bluuebunny/crossref_metadata_2025 huggingface dataset:
Sic-Reinforced Cordierite Composites Formed by Viscous Sintering of Cordierite Powders
Authors: Hardy Anne B. , Rhine Wendell E.
Published: March 2011

One approach for improving mechanical properties of ceramics is to add reinforcing whiskers; however, addition of whiskers often inhibits densification. Formation of SiCcordierite composites by pressureless sintering was studied. The cordierite composites densified by viscous sintering; after densification the amorphous matrix then crystallized. It was shown that high green density composites obtained by using small particle size powder gave the highest sintered density composites. Reducing the aspect ratio of the SiC phase also improved sintered composite densities. Densities greater than 96% were obtained using small particle size cordierite powder formed by a sol-gel process and either classified SiC whiskers or SiC powder at SiC loadings of 20 vol%
Control Over Al2O3 Phase by Use Of Polymer Precursors
Authors: Rees William S. , Hesse Werner
Published: March 2011

Reaction of Et2AIOEt with ethylene glycol or catechol produced polymers of the general form -[-AI(OEt)-O-R-O-]-n, for R = CH2CH2 or C6H4, respectively. Pyrolytic conversion of these polymers to ceramic materials produced A12O3, at mild (∼500°C) temperatures under a flowing atmosphere of dry air. The crystal phase obtained from the thermolysis is highly dependent upon the degree of cross-linking present in the initial polymer. These results are discussed in terms of the required solid-state atomic reorganization necessary to proceed from polymer to ceramic.
Sol-Gel Processing of Glasses and Glass-Ceramics for Microelectronic Packaging
Authors: Sriram M.A. , Kumta P.N.
Published: March 2011

In recent years considerable progress has been made in electronic packaging substrate technology. The future need of miniaturization of devices to increase the signal processing speeds calls for an increase in the device density requiring the substrates to be designed for better thermal, mechanical and electrical efficiency.Fast signal propagation with minimum delay requires the substrate to possess very low dielectric constant. Several glasses and glass-ceramic materials have been identified over the years which show good promise as candidate substrate materials. Among these borophosphate and borophosphosilicate glass-ceramics have been recently identified to have the lowest dielectric constant (3.8). Sol-gel processing has been used to synthesize borosilicate, borophosphosilicate and borophosphate glasses and glass-ceramics using inexpensive boron oxide and phosphorus pentoxide precursors. Preliminary results of the processing of these gels and the effect of volatility of boron alkoxide and its modification on the gel structure are described. X-ray diffraction, Differential thermal analyses and FTIR have been used to characterize the as-prepared and heat treated gels.
Mixed Metal Oxide Synthesis by Thermolyses of Simple Heteropolymetallic Precursors in Oxygen
Authors: Davies Geoffrey , Giessen Bill C. , Shao Hui-Li
Published: March 2011

Stepwise transmetalation of the neutral molecular target (µ4-O)N4 Cu4 C16(N is a monodentate pyridine) with M(NS)n transmealators (NS is a monanionic S-methyl hydrazinecarbodithioate ligand, M is Co (n = 2 or 3), Ni or Zn (n = 2)) in aprotic solvents gives a large family of heteropolymetallic products (µ4 - O)N4 (Co,Ni,Cu,Zn)4 C16 that contain from one to four different metals. Thermolysis of these solid products in flowing O2 at 220 - 250°C gives uniform, highly dispersed mixtures of the respective metal oxides. For example, thermolysis of bulk precursor (µ4 -O)N4 CoNiCuZnCl6 gives a uniform mixture of 1 - 2° particles of Co3 O4, NiO, CuO and ZnO.
Epitaxial Nickel Disilicide Formation by Electron Beam Annealing
Authors: Harper R.E. , Maydell-Ondrusz E.A. , Wilson I.H. , Stephens K.G.
Published: March 2011

A multiply-scanned electron beam was used to form nickel silicides from thin nickel films on unimplanted and arsenic implanted silicon (100) substrates. Films of thickness 300, 660 and 1000Å were annealed using a power density of 7.9Wcm−2 and irradiation times of 5 to 150 secs.

Rutherford backscattering and channelling techniques were used to determine the stoichiometry, thickness and epitaxial quality of the annealed films. The thinnest gave a Xminof ∼ 18% and the thickest a Xmin of ∼ 40%. Resistivities were measured by the four-probe technique. Chemical composition was determined by X-ray and glancing angle electron diffraction (RHEED). Transmission electron microscopy (TEM) was used to estimate grain size of the disilicide phase and scanning electron microscopy (SEM) to study surface textures. The effect of arsenic implantation on growth rate, epitaxial quality and surface texture is demonstrated.
Tin as a Diffusion Barrier For III-V Metallization
Authors: Houghton D.C.
Published: March 2011

The performance of TiN as a diffusion barrier in Au/TiN/InP structures has been studied and compared with Cr and Pt under identical conditions. In order to sensitively monitor interdiffusion, a novel SEM-EDX technique has been used to determine interdiffusion coefficients and activation energies in the temperature range 250–700°C. Extensive intermixing for Cr and Pt was indicated by the SEM-EDX technique and this was confirmed by Auger depth profiling. In addition the heterogeneous formation of the brittle intermetallic phase Au4 in was detected by XRD, and marked the catastrophic failure of the metallization due to delamination. These interfacial reactions and copious interdiffusion may be controlled by a TiN diffusion barrier which remains impervious for periods in excess of 24h at 500°C.
Ion Beam Enhanced Adhesion
Authors: Tombrello T. A.
Published: March 2011

