bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Temperature Silicides for Poly-Silicon Thin Film Transistor Applications
Authors: Sarcona G. T. , Hatalis M. K.
Published: April 2011

Thin films of cobalt, nickel, and tungsten were sputtered on three types of silicon materials to explore their potential for use as silicides in thin film transistor technologies for active matrix liquid crystal displays. The metals were sputtered onto single-crystal, polycrystalline, and amorphous silicon. The metals were annealed in vacuum after deposition over temperatures ranging from 250°C to 750°C. The sheet resistance of the resulting silicide films was measured using a four point probe apparatus. Cobalt silicides with sheet resistance of less than 4 Ω/ were formed at 600°C. Nickel produced films with sheet resistance below 10 Ω/▪ at 350°C, though the surface was required to be vacuum-clean. In this study, tungsten did not produce silicides. Surface preparation has been found to be an important factor in tungsten and nickel silicidation.
Interface Stability of Ti(Sil−yGey)2 and Si1−x Gex Alloys
Authors: Aldrich D. B. , D'Heurle F. M. , Sayers D. E. , Nemanich R. J.
Published: April 2011

The stability of C54 Ti(Si1−yGey)2 films in contact with Si1−xGex substrates was investigated. The titanium germanosilicide films were formed from the Ti − Si1−xGex solid phase metallization reaction. It was observed that Ti(Si1−yGey) 2 initially forms with the same germanium content as the Si1−x Gex substrate (i.e., y = x). Following the initial formation of TiM2 (M = Sil−yGey), silicon and germanium from the substrate diffuse into the TiM2 layer, the composition of the TiM2 changes, and Si1−z Gez precipitates form along the TiM2 grain boundaries. The germanium content of the Ti(Sil−y Gey)2 decreases, and the Sil−z Gez precipitates are germanium rich such that y < x < z. This instability of the TiM2 film and the dynamics of the germanium segregation were examined using the Ti-Si-Ge ternary equilibrium diagram. The relevant region of the ternary diagram is the two phase domain limited by a Si-Ge solid solution and a TiSi2 − TiGe2 solid solution. In this study first approximation Ti(Sil−y Gey)2 -to- Sil−xGex tie lines were calculated on the basis of classical thermodynamics. The tie line calculations indicate that for C54 Ti(Sil−yGey)2 to be stable in contact with Sil−xGex, the compositions of the two phases in equilibrium must be such that y < x. The specific compositions of the two phases in equilibrium depend on the temperature and the relative quantities of the two phases. The dynamic processes by which the Ti(Si1−yGey)2/Si1−x. Gex, system progresses from the as-formed state (y = x) to the equilibrium state (y < x) can be predicted using the tie line calculations.
Silicidation Strategy Of Sub-0.1 μm Junctions for Deep Submicron Devices
Authors: Tsai Jiunn-Yann , Osburn Carlton M. , Hsia Steve L.
Published: April 2011

Two major concerns for silicidation of ultra-shallow junctions, namely the silicon-consumption- induced junction leakage and the series resistance increase, were compared among conventional post-junction-silicide (PJS) contact, silicide-as-a-diffusion-source (SADS) contact, Silicon-On-Insulator (SOI) contact, and elevated-source-drain (ESD) contact. Even though we found that ESD contacts would be the ultimate solution for both problems, SOI and SADS contacts provide better resistance to silicon-consumption-induced series resistance increase over conventional PJS contact because both are able to maintain a high dopant concentration at the silicide/silicon interface and thus a low specific contact resistivity. While there is no junction leakage concern for SOI contact, the SADS junction is also distinguished by low leakage owing to its lack of implant damage in the silicon substrate and uniformly doped junction along the silicide/silicon interface contour. MOSFET devices with SADS source/drain were demonstrated with quarter-μm technology. Epitaxial cobalt disilicide (CoSi2) was formed using the Ti/Co bilayer technique as a diffusion source. While both ESD and SOI processes still suffer from process complexity, integration and materials issues, we conclude that SADS contacting is a promising alternative for deep submicron devices.
Magneto-Transport Properties of Epitaxial Iron-Silicides
Authors: Goncalves-Conto S. , Onda N. , Von Känel H.
Published: April 2011

The phase-breaking time τφ'. in thin α-FeSi2 films was obtained from the analyses of the lowtemperature magnetoresistance (MR). The films were grown by molecular beam epitaxy (MBE) on Si(111) and capped with epitaxial Si. The MR behavior is interpreted in terms of two-dimensional (2D) weak localization with strong spin-orbit interaction and electron-electron interaction (EEI). By fitting the MR data we obtained the temperature dependence of τφ. The results indicate the phase-breaking time to vary as T− over a large temperature range from 1.7 to 15 K, in agreement with the dependence predicted by the EET in 2D systems.
Characterization of Ultra-Thin PtSi Films for Infrared Detectors
Authors: Bender H. , Roussel P. , Kolodinski S. , Torres A. , Donaton R. A. , Maex K. , van der Sluis P.
Published: April 2011

Transmission electron microscopy and grazing incidence X-ray diffraction are used for the structural characterization of ultra-thin PtSi layers on (100) silicon prepared by a two-step rapid thermal annealing process. The roughness of the layers is investigated with atomic force microscopy. Two deposition techniques for the initial Pt layer are compared.
Synchrotron Radiation Studies of Platinum Silicide Thin Films
Authors: Sham T. K. , Naftel S. J. , Bzowski A. , Das S. R. , Xu D.-X. , Heald S. M. , Brewe D. , Kuhn M.
Published: April 2011

