bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual Scale Simulation of Grain Growth Using a Multi Phase Field Model
Authors: Steinbach Ingo , Apel Markus
Published: April 2011

The kinetics of grain growth in multicrystalline materials is determined by the interplay of curvature driven grain boundary motion and interfacial stress balance at the vertices of the grain boundaries. A comprehensive way to treat both effects in one model is given by the time dependent Ginzburg Landau model or phase field model. The paper presents the application of a multi phase field model, recently developed for solidification processes to grain growth of a multicrystalline structure. The specific feature of this multi phase field model is its ability to treat each grain boundary with its individual characteristics dependent on the type of the grain boundary, its orientation or the local pinning at precipitates. The pinning effect is simulated on the nanometer scale resolving the interaction of an individual precipitate with a curved grain boundary. From these simulations an effective pinning force is deduced and a model of driving force dependent grain boundary mobility is formulated accounting for the pinning effect on the mesoscopic scale of the grain growth simulation. 2-D grain growth simulations are presented.
Particle Dynamic Simulation of Semi-Solid Metal Rheology
Authors: Mullis Andrew M.
Published: April 2011

Models of semi-solid processing currently utilise constitutive equations to describe slurry rheology. However, using the techniques of molecular dynamics it may be possible to go beyond this approach to obtain direct relationships between applied shear rates, the resultant microstructural changes and rheology.

The results of a simple molecular dynamics simulation of semi-solid flow within a Couette rheometer are presented and compared with experimental data for the system Sn -15% Pb. We find that the model correctly predicts the apparent viscosity under steady state conditions, up to solid fractions of ≈ 40%.
Atomistic Simulation of kinks for 1/2a<111> Screw Dislocation in Ta
Authors: Wang Guofeng , Strachan Alejandro , ÇaǦin Tahir , Goddard Willam A.
Published: April 2011

We study the structure and formation energy of kinks in 1/2a<111> screw dislocation in metallic Ta Embedded Atom Model Force Field parameterized using quantum mechanical computations. We studied a/3<112> kinks using a simulation cell containing four dislocations in a quadrupole arrangement. We impose periodic boundary conditions in the directions perpendicular to [111] and fixed boundaries in the [111] direction. We find that two, energetically equivalent, core configurations for the 1/2a<111> dislocation lead to 8 distinguishable single kinks and 16 kink pairs. The different mismatches of core configurations along [111] direction cause variations in kink formation energy. The lowest formation energy of a kink pair is determined to be 0.73 eV. The geometric features of such kink pair have been studied with the help of structural analysis of the atomistic model. We also compare the activation energy for dislocation motion via the double kink mechanism with the activation energy for a rigid dislocation motion from a dipole annihilation simulation. We find that the migration energy for dislocation motion via double kink formation is 0.016 eV/b, which is less than the quarter of the migration energy associated with the kink free motion of a straight dislocation, 0.073 eV/b.
Self-interstitial Diffusion in α-Zirconium
Authors: Zhu W.J. , Woo C.H.
Published: April 2011

Self-interstitial Diffusion in α-Zirconium-Zr is studied using Molecular Dynamic (MD) and molecular static (MS) simulation using Ackland's many-body inter-atomic potential. The basal crowdion configuration is found to be the ground state. The diffusion process in Zr is complex. Four types of diffusion jumps can be identified, two in-plane and two out-of plane. The in-plane migration mechanism is dominated by one-dimensional crowdion motion along the [1120] directions, interrupted by occasional out-of-plane and on-line or off-line jumps. The mean lifetime before rotation of the crowdion is reported as a function of temperature. The activation energies for the diffusion processes are obtained. The diffusional anisotropy factor Dc/Da is also obtained, and compares well with experiment results.
Dislocation Nucleation and Propagation During Deposition of Cubic Metal Thin Films
Authors: Liu W. C. , Wang Y. X. , Woo C. H. , Huang Hanchen
Published: April 2011

In this paper we present three-dimensional molecular dynamics simulations of dislocation nucleation and propagation during thin film deposition. Aiming to identify mechanisms of dislocation nucleation in polycrystalline thin films, we choose the film material to be the same as the substrate – which is stressed. Tungsten and aluminum are taken as representatives of BCC and FCC metals, respectively, in the molecular dynamics simulations. Our studies show that both glissile and sessile dislocations are nucleated during the deposition, and surface steps are preferential nucleation sites of dislocations. Further, the results indicate that dislocations nucleated on slip systems with large Schmid factors more likely survive and propagate into the film. When a glissile dislocation is nucleated, it propagates much faster horizontally than vertically into the film. The mechanisms and criteria of dislocation nucleation are essential to the implementation of the atomistic simulator ADEPT.
Characterization of the Activation-Relaxation Technique: Recent Results on Models of Amorphous Silicon
Authors: Malek Rachid , Mousseau Normand , Barkema G. T.
Published: April 2011

