bluuebunny/crossref_metadata_2025 huggingface dataset:
Blocking of Magnetic Long Range Order Between the Monolayer and the Double Layer of Fe(110) on W(110)
Authors: Elmers Hans-Joachim , Hauschild Jens , Liu Guohui , Fritzsche Helmut , KÖhler Ulrich , Gradmann Ulrich
Published: April 2011

In extension of a recent study on submonolayer magnetism of Fe(110) on W(110) [1], we observed the interplay of morphology and magnetic order in Fe(110)-films prepared on W(110) at 300 K, in a range of coverages θ between the pseudomorphic monolayer (θ = 1) and the pseudomorphic double layer (θ = 2), using a combination of STM, SPLEED, CEMS and TOM. Whereas the Curie-temperatures of the monolayer and the double layer are given by Tc(ML) = 230K and Tc(DL) = 450K, respectively, we observe in an interval of 1.20< θ < 1.48 ML a gap of magnetic long range order, for temperatures down to 115K. In CEMS, we observe superparamagnetic fluctuations for T < Tc(ML), but magnetic short range order for T < Tc(ML). The surprising blocking of long range order in the gap can only be explained from a quasi-antiferromagnetic indirect coupling between double-layer islands.
Observation of Micromagnetic Structure in Computer Hard Disks by Lorentz Transmission Electron Microscopy
Authors: Tang K. , Visokay M.R. , Sinclair R. , Ross C.A. , Ranjan R. , Yamashita T.
Published: April 2011

We have observed micromagnetic structure in real computer hard disks with the typical structure of C/Co alloy/Cr/NiP/Al(substrate) using Lorentz transmission electron microscopy (LTEM). A chemical etching method was introduced to successfully prepare LTEM specimens directly from the computer hard disks with both smooth and mechanically textured substrates. Micromagnetic structural features, e.g., ripples and vortices, were studied in disks in bitswritten, ac-demagnetized, and saturation remanent magnetic states.
Pair Ordering Anisotropy In Amorphous Tb-Fe Thin Films
Authors: Hufnagel T.C. , Brennan S. , Clemens B.M.
Published: April 2011

We have studied the structural origins of perpendicular magnetic anisotropy in amorphous Tb-Fe thin films by employing high energy x-ray scattering. The as-deposited films show a clear structural anisotropy, with a preference for Fe-Tb near-neighbors to align in the out-of-plane direction. Upon annealing, the magnetic anisotropy energy drops significantly, and we see a corresponding reduction in the structural anisotropy. The radial distribution functions indicate that the number of Fe-Tb near-neighbors increases in the in-plane direction, but does not change in the out-of-plane direction. Therefore, the distribution of Fe-Tb near-neighbors becomes more uniform upon annealing. We conclude that the observed reduction in perpendicular magnetic anisotropy energy is a result of this change in structure.
Effect of The Orientation of The Magnetic Field on The Giant Magnetoresistance of Fe/Cr Superlattices
Authors: Ustinov V.V. , Minin V.I. , Romashev L.N. , Semerikov A.B. , Del A.R.
Published: April 2011

We study the magnetoresistance of [Fe/Cr]30/MgO superlattices grown by molecular beam epitaxy at a various magnetic field directions. The theory of the orientation dependence of the effect is developed. It is shown that the magnetic field strength dependence of magnetoresistance can be calculated for arbitrary orientation of magnetic field if this dependence is known for in-plane and perpendicular-to-plane magnetic fields. It is noted that the magnetization curve can be obtained by making use of the results of the magnetoresistance measurements.
The Effect of Impurity Doping of The Magnetic Layer on the Magnetoresistance and Saturation Field of FeCr/Cr and CoCu/Cu Multilayers
Authors: Daniels B.J. , Clemens B.M.
Published: April 2011

The effect of doping the magnetic layer on the magnetoresistance and saturation field of epitaxial, sputter-deposited FeCr/Cr(001) and CoCu/Cu(001) multilayers was examined. FeCr/Cr films with a composition of [14 Å Fe1−xCrx(001)/8 Å Cr(001)]50 where x was varied from 0 to 0.5 and CoCu/Cu films with a composition of [8 Å Co1−xCux(001)/21 Å Cu(001)]40 where x was varied from 0 to 0.2 were deposited onto single crystal MgO(001). The bilayer period and epitaxial orientation of these films were determined by x-ray diffraction. In the FeCr/Cr system the room temperature magnetoresistance was constant at approximately 31% for x≤0.2 and decreased for larger Cr concentrations. The spin-dependent scattering (Δp) is increased over the x=0 value for x=0.1 and x=0.2. The magnetic field required to saturate these multilayers decreases linearly with increasing Cr concentration. The net result is that the sensitivity of these films is increased by Cr doping of the Fe layer. In the CoCu/Cu system the room temperature magnetoresistance, saturation field, and saturation magnetization decrease with the addition of Cu to the Co layer. In contrast to the FeCr/Cr system Δp does not increase with doping of the ferromagnetic layer. However, as in the FeCr/Cr films the sensitivity of these multilayers is increased with respect to that of the x=0 CoCu/Cu multilayer.
Magnetic Studies of Paramagnetic Clusters Encapsulated within the Sodalite Cage
Authors: Woodall Lee J. , Anderson P. A. , Armstrong A. R. , Edwards P. P.
Published: April 2011

The magnetic properties of alkali-doped zeolites have been investigated using magnetic resonance spectroscopy. Although paramagnetic centres have been detected, the predominant species, in many cases, is spin-paired.
Nmr Studies of Bulk and Interface Structure in Co Based Multilayers
Authors: Panissod P. , Jay J.P. , Meny C. , Wojcik M. , Jedryka E.
Published: April 2011

