bluuebunny/crossref_metadata_2025 huggingface dataset:
Demonstration of Mixed Metal Oxide Cathode Materials in Prismatic Li-ion Cells
Authors: Ehrlich G. M. , Gitzendanner R. L.
Published: April 2011

Recent advances in mixed metal oxide (LiNi1−xCoxO2) cathode materials for lithium ion (Li-ion) batteries have resulted in a new generation of high capacity cathode materials. High capacity materials are particularly useful for applications where either volume or weight is limited, such as in space applications. These applications also benefit from cell chemistries with high energy efficiency as this permits reduced ancillary energy storage and dissipation apparatus. Mixed metal oxide materials have been evaluated and demonstrated in prismatic Li-ion cells. The capacity of the mixed metal oxide materials is exceptional, reversible capacity of 160mAh/g is demonstrated although the cell voltage is lower than when LiCoO2 materials are used, 3.58V vs. 3.74V, at low (0.5mA/cm2) discharge rates. The high capacity results in a significant improvement in specific energy, further, the sloping discharge curve characteristic of the mixed metal oxide materials facilitates determination of the state of charge based on cell voltage. The design of composite cathode materials using the mixed metal oxide materials has a significant influence on the cell impedance and the rate capability of the material. Results describing the rate capability of these materials is presented.
Ionically Conducting Glasses with Subambient Glass Transition Temperatures
Authors: Dillon R. E. , Shriver D. F.
Published: April 2011

Cryptands and crown ethers along with the lithium salt, LiCF3SO2N(CH2)3OCH3 (LiMPSA) were employed to produce a new type of amorphous electrolyte. The key to producing an amorphous phase was the mismatch between the cavity size of the macrocycle and the diameter of the cation. The addition of poly(bis-(2(2-methoxyethoxy)ethoxy)phosphazene) (MEEP) to the amorphous complex, LiMPSA/2.2.2 Cryptand, imparts improved electrochemical and viscoelastic properties. Conversely, when poly(sodium-4-styrenesulfonate) (PS4SS) is added to the amorphous complex, LiMPSA/2.2.2 Cryptand, the product crystallizes. The ionic conductivity of the MEEP rubbery electrolyte is a full order of magnitude higher when compared to the analogous PS4SS doped electrolyte (3.8×10−5 S cm−1 (MEEP), 1.7×10−6 S cm1 (PS4SS) both at 30°K).
Dry Composite Polymer Electrolytes for Lithium Batteries
Authors: Appetecchi G. B. , Croce F. , Dautzenberg G. , Scrosati B.
Published: April 2011

The synthesis, characteristics and properties of a PEO-based, dry composite electrolyte are presented and discussed. The major feature of this electrolyte is the high stability towards the lithium metal electrode. This unique property makes the electrolyte quite promising for the development of rechargeable polymer lithium batteries.
Thermoelectric Properties and Electronic Structure of BaBiTe3
Authors: Chung Duck-Young , Jobic Stéphane , Hogan Tim , Kannewurf Carl R. , Brec Raymond , Rouxel Jean , Kanatzidis Mercouri G.
Published: April 2011

The compound BaBiTe3 was prepared by the reaction of Ba/Bi/Te at over 700 °C either in K2TE4 or BaTe3 flux and was recrystallized in Ba/Te3 flux. The black rod-shaped polycrystalline material crystallizes in the orthorhombic space group P212121 with a=4.6077(2) A, b=17.0437(8) Å, c=18.2997(8) Å. Its structure is made of interdigitating columnar anionie [Bi4Te10(Te2)] ∞2+ “herring-bone” shaped segments which arrange into layers with Ba ions between them. The electrical conductivity, thermopower, thermal lattice conductivity, infrared absorption properties of this material suggest it is a narrow gap semiconductor.
Nucleation and Growth at Reactive Interfaces Followed by Impedance Measurements
Authors: Voiron F. , Ignat M. , Marieb T. , Fujimoto H.
Published: April 2011

To evaluate the thickness of different constitutive layers of a TiAl multilayer, two different experiments, based on impedance measurements on multilayers, have been performed. In the first one, the thickness of the layer is deduced from resistivity measurements, applied to a parallel resistance model. In the second one, the thickness of the layer is deduced from comparing of calculated and measured values of surface potentials.
Magnetic Transitions Studied by Electrically Based Methods in Mn-Zn Ferrite
Authors: Gutiérrez P. , Peláiz A. , Huanosta A. , Valenzuela R.
Published: April 2011

The thermal variations in electrical conductivity of polycrystalline Mn-Zn ferrites was investigated by impedance spectroscopy. Two well defined semicircles were observed in complex impedance plots, which were associated with grain (or bulk) and grain boundary impedance response, for the high and low frequency ranges, respectively. From these results, the characteristic relaxation frequencies were obtained for each process. The grain boundary frequency exhibited a monotonous behavior as a function of temperature, while the bulk frequency showed a maximum at 132 °C. By a magnetic method, it was verified that this temperature corresponds to the Curie transition. These results show therefore that a magnetic phase transition can be studied by means of electrical methds.
Reflection High-Energy Electron Diffraction as an Intrinsic Material Property Sensor for Machine Condition Transfer Function in Molecular Beam Epitaxial Growth of III-V Compound Semiconductors
Authors: Chen P. , Wangt C. , Madhukar A. , Khant T. , Small A. , Yan Z. , Viswanathan R.
Published: April 2011