The activation-relaxation technique (ART) is a method for finding saddle points in high-dimen- sional energy landscapes. ART has already been applied to a wide range of materials including amorphous semiconductors, Lennard-Jones glasses, and proteins. In spite of its successes, a number of fundamental questions remain to be answered regarding the biases associated with its sampling of the saddle points. We present here results of a detailed analysis of the biases in the simulation of amorphous silicon. We focus in particular on the biases of the method in sampling saddle points, the completeness of the sampling and the sensitivity of these quantities to variations of the different parameters.
A Synchrotron X-Ray Study of Texture Induced by Application of Magnetic Fields During Phase-Transformations in Shape-Memory Ni-Mn-Ga
Authors: Vaidyanathan R. , Yilmaz S. , O'Handley R.C. , Dunand D.C.
Published: April 2011

Ni-Mn-Ga alloys can exhibit a thermoelastic phase transformation near room temperature, which is associated with the shape-memory effect (i.e., temperature-induced strain recovery after twinning) or superelasticity (i.e., strain recovery after a stress-induced phase transformation). This work uses a synchrotron X-ray transmission technique to investigate texture induced by applying magnetic fields during the phase transformation in polycrystalline Ni2MnGa. Synchrotron X-ray radiation is ideally suited for such investigations since the measurements are representative of twinning in the bulk, in contrast with measurements from conventional X-ray sources that represent surface measurements affected by surface relaxation. Magnetic texturing of polycrystalline Ni2MnGa, by cooling through the phase-transformation in the presence of a magnetic field, has potential to lead to polycrystalline materials with more compatible field- induced strains and hence increased twin boundary mobility upon application of a magnetic and/or stress field.
The use of a variety of synchrotron techniques in the study of cementitious materials
Authors: Barnes P. , Colston S.L. , Jupe A.C. , Jacques S.D.M. , Attfield M. , Bailey S. P. , Pisula R. , Hall C. , Livesey P.
Published: April 2011

The electron synchrotron ’revolution’ is barely twenty years old yet its impact on materials science is immeasurable. Fig.1 captures the essence of synchrotron radiation with the dipole magnet, which is associated with a highly collimated fan of radiation due to the centripetal acceleration of electron bunches responding to the inwardly acting Lorentz force; however dipole magnets often play a secondary role in current “third generation” synchrotrons which also utilize more advanced magnet configurations (wigglers and undulators) that are capable of producing even more brilliant sources of X-radiation. The five main attributes of synchrotron X-ray beams are:

• The X-ray beam is intense, such that up to 1012 photons per second might be incident on a sample, thus enabling measurements with excellent counting statistics and/or short collection times.

• The radiation is horizontally polarized in the plane of the electron orbit.

• The X-ray beam is highly collimated, with a typical working divergence of ∼mrads, such that there is less wastage during its passage through the optical components and a superior angular resolution in the eventual measurement.

• The radiation has a smooth continuous 'white' spectrum extending into the hard (penetrating) X-ray region, thus offering the choice of conducting experiments with white radiation or alternatively enabling a free choice of wavelength by use of a monochromator.

• Since the electrons move in bunches the synchrotron X-ray source is actually pulsed, at a frequencies in the region of 3×108 s−1.
Study of TaSi2-Si Crystals with High Energy Synchrotron Radiation as Tunable Wide-bandpass Monochromator and Analyzer Optics
Authors: Rütt U. , Stock S.R. , Rek Z.U.
Published: April 2011

Single crystals of the in situ composite TaSi2-Si are candidates for wide bandpass monochromators and analyzers for x-ray experiments. Two large crystals (32 × 39 × 7 mm3 and 32 x 39 x 30 mm3) were studied in detail using 115 keV synchrotron radiation at the BESSRC beamline at the APS. For transmission geometry, the Si(111) reflection and 39 mm crystal thickness, rocking curve widths of 95 arc sec with reflectivities of 50% were measured over the entire crystal. Turning the crystal to an angle of 45° to the incident beam and translating it through the beam allowed investigation of the influence of crystal thickness on diffracted intensity. For sample thicknesses ranging between 5 mm and 12.5 mm, the full width at half maximum (FWHM) of the rocking curve increased linearly from 29 arc sec to 53 arc sec. The greatest gain in integrated intensity was obtained for 8-9 mm thickness where FWHM = 40 arc sec. If this crystal were used as a monochromator for synchrotron radiation, it would provide 40 times more intensity than a perfect silicon crystal and an energy bandwidth of 1 keV at 115 keV photon energy. With the increase of the rocking curve FWHM, a plateau across the peak maximum developed; its width increased from 5 arc sec to 25 arc sec when the crystal thickness increased from 5 mm to 12.5 mm, respectively. This plateau allows these crystals to be used as analyzer crystals in diffraction experiments, i.e., as very narrow slits to suppress background. A plateau width of about 5-20 arc sec for the analyzer crystal is needed to insure that the entire intensity scattered from a sample is delivered to the detector. The simple expedient of changing the crystal thickness alters the plateau width of the analyzer crystal and tunes its acceptance to the needs of the sample under study.
X-Ray Reflectivity and GISAXS Study of Derelaxation in Kr Implanted Si
Authors: Duč P. , Pivac B. , Milat O. , Bernstorff S. , Zulim I
Published: April 2011

