bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pressure-Induced Amorphization and Disordering on Cooling in Semi-Crystalline Polymers; calorimetrie evidence for inverse melting in one component system
Authors: Rastogi S. , Höhne G. , Keller A. 
Published: April 2011

ABSTRACTWe report some unusual phase behaviour, of general implication for condensed matter, on the polymer poly-4-methyl pentene-1 (P4MP1) induced by changes in pressure (P) and temperature (T), as observed by in-situ X-ray diffraction and high pressure DSC. Upon increasing pressure beyond a threshold value, the polymer, crystalline at ambient conditions, looses its crystalline order isothermally. The process is reversible. This behaviour is observed in two widely separated temperature regions, one below the glass transition temperature (< 50°C) and one close to the melting temperature (250°C), thus showing solid state amorphization and inversion in the melting temperature with increasing pressure. This further suggests inverse melting, i.e. re-entrant of the two widely separated liquid and amorphous phases along the T-axis at fixed P. This is confirmed experimentally as disordering in the crystalline structure on cooling. The inverse melting in P4MP1 raises the possibility of exothermic melting and endothermic crystallization as anticipated by Tammann (1903). The anticipated exothermic melting and endothermic crystallization is confirmed experimentally in the one component system P4MP1. We are observing similar features in a range of polymers.
Nanocomposite particles for the preparation of advanced nanomaterials
Authors: Somasundaran P. , Chen T. 
Published: April 2011

ABSTRACTNew composites based on nano-size particles provide a promising route to the fabrication of novel materials for advanced technology applications. To produce desired materials, it is important to control the composition and distribution of nanoclusters within the bulk or surface coating of nanostructured materials. Towards this purpose, we have developed a novel method of processing nanocomposite materials utilizing colloidal chemistry techniques to tailor their microstructure. Unique composite aggregates of nanoparticles with a core-shell structure were prepared using a special scheme ofcontrolledpolymer adsorption. Polymers which specifically adsorb on both nano- and micron- size particles are used as tethers to enable desired coating of the later particles with the former and to enhance the cluster integrity. Nanocomposite particles consisting of micron-size alumina or silicon nitride as cores and nano-size alumina, titania, or iron oxide as shell particles have been successfully prepared using this process. The surface charge of the core particles is reversed after the adsorption of polyacrylic acid polymers. This promotes the interaction between the core and the shell particles and therefore nanoparticles added subsequently to the core particle suspension coat on core particles by electrostatic as well as possibly hydrogen bonding bridging mechanisms. Success of the process depends to a large extent on the absence of homoflocculation of nanoparticles and this is achieved by removing all the unadsorbed free polymers from the bulk solution before introducing them to coat on the polymer coated core particles. Coating itself is estimated by monitoring change in the zeta potential of core-shell structure. The coating scheme as well as the characterization of these nanocomposite particles are discussed in detail. This processing scheme provides a simple way for the preparation of both bulk and surface coatings with these engineered nanostructured particles as building blocks.
Nanostructured zinc sulphide phosphors
Authors: Vacassy R. , Scholz S. M. , Dutta J. , Hofmann H. , Plummer C. J. G. , Carrot G. , Hilborn J. , Akinc M. 
Published: April 2011

ABSTRACTZinc sulphide (ZnS) particles are efficient phosphors for application in flat-panel displays. Spherical ZnS particles were prepared by precipitation from a homogeneous solution. Nanoparticles of 20 to 40 nm having a very narrow size distribution could be synthesized by using complexing chelates such as acetate and acetylacetonate. Complexing of the precipitating cation with the anions present in the system lead to a limited concentration of free cations in the solution. This strongly influences the kinetics of the primary particle agglomeration/growth, resulting in nanometer-sized ZnS particles. Nanostructured ZnS synthesized in this way are polycrystalline particles composed of crystallites of 5–10 nm. The synthesis of very small, non-agglomerated, nanocrystalline particles in the 5–10 nm size range was also possible, making use of a strong complexing ligand (thioglycerol) during the synthesis. The synthesis of controlled monosized ZnS particles will be presented and discussed. The photoluminescence characteristics of ZnS make this material a suitable candidate as phosphor for application in low voltage display technology. The effect of Mn2+ doping on the luminescence characteristics of ZnS will also be discussed.
Tin Dioxide Nano-Powders for Gas Sensor Applications
Authors: Vacassy R. , Houriet R. , Plummer C. J. G. , Dutta J. , Hofmann H. 
Published: April 2011

