bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-Term Stability of Nickel in Resonant Micro-Mechanical Devices
Authors: Povirk G.L. , Bernstein J. , Brown S.B.
Published: March 2011

A nickel micromechanical device was resonated and the natural frequency of the structure was monitored over time. Any structural rearrangement or damage initiation in the material was expected to cause a corresponding change in the resonant frequency of the device. The resonant frequency of the device was initially about 31.8 kHz and the frequency was found to decline over time at a rate of 0.17 Hz/s.
A Quantitative Model for Interpreting Nanometer Scale Hardness Measurements of Thin Films
Authors: Poisl W.H. , Fabes B.D. , Oliver W.C.
Published: March 2011

A model has been developed to determine the hardness of thin films from the measured change in hardness with indenter displacement using a depth-sensing indentation instrument. The model is developed by dividing the measured hardness into film and substrate contributions based on the projected areas of both the film and substrate under the indenter. The model incorporates constraints on the deformation of the film by the surrounding material in the film, the substrate, and friction at the indenter/film and film/substrate interfaces. These constraints increase the pressure that the film can withstand and account for the increase in measured hardness as the indenter approaches the substrate.

The model is evaluated by fitting the predicted hardness versus depth curves to data obtained from titanium and Ta2O5 films of varying thicknesses on sapphire substrates. The model predicts a lower interfacial strength for Ta2O5 films on sapphire with a carbon layer between the film and the substrate than that obtained for a film without an interfacial carbon layer.
The Analysis of Depth-Sensing Indentation Data: Review of the Special Discussion Session
Authors: Baker Shefford P. , Weihs T.P.
Published: March 2011

In light of recent advances in the analysis of depth-sensing indentation data and of the importance of this technique in the study of the mechanical properties of thin films, a special discussion session was held in order to explore the state of the art and to provide an informal forum for discussion. This is a brief review of that discussion. The discussion was focused by the four main sources of deviation from model behavior described in the previous paper.
Observation and Modelling of Electromigration-Induced Void Growth In AI-Based Interconnects
Authors: Kraft O. , Bader S. , Sanchez J.E. , Arzt E.
Published: March 2011

Accelerated electromigation tests on unpassivated, pure aluminum interconnects were performed. The failure mechanisms were observed by interrupting the tests and examining the conductor lines using an SEM. Because the metal thin film was subjected to a so-called laser reflow process before patterning, grain boundaries were visible in the SEM as thermal grooves. Voids were observed to move along the line and to grow in a transgranular manner, and a characteristic asymmetric void shape was identified which seems to be related to the failure mechanism. It is argued that substantial progress in modelling and understanding of electromigration failure can be made by consideration of such void shape effects.
X-ray Determination and Analysis of Residual Stresses in Uniform Films and Patterned Lines of Tungsten
Authors: Maniguet L. , Ignat M. , Dupeux M. , Bacmann J.J. , Normandon Ph.
Published: March 2011

The determination by X-ray diffraction of the elastic strain tensors and the corresponding stress tensors in uniform films and patterned lines of tungsten was used to investigate the effect of line width. The stresses were found to increase with increasing line width. These experimental results are discussed with respect to the values obtained from a model using a distributed force in the line. The results of the calculations are in agreement with the X-ray measurements. The edge effects appear to be significant for tungsten lines.
Stress in Copper Thin Films with Barrier Layers
Authors: Vinci Richard P. , Bravman John C.
Published: March 2011

Wafer curvature and grazing incidence x-ray scattering (GIXS) techniques were used to investigate the biaxial stresses induced in blanket Cu films during a thermal cycle to 460°C and back to room temperature. Cu was deposited by DC sputtering at ambient temperature. Several different barrier layer materials — SiO2, W, Ta, TiN, and Si3N4 — were used to compare any effect barrier choice might have on Cu microstructure evolution and mechanical behavior. Ta and Si3N4 encouraged a strong (111) Cu texture. A W barrier led to an untextured microstructure which underwent large, uneven grain growth during thermal cycling. Several samples were capped with a Ta layer which affected the stress behavior during cooling by inhibiting dislocation motion. An inverse relationship between strength and thickness was also documented.
Stress Mapping Near Simulated Defects in Thin Film Wiring Using X-ray Microbeam Diffraction
Authors: Dehaven Patrick , Goldsmith Charles
Published: March 2011

The stress distribution about a series of deliberately fabricated defects in a Cu/Ni/Au/Cr redundant metal stack deposited on a Cr/Cu/Cr serpentine has been studied via x-ray microbeam diffraction using the sin2ψ technique. Strong directional anisotropies in the stress were found for both the second level nickel and copper. The extent of nickel stress relaxation from the edge of a defect far exceeded that predicted by a simple metal on substrate model. The size of the defect did not appear to significantly influence the stress distribution in the second level metal; however, the data suggest that the linewidth may influence the magnitude of the stress along the length of a line when near a defect or other sharp discontinuity.
The Influence of Mechanical Stress on Hot-Carrier Degradation in Mosfet'S
Authors: De Wolf Ingrid , bellens Rudi , Groeseneken Guido , Maes Herman E.
Published: March 2011