The structural changes induced in single crystal silicon implanted with Krypton above the amorphisation threshold were studied by X-ray reflectivity together with Grazing Incidence Small Angle X-ray Scattering technique. Silicon samples were implanted with Krypton with two different ion energies. A well-defined layer, 220 nm thick of amorphous silicon, rich in Krypton, was formed below the top, undisturbed layer. A series of samples consist of as-implanted, relaxed, and a number of samples with increased level of defects induced by additional Kr implantation. Additional implantation caused changes in the films composition and thickness, which was well evidenced in reflectivity curve, while only minor changes of surface roughness and critical angle were detected in GISAXS spectra.
In Situ X-ray Absorption Spectroscopy in the Soft Energy Range: Novel Prospects for the Chemical Characterization of Solid State Surfaces at High Pressure And High Temperature
Authors: Schedel-Niedrig Th. , Hävecker M. , Knop-Gericke A. , Reinke P. , Schlögl R. , Lux-Steiner M. Ch.
Published: April 2011

An instrument equipped with total electron yield detectors was designed and constructed for in situ X-ray absorption spectroscopy (XAS) investigations in the soft X-ray range (100 eV ≤ hν ≤ 1000 eV) at elevated pressures (mbar range) and sample temperatures (T ≤ 1000 K) [1]. This allows, for the first time, XAS studies in a surface-sensitive mode of the light elements (Z = 3-15). Furthermore, the gas phase XAS and the surface-related XAS of the solid state phase can be collected simultaneously in order to correlate the gas/solid reaction rate with the surface electronic structure under working conditions in a flow-through mode.

The novel experimental tool represents a contribution to the experimental overcoming of the “pressure gap” in material science. In this work examples are presented belonging to the field of heterogeneous catalysis [2-4] and to the reactivity of diamond surfaces [5]. Additionally, prospects for in situ studies in material science will be given.
Grazing Incidence X-ray Diffraction Studies of Thin Films at the air-liquid Interface
Authors: Alonso Coralie , Renault Anne , Lahav Meir , Leiserowitz Leslie
Published: April 2011

Monomolecular films at the air-water interface can be investigated on the subnanometer scale with grazing incidence X-ray diffraction (GIXD) using synchrotron radiation. This surface semsitive technique utilizes the property of total external reflection of X-rays from a water surface : an evanescent wave generated within the film diffracts in the surface plane giving an image of the film reciprocal lattice. Three applications of GIXD are presented ranging from poorly to highly crystalline thin films. (i) Cholesteryl-L-glutamate forms a crystalline monolayer at the air-water interface within which the glutamate moieties are not closely packed. This system specifically incorporates hydrophobic amino acids from the subphase. (ii) Long-chain cholesteryl esters deposited on the water surface spontaneously self assemble, forming crystalline interdigitated bilayers. The molecular structure, solved at the atomic resolution, was found to be similar to the 3D counterpart. (iii) According to 2-D diffraction theory, the shape of Bragg peaks is related to the mechanical constants of the film. Rigidity of the film can be deduced from a detailed peak analysis for secondary short chain alcohols showing a softening of the monolayer close to melting.
Ultrathin Films of Oriented Bacteriorhodopsin: Nanostructured Films for Investigating the Primary Photoevent in Vision Processes
Authors: Advincula Rigoberto C. , Park Mi-kyoung
Published: April 2011

In this work, a protocol for investigating Bacteriorhodopsin (BR) biomimetic systems as ultrathin films is presented. BR is one of the most well studied proteins important for investigating the primary photo-event in vision processes. The use of macromolecular assembly approaches for deposition onto solid support substrates, e.g. SiOx, gold- or ITO-coated glass (electrode) provide advantages in that surface sensitive measurements can be used to correlate photocurrent generation, photoelectric response, pH change, chromophore behavior, etc. with protein orientation at interfaces. Membrane and protein morphology were correlated to measurements using surface sensitive techniques, such as atomic force microscopy (AFM), ellipsometry, quartz crystal microbalance (QCM), etc. on solid-substrate systems. These studies can lead to applications in optobioelectronic devices (biosensors) including patterning in transducer array configurations, where the film structure is important. Hybrid films are possible with supramolecular assembly approaches, e.g. adsorption of membrane with lipidbilayers. We report our initial results on highly ordered and oriented BR protein arrays of controlled thickness, layer order, and orientation. This was done primarily using the alternate polyelectrolyte deposition (APD) or layer-by-layer (LbL) approach to functionalize substrate surfaces.
InGaN-Channel FETs – Growth, Technology and Characteristics
Authors: Kohn E. , Daumiller I. , Neuburger M. , Seyboth M. , Kirchner C. , Kamp M.
Published: April 2011

Making use of the polar nature of III-nitride heterostructures, a new FET device concept is proposed. The structure contains an InGaN QW channel sandwiched in between two GaN barrier layers. The charge inthis structure is mainly generated by the strain field in the InGaN layer and is an electron/hole dipole sheet charge located at the opposite InGaN/GaN interfaces. To obtain nchannel characteristics the hole charge at the rear interface (for Ga-face oriented material) is compensated by donor doping of the channel or by modulation doping from the real GaN barrier layer. Growth, processing technology and characteristics of first fabricated devices is discussed.
Characterization of GaN and Al0.35Ga0.65N/GaN Heterostructures by Scanning Kelvin Probe Microscopy
Authors: Koley G. , Spencer M. G.
Published: April 2011

