bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoconductivity of Diamond-Like Carbon
Authors: Hie A. , Conway N. , Kleinsorge B. , Rattier M. , Robertson J. , Milne W. I.
Published: April 2011

We have studied the photoconductivity in pure tetrahedral amorphous carbon (ta-C) and hydrogenated tetrahedral amorphous carbon (ta-C:H). Good photoconductive properties are demonstrated for ta-C:H, showing that the hydrogenated form of ta-C is of a higher electronic quality. Transport and recombination parameters are derived. Ta-C:H are low mobility solids with a μτ product of the order of 10−12 cm2 V−1 and a recombination time τr of about 10−7 s. At low energy excitation, the photoconductivity shows a sublinear dependence on the light intensity over a wide temperature range. The relationship between the photoconductivity and the density of spin defect centers is discussed. UV light is used to excite carriers into the extended states. Competitive recombination centers may be involved at high excitation energy.
Optical & Electronic Properties of Carbon Nitride Thin Films
Authors: Chhowalla M. , Aharonov R. A. , Akiyama M. , Amaratunga G. A. J.
Published: April 2011

We have deposited carbon nitride (CNx) films by magnetron sputtering at varying nitrogen pressures and substrate temperatures. The films were deposited on silicon and quartz substrates simultaneously. The incoming ion energy was controlled by a radio frequency power supply. A magnet in front of the substrate holder was used to enhance the plasma density. The films deposited at room temperature (RT) were found to have nitrogen content of ≥ 40%. These films were semiconducting with an optical bandgap of greater than 2 eV and a RT resistivity of 1012 Ω-cm. Films deposited at low nitrogen pressure (< 7 mtorr), at RT and in the presence of a 15 mtesla magnetic field were found to be hard and also exhibited extremely high elastic recovery. The most interesting result we found was that the hard and elastic CN films were also semiconducting with an optical band gap of 1.7 eV, RT resistivity of 107 Ω-cm and an activation energy of 0.8 eV. In all cases the CN films were almost entirely sp2 bonded.
Ab Initio Investigation of the High Pressure Elasticity of Mg2SiO4 Forsterite and Ringwoodite
Authors: Stixrude Lars , Wentzcovitch R. M. , Da Silva C. , Kiefer B.
Published: April 2011

We discuss the behavior of two minerals of the same composition, Mg2SiO4 but different structures: forsterite and ringwoodite. Ab initio plane-wave pseudopotential results are discussed in terms of the full elastic constant tensors of these phases and their elastic anisotropy. The structures of the two minerals, based on pseudo-hep and pseudo-fee packing of oxygens, respectively, show very different behavior at high pressure. While the elastic anisotropy of olivine depends weakly on pressure between 0 and 25 GPa, the anisotropy of ringwoodite decreases with pressure initially, vanishing at 17 GPa before increasing again at higher pressure. This unusual behavior is understood in terms of a change of sign of the combination of elastic constants c2+2c44-c11, and a resulting interchange of fast and slow directions of acoustic wave propagation. To gain insight into the origin of their elastic behavior, the ab initio results are compared with a simple model based on the O sub-lattice.
Phase Transition in Ar(H2)2: Its Relation to Hydrogen Metallization Under Pressure
Authors: Bernard S. , Loubeyre P. , Zerah G.
Published: April 2011

In the general framework of high pressure Hydrogen studies[l][2], it has been recently suggested[3] that hydrogen could metallize at much lower pressures, within experimentally accessible values, in a new compound, Ar(H2)2. Subsequent Raman measurements showed a transition around Pobs=175 GPa, but have not been interpreted satisfactorily up to now. Moreover, the experimental situation is quite confusing. Infra-red measurements on Ar(H2)2 up to 220 GPa[4] did not confirm the Raman results. We have thus carefully investigated the physical properties of Ar(H2)2 in the multimegabar range, especially as the experiments are difficult, and the diagnostics can suffer from spurious effects (such as the influence of the uniaxial component of pressure on the transition) [5].
Growth of Diamond Anvils for High-Pressure Research by Chemical Vapor Deposition
Authors: Israel Andrew , Vohra Yogesh K.
Published: April 2011

Gem quality diamond crystals are employed as anvils in high-pressure diamond cell research. Homoepitaxial growth experiments by microwave plasma-assisted chemical vapor deposition (MPCVD) have produced 1.76 mm (diameter) by 0.65 mm (thickness) sized diamonds. We report fundamental studies on diamond growth rate and quality as a function of reactor pressure and methane concentration, in a hydrogen plasma. By varying the growth conditions, large, single crystal diamond can be produced, which is ideal for manufacturing high pressure anvils.

Traditional high pressure, high temperature (HPHT) techniques for production of synthetic diamond anvils are extremely expensive and chemical vapor deposition (CVD) provides an economically viable alternative. We report diamond growth rates up to 0.32 mg/hr, which are comparable to HPHT growth rates, and crystal quality approaching that of gem diamond. When perfected, diamond anvils produced from chemical vapor deposition methods could replace those manufactured by high pressure, high temperature synthesis.
Use of Hardness Indentation Coupled with Micro-Raman Spectroscopy in High-Pressure Materials Research
Authors: Kailer A. , Gogotsi Y. G. , Nickel K. G.
Published: April 2011

High-pressure phase transformations occurring in materials are important for a wide range of problems in materials science and engineering. Most of the results in this field have been obtained using high-pressure cells.