A new approach is introduced for identifying a relation between the growth parameters measured in two molecular beam epitaxy systems, thereby realizing transfer of optimized growth conditions transfer. Test results show that the proposed approach is promising.
X-ray Diffraction Study of Laser-Material Interactions with an Ultrafast Table-Top X-ray Source
Authors: Guo T. , Rose-Petruck C. , Jimenez R. X. , Squier J. A. , Walker B. C. , Wilson K. R. , Barty C. P. J.
Published: April 2011

X-ray diffraction, employing a table-top, laser-driven x-ray source, has been used to investigate laser-material interactions with simultaneous picosecond and subatomic range distance resolution. The x-ray source, consisting of a table-top terawatt laser system and a moving Cu wire target apparatus, generates ˜ 5 × 1010 photons (4π steradians s)−1 of Cu Kα radiation. The lattice dynamics of the (111) planes of GaAs single crystals has been studied after the crystal is exposed to intense femtosecond laser pulses. The diffraction results have yielded information about the timescale of the lattice dynamics in the picosecond range and an upper limit for the width of the xray pulses. Initial strain, defined as the percentage of lattice distortion resulted from the laser illumination, is as high as 0.25% and is followed by an exponential decay with a time constant of ˜ 150 ps. Increases in the diffraction intensity after the laser irradiation have also been observed, likely due to a transition from dynamic to kinematic diffraction associated with degradation of the crystal.
Million-Line Failure Distributions for Narrow Interconnects
Authors: Bartelt M. C. , Hoyt J. J. , Bartelt N. C. , Dike J. J. , Wolfer W. G.
Published: April 2011

We examine the distribution of failure times in a simple and computationally efficient, yet reasonably authentic, model of interconnect reliability that allows consideration of statistically significant samples. The model includes an approximate description of the distribution of grain sizes and texture in narrow interconnects, an effective treatment of stress evolution associated with mass transport along grain boundaries, and local relaxation of stresses due to void formation. Failure time distributions for populations of idealized structures are analyzed to aid in interpretation of model behavior.
Macro-and Microstrain Relaxation in Annealed Ag Films During Ageing at Room Temperature
Authors: Currie R. C. , Delhez R. , Mitiemeijer E. J.
Published: April 2011

The relaxation of thermally induced strain in 500 nm thick polycrystalline Ag layers electron-beam deposited onto Si wafers was traced during ageing at room temperature. The layers consisted predominantly of matrix crystallites with {111} planes parallel to the surface and twin crystallites with {51 l} planes parallel to the surface. The macrostrain in the plane of the layer was determined from the X-ray diffraction line-profile position and the microstrain from the diffraction-line broadening. The residual macrostress relaxed from 160 MPa to 30 MPa in the matrix crystallites and from 170 MPa to 50 MPa in the twin crystallites. Simultaneously with the decrease in macrostress the microstrain decreases significantly for both texture fractions. The strain relaxation behaviour is governed by movement and subsequent annihilation of defects in the layer.
The Use of X-ray Topography to Map Mechanical, Thermomechanical and Wire-Bond Strain Fields in Packaged Integrated Circuits
Authors: McNally Patrick J. , Rantamäki R. , Curley John W. , Tuomi T. , Danilewsky A. N. , Herbert P. A. F.
Published: April 2011

Thermal processing steps in the production of packaged integrated circuits can lead to thermomechanical stresses. Additionally, the process of bonding wires to contact pads can lead to strain fields attributable to these. Synchrotron x-ray topography has been applied to packaged EEPROM Si ICs in order to produce maps of the strain fields induced by such processing steps. This technique allows for depth-resolved mapping with resolutions currently in the region of 5–10 μm throughout the entire mapping volume.
Improved Tribological Behavior of Boron Implanted Ti-6A1-4V
Authors: Baker N. P. , Walter K. C. , Nastasi M.
Published: April 2011

Previous research has compared the mechanical properties of Ti6A14V implanted with nitrogen using the plasma source ion immersion process and Ti6A14V implanted with boron using the beamline process [1]. Although the nitrogen implanted Ti6A14V had superior wear resistance it was concluded that the wear resistance of boron implanted Ti6AI4V might be improved to comparable levels if boron were implanted at lower energies to increase the concentration of boron at the surface. Boron implantation of Ti6A14V has been conducted at combinations of 32 and 40 keV to supplement that done previously at 75 keV. Shallower boron depth profiles with higher B-concentrations in the Ti64 surface have been obtained by tailoring the combinations of ion energy and dose. This work used three different ion energy and dose combinations of 4×1017 B-at/cm2 at 40 keV plus 2×1017 B-at/ cm2 at 32 keV, 4×1017 B-at/cm2 at 40 keV, and 4×1017 B-at/cm2 at 32 keV plus 2×1017 B-at/ cm2 at 40 keV. Comparisons are made between Ti6A14V with a shallow implanted boron depth profile, Ti6AI4V with a deeper boron depth profile and nitrogen implanted using a plasma source ion implantation process. It has been previously shown that while boron implanted Ti64 has a ~30% higher surface hardness than nitrogen implanted Ti64, the N-implantation reduced the wear coefficient of Ti64 by 25–120x, while B-implantation reduced the wear coefficient by 6.5x or less. The results show that no significant improvement is made in the wear resistance of boron implanted Ti6A14V by increasing the concentration of boron at the surface from approximately 10%to 43%. Transmission electron microscopy (TEM) and selected area diffraction (SAD) indicated the formation of crystalline TiB in the implanted surface layer. Shallower depth profiles result in reductions of the Ti6AI4V wear coefficient by 6.5x or less which is the same result obtained earlier with the deeper boron depth profile. Surface hardness of Ti6A14V with shallower boron depth profiles was improved approximately 10%compared to the results previously acquired with deeper boron depth profiles.
Mechanical and Tribological Properties of a-GeCx Films Deposited by DC-Magnetron Sputtering
Authors: Jacobsohn L. G. , Reigada D. C. , Freire F. L. , Prioli R. , Zanette S. I. , Caride A. O. , Nascimento F. C. , Lepienski C. M.
Published: April 2011

