bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of Reaction Bonded Silicon Nitride from High Purity Si Powders
Authors: Haggerty John S.
Published: March 2011

Significantly improved reaction kinetics and properties have been realized for reaction bonded Si3N4 (RBSN) by using Si powders having unusual physical and chemical characteristics combined with clean, oxygen-free processing conditions. For instance, complete nitridation can be achieved in < 1 h at 1150°C or < 100 m at 1250°C without pre-nucleation, or < 1 h at 1100°C with pre-nucleation. These compare with normal schedules of ∼100 h at 1470-1500°C. Resulting strengths (up to 870 MPa) and oxidation resistances of the RBSN essentially equal those of fully dense Si3N4 even though RBSN includes 25% open porosity. The results show that every aspect of the process, ranging from powder synthesis to < ppm levels of oxygen in the nitriding atmosphere, have demonstrable effects on the reaction kinetics and the resulting properties of the parts. With careful processing, reaction formed ceramics can compete advantageously with fully dense counterparts.
Synthesis of a MoSi2/SiC Composite in Situ Using a Solid State Displacement Reaction
Authors: Henager C. H. , Brimhall J. L. , Hirth J. P.
Published: March 2011

Solid state displacement reactions are being studied at Pacific Northwest Laboratory (PNL) as a method of synthesizing intermetallic and ceramic composites in situ. A high-strength in situ composite of MoSi2/SiC was synthesized using a solid state displacement reaction between Mo2C and Si. Diffusion couples between Mo2C and Si processed at 1200°C revealed the formation of aligned SiC platelets in a MoSi2 matrix. In situ composites were also synthesized by blending Mo2C and Si powders and vacuum hot-pressing the powders at 1350°C for 2 h followed by 1 h at 1700°C. The resulting microstructure consisted of 1-μm diameter SiC particles (30 vol%) uniformly dispersed in a fine grained MoSi2 matrix. Densities of 5.53 g/cm3 were obtained along with a microhardness of 14.2 GPa. Bend bars and chevron-notched bars revealed a strength of 475 MPa and a fracture toughness of 6.7 MPa√m at room temperature. Bend strengths increased to 515 MPa at 1000°C and then decreased to 112 MPa at 1200°C. Measured fracture toughness increased to 10.5 MPa√m at 1050°C.
The Combustion Synthesis of B4C-A1203-Al Composite Materials
Authors: Feng H. J. , Moore John J. , Wirth D. G.
Published: March 2011

The combustion synthesis of the B4C-2Al203-xAl ceramic-metal composite system has been studied using the propagating mode of ignition for the reaction 2B203 + C + (4 + x)Al = B4C + 2Al203 + xAl in which x was varied between 0 and 3. The volatile constituent(s), eg. B2O3, resulted in the formation of an expanded or foamed ceramic with a uniform porous structure. The porosity represents ≥65%, and an expansion of 300-500% occurred mainly in the vertical direction. The effect of green density and reaction stoichiometry on product density, pore morphology, propagation rate and overall activation energy is discussed.
Biomimetic Ceramics: What, Why and How?
Authors: Calvert Paul
Published: March 2011

The role of biomimetic approaches in materials engineering is reviewed. In the case of ceramics, close parallels in structure and function can be seen between synthetic and biological materials. Biological ceramics have resolved difficulties which are limiting the application of synthetic materials, particularly in the need for greater toughness. The enhanced toughness of materials such as shell and tooth enamel can be attributed to microstructural factors. Both natural materials contain a small amount of polymer. If this is essential, then any synthetic mimetic material would be limited by the temperature resistance of the polymer. In fact, much of the toughness is dependent on the elongated particle morphology and does not require polymer. Routes to forming ceramics with such elongated particles are discussed.
Ion-Exchange Strengthening a Mica-Based Machnable Glassceramic
Authors: Chin T.S. , Liu H.S. , Chiu S.Y. , Chen C.I. , Hsu S.E.
Published: March 2011

Ion exchange was carried out on a lithium-doped fluorophlogopite machinable glassceramic with composition, in wt%, 52.2 SiO2, 14.0 Al2O3, 14.2 MgO, 12.5 MgF2, 1.4 Li2O, and 5.7 Na2O, to study the strengthening effect. The crystalline phases after annealings were Na-fluorophlogopite and betaspodumene, with a volume fraction of about 2:1. Ion exchange of Li by K in the glassceramic at 770° C for 4 h improved 2.1 to 2.3 times the three point bending strength (TPBS). Hence strong machinable ceramic with TPBS of greater than 300 MPa can be made. Ion exchange increases 100% electrical resistivity and improves 21% chemical stability, due to a surface layer of about 100 micrometer enriched with K.
Preparation of Homogeneous Aluminosr, Icate Gels by sol/gel Methods
Authors: Reese M. E. , Mccormick A. V. , Sanchez J.
Published: March 2011

The factors affecting the production of homogeneous aluminosilicate gels from alkoxide precursors were investigated. Aluminosilicate gels were made in acidic conditions with a prepolymerization of the silicate precursor followed by the addition of the alumina precursor.