PtSi thin films prepared by UHV sputter-deposition procedures on n-type Si(100) wafers have been studied with the following techniques: (a) X-ray absorption fine structure spectroscopy at the Si K-edge, Si L2,3-edge, and Pt L3-edge; (b) X-ray reflectivity at photon energies below and above the Pt L3-edge threshold and (c) Photoemission. These techniques provide valuable information about the electronic structure, morphology, local structure, thickness, density and roughness, and surface and interface properties of the films. Preliminary results from the application of these techniques to the study of several PtSi thin films (with thickness from several hundreds to thousands of Å) are reported.
Characterization of Atmospheric Impurities in Tungsten Silicide Films by Secondary Ion Mass Spectrometry (SIMS)
Authors: Mitha Salman , Sams David B.
Published: April 2011

Concentrations of atmospheric impurities in tungsten silicide films and impurity areal densities silicide / polysilicon interface can usually only be measured using Secondary Ion Mass Spectrometry (SIMS). Normally these measurements are made using a Cs+ primary beam with negative secondary ions being monitored. This mode is used to achieve the best possible detection limits. However the Relative Sensitivity Factors (RSFs) used to quantify the impurities, as well as the reference matrix signal, change dramatically in going from one matrix to the other. These changes affect the quantification of the impurities at the interface. An alternate mode of analysis would be to use the Cs+ primary beam and monitor MCs+ ions, where M is the impurity, because these ions typically have less matrix dependent RSFs. We measure carbon and oxygen in a tungsten silicide film on polysilicon using both modes of analysis. Preliminary data indicates that we have determined the absolute accuracy of interface areal density to within a factor of 2.2 for oxygen and to within a factor of 1.5 for carbon.
Effect of the Volume Variation on the Superconductivity of TaSi2
Authors: Keller N. , Laborde O. , Gottlieb U. , Madar R.
Published: April 2011

TaSi2, and NbSi2 are superconductors below 353 mK and 130 mK respectively. These compounds, like VSi2 which is not superconducting down to 100 mK, crystallise in the C40 structure. They differ by a slight variation of lattice parameters.

We have systematically investigated the superconducting properties of several samples of TaSi2 by magnetic and resistive measurements. A small difference on Tc is observed for the same crystal by the two techniques. Several explanations are presented for this result.

We also report a change of Tc under pressure in good agreement with those resulting of the volume variation for the two C40 superconductors previously studied.
Formation and Relaxation of Ni(Au) Disilicide
Authors: Mangelinck D. , Ga P. , Gay J. M. , Pichaud B.
Published: April 2011

The formation and the relaxation of NiSi2 films with and without Au are examined by scanning electron microscopy, X-ray diffraction and Rutherford backscattering spectrometry. We studied the solid state reactions between a Ni(7 at.% Au) thin film and a Si substrate which occurs during the solid phase epitaxy before the formation of NiSi2. We show that the addition of Au to the Ni film drastically affects the silicides formation: Ni2Si and NiSi appear simultaneously and the nucleation temperature of NiSi 2 is lowered. The solubility of Au in the three silicides is limited which induces a precipitation of Au. Depending on temperature this precipitation takes various forms: Au enriched surface layer or Au clusters at inner interfaces. The films lattice parameters both parallel and perpendicular to the interface are also measured and compared to the lattice parameters of bulk samples which have been made by solidification from the melt. The relaxation modes are deduced from these measurements.
Post Titanium Silicide Processing
Authors: Grynkewich G. , Ilderem V. , Miller M. , Ramaswami S.
Published: April 2011

Decreasing contact dimensions coupled with the need for planarization to accommodate multiple layers of metal have created many challenges for the contact etch module. For example, contact etch processes are often required to stop on thin titanium silicide while at the same time forming high aspect ratio, straightwalled contacts. In this paper, the impact of various dielectric compositions and contact etch process parameters on etch profile, selectivity, and contact resistance is presented for the formation of high aspect ratio, submicron contacts to thin TiSi2 layers. The etch profile is formed by RIE using a mixture of CHF3 and various amounts of CF4. Surprisingly, the sidewall angle and selectivity to silicide showed little dependence on the percent CF4. Contact resistance measurements, however, varied greatly with percent CF4 and contact aspect ratio. The variation of contact resistance with etch chemistry was attributed to a variation in the extent of fluorocarbon polymer film formation, which in turn depends on the ratio of carbon to fluorine in the plasma. Finally, post contact etch treatments were examined for efficiency in removing the polymer films from the high aspect ratio contacts.
Controlled Grain Size and Location in GE Thin Films on Silicon Dioxide by Low Temperature Selective Solid Phase Crystallization
Authors: Yang C. M. , Atwater Harry A.
Published: April 2011

Selective solid phase crystallization for control of grain size and location in polycrystalline thin Ge films on amorphous silicon dioxide substrates is described. The approach consists of selective solid phase crystal nucleation via an alloy reaction at predefined nucleation sites, which consist of metal islands deposited on top of the amorphous Ge film, followed by lateral solid phase epitaxial growth. Grain sizes as large as 30 μm have been achieved in 50 nm thick Ge films at temperatures less than 475 °C.
Properties and Fracture Resistance of Thin Polycrystalline Aluminum Films on Sapphire Substrates
Authors: Moody N. R. , Medlin D. , Guthrie S. , Hwang R. Q. , McCarty K. F.
Published: April 2011