Owing to the sensitivity of the hyperfine field to the topological and chemical environment of the probe nuclei, NMR spectra can be considered as histograms of the short range order ruling the structure of the material under investigation. Complementary to diffraction techniques this gives a local insight on the structure in the direct space. We review recent structural investigations of cobalt layers imbedded in Co/X multilayers and particularly of buried interfaces. Special attention has been given to the way intermixing takes place at the interfaces as its influence on the multilayer properties may be of considerable importance. Co/Cu multilayers, a case of weakly miscible elements, have been specially investigated owing to their GMR properties. But also cases of solid solution forming elements (Co/Ru or Co/Cr) or compound forming elements (Co/Fe) have been thoroughly studied. The latter case, which shows a stabilization of a bcc Co phase, will be discussed against the bulk alloy phase diagram.
Interactions of Phenol Resin Precursor and Calcium Aluminates
Authors: Hasegawa Masaki , Pushpalal G. K. Dinilprem , Takata Tomonori , Maeda Naomi , Kobayashi Tadashi
Published: April 2011

Here we investigated the interactions of phenol resin precursor and calcium aluminates, in relation to a recently innovated cement based material having a high flexural strength of more than 120MPa. An anhydrous phenol resin precursor was used as the binder and water was not contained in the initial composition.

The method of processing consists of mixing of the cement, the phenol resin precursor, and small amounts of N-methoxymethyl 6-nylon and glycerol under high shear. Addition of the 6-nylon and glycerol was necessary to produce viscoelastic cement paste through a twin roll mill. Setting of calendered sheets takes place during the heat curing at 200° C. The best combination for high flexural strength among all the cements tested is the mixture of calcium aluminate cement and the resole type of phenol resin. Resulting outstanding affinity suggested specific interactions between the phenol resin and calcium aluminate.

We here propose the interaction evidence of phenol moiety-calcium aluminate, based on the experimental data of differential scanning calorimetry and conduction calorimetry.
Rheological Properties of Silica Filled Poly (Methyl Methacrylate)
Authors: Rucker Derek P. , Bike Stacy G.
Published: April 2011

Ceramic fiber spinning is critical to the manufacture of fibrous monolith ceramics, and understanding the interactions between the polymer matrix and ceramic particle filler is necessary to predict the flow properties of these systems. In this study, poly (methyl methacrylate) (PMMA) was filled with octadecanol-coated St6ber silica, and the rheological behavior of the filled polymers investigated at various filler volume fractions. The rheological behavior of these materials was studied in both dynamic and steady-state experiments. The time required for filled PMMA to reach steady-state behavior under constant shear stress was found to be long, on the order of an hour. The steady-state viscosities increased as expected with filler volume fraction, but did not correlate well with existing models. This is hypothesized to be a result of matrix-filler surface interactions, and will be investigated further in future work.
Chemical Stability of SC1-Cleaned Hydrogen Terminated Si(100) Surfaces
Authors: Bjorkman C. H. , Nishimura H. , Yamazaki T. , Alay J. L. , Fukuda M. , Hirose M.
Published: April 2011

Surface contamination and chemical stability of hydrogen terminated Si(100) surfaces have been studied using Fourier Transform Infrared Attenuated Total Reflection (FT-IR-ATR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). Hydrogen terminated Si(100) is obtained by removing the chemical oxide, formed in a low-concentration-NH4OH SC1 clean, in various HF based solutions. Using standard cleaning and loading conditions, we find a direct correlation between surface roughness and the amount of adsorbed C contamination. Oxidation during water rinsing and wafer loading observed by both FT-IR-ATR and XPS indicates that dihydride terminated silicon atoms are preferentially oxidized. Optimizing the water rinse and wafer loading conditions reduces total atomic concentration of C, O, and F surface contamination from 20–30 at.% to less than 6 at.%. These clean surfaces enable XPS-identification of the Si-Hx components of the Si 2p core-level spectra as well as estimation of the relative surface concentration of Si-Hx and contamination species.
Recent Advances in Wet Processing Technology and Science
Authors: Verhaverbeke Steven , Messoussi Rochdi , Morinaga Hitoshi , Ohmi Tadahiro
Published: April 2011

For the cleaning of silicon substrates, a mixture of an oxidizing and an etching agent is often used. One of the first successful mixtures (1970) is the well known APM or SC-1 cleaning (NH4OH/H2O2/H2O) (1). Since then, other mixtures (oxidizing agent/etching agent) such as HNO3/HF (2), H2O2/HF (3) were developed. For the cleaning of silicon substrates, a mixture of an oxidizing agent and an etching agent always results in good particle performance, since the Si under the particles is continuously oxidized and etched simultaneously (2,3).
Study on Sulfur Passivation for CuInSe2 Polycrystalline Thin Film With (NH4)2SX Solution
Authors: Cheng Y. H. , Tseng B. H. , Loferski J. J. , Hwang H. L.
Published: April 2011

In this work, we studied the removal of the native oxide on polycrystalline CuInSe2 thin films by KCN and effect of subsequent chemical sulfurization with (NH4)2Sx solution on these films. As a result of the treatment, a portion of the selenide film was transformed into Culn(S,Se)2 The Auger Electron Spectroscopy and X-ray photoelectron spectroscopy studies showed that KCN removed the oxygen and the sulfurization prevented regrowth of the oxides. The optical bandgap of the sulfurized films increased about 0.27 eV. From these experiments, we concluded that sulfur atoms are incorporated in the CuInSe2 to form a stable and higher bandgap layer, Culn(S,Se)2 which may passivate the CuInSe2 and improve the performance of polycrystalline photovoltaic cells made from it.
Surface Properties of GaAs Passivated With (NH4)2Sx Solution
Authors: Suh Kyung-Soo , Park Hyung-Ho , Lee Jong-Lam , Kim Haechon , Cho Kyung-Ik , Kim Kyung-Soo
Published: April 2011

