bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Dynamics Simulation Of A Cyclic Siloxane Based Liquid Crystalline Material
Authors: Patnaik Soumya S. , Pachter Ruth , Plimpton Steve , WADE ADAMS W.
Published: March 2011

We have used molecular dynamics (MD) to study the room temperature bulk phase behavior of a cyclic siloxane with a pentamethylcyclosiloxane core and biphenyl-4-allyloxybenzoate Mesogens (BCS). This Material exhibits thermotropic liquid crystalline behavior above 120 °C. Bonded and non-bonded interactions were considered and a Molecular Mechanics force field was used to model the structural anisotropy of the siloxane Molecules. Molecular clusters with and without periodic boundary conditions (pbc) were studied to investigate the effect of the finite system size on the time evolution of the molecular structure. The precise nature of the boundary conditions was found to be significant and simulations that exclude pbc were better able to model the molecular system. It was found that molecular shapes associated with low energy conformations were not cylindrically symmetric but more splayed like. An approximate measure of the shape of the mesogens was obtained by describing ellipsoids around the Mesogens, and estimating the molecular length, breadth, and width from the principal axes of the ellipsoids. The orientational order was then calculated by defining the molecular axis to be along the major principal axis.
Observations of Damage and Transport of Hydrogen in Ion Bombarded Polycrystalline Silicon
Authors: Sharp D. J. , Panitz J. K. G. , Seager C. H.
Published: March 2011

A combination of chemical etching and sheet resistivity measurements showed that intense (1.4 mA/cm2 ) low energy (1400 eV) ion beam hydrogenation of polycrystalline silicon having a columnar structure can produce electrical defect passivation to depths in the order of 100 μm. Transmission electron micrographs disclose surface and near-surface features resulting from the ion beam bombardment which suggest that one of the hydrogen transport mechanisms may be defect induced.
Display Quality SOI by Recrystallization of Bridged Silicon Islands on Quartz
Authors: Bak C. S. , Braatz P. O. , Margerum J. D.
Published: March 2011

Arrays of single crystal thin film silicon islands were prepared on fused quartz substrates by a zone melting recrystallization of bridged island patterns of poly-Si. A scanning graphite strip heater technique was used, with the Si islands connected (“bridged”) in the scanning direction by narrow Si strips. These strips generated a self-seeding effect in the crystalline growth, and the recrystallized Si islands were good quality SOI with <100> orientation as shown by x-ray and etch-pit analysis. Protuberances, film cracking and impurity segregation were greatly suppressed in this bridged island SOI as compared to defects normally observed in recrystallized continuous Si films on quartz. MOSFETs were fabricated in the SOI islands, using n-channel enhancement mode devices with a gate length of 5μm and a gate width of 50μm. The average carrier mobility measured on these SOI devices was 470 ± 70 cm2/V.s, which was twice as high as the mobility measured in MOSFETs fabricated concurrently in SOS. Good MOSFETs in the SOI islands showed a switching ratio of about 107 at 6V and a leakage of less than 2pA/μm. These results indicate that high performance drive circuits for liquid crystal displays can be fabricated in SOI recrystallized from bridged island patterns on transparent quartz substrates.
CMOS/SOS VLSI Technology
Authors: Sato Tai , Iwamura Jun , Tango Hiroyuki , Doi Katsuyuki
Published: March 2011

CMOS is considered as a prospective technology in the VLSI era because of its low power consumption and high driving capability. While ordinary bulk silicon CMOS devices are inferior to SOS CMOS devices in chip area, operation speed and latch-up problem due to the need for isolation wells. SOS is an inherent good partner of the CMOS circuits owing to the simple and perfect isolation. SOS technology, however, has the problem of high wafer cost. Consequently, SOS technology is best applied to high performance logic devices. Latest results of 8k-gate CMOS/SOS gate array and 16×16bit multipliers show 0.87ns 2-NAND gate delay and 27ns multiplication time, respectively, which compete with ECL devices. Application of SOS devices down to 1μm is also promising for very high speed operation. A 78ps gate delay is achieved by double solid phase epitaxy and 1μm technology. INTRO
Amorphous Si:H Linear Image Sensor Operated by a-Si:H TFT Array
Authors: Okumura F. , Kaneko S.
Published: March 2011

An amorphous Si:H linear image sensor operated by a-Si:H TFT array has been proposed. This sensor consists of photodiode array, TFT array, matrix circuit, charge transfer capacitor, and external circuit. Mobility for TFT is 0.6 cm2/V.s and 5 μsec/bit read out time was obtained in the conventional matrix mode scanning. Moreover, a novel driving method is applied in order to improve the effective operation speed and an investigation for TFT noise was performed. Experimental data confirm the validity of the concept.
The Formation of Porous Silicon and its Applications to Dielectric Isolation
Authors: Frye R. C.
Published: March 2011

Porous silicon is formed by the anodic dissolution of p-type silicon in aqueous hydrofluoric acid. Because of its very high porosity, this material can be rapidly cKidized to form thick (˜10 μn) oxide layers with minimal stress on the underlying silicon wafer. A remarkable property of porous silicon is that preserves the crystalline orientation of the substrate despite removal of more than half of the silicon in the etched region, providing a suitable surface for the growth of epitaxial layers. Several schemes for dielectric isolation have been suggested which take advantage of these unique properties. In this paper, the mechanism of porous silicon formation will be presented and the relative advantages and disadvantages for practical device applications will be discussed.
Genetically-Engineered Protease-Activated Triggers in a Pore-Forming Protein
Authors: Walker Barbara , Walsh Nathan , Bayley Hagan
Published: March 2011