Non-uniform hot-carrier degradation in n-channel polycide-gate MOSFET's with different thicknesses of the poly-Si film, and in p-channel polycide-gate MOSFET's with TiSi2- or CoSi2-gate-silicide, is studied. The n-MOSFET's with the thinnest poly-Si film, show an increased interface trap generation, while the influence of the gate-silicide material on the degradation behaviour of the p-MOSFET's is found to be very small. The results are evaluated in terms of the effect of mechanical stress on the degradation characteristics: favourable for compressive mechanical stress and unfavourable for tensile stress. A correlation with stress measurements by micro-Raman spectroscopy is made.
Microstructure of Buried Thin Etch Stop Films Formed by Nitrogen Implantation into Silicon
Authors: Romano-Rodriguez A. , El-Hassani A. , Perez-Rodriguez A. , Samitier J. , Morante J.R. , Esteve J. , Acero M.C.
Published: March 2011

The microstructure of buried layers obtained by medium to high dose nitrogen ion implantation in silicon for etch-stop applications is investigated as a function of the implantation conditions (dose and temperature). Samples are analyzed by TEM, SIMS, FTIR and XPS measurements. The correlation between the data from the different techniques allows to characterize the different layers in the structure, determining the phases induced during the process, the crystalline nature of the layers and the presence of structural defects. The obtained data show the gettering of nitrogen after annealing in both a buried layer around the implantation peak and in the surface region. The nitrogen concentration in these regions and the formation and nature of silicon nitride precipitates show strong dependences with the implantation dose and temperature.
Continuum Modeling of Stress-Driven Surface Diffusion in Strained Elastic Materials
Authors: Freund L. B. , Beltz G.E. , Jonsdottir F.
Published: March 2011

The free energy of a deformable crystal is assumed to consist of elastic strain energy and surface energy, and the chemical potential for surface diffusion at constant temperature is obtained under this assumption. The result is applied in considering the phenomena of instability of a flat surface in a stressed material under fluctuations in surface shape, and the development of surface roughness due to the proximity of misfit dislocations to the free surface of the material.
A Misfit Dislocation Blocking Mechanism in Continuous InGaAs Layers Grown on Patterned GaAs
Authors: Patrick Watson G. , Ast Dieter G. , Anderson Timothy J. , Pathangey Balu
Published: March 2011

Previous work showed that misfit dislocations were blocked at trench walls in a unique way in InGaAs strained layers grown on GaAs that was patterned and etched to form a series of mesas separated by trenches. A model is developed to explain the behavior of misfit dislocations in this material. The energy cost of extending the threading dislocation segment, which accompanies a misfit dislocation during glide, can impede the motion of these defects if the trench walls are steep enough.
Stress Dependence of the Velocity of Threading Dislocation Segments in Si - Ge Heteroepggaxial Films.
Authors: Gillard Veronique T. , Noble David B. , Nix William D.
Published: March 2011

This paper presents data for threading dislocation velocities measured in Si-Ge heteroepitaxial thin films during in situ HVTEM annealing experiments. These data are compared to three models which were previously developed to describe the kink mode of dislocation motion. Two of these models, Hirth and Lothe [1] and Seeger-Schiller [2], are based on the discrete narrow kink representation. The other, developed by Büttiker and Landauer [3], is based on the macroscopic bulge model representation of the dislocation line. It is found that both the narrow kink models underestimate dislocation velocities in the stress range of the experiments and that a good representation of the data can be obtained by using the macroscopic bulge model in the dislocation length-dependent regime.
The Effect of Cold-Working on the Crystallization Temperature of Thin-Film Shape Memory Effect TiNi.
Authors: Madsen John S. , Jardine A. Peter
Published: March 2011

The minimum temperature for the crystallization of amorphous TiNi on substrates is of interest in developing thin-film SME material while minimizing chemical interactions with the substrate. Using 20 micron thick free standing TiNi material annealed in a vacuum furnace, X-Ray diffraction of the thin-films indicated that the crystallization occured within 20 minutes at 510°C, 490°C and 480°C. At 450°C, crystallization kinetics were significantly slower, and the foils were fulling crystallized after annealing for 7.5 hrs. To further lower the crystallization temperature, cold working of the foil by rolling was introduced and full crystallization was observed after 7.5 hours annealing at 400°C in a cold-worked foil. Cold working and annealing at 400°C and 350°C for 7.5 hrs did not observably promote lower crystallization temperatures.
Strain-Induced Reconstruction of Impurity States in PbTe(Ga) Films
Authors: Akimov Boris A. , Ryabova Ludmila I. , Slynko Evgeniy I.
Published: March 2011

n-type PbTe(Ga) films were grown by the laser deposition and the hot wall techniques on BaF2 substrates in <111> orientation. Doping results in the appearance of a high-ohmic state with nearly intrinsic free carrier concentration at low temperatures and activation character of conductivity at T∼300 K. Persistent photoconductivity has been observed at T < 100 K. In the hot wall-grown layers a new effect of bistability during the cooling-heating-cooling cycles has been found. On the first stage of the cycle a rapid decrease of resistivity (∼3 orders of magnitude) is observed at To∼50 K. The value of To changes by ± 15 K depending on the cooling rate. After a brief heating up to 80 K the subsequent cooling results in the high-ohmic state of the layer at the low temperatures. This state seems to be unstable. Relaxation to the low ohmic state can be accelerated by the application of electric field. The effect may be understood in terms of bistability of the Ga impurity charge state under the action of strain between the film and the substrate during the cooling-down process.
Structure Development in Polyimide Films
Authors: Coburn John C. , Pottiger Michael T. , Pryde Coralie A.
Published: March 2011

