bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Transformation Characteristics in Thin Film SMA Heterostructures— The Importance of Interfacial Stress Accommodation
Authors: Hua Susan Z. , Su C. M. , Wuttig M. 
Published: March 2011

ABSTRACTShape memory alloy (SMA) thin films have attracted attention due to their potential application as actuators in micromechanical systems. The stress development in Ni50Ti50 films has been measured using a cantilever beam method. It is of interest to study their transformation characteristics. We have investigated a striking change of the stress during the B2-B19 transformation. The magnitude of this stress depends on the film thickness and reflects the interface constraint. In order to obtain direct information about the interface, in situ cross-section TEM observations of NiTi/SiO2/Si heterostructures were performed at various temperatures. A layer of parent phase at the film/substrate interface was found to buffer the transformation induced stress. The origin and effect of this buffer layer was analysed based on the TEM cross-sectional observations of the formation history of the layer.
Theoretical Considerations on Growing Uniformly Thick Films of Perfect Crystallinity
Authors: Van Der Merwe Jan H. 
Published: March 2011

ABSTRACTTheoretical considerations that facilitate the design of procedures to grow epilayers of uniform thickness and perfect crystallinity are briefly reviewed. The attainment of uniformity and crystallinity are respectively best served by growing in the monolayer-by-monolayer mode and below a critical thickness. Equilibrium and non-equilibrium criteria developed to accomplish these goals are briefly dealt with.
Reorientation of Misfit Dislocations During Annealing in InGaAs/GaAs(001) Interfaces
Authors: Chen Y. , Liliental-Weber Z. , Washburn J. , Klem J.F. , Tsao J.Y. 
Published: March 2011

ABSTRACTTransmission electron microscopy is applied to investigate the effect of post-annealing on misfit dislocations in an In0.2Ga0.8As/GaAs(001) heterostructure. An orthogonal array of 60º dislocations along [110] and [110] directions was observed in the interfaces of the samples grown by MBE at 520 ºC. When the as-grown samples were annealed at temperatures ranging from 600 to 800 ºC, the 60º dislocations were gradually reoriented by dislocation reactions occurring at the 90º intersections followed by nonconservative motion driven by dislocation line tension and the residual elastic misfit strain. The final result of this process was a dislocation array lying along [100] and [010] directions. The reoriented u=<100> dislocation has a Burgers vector , which is the same as that of 60º dislocation, but the edge component of its Burgers vector in the (001) interfacial plane is larger than that of 60º dislocation by a factor of , resulting in a greater contribution to elastic strain relaxation. This nonconservative reorientation of 60º dislocations to form the u=<100> dislocations represents a new strain relaxation mechanism in diamond or zinc blende semiconductor heterostructures.
Threading Dislocation Densities in GaAs Grown on Reduced Area Si Substrates
Authors: Knall J. , Romano L.T. , Biegelsen D.K. , Bringans R.D. 
Published: March 2011

ABSTRACTWe have studied the possibilities of reducing the threading dislocation (TD) density in GaAs on Si using free side wall growth on patterned Si substrates and/or using a soft ZnSe interlayer in combination with post growth annealing procedures. TD densities were accurately determined using large area plan view TEM and were found to be unaffected by proximity to free side walls and by the ZnSe interlayer. Post growth heat treatments led to a factor of ∼2 reduction in TD density and to bunching of dislocations throughout the thickness of the film.
Diffusion-Induced Dislocations in Silicon
Authors: Ning X. J. , Pirouz P. 
Published: March 2011

ABSTRACTThe stresses in a silicon wafer which has undergone diffusion by a high concentration of boron are partially relaxed by the generation of dislocations in the boron-diffused regions of Si. It is found that these dislocations nucleate at the Si surface as dissociated half-loops lying on {111} planes inclined to the surface. Expansion of the half-loops to the diffused/virgin Si interface produce segments of misfit dislocations which are of the dissociated 60º type. These misfit dislocations move deeper into the crystal as the diffusion front moves further in the wafer and often intersect other misfit dislocations on intersecting glide planes. In this paper, the misfit dislocations and the reactions between them are characterized and discussed.
Slipline Offset of In.25Ga.75As/GaAs (100) Imaged by Atomic Force Microscopy
Authors: Harvey S.E. , Angelo J.E. , Gerberich W.W. 
Published: March 2011