We have shown that the irradiation of a wide variety of thin film-substrate combinations with MeV/amu ions leads to greatly enhanced adhesion. The systems studied include metal films on dielectric, semiconductor, and metal substrates. For metal coatings on semiconductors the electrical contact which is originally diode-like becomes ohmic. Metal films on metal or polymeric substrates generally require the lowest dose irradiations. For Au on Ta the threshold dose to achieve a constant level of adhesion (“Scotch Tape” test) is consistent with a model of the process in which the dose threshold varies with the electronic excitation part of the energy loss in the material as (dE/dx + Q)−2 . The value of Q obtained corresponds to an exothermic reaction due to the increased binding that liberates ˜70 eV at the interface. This model and a variant of it based on the production of K-shell vacancies in low Z elements in the target will be discussed.
Interaction of Al Films on Single Crystal Si Substrates Induced by Ion Irradiation and Post-Anneal
Authors: Hung L. S. , Chen S. H. , Mayer J. W.
Published: March 2011

Rutherford backscattering and channeling techniques, transmission electron microscopy and Auger electron spectroscopy have been combined to investigate the reordering of implanted amorphous Si in the presence of an Al surface layer and the interdiffusion between these two elements. Recrystallization took place at 200°C and proceeded as the temperature increased. At 350–400°C, better epitaxial layers were obtained and channeling effects became observable. Substantial concentration of residual damage was observed in the regrown layer and persisted to high annealing temperatures. The concentration of Si in the Al film was far beyond the solid solubility at annealing temperatures. When ion implantation was performed at 200°C, the implanted layer was virtually defect free and the diffusion of Si into Al was suppressed.
Interactions between Lattice Dislocations and Interfaces in Solids
Authors: Liu J. S. , Balluffi R. W.
Published: March 2011

Attention is focused on the interactions which occur when lattice dislocations impinge on interfaces (i.e., grain boundaries, crystal/crystal interphase boundaries and crystal/amorphous boundaries) in solids. The lattice dislocations can generally dissociate into interface dislocations possessing smaller Burgers vectors under a driving force produced by a decrease in the elastic energy. For crystal/crystal interfaces, a wide range of possibilities exists, depending upon the grain boundary type, which extends from dissociation into a discrete number of interface dislocations to dissociations into a distribution consisting of, in the limit, an infinite number of interface dislocations possessing infinitesimal Bur.ers vectors. For crystal/ anorphous interfaces, the latter model is applicable. Examples of dissociations in these various interfaces are presented. The dissociation geometries and kinetics are described briefly. Some of the wider implications of these phenomena are mentioned.
Formation of Microtwins in Low Angle Grain Boundaries in Germanium
Authors: Elgat Z. , Carter C. B.
Published: March 2011

The structure of a low angle tilt boundary with a [110] misorientation axis and a (111) initial boundary plane in a bicrystal prepared by a hot-pressing technique has been studied. The boundary consists of a periodic array of dislocations as expected but contains a new feature, namely microtwins which lie parallel to the boundary plane. High resolution transmission electronmicroscopy has been used to characterize the boundary structure and to determine the Burgers vector of the dislocations present. The relationship between the structure of the twin-free regions and the twinned regions is discussed.
XPS Study of the Al/SiO2 Interface Viewed From the SiO2 Side
Authors: Hecht M.H. , Grunthaner F.J. , Maserjian J.
Published: March 2011

We report on the first non-destructive measurement of the chemical and physical characteristics of the interface between bulk SiO2 and thick aluminum films. Both X-Ray Photoelectron Spictroscopy (XPS) and electrical measurements of unannealed, resistively evaporated Al films on thermal SiO2 indicate an atomically abrupt interface. Post metallization annealing (PMA) at 450°C induces reduction of the SiO2 by the aluminum, resulting in the layer ordering SiO2/Al2O3/Si/Al. The XPS measurement is performed from the SiO2 side after the removal of the Si substrate after etching with XeF2 gas and thinning of the SiO2 layer with HF:ETOH. This represents a powerful new approach to the study of metal-insulator and other interfaces.
The Chemisorption of Fluorine on Silicon (111) Surfaces
Authors: Mcfeely F.R. , Morar J. , Shinn N. D. , Landgren G. , Himpsel F. J. , Jugnet Y.
Published: March 2011

High-resolution, soft x-ray photoemission investigations of fluorine chemisorption on silicon (111) surfaces are reported. The distribution of fluorosilyl moieties was found to be strongly dependent upon the surface structure. The 2×1 reconstruction exhibited only monofluoro species, while the 7×7 showed a distribution of mono-, di-, and trifluorosilyl groups.
Thermoelectric Effects Across Solid-Liquid Gallium Interface
Authors: Alvarez J. , Peteves S.D. , Abbaschian G.J.
Published: March 2011

A novel technique is described for directly measuring the Seebeck coefficient across the solid-liquid interface of gallium as a function of temperature and crystallographic orientation. The results are compared with those calculated from the absolute thermoelectric power of solid and liquid gallium. The temperature ranges for the measurements were 248 to 302K for solid gallium, and 278 to 353K for the liquid; the liquid was supercooled up to 25K. The effect of crystal orientation on the thermoelectric power of gallium single crystals grown along the a, b, and c axes was investigated. The anisotropy of the thermoelectric power is discussed based on the electronic properties of gallium.
Crystallography and Interfaces of Epitaxial Fluorite Metals and Insulators on Semiconductors
Authors: Gibson J.M. , Tung R.T. , Phillips J.M. , Poate J.M.
Published: March 2011