ABSTRACTSnO2 nanoparticles are of interest for gas sensor applications because the surface area is much larger compared to conventional powders. Thus, interactions between the material and the gases, which occur on the surface sites of the particles, are increased considerably. The preparation of SnO2 powders has been investigated following two forced precipitation systems: the hydrolysis reaction of SnC14 in an emulsion media and the hydrolysis reaction of Sn2+ in the presence of a complexing ligand (CH3COO−). Spherical nanoparticles in the 10 to 100 nm range and with a narrow size distribution were synthesized by both precipitating routes. In both cases, it has been demonstrated that the most important parameter which controlled the particle size was the nature of the associated anion. When this associated anion or ligand is able to form a strong complex with the colloidal subunits, a barrier against Van der Waals attraction is created which results in little growth. This greatly influences the agglomeration/growth kinetics during the precipitation. The effect of acetate chelating ligands which resulted in the SnO2 nano-powders formed of 5–10 nm crystallites will be presented and discussed. Preliminary results on the gas (N2, NO) adsorption studies on pellets formed from these powders are also presented.
Magnetically assisted impaction coating process to synthesize engineered particulates with controlled surface characteristics
Authors: Ata Ali , Rabinovich Ya. I. , Singh R. K. , Hendrickson W. 
Published: April 2011

ABSTRACTA novel dry coating technique called magnetically assisted impaction coating (MAIC) to synthesize engineered particulates with controlled surface coatings has been developed. In this method, the impaction of magnetic particles, core particles and secondary particles results in dry coating on the surface of the core particle. The attachment of particles to surfaces and factors affecting the efficiency of the process have been discussed.
RDF Analysis of Ion-Amorphized SiO2 and SiC from Electron Diffraction using Post-Specimen Scanning in the Field-Emission Scanning Transmission Electron Microscope
Authors: Bell David C. , Garratt-Reed Anthony J. , Hobbst Linn W. 
Published: April 2011

ABSTRACTRadial density functions (RDFs) provide important information about short- and ntermediaterange structure of topologically-disordered materials such as glasses and irradiation-amorphized materials. We have determined RDFs for irradiation-amorphized SiO2, AIPO4 and SiC by energy-filtered electron diffraction methods in a field-emission scanning transmission electron microscope (FEG-STEM) equipped with a digital parallel-detection electron energy-loss spectrometer. Post-specimen rocking was used to minimize the effects of spherical aberration in the objective lens, which interfere with the acquisition of data collected by pre-specimen rocking. Useful energy-filtered data has been collected beyond an angular range defined by q = 2 sin(Θ/2)/λ = 25 nm−1
Preparation of Hard Coatings on Polycarbonate Substrate by High Frequency Ion Beam, Deposition using CH4/H2 Gases
Authors: Kim S. R. , Song J. S. , Choi Y. J. , Kim J. H. 
Published: April 2011

ABSTRACTPolycarbonate is one of the most widely used engineering plastics because of its transparency and high impact strength. The poor wear and scratch properties of polycarbonate have limited its application in many fields. In order to improve the wear and scratch properties of polycarbonate we have deposited diamond like carbon (DLC) coatings. The diamond like carbon coatings were made using a high frequency ion beam gun by introducing H2 and CH4 gases. The coatings were characterized with scanning electron microscope, Raman spectroscopy, ellipsometer, and microscratch tester. Polymer hard coating was applied onto the polycarbonate substrate before depositing a diamond like carbon coating to see the effect of interlayer on the system's failure mechanism.
The Optical Properties of ION Implanted Silica
Authors: Smith C. C. , Ila D. , Williams E. K. , Poker D. B. , Hensley D. K. 
Published: April 2011

ABSTRACTWe present the results of our investigation of the change in the optical properties of silica, "suprasil", after keV through MeV implantation of copper, tin, silver and gold and after annealing. Suprasil, name brand of silica glass produced by Hereaus Amersil, which is chemically highly pure with well known optical properties. Both linear and nonlinear optical properties of the implanted silica were investigated before and after thermal annealing. All implants showed strong optical absorption bands in agreement with Mie theory. For implants with a measurable optical absorption band we used Doyle's theory and the full width half maximum of the absorption band to calculate the predicted size of the formed nanoclusters at various heat treatment temperatures. These results are compared with those obtained from direct observation using transmission electron microscopic techniques.
High Quality in.Ga1−xas Heterostructures Grown on GaAs With Movpe
Authors: Bulsara M.T. , Fitzgerald E.A. 
Published: April 2011