ABSTRACTWe have discovered a surface instability in In.25GaAs.75/GaAs (100) grown by molecular beam epitaxy (MBE) by direct comparison of atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) investigations. While slipline spacings measured by AFM correspond fairly well with those measured by TEM and SEM, the height displacement measured by AFM was seven times greater than that inferred from dislocations observed with TEM; the number of dislocations are insufficient to produce such dramatic heights. The difference in height measured by AFM with respect to the theoretical height calculated by strain relaxation and TEM dislocation number measurement can be attributed to a surface instability.
Mechanical Properties of the GaAs/Si [001] Interface by X-rays Hybrid Multiple Diffraction
Authors: Morelhão S. L. , Cardoso L.P. , de Carvalho M.M.G. 
Published: March 2011

ABSTRACTIn this work, the directions of the secondary beams which are scattered by each mosaic block within an epitaxial layer allow to explain the position and profile of the LS hybrid multiple diffraction peak in the substrate Renninger Scan (RS). Furthermore, by choosing a secondary beam diffracted almost parallel to the interface, the LS peak is able to provide information even for thin (500Å) layers. The position of the LS peak in the substrate RS of the GaAs layers grown by VCE on Si(001) provides the a║ values necessary to analize the layer stress state. As an external bending moment is applied on the sample to compensate the stress steming from the difference in thermal expansion coefficients a split of both epilayer and buffer layer LS peaks can be observed. This split also indicates the degree of cohesion between these two layers.
Effect of Stress on the Carrier Contribution to Elastic Constants in Thin Films of Small Gap Compounds
Authors: Ghatak Kamakhya P. , Nath Biswas Sambhu 
Published: March 2011

ABSTRACTIn this paper we have investigated the carrier contribution to elastic constants in very thin films of stressed small gap compounds within the domain of theory. It is found, taking stressed ultrathin films Hg1-xCdxTe and In1-xGaxAsyP1-y lattice matched to InP as examples, that the elastic constants increase with increasing electron concentration and decreasing film thickness respectively in oscillatory manners. Besides the stress enhances the numerical values of such contribution to the elastic constants. In addition, the theoretical formulation is in agreement with the suggested experimental method of determining such constants in materials having arbitary dispersion laws.
Ti-W-N Deposition Stress as a Function of Microstructure
Authors: Witvrouw A. , De Bosscher W. , Deweerdt B. , Verbeeck R. , Loosen F. , Roussel Ph. , Maex K. 
Published: March 2011

ABSTRACT160 nm Ti-W-N layers were sputtered on Si/SiO2/Al-Si-Cu substrates with the thickness of the Al-Si-Cu layer varying between 0 and 1000 nm. As a result the apparent grain size of the Ti-W-N increased from 40 to 130 nm and the compressive deposition stress of the Ti-W-N decreased from 1.77 to 0.34 GPa. The relation between stress and the inverse grain size was found to be linear for grain sizes smaller than 130 nm. Assuming a simple model, the excess volume per unit area of grain boundary can be estimated from the slope of the fit and was found to be 0.17 nm.Light scattering measurements can be used as a quick and non-destructive method for evaluating the microstructure of these layers.
Nanoidentation Study of the Mechanical Properties of Granular Metal Thin Films
Authors: Scanlon M. R. , Ferber M. K. , Cammarata R. C. 
Published: March 2011

ABSTRACTNanoindenter techniques have been used to investigate the mechanical properties of Ag-Al2O3 and Fe-SiO2 granular metal films. A discontinuity in the rate of change of hardness as a function of metal volume fraction p was observed. The discontinuity occurs at the percolation threshold pc of the metal, and appears to result from a change in the deformation mechanism at pc. A large peak in compliance (inverse modulus) as measured during indentation unloading was observed in the Ag-Al2O3 films near pc, but was not observed for the Fe-SiO2 films. The compliance peak displayed by Ag-Al2O3 is believed to result from debonding at the metal-ceramic interface and subsequent interfacial sliding, and is not an intrinsic materials property.
Compressive Stress Increase With Repeated Thermal Cycling in Tantalum(Oxygen) Thin Films
Authors: Cabral C. , Clevenger L.A. , Schad R.G. 
Published: March 2011