Crystals with the cubic fluorite structure and small lattice mismatches can be grown epitaxially on cubic semiconductors. In this manner thin-film single-crystal metals (NiSi2 and CoSi2) and insulators (e.g. CaF2 , BaF2) have been grown on silicon, germanium and indium phosphide. With close attention to deposition and growth parameters, afforded either by atomically clean conditions or transient thermal processing, great control can be exerted over the crystallography and interfaces of these systems. This has resulted in films with unique physical properties and exceptionally high quality and reproducibility. We review the microstructure of these films in this paper and identify two important new growth regimes for these materials: very thin films (less than 30Å) and transient thermal processing with ultra-fast laser pulses. Examination of the structure of these films, using high-resolution electron microscopy, provides insight into these nucleation and growth processes. One intriguing observation is that all these fluorite structure thin films have an overwhelming tendency to grow with a 180° rotated orientation (B) on (111) semiconductors.
Growth and Characterization of Epitaxial GaAs on Ge/Si Substrates
Authors: Fletcher Robert M. , Ken Wagner D. , Ballantyne Joseph M.
Published: March 2011

Epitaxial GaAs layers have been grown on Ge-coated Si substrates. Deposition of epitaxial Ge was performed by electron beam evaporation onto a <100> Si substrate. GaAs was then deposited by organometallic vapor-phase epitaxy. Films grown over large areas (∼1 cm2) and by selective epitaxy in stripe patterns (∼50 μm wide) have been evaluated by a number of techniques to determine structural and electrical properties. In addition, we report what we believe to be the first LEDs fabricated in GaAs/Ge/Si heterostructures.
Tem Study of Pt Silicide Formation on Clean Si Surfaces
Authors: Yokota Y. , Matz R. , Ho P.S.
Published: March 2011

The microstructure of the Pt silicide formed on clean Si surfaces has been investigated using transmission electron microscopy. Pt up to 200Å was evaporated on atomically clean Si (100) and (111) substrates under an ultrahigh vacuum condition. The silicide was formed by annealing up to 600°C for (100) substrates in a purified He atmosphere and in-situ UHV for (111) substrates. For the (100) substrate, as-deposited Pt showed a fine polycrystalline structure with grain size of about 10tm. Upon annealing at 250° to 300°C, formation of Pt silicide was observed, which was primarily PtSi with only a small amount of Pt2Si. The silicide coverage was incomplete below about 1.5nm. Upon further annealing, the fraction of PtSi increased although Pt2Si persisted until 400°C. At 600°C, PtSi showed an epitaxial relationship with its c axis perpendicular to the Si (100) surface. On the Si (111) surface, PtSi formed epitaxially above 400°C. The silicide structure showed a multidiffraction pattern with three-fold symmetry, reflecting the three equivalent but strained epitaxial orientations. A high resolution lattice image technique was used to investigate the details of the epitaxial structures of PtSi on Si (100) and (111) substrates.
Epitaxial Growth of NiSi2 on (011)Si
Authors: Chen L.J. , Lin W.T. , Chang M.B.
Published: March 2011

Epitaxial growth of NiSi2 on (011)Si was investigated by the transmission electron microscopy. Both epitaxial and twin related NiSi2 were formed, with the former being predominant, in samples annealed at 850°C for 1/2 h. The silicides were faceted with {111} interfaces being more prominent than {100} interfaces. Interfacial dislocations were found to be of edge type with 1/6<112> Burgers vectors. The average spacing is about 700 Å which is very close to the theoretically expected value 670 Å.

The absence of twins formed on (111) and (111) planes for (011) samples as well as the results obtained for (001) and (111) specimens suggest that there exists a critical resolved shear stress at the interface for the initiation of the formation of twin related NiSi2.
Superlattice Interface and Lattice Strain Study by Ion Channeling
Authors: Pan C. K. , Zheng D. C. , Chu W. K. , Chang C.-A.
Published: March 2011

EXTENDED ABSTRACT

We have studied the interface and the lattice strain of superlattices by ion channeling technique. The objective in this work is to verify the existence of alternating tensile and compressive strain in the superlattice and to develop a method for measuring the lattice strain directly. Alternating layers of GaSb/Al Sb were grown epitaxially by MBE with 10 periods. The thickness of each individual layer is 30 nm. Channeling measurements and analysis were made using a 1.76 MeV 4He ion beam. The measurements reveal higher dechanneling along the [110] axis than along the [100] axis. This is consistent with the dechanneling results published earlier. The high dechanneling along the [110] axis has been considered due to the lattice strain that occurs in the layers caused by the slight mismatch between the lattice constants of the two materials. The strain effect make [110] axis slightly bent from layer to layer (“zigzag”), but it does not occur in [100] axis. The axial angular scan analyses were made around the [110] direction at the different depths using a movable energy window setting. We have found that the angular position of the best alignment shifts from layer to layer. The oscillation of those angular positions with depth is of a direct evidence of the existence of alternating tension and compression strain layers in the superlattice. The “kink” angle at the interface is given by the difference of the angular position between the first and second layer. This is found to be 0.17° ± 0.03 %. This is in a good agreement with the result calculated from elasticity. Preliminary result of this experiment is recently published.3

We are also investigating the interface and lattice strain by planar angular scan across the (110) plane at a position three degrees from [110] axis.