Amorphous carbon-germanium films were grown by dc-magnetron sputtering at different argon plasma pressures ranging from 0.17 and 1.4 Pa. The water-cooled sample holder was grounded. The film thickness were typically 0.5 μm. The ratio between germanium and carbon atomic concentration ranges up to 2.8, as measured by Rutherford backscattering spectrometry (RBS). Elastic recoil detection technique was used to measure hydrogen contamination. The film hardness was measured by nanoindentation techniques and the internal stress was determined by the bending of the substrate. The incorporation of Ge reduces both the film hardness and the internal stress. Hardness and internal stress increases when the films are deposited in lower pressures. Atomic Force Microscopy (AFM) was used to measure the surface roughness, which was found to be insensitive to the pressure and to the Ge content. A possible influence of the thickness on the morphology of pure carbon films is discussed. The friction coefficient measured by AFM is independent on the film composition within experimental errors.
Curling and Annealing Study of Sputtered Thin Spinel Films Delaminated from Lift-Off Polyimide
Authors: Dannenberg Rand , King Alexander H. , Gambino Richard J. , Doctor Alan J.
Published: April 2011

Films of Mnl.56Co0.96Ni0.48O4, 6–10 ¼m thick, were RF-magnetron sputtered onto the high temperature lift-off polyimide PiRL®; (made by Brewer Science, Inc.), and patterned into long, narrow beams using photolithography. The beams would self-delaminate, curling towards the substrate upon cooling from 300°C to room temperature after sputtering, as a result of the stress gradient in the film, caused by the deposition process. The typical radius of curvature is 8000 ¼m. Upon annealing at temperatures as low as 250°C for 10 minutes, the delaminated films continue to curl. The films curl to equilibrium radii that are functions of the annealing atmosphere and temperature. Films annealed in H2/N2 or vacuum curl more slowly than in air. TEM reveals that the first 100 nm of film is relatively porous, nanocrystalline spinel which densify instantaneously when exposed to high electron beam currents. Analysis of TEM photographs before and after annealing at 250°C indicate that the level of porosity decreases in the films by 1% which can account for the change in the curl radius. The first layers of film at the PiRL-film interface are prevented from fully densifying while on the substrate. When the film delaminates and the constraint is removed, the initial layer can densify, sintering at low temperature because the large specific surface area of the nano-crystalline microstructure provides high driving forces. The nature of the substrate-induced constraint is not fully understood. Water vapor and other light elements may be released from the polyimide if it were to continue to imidize during the deposition, and a SIMS study has been undertaken to investigate this possibility. Alternatively, the constraint may be purely mechanical, where the sintering rate is reduced as in constrained sintering of films from slurry. This effect may be important to understand when ceramic films are patterned with lift-off techniques. Empirical expressions describing the curl are developed.
Sorption of Cs+ and Ba2+ on Magnesite
Authors: Shahwan T. , Suzer S. , Erten H.N.
Published: April 2011

Sorption behavior of Cs+ and Ba2+ ions on Magnesite was studied using the radiotracer method complemented by x-ray photoelectron spectroscopy (XPS). 137Cs and 133Ba were used as radiotracers. The batch method was used. Local tapwater containing primarily Na+, K+, Ca2+ and Mg2+ ions was used as the aqueous medium. For kinetic studies samples were shaken for periods ranging from one hour to seven days. Aliquots of the aqueous phase before and after shaking were counted using a 35 cm3 pure Ge detector. Magnesite samples were separated into various size fractions by dry and wet sieving. Both fractionated samples and unfractionated samples (particle size < 107mµ) were used. In the XPS the spectra were recorded using a KRATOS ES-300 spectrometer with Al Kα source. Sorption isotherm studies were carried out at 30, 40, 50, 60 and 70 °C.
Molecular-Dynamics Simulations of Ballistic Damages Caused by an Energetic Recoil Nucleus on a Nuclear Glassy Network
Authors: Delaye J-M , Ghaleb D.
Published: April 2011

We have studied the damage caused by an energetic recoil nucleus on the glassy network, from a ballistic viewpoint, using molecular dynamics method. The energies of the displacement cascades performed have been limited to 6keV up to now. This energy represents approximately one tenth of the energy of a recoil nucleus emitted during ca disintegrations in a real nuclear glass. The composition studied comprises the major elements of the real glass: SiO2, B203, Na20, A1203, ZrO2, and the atomic interactions are represented by Born-Mayer-Huggins potentials with formal atomic charges completed by three-body terms. The study described here must be considered in the light of earlier studies in which the authors investigated the complete sequence of a displacement cascade, revealing atom movements occurring when the Coulomb force field is modified in the glass matrix.