Scanning Kelvin probe microscopy (SKPM) technique operated in feedback mode has been used to characterize GaN (unintentionally n-type doped, n+ doped and semi-insulating), and Al0.35Ga0.65N/GaN heterostructures (with varying Al0.35Ga0.65N thickness) grown by metalorganic chemical vapor deposition and molecular beam epitaxy. SKPM was used to measure the surface potential on these materials. The measurement technique was calibrated using metal calibration samples of Pt, Au, Ni and Al. The BSBH for n-doped GaN was measured to be 0.7 eV, which is in good agreement with values reported in the literature. Growth features such as dislocations present on the surfaces of III-nitrides were also investigated for their electrical properties using SKPM and non-contact mode atomic force microscopy, simultaneously. The dislocations have been found to be negatively charged for GaN as well as Al0.35Ga0.65N/GaN heterostructure samples.
Hole Scattering in p-type Wurtzite Gallium Nitride
Authors: Albrecht J. D. , Ruden P. P.
Published: April 2011

We investigate acoustic phonon scattering processes for holes in wurtzite gallium nitride. Using a six-band Rashba-Sheka-Pikus Hamiltonian description of the valence bands of gallium nitride, total scattering rates are calculated by numerical integration over final states. An examination of the interband and intraband processes shows strong scattering rate anisotropy between holes moving parallel to and perpendicular to the hexagonal plane. Results are given for inelastic acoustic deformation potential and piezoelectric scattering processes involving both longitudinal and transverse acoustic phonon absorption.
Recombination at surface states in GaN
Authors: Reshchikov M. A. , Visconti P. , Jones K. M. , Morkoç H. , Litton C. W. , Molnar R. J.
Published: April 2011

We have studied radiative and nonradiative recombination at surface states in GaN, including as-grown samples and those treated with acids or bases. The surface states manifested themselves in two ways: (i) a reversible increase of the photoluminescence (PL) intensity after ultraviolet (UV) illumination in vacuum and (ii) appearance of new PL bands after treatment with acid or base and subsequent exposure to air. It has been established that the GaN surface physi-sorbs species from air (presumably oxygen) which induce surface states acting as nonradiative recombination centers. It has been found that nonradiative recombination of photogenerated carriers via surface states comprises more than 70% of the recombination in some GaN samples. Another type of the surface state, which participates in radiative recombination, has been found in GaN samples with Ga polarity after brief etching of the surface with hot acid or base and subsequent exposure to air. In such samples, a broad PL band emerges in the blue region of the spectrum at low temperatures. The blue band has been attributed to transitions of photogenerated electrons from donors in the near-surface depletion region to the surface states introduced by the above-mentioned procedure. The changes in the GaN surface caused by etching were examined by atomic force microscopy. In some samples the blue band appeared even when no evidence of the layer etching was found except for quite shallow etch pits formed at dislocation sites. The emerging blue band can be related to the surface states formed on the a-planes of etch pits.
Stable Low Resistance Ohmic Contacts To p-GaN
Authors: Park Mi-Ran , Anderson Wayne A.
Published: April 2011

Stable and low-resistance Ohmic contacts are especially important for laser diodes where high current levels are required. Good contacts are especially difficult on p-type GaN which was the motivation for this study. The GaN was epitaxially grown on (0001) sapphire substrates by MOCVD. Resistivity of this layer was 3.5 Ohm-cm and thickness was 2 microns. After conventional cleaning followed by treatment in boiling HNO3: HCl (1:3), metallization was by thermally evaporating 40 nm Au / 60 nm Ni or 70 nm Au / 55 nm Pd. Heat treatment in O2 + N2 at various temperatures followed, with best results at 600 °C or 700 °C, respectively. Best values of the contact resistance were 1.8×10−4 Ohm-cm2 for Pd/Au and 2.65×10−4 Ohm-cm2 for Ni/Au contacts. After repetitive cycling from room temperature to 600 °C, the Ni contacts were very stable and more stable than the Pd contacts. X-ray photoelectron spectroscopy depth profiling showed the Ni contacts to be NiO followed by Au at the interface for the Ni/Au contacts whereas the Pd/Au contacts exhibited a Pd: Au solid solution. Some contacts were quenched in liquid nitrogen following sintering. These contacts were much more uniform under atomic force microscopy examination and gave a 3 times lower contact resistance with the Ni/Au design. Current-voltage-temperature analysis revealed that conduction was predominantly by thermionic field emission.
Fabrication of 0.1 µm channel diamond Metal-Insulator-Semiconductor Field-Effect Transistor
Authors: Umezawa Hitoshi , Ohba Yoshikazu , Ishizaka Hiroaki , Arima Takuya , Taniuchi Hirotada , Tachiki Minoru , Kawarada Hiroshi
Published: April 2011

Analysis of diamond short channel effect is carried out for the first time. 70 nm channel diamond metal-insulator semiconductor field-effect transistor is realized by utilizing new FET fabrication process on the hydrogen-terminated surface conductive layer. This FET is the shortest gate length in diamond FETs. FETs with thick gate insulator of 35 nm show significant threshold voltage shift and degradation of subthreshold slope S by the gate refining. This phenomenon occurs due to the penetration of drain field into channel. However, the degradation of subthreshold performance and threshold voltage shift are hardly observed in 0.17 µm FET with thin gate insulator 15 nm in thickness.
Packaging for a Sensor Platform Embedded in Concrete
Authors: Cain Russell Paul , Carkhuff Bliss G. , Srinivasan R. , Grossman Kenneth R. , Weiskopf Frank
Published: April 2011

The Johns Hopkins University Applied Physics Laboratory is developing packaging for a sensor platform to be embedded in the harsh environment of concrete structures. The sensors will monitor the corrosive environment of the structure over periods of several decades to aid in scheduling maintenance and repair.