Surface properties of GaAs passivated with (NH4)2Sx solution have been compared with HCl-treated GaAs using X-ray photoelectron spectroscopy, Sulfur treatment on GaAs surface results in the formation of S-Ga and S-As bonds, which remain after successive rinsing for I minute in DI water. The evolution of Ga 2p3 and As 3d peaks in the sulfidation treated GaAs was monitored with the exposing time to air. After 10 days exposure to air, the Ga-O and As-O bonds slightly increased, but maintained almost constant for further exposure. The increase of Ga-O and As-O bonds induces the partial decomposition of sulfur bonds. Decomposition and evaporation behaviors of sulfur and oxygen were observed through the heat treatment of sulfidation treated GaAs under ultra high vacuum (less than l × 10-9 torr). After anneal at 350 – 450 °C, slight decrease of sulfur and oxygen due to the decomposition of As-O bond were observed. No more sulfur was found after anneal at 550 – 650 °C, where the decomposition of Ga-O bond was completed.
Surface Photovoltage Monitoring of Silicon Surface Native and Chemical Oxides following Wafer Cleaning and Rinsing Operations
Authors: Rosato John J. , Hall R. Mark , Parry Thad B. , Lindquist Paul G. , Jarvis Taura D.
Published: April 2011

We report on the use of the Surface PhotoVoltage (SPV) technique to monitor the Si surface bonding arrangement, and the impurity metallic contamination level prior to critical diffusion processes via the indirect measurement of surface charge and diffusion length, respectively. We show that the effectiveness of the pre-diffusion wet chemical cleaning and rinsing sequences can be accurately monitored via the real-time, nondestructive SPV measurement. In particular the nature of the surface passivation/chemical oxide formed during the cleaning and rinsing operations can be monitored by quantitative surface charge measurements. The importance of the prior wafer history is highlighted, as is the role of the Si starting material and measurement parameters.
Impact of Chemomechanical Polishing on the Chemical Composition and Morphology of the Silicon Surface
Authors: Fusstetrer Hermann , Schnegg Anton , Gräf Dieter , Kirschner Helmut , Brohl Michael , Wagner Peter
Published: April 2011

The polishing technology used for manufacturing ultraflat and smooth Si surfaces on a large scale is the chemomechanical polishing (CMP) technique. This technique combines the chemical corrosive removal of silicon atoms and the mechanical transport of the agents. The removal rates strongly depend on the interaction of mechanical parameters and the chemistry involved in the polishing process like the pH of the alkaline polishing slurry used. Removal of Si during CMP is explained by a nucleophilic attack of OH− to silicon atoms catalyzing the corrosive reaction of H2O resulting in cleavage of silicon backbonds. Characterization of the surface chemistry of the silicon wafer after polishing by X-Ray Photoelectron Spectroscopy and High-Resolution Electron Energy Loss Spectroscopy reveals an oxide free, predominantly hydride covered silicon surface displaying hydrophobic properties. Morphological features like microroughness as well as localized surface irregularities on the silicon surface, also referred to as Light Point Defects, depend on different strongly interacting process parameters. Microroughness is reduced by CMP by several orders of magnitude as characterized by lightscattering techniques and Atomic Force Microscopy.
A New Ion Beam Deposition Technique for Low Temperature Silicon Epitaxy
Authors: Mohajerzadeh S. , Selvakumar C.R. , Brodie D.E. , Robertson M.D. , Corbett J.M.
Published: April 2011

We report the results of an investigation to grow thin Si films on Si substrates at low substrate temperatures using ionized SiH4 gas generated with a Kaufman type ion gun. This investigation shows island-growth at higher substrate temperatures (500-700°C) in the form of square-based pyramids. by lowering the substrate temperature to 300°C, we were able to achieve a planar growth. the growth rate can be enhanced by introducing elemental Si from a thermal evaporation source. Scanning electron microscopy, transmission electron microscopy and electron diffraction analysis were used to study the crystalline quality of the samples prepared at different temperatures.
Preparation and Characterization of Chromium Containing amorphous Hydrogenated Carbon Films (A-C:H/Cr)
Authors: Gampp R. , Gantenbein P. , Oelhafen P.
Published: April 2011

Chromium containing amorphous hydrogenated carbon films (a-C:H/Cr) were prepared in a process that combines rf plasma activated chemical vapor deposition of methane and magnetron sputtering of a chromium target. During the deposition the silicon substrates were kept at 200°C and dc biased at -200 V in order to obtain films with high chemical stability which is required for the application as solar selective surfaces. the films with different Cr concentrations (5 to 49 at.%) were characterized by in situ x-ray photoelectron spectroscopy (XPS). Up to 40 at.%, chromium proves to be built into the cermet-like films in the form of chromium carbide clusters. above 40 at.%, chromium is partly metallic. a modification of the a-C:H matrix in the vicinity of the chromium carbide clusters has been observed.
Deposition of aluminum Oxynitride Films by Magnetron Sputtering: Effect of Bombardment and Substrate Heating on Structural and Mechanical Properties
Authors: Smilgys Russell V. , Takamura Eric , Singer Irwin L. , Robey Steven W. , Kirkpatrick Douglas A.
Published: April 2011