Confirming earlier studies, we found that the gel homogeneity is increased when the rate of gelation decreases. The reduction of the water content and/or the aluminum precursor, and more surprisingly the increase of the acid concentration contributed to the gel time increase and thus the gel homogeneity improvement.
Processable Oligomeric and Polymeric Precursors to Silicates Prepared Directly from SiO2, Ethylene Glycol and Base.
Authors: Bickmore Clint , Hoppe Martin L. , Laine Richard M.
Published: March 2011

Bimetallic glycolato silicates of the form M2 Si2(OCH2CH2O)5 where M is an alkali metal, can be synthesized directly from SiO2, ethylene glycol and MOH. Further reaction with HO(CH2CH2O)4H, PEG4, transforms these compounds into rheologically useful polymers. These polymers offer considerable potential for processing novel silicate glass shapes, e.g. thin films, fibers and membranes, from relatively inexpensive precursors materials. In this paper, we describe pyrolysis studies on the model compound Li2 Si2(OCH2CH2O)5 as a prelude to determing the utility of the polymeric precursors. These studies delineate the effects of temperature on the decomposition processes whereby the glycolato silicate transforms into almost phase pure, crystalline Li2O-2SiO2. This work is contrasted with previous pyrolysis studies on K2 Si2(OCH2CH2O)5.
Ambient Effects on Thin Film Interactions
Authors: Chang Chin-An
Published: March 2011

Thin film interactions often show strong dependence on the annealing ambients used. The outdiffusion of a large number of metals and semiconductors through an overcoating gold film and subsequent formation of surface oxides have been observed to be greatly enhanced using a steam or air ambient compared with those using vacuum or inert ambients. The ambient effects become more puzzled when the overcoating metal consists of gold and silver layers, depending on the sequence of these layers. These ambient effects are shown to be well correlated by a surface potential model which considers both the relation between the overcoating metal and the underlying diffusing species, and the effects of ambient on the surface properties of the overcoating metal at the interface. Further ambient effects have been predicted and confirmed, including reduced interactions by oxygen for many systems with different overcoating metals. Different interaction mechanisms have also been observed, including competing ambient effects, competing interactions, and preferential reactions, all affected by the ambients used. Understandings of the various ambient effects not only provide important insights into the interface interactions in general, but also have great impact on metallurgical contacts in device technologies. Future studies for the ambient effects are also discussed.
Effect of Nitrogen and Oxygen Impurities on Tantalum Silicide Formation
Authors: Ho K. T. , Lien C.-D. , Nicolet M-A. , Scott D. M.
Published: March 2011

Tantalum, being a refractory metal, is sensitive to ambient impurities when forming a silicide. By introducing nitrogen and oxygen impurities into a tantalum-silicon system, interesting chemical and physical effects are observed in their subsequent reactions. Nitrogen and oxygen behave similarly in such a system. If initially present in Ta, they segregate into the still unreacted Ta as the silicide layer grows at a somewhat retarded rate. The same impurities, initially present in Si, are immobile in the form of stable compouis and suppress TaSi2 growth. The rare isotopes 15N and 18O are introduced bY implantation and Profiled by 15N(P,α)12C and 18O(P,α)15N nuclear reaction analyses, respectively. In addition, unintentionally incorporated 18O is checked by the 16O(d,α) 14N nuclear reaction. The results are explained in terms of the moving species Si, and of the chemical affinity, solubility and diffusivity of the impurities in their host lattice.
Oxygen Influence on Titanium Silicide Formation
Authors: Bentini G.G. , Berti M. , Cohen C. , Drigo A.V. , Guerri S. , Nipoti R. , Siejka J.
Published: March 2011

The oxygen behaviour and its influence on the annealing properties of the TiO2/Si and Ti/TiO2/Si systems have been investigated. For the TiO2/Si system no reaction at all could be evidenced after vacuum annealing up to 900°C for 30'. In the Ti/TiO2/Si system metallic Ti reacts with the TiO2 film above 400°C and at 600°C a uniform oxygen solid solution at the solubility limit was obtained without any Si reaction. Silicide formation occurs for annealing temperatures higher than 650°C and causes oxygen expulsion from the reacted layer and consequently a rise in its concentration at the surface where Ti oxide precipitation takes place. This surface oxide layer prevents a further growth of the silicide up to 850°C. The reaction of the whole metal film is attained only by annealing at 900°C or above, when the oxide is completely reduced and an important oxygen loss takes place. A model explaining this behaviour is proposed.
RBS and TEM Analysis of Ta Silicides on GaAs
Authors: Kavanagh K.L. , Chen S.H. , Palmstrom C.J. , Carter C.B.
Published: March 2011

Electron-beam and sputter-deposited Ta silicides on GaAs were annealed in an As2 overpressure ambient to temperatures as high as 920°C for 20mim. The films were then characterized with RBS, cross-sectional TEM and both electron and x-ray diffraction. The morphology of sputtered TaSi2/GaAs interfaces did not change, however, some interaction was detected at electron-beam deposited GaAs/silicide interfaces. Arsenic in-diffusion was detected at temperatures above 800°C and it was found to be dependent on the stoichiometry of the films. Arsenic diffusion into Si-rich electron-beam and sputter deposited films was low, whereas significantly more As diffused into the Ta-rich silicide. Some indium (3×l015atoms/cm2), from the InAs used as the source of As2overpressure, was observed to accumulate at all GaAs/silicide interfaces at temperatures above 800°C.
Prediction of Silicide First Phase and Phase Sequence from Heats of Formation
Authors: Pretorius R.
Published: March 2011

An effective heat of formation (δH') is formulated, enabling δH' to be calculated as a function of the concentration of metal and silicon available for interaction to form a silicide. A rule for first phase formation is proposed according to which, “The first silicide compound to form during metal-silicon interaction is the congruent phase with the most negative effective heat of formation at the concentration of the lowest eutectic temperature of the binary system.” The effective heat of formation concept is also extended to predict subsequent phase sequence.
Diffusion of AS, B, and P In Tasi2
Authors: Eichinger P. , Frenzel E. , Neppl F.
Published: March 2011