As in the ballistic collision sequence, network formers and modifiers exhibit different behaviour. Network modifiers react more quickly and more violently to a modification of the Coulomb field, and relaxation of the alkali metal atoms occurs together with the relaxation of the three-dimensional network of formers. Relaxation of the alkali metals is a key factor ensuring more thorough relaxation of the network formers; the authors have previously shown that preventing relaxation of the alkali metals limits network relaxation.

A more comprehensive description of a displacement cascade can thus be proposed. It is important to distinguish between the ballistic collision sequence per se, which begins first and displaces mainly network formers and oxygen atoms by individual movements, and the network relaxation sequence due to modification of the Coulomb fields, which begins with a slight delay following the collision sequence.
From Laboratory Experiments to a Geological Disposal Vault: Calculation of Used Nuclear Fuel Dissolution Rates
Authors: Sunder S. , Shoesmith D.W. , Kolar M. , Leneveu D.M.
Published: April 2011

Calculation of used nuclear fuel dissolution rates in a geological disposal vault requires a knowledge of the redox conditions in the vault. For redox conditions less oxidizing than those causing UO2 oxidation to the U3O7 stage, a thermodynamically-based model is appropriate. For more oxidizing redox conditions a kinetic or an electrochemical model is needed to calculate these rates. The redox conditions in a disposal vault will be affected by the radiolysis of groundwater by the ionizing radiation associated with the fuel. Therefore, we have calculated the alpha-, beta- and gamma-dose rates in water in contact with the reference used fuel in the Canadian Nuclear Fuel Waste Management Program (CNFWMP) as a function of cooling time. Also, we have determined dissolution rates of UO2 fuel as a function of alpha and gamma dose rates from our electrochemical measurements. These room-temperature rates are used to calculate the dissolution rates of used fuel at 100°C, the highest temperature expected in a container in the CNFWMP, as a function of time since emplacement. It is shown that beta radiolysis of water will be the main cause of oxidation of used CANDU fuel in a failed container. The use of a kinetic or an electrochemical corrosion model, to calculate fuel dissolution rates, is required for a period of ∼ 1000 a following emplacement of copper containers in the geologic disposal vault envisaged in the CNFWMP. Beyond this time period a thermodynamically-based model adequately predicts the fuel dissolution rates. The results presented in this paper can be adopted to calculate used fuel dissolution rates for other used UO2 fuels in other waste management programs.
Influence of Temperature on Hydraulic Conductivity in Compacted Bentonite
Authors: Cho W. J. , Lee J. O. , Chun K. S.
Published: April 2011

The hydraulic conductivities in water saturated bentonites at different densities were measured within temperature range of 20 to 80 °C. The results show that the hydraulic conductivities increase with increasing temperature. The hydraulic conductivities of bentonites at the temperature of 80 °C increase up to about 3 times as high as those at 20 °C. The measured values are in good agreement with those predicted. The change in viscosity of water with temperature contributes greatly to increase of hydraulic conductivity.
Simulation of Transport of Uranium (VI) Species Through the Bed of Bentonite
Authors: Ştamberg K. , Vopálka D. , Škrkal J. , Beneš P. , Chalupská K.
Published: April 2011

The transport of six U(VI) species, HCO31−and CO32−, through the bentonite bed was modelled as diffusion in pore water combined with sorption/desorption on the surface of bentonite particles. The studied system consisted of the Czech commercial sodium bentonite SABENYL and synthetic granitic water spiked with233U(VI), where equilibrium distribution of233U was experimentally determined at first. The transport was simulated by means of eight dynamic, 1 D- partial differential equations while the equilibrium sorption/desorption was assumed. Three types of surface complexation models, namely the Constant Capacitance Model (CCM), Diffuse Double Layer Model (DLM) and the so-called Chemical Equilibrium Model (CEM), were used for the description of sorption/desorption interaction processes. The characteristic parameters of the individual models were obtained from evaluation of experimental data. The results of the simulation were expressed as path-length dependent concentrations of total U(VI), total carbonates and of individual migration species, as path-length dependent pH and uraniumKd, values at a given time and as time dependent concentrations of the total U(VI) at a given migration distance. It has been found that the transport of U(VI) through the bentonite bed is significantly influenced first of all by the value of pH and by total carbonates concentration. The important length dependent changes of the pH andKdvalues were determined.
Coprecipitation of Ni With Calcite: An Experimental Study
Authors: Carlsson T. , Aalto H.
Published: April 2011

At the Finnish candidate sites for a nuclear waste repository calcite (CaCO3) is a common fracture mineral, that may participate in coprecipitation processes. The objective of this work was to study the coprecipitation of the trace element Ni with CaCO3 under controlled conditions. The experiments were carried out at 30 °C in vessels closed to the atmosphere. Calcite-saturated 0.05 M NaCI solutions containing trace amounts of Ni2+ were contacted with calcite for periods of up to 42 days. The experimental data indicate that Ni coprecipitates with calcite as a result of recrystallization. The amounts of coprecipitated Ni and recrystallized calcite were determined using liquid scintillation counting and the isotopes 63Ni and 45Ca. The results are supported by a complementary SEM/EDS analysis of the solid phase.
Gas Flow Through Water-Saturated Shear Zones: Field and Laboratory Experiments and Their Interpretation
Authors: Marschall P. , Croisé J. , Fischer U. , Senger R. , Wyss E.
Published: April 2011