Aluminum oxynitride films, 1 μm thick, are deposited onto glass substrates by planar magnetron sputtering from an alumina target in a mixture of nitrogen and argon. one set of films is deposited onto glass substrates that are heat sunk to a holder, whose temperature is held below 100°C. a second set of films is deposited onto glass substrates that are mechanically clamped to a holder, whose temperature is allowed to rise up to 250°C. Characterization by continuous indentation testing, secondary electron microscopy, and x-ray diffraction reveals significant differences in mechanical properties and surface structure between the two sets of films. Films deposited with holder cooling have a smooth surface and no evidence of crystallinity; films deposited without holder cooling have etch pits on their surface that vary with position across the substrate. the later films show crystallinity and have twice the hardness and a 60% greater elastic modulus.
Electron Beam Assisted Chemical Vapor Deposition of Gold in an Environmental Tem
Authors: Kouvetakis John , SharmA Renu , Ramakrisna B. L. , Drucker Jeff , Seidler Paul
Published: April 2011

We demonstrate a novel technique for in situ observation of the chemical vapor deposition of high purity gold using ethyl(trimethylphosphine)gold(I). an environmental transmission electron microscope with 3.8 eV resolution was used to observe and compare the growth of the material with or without electron beam irradiation (120 keV) with Si (100) substrate temperatures ranging from 125-200 °C. Typical precursor pressures of 10-4 Torr and E-beam irradiation resulted in rapid growth of virtually continuous gold films. thermal deposition without the beam resulted in low nucleation densities, low deposition rates, and island-like growth. Images and diffraction patterns acquired during the deposition process indicated polycrystalline gold and elemental analysis at the nanometer scale showed that the films had excellent chemical purity. atomic force microscopy was also used to investigate the three dimensional morphology of the materials. the most notable result of the deposition process is the dramatic enhancement of the growth rate due to the beam irradiation.
Surface Damage During Kev Ion Irradiation: Results of Computer Simulations
Authors: Averback R.S. , Ghaly Mai , Zhu Huilong
Published: April 2011

MD simulations have been employed to investigate damage processes near surfaces during keV bombardment of metal targets. For self-ion implantation of au, Cu, and Pt in the range of 5-20 keV, we have found that the proximity of the surface leads to significantly more damage and atomic mixing in comparison to recoil events occurring in the crystal interior. IN some cases, large craters are formed in a micro-explosive event, while in others a convective flow of atoms to the surface creates adatoms and leaves dislocations behind. Both the amount damage created in the surface and its morphology depend sensitively on the details of the energy deposition along individual ion trajectories. the results of these simulations will be summarized and compared to recent scanning tunneling microscopy studies of individual ion impacts in Pt and Ge.
Smoothing During Ion-Assisted Growth by Transient Ion Beam-Induced Defects
Authors: Kellerman B.K. , Chason E. , Floro J.A. , Picraux S.T. , White J.M.
Published: April 2011

Several studies have shown that the surface morphology can be smoother during simultaneous ion bombardment and growth than during growth alone, however, the atomistic mechanism responsible for the smoothing effect has been difficult to determine. We have developed Monte Carlo simulations of growth and defect diffusion to model the interaction between growth atoms and ion-induced defects and to present a simple atomistic mechanism that describes the effects of low-energy ion bombardment during ion-assisted growth of germanium. Measurements of ion-induced point defect production indicate that a large number of defects exist only temporarily on the surface at typical growth temperatures, because the defects have sufficient mobility to recombine and annihilate. We propose that this ion-induced transient defect population plays a significant role in modifying the dynamic surface morphology. the simulations support a surface smoothing mechanism that involves the destabilization of adatom islands by the transient ion-induced defects. the optimum simulated steady-state surface morphology can be achieved with ion-induced defect production rates less than or equal to 10 defects/ion. We find that low-energy ion bombardment during growth effectively lowers the temperature at which step-flow growth can be achieved.
Observation of the Early Stages of B-Axis Oriented Prba2Cu3O7-x Thin Film Growth by AFM
Authors: Yong Sung Gun , Dae Suh Jeong , Jung Sang-Don
Published: April 2011

The initial stages of the growth of b-axis oriented PrBa2Cu3O7-x (PBCO) films on LaSrGaO4 (100) substrates were investigated by atomic force microscopy to follow the growth of the thin films. Series of films with thickness ranging between 0.34 nm and 100 nm were prepared under identical pulsed laser deposition conditions. No sprial-topped or flat-topped islands were observed and the scale of the surface roughness was lower than that of the c-axis oriented growth mode. the 300 nm-thick in-plane aligned a-axis oriented YBCO films have the root mean square (RMS) surface roughness of 2 nm. It is considered that the b-axis oriented PBCO films on LaSrGaO4 (100) substrates were nucleated and grown by layer-by-layer like growth mode.
Pulsed Laser Deposition of Cadmium Stannate, a Spinel-Type Transparent Conducting Oxide
Authors: Mcgraw Jeanne M. , Parilla Philip A. , Schulz Douglas L. , Alleman Jeffrey , Wu Xuanzhi , Mulligan William P. , Ginley David S. , Coutts Timothy J.
Published: April 2011