Protease-activated triggers have been introduced Into a pore-forming protein, staphylococcal a-hemolysin (αHL). The hemolysin was remodeled by genetic engineering to form two-chain constructs with redundant polypeptide sequences at the central loop, the Integrity of which Is crucial for efficient pore formation. The new hemolysins are activated when the polypeptide extensions are removed by proteases. By alterating the protease recognition sequence in the loop, selective activation by specified proteases can be obtained. Protease-triggered pore-forming proteins might be used for the selective destruction of cancer cells that bear tumor-associated proteases. When certain two-chain constructs are treated with proteases, a full-length polypeptide chain forms as the result of a protease-mediated transpeptidation reaction. This reaction might be used to produce chimeric hemolysins that are Inaccessible by conventional routes.
A Versatile Low Density Polysaccharide Matrix
Authors: Rohrbach Ronald P. , Unger P. D.
Published: March 2011

A material having the characteristics of very low density and high mechanical stability has been developed. This material is prepared by crosslinking the biopolymer alginic acid. Bulk densities as low as 0.15 g/cc have been obtained, while still possessing useful strength, 10% deformation at 347 psi. The physical properties can be varied by controlling the processing conditions, which affect pore volume, pore diameter, bulk density and surface area. Preparation of this material involves solvent exchange and subsequent crosslinking. The resin's minimum compressibility and physical strength allow this material to be considered for a number of applications including adsorbents, insulation and as a polymeric carrier for time release.
Failure And Energy-Absorbing Mechanisms of the Bessbeetle Cuticle
Authors: Thorp Katie E. G. , Gunderson Stephen L.
Published: March 2011

The failure processes of the bessbeetle cuticle were studied through the use of scanning electron microscopy, light microscopy, and image analysis techniques. Specimens of elytra and pronotum were failed in tension under the light microscope. The failure process was documented in real time through the use of image analysis equipment and a video camera. Failure occurs primarily in a mixed-mode fashion due to the inherent curvature of the cuticle specimens and their complex hierarchical microstructure. A variety of energy-absorbing mechanisms were observed including remote microcracking, fiber pullout, and crack bridging. Damage accumulation around the failed region is extensive consisting of a significant amount of delamination, fiber-matrix disbonds, microcracking, and intra-fiber failure. The experimental methods and results will be discussed.
Precipitation in and on Polymers
Authors: Calvert Paul
Published: March 2011

Mineralized biological tissues form by growth of inorganic phases in or on polymers and membranes. This paper discusses the mechanisms for these processes from a bio-mimetic point of view. Mineralization within a polymer or gel can lead to very fine precipitates because particle agglomeration is prevented and solute diffusion rates are low.

Localization of mineralization appears to occur in biology by activation of particular surfaces. The possibility is discussed that this may be due to a close lattice match between the spacing of groups on the polymer and the spacing of ions in the mineral. It is shown that this mechanism is unlikely and other possibilities are discussed.
Proliferation and Interactions of Several Cell Types Encapsulated Within Dense (Non-Porous) Protein-Permeable Polyurethane Membranes
Authors: Wang Albert Y. , Ward Robert S. , White Kathleen A. , Kuhn Robert W. , Taylor Julie E. , John Judith K.
Published: March 2011

Protein-permeable dense (non-porous) urethane membranes have been evaluated forin vitrocell culture, and in vivo cell encapsulation. Polyurethane membranes were designed to exhibit permeability to proteins, gases, and nutrients without the existence of pores. The membranes are non-cytotoxic, angiogenic, and permeable to gases, nutrients, secretagogues and cell products via purely concentration-driven transport. Non-anchorage and anchorage dependent cells were grown encapsulated within the membrane and with the membrane as a growth substrate. Several non-anchorage dependent cell types proliferated within the membrane bothin-vitroandin-vivo. Anchorage-dependent cells were grown on the membranes as a substrate. Encapsulated cells have been maintained in culture for up to six months with nutrients supplied only by the external media. Immuno-isolation has been demonstrated with cells implanted into murine hosts. Explants of membrane encapsulated cells exhibited a high degree of vascularization, with little or no fibrous tissue. The ability to support cell growth and function, and the ability to protect xenogenic cells from immunologic rejection suggest that the membranes would be useful in the construction of hybrid artificial organs, devices for cell transplantation, and substrates for cell and tissue culture.
Novel Preparation of Poly(Vinyl Alcohol) Microparticles without Crosslinking Agent for Controlled Drug Delivery
Authors: Ficek Becky J. , Peppas Nicholas A.
Published: March 2011

Poly(vinyl alcohol) microparticles were prepared by a novel freezing-thawing process in the absence of a crosslinking agent. An aqueous PVA solution to which 1.25 wt% sodium lauryl sulfate was added was dispersed in corn oil. The system was agitated and the ensuing suspended droplets of PVA solution were solidified by a cyclic freezing-thawing process. Key parameters of the process were the PVA to corn oil ratio, the amount of surfactant added, agitation speed, number of freeze cycles, temperatures of freezing and thawing, and presence of additional components.