ABSTRACTStresses which build up in thin films, such as tantalum, during thermal processing, can cause major reliability problems in x-ray optics and electronic applications. We have demonstrated that 50 nm to 200 nm thick sputtered beta tantalum thin films undergo repeated compressive stress increases when thermally cycled from room temperature to 400°C (at 10°C/min) and back in a purified He ambient because of low levels of oxygen gettered by the tantalum. The oxygen contamination is a result of the poor quality of the quartz annealing chamber atmospheric seal. As-deposited stress in the sputter deposited tantalum films ranges from -1 to -4 GPa. The compressive stress build up was monitored in situ and was shown to increase -0.5 GPa on average after each thermal cycle for a final value of -6 to -7 GPa after seven cycles. After being cycled thermally seven times any perturbation of the film such as a four point probe resistivity measurement can cause the film to instantaneously crack in a serpentine pattern relieving the large compressive stress. Auger electron spectroscopy depth profiling analysis indicated that the as-deposited films contained one atomic percent oxygen which increased to eight to twelve percent after seven thermal cycles accompanied by an approximate doubling in resistivity. In conclusion, the increase in oxygen concentration in tantalum thin films which occurs upon thermal cycling leads to a repetitive increase in compressive stress which could be detrimental when the films are used in x-ray or electronic applications.
Mechanical Properties of Pyrolytic "SiOCN" Thin Coatings
Authors: Bec Sandrine , Tonck André , Loubet Jean-Luc 
Published: March 2011

ABSTRACTPyrolysis of polymer precursors (polysilazane) is a technologically and economically interesting way to produce thin ceramic coatings. However, many cracks appear and decohesion occurs during pyrolysis when the ceramic coatings (SiOCN) are thicker than 0.5 micrometers. In order to understand these cracking phenomena, the coatings are mechanically characterized by nanoindentation at different stages of the pyrolysis heat treatment.During pyrolysis, the cracking temperature is detected by in-situ optical observation. The thickness of the coatings varies during pyrolysis from 3 micrometers at the polymeric state to 1 micrometer at the ceramic state. The coatings' properties, hardness and Young's modulus are evaluated after heat treatment, taking into account the substrate's influence. A large variation of these properties occurs at the cracking temperature. Both the hardness and the Young's modulus are multiplied by a factor of 10. By analysing these results, we show that cracking is correlated with the evolution of the coatings' mechanical properties during the transformation.
Influence of the structure on the mechanical properties of electrodeposited metallic thin films
Authors: Delplancke J.-L. , Winand R. , Dille J. , Charlier J. 
Published: March 2011

ABSTRACTProduction of thin (10 to 200 microns thick) metallic (Cu, Co and Ni-P) foils is performed by electrodeposition on various substrates. A competition between substrate-induced and electroplating-induced inhibition of crystal growth appears. Film structures observed by SEM, TEM and X-Ray diffraction are related to the mechanical properties of the films (stress-strain curves, microhardness and work hardening bend test).In some cases, copper thin films with a large number of submicron crystals are obtained. These films recrystallize at room temperature and their mechanical properties are completely modified by this ageing process.
Tribomechanical Properties of Ion-Beam-Densified Sol-Gel Zirconia Thin Films on Cubic Zirconia
Authors: Levine Timothy E. , Revesz Peter , Mayer James W. , Giannelis Emmanuel P. 
Published: March 2011

ABSTRACTWe have investigated the tribomechanical properties of ion-beam-densified sol-gel zirconia overlayers on bulk zirconia. Ion irradiation of the sol-gel films leads to hydrogen, oxygen, and carbon losses as indicated by Rutherford backscattering spectrometry and forward recoil energy spectroscopy. Ellipsometry measurements show that the film thickness decreases with increasing dose. The microhardness exhibits an increase and subsequent decrease with dose. Friction measurements along with profilometry measurements indicate that severe abrasive wear of the film takes place in the first 1000 cycles after which point the substrate is in direct contact with the pin.
Micromechanical Behaviour of Amorphous Hydrogenated Silicon Carbide Films
Authors: Meneve J. , Jacobs R. , Lostak F. , Eersels L. , Dekempeneer E. , Smeets J. 
Published: March 2011