We present the first report of the synthesis of Cd2SnO4 films by pulsed laser deposition. Controlling the substrate temperature and the ambient atmosphere allowed for the synthesis of films ranging from amorphous to crystalline with some crystalline films exhibiting strong texture. Highly transparent films with large mobilities were obtained for both the amorphous and crystalline films. Sheet resistances of 15.5 Ω/square and mobilities of up to 44.7 cm2/V.s were observed. Typical carrier concentrations showed the crystalline films to be degenerate with carrier concentrations of 5 х 1020cm-3 while amorphous films had carrier concentrations lower by about half. Band gaps for the films ranged between 3.1-3.8 eV. these films are attractive candidates for TCO applications in thin film photovoltaic devices, flat panel displays, electrochromic windows, and as plasma filters for thermophotovoltaic devices.
XPS Studies of the Interface Properties of Conductive Adhesive/Eutectic Solder
Authors: Koo Y. C. , Jennings M. C. , Davidson R. D. , McIntyre N. S.
Published: April 2011

The continuing shrinkage of feature size and environmental concerns regarding the use of lead containing solder are major driving forces in the search for alternative technologies for metal interconnects in electronic packaging. Electrically conductive adhesives are considered a potential substitute for the lead-tin solder. This study concentrated on interfacial properties of eutectic solder and silver-filled epoxy adhesives. A freeze fracture technique was employed in order to preserve interfacial information. The chemical composition of the fractured faces varied; the adhesive side was rich in tin, whereas the eutectic solder side showed lead-rich characteristics.
Adhesion of Screen Printed Conductors on Laser Reduced AlN
Authors: Gopalakrishnan S. , Lumpp Janet K.
Published: April 2011

Aluminum Nitride (AlN) has not attained the type of success alumina has had with thick film materials. This project is aimed at increasing the number of thick film inks compatible with AIN. Excimer laser reduced AIN is metallic, but not sufficiently conductive to act as an interconnection for microelectronic circuits. The reduced surface acts as a bonding layer to promote adhesion of screen printed metal films.

Design of Experiments (DOE) plays a critical role in determining the success of a research project. Completely Randomized Nested Classification design strategy is used in these experiments. The Ag-Pd ink formulated for alumina is screen printed on AIN and alumina substrates in a random order and fired. Wires are soldered to the pads and a pull test is done. Analysis of Variance (ANOVA) is used to compare the adhesion strength of Ag-Pd ink formulated for alumina screen printed on Al2O3 and laser reduced AIN substrates.
Chemical Interactions of Au and Ag Conductors in Ceramic Based Electronic Packages
Authors: Vajo John J. , Momoda Leslie A. , Harshbarger Richard W. , Elwell Dennis F.
Published: April 2011

In electronic packages consisting of glass-alumina composite dielectric layers and thick film conductors, Au and Ag conductors on separate layers may alloy. Alloys are formed by Ag+ ion diffusion through the intervening dielectric. The extent of alloy formation is dependent upon whether the Au and Ag conductors are electrically isolated or connected. When the Au and Ag conductors are electrically isolated, alloying is self-limiting and occurs by reduction of Ag+ ions and dissolution of the metallic Ag into the Au. In this case, the reduction of Ag+ is accompanied by oxidation of the lattice oxygen anions forming O2 gas which accumulates to form blisters. If the Au and Ag conductors are electrically connected, then the alloying is not self-limiting and occurs without the formation of O2. In this study, we quantitatively characterize the alloying reactions which occur during firing and propose mechanisms for specific dielectric and conductor packages. The presence of these alloying reactions can affect the reliability and the performance of the electronic ceramic package.
Advances in Liquid Encapsulated Chip-on-Board / MCM-L Technology
Authors: Robinson Dale L. , Clegg David B.
Published: April 2011

Chip-on-Board technology (COB), or the currently more often used MCM-L acronym (MultiChip Module - Laminate), has long been touted as the low cost, high density electronics packaging choice of the future. Unfortunately, poor reliability performance in comparison to traditional plastic packaging, has been a trademark of COB/MCM-L. Recent advances in processes and materials for COB/MCM-L are providing a paradigm shift in reliability, and providing cost effective high reliability packaging solutions for COB/MCM-L. This paper examines the history of recent advances in liquid encapsulated COB/MCM-L and provides guidelines for selecting appropriate materials and processes for their successful implementation into cost effective manufacturing.
Mold Compounds: Linking Material Science and IC Package Reliability
Authors: Groothuis Steven K. , Heinen K. Gail
Published: April 2011

Making the transition from mechanical testing of mold compounds to actual Integrated Circuit (IC) plastic package reliability requires an understanding of material behavior under the influences of moisture, temperature, and varying load conditions. This paper will focus on the role of material strengths, strain energy, and nonlinear effects in determining plastic package reliability. Examples of correlation between materials testing and reliability data will be presented.
Thin Film Epitaxial Oxide Optical Waveguides
Authors: Fork D. K. , Armani-Leplingard F. , Kingston J. J. , Anderson G. B.
Published: April 2011

One of the most challenging applications of ferroelectric thin films is the formation of technologically practical optical waveguideing devices, particularly in the context of a dynamically changing environment where competing light sources and optical materials simultaneously undergo rapid improvement. In order to assess the prospects of this technology, a fundamental understanding of waveguide loss is being pieced together. This includes the relative contributions of surface scattering, and grain boundary scattering to optical losses. With computational models, it is possible to predict the surface losses from measured topographic data. This tool provides a method to probe the residual effects of grain boundaries, defects and impurities on optical losses. A comparative anatomy of various thin film structures and their loss characteristics will be provided in the context of these experiments.
Evaluation of Hylan B (Hylan Gel) as Soft Tissue Dermal Implants
Authors: Larsen N.E. , Leshchiner E. , Pollak C.T. , Balazs E.A.
Published: April 2011