Crystallization was observed during the freezing-thawing process. The degree of crystallinity was measured with differential scanning calorimetry. Bovine serum albumin was incorporated into the particles by an absorption technique. Studies of BSA release from the microparticles in vitro showed that the release could be prolonged for up to 7 days. BSA diffusion coefficients were calculated from these data and the release mechanism was identified.
Bioactive Glass Templates for the Synthesis of Bone-Like TissueIn Vitro
Authors: Ei-Ghannam A. , Ducheyne P. , Shapiro I. M.
Published: March 2011

Porous glass templates of pore size 75–200 14m and 20–30% porosity were synthesized. The glass disks were conditioned in a modified tris buffer (SBF) for 48 hrs and then treated with tissue culture medium (TCM) for 1 hr at 37°C. Other porous glass templates were treated with either SBF or TCM. The conditioned glass disks were seeded with 106neonatal rat calvaria osteoblasts and maintained in culture for 2, 5 or 7 days. It was found that the bioactive glass was rapidly invaded by cells which colonized the porous template. Morphological and biochemical analyses suggested that a bone-like tissue was formed inside templates conditioned with both SBF and TCM. By 7 days, the cells exhibited high alkaline phosphatase activity and synthesized osteocalcin. SDS-PAGE indicated the presence of type I collagen. SEM-EDAX analysis showed the formation of a bone-like tissue throughout the entire sample, while inspection of the Ca:P ratio indicated that the cells synthesized a mineral phase. Indeed, the FTIR spectra of the mineral confirmed that it was a biological hydroxyapatite. The rapid formation of the bone-like material within the templatein vitrosuggests that this template may be valuable clinically for the repair of bone lesions.
Use of a Multiple Lumen Cuff for Nerve Regeneration
Authors: Greer Raymond , Daniel John , Uemura Etsuro , Kudej Raymond , Chen Yueh-Sheng , Chung Chih-Hui
Published: March 2011

Initial studies using the rat sciatic nerve demonstrated the ability to adapt a multiple lumen cuff face to a nerve stump repair site. The neurons in the proximal stump grew through the individual conduits of the silicone rubber cuff, crossed a 5 mm gap, and continued into the distal stump. The effect of the cuff design on axonal regeneration was studied by comparing macroscopic and microstructural results for experimental groups of Sprague-Dawley rats with controls at 8, 12, 16, and 24 weeks post-implantation. The several individual nerve bundles which formed within the cuff lumens during these periods maintained their alignment on the distal side of the gap. The use of the multiple lumen system provided suitable scaffolding support and control of orientation and direction for fibers and established a sized, controlled environment for regeneration within each of the separate nerve cuff compartments.
Stabilizing Fiber-Based Cell Delivery Devices by Physically Bonding Adjacent Fibers
Authors: Mooney D. J. , Mazzoni C. L. , Organ G. M. , Puelacher W. C. , Vacanti J. P. , Langer R.
Published: March 2011

Non-woven meshes of polyglycoiic acid (PGA) fibers are attractive candidates to transplant cells and engineer new tissue. However, these devices typically lack the structural stability to resist compressive forces, and collapse in vivo. To determine whether these devices could be stabilized by physically bonding adjacent PGA fibers, we have sprayed solutions of poly (L-lactic acid) (PLLA) and a 50/50 copolymer of poly (D,L-lactic-co-glycolic acid) (PLGA) dissolved in chloroform over PGA meshes formed into hollow tubes. After the chloroform evaporated, the PLLA and PLGA formed a coating over the PGA fibers and bonded adjacent fibers. The pattern and extent of fiber bonding was found to depend on both the concentration of polymer in the spraying solution, and the total mass of polymer sprayed on the device. The compression resistance of sprayed devices increased with increasing extent of bonding, and devices bonded with PLLA resisted compressive forces better than devices bonded with PLGA. For example, under a compressive force of 200 mN, devices sprayed with PLLA compressed approximately 20%, while devices sprayed with PLGA were completely crushed. To determine whether stabilized devices such as these can guide the development of neointestine and neocartilage by transplanted cells, intestinal cells and chondrocytes have been attached to PLLA bonded devices and transplanted into experimental animals.
Controlled Release of Trimaterene from Poly(DL-Lactide-Co-Glycolide) Microspheres
Authors: Ouellete Amy D. , Peppas Nicholas A.
Published: March 2011

Release of triamterene from 150–300 gm poly(DL-lactide-co-glycolide) (PLGA) microspheres was investigated in vitro as a function of lactic acid/glycolic acid (LA/GA) copolymer ratio and drug loading both with free microspheres and with microspheres embedded in a silicone matrix. Biphasic release consisting of diffusion controlled release followed by erosion controlled release corresponding to polymer degradation was observed in all samples. Drug release from PLGA 50:50 copolymer microspheres was three times faster than the release from PLGA 75:25 microspheres for the higher drug loading (20 wt%) and slightly faster for the lower drug loading (10 wt%). Release rates from spheres containing the higher drug loading were approximately one order of magnitude faster than release from spheres containing the lower drug loading for the same PLGA copolymer. The same qualitative results were observed for the spheres embedded in silicone matrices; however, the overall release was much slower. The results demonstrate that release behavior may be altered by changing LA/GA copolymer ratio, drug loading, and microsphere environment to obtain the desired release characteristics.
Double-Walled Microspheres for Drug Delivery
Authors: Pekarek Kathleen J. , Jacob Jules S. , Mathiowltz Edith
Published: March 2011

Present microsphere delivery system technology consisting of a single drug dispersed within a polymer matrix has several drawbacks. One is the problem of the so-called “burst effect”. By exploiting the phenomenon of phase separation between two immiscible polymers dissolved in a mutual solvent, a double-walled microsphere could be manufactured with the second polymer coating the polymer/drug matrix. This one-step process would give a consistent coating of even very small microspheres not achievable via normal, two-step coating processes and would help to smooth out the release curve by lessening the “burst effect”. Along with solving the problem of the “burst effect”, this concept of double-walled microspheres could be used to achieve constant release of the drug over long periods of time. So far, this has only been achieved with a limited number of geometric configurations. Since every polymer has its own characteristic release rate, the release could be kept much more constant by changing the polymer type and/or properties. By combining these layers so that the release rate of one layer would complement the slowing of release due to decreased surface area or increased diffusion distances.
Selective Growth of Diamond Films On Mirror-Polished Silicon Substrates
Authors: Mao M.Y. , Tan S.S. , Zhang X.K. , Wang W.Y.
Published: March 2011