The United States has recognized the risks associated with its aging infrastructure and is actively replacing deteriorated/high risk structures as well as simultaneously developing the tools and techniques to monitor new infrastructure as it ages. JHU/APL has reviewed the sensing requirements for infrastructure monitoring, especially bridge decks, and developed a concept based on distributed, embedded sensors. The Wireless, Embedded Sensor Platform (WESP) will implement the concept of a low-cost, customizable sensor platform suitable for long-term field measurements. The WESP is designed to be powered and queried remotely as often as required and can be used to measure the evolution of the corrosive environment over time.

The objective of this research and development is to design, implement, and demonstrate packaging techniques for embedded sensor suites commensurate with a 50-year lifetime when embedded in concrete having a pH greater than 13, and exposed to harsh environments of salt, and mechanical and thermal stress. To meet this objective, the WESP construction will use a commercial ceramic IC package and unique manufacturing and assembly techniques.

The prototype is expected to provide sensor identification, temperature, pressure, and conductivity data within a package volume less than 2.5 cm3 (0.15 in3). Reliability test results will be reviewed and specialized tests will be performed to evaluate the performance of the packaging design. These include such tests as freeze/thaw cycling, thermal shock, thermal cycling, Highly Accelerated Stress Test (HAST), 85% relative humidity/85°C, and accelerated life testing. Future developments are expected to reduce size and implement additional sensor types to fully characterize the concrete environment.
Carrier-Level Packaging and Reliability of a MEMS-Based Safety and Arming Device
Authors: Deeds Michael , Cochran Kevin , Swaminathan Rajesh , Sandborn Peter
Published: April 2011

Packaging of MEMS devices introduces new challenges to the package architecture. MEMS systems include interfaces, processes, and materials foreign to the IC packaging industry. To build reliable MEMS systems, failure modes must be identified and understood. In addition, measurement techniques must be developed to interrogate critical aspects of the package.

The present work addresses the architecture of the carrier-level packaging for a MEMS-based Safety and Arming device (S&A). The impact of moisture on packaged MEMS systems and test structures are investigated through an environmental conditioning program that includes thermal cycling and accelerated aging. MEMS switches are packaged in hermetic, non-hermetic, and ventilated configurations to facilitate in-situ monitoring of device health. A MEMS humidity sensor is included in these packages to allow interrogation of package environment characteristics.

Mechanical MEMS test structures are put through the same environmental conditions as the MEMS switches. These structures provide additional data on the failure modes of the packaged switches. Push test structures provide cumulative data on friction, stiction, and material properties and dog bone structures isolate material property influences.
Mechanical Bending Fatigue Reliability and Its Application to Area Array Packaging
Authors: Skipor Andrew F. , Leicht Larry
Published: April 2011

Fine pitch area array packages are often assembled to flexible printed circuit boards, which require numerous low-frequency mechanical deflections. The interconnect package reliability emphasis has become focused more on isothermal bending fatigue. The interconnect failures due to bending fatigue were found to be different than those which occur if the packages were subjected to accelerated temperature cycling. A test method has been developed to evaluate isothermal mechanical bending fatigue reliability of area array packaging. Mechanical fatigue results of 1.0, 0.8, and 0.75 mm pitch packaging will be presented, demonstrating the effect of package substrate material properties on fatigue life and fracture morphology. Numerical finite element analysis results will also be presented to support and expand the findings in this study.
Estimation of the Interfacial Fracture Energy of Metal/Polymer System in Microelectronic Packaging
Authors: Song J.Y. , Yu Jin
Published: April 2011

The interfacial fracture energies of flexible Cu/Cr/Polyimide system were deduced from the T peel test. The T peel strength and peel angle were strongly affected by the metal thickness and the biased rf plasma power density of the polyimide pretreatment. The plastic bending works of metal and polyimide dissipated during peel test were estimated from the direct measurement of maximum root curvatures using the elastoplastic beam analysis. The interfacial fracture energy between Cr and polyimide increased with the rf plasma power density and saturated, but was pretty much independent of the metal film thickness and the peel angle.
High Tg, Low Dielectric Constant Aromatic Benzoxazoles Containing Allylether Pendent Groups for Use in Microelectronic Packaging
Authors: Alexander Max D. , Dang Thuy D. , Specker Christina E. , Houtz Marlene , Spry R.J. , Arnold Fred E.
Published: April 2011

Next generation microelectronic packaging requirements are driving the need to produce increasingly lower dielectric constant materials while maintaining high thermal stability and ease of processing. Polymer candidates with exceptionally low dielectric constant (2.0-2.4), high thermal stability (degradation temperature higher than 400°C), high glass transition temperature (greater than 350°C), low water uptake (less than one percent), solubility in selected organic solvents, and low thermal expansion are all required. We have successfully synthesized and characterized several candidate polymers in an effort to address these needs.
Dislocation Boundaries and Slip Systems in Uniaxially Deformed Crystals
Authors: Winther Grethe , Huang Xiaoxu , Nielsen Søren Fæster , Wert John
Published: April 2011

