bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractMonomolecular 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

ABSTRACTIn 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

ABSTRACTMaking 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

ABSTRACTScanning 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

ABSTRACTWe 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

ABSTRACTWe 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

ABSTRACTStable 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

ABSTRACTAnalysis 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

ABSTRACTThe 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

ABSTRACTPackaging 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

ABSTRACTFine 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

ABSTRACTThe 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

ABSTRACTNext 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

ABSTRACTThe 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

ABSTRACTA 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

ABSTRACTNickel 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

ABSTRACTThe 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.