The influence of processing conditions on the structure and properties in spin coated polyimide films prepared from flexible, semi-rigid and rigid chemistries was investigated. While the relationship between processing, structure and properties is different for each chemistry, some general trends were observed. Curing above the glass transition in the flexible polyimide BTDA//ODA/MPD, that is incapable of crystallizing and has very little in-plane orientation, has virtually no effect on the structure or properties compared to curing below the glass transition. Curing at temperatures above the glass transition in cry stall izable stiff polyimides such as BPDA//PPD and PMDA//ODA results in an increase in birefringence, in-plane CTE and biaxial stress. In BPDA//PPD, the increase in birefringence is attributed to an increase in polarizability and possibly, an increase in the overall in-plane alignment of the imide ring as evidenced by IR analysis. The increase in in-plane CTE is attributed to a loss in chain axis orientation caused by relaxation effects. The increase in stress is attributed to the increase in the in-plane CTE and also from shrinkage forces arising from crystallization. Rapid heating during cure in the flexible amorphous BTDA//ODA/MPD has essentially no effect on structure or properties compared to slow heating. In the semi-crystalline polyimides, rapid heating during cure leads to higher levels of crystallinity and significantly higher stresses. The increase in stresses is attributed to a loss in chain axis orientation in the plane of the film and shrinkage forces arising from additional crystallization. The directional dependence of the coefficient of thermal expansion, an important functional property, is extremely sensitive to molecular anisotropy. BTDA//ODA/MPD, which is almost isotropic, has an out-of-plane CTE that is approximately 20 percent higher than the in-plane CTE. In contrast, the out-of-plane CTE for the most anisotropic polyimide in this study, BPDA//PPD, is 25 times larger than the in-plane CTE. This sensitivity of the CTE to molecular orientation must be taken into account when modeling stress in, or designing, electronic devices.
Microindentation on Gelatin Films with a Spherical Indenter -- A Viscoelastic Analysis
Authors: Ni Beta Y. , Bisson Gary R. , Tsou Andy H.
Published: March 2011

A finite element model was employed to analyze the microindentation test with a spherical indenter on gelatin films. The deficiency of using elastic-plastic constitutive law to describe indentation response of gelatin film was recognized and a viscoelastic model was proposed for the first time to analyze indentation experiments on polymeric materials. Based on viscoelastic analysis, it was found that gelatin is nonlinear viscoelastic. In addition, modulus in the thickness direction of a gelatin film was determined to be 2.5–2.9 GPa as compared with its tensile modulus of 4.6 GPa in the transverse direction.
Growth Mechanism, Local Stresses, and Young's Moduli of Micro-Deformation Zones in Glassy Polymers Films by AFM
Authors: Yang A.C.-M. , Kunz M.S. , Wu T.W.
Published: March 2011

By studying the topography of crazes and shear deformation zones in polymer films with the Atomic Force Microscope (AFM), it was found that crazes and shear deformation zones grew by a micro-necking process. This discovery indicates that when a glassy polymer undergoes local deformations, the material drawn into the deformation zones continues to be deformed until a much later time than that previously understood. Details of the craze micro-necking mechanism and its important implications will be discussed. Based on the necking mechanics, it was shown that craze initiation and growth can be examined using a modified Considere construction, and the stress distribution within a micro-deformation zone was investigated by assuming the Bridgman's theory. The results of the stress analysis are in excellent agreement with the breakdown behavior of crazes observed experimentally. The Young's moduli of the crazed and sheared polymers within the tiny deformation zones were also measured using a simple new AFM technique. Evidence of strain softening was clearly observed in that both the Young's moduli of crazes and shear deformation zones were very low compared to that in the bulk.
Studies of Sputter Deposited CU1-XTAX Alloys
Authors: Wang Hong , Zaluzec M. J. , Liu Y. , Mazumder J. , Rigsbee J. M.
Published: March 2011

Copper-refractory metal composites/alloys are of interest for aerospace and related applications requiring good thermal conductivity and high strength at elevated temperatures[1]. These materials, due to generally very low mutual solubilities, may allow high strength microstructures to be developed which are stable at temperatures exceeding those suitable for precipitation strengthened alloys. Phase stability and mechanical property characteristics of bulk fabricated Cu-refractory metal composites were recently reviewed[2-3]. This paper reports the results of structure-property studies of a series of Cu1–xTax alloys created by RF sputter deposition. It will be shown that nanoscale face-centered-cubic and body-centered-cubic Ta particles form in the Cu matrix and that these Ta particles are very resistant to coarsening at temperatures up to 900ºC. Nanoindentation studies of these alloys reveal that their strengths are also essentially unaffected by exposure to 900ºC for times up to 100 hours.
Mechanical Testing in Electroless Ni Modified TiN Coating
Authors: Duh J. G. , Doong J. C. , Huang C. T.
Published: March 2011

TiN films are prepared by reactive rf magnetron sputtering on carbon steel substrates which are widely applied as structural materials. The electroless Ni-P plating is introduced as an interlayer in the surface modification of TiN coating. The electroless Ni-P deposit crystallizes during rf sputtering due to the elevated sputtering temperature and thus a TiN/Ni3P/Fe coating assembly is formed.