Gas threshold pressure tests and gas tracer tests have been performed at the Grimsel Test Site to study two-phase flow processes in a shear zone. In addition, capillary pressure and gas permeability measurements were carried out in the laboratory on drillcore samples. The laboratory investigations were complemented by assessing the pore structure of the shear zone material. The interpretation of the field tests with numerical models indicated that the structural and two-phase flow parameters to be determined are highly correlated with one another and, consequently, the parameter estimates can be rather uncertain. The joint interpretation of field and laboratory results, however, led to a more stringent description of the two-phase flow processes, expressed by a better overall fit of the test data and smaller uncertainty ranges of the estimated parameters. The results showed that the gas mobility in the shear zone was very high even at high water saturation and gas flow was limited to the narrow zones of brittle deformation along the shear zone.
PHOTO- AND DARK CURRENT NOISE IN a-Si:H PIN DIODES AT FORWARD AND REVERSE BIAS
Authors: Blecher F. , Seibel K. , Bohm M.
Published: April 2011

The noise spectra of hydrogenated amorphous silicon pin diodes are measured in the dark and under illumination at reverse and forward bias. The noise coefficients of 1/f noise at different operating points are determined. The superposition of the different noise mechanisms is investigated. A new empirical model and a method to calculate the noise in pin diodes is suggested. Transport and noise mechanisms are discussed.
Refinement of Plas Samples by Using Afm Image and First Observation of Plas Signals on Amorphous Carbon Nitridea-CNx Films
Authors: Furukawa H. , Nitta S. , Hioki M. , Iwasaki T. , Itoh T. , Nonomura S.
Published: April 2011

The shape of several waveguide end of samples for photoluminescence absorption spectroscopy (PLAS) was studied by atomic force microscope (AFM), because there was an experimental problem where some samples for PLAS did not work. Using the result of AFM, the waveguide end was reshaped by plasma dry etching. The shortening of the etching time was an effective method to improve the structure of the waveguide end. Secondly, the PLAS method was extended to the other materials from a-Si:H. The PLAS signal of amorphous carbon nitride a-CNx was detected for the first time. Amorphous carbon nitride a-CNx film itself and the interface between a-CNx and a-Si02 are found as good as a-Si:H and the interface between a-Si:H and a-Si 3N4+x:H, respectively.
Longitudinal Vibrational Absorption Modes of Hydrogenated Amorphous Silicon Nitride Thin Films
Authors: Li Tong , Kanicki Jerzy
Published: April 2011

We have identified longitudinal and transverse optical modes of Si-N bond in vibrational absorption spectrum of hydrogenated amorphous silicon nitride thin films. The locations of longitudinal optical resonances coincide with transverse mode of Si-O and closely neighbor bending modes of N-H, Si-H2 bond. Furthermore, the conventionally assigned asymmetric and symmetric stretching modes of Si-N bond are merely transverse modes of Si-N bond. Features of pure longitudinal vibrational modes can be revealed by subtracting appropriately scaled transverse mode components from the vibrational absorption spectrum. Analysis of the longitudinal spectrum indicates that, in addition to their association with Si-N bond, the density of the peak located at about 1215 cm−1 is also well correlated to hydrogen and nitride content in the film, while the density of the peak located at about 880 cm−1 is closed related to silicon density in the film. Peak located at about 1040 cm−1 is the longitudinal mode associated with Si-N bond.
Light-Induced Degradation Effects in a-Si:H Observed by Raman Scattering Measurements
Authors: Stradins P. , Kondo M. , Hata N. , Matsuda A.
Published: April 2011

We have attempted to observe changes in the Raman scattering spectrum of a-Si:H due to light exposure. We do not find any detectable shift of the position or change in the width of the TO phonon peak. We find, however, other unexpected degradation phenomena in the Raman spectrum of a-Si:H samples which are attributed to light induced changes in the high energy tail of room temperature luminescence. Raman scattering has a relatively large (10-20% of TO peak height) broad background which extends to 2000cm−1 in the Stokes region and tails into the anti-Stokes region. Multiple phonon processes, geminate radiative recombination and surface oxide contributions are considered. Degradation phenomena and the broad background signal are observed in a-Si:H deposited on different substrates as well as in free-standing films. Degradation processes in bare fused quartz substrates are also investigated. Small structural changes surrounding the light-induced defects are proposed and discussed.
Reduction of Neutral Dangling Bond Density by Light Soaking in Nanocrystalline Silicon
Authors: Matsumoto Takahiro , Masumoto Yasuaki , Kondo Michio
Published: April 2011

The effects of light exposure on neutral defect density at the surface of nanocrystalline Si are investigated by electron-spin resonance (ESR) experiments. A decrease of the neutral dangling bond density by light soaking was observed in this nanostructure. The reduction rate of ESR signal intensity becomes large with increasing light exposure intensity, and the reduction occurs from the excitation energy higher than 2 eV in vacuum. The reduction of the defect density can be explained in terms of the conversion of neutral states to charged states by carrier trapping.
Chimney-Shaped and Plateau-Shaped Gate Electrode Field Emission Arrays
Authors: Tarntair F. G. , Wang C. C. , Hong W.K. , Huang H. K. , Cheng H. C.
Published: April 2011