In this work, we demonstrate that high-pressure phase transformations also take place during mechanical contact of hard solid materials. These solid-state transformations can be studied by simply combining hardness indentation tests with micro-Raman spectroscopy. In contrast to diamond anvil cell (DAC) experiments, the stress conditions during mechanical contacts are highly non-hydrostatic, i.e. very high shear stresses affect the transformation behavior. Nevertheless, the obtained results can be discussed in the light of the phase transformations as known from DAC experiments. The examples of our research presented here include Si, Ge, SiO2 and ZrO2, and show that phase transformations and amorphization at mechanical contacts are a quite common phenomenon, which has important implications.
A New Pressure Induced Phase in Silica
Authors: Chelikowsky J. R. , Wentzcovitch R. M. , Da Silva C. , Binggeli N.
Published: April 2011

We predict a new pressure induced phase for silica via first principles variable-cell-shape molecular dynamics. The structure results from annealing a-quartz at pressures near a phonon instability. The mechanism which produces this new phase is similar to that proposed for structural transitions in silicate melts. The diffraction pattern of the new phase compares favorably with that of the unidentified intermediate crystal phase found in silica near the pressure induced amorphization transformation.
Image Plate X-Ray Diffraction Study of Distorted FCC Phase in Rare Earth Metals at High Pressures
Authors: Beaver Steven , Chesnut Gary N. , Vohra Yogesh K.
Published: April 2011

A high-pressure phase of gadolinium is completely described for the first time. This phase, HR24, is found to exist at 46 GPa. The structure is examined for evidence of delocalization of the f shell, and the evolution of the HR24 phase with increasing pressure is discussed.
Shock-Induced Defects in Bulk Materials
Authors: Gray George T.
Published: April 2011

In this paper examples of the shock-induced defects produced during shock compression which correlate with microstructure / mechanical property changes induced in materials due to shock prestraining are discussed. The characteristics of the shock impulse(peak shock pressure, pulse duration, and rarefaction rate) imparted to the material under investigation and the shock-induced defects produced in numerous metals and alloys are compared with their deformation behavior at ordinary rates of deformation. Examples of the range of defects observed in shock-recovered metals and alloys, include: dislocations, deformation twins, point defects, and residual metastable remnants from pressure-induced phase transformations. Results concerning the influence of interstitial content on the propensity of ω-phase formation and its structure in high-purity and A-70 Ti are presented. The influence of shock-wave deformation on the phase stability and substructure evolution of high-purity (low-interstitial) titanium and A-70 (3700 ppm oxygen) titanium were probed utilizing real-time velocity interferometry (VISAR) and “soft” shock-recovery techniques. Suppression of the α-ω pressure-induced phase transformation in A-70 Ti, containing a high interstitial oxygen content, is seen to simultaneously correspond with the suppression of deformation twinning.
Dispersion and Lorentz Microscopy of Samarium Cobalt Nanoparticles in a Polymer Matrix
Authors: Jin Yan , Majetich Sara A. , Giri Anit
Published: April 2011

A new method for dispersing magnetic nanoparticles in a polymer matrix is described. SmCo5 nanoparticle powders are first prepared by ball milling, and then embedded in thermoplastic powder by further milling. The nanoparticle-embedded thermoplastic powder was compacted to form solid magnetic composites which were characterized by transmission electron microscopy (TEM) and by SQUID magnetometry. The conventional TEM measurements on microtomed sections of the composites showed spherical nanoparticles clearly separated from their nearest neighbors, thereby eliminating exchange interactions and greatly reducing magnetostatic interactions. Lorentz microscopy illustrated the potential for imaging single particles and determining the magnetization directions of isolated and interacting particles. Magnetic measurements on dilute samples show that the processing method does not degrade the magnetic properties of the particles.
Surface enhanced Raman Active Nanoparticles in Plasma Treated Silver surfaces
Authors: Compagnini G. , Pelligra B. , Pignataro B.
Published: April 2011

A plasma oxidation-reduction process has been found to be suitable to produce silver surfaces showing Surface Enhanced Raman (SER) activity. SER spectra of monodisperse polystyrene films and of other smaller molecules like alkanethiole, have been obtained in order to study the correlation between enhancement and nanomorphology as probed by Atomic Force Microscopy. It was found that the enhancement is strongly correlated with a coalescence of the initially present silver grains (10–50 nm in size). This coalescence leads to the formation of 100–300 nm silver hills in which each silver grain is still clearly distinguishable. The increase of the effective surface area due to the particle coalescence has been correlated to the SERS enhancement in straightforward fashion while self assembled alkanethiole monolayers have been used as spacer for electromagnetic SERS enhancement of polystyrene.
Preparation and characterization of concentric-tubular composite microstructures using the template synthesis method
Authors: Cepak Veronica M. , Martin Charles R.
Published: April 2011

The template method has been used to prepare concentric-tubular composite microstructures. These composite structures consist of an outer tubule composed of one material encapsulating concentric inner tubules composed of other materials. Tubular composites of this type consisting of metals, semiconductors, polymers, and Li-ion intercalation materials have been prepared. The chemical strategies used to prepared these composite structures include electroless plating of Au, electropolymerization of electronically conductive and insulating polymers, electrodeposition of metals and semiconductors, and sol-gel synthesis.
Preparation and characterization of SiO2/Au nanocomposites by R.F. Sputtering
Authors: Terauchi Shinya , Umehara Hiroyuki , Koshizaki Naoto , Sasaki Takeshi
Published: April 2011