The employment of electroless Ni-P deposit results in an increase in the surface microhardness and adhesion strength. The surface hardness as high as 2266HK1 close to the hardness of bulk TiN can be achieved in the Ni3P interlayer modified TiN coating. With respect to the wear-resistance, the adhesion of the TiN coating plays an important role for the sliding wear-resistance and the interlayer Ni3P acts as a hard , barrier instead of the soft carbon steel substrate.
Stress, Mechanical Properties and Composition Measurements in Sputtered Thick Alumina Films
Authors: Ross C. A. , Barrese J. J.
Published: March 2011

Thick r.f.-sputtered alumina is used as an overcoat material in microelectronic applications. The stress in the material is compressive and its magnitude is influenced by the sputtering conditions including the power, gas pressure and r.f. substrate bias. These parameters also affect the deposition rate, stoichiometry and sputter gas (argon) content of the material and its etch rate in hydroxide solutions. Nanoindentation measurements of the elastic modulus and hardness are presented for alumina sputtered under different bias conditions and show that the zero bias material appears to be harder and suffer than material deposited at -100V bias.
Micromechanical Characterization of Dielectric Thin Films
Authors: Grow James M.
Published: March 2011

A nanoindenter has been used to obtain Young's modulus and hardness data for a variety of dielectric thin films including silicon carbide, boron nitride, silicon carbonitride, and silicon oxide. These films, were synthesized by low pressure and plasma enhanced chemical vapor deposition, and had a thickness from 0.25 to a few microns. For the BN films, the modulus and hardness of the films decreased significantly as the deposition temperature increased while the reverse was true for the SiC films. In both cases, these changes were related to variations in the compositions of the deposits due to the onset of different reactions as the temperature is increased. Silicon carbonitride films oxidized slowly when synthesized at temperatures below 200º C and the Young's modulus of these films increased at higher deposition temperatures. For silicon dioxide, there was little change in the composition of the films over the deposition temperature range investigated (375–475º C), thus correspondingly, small variations in the micromechanical properties of the material. However, moisture and hydrogen removal caused by an anneal at 800º C resulted in an significant increase in the modulus and hardness of these films.
Adhesion in Metal-Ceramic Systems
Authors: Venkataraman Shankar K. , Gerberich William W. , Kohlstedt David L.
Published: March 2011

The adhesion of Pt thin films to NiO substrates has been studied using the continuous microscratch technique. Films of Pt ranging from 65 to 1080 nm in thickness were sputter deposited onto single crystals of NiO. Continuous microscratch experiments were performed by driving a conical diamond indenter, with a nominal radius of 5 μm, simultaneously into and across the film until a load drop was observed indicating that the film had delaminated. The practical work of adhesion was calculated using a theoretical model developed for metal-ceramic systems. The practical work of adhesion increases from 0.03 to 4.7 J/m2 as the film thickness increases from 65 to 1080 nm. The practical work of adhesion includes the true work of adhesion — the energy to produce two new surfaces — and terms involving the plastic deformation of the film and substrate. Extrapolation of the practical work of adhesion versus film thickness data to zero thickness yields a first order estimate of the true work of adhesion. The true work of adhesion for the as-sputtered Pt/NiO system is determined to be 0.025 J/m2, a value of the same order as the Van der Waal’s energy.
Effect of Heat Treatment on Adhesion in the Cr/Al2O3 System
Authors: Viswanathan Sriram , Kohlstedt David L.
Published: March 2011

Continuous microscratch experiments have been carried out to investigate the effect of various heat treatments on adhesion in the Cr/Al2O3 system. After samples were prepared by vapor depositing 0.32 µm thick Cr films on (1102) surfaces of single crystal sapphire substrates, they were annealed at different temperatures at controlled oxygen partial pressures. In the subsequent continuous microscratch tests, a conical diamond indenter with a 1 µm tip radius was driven simultaneously into and across the sample until a load drop occurred. Optical and scanning electron microscopy observations demonstrate that a portion of the Cr film delaminated from the Al2O3 substrate at that point. The interfacial strain energy release rate was calculated from the load at failure combined with the size and geometry of the delaminated region. The work of adhesion was found to decrease dramatically on annealing in an H2-Ar mixture at 250°C.
Interface Structure and Adhesion of Sputtered Ti-Ni Layers on Silicon
Authors: Kondo Ichiharu , Yoneyama Takao , Kinbara Akira
Published: March 2011

Interface structure and adhesion between a Si substrate after an Ar ion bombardment pretreatment and Ni(100–1500 nm)/Ti(250 nm) double layers prepared in a dc magnetron sputtering apparatus have been investigated.

Two extra layers were generated between the Ti layer and the Si substrate in as-deposited condition. One was an amorphous Si (a-Si) layer(∼ 2 nm) formed on the single crystal Si substrate surface which contains Ar atoms. Another is an amorphous Ti-Si (a-Ti · Si) mixed layer( ∼ 3 nm) on the a-Si layer. A peeling test with an adhesive tape showed that the peeling occurred at the interface between the a-Si and the a-Ti · Si. Ar atoms appeared to be distributed at the interface and the direct contact of the a-Ti · Si layer with the Si substrate seems to be prevented.