Hylan B gel is a viscoelastic insoluble crosslinked derivative of the natural hyaluronan (hyaluronic acid, HA) polymer. Hyaluronan derivatives such as hylan B have enhanced rheological properties and possess the desired biological properties of natural hyaluronan. Hylan B was evaluated in nonclinical in vivo studies for biocompatibility and residence times in dermal tissues. In one study, residence time of radiolabeled [14C]-hylan B was evaluated in guinea pigs following intradermal administration with serial sacrifice (0, 1, 4, 12, 24 weeks). Analysis of radioactivity revealed that at 6 months post-implantation up to 98% of the radioactivity was recovered from the specific injection site (mean 76.7± 29.4%). A half-life time of 12.2 months was estimated from analysis of the data. In another study, the behavior of hylan B gel implanted in the intradermal and subcutaneous tissue of guinea pigs was evaluated at 3 days and at 1, 2, 4, 9, 13, 26 and 52 weeks. In this study, collagen implants were evaluated in parallel with hylan B gel implants in the same animals. Hylan B gel was found to be biologically compatible and stable in the dermal tissue. At one year post-implantation, hylan B gel was detected in a majority (12/16) of test sites. None of the collagen implant materials was detected at one year post-implantation.
The in Vitro Mechanical Strength and in Vivo Bone Ingrowth of a Degrading Polymeric Composite Biomaterial
Authors: MJ Yaszemski , RG Payne , TB Aufdemorte , WC Hayes , R Langer , AG Mikos
Published: April 2011

Clinical situations that require techniques to fill defects of bone are common in the surgical care of Orthopaedic patients. The options currently available to the surgeon are autograft bone (bone from the same person), allograft bone (bone from a deceased donor), and bone cement. Each of these options has a mix of desirable and undesirable properties, and the choice of one of them necessarily involves some degree of compromise. We have been developing a novel, degradable, polymeric composite biomaterial to function as an alternative to the currently available options. The design goals for this biomaterial are that the material be sterilizable without loss of its mechanical and biological properties, available to the surgeon in the sterile operating field on short notice, moldable such that it can fill irregularly shaped defects, harden over a time span of ten to fifteen minutes, provide the reconstructed skeletal region with mechanical properties of the same order of magnitude as those of the bone it replaces, degrade over a period of weeks to months, be replaced by new bone, and maintain a specified minimum mechanical strength during the period of degradation and new bone growth. In this study we asked two questions. First, would the material maintain a minimum compressive strength greater than 5 Megapascals (MPa) and a minimum compressive modulus greater than 100 MPa over a twelve week period in a simulated body fluid environment? Second, would the material degrade in vivo in a rat proximal tibia model?
Dacron-Urethane Composite for Reconstructive Surgery
Authors: Leake Donald
Published: April 2011

A composite biocompatible material made of polyethyleneterephalate (Dacron) and polyetherurethane was fabricated as an aid to bone grafting for the reconstruction of large bony defects of the craniomaxillofacial regions. Bone graft material is placed within the confines of the Dacron-urethane implant and new bone forms to the shape imposed by the implant.

The principle application of this material has been for the reconstruction of defects of the neurocranium and of the mandible [1–5]. A number of other applications have been studied including reconstruction of long bone discontinuity defects [6], reconstruction of an infant's anterior chest wall [19], the prosthetic replacement of large defects of the cervical trachea [7] and as a potential material for a thrombo-resistant small diameter vascular prosthesis [8].
Degradation of Poly(Anhydride-Co-Imides): Novel Polymers for Orthopedic Applications
Authors: Uhrich Kathryn E. , Ibim Sobrasua E. M. , Laurencin Cato T. , Langer Robert
Published: April 2011

Novel polymers with good mechanical properties are being developed as degradable matrices for bone growth and regeneration. The poly(anhydride-co-imides) were synthesized from trimellitylimidoglycine and 1,6-bis(p-carboxyphenoxy)hexane in molar compositions of 10:90, 30:70 and 50:50. These polymers have compressive strengths (23–57 MPa), which are similar to human cortical bone. 1 In vitro degradation was performed under acidic (pH 5), physiological (pH 7.4), and basic (pH 10) conditions. The degradation rate increased under basic conditions and by increasing the amount of trimellitylimidoglycine in the polymer backbone. Two erosion zones were observed in the polymers by microscopy. In vivo polymer degradation was evaluated by characterizing polymer discs implanted in subcutaneous tissue of rats over a 56 day time period. Copolymers with the highest ratio of trimellitylimidoglycine in the polymer backbone were completely degraded by 56 days, the other compositions remained in the tissue as solid pellets at this time. In vivo degradation was much slower than the corresponding in vitro degradation.
The Sustained Release of Galardin and Taxol from Gelatin Chondroitin Sulfate Coacervate Films
Authors: Heller Phillip F. , Jenkins G. Mark , Cheng Linda , Leong Kam , Shao Wen , Brinker Jeffrey , Hope Earl , Nater Cynthia , Lakatta Edward , Froehlich Jeffrey P.
Published: April 2011

Coronary artery atherosclerosis is the leading cause of death in the United States. Restenosis following percutaneous transluminal balloon angioplasty (PTCA) remains the limiting factor in the use of this treatment for coronary artery disease. Restenosis occurs in 30% of patients within 6 months. The restenotic lesion is a fibroproliferative response with resulting smooth muscle cell migration, proliferation and extracellular matrix production. Despite a decade of research there is no effective strategy for preventing restenosis in man.
Poly(L-Lactic Acid-Co-Aspartic Acid): Interactive Polymers for Tissue Engineering
Authors: Hrkach Jeffrey S. , Ou Jean , Lotan Noah , Langer Robert
Published: April 2011