We fabricated SiO2/Au nanocomposites using alternate sputtering method. The size of the Au particles seem was unchanged by the SiO2 sputtering and well controllable by the sputtering parameters. The nanoparticles in SiO2 were observed by TEM and the nanocomposites were characterized using XPS technique. TEM observation revealed the size of Au nanoparticles to be 2–15 nm. We observed a chemical shift of the Au4f peak in the XPS study. We demonstrate the efficiency of the technique for controlling the size and quantity of nanoparticles dispersed in nanocomposites.
Modeling of strain distribution in non-hydrostatically pressed nanocrystalline sic; in-situ x-ray diffraction study
Authors: Pielaszek R. , Stel'Makh S. , Aloshina M. , Gierlotka S. , Palosz B.
Published: April 2011

Grain size and strain distribution functions of polycrystals of SiC with nanosize grains were examined based on X-ray diffraction data and ab initio calculations of scattered intensity from Debye functions. A tentative model of distribution of strain induced under high isostatic pressure in nanoparticles with different grain size is presented. Nanocrystalline SiC powders with grains down to 80Å in diameter were examined. In situ high pressure diffraction experiments were performed in cubic anvil cell MAX80 (up to 6 GPa) and in Diamond Anvil Cell (DAC) (up to 45 GPa) at HASYLAB, Hamburg, Germany. Shape of the Bragg lines was analysed with the use of two methods: (i) calculation of theoretical diffraction patterns based on modeling of one-dimensional disordering and ab initio calculation of scattered intensity starting from Debye functions and, (ii) approximation of the experimental shape of Bragg reflections by a combination of two functions: Gaussian (G) and Lorentzian (L).
Synthesis and Characterization of Antimony-Doped Tin Oxide Nanophase materials for Electrochromic Applications
Authors: Liu J. , Coleman J. P. , Madhukar P.
Published: April 2011

Antimony-doped tin oxide (ATO) nanophase materials containing up to 43 mole% antimony have been synthesized by a wet-chemistry method. These ATO materials exhibit enhanced electrochromic properties for display devices. The performance of the display devices is related to the nanostructure of the synthesized ATO materials. The average sizes of the ATO nanocrystallites depend on dopant level, annealing conditions, and synthesis processes. Antimony inhibits the growth of tin dioxide nanocrystallites during annealing at moderate temperatures. At higher annealing temperatures, however, antimony segregates to form separate oxide phases and ATO nanocrystallites grow significantly. A systematic study of the structural evolution of the synthesized ATO materials is presented and the relationship between the nanostructure of the ATO materials and the enhanced performance of the corresponding electrochromic devices is discussed.
Mechanism of Enhanced Diffusion of Aluminum in 6H-SiC in the Process of High-Temperature Ion Implantation
Authors: Usov Igor O. , Suvorova A. A. , Sokolov V. V. , Kudryavtsev Y. A. , Suvorov A. V.
Published: April 2011

The diffusion of Al in 6H-SiC during high-temperature ion implantation was studied using secondary ion mass spectrometry. A 6H-SiC wafer was implanted with 50 keV Al ions to a dose of 1.4E16 cm−2 in the high temperature range 1300°–1800TC and at room temperature. There are two diffusion regions that can be identified in the Al profiles. At high Al concentrations the gettering related peak and profile broadening are observed. At low Al concentrations, the profiles have a sharp kink and deep penetrating diffusion tails. In the first region, the diffusion coefficient is temperature independent, while in the second it exponentially increases as a function of temperature. The Al redistribution can be explained with the substitutional-interstitial diffusion mechanism.
A Model for Irradiation-Induced Amorphization
Authors: Wang S. X. , Wang L. M. , Ewing R. C.
Published: April 2011

A model based on cascade melting and recrystallization is derived to describe ion irradiation-induced amorphization. The accumulation of amorphous volume fraction during irradiation is represented in a single equation. Depending on the extent of recrystallization of a subcascade, the amorphous volume accumulation can be described by a set of curves that change from exponential to sigmoidal functions. The parameters (including temperature, cascade size, crystallization rate, glass transition temperature, dose rate) that affect the extent of recrystallization are included in the model. The model also describes the temperature dependence of critical dose for amorphization.
Magnetostriction Related Effects in Pulsed Laser Irradiation of Amorphous Magnets
Authors: Sorescu Monica , Schafer S. A.
Published: April 2011

Samples of Fe66Co18B15Si1, Fe40Ni38Mo4B18 and Fe72.6Cr22Al4.8Si0.3Y0.3 metallic glasses were irradiated with a pulsed alexandrite laser (λ=750 nm, τ=60 μs) using different laser fluences. Irradiation-induced structural and property modifications were characterized using Mössbauer spectroscopy. Complementary information was obtained from hysteresis loop measurements and scanning electron microscopy (SEM). The experimental data obtained demonstrate the key role played by the magnetostriction constant in explaining the mechanism of irradiation-induced phase transformations in amorphous magnets.
Electronic Excitation Effects on Defect Production and Radiation Annealing in Fe Irradiated at ∼80K with Energetic Particles
Authors: Chimi Y. , Iwase A. , Ishikawa N.
Published: April 2011