After preparing the film and subjecting it to heat treatment at 623 K for 30 min, the adhesion decreased by the accumulation of Ar atoms at the interface. At 723 K for 30 min treatment, however, the adhesion increased probably because of Ar atoms diffusion. It is considered that the Ar atoms incorporated at the interface plays an important role on adhesion of the layer.
Phenomenological Explanation of Elastic Anomalies in Superlattices
Authors: Grimsditch M. , Fullerton Eric E. , Schuller Ivan K.
Published: March 2011

The experimental fact that measured elastic and structural properties of superlattices are strongly correlated can be understood on the basis of a simple model based on the packing of hard spheres. The model is consistent with features of many models that have been proposed to explain the supermodulus effect, but contrary to previous explanations, it allows predictions for a given pair of constituents to be made. For an arbitrary pair of elements, it predicts the existence or non-existence of an elastic anomaly, and a rough estimate of its magnitude.
Residual Stress and Microstructure of CU/W Multilayers
Authors: Goudeau Ph. , Badawi K.F. , Naudon A. , Durand N.
Published: March 2011

We have determined residual stresses and the layer microstructure in as-prepared Cu/W multilayers of different periods ranging from 5.2 to 20 nm by both X-ray diffraction and the curvature radius method. The magnitude of the principal in-plane stress is large in the W layers (around - 6 GPa) and small in the Cu layers (-0.5 - + 0.5 GPa). The stress state is independent of the multilayer period. Under the compressive stress, the W cubic unit cell becomes monoclinic-like. The stress-free lattice parameter is found higher than the bulk one.

We also studied the stress relaxation and the layer microstructure modification in W layers induced by Kr ion irradiation., the relaxation is almost achieved after only low fluence irradiations and the decrease of the stress-free lattice parameter in W layers observed for higher fluences is attributed to the formation of a sursaturated solid solution W(Cu).
Thin Film Stress in Metal/Ceramic Microlaminates
Authors: Inturi R. B. , Barnard J. A. , Chinmulgund M. , Jarratt J. D.
Published: March 2011

Al/SiC multilayer microlaminates grown by sequential deposition of sputtered Al and SiC layers were used as a model system to study stress and mechanical properties of metal-matrix composites. The average stress in as-deposited and annealed microlaminates was determined as a function of laminate geometry. Film stress tends to approach constant values for increasing Al layer thickness, large numbers of bilayers, and high layer densities. Microlaminates with thin Al and SiC layers showed purely elastic deformation in σ -T tests to 400ºC. Even though the total measured film stress in a microlaminate geometry exhibited deviations from a simple rule of mixtures, the rate of change of stress with temperature in a microlaminate in the elastic region equals the sum of the slopes obtained separately from each of the individual layers.
Crack-Dislocation Modeling of Ductile-To-Brittle Transitions in Multilayered Materials
Authors: Anderson Peter M. , Li Canhao
Published: March 2011

Using elastic fields of dislocations in a layered material, a simple form of a periodic potential is proposed to account for the fluctuation in dislocation line energy with position in a multilayer. This potential is incorporated into a fracture analysis which uses a Rice-Thomson criterion for dislocation emission [1] and a corresponding local stress intensity factor condition for cleavage extension. The analysis is rate-dependent, in that the velocity of a nucleated dislocation is proportional to the energetic force on that dislocation. Predictions of dislocation patterns in the vicinity of a crack parallel to the interface, as well as initial R-curve behavior, are discussed as a function of loading rate, layer thickness, and elastic properties of a two-component multilayer.
Studying Structure of Metallic Superlattices by "Symmetric" and "Asymmetric" X-rAY Diffraction
Authors: Gladyszewski G. , Goudeau Ph. , Badawi K.F. , Naudon A.
Published: March 2011

"Symmetric" and "asymmetric" x-ray diffraction measurements are proposed as a tool for quantitative and complete determination of the superlattice structure. A general procedure which takes into account the atomic structure of the sublayers as well as structural disorder are presented. The "asymmetric" geometry using the "sin2psi" method is particularly emphasized.
Molecular Dynamics Modeling of the Mechanical Behavior of Metallic Multilayers
Authors: Belak James , Boercker David B.
Published: March 2011

Constant-stress molecular dynamics simulations are used to study the mechanical properties of equal concentration Cu-Ni (111) metallic multilayers of repeat lengths 0.4–5.0 nm. Uniaxial stress is applied along the close-packed [110] and perpendicular to the close-packed [112] directions within the (111) plane. The observed elastic modulus does not display a super-modulus effect as observed in experimental bulge tests for the biaxial modulus. However, both the average interlayer spacing and the out-of-plane Poisson ratio display anomalous effects for multilayer repeat lengths below about two nanometers.
Using the Rule of Mixtures to Examine the Hardness of Cu/Cu-Zr Multilayers
Authors: Weihs T.P. , Barbee T.W. , Wall M.A.
Published: March 2011