AbstractInxGa1−xAs structures with compositionally graded buffers were grown by metal-organic vapor phase epitaxy (MOVPE) on GaAs substrates and characterized with plan-view and cross-sectional transmission electron microscopy (PV-TEM and X-TEM), atomic force microscopy (AFM), and x-ray diffraction (XRD). The results show that surface roughness experiences a maximum at growth temperatures where phase separation occurs in InxGa1−xAs. The strain energy due misfit dislocations in the graded buffer indirectly influences phase separation. At growth temperatures above and below this temperature, the surface roughness is decreased significantly; however, only growth temperatures above this regime ensure nearly complete relaxed graded buffers with the most uniform composition caps. With the optimum growth temperature for grading InxGa1−xAs determined to be 700°C, it was possible to produce In0.33Ga0.67As diode structures on GaAs with threading dislocation densities < 8.5 × 106/cm2
Recent Progress in Crystal Growth and Conductivity Control of Wide Bandgap Group III Nitride Semiconductors
Authors: Akasaki I. 
Published: April 2011

AbstractRecent progress in crystal growth of wide bandgap group III nitrides on highly-mismatched substrates has enabled us to produce high-quality GaN, A1GaN, GaInN and quantum well structures. High-performance blue and green light-emitting diodes and room temperature operation of nitride-based laser diodes have also been realized. Today, steady progress is being made in the areas of crystal growth and device performance. However, much further advances are required in many areas of materials science and device fabrication of the nitrides
Theoretical Analysis of the Minority Carrier Lifetime in a Multicrystalline Wafer with Spatially Varying Defect Distribution
Authors: Sopori Bhushan , Chen Wei , Ravindra N. M. 
Published: April 2011

AbstractMulticrystalline Si (mc-Si) wafers, used for the commercial solar cell fabrication, have spatial nonuniformities in the material properties that cause strong variations in the minority carrier lifetime, τ. We present the results of two-dimensional modeling to show carrier generation, recombination and transport in such a material. These results are used to infer measurement conditions that can yield meaningful spatially weighted average value of τ.
Electrical Properties of Iron-Related Defects in Cz- And Fz-Grown N-Type Silicon
Authors: Kitagawa Hajime , Tanaka Shuji 
Published: April 2011

AbstractElectrical properties of iron-related defects (IRD) introduced in n-type floating zoned (FZ) and Czochralski (CZ)-grown silicon are studied by deep level transient spectroscopy and Hall effect. Electrically active IRD have been observed for the first time in n-type CZ silicon. Enthalpy and entropy factors of electron emission rate of IRD are equivalent between those observed in CZ and FZ silicon. In-diffusion process at 1160° and isothermal annealing process at 150° also indicate the identical nature of IRD between CZ and FZ silicon, which can be understood in terms of the consecutive progress of iron-related complex-formation reactions including interstitial iron atoms (Fei) in the silicon crystal. The IRD is independent of oxygen and phosphorus atoms. Only a small fraction of Fei forms electrically ionizable complexes
The transformations of the EL6 deep level defect in n-GaAs: Is EL6 a DX-like center?
Authors: Reddy C.V. , Fung S. , Beling C.D. 
Published: April 2011

AbstractBased on the charge redistribution effect, as observed by the present authors, and the earlier reported large lattice relaxation and persistent photoconductivity phenomena associated with the EL6 defect seen in doped, undoped, semiinsulating(SI) and low temperature grown GaAs LT-GaAs), it is suggested that this defect be classified as a DX-center. A tentative unified atomic model is proposed for all the native defects EL2, EL3, EL5, and EL6 observed in GaAs.
Baseline Particle Reduction of Downstream Oxide Etchers Etching Contacts and Vias
Authors: Williams Bradley 
Published: April 2011