We employed nanoindentation, continuous microscratch testing, and high resolution TEM to determine the effect of structure on the properties and resistance to fracture of thin polycrystalline aluminum films deposited onto single crystal sapphire substrates at 25°C and 250°C. These films had a nominal thickness of 90 nm and a grain size of 160 nm. The elastic and plastic properties were similar for both films. The elastic moduli superimposed, increasing from bulk aluminum values at the surface to sapphire values at the interface. Hardness values also superimposed, but were constant through the film thickness at a value between aluminum and sapphire. In contrast, susceptibility to fracture varied markedly between the films with the 25°C film exhibiting abrupt failure along the film-substrate interface while the 250'C film gave no indication of fracture in the film, along the interface, or in the substrate under the conditions tested.
Giant Magnetoresistivity in Electrochemically Produced Cobalt-Copper Multilayers
Authors: Lashmore David S. , Hua Susan Z.
Published: April 2011

The electrodeposition of cobalt-copper multilayers will be described and the dependence of their magnetoresistivity on layer thickness and deposition parameters will be presented. For a wide variety of layer thicknesses electrochemically produced Co(Cu)-Cu thin polycrystalline layered alloys exhibit a giant magnetoresistivity (GMR). Further, upon annealing, the materials undergo a combination of grain growth and grain boundary diffusion. At certain conditions, this phenomena is believed to lead to a break up of the layered structure so that a magnetostatic coupling occurs and contributes to the GMR behavior. It is further shown that, by careful control of the deposition parameters, a quasilinear GMR response (low sensitivity) can be created over a large magnetic field or, conversely, a high sensitivity material can be grown, although at the sacrifice of introducing hysteresis in the response curve. The major deposition parameter affecting this behavior is mass transport in the electrolyte; however, substrate grain size, layer spacing and annealling history also play an important role.
Evolution of the Surface Structure of CVD Tungsten During Annealing
Authors: Briant C. L. , Wilson R. H. , Bigio L. , Morris W. G.
Published: April 2011

This paper reports a study in which a rough tungsten surface was prepared by chemical vapor deposition of tungsten on a tungsten ribbon. The samples were then heated to study the smoothing behavior of the rough surface. The results show that at 1600°C the surface becomes smooth after approximately five to ten hours. At 2400°C the surface becomes smooth within 15 minutes.
Application of Rapid Thermal Annealing on LPCVD Polysilicon Films for Piezoresistivity
Authors: Kleimann P. , Berre M. Le , Barbier D. , Pinard P.
Published: April 2011

Polycrystalline silicon is used as a transducing material in pressure microsensors. Its piezoresistive properties are strongly dependent on the processing steps and its properties -which define the sensor characteristics- vary sharply with temperature. LPCVD boron implanted polysilicon thin films have been annealed by RTA at 1100°C or below under conditions ensuring a uniform dopant distribution accross the film thickness. The resistivity as well as the gauge factor have been measured and compared with other authors' results. The gauge factor has been measured using the clamped beam technique between room temperature and 200°C with a specially designed apparatus. Technological parameters such as the Temperature Coefficient of Resistance (TCR) and the Temperature Coefficient of the Gauge Factor (TCK) are deduced as a function of doping. It appears that such coefficients do not satisfactorily describe the resistivity and gauge factor behavior at high temperature.
Damageless Magnetron Sputtering Deposition of SnO2:Sb Thin Films with Compensation Methods
Authors: Shin Sung Ho , Song Kug-Hyun , Park Kwang Ja , Ishida Tadashi , Tabata Osamu
Published: April 2011

Phenomena and solving methods for damage of Sb-doped SbO2 thin films deposited by RF magnetron sputtering have been investigated by observing in the main the positional difference of film electrical resistivity. A ring plate mask was used to disperse the energetic particles and sputtering parameters were controlled such a manner that effects by the parameters were compensated each other. By the control, positional differences in resistivity and XRD patterns of the films could be reduced to a minimum value; The films became nearly uniform ones.
Microstructure and Electrical Properties of Zinc Films on InP
Authors: Kamiinska E. , Piotrowska A. , Barcz A. , Kasjaniuk S. , Mizera E. , Dynowska E.
Published: April 2011

The interactions between thin films of Zn and (100)InP were analysed with secondary ion mass spectrometry, X-ray diffraction and transmission electron microscopy. Zn was found to penetrate the native oxide on InP surface during deposition, and to form an ohmic contact when deposited on n-type InP. Under heat treatment Zn protrudes into InP, and beneath Zn/InP interface a tetragonal Zn3P2 phase lattice matched to InP grows.
Optical and Electrical Real-Time Characterization of the Color-Switching Process in Thin Film Electrochromic Devices
Authors: Martí J. , Gimeno S. , Lousa A. , Bertran E.
Published: April 2011

Multilayer structures for electrochromic devices have been produced using vacuum evaporation and electrochemical deposition, and have been optically and electrically characterized by real time measurements. The deposited structures consist of a five layer stack comprising a transparent electrode (indium tin oxide) on glass substrates, an electrochromic active layer (W03), an electrolyte, a complementary electrochromic film (prussian blue) acting as a reservoir for the active layer, and a second transparent or reflecting electrode. In order to determine the process dynamics, real time transmittance and reflectance spectral analysis on the visible range have been performed using a multiple analysis system (OMA), during colorswitching of the device, in coordination with electrical characterizations of the switching process by current and charge transfer measurements. These measurements were performed as a function of time and of the driving voltage, and provide a means of determining the structural parameters of the device through the switching time and the current transient.
Microstructure and Activity of Thin Films for a Microelectronic Gas Sensor
Authors: Patel Sanjay V. , Dibattistam Michael , Gland John L. , Schwank Johannes W.
Published: April 2011