Polycrystalline diamond thin films have been selectively grown on mirror-polished silicon substrates using bias-enhanced microwave plasma chemical vapour deposition (MPCVD) to increase diamond nucleation density. A slight etching of Si02 mask was employed after the nucleation treatment to remove the diamond nuclei on the mask. Perfect diamond patterns with smooth surface (particle size <0.5µm) and sharp boundaries were obtained. The diamond film gears with 400µm in diameter and 5µm in thickness were first fabricated by this technique.
Real Time Control of III-V Semiconductor Surfaces During Movpe Growth by Reflectance Anisotropy Spectroscopy
Authors: Ploska K. , Richter W. , Reinhardt F. , JÖnsson J. , Rumberg J. , Zorn M.
Published: March 2011

Reflectance anisotropy spectroscopy (RAS) is presented as real time analytical tool for metalorganic vapourphase epitaxy (MOVPE) of III-V-semiconductors. This optical method derives its surface sensitivity from the anisotropy of surface structures. It is shown that it is possible to monitor with RAS the oxide desorption from the substrate and that the substrate surface conditions thereafter, still in the pregrowth stage, can be correlated with certain reconstructions of the (001)-surfaces of InP and GaAs. The latter is possible through simultaneous RAS and RHEED measurements during MBE (molecular beam epitaxy) or MOMBE (metalorganic molecular beam epitaxy). Characteristic spectral features are also observed for other binary or ternary III-V-semiconductors. Time resolved measurements during growth give monolayer resolution for the growth rate in the case of GaAs. In the study of heterointerface growth exchange reactions between As and P together with their corresponding reaction time constants can be monitored and conclusions for the epitaxial growth procedure can be drawn.
Kinetics of Low-Pressure Mocvd Of GaAs from Triethyl-Gallium and Arsine
Authors: Ingle N.K. , Theodoropoulos C. , Mountziaris T.J. , Wexler R.M. , Smith F.T.J.
Published: March 2011

The growth of undoped GaAs films from Ga(C2H5)3 (TEG) and AsH3 by Metalorganic Chemical Vapor Deposition (MOCVD) has been studied in a low-pressure reactor operating at 3 Torr. This precursor combination is known to produce GaAs films with very low carbon incorporation when compared to films grown from Ga(CH3)3 (TMG) and AsH3. A kinetic model of the growth process has been developed that includes both gas-phase and surface reactions based on reported decomposition mechanisms of TEG and AsH3. The kinetic model was coupled to a transport model describing flow, heat and mass transfer. Finite element simulations were performed to determine the rate constants of the growth reactions that provide the best fit between predicted and observed growth rates. Under typical operating conditions the surface reactions were found to dominate the growth process and a reduced surface kinetic model was identified by sensitivity analysis. The proposed reaction-transport models can successfully predict observed growth rates of GaAs films and they can be used for identifying optimal operating conditions in MOCVD reactors.
Tetraalkyldiarsines As Potential Precursors for Electronic Materials: Synthesis and Characterization Of Various Iso-Propyl Arsenic Compounds
Authors: Brough Lawrence F. , Gang Liu , Lipkovich Matthew A. , Colacot Thomas J. , Goedken Virgil L. , Rees William S.
Published: March 2011

Tetrakis(iso-propyl)diarsine was synthesized by the reaction of (i-Pr)2AsLi with (i-Pr)2AsI. The lithium salt of the secondary arsine was produced following deprotonation of (i-Pr)2AsH, obtained by reduction of (i-Pr)2AsI, which was prepared by the thermolysis of (i-Pr)3Asl2. The X-ray crystal structure of \(i-Pr)3AsI]\I] has been determined on the product of the reaction of (i-Pr)3As and 12. Compounds of the general form E=As(i-Pr)3 (E = O, S, Se) have been prepared.
New Zinc-bis(Dialkylamides) Potentially Usable as Site-Selective Dopants For p-Type ZnSe.
Authors: Rees William S. , Just Oliver
Published: March 2011

In earlier work, the effective utilization of Zn {N\Si(CH3)3]2}2 as a site-selective dopant for the production of p-type ZnSe by OMVPE was demonstrated. Several new zinc-bis(dialkylamides) of the general form (R)(R′)NZnN(R″)(R‴) now have been prepared. They have been characterized by 1H- and 13C-NMR, GC/MS and elemental analysis. Vapor pressures and gas phase decompositior profiles have been examined. Correlations of vapor pressure and structure are discussed for this series of compounds. A mechanism for the site-selectivity observed in the incorporation of nitrogen is proposed.
Nanosecond and Femtosecond UV Laser Ablation of CdTe (100): Time-Of-Flight and Angular Distributions
Authors: Brewer P.D. , Späth M. , Stuke M.
Published: March 2011