ABSTRACTAmorphous hydrogenated silicon carbide (a-Si1-xCx:H) films (x = 0.65 to 1) were deposited by radio frequency plasma assisted chemical vapour deposition (RF-PACVD). Their friction and wear properties were investigated by means of a conventional ball-on-disk apparatus. The results were correlated with film mechanical properties. It was found that adding silicon to a-C:H (also called diamond-like carbon (DLC)) films reduces the hardness, elastic modulus and internal stress values by 15 to 30 %. Scratch testing induces film spallation from stainless steel substrates at low loads (1 N). In the low normal load (1 N) ball-on-disk tests under humid N2 conditions, a-Si1-xCx:H films (0.7 < x < 0.9) combine a very low wear rate of both the film and the counterbody with a steady state low friction coefficient below 0.1. For higher loads (5 and 10 N), however, this low friction coefficient only lasts for a relatively short time. In this case, the harder diamond-like carbon films perform tribologically better because of their higher wear resistance, low wear rate of the counterbody and generally low friction coefficients between 0.15 and 0.35 in a humid ambient atmosphere. In a dry N2 atmosphere, pure DLC films perform tribologically better than a-S1-xCx:H films in all respects.
Stress in Thin Layers Applied by Substrate Bending; Calibration and Potentialities
Authors: Chroboczek J.A. , Stöhr M. , Whall T.E. 
Published: March 2011

ABSTRACTUniaxial stresses up to 0.3GPa, both compressive and tensile, can be generated in thin epitaxial layers by substrate bending. We demonstrate the feasibility of the method and calibrate the stress, measuring piezoresistance at temperatures below the impurity freeze-out, on lightly B-doped silicon MBE layers, using the known expression for a surface stress in a bent cantilever beam. The ground state energy displacement of B in Si thus obtained can vary by ±5meV, suggesting potential applications of the technique in tunable devices, involving doped semiconductors or heterostructures.
Evaluation of Adhesion Strength in a Ti/Al2O3 Composite
Authors: Wang Hsin-Fu , Nelson John C. , Lin Chien-Li , Gerberich William W. , Skowronek Charles J. , Deve Herve E. 
Published: March 2011

AbstractThe mechanical properties of interfaces in Ti/Al2O3 composites were characterized by four point bending and fiber pushout tests. To determine the bi-material fracture toughness with four point bending tests, planar interfaces were evaluated as sandwich composites. By changing the processing temperature from 700°C to 1000°C, the interfacial fracture energy was found to increase ug to 950°C. It then decreases when the processing temperature is further increased to 1000°C. This is because of the formation of the intermetallic compound (Ti3Al). Interfacial shear strength and interfacial frictional stress of 323MPa and 312 MPa were obtained, respectively, by performing pushout tests of the Al2O3 fiber reinforced Ti matrix composites. These values are smaller than the shear yielding strength of the Ti matrix which is 525 MPa.
Stress-Corrosion Cracking at Ceramic-Metal Interfaces
Authors: Card J. C. , Cannon R. M. , Dauskardt R. H. , Ritchie R. O. 
Published: March 2011

AbstractIt is known that the fracture resistance of glass-copper interfaces depends strongly on the water content in ambient gaseous environments. In the present study, subcritical crack growth stimulated by water and other environmental species is investigated for such interfaces. Tests were conducted in various liquids, namely water, N-methylformamide, and n-butanol. All were found to accelerate fracture with the greatest effects from liquid water. Results are considered in the context of current models for stress-corrosion crack growth.
High Speed Joining of Aluminum Metal Matrix Composites Using Continuous Wave and Pulsed Lasers
Authors: Khan Parwaiz A. A. , Paul Anand J. 
Published: March 2011

AbstractDue to their superior mechanical properties and high strength to weight ratio, metal matrix composite materials are increasingly being used in aerospace, automotive and defense industries. The use of a fusion related conventional joining technique, such as arc welding, leads to the formation of undesirable non-equilibrium phases in the weld zone, where as diffusion and adhesive joining techniques are rather slow. Non contact multi-kilowatt laser joining, though fully developed for high speed autogenous joining of different alloys, is not yet adequate for joining of metal matrix composites. Efforts have been made by several researchers to control the composition and microstructure of laser joined aluminum metal matrix composites by controlling the energy input and by the use of filler wires. In view of the current industry trend to use more light weight structural composite materials, and greater use of high energy density beams for a variety of metalworking applications, the authors have reviewed the current status of high speed laser joining of metal matrix composites. Emphasis is placed on problems and various techniques which can be used to achieve a better control on composition and microstructure during high energy laser joining of aluminum metal matrix composites.
CD Weld Interfacial Structure for Al-Fe Based Couples
Authors: Dogan C. P. , Wilson R. D. , Hawk J. A. 
Published: March 2011