Defect accumulation behavior in Fe irradiated with high energy (∼100MeV) ions, low energy (∼1MeV) ions and 2MeV electrons was studied by measuring the electrical resistivity change of the specimen at ∼80K as a function of particle fluence. From the experimental results, the defect production cross-section, the defect annihilation cross-section and the damage efficiency (the ratio of the experimental defect production cross-section to the calculated one) were derived for each irradiation. By comparing the results for high energy ion-irradiations with those for low energy ion- and electron-irradiations, the dependence of defect production and radiation annealing on the electronic excitation is discussed.
Metastable Materials Formation by ion Beam Assisted Deposition: Application to M Clusters in Ceramic Matrices
Authors: Carosella C. A. , Hubler G. K. , Cotell C. M. , Schiestel S.
Published: April 2011

The collision cascade, the fundamental event in ion-solid interactions, is responsible for the beneficial effects on thin films deposited by low energy ion beam assisted deposition (IBAD) or by energetic ion assisted deposition processes in general. However, the fundamental implications of the marriage of collision cascades and film growth processes have yet to be fully realized. The first half of this paper reviews the effects of ion bombardment on film growth and reaches some new conclusions. We propose that IBAD represents a different ion-solid interaction in a fundamental sense, and that as such, it should lead to new microstructures unattainable by other materials synthesis methods.

The second part of this paper discusses the deposition of metal nanoclusters in a dielectric matrix by means of beam assisted phase separation (BAPS), a term coined here to describe deposition of phase-separated multicomponent materials. Examples discussed are gold nanoparticles in both niobium oxide and silica matrices.
Effect of Ion Energy on Structural and Chemical Properties of Tin Oxide Film in Reactive Ion-Assisted Deposition (R-Iad)
Authors: Cho Jun-Sik , Choi Won-Kook , Yoon Ki Hyun , Cho J. , Yoon Young-Soo , Jung Hyung-Jin , Koh Seok-Keun
Published: April 2011

Tin oxide films were deposited on in-situ heated Si (100)substrates using reactive ionassisted deposition and the effect of average impinging energy of oxygen ions on the crystalline structure and the stoichiometry of deposited films were examined. The transformation from SnO phase to SnO2 phase of the films was dependent on the change of the average impinging energy of oxygen ion (Ea), and the relative arrival ratio of oxygen to tin. Perfect oxidation of SnO2 was performed at Ea = 100, 125 eV/atom at as low as 400 Å substrate temperature. The composition (No/Nsn) of films increased from 1.21 to 1.89, and was closely related to the average impinging energy of oxygen ion. The surface morphology of the films was also investigated by scanning electron microscopy.
Improving the Thermal Stability of Photoresist Films by Ion Beam Irradiation
Authors: Zawislak F. C. , Garcia Irene T. S. , Samios D. , Baptista D. L. , Fichtner P. F. P. , Alves E. , Silva Maria F. Da , Soares J. C.
Published: April 2011

The thermal stability of ion irradiated 1.7 μm thick AZ-1350J photoresist films was investigated using the RBS and ERDA techniques to measure the composition of the irradiated and annealed films. The films have been irradiated with He, N and Ar ions at energies from 380 to 760 keV and fluences between 2 × 1015 and 1016 ions cm−2. A considerable increase in the thermal stability of the He irradiated film is observed from ≈200°C – when the non-irradiated film starts to decompose – to 400°C after the irradiation. The FTIR spectroscopy and the SEM observations were used to study the chemical structural changes and the surface morphology of the irradiated samples. The results are discussed in terms of the energy density deposited by the ions, the large loss of H during irradiation, and the resulting increase in cross-linking density.
Hydrogen Diffusion in Boron Doped Diamond: Evidence of Hydrogen-Boron Interactions
Authors: Chevallier J. , Theys B. , Grattepain C. , Deneuville A. , Gheeraert E.
Published: April 2011

Deuterium diffusion has been investigated in boron doped diamond as a function of the diffusion temperature and the boron concentration. The results show that, up to 480°C, hydrogen diffusion is limited by the boron concentration with a diffusion activation energy of 0.35 eV for [B] = 5×1019 cm−3. This first experimental evidence of deuterium-boron interactions in diamond is interpreted as the result of hydrogen ionization and diffusion of fairly mobile protons which form pairs with negatively charged boron acceptors
First-Principles Study of N Impurities in SiC Polytypes
Authors: Windl W. , Demkov A. A.
Published: April 2011

We investigate theoretically the energetics of nitrogen impurities in β-SiC, their geometrical relaxation, and electronic properties. We find that density-functional theory is able to calculate donor-ionization energies accurately once large enough simulation cells are used. For neutral interstitial defects, we find that configurations where N is three-fold coordinated have very low formation energies and high binding energies with the involved native defects. At the same time, such configurations introduce deep levels into the gap which may result in a non-activation of the donor
Iron and Nickel Solubilities in Heavily Doped Silicon and their Energy Levels in the Silicon Band Gap at Elevated Temperatures
Authors: McHugo S.A. , McDonald R.J. , Smith A.R. , Hurley D.L. , Istratov A.A. , Hieslmair H. , Weber E.R.
Published: April 2011