One of the challenges in the field of tissue engineering is the development of optimal materials for use as scaffolds to support cell growth and tissue development. For this purpose, we are developing synthetic, biodegradable polymers with functional sites that provide the opportunity to covalently attach biologically active molecules to the polymers, so they can predictably interact with cells in a favorable manner to enhance cell attachment and growth. The preparation of poly(L-lactic acid-co-aspartic acid) comb-like graft copolymers from poly(L-lactic acid-co-β-benzyl-L-aspartate), and the casting of polymer films by solvent evaporation were carried out.
Parasitic Reactions between Alkyls and Ammonia in OMVPE
Authors: Chen C.H , Liu H. , Steigerwald D. , Imler W. , Kuo C.P. , Craford M.G
Published: April 2011

The parasitic reactions between ammonia and commonly used alkyls have been studied in a horizontal OMVPE reactor. The results indicate that parasitic reactions between TMA1 and NH3 is severe, leading to the necessity to grow A1N at low reactor pressure. On the other hand, parasitic reactions between TMGa+NH3 and TMIn+NH3 are not significant and it is possible to grow GaN and GaInN at any reactor pressure.
Growth of InGaN Films by MBE at the Growth Temperature of GaN
Authors: Singh R. , Moustakas T.D.
Published: April 2011

We report the growth of InGaN alloys over practically the entire composition range at the growth temperature of GaN (700–800 °C) by MBE. We found that when the grown films are thick (> 0.3 μm), incorporation of more than about 30% indium results in phase separation of InN, which is consistent with spinodal decomposition. On the other hand we discovered that such phase separation is absent in thin InGaN films ( < 600Å) grown as GaN/InGaN/GaN heterostructures. In such configurations we were able to incorporate up to 81% In, which is the highest yet reported.
Effect of Carrier Gas on the Surface Morphology and Mosaic Dispersion for GaN Films by Low-Pressure MOCVD
Authors: Kistenmacher T. J. , Wickenden D. K. , Hawley M. E. , Leavitt R. P.
Published: April 2011

Low-pressure metal-organic chemical vapor deposition (MOCVD) has been used to deposit unnucleated and self-nucleated GaN thin films on (00.1) sapphire substrates. For the self-nucleated films, initial layers were grown at 540°C using trimethylgallium and ammonia as elemental sources and either nitrogen or hydrogen as the carrier gas. Using these same gas phase conditions, overlayers on native (00.1) sapphire substrates or the GaN-nucleated (00.1) sapphire substrates were deposited at 1025°C. The surface morphology and mosaic dispersion of these unnucleated and self-nucleated GaN thin films have been surveyed by a combination of real space images from atomic force microscopy and reciprocal space intensity data from X-ray scattering measurements. As expected, the unnucleated GaN films show a large-grained hexagonal relief, typical of three-dimensional island growth. However, the self-nucleated films are shown to be dense mosaics of highly oriented islands, emblematic of a more two-dimensional growth.
Deposition of Gallium Nitride Films using Ammonia and Triethylgallium Seeded Helium Beams
Authors: Sumakeris J. J. , Chilukuri R. K. , Davis R. F. , Lamb H. H.
Published: April 2011

Gallium nitride films have been deposited on Si(100) and Al2O3(0001) substrates using triethylgallium and ammonia seeded into highly expanded helium gas streams. A two step deposition process that reproducibly results in continuous crystalline GaN films has been developed. The microstructure and composition of the resultant films were characterized by scanning electron microscopy, reflection high energy electron diffraction and Auger electron spectroscopy and film character was correlated to deposition conditions.
Structural Defects in Heteroepitaxial and Homoepitaxial GaN
Authors: Liliental-Weber Zuzanna , Ruvimov S. , Kisielowski CH. , Chen Y. , Swider W. , Washburn J. , Newman N. , Gassmann A. , Liu X. , Schloss L. , Weber E.R. , Grzegory I. , Bockowski M. , Jun J. , Suski T. , Pakula K. , Baranowski J. , Porowski S. , Amano H. , Akasaki I.
Published: April 2011

The microstructure and characteristic defects of heteroepitaxial GaN films grown on sapphire using molecular beam epitaxy (MBE) and metal-organic-chemical-vapor-deposition (MOCVD) methods and of homoepitaxial GaN grown on bulk substrates are described based on transmission electron microscopy (TEM), x-ray diffraction, and cathodoluminescence (CL) studies. The difference in arrangement of dislocations along grain boundaries and die influence of buffer layers on the quality of epitaxial films is described. The structural quality of GaN epilayers is compared to diat of bulk GaN crystals grown from dilute solution of atomic nitrogen in liquid gallium. The full width at half maximum (FWHM) of the x-ray rocking curves for these crystals was in the range of 20–30 arc sec, whereas for the heteroepitaxially grown GaN the FWHM was in the range of 5–20 arc min. Homoepitaxial MBE grown films had FWHMs of about 40 arc sec. The best film quality was obtained for homoepitaxial films grown using MOCVD; these samples were almost free from extended defects. For the bulk GaN crystals a substantial difference in crystal perfection was observed for the opposite sides of the plates shaped normal to the c direction. On one side the surface was almost atomically flat, and the underlying material was free of any extended structural defects, while the other side was rough, with a high density of planar defects. This difference was related to the polarity of the crystal. A large difference in crystal stoichiometry was also observed within different sublayers of the crystals. Based on convergent beam electron diffraction and cathodoluminescence, it is proposed that GaN antisite defects are related to the yellow luminescence observed in these crystals.
Simulated Thermal Effects on Structural and Electronic Properties of GaN
Authors: Serra S. , Miglio L. , Fiorentini Vincenzo
Published: April 2011