The similar oscillatory results have been found for {110} planar channeling and the “kink” angle measurement is in a good agreement with the results from axial angular scan.

We believe that the method of ion beam channeling and angular scan is very effective in strain measurements in multi-layered heteroexpitaxy system.

3. W. K. Chu, C. K. Pan and C.-A. Chang, Phys. Rev. Rapid Communication B28, 4033 (1983).
Lateral Solid Phase Epitaxy of Evaporated Amorphous Si Films onto SiO2 Patterns
Authors: Yamamoto H. , Ishiwara H. , Furukawa S. , Tamura M. , Tokuyama T.
Published: March 2011

Lateral solid phase epitaxy (L-SPE) of amorphous Si (a-Si) films vacuum-evaporated on Si substrates with SiO2 patterns has been investigated, in which the film first grows vertically in the regions directly contacted to the Si substrates and then grows laterally onto SiO2 patterns. It has been found from transmission electron microscopy and Nomarski optical microscopy that use of dense a-Si films, which are formed by evaporation on heated substrates and subsequent amorphization by Si+ ion implantation, is essentially important for L-SPE. The maximum L-SPE length of 5–6μm was obtained along the <010> direction after 10hourannealing at 600°C. The kinetics of the L-SPE growth has also been investigated.
Abnormal Grain Growth in Ultra-Thin Films of Germanium on Insulator
Authors: Yonehara T. , Tihompson C.V. , Smith Henry I.
Published: March 2011

The growth of large secondary grains with (112) texture, and solid-state agglomeration to single-crystal islands have been observed by annealing ultra-thin (less than 1000Å) films of Ge. A driving force proportional to surface-energy anisotropy and inversely proportional to film thickness is believed to be responsible for both phenomena. The temperature for agglomeration decreases with film thickness, and is further depressed by the presence of Sn vapor. Patterning Ge into stripes increases secondary grain size and population. Encapsulation with a film of SiO2 suppresses agglomeration and alters crystallographic texture. A surface-relief structure of 0.2μm period and 300Å depth induces a (100) texture in some cases, and alters the morphology of agglomerated islands.
Specific Contact Resistance Measurements on Multilayer Interconnect Structures.
Authors: Harrison H.B. , Reeves G.K.
Published: March 2011

An integral part of very large scale integrated (VLSI) circuits is the multilayer structures for electrical interconnection and insulation. Many conducting materials are used for interconnection including polysilicon, silicon, silicides, polycides and metals. An important point in considering these materials is the interconnection between them and the corresponding characterization of the interface by way of the specific contact resistance, which directly affects the interfacial contact resistance.

For a planar ohmic contact formed between a metal and any layer with a much larger sheet resistance (for example single crystal silicon) a technique based on the transmission line model provides a method of characterizing these contacts. However, for planar contacts between layers with comparable sheet resistivities for example polysilicon to single crystal silicon this technique must be modified. In this paper we review the transmission line approach used to obtain the specific contact resistance between such layers and provide initial results of measurements made on the poly to single crystal interface. We also present a series of test structures, currently under fabrication that will provide more detailed experimental data.
Tem Studies of Cosputtered Tisi 2 Films Containing Excess Silicon.
Authors: Beyers R. , Sinclair R. , Thomas M. E.
Published: March 2011

The effect of excess silicon on the growth and microstructure of cosputtered TiSi 2 was investigated. Cosputtered films, with Si/Ti ratios between 2.5 and 4.5, were deposited on (100) Si substrates and reacted at temperatures from 650° to 1050°C. Excess Si in the asdeposited films formed a layer of epitaxial Si on the Si substrate. In addition, Si and SiO2 precipitates formed within the grains. The films became discontinuous when reacted at 1050°C.
Rectifying Structures Resulting from Gold, Cadmium and Thallium Deposited on Selenium
Authors: Champness C.H. , Nerguizian V. , Nerguizian C. , Chan A.
Published: March 2011

Structures of the form Al-Bi-Se-metal were fabricated by deposition of the metals gold, cadmium, bismuth and thallium as thin films on a layer of crystallized selenium. The selenium was itself evaporated on a layer of bismuth on an aluminum base. This Al-Bi-Se base contact was rendered ohmic by substrate heating during the selenium deposition. The diodes showed forward-to-reverse current rectification ratios ranging from large for thallium to small for gold. At small forward voltage, the current density increased with increasing work function from thallium to gold, whereas the voltage intercepts Vo on plots of (capacitance)−2 versus reverse voltage decreased with increasing work function. From these Vo values and the slopes of the latter plots, barrier heights were deduced and plotted against work function. From this plot showing a decrease of barrier height with decreasing work function, it was possible to estimate an interface state density of 1013 cm−2 volt−1 assuming the existence of an interfacial layer 100Å in thickness. While the Se-Tl contact showed excellent rectification, it exhibited rapid degradation with time from atmospheric oxidation.
Pt and Pd Silicides and Pd Germanide as Contact Metallizations for GaAs
Authors: Marshall E. D. , Wu C. S. , Scott D. M. , Lau S. S. , Kuech T. F.
Published: March 2011