Scanning force microscopy is used to study the structure of various sensing films after chemical and thermal treatments. An example chemical modification of the sensing film can be achieved by heating a Pt/Ti sensing film in an oxygen environment. 1 With Pt acting as a catalyst, the Ti can become partially oxidized, resulting in a Pt/TiOx film which has different electronic properties than a metallic film. By further oxidizing the film, an insulating layer of TiO2 may be achieved. Or as in the case of hydrogen sensing, the Pt/TiOx film may revert to a more metallic state via the reduction of TiOx. The chemical interactions of these sensing films may be associated with large scale microstructural changes. The sensing activity and the structure of Ti, Pt/Ti, and Au/Ti films to gases such as hydrogen, and propylene has been studied. These chemical and morphological changes can be monitored by measuring the resistance of the thin sensing films. Pt/Ti films were found to have the best response to hydrogen (200 ppm) and propylene (150 ppm), while Au/Ti films showed weaker response to propylene (500 ppm) and CO (1000 ppm). The Pt/Ti films also showed shifts in temperature with changing propylene concentration possibly due to catalytic combustion.
X-ray Diffraction and Modelling Studies of Multilayer SnO2 Thin Film Gas Sensors
Authors: Depero L. E. , Perego C. , Sangaletti L. , Sberveglieri G.
Published: April 2011

Structural studies have been carried out on SnO2 multilayer thin film grown by the Rheotaxial Growth and Thermal Oxidation method on A120 3 substrates. A preliminary analysis of the X-ray diffraction patterns shows that, in addition to the Sn0 2 cassiterite phase, a strong contribution from an orthorhombic Sn02 phase is present.

In the case of the 3-layer film, the orthorhombic phase is structurally and microstructurally stable after an annealing up to 32 h at 400 'C. The cation coordination is similar to that found in cassiterite, but the chains of edge-sharing [SnO6]8- octahedra run in a zig-zag fashion along the [100] direction, each straight unit containing four octahedra. The relationship between the two phases is discussed on the basis of structural simulations including twinning planes in the crystal structure.
Morphology and Domain Structure of Unsupported PbTiO3Thin Films Prepared by Sol-Gel Process
Authors: Lu C. J. , Ren S. B. , Shen H. M. , Wang Y. N.
Published: April 2011

The morphology and domain structure of unsupported PbTiO3thin films with fine grains (>200 nm) were investigated by TEM technique. The unsupported PbTiO3thin films were successfully prepared by sol-gel process onto NaCI substrates and followed by dissolving away the substrates. Electron diffiraction patterns showed that the unsupported PbTiO3thin films had slight <110> preferred orientation perpendicular to the film surfaces. Grain size and morphology vary significantly with the thickness of the films or the annealing temperatures. Even though the grain size is rather small (40–180 nm), the domains are clearly visible. Most of the grains show single domain, while some irregular and curved domain walls appear only in a small portion of the fine grains. The number of single-domained grains increases with decreasing grain size. Almost all domain walls observed are 90° walls.
Composition Control of Lead or Bismuth Based Ferroelectric Thin Films Prepared by Sputtering Method
Authors: Yamakawa K. , Trolier-McKinstry S. , Dougherty J. P.
Published: April 2011

Composition control in lead or bismuth based ferroelectric thin films was studied for rf magnetron, dc magnetron and ion beam sputter depositions with metal or oxide targets. For room temperature depositions, (1) control of the target surfaces, (2) suppression of harmful effects from negative ions and (3) control of oxygen content in the films were significant. The surface of the lead target gradually degrades and alters the lead flux extracted from the target. At low pressures resputtering from the film occurs by negative oxygen ions. It is necessary to put more oxygen into the films in the sputter depositions with metal targets and the ion beam sputter depositions. For high temperature depositions, a composition self control was observed for films deposited in excess lead environments.
A Microstructural Model of the Electrical Failure of an Interconnect Resulting from Flux Divergences
Authors: Rickman J. M. , Smith D. A. , Nichols C. S.
Published: April 2011

A simplified microstructural model of an interconnect is considered in order to develop a criterion for failure due to void production induced by electromigration. The kinetics of growth of individual voids at grain triple junctions are calculated and the time dependence of the change in conductance of an interconnect estimated from the time dependence of the total volume of voids produced. It is found that the time to failure increases with increasing grain size, i.e., decreasing density of sites for flux divergence, consistent with observations.
Representation of Finite Cracks by Dislocation Pileups: An Application to Atomic Simulation of Fracture
Authors: Shastry Vijay , Farkas Diana
Published: April 2011