Cu/Cu-Zr multilayer foils were fabricated and indented to determine the degree to which multilayer hardness is enhanced by increasing the volume fraction of the harder phase. Using sputter deposition and thermal processing a series of foils was fabricated in which the thicknesses of the Cu layers remained fixed while the thicknesses of the alternate Cu-Zr layers varied. These samples were then indented both parallel and normal to their layering. In general, hardness increased as the volume fraction of the harder Cu-Zr phase rose. When the films were loaded parallel to their layering, the measured hardnesses were higher and the dependencies on volume fraction of the Cu-Zr phase were stronger than when the films were loaded normal to their layering. These results agree with predictions based on isostress and isostrain theories. The relationships between hardness and volume fraction are used to compare the hardnesses of the Cu-Zr phases: amorphous Cu-Zr, Cu51Zr14 and Cu9Zr2, and to show that the hardness of the textured, as-deposited Zr layers is highly anisotropic .
Tailoring of Mechanical Properties in Microlaminates
Authors: Vill M. , Adams D. P. , Yalisove S. M. , Bilello J. C.
Published: March 2011

A multiscalar approach is used to demonstrate the ability to control strength and toughness in microlaminates composed of molybdenum and tungsten. Here, two different thickness scales are utilized; an alternating stack of molybdenum and tungsten layers having thicknesses on the nanometer scale are combined with a layer of molybdenum having a thickness on the micron scale. The stack of thin layers acts as a strong phase and the thick layer acts as a tough phase. Multilayers of two configurations were fabricated which had total thicknesses of 31μm and 50μm. The tough phase thickness was 5μm for the 31μm multilayer and 1μm for the other. The strong phase contained a stack of 29 alternating 4nm thick layers of molybdenum and tungsten. Uniaxial tensile testing was performed using a standard Instron tensile testing machine, followed by optical analysis of specimen fracture surfaces. Fracture toughness ranged from 2.4 to 9.5MPa(m)1/2, and tensile strengths were observed from 126MPa to 883MPa. Control of mechanical properties was demonstrated by an increase in the upper bound fracture toughness from 2.7 to 9.5MPa(m)1/2when the tough layer thickness was increased from 1μm to 5μm.
Stress Relaxation During Diffusional Phase Transformation Under Induced Thermal Stress
Authors: Zingu E C , Mofokeng B T
Published: March 2011

Thermal mismatch between the expansion coefficients of a substrate and deposited thin film gives rise to extrinsic stress in the film. Different stress states are induced into the Co/Si thin film combination by depositing the multi-layers on Al and Si substrates respectively. Interdiffusion at 360°C is found to be influenced by the extrinsic stress in the films. The difference in Co2Si growth rate on different substrates is ascribed to the difference in composition (Co molar fraction) at the Co/Co2Si and Co2Si/Si interfaces due to different stress states.
Joining Ceramics Using Microwave Energy
Authors: Ahmad Iftikhar , Silberglitf Richard
Published: March 2011

In the past several years there has been an explosive growth in the use of microwave energy for the processing of a host of materials. Microwave energy provides rapid internal heating which results in an overall reduction in the processing time. The important features of microwave processing are described, as well as several applications.

Microwave energy has been used by a few groups for the joining of alumina, mullite, silicon nitride and silicon carbide. The work performed by these groups will be reviewed. Typically, a single mode microwave applicator has been used to join ceramics at temperatures ranging between 1250°C - 1800°C. Microwave joining of ceramics was achieved in a matter of minutes, in contrast to hours reported by conventional methods. The strength of the joints was equal to or greater than the as-received materials. Joining of specimens of sintered silicon carbide (Hexoloy ™ ) using interlayers, and direct joining of reaction bonded silicon carbide (RBSC) to itself and Hexoloy™ has been accomplished recently. Both single mode and multimode microwave applicators were used and larger specimens of RBSC having complex shapes were joined using hybrid heating. The paper describes microwave joining apparatus, techniques and results.
Mechanisms of Wetting in Reactive Metal/Oxide Systems
Authors: Eustathopoulos N. , Drevet B.
Published: March 2011

It is shown that for metal/oxide systems with weak or moderate reactivity, wetting depends mainly on parameters related with the detailed chemistry and structure of interfacial reaction products rather than on parameters related with the intensity of interfacial reactions. Consequently, wetting can be promoted by alloying a metal matrix M with a reactive solute B capable of modifying in a favourable sense the metal/oxide interface. This can be achieved via two mechanisms depending on the value of the Wagner's interaction parameter εBo. When εBo<0 (moderate interactions between solute B and dissolved oxygen), the solute B can modify the liquid-side of the interface by adsorption, an effect that can be strongly enhanced by oxygen coming from dissolution of the oxide substrate. When εBo<<0 (strong O-B interactions in M), the solute B can lead to the formation, at the solid-side of the interface, of a new phase. When this new phase features metallic bonding wetting can be strongly improved.
Capacitor Discharge Weld Modelling Using Ultra High Speed Photography
Authors: Wilson R. D. , Hawk J. A. , Devletian J. H.
Published: March 2011