Implantation range parameters and diffusion characteristics of As, B, and P in TaSi2 have been investigated, mainly by SIMS. It is shown that dopant diffusion in the silicide is much faster than in polycrystalline Si. Significant outdiffusion is observed for P, segregation effects are seen with B only. No dopant penetration through gate oxide is detected.
Ion Beam Enhanced Adhesion of Thin Films
Authors: Baglin J. E. E. , Clark G. J. , BØttiger J.
Published: March 2011

Ion beam enhanced adhesion has been studied for the case of thin Cu films deposited on substrates of alumina, fused quartz and glass-ceramic. Beams of He+ (200 keV) and Ne+ (280 keV) were used, in order to test the respective roles of nuclear and electronic interactions in this process. Peel tests were used to produce the first quantitative studies of adhesion strength as a continuous function of ion dose. Bond strengths improved after irradiation at modest doses, sometimes by a factor of 20. Subsequent heating in a helium furnace produced as much as an order of magnitude further adhesion improvement in irradiated samples. Similar tests for Cu on Teflon produced excellent bonding for ion doses of ∼ 1014/cm2. The results indicate bond breaking and reconstruction at a sharp interface, with no significant metalsubstrate intermixing. The new bond is stable under heat cycling.
Phase Formation and Kinetic Processes in Silicide Growth.
Authors: Ottaviani G.
Published: March 2011

Twenty years of research have now been devoted to investigating reaction products obtained by annealing metal-layer/silicon structures. A wide variety of cases have been analyzsed and a considerable amount of data has been produced. Despite the vast amount of information available, several aspects concerning phase formation and kinetic processes are not yet well established. The purpose of this paper is to investigate the mechanisms of phase formation and to show the importance of kinetic factors in the appearance of various compounds. Results will be shown for a single metal layer deposited on silicon, for bilayers. and for alloys. Depending upon the starting structure, metal-rich or silicon-rich silicides can be formed. Moreover, by modifying the boundary conditions, it is possible to change the growth kinetics of the silicide phase that forms.
An Interface-Sensitive Conversion Electron Mössbauer Spectroscopic Study of the Ion Beam Induced Reactions at Fe-Si Interface.
Authors: Godbole V.P. , Bhide V.G. , Ghaisas S.V. , Kanetkar S.M. , Joshee R.S. , Ogale S.B.
Published: March 2011

The ion beam induced reactions at Fe-Si interface are studied for the first time using a novel interface-sensitive Mössbauer probe.The samples used in these studies are prepared by depositing a thin layer (<450A°) of enriched Fe57 isotope (95.45% by composition) on a freshly cleaned silicon (111) substrate followed by a deposition of a 150Ao film of natural iron (Fe 57 only 2.2%).These samples are subjected to Xetion bombardment at an incident ion energy of 100 keV and a dose of 6 × 1015 ions/cm2 The technique of Conversion Electron Mössbauer Spectroscopy (CEMS) is used to characterize the formation and growth of different phases as a function of annealing treatment. The spectra are leastsquare fitted using the MOSFIT programme.The MHssbauer lines for as-deposited and ion bombarded samples show a considerable broadening, which is a clear signature of a large concentration of defects formed at the interface due to ion beam induced collision cascades. As the samples are annealed the resonance lines are sharpened indicating recovery of stoichiometrically well-defined phases from an initial defective state. The present study indicates formation of FeSi and Fe3 Si phases after the annealing treatment-RBS measurements are used to confirm the mixing.These results are analyzed in terms of the non-equilibrium features of the directed energy processing of interface.
Precipitation of Copper in Transmutation Doped Silicon
Authors: Gleichmann R.
Published: March 2011

During the long-time diffusion of transmutation doped silicon a variety of large CuSi precipitates is introduced into the material. The precipitates have been found to be metastable and transform during subsequent heat treatments. One of the most surprising results of such a transformation is the generation of large, extended monolayer precipitates, which are shown to represent the stable configuration of the precipitate system.
The Growth and Characterization of Epitaxial Fluoride Films on Semiconductors
Authors: Phillips Julia M. , Gibson J. M.
Published: March 2011

This review considers the growth and characterization of epitaxial alkaline earth fluoride compounds on semiconductors. The field has developed quite rapidly in recent years, from the original demonstration of epitaxial growth in these systems to the investigation of the structure and properties of the layers. Two recent developments are reviewed in detail: the epitaxial relations which have been discovered between fluoride films and semiconductor substrates and the variety of interface structures which these systems display. These findings are beginning to lead to an understanding of the epitaxial growth process in these systems and how it relates to that in other more thoroughly studied systems.
Epitaxial Growth of Fluoride Films on Silicon Substrates
Authors: Ishiwara Hiroshi , Asano Tanemasa
Published: March 2011

Growth conditions and structural properties of vacuumevaporated fluoride films on Si(lll) and (100) substrates are reviewed. It has been found that single crystal CaF2 films are grown on both (111) and (100) substrates at temperatures of 600–800°C and 500–600°C, respectively. It has also been found that SrF2 and BaF2 films of good crystalline quality are grown on Si(lll) at temperatures around 600°C, but that the films grown on Si(100) contain (111) oriented crystallites. In epitaxial growth of a Si/CaF2/Si structure, a novel growth method is presented, in which a thin Si layer is deposited at room temperature prior to deposition of a thick Si film at elevated temperature. Investigations on growth of mixed fluoride films, radiation damage in CaF2 films, and epitaxial relations in the fluoride/Si heterostructures are also presented.
On the Structure of Metal Silicide:Silicon Interfaces.
Authors: Cherns D. , Pond R.C.
Published: March 2011