The elastic displacement field solution of a semi-infinite crack in an anisotropic body, calculated using a complex variable approach due to Sih and Liebowitz, is usually used by atomistic simulations of fracture. The corresponding expression for the displacement field of a finite crack is numerically cumbersome since it involves multiple square roots of complex numbers. In this study, displacement field of the crack is calculated by superposing the displacements of dislocations in an equivalent double pileup, equilibrated under mode I conditions. An advantage of this method is its extensibility to atomistic studies of more complex systems containing multiple cracks or interfaces. The pileup representation of the finite crack is demonstrated as being equivalent to its corresponding continuum description using the example of a double ended crack in α-Fe, loaded in mode I. In these examples, the interatomic interaction in α-Fe is described by an empirical embedded atom (EAM) potential.
Dislocation Kink Motion - Ab-Initio Calculations and Atomic Resolution Movies
Authors: Spence J. C. H. , Kolar H. R. , Huang Y. , Alexandera H.
Published: April 2011

The results of recent ab-initio, relaxed, computations for the energy barrier to the motion of a kink on a 30° partial dislocation in silicon are summarised. The electronic structure and charge density are given. We suggest that the shearing motions involved with ductility and kink motion are controlled by the band structure energy involving valence electrons, whereas the tensile forces involved in fracture depend on both ion-ion and valence forces. Experimental atomic resolution TEM images of dissociated dislocation lines in silicon are discussed. These are formed using “forbidden reflections” with the dislocation lines lying on (111), normal to the electron beam. For images of samples at 600 C recorded at video rates, differences between successive frames reveal the motion of individual kinks, from which the kink velocity and migration energy can be estimated.
An Ab Initio Investigation of a Grain Boundary in a Transition Metal Oxide
Authors: Dawson I. , Bristowe. P. D. , Payne M. C. , Lee M-H.
Published: April 2011

We have used ab initio total energy plane wave pseudopotential methods to perform the first completely ab initio investigation of the atomic and electronic structure of a grain boundary in a transition metal oxide. The ∑ = 15 (210)[001] tilt boundary in rutile TiG2 is studied using the conjugate gradients iterative minimisation technique for performing total energy calculations within the LDA and pseudopotential approximations. The stability of the experimentally observed translation state of the boundary is confirmed, and some insight is gained into its electronic structure.
Equation of State for PdH by a New Tight Binding Approach
Authors: Papaconstantopoulos D. A. , Mehl M. J.
Published: April 2011

We present an extension of a newly proposed tight-binding method of calculating total energies and related quantities to the study of binary compounds. As an example, we discuss the equation of state of the palladium-hydrogen system.
Cu-Au Alloys Using Monte Carlo Simulations and the BFS Method for Alloys
Authors: Bozzolo Guillermo , Good Brian , Ferrante John
Published: April 2011

Semi empirical methods have shown considerable promise in aiding in the calculation of many properties of materials [1,2]. Materials used in engineering applications have defects that occur for various reasons including processing [3]. In this work we present the first application of the BFS (Bozzolo, Ferrante and Smith) method for alloys [1] to describe some aspects of microstructure due to processing for the Cu-Au system (Cu-Au, CuAu3 , and Cu3Au). We use finite temperature Monte Carlo calculations, in order to show the influence of ’heat treatment‘ in the low-temperature phase of the alloy. Although relatively simple, it has enough features that could be used as a first test of the reliability of the technique. The main questions to be answered in this work relate to the existence of low temperature ordered structures for specific concentrations, for example, the ability to distinguish between rather similar phases for equiatomic alloys (CuAu I and CuAu II, the latter characterized by an antiphase boundary separating two identical phases).
Some Computer Simulations of Semiconductor Thin Film Growth and Strain Relaxation in a Unified Atomistic and Kinetic Model
Authors: Madhukar A. , Yu W. , Viswanathan R. , Chen P.
Published: April 2011

An overview is provided of an evolving atomistic and kinetic model of semiconductor growth that unifies the main features of strain relaxation in low and high lattice misfit heteroepitaxy. The model reveals a kinetic pathway for dislocation formation during growth with little or no energy cost at low misfits, thus providing a way out of the longstanding dilemma of too high dislocation nucleation energies predicted by classical theories of the equilibrium behaviour of a fixed number of particles at low misfits. The essential kinetic processes underlying the model are identified on the basis of comparison of the predictions of kinetic Monte-Carlo simulations of growth with real-time or in-situ data obtained in such experiments as reflection high-energy electron diffraction (RHEED) and scanning probe microscopy (SPM). Relative significance of these atomistic kinetic processes is shown to naturally lead to strain relaxation via defect initiation at low misfits while maintaining smooth surface morphology or at high misfits change to 3-dimensional morphology while initially maintaining coherence. The potential role of steps in providing sources for defect formation is examined through molecular dynamics simulations of Ge overlayers on Si (001) stepped surfaces.
Ab Initio Molecular Dynamics Simulations of Molecular Crystals
Authors: Tuckerman Mark E. , Rosenvinge Tycho von , Klein Michael L.
Published: April 2011

Molecular crystals are studied using the Car-Parrinello ab initio molecular dynamics simulation technique. In particular, the motion of protons in a variety of systems is considered. Results are presented on the rotation of the methyl group in solid nitromethane and proton transfer through a hydrogen bond in hydrogen chloride dihydrate crystal.
Embrittlement of Cracks at Interfaces.
Authors: Emeritus Robb Thomson , Carlsson A. E.
Published: April 2011

This paper presents a synopsis of already published work for cracks on interfaces and new results on the effect of changing the chemistry of the atoms at the interface. Once the appropriate cut-off for the oscillatory singularity in the interface analysis is determined, the physics of the crack is determined in terms of an appropriate driving force for a particular event of interest, and a lattice resistance to the event. Analytic approximations are available for the driving forces, and the lattice resistance is determined on the basis of a block construction for the lattice. We show that for the case where the chemical bonding at the interface is different from that in the matrix, the same ideas are applicable, provided the different chemistry is incorporated correctly in the lattice resistance construction.
Mixed Mode Interface Toughness Of Metal / Ceramic Joints
Authors: Wei Yueguang , Hutchinson John W.
Published: April 2011