Capacitor discharge welding (CDW) is a rapid solidification joining process where high cooling rates (106 K/s) are obtained as a result of the large weld surface area to small weld volume. The objective of this study, directed by the U.S. Bureau of Mines and the Oregon Graduate Institute of Science and Technology, was to use ultra-high speed photography to quantify transient arc behavior during the CDW cycle. The simple cylindrical geometries of the CD welds have been used to formulate analytical models which are compared to the high speed photographs of the welding process. The high speed photographs were analyzed with respect to welding time and process weld variables and compared to predicted values from the analytical model. The detailed photographic analyses revealed that material is continuously ejected as a plasma from the weld area due to induced magnetic forces, rather than having the liquid metal squeezed out of the weld upon contact. It was found that welding time was controlled by tip length and drop height. Results from high speed photographs found the arc travel speed around tube welds to be 109m/s. Finally, the high speed photographs revealed that the velocity of arc propagation during ignition was fast enough to allow the CDW process to be modelled as onedimensional heat flow.
Self-Propagating, High Temperature Synthesis As A Technique To Join Metals
Authors: Hawk J. A. , Petty A. V. , Dogan C. P. , Rawers J. C.
Published: March 2011

Self-propagating, high temperature synthesis (SHS) can be used to bond both similar and dissimilar metals. A unique feature of this technique is the ability to stack either metal foils or metal foils and powder, and to process them to form two-dimensional, layered composites with a “graded” intermetallic interface between layers. This process can also be used to modify a surface for corrosion or wear resistance. To date Bureau of Mines research has focused on making iron-, titanium-, and nickel-aluminum composites. The elemental metal foils are stacked and placed in a hot press, and the temperature is raised until the composite sandwich undergoes the SHS reaction. At approximately 660°C (i.e., the melting point of aluminum), the aluminum reacts with the transition metal to form intermetallic phases. The SHS process is mass and energy limited; i.e., mass transport controls the chemical reaction rates, while the energy liberated by the chemical reaction is distributed to the surroundings by heat conduction, convection and radiation.
A Novel Brazing Technique for Aluminum and Other Metals
Authors: Timsit Roland S. , Janeway B. J.
Published: March 2011

In the novel brazing technique, the aluminum components in the joint assembly are coated with a powder mix consisting of elemental Si and a potassium fluoroaluminate flux. During brazing at −600°C in nitrogen gas, the flux melts and removes the native Al2O3 surface film from the coated aluminum components. This action allows the silicon to diffuse into the aluminum to generate in-situ a layer of Al-Si filler metal of eutectic composition.The liquid metal then flows into thejoint and yields a metallurgical bond on cooling.

This brazing technique maybe exploited with aluminum using intermediary elements other than Si. The technique may also be used for joining other metals.
Indirect-Bonded Metallization of Aluminum Nitride
Authors: Norton M. Grant
Published: March 2011

The use of aluminum nitride (AIN) as a substrate and packaging material for microcircuit applications is of present interest due to its many advantageous physical properties. A limitation to the widespread use of AIN is the lack of an adequate metallization system. The most common method of achieving high-integrity metallized ceramics is through the use of indirect-bonded metallizations. A wide range of intermediate bonding materials are used, for example glasses, oxide mixtures, and active metals. In this paper, the indirect-bonded metallization of AIN will be reviewed and discussed. Requirements which must be considered in producing successful metallizations include; wetting of the substrate and the metal by the intermediate phase and the reactivity between the intermediate phase and the substrate. The reactions which occur in many of the systems considered can be predicted by examination of thermodynamic data.
A Joining Technique Using Multilayer Lead-Indium-Gold Composite Deposited In High Vacuum
Authors: Lee Chin C. , Wang Chen-Yu , Chen Yi-Chia , Matijasevic Goran
Published: March 2011

A joining technique for electronic devices has been developed. This technique uses a leadindium- gold multilayer composite solder deposited directly on GaAs wafers in high vacuum to prevent indium oxidation. The gold layer on the composite further protects the indium layer from oxidation in atmosphere. The GaAs dies are bonded to a gold-coated alumina substrate at a process temperature of 250°C. Nearly perfect joints are achieved as verified by a scanning acoustic microscope (SAM). SEM and EDX results indicate that the alloy joint consists of AuIn2 grains embedded in an In-Pb solid solution phase, as predicted from the Au- In-Pb phase diagram. Compared to lead-tin solder, indium-lead solder has been shown by others to exhibit much better fatigue resistance and have much less of a scavenging effect. Thermal shock as well as shear tests confirm that a good die attach is obtained with the leadindium- gold composite.
Diffusion Bonding of Advanced Aerospace Metallics
Authors: Dunford David V. , Wisbey Andrew
Published: March 2011

Advanced aluminium and titanium alloys, metal matrix composites (MMC's) and intermetallic compounds are of considerable interest to the aerospace industry. These materials offer significant mechanical improvements over many conventional materials. Appropriate joining technologies are being developed to utilise the advantages these materials offer in aerospace applications. Diffusion bonding offers considerable potential as a joining process. This keynote paper will review diffusion bonding with reference to these advanced metallic systems.
Reliability Factors in Ceramic/Metal Joining
Authors: Suganuma Katsuaki
Published: March 2011