We have directly measured the solubility of iron and nickel in high and low boron-doped silicon using Instrumental Neutron Activation Analysis. Boron doping levels were 1.5×1019 and 6.5× 1014 atoms/cm3. Iron and nickel impurity concentrations were measured after extended indiffusions at 800, 900, 1000 and 1100°C for iron and 600, 700 and 800°C for nickel. We have measured a significant enhancement of Fe and Ni concentrations in high boron-doped silicon as compared to low boron-doped silicon. Based on these measurements, we show the iron donor energy level shifts towards the valence band with increased temperature, e.g. at 900°C the donor level is 0.24eV above the valence band as opposed to 0.39eV at room temperature. These results demonstrate that the impurity energy level shift with temperature must be accounted for in any prediction of segregation gettering of metal impurities into heavily doped substrates and heavily implanted doping layers. Additionally, our results suggest that either Ni solubility is greatly enhanced and/or the Ni diffusivity is greatly decreased with high boron doping of silicon.
Vacancy-Type Defects in Electron and Proton Irradiated II-VI Compounds
Authors: Brunner S. , Puff W. , Mascher P. , Balogh A.G.
Published: April 2011

In this contribution we present a study aimed at comparing results of positron-lifetime and Doppler-broadening measurements on the wide-band-gap compound semiconductors ZnS, ZnSe, and ZnTe. To investigate the basic properties of intrinsic and radiation induced defects the samples were irradiated either with 3 MeV protons or 1 MeV electrons. The isochronal annealing was performed in an Ar atmosphere. It was found that electron and proton irradiation cause different changes in the positron annihilation characteristics. Several annealing stages were observed, related to the annealing of variously sized vacancy complexes.
Characterization of the Structure and Polarity of Twin Boundaries in GaP
Authors: Cohent Dov , Medlin D.L. , Barry Carter C.
Published: April 2011

The structure of planar defects in GaP films grown by MBE on Si (110) was investigated by transmission electron microscopy. Growth of GaP films on the (110) surface produced numerous microtwins which formed both first and second order twin boundaries. Using high-resolution transmission electron microscopy, the atomic structure of Σ=3 and Σ=9 twin boundaries were studied. Both the Σ=3 and Σ=9 interfaces were observed to facet along specific crystallographic planes. Geometric models of the Σ=9 {221} twin boundary accounting for different polar bonding configurations were proposed and compared with experimental observations.
Impurity Segregation in Al Doped GaSb Studied by Cathodoluminescence Microscopy
Authors: Hidalgo P. , Mendez B. , Piqueras J. , Dutta P.S.
Published: April 2011

Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to investigate the effect of doping with an isoelectronic dopant, aluminum, on the native acceptors and on the general structure of extended defects of gallium antimonide single crystals. While there is no significant change in the native defect content, decoration of non-radiative recombination centers or extended defects occurs as a result of aluminum doping.
Electroplating of Gold-Tin Solder for Optoelectronic Applications
Authors: Sun Wenzhen , Ivey Douglas G.
Published: April 2011

Au-Sn eutectic solder is widely used in optoelectronic packaging. Electroplating of Au-Sn alloys is attracting increasing research interest because of its lower cost and potential to minimize voiding in bonding layers. The challenge in developing a non-cyanide Au-Sn electroplating bath lies in bath stability and deposit composition control. In this paper a relatively stable electroplating bath is developed based on a chloride solution using citrate as a buffering agent. Direct current plating and pulse current plating are performed and compared. The effects of Au and Sn concentrations in the bath, current density, and ON time on deposit composition and microstructures are also studied.
Fracture Behavior of Epoxy-Based, Hybrid Particulate Composites
Authors: DiBerardino M. F. , Pearson R. A.
Published: April 2011

Epoxy-based, particulate composites are commonly used in packaging applications for the microelectronics industry. For example molding compounds, die attach adhesives, and encapsulant resins are all polymer matrix, particulate-reinforced composites. The mechanical behavior of these materials is a function of the type of resin, the shape and size of the reinforcing particles, the filler content, etc. In this paper, we will examine the interactions of the toughening mechanisms between rubber particles and the reinforcing particles. Hybrid-particulate composites are prepared by compounding both rubber particles and disc-shaped boron nitride particles in a bisphenol A-based epoxy cured with piperidine. Interestingly, there are combinations of rubber and reinforcing particles that lead to synergistic toughening. The underlying causes for synergistic toughening will be discussed.
Flip Chip Metallurgies for Lead-Free Solders
Authors: Korhonen T. M. , Hong S. J. , Korhonen M. A. , LI C.-Y.
Published: April 2011

The most commonly used lead-free solders contain large amounts of tin, which makes them incompatible with the conventional Cu-based underbump metallization (UBM) schemes. The tin in the solder reacts with the copper layer of the UBM, depleting the UBM of copper and causing loss of adhesion and a weak interface. Use of new under bump metallization schemes with Ni or CuNi alloys as the solderable layer were investigated in this study. Instead of Cr, a Tibased adhesion layer was used to decrease the amount of stress in the CuNi layer. Flip chip solder joints were made in which three Sn-Bi-Ag based lead-free solders were reflowed to several UBM pads of different compositions. The resulting interfacial microstructures were examined by SEM/EDX analysis of cross-sectioned samples. The joints were also mechanically tested in fatigue and shear to assess the quality and reliability of the interface.
Modeling Complex Aftereffect Behavior in Recording Materials Using a Preisach-Arrhenius Approach
Authors: Della Torre E. , Bennett L. H. , Swartzendruber L. J.
Published: April 2011