A new crystallographic theory of interfacial structure is applied to the case of interfaces between NiSi2, CoSi2 and Pd2Si grown epitaxially on Si. In the case of NiSi2 layers grown in parallel orientation it is shown that dislocations with Burgers vectors ¼<111> separate energetically degenerate interfacial domains on {hko} interfaces. Observations, of such defects on (001) interfaces, using transmission electron microscopy, are presented and show detailed agreement with the theory.
Domain and Interface Structures of Epitaxial PtSi
Authors: Kawarada H. , Ohdomari I. , Horiuchi S.
Published: March 2011

The crystalline perfection of epitaxial PtSi thin films and the microstructure of the PtSi/Si interface have been examined using transmission electron microscopy (TEM), including lattice image techniques. Epitaxial PtSi layers grow with domains which have three different positions on a (111) Si substrate. Inside a domain the crystalline perfection is high, and at the domain boundary no intermediate region has been observed. The undulation of the PtSi/Si interface is larger than that of other epitaxial silicide/Si interfaces. Despite the large undulation, a cross-sectional lattice image shows the epitaxial layer extends to the interface. The interface is abrupt in the epitaxial PtSi/Si system.
Grain boundary Diffusion of Ni through Pd2Si
Authors: Zingu E. C. , Mayer J. W.
Published: March 2011

Interdiffusion in the Si<100>/Pd2Si/Ni and Si<111>/Pd2Si/Ni thin film systems has been investigated using Rutherford backscattering spectrometry. Nickel is found to diffuse along the grain boundaries of polycrystalline Pd2Si upon which it accumulates at the Si<100>Pd2Si interface. The high mobility of Ni compared to that of si suggests that Pd diffuses faster than Si along the Pd2Si grain boundaries. An activation energy of 1.2 eV is determined for Ni grain boundary diffusion in Pd2Si.
Ion Channeling in Elastically Strained Superlattices
Authors: Barrett John H.
Published: March 2011

A review is given of the channeling behavior observed in superlattice materials. Elastic strains within the layers have been shown to be the source of the unusual ion dechanneling observed originally in InAs/GaSb and since observed in several other semiconductor superlattices. These strains occur because of the slight mismatch between the lattice constants of the two materials and cause the rows and planes of atoms in the crystal that are inclined to the surface normal to have small directional misalignments at the interfaces between the layers. The effects of these misalignments have been studied by computer simulations of ion trajectories in the crystal and shown to account in a reasonable manner for the observed dechanneling behavior. Calculations have been done as a function of the amount of misalignment to give an indication of how much dechanneling might be expected in other superlattices formed of any pair of materials that have slight mismatches. Various ways of measuring the amount of misalignment have also been studied by simulations and experiments.
Tetragonal Strain in MBE GexSi1-x Films Grown on (100) Si Observed by Ion Channeling and X-Ray Diffraction
Authors: Fiory A. T. , Feldman L. C. , Bean J. C. , Robinson I. K.
Published: March 2011

Structure of GexSi1-x alloy films grown on (100) Si by molecular beam epitaxy is analyzed by MeV He+ ion channeling and X-ray diffraction as functions of Ge concentration, film thickness and growth temperature. Critical thicknesses for pseudomorphic growth are determined for x ≤ 0.5, where coherent tetragonally-strained layers are observed. The average strain decreases approximately as the square-root of thickness when the critical thickness is exceeded. At temperatures near the threshold for islanding growth, surface roughness appears as a precursor to degradation of strained-layer epitaxy. No effect on the amount of the tetragonal strain was found in a study of ion-beam damage.
Sub-Boundary Formation and Suppression in Silicon films Recrystallized by Scanned Zone Melting
Authors: Pfeiffer Loren , Gibson J. M. , Kovacs T.
Published: March 2011

We observe that the formation of low angle grain boundaries (sub-boundaries) depends strongly on the thickness of the recrystallized Si film. The average lateral spacing between adjacent sub-boundaries increases from 40 μm for 4000Å films to 500 μm for unseeded Si films 30 μm thick. For seeded 30 μm Si films on 1.6 mm by 1.6 mm buried oxide islands, areas exceeding 1.0 mm by 1.0 mm have been recrystallized which are free of all sub-boundaries, but which contain dislocations in other configurations.
An Auger Electron Spectroscopy (AES) Investigation into the Effect Annealing on the Phase Distribution of Ion Implanted Oxygen in Silicon
Authors: Tuppen C G , Davies G J , Taylor M R , Heckingbottom R
Published: March 2011

Buried oxide layers, formed by high dose ion implantation, have been examined using Auger depth profiling. The phase distribution of oxygen in the wings of the implant profile and effects of high temperature annealing, have been investigated. Ion beam induced cascade mixing, which occurs during sputter etching, limits the minimum detectable size of SiO2 precipitates. However, it is possible to minimise this effect by reducing the ion beam energy. At very small precipitate sizes (<100Å) silicon atoms at the edge of the precipitate particles will make a major contribution to the Si KLL Auger spectrum. A previously reported theoretical model has been expanded to take account of this phenomenon.
X-ray Microanalysis and High Resolution Imaging of Ge-Au-Ni Metal Layers on Gallium Arsenide
Authors: Fathy D. , Krivanek O. L. , Spence J. C. H. , Paulson W. M.
Published: March 2011