We present preliminary results of tight binding molecular dynamics (TBMD) simulations concerning the thermal effects on the structural and electronic properties of GaN. We derived a semiempirical tight binding (TB) potential which is able to reproduce the band structure and the phase diagram of GaN for zincblende, wurtzite and rock-salt phases. We have found that even at few hundreds K above the experimental melting temperature the local ordering is fairly well conserved, with the fraction of wrong bonds quite low. Defects states appear in the gap at approximately 2.3 eV in agreement to the experimental indication for annealed films.
Excitation Wavelength and Saturation Effects on Gallium Nitride Photoluminescence
Authors: Banas Mike , Liu Guangtian , Ramer Jeff , Zheng Kang , Hersee Steve , Malloy Kevin
Published: April 2011

We report on the excitation wavelength and power dependence of LPMOCVD grown GaN photoluminescence (PL). A mode-locked Ti:Sapphire laser that is doubled to provide a tunable wavelength range of 350-500 nm is used to pump the GaN samples. Special attention has been paid to the “yellow” (∼567 nm) luminescence. Different power dependence characteristics of the yellow emission are observed when pumping above and below the bandgap. A measurement of the photoluminescence excitation spectrum of the yellow peak (∼567 nm) is also performed and this spectrum shows a peak at room temperature at 3.36 eV (369 nm), an additional broad peak at 77 K and only the broad peak at 7 K. An excitation model is used to explain the behavior of the yellow emission, suggesting the neutral donor serves as a key species for the yellow emission.
Hydrazoic Acid: A Potent ‘Active Nitrogen’ Precursor for Group III Nitride Growth
Authors: Freedman Andrew , Robinson Gary N.
Published: April 2011

Hydrazoic acid, HN3, was shown to be an extremely reactive molecule and an effective precursor species for 'active nitrogen'. At room temperature, hydrazoic acid dissociatively chemisorbed on GaAs (110) surfaces to form the NH radical and N2. At 473 K, the NH fragment reacted with the substrate, broke Ga-As bonds and formed GaN and AsN species. At 673 K, an anionic exchange mechanism commenced; the surface became completely depleted of As and a thin film of GaN formed. When the surface was dosed at 773 K, a 20 Å thick GaN film was grown. This evidence demonstrates that hydrazoic acid is highly reactive at comparatively low surface temperatures and offers a viable alternative to ammonia as a nitrogen precursor gas.
InGaN Light-Emitting Diodes with Quantum-Well Structures
Authors: Nakamura Shuji
Published: April 2011

InGaN single-quantum-well-structure (SQW) light-emitting diodes (LEDs) with an emission wavelength between violet and orange were fabricated. The maximum on-axis luminous intensity of green LEDs was 12 cd and the external quantum efficiency was as high as 6.3 % at a forward current of 20 mA, while those of blue LEDs were 2 cd and 9.1 %, respectively. The peak wavelength and the full width at half-maximum of the green LEDs were 520 nm and 30 nm, respectively, while those of blue LEDs were 450 nm and 20 nm, respectively. The color of green InGaN SQW LEDs was greener than those of conventional GaP and AlInGaP LEDs.
Electric Breakdown in Nitride PN Junctions
Authors: Dmitriev V.A. , Kuznetsov N.I. , Irvine K.G. , Carter C.H.
Published: April 2011

Electric breakdown of mesa terminated GaN and AlGaN pn diodes was investigated. The nitride pn structures were grown on 6H-SiC (0001) wafers by metalorganic chemical vapor deposition (MOCVD). Mesa structures were fabricated by reactive ion etching (RIE). Capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the pn junctions were measured. It was found that the junctions were linearly graded. Microplasmic breakdown was observed. The breakdown voltage for GaN and AlGaN diodes ranged from 40 to 150 V and from 40 to 100 V, respectively. The electric breakdown field and temperature coefficient of the breakdown voltage were measured.
Deposition of Nbtex Thin Films Using Laser Ablation: Crystallographic Structure And Spatial Composition of Deposits
Authors: Sassoli H. , Grangeon F. , Mathey Y. , Autric M. , Pailharey D. , Marine W.
Published: April 2011

Pulsed laser deposition (PLD ) is known for its capacity to reproduce a target composition on a substrate. We have used this deposition technique to produce thin films of transition metal chalcogenides. However, the deposits were always deficient in Te relative to the starting material ( composed by a refractory metal ( niobium ) and a chalcogene ( tellurium ) ). Variations of the interreticular distances have been observed with respect to fluence and substrate temperature. We show that spatial composition of the films is determined by a degree of crystallinity of deposit and by the reaction of formation of Te2 molecule within laser induced plume Two kinds of deposits have been obtained : Nb5Te4-type thin films which have a one-dimensional structure and NbTe2-type thin films which have a two-dimensional structure. While NbTe2 films have been realized by sputtering, it is the first time that Nb5Te4 films have been deposited.
Strained Linbo3/Sapphire Heterostructures Grown by Pulsed Laser Deposition
Authors: Shibata Yoshihiko , Kuze Naohiro , Matsui Masahiro , Kanai Masaki , Kawai Tomoji
Published: April 2011

Thin LiNbO3 films are deposited on (001) sapphire substrates by Ar F pulsed laser ablation. The films are evaluated by X-ray diffraction analysis at various temperatures, as well as high-resolution transmission electron microscopy (TEM). The deposited films are highly epitaxial but that are strained, that is, the a-axis is longer and the c-axis is shorter than those of LiNbO3 single crystals. X-ray diffraction analysis at deposition temperature, as well as TEM show that the strain is caused by the difference in thermal expansion coefficients between LiNbO3 and sapphire substrates.