A Preisach-Arrhenius aftereffect model, that accurately calculates the entire relaxation process, including the linear log-time region, is used to describe some other characteristics of the time decay. The location of the peak of the decay coefficient is shown to be less than the peak of the irreversible coercivity by an amount that is a function of the standard deviation of the critical field, the fluctuating field, and the moving parameter. The model computes a magnetization decay that includes nonmonotonic behavior under certain circumstances, depending upon the applied field history. A conclusion of this paper is that procedures for accelerated testing of magnetic media are suspect.
AFM Nanoindentation as a Method to Determine Microhardness of Hard Thin Films
Authors: Bao T. , Morrison P. W. , Woyczynski W.
Published: April 2011

This paper presents experimental and analytical studies of AFM nanoindentation as a method to determine microhardness of hard thin films. Indentations are performed on Au, Si, and DLC using triangular pyramidal diamond probes to determine microhardness. We examined the effects of indentation force and three different methods to measure the indentation area (direct area measurement for a triangular indentation, size analysis of an inverted AFM image of the indentation, and prediction of area from indentation depth based on a tip shape function). The responses are indentation depth, projection area, and microhardness. Relationship of responses with indentation force is examined. At a low depth range, microhardness based on pyramidal shape function is erroneously higher than the other two methods. However, all three methods generally agree with each other when indentation force exceeds 16μN. Size analysis of inverted images gives more consistent microhardness with the least variability over the whole force (4∼30μN) or depth (0.5∼70 nm) range. Tip shape models are developed to predict microhardness. The ellipsoidal tip model is a good approximation at low depth ranges, while the pyramidal model works better for deeper indentations. The force vs area curves are also significantly nonlinear which can distort the hardness measurements.
Synthesis of Nanostructured Iron Oxide(III) Powders by Rapid Expansion of Supercritical Fluid Solutions
Authors: Burukhin A.A. , Churagulov B.R. , Oleynikov N.N. , Kolen'Ko Yu.V.
Published: April 2011

Nanostructured a-Fe2O3 powders were generated by rapid expansion of supercritical fluid solutions (RESS, T=773 K, P=100 MPa) and by rapid thermal decomposition of precursors in solution ( RTDS, T=623 K, P=100 MPa) on lab RESS-setup from 0,040 M and 0,10 M aqueous solutions of Fe(NO3)3. The size of subcrystallites is about 22-29 nm. Comparison of reactivity of α-Fe2O3 powders in a model solid state reaction between a-Fe2O3 powders (generated by RESS from 0,040 M solution) and Li2CO3 (mole ratio 1:1) with literature data on a-Fe2O3 powders produced by other methods shows that its reactivity is markedly higher. A basic essence possibility of zinc ferrite ZnFe2O4 formation immediately at the stage of the rapid expansion (T=773K; P=100 MPa) of a supercritical aqueous solution of zinc and iron nitrates (molar ratio Zn:Fe=1:2; C=0. 1 M) was shown.
Compatibilization Mechanism of Polyimide-Silica Hybrids with Organofunctional Trialkoxysilanes
Authors: Menoyo J. D. C. , Mascia L. , Shaw S.J.
Published: April 2011

The polyimide hybrids that have been most widely studied by the authors contain a silica phase produced from tetraethoxysilane by the sol-gel method. Despite the expected strong interactions, through H-bonds, between the polyamic acid precursor for the polyimide and the large number of hydroxyl groups from the silica phase, it is rather difficult to prevent phase separation and rapid coarsening of the morphology upon removal of the solvent from the original solution mixture. These systems can be compatibilized, however, with the selective use of functionalized trialkoxysilane coupling agents, such as glycidyl and isocyanate types.

In the present work we have established that compatibilty is achieved only upon exceeding a critical concentration of coupling agent, which increases linearly with the total silica content up to a certain level. This was found to be connected with the ability of the coupling agent to displace the strongly associated solvent molecules with the amic acid units of the polymer chains in order to develop the required level of interactions across the interface between the organic and inorganic components.
Strain Rate Effects in Porous Materials
Authors: Lankford J. , Dannemann K. A.
Published: April 2011

The behavior of metal foams under rapid loading conditions is assessed. Dynamic loading experiments were conducted in our laboratory using a split Hopkinson pressure bar apparatus and a drop weight tester; strain rates ranged from 45 s−1 to 1200 s−1. The implications of these experiments on open-cell, porous metals, and closed- and open-cell polymer foams are described. It is shown that there are two possible strain-rate dependent contributors to the impact resistance of cellular metals: (i) elastic-plastic resistance of the cellular metal “skeleton,” and (ii) the gas pressure generated by gas flow within distorted open cells. A theoretical basis for these implications is presented.
Mechanical Properties of a Structural Polyurethane Foam and the Effect of Particulate Loading
Authors: Goods S. H. , Neuschwanger C. L. , Whinnery L. L.
Published: April 2011

The room temperature mechanical properties of a closed-cell, polyurethane encapsulant foam have been measured as a function of foam density. Tests were performed on both unfilled and filler reinforced specimens. Over the range of densities examined, the modulus of the unloaded foam could be described by a power-law relationship with respect to density. This power-law relationship could be explained in terms of the elastic compliance of the cellular structure of the foam using a simple geometric model found in the literature. The collapse stress of the foam was also found to exhibit a power-law relationship with respect to density. Additions of an aluminum powder filler increased the modulus relative to the unfilled foam.
Complex Foamed Aluminum Parts as Permanent Cores in Aluminum Castings
Authors: Simančík F. , Schoerghuber F.
Published: April 2011