AbstractIn the process of etching contact and via openings with a downstream oxide etcher, plasma etch byproducts form polymer that collects on process chamber components. Polymer build up over time will begin to separate from chamber components and deposit on the wafer, blocking the etch and creating incomplete contact and via openings, which result in device failure. When this phenomena occurs, complete disassembling and cleaning of the chamber (wet clean) is required before particle levels are acceptable again for processing wafers. Over half of the time wet cleans are performed at or before 1500 wafers processed.Experimentation was performed to isolate one particular chamber component causing particle deposition on the wafer. Once a chamber component was isolated, possible solutions were designed so that original process parameters were not altered. The first experiment was a maintenance procedure to disassemble and clean one chamber component at set intervals between wet cleans. The second was a no wafer, high concentration Oxygen plasma chamber clean.It was found that changing a particular chamber component after 1250 wafers processed, and then again after 2500 wafers, made it possible to run to 3750 wafers before performing a wet clean. Overall particle levels were also reduced by 30% with the plasma cleans after every 100 wafers processed. The combined solutions resulted in a greater than 30% reduction in overall particle counts. Also, maintenance down time for particle failures was reduced from 57% to 19%. During the time frame of implementation of these solutions, overall factory defectivity of finished product wafers was reduced up to 25%, which relates to a 15 to 25% yield increase. The reduction of defects on the downstream oxide etcher is a contributing factor to device yield improvements.
Behavior of Electron Traps Induced by Phosphidization and Nitridation of GaAs Surfaces
Authors: Nozu Satoshi , Matsuda Koichiro , Sugino Takashi 
Published: April 2011

AbstractGaAs is treated with remote PH3 and N2 plasmas. Electron traps induced by plasma treatments are investigated by isothermal capacitance transient spectroscopy measurements. The EL2 trap is detected in the as-grown GaAs. The TP1 trap(Ec-0.26eV) is generated in GaAs phosphidized for 10min, while the TN1 trap(Ec-0.66eV) is induced in GaAs nitrided for 30min. It is found that the TP1 trap is changed to the another trap with an energy level as shallow as 0.16eV below the conduction band edge and a capture cross section as small as 1.8×10−21cm2 by treating with N2 plasma subsequently after PH3 plasma treatment.
Carbon Doping into GaAs Using Low-Energy Hydrocarbon Ions
Authors: Sanpei Hirokazu , Shima Takayuki , Makita Yunosuke , Kimura Shinji , Fukuzawa Yasuhiro , Nakamura Yo-ichi , Sandhu Adarsh 
Published: April 2011

AbstractThe role of hydrogen (H) in carbon (C)-doped GaAs was examined by co-doping of C and H atoms using low-energy hydrocarbon (CH+ and CH3+) ions. Experiments were carried out using the combined ion beam and molecular beam epitaxy (CIBMBE) system. Samples were characterized by low-temperature photoluminescence at 2K and Hall effect measurements at room temperature. Results show that incorporated C atoms are optically and electrically activated as acceptors even by hydrocarbon ion impingement. The effect of H incorporation was found to be noticeable when impinged current density of CH3+ ion beam is high that produces equivalent net hole carrier concentration greater than ∼1018 cm−3
Underflow Process for Direct-Chip-Attachment Packaging
Authors: Li P. C. , Lehmann G. L. , Cascio J. , Driscoll T. , Huang Y. J. , Cotts E. J. 
Published: April 2011

ABSTRACTIn flip-chip packaging an underfill mixture is placed into the chip-to-substrate standoff created by the array of solder bumps, using a capillary flow process. The flow behavior is a complex function of the mixture properties, the wetting properties, and the flow geometry. This paper reports on the use of a plane channel capillary flow to characterize underfill materials. The measured flow behavior provides evidence that both the contact angle (θ) and the suspension viscosity (μapp) vary with time under the Influence of changing flow conditions. This nonlinear fluid behavior is modeled for the flow of both model suspensions and commercial underfill materials using an extended Washburn model.
Effect of Humidity on Charge Profiles and Thermal Properties of 1.7 μM Polyimide Films on Silicon Substrates
Authors: Bloss P. , Reggi A. S. De , Schafer H. 
Published: April 2011