Ohmic contacts to GaAs have been studied using a high resolution TEM, an SEM and a STEM with an energy dispersive x-ray attachment. Two different deposition sequences of the constituent Au-Ge-Ni metals yielded specific contact resistivities that varied by one order of magnitude. Crosssection images of the interface between the GaAs and the metal Au-Ge-Ni layers following alloying showed protrusions at the interface. Contacts with low specific resistivities showed deeper protrusion and also significantly more Ge and Ni in the GaAs.
Low Temperature (150–250°C) Deposition of n+ and p+ Microcrystalline Silicon for VLSI Device Contacts
Authors: Rajeswaran G. , Vanier P. E. , Kampas F. J. , Corderman R. R.
Published: March 2011

The rf glow discharge decomposition of dilute mixtures (∼1%) of SiH4 in H2, with suitable doping agents such as PH3 or B2 H6 added, produces n+ and p+ microcrystalline (μc) silicon films with resistivities (ρ) in the 10−1 Ω.cm range at exceedingly low substrate temperatures Ts (150–250°C). The μc-Si films consist of two phases with crystalline clusters embedded in an amorphous matrix. The films are stable when temperature-cycled in the 30–400°C range and the resistivity decreases when annealed above the original deposition temperature. A model of microcrystalline film growth involving the reactions between the gas phase radicals and the growing film surface is proposed.
Analysis of Implanted Boron Profiles Across the Si-SiO2 Interface by Secondary Ion Mass Spectrometry.
Authors: Deline V. R. , Johnson N. M. , Christel L. A.
Published: March 2011

Depth profiles of boron implanted across the SiO2-Si interface have been measured by secondary ion mass spectrometry and compared with model calculations of the impurity distributions. Analysis of the sputtering and ion yield processes near the interface are used to reconstruct the measured boron profile for comparison with the model calculations. Applicability of the method of profile reconstruction near the interface to other materials and impurities is discussed.
Quantitation of Secondary Ion Mass Spectrometry (SIMS) for HgCdTe.
Authors: Lapides Lawrence E. , Whiteman George L. , Wilson Robert G.
Published: March 2011

Quantitative depth profiles of impurities in LPE layers of HgCdTe have been determined using relative sensitivity factors calculated from ion implantation profiles. Standards were provided for Li, Be, B, C, F, Na, Mg, Al, Si, P, S, Cl, Cu, Ga, As, Br, and In. Relative sensitivity factors as a function of ionization potential for O2+ primary ion SIMS and electron affinity for Cs+ primary ion SIMS have been calculated in order to extend quantitation to elements not yet implanted. Examples of depth profiles for implant standards and unimplanted layers are given.
A Comparison of Thermal, Line-Source Electron Beam and CW Laser Annealing for the Fabrication of Ersi2 Schottky Barrier on Si.
Authors: Wu C. S. , Scott D.M. , lau S. S , Wakita A. , Sigmon T. W. , Knapp J. A. , Picraux S. T.
Published: March 2011

ErSi2 contacts formed by reacting Er with single crystal silicon using conventional furnace heat treatment are dominated by pits. Recently rapid electron and laser beam heating have been used to form pit-free ErSi 2 layers on Si by reacting Er with the Si substrate. For this investigation we studied the electrical properties of erbium silicide/Si
 contact prepared by thermal, laser and electron beam annealing. We prepared and annealed three types of samples; (I) Er(600Å)/Si
, (II) Si(100Å)/ Er(600Å)/Si
 and (III) Si(900Å)/Er(600Å)/Si
.The barrier height of the pit-free thermal annealed samples (type III) was ∼0.78 eV. All laser and e-beam annealed samples were observed to be pit-free. The barrier heights for the laser annealed samples varied from ∼ 0.63 eV for type I samples to ∼ 0.77 eV for type III samples. The e-beam annealed samples gave barrier heights ∼ 0.71 eV (type I and II) and ∼ 0.77 eV for type III. The barrier heights of beam processed diodes shifted towards the 0.78 eV range upon post-annealing. We model these results in terms of defects created at the ErSi2-Si interface.
Manufacture of Penetrating-Pores Metals by High Gas Pressure
Authors: Okumoto Yoshihiro , Takata A. , Ishizaki K.
Published: March 2011

Open porous metals can be made by direct hot isostatic press (HIP) treatment on a cold isostatic pressed body. In this work, porous metals with uniaxially penetrating pores were produced using a modified HIP method.

Penetrating pores from one surface to the other surface are useful for filter applications, and were produced by forcing pressurized gas to travel through samples by alternating the HiPping pressure during sintering.

In this experiment, copper powder was used. Samples produced with this new method have higher permeability coefficient than those produced by the normal HIP method.
Fiber Dispersed Porous Alumina Sintered under Direct High Gas Pressure for High Thermal Shock Resistant Application
Authors: Kurushima Toyokazu , Ishizaki K. , Osaki S.
Published: March 2011

Fiber dispersed porous alumina ceramics were produced by a direct high gas pressure sintering method. The produced materials exhibited relative densities of 75–85%, high bending strength and good thermal shock resistance. The alumina ceramics were characterized by lower closed porosity and higher open porosity. These characters strengthen the thermal shock resistance of porous ceramics. This high gas pressure sintering by the direct high gas pressure sintering method densifies only bridge parts of alumina ceramics which support pores. This process is concluded to be effective to produce materials with higher strength, better thermal shock resistance and higher open porosity.
HIP of Powder Mixtures
Authors: Funkenbusch P.D. , Li E.K.H.
Published: March 2011