The dislocations in the extended planar dislocation boundaries formed during deformation are generated by the active slip systems. Investigation of the boundaries is therefore a tool to obtain information on the active slip systems. Here, the orientation of the dislocation boundaries in uniaxially deformed aluminum poly- and single crystals are compared. It is found that the single crystal boundary planes are consistent with those found in polycrystals, indicating that the active slip systems in single and polycrystals are the same. However, boundaries are closer to the slip planes in the single crystals. This is taken as an indication that the secondary slip systems are more active in the polycrystal. The orientation of the boundary plane varies with the crystal orientation in a way that is consistent with activation of the five most stressed slip systems.
Stress Patterns of Deformation Induced Planar Dislocation Boundaries
Authors: Khan Shafique M. A. , Zbib Hussein M. , Hughes Darcy A.
Published: April 2011

A Multi-scale model coupling discrete dislocation dynamics with continuum plasticity and finite element analysis is used to study the self-stress field of geometrically necessary (dislocation) boundaries (GNBs). The results for a single GNB are presented here. The internal structure of the GNB is obtained from the Frank's formula using experimentally measured misorientation angle/axis pair as the input. Several different types of model boundary conditions (using FEA) are analyzed together with the effect of different parameters like the domain length and mesh sensitivity. It is shown that choosing the right boundary conditions for the FEA strongly affects the predicted internal stress fields of these dislocation boundaries, particularly the long-range effect.
Deformation Band Velocities and Local Strain Rates in a Ni-Cr-Fe Alloy (Inconel)
Authors: Jones Harry N. , Feng C. R.
Published: April 2011

Nickel based alloys with nominal compositions similar to 78Ni -15Cr -7Fe, commonly referred to as “Inconel”, exhibit serrated flow (Portevin-LeChatelier effect) in the temperature interval of 230-730°C. Within this temperature range a series of thermally activated processes can also be observed when a wire sample of the alloy is heated with the direct resistance method under dead-weight loading while stressed above the room temperature yield. These processes include the expected initial period of plastic deformation at the start of heating followed by its complete arrest at a higher temperature, a behavior that is completely at odds with models for the thermal activation of plastic flow in metals. As the temperature is increased after this first arrest a cascade of two or three large plastic instabilities involving the high velocity propagation of narrow deformation bands is observed. Measurements of the band velocities using the time of flight within a 50.8 mm gage length extensometer indicate that they can exceed 2 m/s in some cases. Estimates of the maximum local strain rate attained within the deformation bands, obtained with a diametral extensometer, approach 15-18 s−1. The localization of plastic flow into narrow, high velocity bands in this material is the result of the collective behavior of dislocations interacting at a high density. As demonstrated by TEM examination of the complex dislocation structures associated with these various events, however, it is difficult to rationalize a specific mechanism for these effects. If one assumes that both serrated flow and the thermally activated strain bursts are manifestations of the same basic mechanism these observations pose a challenging problem for interpretation with models for the Portevin-LeChatelier effect in this material.
Enhancement of Undergraduate Materials Education through Research and Industry-Academia Interactions
Authors: Ray Asit K.
Published: April 2011

The Chemical Engineering Department at Christian Brothers University (CBU) offers an introductory courses on materials at the sophomore level followed by a course on polymer science and engineering at the senior level complete with laboratory. Students desiring further exposure to materials processing are connected with local polymeric materials companies where they work as interns. These students have the opportunity to be involved in undergraduate materials research in the CBU Polymer Laboratory with the author funded by the university or local polymer companies. Their works are acknowledged in terms of student paper presentations at local or regional research seminars. In 1998, CBU Engineering School's research involvement with the polymeric materials industry was expanded when local polymer company personnels were allowed to conduct proprietary research at the institution's Polymer Engineering Laboratory with the help of paid undergraduate chemical engineering students. Recently the Chemical Engineering Department at CBU initiated collaborative research with the engineering school of a local university and a local biomaterials company. In order to meet the growing needs of packaging engineers in this area, local companies (polymer and others) that have packaging departments and the School of Engineering at CBU recently joined forces to develop a packaging teaching and training program for students as well as employees of these companies. This program would include packaging materials and engineering. The details of Phase I and Phase II of this joint venture are described in the main body of the paper that follows.
Industrial/Academic Internships at IBM-Almaden Under NSF Programs
Authors: Wade Charles G. , Miller Dolores , Pesek Joseph , Scharberg Maureen , Waller Brenda , Pauly Malinda , Goldman Marni
Published: April 2011