A mechanics study of the interface toughness of joints comprised of ceramic substrates joined by a thin ductile metal layer is carried out for arbitrary combinations of mode I and mode II loading. The crack lies on one of the metal/ceramic interfaces, and the mechanism of separation at the crack tip is assumed to be atomic decohesion. The SSV model proposed by Suo, Shih and Varias is invoked. This model employs a very narrow elastic strip imposed between the substrate and the ductile layer to model the expected higher hardness of material subject to high strain gradients and possible dislocation-free zone in the immediate vicinity of the crack tip. The criterion for crack advance is the requirement that energy release rate at the crack tip in this narrow elastic strip be the atomistic work of fracture. The contribution of plastic dissipation in the metal layer to the total work of fracture is computed as a function of the thickness and yield strength of the layer and of the relative amount of mode II to mode I. Ductile joints display exceptionally strong thickness and mixed mode dependencies.
The Non-Linear Behaviour Of A Model Related To The Fracture Of Composite Materials
Authors: Varone Alberto , Meloni Franco , Ginesu Francesco , Aymerich Francesco
Published: April 2011

The fracture of a fibre reinforced graphite peek polymer is considered when dynamic load is applied. The energy-time diagram shows various critical points during cyclic tensile loading. A quantitative analysis based on the study of the fractal dimension of the chaotic attractor in the representative phase space will allow us to individuate the physical parame ters responsible of the stability range of the material. A new simple model has been derived and successfully tested from a non-linear chaotic scheme. The present approach appears very promising for a future interdisciplinary study for evaluating the physical response of real massive materials under stress.
On The Response Of Dynamic Cracks To Increasing Overload
Authors: Gumbsch P.
Published: April 2011

One of the most interesting questions in the dynamics of brittle fracture is how a running brittle crack responds to an overload, i.e. to a mechanical energy release rate larger than that due to the increase in surface energy of the two cleavage surfaces. To address this question, dynamically running cracks in different crystal lattices are modelled atomistically under the condition of constant energy release rate. Stable crack propagation as well as the onset of crack tip instabilities are studied.

It will be shown that small overloads lead to stable crack propagation with steady state velocities which quickly reach the terminal velocity of about 0.4 of the Rayleigh wave speed upon increasing the overload. Further increasing the overload does not change the steady state velocity but significantly changes the energy dissipation process towards shock wave emission at the breaking of every single atomic bond. Eventually the perfectly brittle crack becomes unstable, which then leads to dislocation generation and to the production of cleavage steps. The onset of the instability as well as the terminal velocity are related to the non-linearity of the interatomic interaction.
Scaling And Universality In Real Cracks
Authors: Daguier Pascal , Bouchaud Elisabeth
Published: April 2011

The morphology of fracture surfaces in complex metallic alloys is analysed. The simultaneous use of Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) allows the measurement of the universal roughness exponent ζ┴ = 0.78 over five decades of lengthscales (0.5 nm - 0.5 mm). Furthermore, a small lengthscales regime (lnm - 1 μm) is shown to be characterised by a roughness index ζ┴QS ≃ 0.5.

On the other hand, cracks fronts stopped during their propagation at pinning microstructural obstacles in two different metallic alloys is analysed, and their “in-plane” roughness index is determined for the first time. In the case of the 8090 Al-Li alloy, which has a very anisotropic microstructure, the roughness of the tensile crack front propagating along the grains length is equal to ζ ≃ 0.60. On the other hand, the roughness of the purely three-dimensional fatigue crack front in the Superα2 Ti3Al-based alloy is equal to ζ ≃ 0.54.
Atmospheric Pressure Chemical Vapor Deposition of 3C-SiC
Authors: Russell Michael W. , Freitas Jaime A. , Berry Alan D. , Butler James E.
Published: April 2011

Optically transparent SiC deposits were grown via atmospheric pressure chemical vapor deposition (APCVD) on graphite substrates from methyltrichlorosilane (MTS) in hydrogen in a cold-walled, RF-induction furnace. Structural morphology was examined by scanning electron microscopy and correlated to substrate temperature, MTS/H2 ratio, and hydrogen flow. Photoluminescence revealed that high quality cubic material was grown. The PL spectra exhibited a zero phonon line (2.3787 eV) attributable to an exiton bound to a neutral nitrogen donor, in addition to TA, LA, TO, and LO phonon replicas. Observed broadening and splitting of the PL spectral lines was associated with the morphological habit and internal strain of individual crystallites. In addition, the PL spectra for samples grown at higher MTS/H2 ratios and low H2 flows exhibited weak shoulders on the low energy side of the five-line spectra which might be associated with nonstoichiometric defects such as Si interstitials or C vacancies.
Adhesion of ZrN And SiC Thin Films on Titanium and Nickel Alloys
Authors: Gruss K. A. , James R. D. , Davis R. F.
Published: April 2011