Angularly resolved time-of-flight (TOF) measurements have been used to probe the velocity and angular distributions of Cd atoms and Te2 molecules ejected from CdTe (100) substrates under irradiation by 248 nm nanosecond and sub-picosecond laser pulses. These experiments employ a dye laser TOF mass spectrometer with resonance enhanced multiphoton ionization for sensitive, high resolution detection of the desorbed products. The velocity distributions are well described by Maxwell-Boltzmann distributions for low fluence nanosecond (<60 mJ/cm2) and sub-picosecond (<3.3 mJ/cm2) pulses. Angular flux distributions for nanosecond irradiation are observed to be highly forward peaked about the surface normal, whereas, for sub-picosecond irradiation the distribution approaches cos3θ.
Gas-Phase Silicon Atom Densities in the Chemical Vapor Deposition of Silicon from Silane
Authors: Coltrin Michael E. , Breiland William G. , Ho Pauline
Published: March 2011

Silicon atom number density profiles have been measured using laser-induced fluorescence during the chemical vapor deposition of silicon from silane. Measurements were obtained in a rotating-disk reactor as a function of silane partial pressure and the amount of hydrogen added to the carrier gas. Absolute number densities were obtained using an atomic absorption technique. Results were compared with calculated density profiles from a model of the coupled fluid flow, gas-phase and surface chemistry for an infinite-radius rotating disk. An analysis of the reaction mechanism showed that the unimolecular decomposition of SiH2 is not the dominant source of Si atoms. Profile shapes and positions, and all experimental trends are well matched by the calculations. However, the calculated number density is up to 100 times smaller than measured.
The Effects of Deposition Parameters on the Properties of SiO2 Films Deposited by Microwave Ecr Plasmas
Authors: Chau T. T. , Lam P. M. , Kao K. C.
Published: March 2011

Electronic and physical properties of SiO2 films deposited by microwave ECR plasmas of the mixtures of SiH4 and N2O have been measured as functions of the pressure and the gas-flow ratio of N2O to SiH4 gases in the processing chamber. Experimental results show that the film deposition rate increases with increasing SiH4 concentration, that is, with decreasing gas-flow ratio. The films deposited at N2O/SiH4 gas-flow ratios smaller than 10 tend to have a refractive index higher than the thermally grown oxide. However, for the N2O/SiH4 gas-flow ratios between 10 and 20, the films have the refractive index close to that of thermally grown oxide, which is about 1.45-1.46. The film deposition rate increases linearly with increasing pressure. In general, the films deposited at high pressures (>100 mTorr) have a higher refractive index as compared with the thermally grown oxide; also films deposited at high pressures have more electron traps. Good quality SiO2 films can be deposited at pressures with the range of 20 -50 mTorr and the N2O/SiH4 gas-flow ratio of 10.
High Rate Deposition of SiO2 by the Remote Pecvd Technique
Authors: Ishida Arichika , Hiramatsu Masato , Kawakyu Yoshito
Published: March 2011

The deposition of SiO2 by remote PECVD using microwave activated oxygen species and SiH4 were examined. The deposition rate has been found to be greatly enhanced by reducing the distance between the substrate surface and the end of the supplying nozzle for the plasma excited oxygen species.

The deposition rate decreased with increasing substrate temperature under the condition that the activated oxygen species and SiH4 molecules collide with each other many times. Its activation energy was -0.27 eV.

It has been found that the gas phase reaction caused by the collision is important to obtain high quality films. A SiO2 film with a resistivity larger than 1×1016 Ω·cm was able be obtained with high deposition rates beyond 200 nm/min, at low temperatures below 400°C. The minimum interface state density was 4.3×1010 cm−2eV−1 for a film deposited at 230 nm/min, and 2.0×1010 cm−2eV−1 for a film deposited at 30 nm/min.
New Dry-Etch Chemistries for III-V Semiconductors
Authors: Pearton S. J. , Chakrabarti U. K. , Ren F. , Abernathy C. R. , Katz A. , Hobson W. S. , Constantine C.
Published: March 2011

For some dry etching applications in III-V semiconductors, such as via hole formation in InP substrates, the currently used plasma chemistries have etch rates that are up to a factor of 30 too slow. We report on the development of 3 new classes of discharge chemistries, namely C12/CH4 /H2/Ar at 150°C (yielding InP etch rates of >1 μm · min−1 at 1 mTorr and –80V dc), HBr/H2 for selective etching of InGaAs over AlInAs, and iodine-based plasmas (HI/H2, CH3 I/H2) that offer rapid anisotropic etching of all III-V materials at room temperature. In all cases, Electron Cyclotron Resonance sources (either multipolar or magnetic mirror) with additional rf biasing of the sample position are utilized to obtain low damage pattern transfer processes that generally use metal contacts on device structures as self-aligned etch masks. The temperature dependence of etch rates with these new chemistries display non-Arrhenius behavior in the range 50-250°C and a detailed study of the phenomenon are reported. Electrical, optical and chemical analysis of the etched surfaces show that it is possible to achieve essentially damage-free pattern transfer.
New Damage-Less Patterning Method of A GaAs Oxide Mask and Its Application to Selective Growth by Mombe
Authors: Yoshida Seikoh , Sasaki Masahiro
Published: March 2011

A new damage-less patterning method of the photo-oxidized GaAs mask used for the selective-area growth of GaAs has been developed. We have found a new characteristic of the GaAs oxide: a metal Ga deposition onto the GaAs oxide surface lowers the desorption temperature of the oxide. The patterning method employed is based upon this characteristic. The GaAs oxide where 15 atomic layers (ALs) of Ga is deposited is locally removed at 540°C to form an opening area in the oxide mask. After forming this opening area, GaAs is selectively grown there by metal-organic molecular beam epitaxy (MOMBE).
Pyrolytic Lcvd of Silicon Using A Pulsed Visible Laser - Experiment and Modelling
Authors: Ivanov B. , Popov C. , Shanov V. , Filipov D.
Published: March 2011