This paper reviews the processing factors in joining ceramics to metals concerning the reliability. Thermal expansion mismatch has a great influence not only on the absolute value of strength but also on the reliability of joints. Large thermal stress increases the scatter of joint strength because of the presence of defects induced during joining process. One should insert an appropriate interlayer to relax the stress between a ceramic and a metal. Surface roughness also has some influence on the reliability. A roughly ground bond face leads large scatter in strength. Scratches must be removed before joining. Unjoined area reduces joint strength especially in solid-state joining. In brazing, the homogeneity in the braze layer should be also controlled carefully. A slight applied pressure during brazing can preserve the integrity of joints.
Interface Science of Controlled Metal/Metal and Metal/Ceramic Interfaces Prepared using Ultrahigh Vacuum Diffusion Bonding
Authors: King Wayne E. , Campbell G. H. , Coombs A. W. , Johnson G. W. , Kelly B. E. , Reitz T. C. , Stoner S. L. , Wien W. L. , Wilson D. M.
Published: March 2011

We have designed, constructed, and are operating a unique capability for the production of highly controlled homophase and heterophase interfaces: an ultrahigh vacuum diffusion bonding machine. This machine is based on a previous design which is operating at the Max Planck Institut für Metallforschung, Institut für Werkstoffwissenschaft, Stuttgart, FRG. In this method, flat-polished single or polycrystals of materials with controlled surface topography can be heat treated up to 1500°C in ultrahigh vacuum. Surfaces of annealed samples can be sputter cleaned and characterized prior to bonding. Samples can then be precisely aligned crystallographically to obtain desired grain boundary misorientations. Material couples can then be bonded at temperatures up to 1500°C and pressures up to 10 MPa. Results are presented from our initial work on Mo grain boundaries and Cu/Al2O3 interfaces.
Interfacial Reactions Between Titanium and Borate Glass
Authors: Brow R. K. , Saha S. K. , Goldstein J. I.
Published: March 2011

Interfacial reactions between the melts of several borate glasses and titanium have been investigated by analytical scanning electron microscopy (ASEM) and by x-ray photoelectron spectroscopy (XPS). A thin titanium boride interfacial layer is detected by XPS after short (30 minutes) thermal treatments. ASEM analyses after longer thermal treatments (8–120 hours) reveal boron-rich interfacial layers and boride precipitates in the Ti side of the interface.
Combustion Synthesis of Molybdenum Disilicide and its Composites
Authors: Deevi Seetharama C.
Published: March 2011

A combustion wave originating from an exothermic reaction between Mo and Si propagates through the reactants converting Mo-2Si mixture to Mosi2. X-ray analysis of the product confirmed that the product is single phase Mosi2 with no second phase or reactants when combustion synthesis experiments were carried out in argon. The oxygen content of the product was 0.22 wt.%. When the mixture was reacted under pressure in a hot press, the product obtained was also Mosi2, and a theoretical density up to 92% could be achieved. Heating of a mixture of Mo and Si with C leads to the formation of Mosi2 with a dispersed SiC phase.
Thermo-Chemical Synthesis of Nanostructured Chromium Silicide / Silicon Carbide and Molybdenum Silicide / Silicon Carbide Composite 'Powders
Authors: Luo Ping , Strutt Peter R. , Gonsalves Kenneth E.
Published: March 2011

Intermetallic silicides and silicon carbide composites are potential useful materials in high temperature applications requiring superior strength combined with enhanced fracture toughness. This paper presents results obtained on these materials in nanostructured form, since structural reduction to this scale offers a way for achieving unique properties.

Chromium silicide / silicon carbide and molybdenum silicide / silicon carbide composite powders were readily synthesized by thermal conversion from spray dried precomposites at 1250°C. Basically, the process involves spray drying the aqueous chemical solution to a precomposite, followed by thermal conversion in a tube furnace reactor. The phases present in the composites are hexagonal Cr5−XSi3−XCX+Y (Cr5Si3Cx) / cubic β-SiC and tetragonal MoSi2, hexagonal Mo5Si3CXx/ cubic β-SiC. The volume fraction of these phases can be controlled through the solution preparation of the precursors. Characterization of composite powders include x-ray diffraction spectrometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Particle size distribution of the synthesized chromium silicide and silicon carbide composite was conducted by a computerized image analyzer and the statistical result was obtained.
Microcracking, Strain Rate and Large Strain Deformation Effects in Molybdenum Disilicide
Authors: Hardwick D. A. , Martin P. L.
Published: March 2011

High purity molybdenum disilicide was deformed in compression to strains ranging from 5 to >50%. The deformation was accomplished at temperatures in the range 1200°-1400°C and at strain rates from 10−3 to 10−5 sec−1. The strength of this high purity material was found to be at least twice that of MoSi2 produced by the hot pressing of commercial powder. Microstructural examination revealed that subgrain formation resulted from modest strains (≈10%) while dynamic recrystallization was observed following large strains. Transmission microscopy revealed a significant change in the dislocation substructure after straining as the temperature was increased from 1300°C to 1400°C.
High Temperature Oxidation Behavior of Strucflural Siucides
Authors: Ramberg C. E. , Beatrice P. , Kurokawa K. , Worrell W. L.
Published: March 2011

The factors which control the formation of a protective silica (SiO2) layer on structural silicides at high temperature are summarized. The thermodynamic and kinetic conditions under which both silica and a metal oxide can form are also described. Molybdenum disilicide (MoSi2) forms highly protective silica scales and has the best oxidation resistance at high temperatures. Although the preparation method has little influence, the heating rate and the structure of the silica layer have significant effects on the oxidation behavior of MoSi2.