Chemically inert ceramic coatings are currently being investigated to extend the lifetime of metallic components operating in severe environments. Polycrystalline ZrN and amorphous SiC coatings were deposited by cathodic arc evaporation and by PACVD, respectively, on Titanium Grade 12 and Incoloy 825 metal substrates. The structure of the coatings was verified by SEM and XRD. Residual stress analyses were performed on the ZrN coatings via XRD using the sin2 φ method. Compressive stresses of 3.7 GPa and 2.5 GPa were calculated in the ZrN on the Incoloy and Titanium substrates, respectively. Studies of the interfacial chemistry via AES revealed chemically abrupt interfaces. Scratch tests were employed to assess the critical load for interfacial failure and fracture mechanisms for the various coating systems. Critical loads, charaterized by a kidney-shaped crack patterns found in the scratch tracks, occurred at 12 N for ZrN on Titanium and 20 N for ZrN on Incoloy. Interfacial failure of SiC on Titanium was dominated by brittle fracture of the SiC coating at 3N loads.
Processing and Mechanical Properties of SiC-Metal Interpenetrating Composites
Authors: Hozer Leszek , Chiang Yet-Ming , Ivanova Svetlana , Bar-On Isa
Published: April 2011

In this paper we demonstrate a liquid exchange process to introduce a ductile metal reinforcement phase in the amount of 10–30 vol. % into reaction-bonded silicon carbides (RBSCs). Immersion of RBSC in pure Al or Al-Si melts enables diffusional replacement of secondary phase silicon with metal. The Al and Al-Si exchanged composites show improvement in fracture toughness (single edge precracked beam technique) to 6–7 MPa·m1/2 as compared to 3–4 MPa·m1/2 in otherwise similar siliconized silicon carbide. Increased fracture strength (four point flexure) was also observed after the liquid exchange process.
The Reaction of NH3 With TiN: Implications for CVD
Authors: Schulberg Michelle T. , Allendorf Mark D. , Outka Duane A.
Published: April 2011

Since NH3 is an important component of TiN chemical vapor deposition (CVD) processes, understanding the NH3/TiN surface interaction is crucial to developing a model for the overall reaction. Temperature programmed desorption experiments show that NH3 adsorbs molecularly on amorphous TiN surfaces. Chemisorption occurs at only ∼5% of the surface sites, with an activation energy for desorption of 24 kcal/mol. The sticking probability into this state is 0.06 at 100 K. In addition, NH3 adsorbs with high probability into a multilayer state with an activation energy for desorption of 7.3 kcal/mol, similar to that found in other systems. NH3 does not dissociate on TiN. Under CVD conditions, however, the reactivity of NH3 on TiN may increase and surface reactions may play a part in film growth.
Electrical and Optical Properties of Defects in N-Type 4h-Sic
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C.
Published: April 2011

Several n-type 4H-SiC samples grown by the physical vapor transport technique were studied using both thermal and optical admittance spectroscopy. The ionization energy ED for nitrogen donors in 4H-SiC was determined to be 0.053 eV and 0.10 eV below the conduction band. This agrees reasonably well with the values of 0.052 eV and 0.092 eV determined by IR absorption measurements. It is believed that EC-0.053 eV is the ionization energy of the nitrogen atom occupying the hexagonal site (h). The 0.10 eV activation energy has been attributed to the nitrogen atoms occupying the cubic sites(k).

The optical admittance studies reveal five conductance peaks. One of these corresponds to the band-to-band transitions from which the bandgap of 3.41 eV was determined at 40K. The other four conductance peaks correspond to transitions from defect levels to the conduction band. These defects are located at EC-1.73 eV, EC-1.18 eV, EC-0.87 eV, and EC-0.72 eV.
Characterization of Mineral Deposits on Plasma-Sprayed HA-Coated Ti-6Al-4V
Authors: Benezra V. , Spector M. , Hobbs L. W.
Published: April 2011

Plasma-sprayed hydroxyapatite (PSHA) coatings are often used as the attachment vehicle for the femoral component of a total hip prosthesis. The key to successful hip replacement is the attachment of the femoral stem to the surrounding bone.

Within hours of implantation of PSHA-coated Ti-6AI-4V rods in canine bone, bone mineral deposits on the HA coating. These deposits take the form of globular networks of fibrous crystallites. The crystallinity of these deposits was confirmed via high-resolution transmission electron microscopy (TEM) and electron diffraction. We have also characterized the composition of these deposits using x-ray energy-dispersive spectroscopy (XEDS) in the scanning TEM. Finally, we have studied the morphology of the fiber-like crystallites by stereography in the TEM.
Engineering Biomaterials that Exhibit Recognition and Specificity
Authors: Ratner B. D. , Boland T. , Johnston E. E. , Tidwell C. D.
Published: April 2011

A set of methods that can be used to create surfaces to accurately control biological reactions is described. These include strategies for inhibiting non-specific reactions, making highly organized surfaces, spatially arraying recognition moieties and characterizing complex surfaces.
Pulsed Laser Deposition of Collagen Thin Films
Authors: Conklin J. A. , Cotell C. M. , Barnett T. W. , Hansen D. C.
Published: April 2011