Refractory metal silicides have been shown to form stable Schottky barriers on GaAs up to an annealing temperature of ∼850°C. In this study, the metallurgical and electrical stability of near noble metal (Pd and Pt) silicide contacts to GaAs have been investigated. It is observed that Pd and Pt silicides are metallurgically more stable than Pd and Pt alone on GaAs. A correlation between the stability of silicide contacts and the heat of formation of the silicides normalized to per metal atom is found, thus allowing the prediction of contact stability of other silicides on GaAs. We have also investigated the feasibility of using solid-phase epitaxy (SPE) to grow a highly doped Ge epitaxial layer on GaAs to form a non-alloyed ohmic contact. This approach of forming a Ge/GaAs heterojunction alleviates the high vacuum requirement of MBE techniques. Our preliminary results indicate that relatively low contact resistivities can be obtained by SPE using the Ge-Sb-Pd system.
Removing Grain Boundary Effects in Polycrystalline Silicon Using a Minority Carrier Mirror Concept
Authors: Kai F. Y. T. , Jackson M. A. , Thayer M. , Anderson W. A.
Published: March 2011

The boron minority carrier mirror (MCM) concept has been applied to Wacker poly-Si for passivation of active grain boundaries (GB). Photovoltaic, spectral response, laser beam induced current, electron beam induced current and interface state data show the MCM process to significantly improve solar cell performance. For example, an efficiency improvement from 6.4% to 8.8% was observed in part of the study. This appears to be a simple technique to produce stable solar cells with future application to fine grain poly-Si.
Structure of Au/Ge/Au Multilayer Ohmic contacts to GaAs
Authors: Kim Tae-Il , Chung D. D. L.
Published: March 2011

The presence of a 500 Å Ge layer in Au/Ge/Au ohmic contacts to GaAs was found to hinder the agglomeration of Au upon heating. An ohmic contact as uniform as the asdeposited metallization was achieved after heating at 300°C. Heating at 350–500°C resulted in various morphological entities in a Au-rich matrix. The microstructure changed from one with a Au-rich matrix to one with a GaAs-rich matrix and dendritic Au-rich islands at 525±25°C. Heating at 400°C or above resulted in Au-Ga phases with the epitaxial relationships α' (110) ‖ GaAs (100) and Au2Ga (112) ‖ GaAs (100).
Reaction Sintering Property of Green Compact of Si and TiC Mixed Powders in Nitrogen
Authors: Yasutomi Yoshiyuki , Sobue Masahisa , Shinozaki Shin-Ichi S. , Hangas John , Shinozaki Shin-Ichi S.
Published: March 2011

We have developed a new type of near net shape sintering process using nitridation of Si and other inorganic powders. In this report, the sintering property of powder mixture compacts of TiC (10μm or 0.9μm) and Si (0.9μm) in a nitrogen atmosphere at 1350°C was investigated.

A large portion of the Si formed Si3N4 on reaction with nitrogen, while TiC formed TiN and free carbon. A small portion of this free carbon was converted into β-SiC on reaction with Si and about 98% of the free carbon remained in the sintered body. Thus, composite ceramics having a composition of Si3N4·TiC·TiN·C·β-SiC were obtained. The porosity of this composite was much smaller than that of ordinary Si3N4 bonded ceramics, because of the large volume expansion for formation of free carbon. The pore size under 5μm can be got using TiC powder with an avarage size of 0.9μm.
Atmosphere Controlled HIP of Mn-Zn Ferrite
Authors: Kakizaki Masao , Matsumoto Osamu , Utsuno Satoshi
Published: March 2011

Control of HIP of Mn-Zn ferrite through the composition of the ambient gas was investigated as an alternative to the powder embedding method. Optimized conditions for this approach are described.
Effect of Isostatic GAS Pressure on Optical Quality of MgAl2O4 Spinel
Authors: Hsu S.E. , Wang C.T. , Tsai D.S. , Yang S.J.
Published: March 2011

Optical transparent MgAl2O4 spinel is obtained by processing with high gas pressure to eliminate or reduce the residual pores. Both hot–pressed and sintered specimens are post–treated by the high argon hipping process here. The densities of all the specimens before hipping are over 99% theoretical density. In the high gas pressure process, the pressure ranges from 2000 to 30000psi at 1500°C for 2hrs. The transmittance from visible to IR are measured before and after gas pressure treatment. The transparency from visible to IR increases significantly with the HIP process. When applied pressure less than 6000psi, bulk density is proportional to the logarithm of the pressure and the logarithm of the absorption coefficient is proportional to the porosity. Bimodal grain–size distribution exists in the sintered and hipped specimens but is not observed in the uniaxial–hot–pressed–only samples. XRD analysis indicates the width of the diffraction peaks in the HIP specimens is less than that in UAHP specimens. The result illustrates the HIP process improves the spinel crystallinity.
High Active GAS (O2 or N2) Pressure Crystal Growth and Phase Diagram of YBaCuO Phases and GaN
Authors: Karpinski J. , Kaldis E. , Conder K. , Rusiecki S. , Jilek E.
Published: March 2011

A review of the phase diagram studies of the YBaCuO and GaN systems under high active gas (O2 or N2) pressure is given. The P,T equilibrium conditions for three superconducting phases existing in YBaCuO system vary as a function of Cu content. Application of high O2 pressure allows crystal growth of the 124 and 247 compounds and high N2 pressure alow crystal growth of GaN. We discuss also indications, that other YBaCuO compounds may exist.
The Role of Oxygen in the Hot Isostatic Pressing of High Tc Superconductors
Authors: Niska John V. , Loberg Bengt
Published: March 2011