A triode structure of chimney-shaped field emitter arrays is proposed in this article. This triode structure includes the chimney-shaped emitter, thermal oxidation dioxide, and the plateau-shaped singlecrystalline silicon gate electrode. For the application of the matrix-addressable and large area flat panel display, the uniform structure of the emitters and the yield become critical manufacturing issues when attempting to control nano-meter size features. The uniformity and yield of the chimney-shaped emitters are very well controlled. The nano-sized gate-to-emitter separations can be created by the changing thickness of the insulator. The uniformity of the insulator and emitter material can be controlled within 3% which can be obtained by most large area thin film deposition tools, not by photolithography.
Characterization of Tetrahedrally Bonded Amorphous Carbon Via Capacitance Techniques
Authors: Palinginis Kimon C. , Ilie A. , Kleinsorge B. , Milne W.I. , Cohen J. D.
Published: April 2011

We report the results of junction capacitance measurements on thin tetrahedral amorphous carbon (ta-C) films to deduce their defect densities. We find defect densities in the range 3 - 7 × 1017 cm−3 in the undoped ta-C films, and roughly an order of magnitude larger in the nitrogen doped (n-type) films. In some cases fairly uniform defect profiles were obtained covering a thickness of a couple of hundreds angstroems. We also observed a thermal activation process of carriers from defect states at the ta-C/c-Si interface with an activation energy in the range of 0.4eV to 0.5eV.
Optical Birefringence to Determine Morphological Changes in Low-K Thin Film CVD Polymers
Authors: Senkevich Jay J. , Simkovic Viktor , Desu Seshu B.
Published: April 2011

A great interest exists to reduce power consumption, cross-talk, and RC-delay in ULSI devices by replacing SiO2(k=3.9−4.3) with a polymeric material (k<3.0). Unlike SiO2, polymeric thin films exhibit a complex morphology which varies with the polymer's thermal history, deposition temperature, and film thickness. Since the morphology of the polymer thin film ultimately affects its properties such as its dielectric constant, methods need to be developed to understand the morphological changes in polymer thin films. Further, the polymer thin films must exhibit a high thermal stability due to the relatively high back-end-of-line (BEOL) processing temperature. The polymers which exhibit high thermal stability often contain a mainchain benzene ring. Since benzene has a high anisotropic molecular polarizability, optical birefringence can be used to monitor the polymer chain conformation as a function of the polymer's thermal history, thickness or deposition conditions. Poly(p-xylylene) and poly(tetraflouro-p-xylylene) are shown to have a large negative birefringence, increasing until polymer decomposition. Poly(p-xylylene) becomes increasingly more negatively birefringent after a crystallographic phase change at 220°C. A high negative birefringence results in a large in-plane capacitance, negatively impacting the polymers potential benefit. owever, poly(chlorop-xylylene) and poly(dichloro-p-xylylene) exhibit positive birefringence, which increases until their crystalline melting points at ∼290°C and ∼380°C and thereafter decreases due to film disruption. Conclusions will be drawn based on this positive birefringence for the future molecular design of CVD polymers to decrease their in-plane dielectric constant. Urther poly(chloro-p-xylylene) and poly(p-xylylene) are investigated as a function of deposition temperature and film thickness.
Comparative Study Of Gan Movpe Growth Processes Using Two Different “Surface Preparation-Carrier Gas” Combinations
Authors: Vennegues P. , Haffouz S. , Bouille A. , Leroux M. , Beaumont B.
Published: April 2011

The growth modes and resulting microstructures of GaN films grown by Metalorganic Vapor Phase Epitaxy (MOVPE) on (0001) sapphire with either a simple nitridation of the surface and N2 as carrier gas or with a treatment of the nitridated surface under silane and ammonia with a mixture of H2 and N2 as carrier gas have been investigated. The second process results in a three dimensional first stage of the growth before a coalescence of the islands and the smoothing of the surface. Using this growth process, the defects density can be decreased down to 3.108 cm−2. This reduction in defect density has a drastic effect on photoluminescence properties of the material, and the luminescence efficiency can be increased by a factor of 20. It is also observed that the strain of this material is much higher as compared with material grown with the first process.
Influence of C, N and O Ion-Implantation on Yellow Luminescence
Authors: Zhang R. , Zhang L. , Perkins N. , Kuech T. F.
Published: April 2011

Influence of C, N and O ion-implantation on the yellow luminescence (YL) of halide vapor phase epitaxy (HVPE) and metal-organic vapor phase epitaxy (MOVPE) grown GaN has been studied by photoluminescence (PL) spectroscopy. For the HVPE-grown samples, only C implantation produces a significant enhancement of YL while its corresponding overall PL integrated intensity is only ˜72% of its original value. Implantation of O or N do not appreciably change the YL but decrease the BE integrated intensities by a factor of ten. The full-width-halfmaximum (FWHM) of the BE band expanded to about 1.4 × of the original value in all three cases. These results indicate that one source of the YL is strongly correlated to incorporation of C into the GaN film. The C-induced defect complexes in GaN are optically active while O or N does not lead to any new luminescence features. The variable-temperature PL measurements on the C-implanted HVPE-grown GaN reveal that the FWHM of the YL band increases linearly and the peak energy of the YL changes very little with the increasing measurement temperature, while the integrated intensity of the YL band decreases monotonically. This trend of the YL FWHM and peak energy with the measurement temperature can be explained by a two-channel transition model. For MOVPE-grown GaN films., all ion-implanted samples exhibit a significant loss of both the YL and overall integrated PL intensity. Residual C contamination in the MOVPE samples could be large compared to the additional ion-implanted carbon leading to a reduced impact of the ion-implanted carbon.
Polar Optical Phonon Instability and Intervalley Transfer in Gallium Nitride
Authors: Foutz B. E. , O'leary S. K. , Shur M. S. , Eastman L. F. , Gelmont B. L. , Stroscio M.
Published: April 2011