Thin films of collagen were prepared by pulsed laser deposition (PLD) at room temperature on Si substrates using a KrF laser (248 nm) over a fluence range from 0.2–1.5 Jcm-2. The effects on film composition and morphology of ambient gas (Ar, Ar/H2O vapor), quenching atmosphere (Ar, Ar/H2O vapor), and fluence were examined. Fourier transform infrared spectroscopy (FT- IR) demonstrated that, independent of deposition parameter, the PLD films contained the characteristic Amide I and II functionalities of the collagen target and indicated that the secondary structure was altered by the PLD process. The surface morphology of the films was a function of the laser fluence and the gas environment during either film deposition or quenching at the end of deposition. Preliminary gel electrophoresis examination of deposited films suggested the collagen had not maintained the triple helical structure of the native collagen. X-Ray diffraction (XRD) indicated that all of the films, deposited under any conditions, were predominantly amorphous.
Aerotaxy: A New Route to Formation of GaAs Nanocrystals from Ga Droplets
Authors: Samuelson Lars , Deppert Knut , Malm Jan-Olle
Published: April 2011

A new process, named Aerotaxy, has been developed for growth of quantum dots (QDs) with identical sizes and properties. Self-assembly and intrinsic control of the nanocrystal properties is obtained by (i) an initial selection of spherical droplets of gallium (Ga), all having identical sizes within a few %, employing standard aerosol technology. In a second processing stage (ii) these droplets of gallium are allowed to react with arsine (AsH3), by which the metallic Ga droplets are completely converted into a monodisperse ensemble of galliumarsenide (GaAs) nanocrystals at temperatures as low as 260°C. GaAs nanocrystals, of approximate diameter 10 nm, have been produced and deposited on various substrates. The good crystallinity and stoichiometry of the formed particles are confirmed by transmission electron microscopy studies of individual nanocrystals.
Effect of Interdiffusion on the Subbands in an In0.65Gs0.35As/GaAs Multiple-quantum well Structure on GaAs Substrate at 1.55μm Operation Wavelength
Authors: Chan M. C. Y. , Li E. Herbert , Chan K. S.
Published: April 2011

Analysis of high indium concentration in interdiffused In0.65Gs0.35As/GaAs multiple quantum well (MQW) structure on GaAs Substrate is being studied. This material can achieve operating wavelengths around 1.5gtm Ifor applications in fiber optics communications. The large lattice mismatch problem (over 4.5% in this study) can be solved by using a linearly-graded InGaAs buffer layer for reducing any dislocation between the adjacent layers. Interdiffusion in the MQW structure can modify the composition profile in order to tailor the optical absorption and refraction properties. Results show that this system can have promising device performance operates at around 1.55μm and which base on the more matured and reliable GaAs technology.
Optimal Growth of InGaAs/InAlAs Distributed Bragg Reflectors Lattice-matched on InP Substrates
Authors: Choi S. W. , Lee J. H. , Baek J. H. , Lee E. H. , Lee B.
Published: April 2011

Distributed Bragg reflectors composed of InGaAs/InAlAs alternating layers have been grown on InP substrates by MOCVD. To obtain high performance, the growth condition has been traded off between surface roughness and crystal quality. Using in-situ laser reflectometry, the precise control of layer thickness and composition has been achieved for reproducible DBR growth. The optimal mirror performance and sharp interfaces have been observed in the DBR grown at 650'C. In order to avoid band-edge absorption 6% of Al has been added to In 0.53Ga0.47As to produce quarternary In0.53Ga 0.41Al 0.06As/InAlAs Bragg reflector exhibiting high reflectivity at 1.55 μm.
Luminescence Properties of Ytterbium and Oxygen Coimplanted InP
Authors: Lozykowski H. J. , Alshawa A. K.
Published: April 2011

In this work we report a systematic study of the effect of oxygen on ytterbium 4f- 4f emission by coimplanting Yb and O into InP. The PL spectra of InP: Yb and InP: (Yb+O) as a function of annealing temperature and duration were studied. In addition the photoluminescence and kinetic processes were investigated as a function of temperature and excitation intensity.The investigation shows that the codoped oxygen reduces drastically the Yb3+emissioon from SI and n-type InP:Yb under intrinsic excitation. The codoping of Yb and 0 may create a complex involving a YbInand Op. This structured isoelectronic (YbIn- Op) complex, may behave as a deep trap (or a deep donor) located approximately at the middle of bandgap. Exciton bound to such centers will not have sufficient energy to excite the core Yb 4f electrons by Auger direct energy transfer process.
Studies on Domain Inversion in LiNbO3and LiTaO3
Authors: Zhu Y. Y. , Zhu S. N. , Zhang Z. Y. , Ming N. B.
Published: April 2011

Domain inverted structures in LiNbO3 (LN) and LiTaO3 (LT) are fabricated by proton exchange followed by rapid heat treatment. The formation and development of the effects of pyroelectric field on domain inversion are investigated. The proton and lithium profiles are measured by SIMS. The Curie temperature of the proton exchanged LT is evaluated by DSC. An internal electric field model is proposed to explain the domain inversion mechanism.
Magnetoluminescence Studies in Ordered InGap2
Authors: Jones E. D. , Schneider R. P. , Mascarenhas A.
Published: April 2011

Photoluminescence measurements on ordered InGaP2 were studied as a function of temperature, laser power density, and magnetic field. The temperature varied between 1.4 and 300 K, the laser power densities ranged from 10 nW/cm2 to 20 W/cm2, and the maximum magnetic field was 13.6 T. The data show two spectra, excitonic and band-to-band transitions, depending upon the incident laser power density. A consistent interpretation of the band-to-band spectrum leads to a spatially separated electron-hole transitions between the ordered domains. Three different mechanisms for spatially indirect transitions are presented. An analysis of the linear data also allows a determination of the valence-band mass in the 100 direction of mv ∼0.25 m0.