The feasibility of complex shaped aluminum foam parts as permanent cores in aluminum castings has been investigated. The foamed samples were prepared by injection of the foam into sand molds. It turned out that sound castings can be produced if the foam core is properly preheated and/or surface treated before casting. The effect of the foam core on the performance of the casting was evaluated by in compression testing and by measuring structural damping. The gain in the related properties turned out to be much higher than the weight increase of the casting due to the presence of the core. The weight increase may be partially offset through a reduction of the wall-thickness of the shell.
Structural Graphitic Carbon Foams
Authors: Kearns Kristen M. , Anderson David P. , Anderson Heather J.
Published: April 2011

Graphitic carbon foams are a unique material form with very high structural and thermal properties at a light weight. A process has been developed to produce microcellular, open-celled graphitic foams. The process includes heating a mesophase pitch preform above the pitch melting temperature in a pressurized reactor. At the appropriate time, the pressure is released, the gas nucleates bubbles, and these bubbles grow forming the pitch into the foam structure. The resultant foamed pitch is then stabilized in an oxygen environment. At this point a rigid structure exists with some mechanical integrity. The foam is then carbonized to 800°C followed by a graphitization to 2700°C.

The shear action from the growing bubbles aligns the graphitic planes along the foam struts to provide the ideal structure for good mechanical properties. Some of these properties have been characterized for some of the foam materials. It is known that variations of the blowing temperature, blowing pressure and saturation time result in foams of variously sized with mostly open pores; however, the mechanism of bubble nucleation is not known. Therefore foams were blown with various gases to begin to determine the nucleation method. These gases are comprised of a variety of molecular weights as well as a range of various solubility levels. By examining the resultant structures of the foam, differences were noted to develop an explanation of the foaming mechanism.
Formation of Ordered Gas-Solid Structures VIA Solidification in Metal-Hydrogen Systems
Authors: Shapovalov V. I.
Published: April 2011

This work contains theoretical discussions concerning the large amount of previously published experimental data related to gas eutectic transformations in metal-hydrogen systems. Theories of pore nucleation and growth in these gas-solid materials will be presented and related to observed morphologies and structures. This work is intended to be helpful to theorists that work with metal-hydrogen systems, and experimentalists engaged in manufacturing technology development of these ordered gas-solid structures.
GASAR Porous Metals Process Control
Authors: Apprill J. M. , Poirier D. R. , Maguire M. C. , Gutsch T. C.
Published: April 2011

GASAR porous metals are produced by melting under a partial pressure of hydrogen and then casting into a mold that ensures directional solidification. Hydrogen is driven out of solution and usually grows as quasi-cylindrical pores normal to the solidification front. Experiments with pure nickel have been carried out under processing conditions of varying H2 partial pressure, total pressure (H2 + Ar), and superheat. An analysis that considers heterogeneous bubble nucleation was developed that identifies processing conditions in which hydrogen bubbles are stable in the liquid before solidification. It is hypothesized that these conditions lead to low porosity because these bubbles float out of the melt and “escape” the advancing solidification front. Experimental data are shown to support this hypothesis.
Growth And Characterization of Thin Wet Oxides Grown by Rapid Thermal Processing
Authors: Sharangpani R. , Das J. , Tay S. P. , Thakur R. P. S. , Yang T. C. , Saraswat K. C.
Published: April 2011

The growth of high quality thin (<10 nm) oxides is one of the most critical steps in the fabrication of the entire spectrum of silicon based devices. Rapid thermal wet oxidation is emerging as a promising technique for this application due to features such as higher throughput, superior oxide quality, faster response and precise thickness control. In this paper, an integrated pyrogenic steam generator -RTP system is described. Theoretical and experimental growth curves along with thickness contour maps and preliminary reliability results are presented.
Selective Oxidation of Si in the Presence of W and Wn
Authors: Lin Boyang , Hwang Ming , Lu Jiong-Ping , Hsu Wei-Yung , Pas Mike , Piccirillo Joe , Miner Gary , OConnor Kathy , Xing Gary , Lopes Dave
Published: April 2011

In various device fabrication processes, such as in metal gate and low resistance word line fabrication, one needs to be able to oxidize Si without oxidizing metals present. We developed such a process using a combination of H2 and O2 in the H2 rich regime. The process developed is safe and is production worthy with excellent uniformity.