ABSTRACTUsing an improved version of the thermal pulse (TP) method for determining electric field profiles and thermal parameters, we have obtained for the first time field profiles in 1.7 μm thick polyimide (PI) films spin-coated on Si wafers. As-coated films were found to have an internal field caused by negative charges within 200 nm of the free (pulsed) surface believed due to electrochemical reactions involving water. The change near the pulsed surface was stable up to 200 °C and would not be switched by applied fields of ±1 V/μm. The charge distribution and the thermal parameters were found to be sensitive to humidity
Direct Measurements of Thermal Stress Distributions in Large Die Bonds for Power Electronics
Authors: He Jun , Shaw M. C. , Sridhar N. , Cox B. N. , Clarke D. R. 
Published: April 2011

ABSTRACTLarge semiconductor devices can be subject to significant mechanical stress resulting from thermal expansion mismatch between the devices and packaging materials. This stress can either cause mechanical failure or change the operational characteristics of the device. Furthermore, this stress governs the reliability of the system during use. Therefore, a complete understanding is required of the nature of stress evolution during packaging, and its time and temperature dependence during subsequent service. In the present investigation, the absolute magnitudes and spatial distributions of time-dependent thermal residual stress are measured directly by piezospectroscopic techniques. These measurements are performed with high stress (±15 MPa) and spatial (1 μm) resolution in silicon specimens attached to substrates. Measurements are performed at room temperature on 25 mm square specimens, with continuous, layered solder joints in model specimens of silicon/solder/copper. Room temperature creep relaxation is also investigated. The stress data are then analyzed according to fundamental micromechanical models.
Determination of Critical Volumes in Recording Media
Authors: O'Grady K. , Dova P. , Laidler H. 
Published: April 2011

AbstractIn this overview paper the concept of thermal activation of magnetisation reversal is reviewed in terms of the Wohlfarth-Gaunt formalism. This formalism gave rise to the concept of an activation volume of reversal. Other techniques have been developed for the determination of activation or critical volumes of reversal and these are reviewed. It is found that these methods give the same approximate value for the activation volume but the only method based on micromagnetism is the waiting time experiment which is consistent with Gaunt. Factors which affect the activation volume such as incoherent reversal and intergranular coupling are discussed together with measures that may be required in order to generate ultrahigh density recording media that are relatively free from thermal loss of signal.
Structure and Magnetic Properties of Co, Ni, Mn, Cr and Cu Substituted Magnetites
Authors: Sorescu M. , Mihaila-Tarabasanu D. , Diamandescu L. 
Published: April 2011

AbstractCo, Ni, Mn, Cr and Cu substituted magnetites were prepared by the hydrothermal method at 300°C, with concentrations x ranging from 8.2 to 12.5%. Transmission electron microscopy determined the average particle diameter <Φ> to be in the hundred of nm range and the morphological modifications induced by the various substitutions employed. Hysteresis loop measurements were performed to determine the coercive field Hc and saturation magnetic moment ms. While Hc decreased with increasing <Φ>, the particle shape was found to play an important role in explaining the dependence of ms on <Φ>. Transmission Mössbauer spectroscopy was used to determine the site preference of the substitutions and their effect on the hyperfine magnetic fields. The room temperature Mossbauer spectra were analyzed assuming a random distribution of substitutents using the binomial distribution from the ionic crystal point of view. Superparamagnetic particles were observed at room temperature in the case of Cu and Cr substituted magnetites.
A Method for Laser Zone Texturing of Glass Based Magnetic Media Using Nd:Yag Lasers
Authors: Rosenblum M. P. , Ross C. A. 
Published: April 2011

AbstractLaser zone texturing of nickel-plated, aluminum based magnetic media has become a preferred method of providing a precisely controlled head landing zone. The Nd:YAG lasers used for this process are not suitable for directly texturing glass substrates. A novel method has been developed which allows the use of the existing Nd:YAG laser systems to zone texture glass based magnetic media.An amorphous sputtered film of a non-magnetic Ni alloy provides a texturing layer which absorbs the laser pulse and controllably forms regular, small protrusions. Optimization of the alloy composition results in small cone-shaped bumps. Laser power sensitivity exhibits a region of invariance for a range of film thickness. This behavior provides a wide margin for manufacture by reducing the effect of thickness variation on laser bump height.Disks fabricated using this form of laser zone texture exhibit excellent tribology performance. TEM images show the Ni alloy to be amorphous and featureless. The sputtered film does not influence the properties of the subsequently sputter deposited isotropic magnetic films.