforming niobium particles on the process of toughening. In particular, the behavior of the ductile phase was monitored and related to the toughness values obtained. In an attempt to vary the behavior of the ductile phase, the composite materials were exposed to a variety of gaseous environments and subsequently tested in air. The resulting toughness, resistance-curve behavior, and in situ test results highlight the importance of the behavior of the ductile phase on subsequent properties.
Application of Tungsten Alloys in the Lighting Industry
Authors: Bartha L.
Published: March 2011

The properties of W alloys are determined by the extremely high melting point of the W. The alloys can be prepared mainly by powder metallurgical processing. Their equilibrium concentration is limited by the partial pressure of the alloying component at the temperature of preparation or application and is generally low.
Potassium in Grain Boundaries of Tungsten
Authors: Vukcevich Milan R.
Published: March 2011

Most of the recent work on the role of potassium in tungsten wire deals with the origin of bubbles and their effect on the recrystallization process. Two very important areas are neglected: the effect of potassium strings on the mechanical properties of wire during manufacturing, and the differences in distribution of bubbles in the grain boundaries vs. the bulk. Although other advances in our understanding of potassium in tungsten are reviewed, the main attention is on these two neglected areas. Derived are expressions for the yield point of the fibrous wire structure, and for the increased concentration of bubbles in the transverse boundaries. The theory and experiments are in good agreement.
Various Properties of Sputtered TaxAl1-x Films
Authors: Minkiewicz V.J. , Moore J.O. , Keller G. , Woodman S.J. , Dobbertin D. , Savoy R. , Eldridge J.M.
Published: March 2011

Films of TaxxAl1-x have been prepared by diode sputtering from a target consisting of an Al mask placed on the face of a Ta target. The Ta target was 8″ in diameter while the Al mask was 0.125″ thick and machined with a grid-like shape. Films were deposited for a range of pressure, at a power of 300 watts, onto oxidized 100 mm diameter Si substrates that were placed on a planetary table beneath the target. The Al/Ta area ratio of the composite target was determined on the basis of the relative sputtering rates for these metals with the intent of producing a film composition with x = 0.5. The film composition was found to vary with argon pressure, going from 24 at.% Al at 4 mtorr to 72 at.% Al at 30 mtorr. This finding was quite unexpected. This result made it possible to deposit a wide range of film compositions from one composite target. The electrical resistivity has a broad maximum of,≈ 240 micro-ohm/cm between x=0.3 and 0.6. These results compliment and extend the earlier observations by Steidel \1] The as-deposited stress of the films varied from -400 to +150 MPa as x was decreased from 0.76 to 0.28. The temperature dependence of the film stress is hysteretic on the first cycle to 475 C. After the first cycle the films are driven more into tension by as much as 500 Mpa. The oxidation characteristics of one composition Ta0.66Al0.34 were characterized in some detail using a combination of electrical resistance, AES and XPS measurements. The results show that such films oxidize at temperatures in the 300 to 600C range via a diffusion-controlled process with an activation energy of 0.98 eV. Such films are substantially more oxidation-resistant than either ccα-or β-tantalum.
The Application of Reactive Hot Compaction and In-Situ Coating Techniques to Intermetallic Matrix Composites
Authors: Doty H. , Somerday M. , Abbaschian R.
Published: March 2011

An overview of the application of the reactive hot compaction (RHC) process to fabricate various intermetallics such as silicides and aluminides is presented. Specific examples with the in-situ formation of diffusion barrier coatings on refractory metal reinforcements during RHC are also given. The processing involves blending the elemental powders with pre-treated refractory metal filaments and reactively synthesizing the mixture at elevated temperatures. During this process, the treated surfaces of the filaments react with one of the components (e.g. Al for aluminides or Si for silicides) to form in-situ a protective surface coating. The important influence of the RHC reaction sequence and rate on the consolidation of the composite are discussed. Finally, the fracture toughness of the composites are related to the various toughening mechanisms, with special emphasis on the role of the interfacial layer.
Ge+ Preamorphization of Si: Effects of Dose and Very Low Temperature Thermal Treatment on Extended Defect Formation During Subsequent Spe
Authors: Myers E. , Rozgonyi G. A. , Sadana D. K. , Maszara W. , Wortman J. J. , Narayan J.
Published: March 2011

Cross-section transmission electron microscopy (X-TEM) has been used to illustrate the amornhous/ crystalline (a/c) micromorphology dependence of various low dose Ge+ preamorphizatlon implants in Si. Ge+ Implants were done at room _emperature at energies of 150 and 300 keV in the dose range of 1 to 9E14 cm−2. These implants result in the formation of either a buried or a continuous amorphous layer, with rough a/c interfaces. Nucleation of spanning “hairpin” dislocations during subsequent solid phase epltaxy (SPE) regrowth is known to be related to rough a/c interface morphology. Very low temperature anneals (VLTA),less than 500°C where the rate of SPE is minimal, were utilized to sharpen rough a/c interfaces prior to subsequent SPE regrowth. Sharpening of rough a/c interfaces is shown to result from an unexpected reverse crystalline to amorphous phase transition. This reverse phase transition results in the dissolution of detached microcrystallltes located within the amorphous layer near the a/c interface. Utilization of VLTA interfacial smoothing prior to SPE regrowth therfore, results in the reduction of residual spanning “hairpin” dislocations along with homogenization of the amorphous material.