Industrial experience can be a significant factor in materials science education, and internships at our laboratory under two NSF programs directly impact undergraduates and high school teachers. In these programs, the participants become a member of individual, existing research groups under a mentor on a technical project relevant to IBM. The research is publishable but closely related to a technical area important to IBM. During the summer the participants become members of the research group, attending departmental meetings and informal discussions. In addition, they attend a special seminar series on industrial research frontiers, receive career-training discussions, and participate in a variety of other programs sponsored for summer interns by IBM. Every participant presents a poster at an internal technical meeting at IBM or a technical meeting at Stanford (or both) at the end of the summer. One of the programs, an NSF MRSEC “Center for Polymer Interfaces and Macromolecular Interfaces” (CPIMA), involves a partnership with Stanford University and the University of California at Davis. The CPIMA program has an active group of postdoctoral scientists, graduate students, undergraduate (summer) students and (summer) high school teachers. In addition to IBM, summer students in CPIMA may work with other industrial firms who are industrial affiliates of CPIMA. In addition, CPIMA has a public science and K-12 component in materials science in educational outreach with the The Tech Museum of Innovation in San Jose. The other program, an NSF GOALI grant on “Surface and Analytical Chemistry of Materials” with San Jose State University, involves undergraduate and graduate (masters) San Jose State University students during the academic year who work on collaborative research projects between IBM scientists and San Jose State University professors. In addition, this project also has a large summer program with undergraduates from across the US and with high school teachers. The impact of the programs on the students, teachers, and institutions will be reviewed, with a special emphasis on the impact on the industrial partner.
Innovative Curriculum on Electronic Materials Processing and Engingeering
Authors: Chang Jane P.
Published: April 2011

Recognizing that the traditional engineering education training is often inadequate in preparing the students for the challanges presented by this industry's dynamic environment and insufficient to meet the empoyer's criteria in hiring new engineers, a new curriculum on Semiconductor Manufacturing is instituted in the Chemical Engineering Department at UCLA to train the students in various scientific and technologica areas that are pertinenet to the microelectronics industries. This paper describes this new mutidisciplinary curriculum that provides knowledge and skills in semiconductor manufacturing through a series ofcourses that emphasize on the application of fundamenta engineeering disciplines in solid-state physics, materials science of semiconductors, and chemical processing. The curriculum comprises three major components:(1)a comprehensive course curriculum in semiconductor manufacturing; (2) a laboratory for hands-on training in semiconductor device fabrication; (3) design of experiments. The capstone laboratory course is designed to strengthen students’ training in “unit operatins” used in semicounductor manufacturing and allow them to practice engineering principles using the state-of-the-art experimental setup. It comprises the most comprehensive training(seven photolithographic steps and numero0us chemical processes)in fabricating and testing complementary metal-oxide-semiconductor (CMOS) devices. This curriculum is recentyaccredited by the Accreditation Board for Engineering and Technology(ABET).
Dealing With Variation In Measurements & Processes: Experiments For An Undergraduate Laboratory
Authors: Vanasupa Linda , Smith Heather , Gleixner Stacy , Young Greg , Allen Emily
Published: April 2011

Being able to obtain and analyze quantitative data are an essential components of any undergraduate education in science or engineering. At the most basic level, this begins with characterizing the measurement system using proper statistical techniques. Although most undergraduates in the sciences and engineering are required to take a course in statistics, the knowledge gained in the statistics course does not always find its way into practice. In this paper we will present 4 experimental modules that will enable the student to: 1. Assess the precision of a measurement system; 2. Determine if the system is stable with respect to a number of variables; 3. Quantify the amount of variation that exists within a particular sample; 4. Quantify the amount of variation from sample to sample (i.e., process variation). Our modules were applied to the measurement of silicon dioxide thickness from an oxidation process. However, they generally apply to any process that involves measuring a physical quantity. Assessing these sources of variation in a process form the foundation for more advanced techniques such as process control and experimental design.
Incorporating Information Competence into Classes
Authors: Chen Katherine C. , Adalian Paul T.
Published: April 2011

Enabling students to become independent learners is a desirable goal for many educators. However, the task is not always easily addressed with the long lists of concrete, technical objectives that must usually be covered in classes. As a result, information often follows a oneway path from the instructor to the student, and students can develop a reliance on “packaged” knowledge and answers from only teachers and textbooks. In efforts to engage students in the learning process and to encourage the self-directed exploration of knowledge, “information competence” [1] has been incorporated into an upper-level materials course. Using current topics in materials science and engineering, students formulate questions to address specific issues and then locate pertinent information. A variety of resources, such as newspapers, web sites, and scholarly journals, are explored and evaluated. The instructor acts as a facilitator that assists with search strategies and evaluation of the information. Students develop the ability to process and reorganize the information into useful forms (e.g., reports, oral presentations). Providing the tools and instructions to function effectively in this Information Age will hopefully promote lifelong learning in today's students.
A Study of Charge Control and Gate Tunneling in a Ferroelectric-Oxide-Silicon Field Effect Transistor
Authors: Lin Yih-Yin , Zhang Yifei , Singh Jasprit
Published: April 2011