The bismuth-based 2212 and 2223 superconductors and the yttrium-based 123 and 124 high Tc superconductors are oxide ceramics, so that oxidizing conditions must be maintained in the HIP to avoid oxygen loss and decomposition. This has been done in an argon gas HIP by using glass encapsulation, but internal gas pressure retards densification. The thermodynamics of the release of oxygen by the superconductive ceramics and the stability of the metal to oxygen can be shown on a free energy diagram (Ellingham diagram). The base metals (as Fe and Cu) are reactive with respect to superconductive ceramics but not silver.
Fabrication of Volumetric Dilatometer Using Buoyancy Under High Pressure Gas
Authors: Nanko Makoto , Sakayori W. , Ishizaki K. , Uehara K. , Ueda M.
Published: March 2011

Sintering processes are monitored by dilatometry. A conventional dilatometer under high gas pressure (typical HIPping conditions) is constructed using graphite rods to examine linear thermal expansivity of one sample. This method has a few disadvantages, such as the pressure of graphite rods acting as a uniaxial hot press. The advantage of a HIP method, compared to a hot press sintering is the capacity to process many samples at a time. The graphite rod method is applicable for only one sample. A volumetric dilatometer was developed using buoyancy under high gas pressure, which can monitor HIP sintering processes of many samples and check for capsule failure.
Bimetallic Coatings for Twin - Screw Extruder Barrels
Authors: Archer G.F. , Stephenson D.J.
Published: March 2011

In this paper the development of novel wear/corrosion resistant coatings for twin screw extruders used in the food industry is discussed. The conventional materials used for extruder applications are reviewed and their limitations highlighted. The requirements for a new surface engineering philosophy are introduced and utilised to develop a new manufacturing system for the coating of extruder barrels. These coatings are based on Ni/Cr/B/Si/Fe alloys containing WC particulate. The processing route combines conventional PM technology with consolidation of the coating by hot isostatic pressing (HIPping). The HIP cycle is tailored to optimise the coating/substrate adhesion and the coating microstructure. Examples are given which illustrate the superior performance of these HIPped bimetallic coatings compared to conventional surface treatments.
The Resorbable Bioglassceramics Based on Calcium Biophosphate
Authors: Chin Tsung-Shune , Wu D. C. , Liu H. S. , Hung M. P. , Wang C. P.
Published: March 2011

Novel resorbable bioglassceramic artificial tooth roots based on calcium biphosphate were synthesized, implanted into rabbits, and assessed. They were prepared by melting a glass composition of CaO/(CaO+P205) = 0.33, casting, crushing, loose powder sintering and crystallization annealing. The resultant porosity is 3 to 36 μm. The three point bending strength is 33 to 150 MPa depending on annealing treatment. The crystallized phases are β-Ca2P2O7 and CaP206. These porous implants show remarkable biocompatibility with the old bone and induce the growth of new bone within 30 days. The implants are partly resorbed after 90 days and replaced by new bone. The ingrowth of blood vessels into the implant is abundantly seen after 90 days despite a small original porosity, due probably to enlarged pores by preferential resorption of the implant material. The new ceramics are good candidates for resorbable bone bioimplant.
In Vivo Interactions with (Tissue Culture Pretreated) Dermal Sheep Collagen
Authors: van Wachem P. B. , van Wachem P. B. , Damink L. H. H. Olde , Dijkstra P. J. , Feijen J. , Nieuwenhuis P.
Published: March 2011

Pretreatment in tissue culture (TC) was previously found to markedly reduce the in vitro cytotoxicity of two types of crosslinked dermal sheep collagens (DSC's). This in vivo study confirms our in vitro results, in that TC-pretreatment of crosslinked DSC's resulted in the marked reduction or elimination of cytotoxic effects, such as increased cell infiltration, a deviant neutrophil-morphology, lipid formation and cell death. TC-pretreatment affected the crosslinked state of both DSC's in a different way, which could be deduced from the differences in gelatin-formation and presence of giant cells from macrophage- or fibroblast-origin. The results are explained in view of the differences in crosslinking.
Develoapmet of a Tissue Analog for Cartilage Repair
Authors: Pachence J. M. , Frenkel S. R. , Lin H.
Published: March 2011

Purified type I collagen was formed into matrices whose pore sizes were defined on the basis of previous results. The first series of in vitro studies measured the metabolism of chondrocytes grown in matrices with various pore sizes; results revealed that the growth rate was independent of the average matrix pore size, but that ckmdrocyte infiltration throughout the matrix was optimal for pore sizes of 100 to 150 un. In a second series of studies, type I collagen was combined with hyaluranic acid; the HyA/collagen matrices had little effect on chcrdrocyte cell growth versus the collagen matrices. A third set of in vitro studies used collagen matrices incorporating varying cornentrations of insulin-like growth factor. It was found that the IGF-1/collagen matrices can significantly effect the growth and metabolism of the clxrihrocytes. These experiments were vital in establishing the collagen matrix parameters which will be used in subsequent in vivo studies.
Tissue Fabrication: Reconstitution and Remodeling in Vitro
Authors: Bell Eugene , Scott Sumi
Published: March 2011