When carrying out the selective oxidation using H2/O2, a high Si oxidation rate is preferred which requires a high oxygen concentration. At the same time, the increase in metal sheet resistance, if any, must be small. We found that with an oxygen concentration as high as 20%, the increase in W sheet resistance is small. We present data on the oxidation rate of Si under different conditions as well as the selectivity of the process with respect to W and WN.
Improved Thermal Stability of CVD WSi. During Furnace Oxidation by a Rapid Thermal Anneal Pretreatment
Authors: Blosse Alain P.
Published: April 2011

In this paper, we report new results on tungsten silicide ( WSix ) degradation during furnace oxidation. During Poly-oxidation step performed after gate patterning, a deformed oxide is grown on WSix /Poly gate lines giving rise to protrusions (or nodules) at the interface between the two materials. Different parameters were evaluated including oxidation conditions, WSix deposition parameters, WSix capping dielectric and thermal treatments. The first conclusion of these experiments is that protrusions can be eliminated if Si/W ratio in as-deposited material is greater than 2.6 when no furnace thermal treatment is done on the WSix. /Poly stack before furnace oxidation. The more important conclusion is that addition of a Rapid Thermal pretreatment with a temperature range between 700 and 1000 degrees done just after WSix /Poly etch and before furnace oxidation eliminates totally the defects. Both results can be explained with internal stress reduction in the WSix film which lead to suppression of accelerated oxidation kinetics at the interface between polysilicon and WSix films during furnace oxidation after gate patterning.
Advances in Rtp Temperature Measurement and Control
Authors: Peuse Bruce , Miner Gary , Yam Mark , Elia Curtis
Published: April 2011

This paper reviews work to develop and improve the temperature measurement and control technology of a commercial rapid thermal processing (RTP) system. A description of the main features of this system is given, which includes a concentric multi-zone lamp heating source, multi-point temperature measurement system and real time wafer temperature control. Innovations in RTP optical thermometry are described which resulted in improved low temperature performance, a real time spectral emissivity measurement tool which enables emissivity independent temperature measurement and an improved temperature calibration capability. The multi-input multi-output (MIMO) optimal wafer temperature control methodology is discussed. Process results demonstrating an equivalent process temperature performance of 4°C, 3-sigma, all-points-all-wafers will be presented.
Stabilization of Thick Fcc Cobalt Layers by One Monolayer of Manganese in Co/Mn Superlattices
Authors: Pierron-Bohnes V. , Michel A. , Jay J.P. , Panissod P.
Published: April 2011

Epitaxial Co/Mn superlattices (0.6 to 4.8 nm thick Co) have been grown on (0002) hcp Ru buffer layer on mica substrates. The face centered cubic (fcc) phase of cobalt is stabilized by the very thin manganese layer. The structural properties of these layers have been studied through x ray diffraction and nuclear magnetic resonance.
Atomic Interactions and the Stability of Surface Clusters
Authors: Koh Seong Jin , Ehrlich Gert
Published: April 2011

Interactions dictating the shape and stability of surface islands have been examined for a simple model system, palladium clusters on the W(110) plane. Observations in a field ion microscope of the distribution of two Pd adatoms over the surface yield quantitative values for pair interactions. These are found to be complex, extending over distances longer than 10 A and to vary strongly with the orientation of the pair axis on the (110) surface. Using the measured pair energies it has been possible to infer the magnitude of many-atom effects necessary to account for the equilibrium shape of the clusters. Many-atom interactions turn out to make by far the largest contribution to cluster cohesion; modeling of growth phenomena in terms of nearest-neighbor bonds only is clearly problematic.
Cellular Automaton Modeling of Alloy Solidification Using Local Anisotropy Rules
Authors: Napolitano R. E. , Sanders T. H.
Published: April 2011

The evolution of dendritic morphology is simulated for a binary alloy using a two-dimensional cellular automaton growth algorithm. Solute diffusion is modeled with an alternate-direction implicit finite difference technique. Interface curvature and kinetic anisotropy are implemented through configurational terms which are incorporated into the growth potential used by the automaton. The weighting of the anisotropy term is explored and shown to be essential for overcoming grid-induced anisotropy, permitting more realistic development of dendritic morphologies. Dendritic structures are generated for both uniform and directional cooling conditions.
Bonding Regeneration: The Driving Force of Hetero-Epitaxial Diamond Grain Coalescence on (001) Silicon
Authors: Zhang R.Q. , Jiang X. , Jia C.L. , Lee S.-T.
Published: April 2011

The grain coalescence phenomenon in the growth of heteroepitaxial diamond film on (001) silicon substrate by microwave plasma chemical vapor deposition was examined by using high-resolution electron microscopy. It was shown that this phenomenon evidently occurs between two diamond grains with a small-angle tilt. The coalescence was completed after some more growth steps following the meeting of such two grains, indicating the difficulty for the lattice matching in grain boundary. By performing simulation of a step-by-step growth of two diamond grains on a (001) silicon substrate with molecular orbital PM3 method, it was shown that the bonding regeneration between the two grains is essential for the coalescence and the coalescence is only possible when the orientation difference between the grains is sufficiently small so as to allow efficient overlap of electron cloud in the grain boundary. This study indicates that single crystal diamond growth may be possible by the current CVD growth techniques via further reduction of the surface roughness to gain a heteroepitaxy with very small grain tilting.
Activation Energy for Strength Degradation of Fused Silica Optical Fibers
Authors: Shiue Yunn-Shin , Matthewson M. John
Published: April 2011

The strength degradation behavior of fused silica optical fiber is well known to be sensitive to the temperature and an apparent activation energy can be determined. In addition, it has been observed that the activation energy also depends on the applied stress and the nature of the environment. However, no consistent model for this behavior has emerged. We propose a chemical kinetics model which accounts for the temperature dependence of the dissociation of water which predicts that degradation should be faster in pH 7 buffer than in pure water. Static fatigue of fused silica fibers in both water and pH 7 buffer solution has been carefully studied as a function of temperature to test the model. The apparent activation energies are stress dependent, and, while the dependency is not clear, different environments give different dependencies. These observations support the proposed model.