It is known that conventional metal-oxide-silicon field-effect transistor (MOSFET) devices will have gate tunneling related problems at very thin oxide thicknesses (dox ≤ 20 Å). In this paper we discuss the potential of polar and non-polar high-dielectric films for gate tunneling suppression and charge control. We also examine ferroelectric thickness effects in ferroelectricoxide- silicon field effect transistors (MFISFETs). Our formalism is based on a blocking-layer model for the ferroelectric film and a self-consistent solution of the Poisson and Schrodinger equations. We show that the polarization effects of ferroelectrics can allow greater controllability of the silicon interface (mobile) charge density and also the high dielectric constant effectively suppresses gate tunneling probability. In addition, the effects of ferroelectric film thickness are quite important in a MFISFET device and allow a small control of the threshold voltage. Results will be presented for the capacitance-voltage curve, tunneling probability, and leakage currents. As an example, we find for a sheet charge of 1013 cm−2, the gate tunneling probability in a MOS structure is 10−6 (dox = 13 Å), while that in a MFISFET is 10−14 with the same equivalent oxide thickness. Our studies also show that details of the blocking layer model (dead layer thickness, coercive field, and polar charge) can be estimated from C-V measurements.
Effect of Bottom Electrodes on Structural and Electrical Properties of Laser Ablated SrBi2Ta2O9 Thin Films
Authors: Das Rasmi R. , Pérez W. , Bhattacharya P. , Katiyar Ram. S.
Published: April 2011

We have grown SrBi2Ta2O9 (SBT) thin films on various bottom electrodes such as Pt/TiO2/SiO2/Si (Pt) and LaNiO3/Pt/TiO2/SiO2/Si (LNO) substrates. The substrate temperature and oxygen pressure for the SBT film was maintained at 500 °C and 200 mTorr. As-grown films were post-annealed at a temperature of 800 °C. X-ray diffraction studies revealed that as-grown films were amorphous and crystallized to single phase after annealing. The difficulty of obtaining lowest Raman modes of SBT on platinized silicon substrate was overcome by using conducting oxide electrodes. Films grown on platinized silicon showed maximum value of remanent polarization (2Pr ∼ 21.5 μC/cm2) with coercive field (Ec) of ∼ 67 kV/cm. The degradation of ferroelectric properties of the films was observed with the introduction of 50 nm conducting LaNiO3 electrode at the interface of Pt and SBT film, which was attributed to high resistivity of the oxide electrode layers. Leakage current density was studied with the consideration of the Schottky emission model. The barrier height of the films grown on Pt and LNO were estimated to be 1.27 eV and 1.12 eV, respectively. The reduction of barrier height was attributed to the lower work function of the LNO electrode.
Improvement of Surface Crystalline Quality of an Epitaxial (100)ZrN Film as a Bottom Electrode Diffusion Barrier for Ferroelectric Capacitors
Authors: Horita Susumu , Horii Sadayoshi , Toda Takeo
Published: April 2011

We fabricated the double epitaxial layers of Ir on barrier metal ZrN for Pb(ZrxTi1−x)O3 (PZT), using reactive sputtering. In order to remove the surface oxide layer of the ZrN film prior to depositing the Ir film, we used a new treatment method, in which the ZrN film is dipped into a 0.5% buffered HF solution for less than 30 seconds and then immediately dipped into a hydrazine (N2H4) monohydrate solution for 60 seconds. Also, in order to suppress the generation of twin boundaries and to improve crystalline quality, the ZrN film is deposited using a two-step method, which consists of an initial high temperature deposition step at 850s°C followed by a lower temperature step at 600°C. On the ZrN film prepared by these methods, we can obtain a mainly (110)-oriented epitaxial Ir film.
Characterization of (Ba,Sr)RuO3 Films Deposited by Metal-organic Chemical Vapor Deposition
Authors: Choi Duck-Kyun , Kang Joong-Seo , Kim Young-Bae , Hong Duck-Hwa , Kim Hyun-Chul , Kim Sung-Tae , Yoo Cha-Young
Published: April 2011

Thin film electrodes of the perovskite oxide (Ba,Sr)RuO3 (BSR) were deposited on 4 inch ptype Si wafers by metal organic chemical vapor deposition (MOCVD) for the practical (Ba,Sr)TiO3 (BST) capacitor application using a new single cocktail source. The source materials used for the MOCVD BSR process were Ba(METHD)2, Sr(METHD)2 and Ru(METHD)3 and these were dissolved in n-butyl acetate. The source-feeding rate was precisely controlled by liquid mass flow controllers (LMFC). As-deposited BSR films possessed a (110)-oriented structure, with good uniformity and adherence on bare Si wafer. The phase formation was strongly affected by the oxygen flow rate and the input source rate. As the oxygen flow rate increased, the Ru/(Ba+Sr) composition ratio in the film decreased, while the Ba/(Ba+Sr) ratio was almost independent of the oxygen flow rate. The dielectric constants of BST capacitors fabricated using these electrodes was greater than 500.
Origin of Lowered Crystallization Temperature in SBT-BTT Ferroelectric Thin Films
Authors: Kwak Woo-Chul , Kumar Gopinathan M. A. , Jung Se-Yon , Hwang Seung-Joon , Sung Yun-Mo
Published: April 2011

The crystallization kinetics of SBT and SBT-BTT thin films formed by sol-gel technique on Pt substrate was studied. Phase formation and crystal growth are greatly affected by the film composition and crystallization temperature. Isothermal kinetics analysis was performed on x-ray diffraction (XRD) patterns of the thin films heated in the range 730 to 760° at 10° intervals. Activation energy and Avrami exponent values were determined for the fluorite to Aurivillus phase formation. A reduction of ∼55 kJ/mol in activation is observed for the SBT-BTT system. A comparison has been made and the possible crystallization mechanism is discussed.