Maskless deposition of silicon from silane on Si monocrystalline wafer using copper bromide vapor laser (CBVL) is investigated. Morphology and geometric parameters of the stripes obtained are studied and some conclusions for the process mechanism are made. Applying Kirchoff's transform and Green's function analysis nonlinear heat diffusion problem for different pulse shapes was solved. The influence of pulse shape on the temperature distribution and its time evolution was studied. Nonisothermal and non-stationary deposition kinetic models using the obtained results were developed.
Low Temperature CVD of TiN from Ti(NR2)4 and NH3: FTIR Studies of the Gas-Phase Chemical Reactions
Authors: Weiller Bruce H.
Published: March 2011

The gas-phase chemical reaction between Ti(NMe2)4 and NH3 is a critical step in the Metallorganic Chemical Vapor Deposition (MOCVD) of TiN at low temperatures. We have examined this reaction using a flow-tube reactor coupled to an FTIR spectrometer. A sliding injector provides control over the reaction time and the kinetics of reactive species can be measured as a function of the partial pressure of an added reagent. The disappearance of Ti(NMe2)4 was measured as a function of reaction time and NH3 pressure at 26°C. The resulting bimolecular rate constant is (1.1±0. 1) x 10-16 cm3molecules−1s−1 Dimethylamine is observed as a direct product from this reaction consistent with other studies. We have also measured the rate constant using ND3 and find a substantial isotope effect, kh/kd ≈2.4± 0.4. This indicates that H-atom transfer is involved in the rate limiting step. We show that these results can be explained by a mechanism comprised of transamination reactions with NH3.
Theoretical Modeling of Chemical Vapor Deposition of Silicon Carbide in a Hot Wall Reactor
Authors: Gao Feng , Lin Ray Y.
Published: March 2011

A theoretical model, which describes the coupled hydrodynamics, mass transport and chemical reaction, has been developed to simulate chemical vapor deposition (CVD) of silicon carbide (SiC) from gas mixture of methyltrichlorosilane (MTS), hydrogen and argon in a hot wall reactor. In the model analysis, the governing equations were developed in the cylindrical coordinate, and solved numerically by using a finite difference method. A kinetic rate expression of CVD-SiC deposition from the gas mixture was obtained from this study. The deposition rate has an Arrhenius-type dependence on the deposition temperature and is first order with respect to the MTS concentration. Estimated activation energy is 254 kJ/mol. Predicted deposition rate profiles by the model analysis incorporated with the obtained kinetic rate expression showed excellent agreement with experimental data over a variety of applied deposition conditions.
Synthetic Strategies for MOCVD Precursors for HTcS Thin Films
Authors: Meinema Harry A. , Timmer Klaas , Linden Hans L. , Spee Carel I. M. A.
Published: March 2011

In recent years much attention has been given world-wide to the development of suitable MOCVD precursors for the deposition of HTcS thin films. Synthetic research has been and is concentrated on the development of superior Ba-, Sr-, Ca- and Y-precursors. Most emphasis is given to the synthesis of thermally stable volatile barium compounds. Synthetic strategies are based on encapsulating the central metal atom, by use of multidentate ligand systems and/or bulky substituents. Most attention is given to the development of thermally stable volatile ß-diketonate complexes, fluorine-free and fluorine-substituted, with auxiliary ligands. Thermally stable monomeric complexes of fluorine-substituted ß-diketonates with polyethers are by far the most volatile Ba-, Sr-, and Ca-precursors presently available. Low melting Y(thd)3.L complexes where L is 4-Et- or 4-t-Bupyridine- N-oxide can be used as liquid yttrium MOCVD precursors at temperatures above 100°C. This paper gives a survey of the trends in recent research activity and developments in these areas.
Advances in Precursor Development for CVD of Bariumcontaining Materials
Authors: Vaartstra Brian A. , Gardiner R. A. , Gordon D. C. , Ostrander R. L. , Rheingold A. L.
Published: March 2011

Barium titanate and barium-strontium titanate (BST) are high dielectric materials, likely to replace state-of-the-art capacitor materials for memory applications. Chemical Vapor Deposition (CVD) of these materials has been hampered, particularly by the lack of suitable precursors for barium. Although attempts to make volatile metal-organic barium compounds have met with some progress, a suitably stable, volatile barium source is still in demand. This paper will highlight recent developments at ATM, including syntheses and structures of polyamine and glycol ether adducts which have been designed to limit aggregation of barium diketonates, and stabilize the adducts with respect to ligand dissociation.
Structure and Kinetics Study of MOCVD Lead Oxide (PbO) from Lead BIS-Tetramethylheptadionate (Pb(thd)2)
Authors: Hendricks Warren C. , Desu Seshu B. , Tsai Ching Yi
Published: March 2011

Lead bis-tetramethylheptadionate (Pb(thd)2) is an extremely useful precursor for the preparation of lead-based thin films such as PZT, lead titanate, etc. In this paper, lead oxide was deposited from Pb(thd)2 in a hot-walled CVD reactor using oxygen as a reactive species and diluent gas. XRD and SEM were used to determine the structure of the material deposited by the CVD process. The CVD process consistently produced the monoxide of lead which was found to consist of a mixture of orthorhombic PbO with small tetragonal PbO platelets. TEM was used to determine the orientation of the individual platelets which was found to be consistently normal to the <201> family of zone axes. Deposition rates were determined and simulated using an FEM computer model to determine the rate constants for the overall deposition process.
Liquid Delivery of Low Vapor Pressure MOCVD Precursors
Authors: Gardiner R. A. , Van buskirk P. C. , Kirlin P. S.
Published: March 2011