We develop a simple, one-dimensional, analytical model, which describes electron transport in gallium nitride. We focus on the polar optical phonon scattering mechanism, as this is the dominant energy loss mechanism at room temperature. Equating the power gained from the field with that lost through scattering, we demonstrate that beyond a critical electric field, 114 kV/cm at T = 300 K, the power gained from the field exceeds that lost due to polar optical phonon scattering. This polar optical phonon instability leads to a dramatic increase in the electron energy, this being responsible for the onset of intervalley transitions. The predictions of our analytical model are compared with those of Monte Carlo simulations, and are found to be in satisfactory agreement.
A New Method Of Measuring Hydrogen Diffusivity By Hydrogen Permeation Technique II: Experimental Studies
Authors: Zheng Yong-Ping , Zhang Tong-Yi
Published: April 2011

In order to verify the results predicted by the model in Part I of this work [1], permeation experiments were conducted at room and high temperatures on fully-annealed-commerciallypure iron with two kinds of surface treatment, one group with plasma cleaning and presputtering and the other without it. The experimental results show that the diffusivity evaluated by the new model is independent of sample thickness and surface treatment, while the diffusivity evaluated by the time-lag model varies two orders of magnitude. The experimental results confirm that a fine surface treatment yields a low energy barrier for desorption. The energy barrier for either group is higher than the activation energy of diffusion. Consequently, the ratio of drift velocity through surface to that in bulk increases with increasing temperature and makes the time-lag method appropriate at elevated temperatures.
Determination of Hydrogen in Metals, Semiconductors, and Other Materials by Cold Neutron Prompt Gamma-Ray Activation Analysis
Authors: Paul R. L. , Lindstrom R. M.
Published: April 2011

Cold neutron prompt gamma-ray activation analysis has proven useful for nondestructive measurement of trace hydrogen. The sample is irradiated in a beam of neutrons; the presence of hydrogen is confirmed by the emission of a 2223 keV gamma-ray. Detection limits for hydrogen are 3 mg/kg in quartz and 8 mg/kg in titanium. We have used the technique to measure hydrogen in titanium alloys, germanium, quartz, fullerenes and their derivatives, and other materials.
Hydrogenation of Undoped and Nitrogen Doped Cdte and ZnSe Grown by Molecular Beam Epitaxy
Authors: Hirsch L. S. , Setzler S. D. , Ptak A. J. , Giles N. C. , Myers T. H.
Published: April 2011

Hydrogen incorporation in both undoped and nitrogen-doped CdTe and ZnSe is investigated. Evidence for a strong nitrogen-hydrogen interaction is presented. Preliminary data indicate that the growth of CdTe and ZnSe under an atomic hydrogen flux results in a significant concentration of paramagnetic defects possibly accompanied by enhanced auto-doping from residual impurities.
Optical Absorption Study of Hydrogen In Zn-Doped Si
Authors: Suezawa M.
Published: April 2011

We studied the interaction between hydrogen (H) and Zn or Zn-related defects in Zn-doped Si crystals from the measurements of optical absorption spectra of hydrogen bound to Zn or Znrelated defects. We doped Si crystals with Zn by annealing the crystals in Zn vapor at 1200°C followed by quenching. After Zn-doping, we doped specimens with H by annealing them in a hydrogen atmosphere followed by quenching. We measured optical absorption spectra of the above specimens at about 6 K by means of FT-IR spectrometry. Many optical absorption peaks were observed; some are due to electronic transitions and some are due to vibrational transitions of H vibration. Hydrogen atoms are known to passivate Zn acceptors since the optical absorption intensity associated with electronic transitions become much weaker after hydrogenation. Absorption peaks associated with H vibration are known to be related to complexes composed of one Zn atom and two hydrogen atoms. We concluded this from studies on the effect of co-doping with H and deuterium and the effect of Zn isotopes on the optical absorption spectra due to H.
Hydrogen and Hydrogen-Related Defects in CVD Diamond
Authors: Rutledge K. M. McNamara
Published: April 2011

Hydrogen is a detrimental impurity in many chemical vapor deposited (CVD) materials, particularly those involved in electronic or optical applications. For example, active hydrogen defects have been observed in materials such as silicon, Si, gallium arsenide, GaAs, and diamond, C, thin films. Hydrogen and its related defects can be identified, quantified, and observed using magnetic resonance techniques. These techniques allow a unique quantitative, non-destructive view of hydrogen in the solid-state. Nuclear magnetic resonance (NMR) is used to study hydrogenated defects directly, while electron paramagnetic resonance (EPR) is used to observe hydrogen associated with paramagnetic defects. These observations can enhance our understanding of the effects of hydrogen incorporation on the properties of such materials.
The Influence of Surface Morphology and Oxide Microstructure on the Nucleation and Growth of Uranium Hydride on Alpha Uranium
Authors: Hanrahan R. J. , Hawley M. E. , Brown G. W.
Published: April 2011