Models of pressure-sintering and consolidation (such as that found in the HIP process) often assume a uniform spherical powder. However, it is known that use of mixtures, containing particles of differing composition and/or size, alters the initial powder packing and subseguent HIPing behavior. We have experimentally investigated these effects using the simplest form of mixture; a bi-modal powder with various size ratios and particle fractions. Packing experiments confirm the existence of “optimum” packing fractions for which the density is maximized over both monosized and the as-received (continuously distributed) powders. During HIPing these powder mixes remain relatively more dense than monosize packings. The consolidation of composite powder mixtures as well as microstructural evolution during HIP are also discussed. Results are compared with those predicted by modeling.
Effect of Applied Pressure of Hip on the Removal of Processing Void in Alumina Ceramics and the Resultant Improvement of Mechanical Property
Authors: Miyashita Masayori , Kim Jin-Young , Uchida Nozomu , Uematsu Keizo
Published: March 2011

Alumina ceramics prepared at various processing conditions were subjected to hot isostatic pressing (HIP) to remove processing-originated voids. Transmission optical microscope was used for characterizing voids in specimens before and after HIP, and for understanding the effect of HIP condition on the removal of void. The strengths of all specimens were measured to discuss the relation between void and strength. Voids of large size and high concentration were present in all sintered alumina ceramics. The size and concentration of void increased with decreasing pressure used in powder compaction process. HIP was found to be very effective for removing these voids which are the major processing defects in ceramics. The strength of alumina ceramics increased markedly with decreasing size and concentration of voids. The strength distribution of alumina ceramics was explained in terms of the measured void size distribution.
Containerless Hot Isostatic Processing of Titanium Diboride Ceramics
Authors: Concannon Michael , Hodge Edwin S. , Turmel Christopher
Published: March 2011

Dense titanium diboride (TiB2) ceramics were fabricated by near-net processing based on containerless hot isostatic pressing. Resultant materials displayed good mechanical strength and high fracture toughness.
Tailored Microstructure and Properties through Powder Metallurgy and Hot Isostatic Pressing
Authors: Buekenhout Louis
Published: March 2011

It is a very well known fact that there exists a narrow relationship between the structure and the properties of materials.

Structure can be modified by changing the composition of the material and for a selected composition by adapting its elaboration process. Powder metallurgy (P/M) and hot isostatic pressing (HIP) can be part of the elaboration process and permit to realize mono or multi-materials with or without complex shapes which can eventually be characterized by specific properties which are not possible to be obtained through the conventional metallurgy road.

The objective of this presentation is to illustrate this through a few examples.
Refinement of Electronic Ceramics by HIP
Authors: Takata Mitsuhiro , Toyota Sachio , Suenaga Yoshihiro
Published: March 2011

MnZn ferrites and PLZT with fine and uniform microstructures were prepared by hot isostatic pressing.

Initial permeability of MnZn ferrites with grain size of 2.0 and 1.2 μ m was 600 at 10 MHz.

An optical shutter array was made using PLZT with grain size of 2μ m. Optical transmittance was dependent upon the amount of PbO in HIP'ed PLZT. A slight deficiency of PbO in PLZT increased the transmittance at short wave length (400 nm).
Hip Phase Diagram of YBCO Type Superconductor
Authors: Sawai Yuichi , Ishizaki K. , Takata M. , Kuzjukevics A. , Narukawa Y.
Published: March 2011

The oxygen partial pressure - temperature phase diagram of YBCO type superconductors reported before by us showed that the YBa2Cu4Ox phase formation from Y2Ba4Cu7Oz with CuO, as well as from YBa2Cu3Oy, with CuO are oxidation reactions. The total gas pressure - temperature phase diagram shows that the YBa2Cu4Ox, phase formation temperature from Y2Ba4Cu7Oz with CuO increases with increasing the total gas pressure. On this phase boundary line, the fugacity of oxygen increases with increasing the total gas pressure even at constant oxygen partial pressure.
Formation of Superconducting La2−xSrxCaCu2O6−δ Ceramic with Application of O2-HIP Technique
Authors: Oshima Kiyoshi , Watanabe Yuichi , Takata Masasuke , Ishizaki Kozo
Published: March 2011

Superconducting La2−xSrxCaCu2O6−δ ceramics (x=0−0.6) were prepared with application of the oxygen-hot-isostatic pressing (O2-HIP) technique. The Tc of various samples was found to depend on both the Sr content and the applied oxygen partial pressure in the HIP treatment. The maximum Tc onset of 50K was observed for samples of the composition x=0.3 and 0.4 HIPped at 1050°C under 60atm oxygen partial pressure, and x=0.1 and 0.2 HIPped at 1050°C under 400atm oxygen partial pressure, respectively. From the analysis of x-ray diffraction patterns for superconducting substances, it was found that there existed a strong correlation between superconducting properties and the lattice parameters.
Polyurethane Copolymers Containing Covalently Attached RGD-Peptide: Synthesis and Cell Adhesion Studies
Authors: Lin Horng-Ban , Cooper Stuart L.
Published: March 2011