A significant limitation in MOCVD processing of advanced materials is the ability to deliver low volatility precursors, in a repeatable fashion, to the deposition reactor. Apparatus for delivering low volatility precursors in gaseous form, wherein a precursor source liquid is flash vaporized at elevated temperature has been developed. Stable, reproducible delivery of liquid precursors for TiN and Ta2O5 has been demonstrated. For multicomponent ceramic material systems simultaneous delivery of multiple cation species via a single source liquid has been achieved. The effect of flash vaporization on precursors for PZT was investigated. Pb, Zr and Ti precursors were dissolved in an organic medium with a defined cation ratio. The source solution was vaporized, the precursors transported as vapor then collected and analyzed by 1H and 13C nmr. No decomposition of the precursors was observed post vaporization and source solution stoichiometry was maintained in the collected material. The use of this flash vaporization technique has already been particularly successful for MOCVD of BaTiO3, MgAl2O4, YBa2Cu3O7−x, YSZ, LaSrCoO3 and Cu metal.
Local Equilibrium Phase Diagrams for SiC Deposition in a Hot Wall LPCVD Reactor
Authors: Chiui Chien C. , Desu Seshu B. , Chen Zhi J. , Tsai Ching Yi
Published: March 2011

The traditional CVD phase diagrams are only valid for cold wall reactors because of the neglecting of the depletion effects in hot wall reactors. Due to the depletion effects along the reactor, the traditional CVD phase diagrams can not accurately predict the phases deposited on the substrate in a hot wall CVD system. In this paper, a new approach to calculate the local equilibrium CVD phase diagrams in a hot wall reactor is presented by combining the depletion effects with the equilibrium thermodynamic computer codes (SOLGASMIX–PV). In this study, the deposition of SiC using methyltrichlorosilane (MTS)–hydrogen (H2) was chosen to verify this new approach. The differences between the new CVD phase diagrams and the traditional phase diagrams were discussed. The calculated CVD phase diagrams were also compared with the experimental data. The single phase of SiC predicted by this approach is much better than the traditional phase diagrams. The experimental regions for depositing single phase SiC are larger than the calculated local phase diagrams because of the higher linear velocity of the gas flux under low pressure and the polarity of the Si carrying intermediate species.
Plasma-Enhanced MOCVD of Superconducting Oxides
Authors: Ebihara Kenji , Fujishima Tomoyuki , Shiga Masanobu , Jia Quanxi
Published: March 2011

The plasma-enhanced MOCVD is developed to prepare high-Tc oxide superconducting thin films. Plasmas generated by microwave and rf discharges decompose effectively the source materials ( β-diketonate chelates) into their elements and oxides. YBaCuO thin films were deposited on the MgO substrate of 500–650 °C at total pressure of 0.6–5 Torr with O2 contents less than 30%. The as-grown films produced by two kinds of plasma enhancement were porous and consisted of crystalline grains, but showed the superconducting transition after heating procedure at around 800 °C. It is shown that the inherent crystalline orientations of the as-grown films determine the crystal structure of the post-annealed films. The film of the metal atomic ratios of 0.91 for Ba/Y and 2.64 for Cu/Y showed the superconducting properties with Tc(zero) of 89 K and the critical current density (at 77 K) of 5×104 A/cm2. Spectroscopic analysis showed that the plasmas are composed of many excited species such as Y, Y+, Ba, Ba+, Cu, YO, BaO, CuO. Formation of the metal-oxides through the gas phase reaction is essential for the high-quality YBaCuO superconducting thin film preparation in the PEMOCVD.
Metal-Organic Chemical Vapor Deposition of Epitaxial Tl2Ba2Ca2Cu3O10−x Thin Films
Authors: Hinds Bruce J. , Schindler Jon L. , Han Bin , Neumayer Deborah A. , Degroot Donald C. , Marks Tobin J. , Kannewurf Carl. R.
Published: March 2011

Superconducting thin films of Tl2Ba2Ca2Cu3O10−x (TL-2223) have been grown on single crystal (110) LaAlO3 using a two-step process. Ba2Ca2Cu3Ox precursor films are deposited via metal-organic chemical vapor deposition (MOCVD) in a horizontal hot walled reactor. The second generation precursors Ba(hfa)2•tet, Ca(hfa)2•tet, and Cu(hfa)2 (hfa = hexafluoroacetylacetonate, tet = tetraglyme) were used as volatile metal sources due to their superior volatility and stability. Tl was introduced into the film via a high temperature post anneal in the presence of a Tl2O3:BaO:CaO:CuO pellet (1:2:2:3 ratio). Low O2 partial pressures were used to reduce the temperature in which the TI-2223 phase forms and to improve the surface morphology associated with a liquid phase intermediate. Films are highly oriented with the c-axis perpendicular to the substrate and a-b axis epitaxy is seen from x-ray φ- scans. The best films have a resistively measured Tc of 115K and a magnetically derived Jc of 6×105 A/cm2 (77K, 0 T). Preliminary surface resistance measurements, using parallel plate techniques, give Rs = 0.35 mΩ at 5K (ω = 10 GHz).
MOCVD of Group III Chalcogenide Compound Semiconductors
Authors: Barron Andrew R.
Published: March 2011