Two approaches to the reconstitution of tissues and organs are reviewed. The first consists of imitating the architecture of actual tissues and organs by combining cultured specialized cells with extracellular matrix components to produce a connective tissue substrate on or in which epithelial, mesothelial or endothelial cells can be plated or seeded and subsequently differentiate into mono or multilayered tissues and other structures. The second consists of providing an acellular framework of extracellular matrix constituents that can be occupied by adjacent host tissues after implantation in vivo and be remodeled by them to resemble the host tissues it is designed to replace. A paradigm for events in vivo, designed to study the process of remodeling of acellular matrices in vitro has been developed. The living skin equivalent (LSE), an example of a product fabricated using the first approach to tissue engineering, has been adapted to study events of extracellular matrix remodeling, relevent to the second approach to tissue engineering. After creating a disc shaped wound bed in an LSE, the wound is filled with a collagen matrix with or without added supplements and the process of epidermal wound closure and associated events in the dermis are followed. It is shown that fibroblast conditioned medium or a simple molecule such as ascorbic acid, added with no additional growth factors to the collagen matrix used to fill the wound bed, strongly stimulates the process of repair. Dermal fibroblasts from the adjacent tissue invade the collagen lattice that forms in the wound bed, and keratinocytes recruited from the wound edge overgrow the new dermal tissue. The applicability of the paradigm to the repair of vascular and other tissues will be discussed and approaches to optimizing the composition of acellular constructs considered.
Reconstituted Collagen Produces Different Healing Reactions in Bony and Soft Tissue Compartments
Authors: Todescan Reynaldo , Davies Johne E.
Published: March 2011

Using both in vivo and in vitro experiments we have demonstrated that: reconstituted collagen will undergo mineralization in a healing bony compartment; that this mineralization is the result of spontaneous precipitation of calcium salts due to the presence of alkaline phosphatase produced by the bone cells, and that once calcified, the collagen will undergo cellular resorption by tartrate-resistant multi-nucleate giant cells similar to osteoclasts. This sequence of events is quite different to that in the supra-bony soft-tissue compartment where no calcification of the collagen is apparent, the collagen matrix becomes infiltrated with fibroblast-like cells and little resorption of the matrix occurs during implantation.

We conclude that reconstituted collagen may be employed as both a tissue barrier, enhancing guided tissue regeneration, and a bone-substitute material, which becomes replaced by natural bone tissue.
The Influence of Surface Microgeometry on Fibroblast Colonization of Synthetic Surfaces
Authors: Ricci J. L. , Alexander H. , Howard C.
Published: March 2011

Tissue response to any synthetic implant—whether vascular device, dental implant, orthopaedic device, or any other implant that is in contact with soft connective tissue or mineralized tissue—has been found to correlate with the composition, surface chemistry, and surface microgeometry of the implant material.
Surface Modification of Bio-Active Ceramic (Artificial Bone) by Ion Implantation
Authors: Takaoka G. H. , Tanaka R. , Usui H. , Koh S. K. , Current M. I. , Yamada I. , Akamatsu S. , Kokubo T.
Published: March 2011

Glass-ceramics (A-W) containing apatite and wollastonite phases have been developed that show good bio-compatibility and rapidly form chemical bonds with living bone. The glass-ceramic (A-W) was implanted with 200 keV Zr and Ar ions at doses of 1E15 to 1E17 ions/sq.cm. It was found that the Zr ion implantation was effective for obtaining high mechanical strength in simulated body fluid. The increase of the mechanical strength can be considered to be due to the formation of Zr and O bonds by ion implantation. The bioactivity of the implanted ceramics remained, and was improved after soaking in the simulated body fluid. In the case of Ar ion implantation, the fracture strength was not improved. However, the bioactivity was strong and improved with increase of the time soaked in the simulated body fluid.
Effects of Metal Ions on Apatite Formation and Bone Mineralization
Authors: Blumenthal N. C. , Cosma V.
Published: March 2011

Certain metals (such as Al) are known to cause bone pathologies in humans and animals. While little is known about the mechanism of action of metals on either the formation of bone or on the physical-chemical properties of the mineral phase, there is considerable evidence that (1) Al and Cd directly affect the formation and properties of HA and thus are a causative factor in metal-related defective bone formation—in addition to any cellular effects which they may induce; (2) that other transition metals (such as Cr, V, Ti, Ni, Co), which are used in joint prostheses, significantly affect HA formation; and (3) gallium, the most effective antihypercalcemic agent, affects apatite formation and solubility.
Cellular Interaction with Biomaterials Modified by Arg-Gly-Asp Containing Peptides
Authors: Glass James R. , Craig William S. , Dickerson Ken , Pierschbacher Michael D
Published: March 2011

Because cells can recognize and attach to short synthetic peptides containing the tripeptide sequence, arg-gly-asp (RGD), we have designed peptides which will spontaneously bind and present an active RGD sequence on biomaterial surfaces. We have analyzed a number of synthetic peptides and fully characterized one which fulfills this functional criteria. This peptide has been named PepTite-2000™. When biomaterials are placed in aqueous buffers containing PepTite-2000, the peptide rapidly binds to the surface and provides a site for cell attachment. Cell attachment occurs to PepTite-2000 coated materials by an RGD dependent mechanism using the αvβ3 integrin. This coating protocol is widely applicable, and the peptide will coat and promote cell attachment to all the commonly used biomaterials we have tested including dacron, teflon, titanium and silicone. Analysis of the soft tissue response to dacron implants coated with PepTite-2000 demonstrates that the coating results in more rapid tissue ingrowth and less giant cell recruitment around the implanted materials. These data demonstrate that PepTite-2000 can be used to modify biomaterial surfaces and present a more “natural” site for cell interactions.
Principles of Tissue Engineering and Reconstruction Using Polymer-Cell Constructs
Authors: Mooney David J. , Cima Linda , Langer Robert , Johnson Lynt , Hansen Linda K. , Ingber Donald E. , Vacant Joseph P.
Published: March 2011