Synthesis of novel polyurethane copolymers containing covalently attached, well-oriented Arg-Gly-Asp (RGD) peptides was explored. A poly(tetramethylene oxide) based polyurethane was synthesized, and a bimolecular nucleophilic substitution reaction was then employed to incorporate ethyl carboxylate groups onto the polymer backbone. Cell-adhesive peptides Gly-Arg-Gly-Asp-Ser-Tyr (GRGDSY) and Gly-Arg-Gly-Asp-Val-Tyr (GRGDVY) were covalently bound to the polyurethane backbone via the formation of amide bonds. Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies were used to monitor the reactions. The amount of grafted peptide was determined by amino acid analysis. Electron spectroscopy for Chemical Analysis (ESCA) suggested the presence of the grafted peptide at the polymer-air interface in vacuo. Dynamic contact angle analysis showed that, in water, the peptide-grafted polyurethane surfaces were more polar than the underivatized polyurethane. The attachment and spreading of human umbilical vein endothelial cells (HUVECs) on the underivatized and peptide-grafted polyurethanes was investigated. The GRGDSY-and GRGDVY-grafted substrates supported cell adhesion and spreading even without serum in culture medium. The GRGDVYgrafted substrate supported a larger number of adherent cells and a higher extent of cell spreading than the GRGDSY-grafted substrate. These RGD-containing peptide grafted polyurethane copolymers may be useful in providing an easily prepared cell-adhesive substrate for various biomaterial applications.
Measurement of Cell Adhesion and Migration on Protein-Coated Surfaces
Authors: DiMilla Paul A. , Stone Julie A. , Albelda Steven M. , Lauffenburger Douglas A. , Quinn John A.
Published: March 2011

The performance of biomaterials forin vivoandin vitroapplications can depend critically on tissue cell adhesion and migration. We have been investigating the role that specific reversible interactions between cell adhesion receptors and complementary substratum-bound ligands play in the regulation of cell adhesion and migration. With an axisymmetric radial flow detachment assay (RFDA) [1] we measured cell-substratum adhesive strength for human smooth muscle cells (HSMCs) on surfaces coated with type IV collagen (CIV). We found that the critical shear stress for detachment increased linearly with increasing CIV coating concentration. Using time-lapse videomicroscopy and image analysis we tracked the movement of individual HSMCs over similar CIV-coated surfaces. Cell speed and persistence were determined for variations in CIV coating concentration by applying a persistent random walk model for individual cell movement. Cell speed reached a maximum at an intermediate concentration of CIV, supporting the hypothesis that an optimal cell-substratum adhesiveness exists for HSMC movement. This combination of techniques for measuring adhesion and motility provides a valuable tool to examine the role of cell-biomaterial interactions on cell behavior.
The Effect of Hard Segment Chemistry on the In-Vivo Biostability of Polyurethanes
Authors: Hergenrother Robert W. , Cooper Stuart L.
Published: March 2011

Four polyurethanes that were synthesized with different hard segments as well as four commercial polyurethanes were investigated for in-vivo biostability. The four polyurethanes with the varying hard segments were based on a 3/2/1/ mole ratio of methylene diphenylene diisocyanate (MDI) or methylene dicyclohexylene diisocyanate (H12MDI); butanediol (BD) or ethylene diamine (ED); and polytetramethylene oxide (PTMO) (MW=I000). Two commercial polyurethanes were also used: Biomer (Ethicon, Inc.) and Pellethane (Dow).

Films of the polymers were implanted subcutaneously in rats for up to three months to assess their biostability. Polymer films were implanted with either a 100% strain applied or in the unstressed state. Measurement of tensile properties and surface properties before and after implantation was used to assess the stability of each of the polymers. Surface cracking was observed with scanning electron microscopy and the extent and depth of cracking was determined.

It was found that BD chain extended polymers maintained their tensile properties better than the ED chain extended polymers after implantation. H12MDI-based polyurethanes were more susceptible to surface cracking than MDI-based polyurethanes, possibly due to the lack of a crystallizable hard segment.
Controlled Release of Fibroblast Growth Factor: Activity in Cell Culture
Authors: Nugent Matthew A. , Chen Oliver S. , Edelman Elazer R.
Published: March 2011

Basic fibroblast growth factor is a multi-potent cell regulatory factor that stimulates proliferation and angiogenesis. Controlled studies of basic fibroblast growth factor in animals have been hindered by the instability of this protein. In addition, many cells appear to require the continuous addition of basic fibroblast growth factor for optimal growth and function in culture. A system for the sustained delivery of active basic fibroblast growth factor might provide both a means to conduct log-term studies on activity and provide a practical alternative to multiple growth factor additions to cell cultures. Basic fibroblast growth factor was incorporated into standard polymer matrices, but the released growth factor had lost over 99% of its bioactivity. Loss of basic fibroblast growth factor activity was found to result from both physical inactivation and adsorption of the protein to surfaces. These problems were avoided by incorporating the growth factor into calcium cross-linked alginate microspheres containing heparinsepharose beads. Basic fibroblast growth factor was incorporated into these microspheres with 71% efficiency and active growth factor was released with predictable kinetics for up to 7 weeks. Release from these microspheres was controlled by the amount of heparin within the device and could be manipulated by simply altering the heparin content during fabrication. Alginate/heparin-sepharose microspheres were placed into growing cultures of bovine aortic endothelial cells and no cytotoxic effects were observed. Furthermore, microspheres containing growth factor provided long-term stimulation of cell proliferation and maintenance of endothelial cell morphology.
Diffusion of Fibroblast Growth Factor from a Plaster of Paris Carrier
Authors: Rosenblum S. , Frenkel S. , Ricci J. , Alexander H.
Published: March 2011

Fibroblast growth factor (FGF) is a polypeptide found in two forms: basic and acidic. The basic form is produced by many more types of cells than the acidic form, although both bind to the same receptor. These proteins act on a variety of mesodermally and ectodermally derived cells, including chondrocytes, glial cells, myoblasts, endothelial cells, cornea and lens epithelia, adrenal cortical cells, ovarian granulosa cells, periosteal fibroblasts, and osteoblasts. Basic FGF was chosen for the present study for a variety of reasons. First, it has significant cross-species homology, with 98.7% correlation between human and both bovine and avian FGF. Less conservation has been observed in the acidic form. In addition, the basic form has been shown to be 30- to 100-fold more potent, depending on the target tissue.
Pulsed Laser Deposition of Biocompatible Thin Films: Calcium Hydroxylapatrte and Other Calcium Phosphates
Authors: Cotell C. M. , Chrisey D. B. , Grabowski K. S.
Published: March 2011