A review is presented of recent advances in the metal-organic chemical vapor deposition (MOCVD) of thin films of group III-chalcogenides. The deposition of thermodynamic phases of composition ME and M2E3 (M = Ga, In; E = S, Se. Te) will be presented. Also included is a discussion of the development of molecular control over the structure of deposited films and the atmospheric pressure MOCVD growth of the high pressure phase of InS and a meta-stable cubic phase of GaS.
Nucleus of Spheroidal Graphite in Cast Iron
Authors: Kusakawa Takaji , Ogame Akito , Xu Xingcheng , Lin Hanton
Published: March 2011

The Spheroidal Graphites in cast iron and Ni-C alloy are extracted by using chloric acid or aqua regia and clean up using hydro-fluoric acid and hot water. The spheroidal graphite is crushed down till under five micron thickness wrapped by aluminium foil. The nucleus of spheroidal graphite can be observed by electron probe micro-analyser. Magnesium, Calcium, Cerium, Oxygen, Sulphur and Silicon etc. are recognized in the nucleus of spheroidal graphite.
On the Problems with Carbide Formation in Gray Cast Iron
Authors: Gundlach R. B. , Janowak J. F. , Bechet S. , Rohrigtt K.
Published: March 2011

Gray iron technology has advanced greatly in the past half century. Much has been learned about the mechanisms of nucleation and solidification and about solid state transformations. This information has alloweu gray iron castings to remain competitive for structural components. Low cost and excellent castability make them versatile for a wide variety of industrial components including engine blocks, cylinder heads, housings, manifolds, hydraulic valve bodies and many other castings of similar complexity. Gray cast iron provides the technical advantages of high strength, soundness, good machinability, dimensional stability and uniformity of properties usually required by such cast components. Achieving these characteristics is dependent, however, on achieving proper and uniform structures tnrougnout all sections of the casting. This objective is reaoily attainable in judiciously alloyed gray cast iron.
Computer Simulation of the Structure Formed During Solidification of Cast Iron
Authors: Fredriksson Hasse , Svensson Ingvar L.
Published: March 2011

By combining heat extraction laws with kinetic growth laws, the solidification process of nodular, grey and white cast iron have been calculated. The risk for formation of white structure during solidification of grey and nodular cast iron was calculated. The calculations was done for different thickness of the casting as well as, as a function of the number of growing units. The fraction of white structure was also calculated.
Effect of Minor Additives on First Stage Graphitisation in White Cast Iron
Authors: Roy P. L. , Chakrabart A. K. , Banerjee P.
Published: March 2011

Minor additions (0.05-0.2 wt.%) of sodium chloride, hexachloroethane and elemental sulphur to commercial white iron melts have been found to enhance the kinetics of first stage graphitisation during subsequent annealing of white iron samples. The optimum dose of sodium chloride and hexachloroethane addition is around 0.1%. Yield strength and ductility of annealed test bars treated with NaCl or C2Cl6 compare favourably with those of untreated test bars. Sulphur treatment causes slight deterioration in mechanical properties. Fully grown nodules in both treated and untreated samples appear porous under SEM. Possible mechanisms of acceleration of graphitisation in the treated samples have been suggested.
Effect of Twin/Tilt on the Growth of Graphite
Authors: Peiyue Zhu , Rozeng Sha , Yanxiang Li
Published: March 2011

The effect of twin/tilt initiated in the process of graphite growth making the graphite curling and change from flake to vermicular and spheroidal is discussed. With the developing of the solidification process,the modifying elements enrich in the front of solid-liquid interface, the amount of twin defects in the graphite increases,its tilt fashion changes and the graphite formed varies from flake to vermicular and spheroidal. The modifying elements promote the formation of twin/tilt. When the modifying elements are insufficient for spheroidizing,the tilt orientation of twins is changeable,and the graphite formed is twisted. When the modifying elements are sufficient enough, the tilt orientation of twins becomes singular, and the graphite formed tends to be round. According to the energy and kinetics consideration of the formation of twin/tilt boundary, it is predicted that the twin plane would firstly adopt (10Tm), especially the (10T2) plane. This result coincides well with the experimental observations. It is proposed that the formation of SG can be divided into two steps: growth of graphite nucleus into spherulite by twin/tilt mechanism and brancing on it in a spiral mode.
The Effect of Alloying Elements on the Bainiite Transformation in Ductile Iron
Authors: Stenfors Sven-Eric
Published: March 2011

The formation of retained austenite in nodular cast iron by austenitizing and heat treating at 450 or 350 C has been studied by X-ray measurements and metallographic examination. It has thus been related to the detailed mechanism of the bainite transformation.

The effects of the addition of a few tenths of a percent of Mn, Cr and Mo were examined and the effect of higher contents was estimated from literature data. Already small additions increase the maximum amount of retained austenite but larger additions are needed in order to increase the time for complete transformation substantially.

A small addition of Sn which has a strong effect on the transformation to pearlite had no effect on the transformation to bainite.
Cast Iron Structures Produced by Laser Surface Melting and Alloying
Authors: Hawkes I. , Lundberg L. , Walker A. M. , Steen W. M. , West D. R. F.
Published: March 2011

Laser surface melting and alloying provide a flexible route for modifying surface structures and properties. Potential technological benefits include improvement of properties such as resistance to corrosion and wear. The technique can also be used to obtain basic structural information for materials solidified over a range of rapid solidification rates. Laser surface melting of cast irons has been quite widely investigated [e.g. 1–4] using various initial structural states, including flake and spheroidal graphite irons; substantial surface hardening has been achieved from the white iron structures resulting from the rapid solidification. In the field of laser surface alloying a number of investigations have used ferrous substrates [5–9].