AbstractThe U.S. Bureau of Mines has studied the capacitive discharge weld interface between Al and Fe using optical and transmission electron microscopy (TEM). Capacitive discharge welding (CDW) is a rapid solidification process in which the amount of molten metal at the interface is small compared to the sample size. As a result, high cooling rates (106 K/s) can be achieved, providing a weldment made up of small grains. Large magnetic fields produced by the process tend to mix the molten metals at the interface to form a complex alloy, the nature of which depends upon the starting electrode materials. This effect is characterized by a marblecake pattern in optical micrographs. The amount of mixing is related to the melting temperature of the cathode with respect to the anode. Increased mixing occurs when the melting temperature of the cathode is higher than the melting temperature of the anode. TEM has revealed that when aluminum is the anode material, the iron grains of the cathode are surrounded by a layer of aluminum. When the iron is the anode, a thin layer of iron surrounds the aluminum grains.
Fundamentals of The Shs Joining Process
Authors: Messler Robert W. , Orling Timothy T. 
Published: March 2011

AbstractThe process of self-propagating high-temperature synthesis offers potential for joining similar or dissimilar combinations of heat-resisting or refractory metals and refractory or corrosion resistant oxide or nonoxide ceramics or intermetallics by using the exothermy inherent in the synthesis reaction. The process offers unique capability for producing functionally gradient material joints between dissimilar materials to overcome mismatches in chemical, mechanical and physical properties, facility for incorporating reinforcing phases in the filler, and exceptional efficiency given that the energy for joining is largely internally generated. A systematic study of the fundamentals of the process critical for joining in either a primary or a secondary mode is being undertaken. Specialized fixtures are being employed to study the role of substrate temperature in bond formation and strength, and the role of precompaction density and applied pressure on joint density. A Gleeble thermomechanical simulator is being used to study the role of reactant composition, reactant particle size, heating rate and reaction mode, precompaction and applied pressure, and atmosphere. Ultimately, a model of the SHS process for joining will be developed to facilitate joint design, predict joint properties, and enable intelligent control.
Reaction Processing and Properties of Sic-To-Sic Joints
Authors: Rabin B. H. , Moore G. A. 
Published: March 2011

AbstractReaction processing methods have been developed for fabricating SiC-to-SiC joints that can be used in elevated temperature applications. Processing steps include tape casting thin sheet SiC+C interlayer precursors, clamping the tape between the ceramic parts, providing a source of Si adjacent to the joint, and heating above the melting point of Si in argon. Molten Si infiltrates the tape via capillary action forming a reaction bonded silicon carbide (RBSC) interlayer and simultaneously joining the ceramic parts. Four-point bending strength and fracture toughness of joined pressureless sintered α-SiC test specimens have been evaluated at room and elevated temperatures. At low temperatures the joint mechanical properties were comparable to those reported for bulk SiC, while at elevated temperatures the joint properties were characteristic of the RBSC interlayer.
Joining of Metal Films to Carbon-Carbon Composite Material by Metal Plasma Immersion Ion Implantation
Authors: Anders André , Anders Simone , Brown Ian G. , Chow Peter 
Published: March 2011

AbstractAdhesion of metal films to carbon-carbon composite materials is a problem when using conventional techniques such as sputter deposition. Metal plasma immersion ion implantation is a novel technique which in combination with metal plasma deposition can produce metal-tocomposite bonding with very good adhesion characteristics. The substrate is immersed in a metal plasma which is produced by a pulsed vacuum arc. When the substrate is biased to high negative voltage the metal ions are accelerated toward and implanted into the substrate. A repetitively pulsed bias (Its pulses) is used to avoid arcing and other deleterious effects. Between high voltage pulses, metal plasma is deposited onto the surface with an energy typical of vacuum arcs, about 50–100 eV. The underlying idea of this mixed implantation-deposition technique is the formation of an extended substrate-film intermixed layer. We have demonstrated the technique for nickel films on carbon-carbon composite materials.