Calcium phosphate-based ceramics were deposited on Ti, Ti-6Al-4V and Si substrates by pulsed laser deposition. The calcium phosphate phase (amorphous, α- or β-tricalciumn phosphate, tetracalcium phosphate, or hydroxylapatite), Ca/P ratio and surface morphology of the films were related to deposition conditions. At substrate temperatures <400°C, films were amorphous. Above 400°C, the gaseous environment during deposition determined the crystalline phase of the films. In O2, deposition of α-tricalcium phosphate was favored between 400 and 700°C and β-tricalcium phosphate was favored above 700°C. Films deposited in low pressures of O2 (<0.05 Torr) were P-deficient. The correct stoichiometry was approached as the pressure of O2 in the chamber during deposition increased. In water vapor-enriched inert gas environments, deposition of hydroxylapatite was observed at temperatures between 400 and 700°C and tetracalcium phosphate was observed at temperatures above 700°C. The surface morphology of hydroxylapatite films depended on the temperature of deposition. Surfaces deposited at higher substrate temperatures showed more recrystallization than those deposited at lower substrate temperatures.
Implantation of Cell-Seeded Biodegradable Polymers for Tissue Reconstruction
Authors: Ito Kazushi , Fujisato Toshiya , Ikada Yoshito
Published: March 2011

The aim of this work is to use biodegradable polymers as a scaffold for self-reconstruction of defective tissue which has the capacity to regenerate; for instance, cartilage, blood vessel, bone, peripheral nervous system, and liver. After seeding parenchymal cells of the target tissue on the scaffold, the cellpolymer composite will be implanted as the core tissue for reconstruction. There is another approach for this purpose, that is, the use of hybrid-type artificial organs, but they have several problems such as poor viability and low capacity. In addition, it is difficult to culture cells on a large enough scale to maintain biofunctionality. However, these problems may be solved if tissue is self-reconstructed in body on a scaffold seeded with the cells originated from the objective tissue [1]
Bilayer Composite Hydrogels for Corneal Prostheses
Authors: Perez Edward , Cima Linda G. , Miller David , Merrill Edward W.
Published: March 2011

A two-layer composite material composed of a thin-layer of corneal tissue and a synthetic polyethylene oxide (PEO) hydrogel is described. The material is designed to provide a suitable substrate for corneal epithelial cell growth while maintaining the desirable characteristics of hydrogels, i.e. clarity, flexibility, and ability to allow diffusive flow of nutrients. The gels are synthesized via electron irradiation induced crosslinking of an aqueous solution of PEO onto a thin layer of collagenous tissue substrate. light microscopic studies indicate that the interface between the corneal tissue and PEO gel appears well adherent with no gaps in the interface. SEM studies of the material surface show an architecture similar to that of normal corneal tissue. Surface analytical techniques were used to identify amino-acids covalently bound to the gel at the gel/collagen interface after the proteinaceous material was removed. ESCA survey scans identified the presence of nitrogen on exposed gel/collagen interfaces and amino acid labelling confirmed the presence of amino acids. ATR-IR studies identifed increased absorption for the gel collagen interfaces at 1640 cm− 1and 1540 cm−1indicative of bound amino acids.
The Influence of Molecular Structure on Apatite Adsorption
Authors: Mats S. A. Johnsson , Raj P. A. , Levine M. J. , Nancollas G. H.
Published: March 2011

The hydroxyapatite (HAP) adsorption of salivary statherin, cystatins, proline-rich proteins and histatins has been compared to the influence of these molecules on HAP crystallization in supersaturated solution. This may yield, in many cases, information about protein conformation in the adsorbed state. The results of studies involving both parent molecules and their fragments, indicated that statherin binds to HAP primarily with a 2–5 residues segment in the N-terminal part while the cystatins and proline-rich proteins bind through a segment 2–3 times larger.
Ultrastructure of the Mineralized Tissue/Calcium Phosphate Interface in Vitro
Authors: de Bruijn Joost D. , Davies John E. , Flach Jim S. , de Groot Klaas , van Blitterswijk Clemens A.
Published: March 2011

An in vitro rat bone marrow cell (RBMC) system was used to examine the structure of the interface established between calcium phosphates (Ca-P) and mineralized tissue. The Ca-P used, varied either in chemical structure or crystallinity. Therefore, not only the influence of chemical composition, but also the effect of degradation of Ca-P ceramics could be studied. The interfaces were examined with scanning and transmission electron microscopy (SEM and TEM).

SEM showed that deposition of mineralized extracellular matrix on the different materials examined varied both in time and morphology. Mineralization started with the formation of afibrillar globules with which collagen fibres became integrated. With TEM, three distinctly different interfacial structural arrangements were observed which were dependent on the presence or absence of an electron dense layer and/or an amorphous zone. The former was considered to be at least partially caused by protein adsorption, which would precede biological mineralization events, whereas the latter was considered to represent partial degradation of the ceramic surfaces.

The results of this study showed that interfacial reactions were not only influenced by the chemical structure, but also by the crystallinity of Ca-P ceramics. Thus, characterisation of Ca-P implant materials is of critical importance in achieving a better understanding of the phenomena that occur at the bone-biomaterial interface.