The fields of materials science, cell and molecular biology, and surgical reconstruction are merging to create new devices for surgical transplantation and reconstructive applications. The field of artificial devices for implantation has matured over the last 40 years. Likewise, the field of transplantation and tissue reconstruction has undergone enormous change and improvements over the last 30 years. It has been proposed that these fields merge to create new tissue substitutes for functional replacement, therapy or reconstructive applications. Over the last five years, our lab has experimented with the concept of using man-made, biodegradable polymer systems as scaffolding for cell implantation devices. They have been designed to maximize diffusion parameters allowing nutrient exchange, gas exchange, and waste exchange. Vascular ingrowth occurs in the implant with subsequent resorption of the original polymer. This leaves a permanently engrafted new tissue which is a chimera of donor cells for functional replacement and recipient mesenchymal elements including blood vessels and supporting tissue. We have experimented in several model systems including hepatocyte implants, chondrocyte implants for cartilage reconstruction, urethelial implants for urinary reconstruction, and more recently small bowel and bone. Across this broad front of tissue types, much new knowledge has been gained and there continues to be hope that this will achieve clinical application.
Biodegradable Cell Transplantation Devices for Tissue Regeneration
Authors: Mikos Antonios G. , Wald Heidi L. , Sarakinos Georgios , Leite Susan M. , Langer Robert
Published: March 2011

Biodegradable polymers can be utilized as templates for cell transplantation and regeneration of metabolic organs and structural tissues. Candidate materials must be adhesive substrates for cells, promote cell growth and allow for retention of cell function. However, the processing requirements of such materials into highly porous three-dimensional structures with large surface per volume and an interconnecting pore network limits their potential application for tissue regeneration. A new processing technique was developed to produce uniform, three-dimensional cell transplantation devices of poly(lactic-co-glycolic acid). The process involved the preparation of highly porous membranes by a solvent-casting and particulate-leaching technique followed by their lamination. The device structural and mechanical properties depended on those of their constituent membranes, as evaluated by mercury porosimetry, scanning electron microscopy, and thermomechanical analysis. Cells to be seeded into the devices were injected from catheters incorporated within their structure. In vitro studies with model suspensions of dyed microspheres allowed for visual evaluation of the internal pore structure of various layered devices. From these studies, numerous parameters of device design for cell seeding were determined including pore size and injection rate. The membrane lamination technique produced devices without interfaces between layers as determined by microsphere injection and scanning electron microscopy.
Organoapatites: New Materials for Regenerative Artificial Bone
Authors: Stupp Samuel I. , Hanson Jacqueline A. , Ciegler Glenn W. , Mejicano G. C. , Eurell Jo Ann , Johnson Ann L.
Published: March 2011

The objective of this work is to identify synthetic pathways for materials useful in the effective repair of the skeletal system. Ideally a universal artificial bone would be identified that can function as a cementitious, pseudoplastic, or structural material. The cementitious form would be very important for bone adhesives that repair bone fractures and restore bone defects. The pseudoplastic form would aid in the in situ reconstruction of anatomical defects and the structural material could be used to prefabricate prostheses. It is critical of course for all these forms of the artificial bone to have strongly regenerative properties so that as implants they would integrate microscopically with natural bone.
Two Methods for Analyzing Waves in Composites with Random Microstructure
Authors: Willis John R.
Published: March 2011

The problem of calculating the mean wave in a composite with random microstructure is addressed. Exact characterizations of the problem can be given, in the form of stochastic variational principles. Substitution of simple configuration-dependent trial fields into these generates approximations which are, in a sense, ‘optimal’. It is necessary in practice to employ only trial fields which will generate, in the variational principle, no more statistical information than is actually available. Trial fields that require knowledge of two-point statistics generate equations that can also be obtained directly, through use of the QCA. The same fields can be substituted into an alternative variational principle to yield an approximation that makes use of three-point statistics – this approximation is less easy to obtain by direct reasoning. When not even two-point information is available, some more elementary approximation is needed. One such approximation, which is simple and direct in its application, is an extension to dynamics of a “self-consistent embedding” scheme which is widely used in static problems. This is also discussed, together with some illustrative results for a matrix containing inclusions and for a polycrystal.
Effective Properties of Discrete Random Composites Wherein the Host and Inclusion Phases Obey Different Constitutive Relations
Authors: Varadan V V. , Apparao R. T. , Varadan V. K.
Published: March 2011

In studying the effective medium theories, polarization is hardly given a consideration in deciding the effective properties of a composite where the host and inclusion phases follow different constitutive equations. A significant conclusion of this paper is that eventhough the composite has discrete inclusions, with the inclusion phase obeying different constitutive properties than the host, the effective medium shows a preference for the inclusion behavior rather than the host which is continuous. As an example, results on polarization study are detailed for the specific case of chiral composites. Application of similar principles is presently explored in more complex problems like the elastic wave propagation through piezoelectric composites and the acoustic wave propagation through sediments.