While the bulk kinetics of the uranium-hydrogen reaction are well understood, the mechanisms underlying the initial nucleation of uranium hydride on uranium remain controversial. In this study we have employed environmental cell optical microscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy, (AFM) in an attempt to relate the structure of the surface and the microstructure of the substrate with the susceptibility and site of hydride nucleation. Samples have been investigated with varying grain size, inclusion (carbide) concentration, and thermal history. There is a clear correlation to heat treatment immediately prior to hydrogen exposure. Susceptibility to hydride formation also appears to be related to impurities in the uranium. The oxidized surface is very complex, exhibiting wide variations in thickness and topography between samples, between grains in the same sample, and within individual grains. It is, however, very difficult to relate this fine scale variability to the relatively sparse hydride initiation sites. Therefore, the surface oxide layer itself does not appear to control the sites where hydride attack is initiated, although it must play a role in the induction period prior to hydride initiation.
Monte Carlo Atomistic Simulation of Polycrystalline Aluminum Deposition
Authors: Rubio J. Emiliano , Jaraíz Martín , BaiIón Luis A. , Barbolla Juan , López M José , Gilmer George H.
Published: April 2011

A new atomistic scheme for simulating polycrystalline thin film deposition based on a Monte Carlo approach has been developed. Simulations of polycrystalline aluminum deposition and annealing at different temperatures are presented. The time evolution of the film morphology for those temperatures is discussed. During deposition, columnar growth is observed at low temperatures. Grain growth takes place mainly during annealing. Faceting and selection of preferred crystal orientations (texture) is observed.
Morphology of NISI Film on Si(100): Role of the Interface Strain
Authors: Maillard-Schaller Eliane , Boyanov B. I. , English S. , Nemanich R. J.
Published: April 2011

The role of strain on the thermal stability of NiSi has been studied by deposition and annealing of Ni on strained and relaxed Si(100) n-type substrates. Strained Si substrates have been produced by depositing a pseudomorphic silicon film on top of a 3000 Å thick relaxed Si0.8Ge0.2film. Raman spectroscopy has proved the top silicon film to be strained. The presence of the characteristic hatch-cross pattern has been confirmed by Atomic Force Microscopy (AFM). Scanning electron microscopy (SEM) and Photoelectron emission microscopy (PEEM) show that the islanding of the NiSi film appears at lower temperature on the bulk silicon substrate (600°C) than on the strained silicon substrate (700°C). The improved thermal stability of NiSi on strained Si can be explained by the difference in relative interface energy of NiSi on strained and relaxed silicon. The thermal expansion coefficient of Ni being 3 times larger than that of Si, NiSi is in compression on Si at 500°C already. The correlation of this compression state with the lattice parameters of bulk and strained Si (100) produces an increased NiSi islanding probability on bulk Si (100) with respect to strained Si.
Solution Delivery for Copper CVD Using Cu(HFAC)2 Reduction
Authors: Zeng C. , Borgharkar N. S. , Griffin G. L. , Fan H. , Maverick A. W.
Published: April 2011

We have developed a solution delivery technique for performing copper CVD using the reduction of Cu(hfac)2 [where H(hfac) = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionel. We have obtained deposition rates of up to 3.6 mg cm−2 hr−1 (ca. 60 nm min−1) for a deposition temperature of 300 °C and reactor conditions of 40 Torr H2, 12 Torr isopropanol, and 1 Torr Cu(hfac)2. The increased rates are several times faster than growth rates observed using conventional Cu(hfac)2 sublimation with pure H2 as the carrier gas. We compare growth rates and film microstructure using TiN- and WNx-coated substrates. We also give preliminary results showing how the partial pressures of H2, i-PrOH, and Cu(hfac)2 each influence the deposition rate.
Effect of Oxygen on the Degradation of Ti-Si-N Diffusion Barriers in Cu Metallization
Authors: McArthur W. F. , Ring K. M. , Morgan B. , Hurst Q. , Serber D. , Clark A. , Kavanagh K. L.
Published: April 2011

Amorphous Ti-Si-N thin films are effective barriers to Cu diffusion in integrated circuits that use Cu interconnects. These films are believed to fail as diffusion barriers due to crystallization and subsequent diffusion of Cu along grain boundaries. We prepare thin films of Ti-Si-N by RF magnatron co-sputtering of Ti and Si in Ar/N2. Ti-Si-N films with Si concentrations of 6 to 22% have resistivities <500μΩ-cm. In previous reports we have shown that Si pn-junction diodes metallized with 20nm Ti40Si15N45/Cu do not fail (increased reverse leakage current) until 600%C. When annealed, these films crystallize to yield TiN and Si3N4. In this work we have studied the effect of oxygen on the degradation of the barrier via TEM, diode I-V measurements, and RBS. Oxygen incorporated into the film deposition process improves the barrier effectiveness as measured by diode I-V reverse leakage current. We find no correlation between the amount of O2in the process gas feed stream and the film composition with O resonance analysis (RBS) or crystallinity (TEM).
TEM Observations on the Evolution of Grain Structure in Pressurized Al-0.5Cu Thin Films
Authors: Yang H.D. , Kim C.-U. , Saran M. , Le H.A.
Published: April 2011

This paper reports the observations of the grain-refining mechanism found in Al-0.5Cu thin films that are subjected to hydrostatic compressive pressure during the annealing process. The films are deposited on Si substrates and subsequently placed under 60 MPa Ar gas pressure at 400°C. Transmission electron microscopy on these films reveals that plastic deformation occurs by dislocation slip and induces a refined grain structure. Polygonization is the primary mechanism for grain refining, resulting in the formation of sub-grain boundaries.
Bulge Test Investigation of The Influence of Moisture on Mechanical Properties of Thin Polymer Layers
Authors: Nakladal A. , Buchhold R. , Köhler R. , Gerlach G. , Stavrev M. , Wenzel C. , Baumann K. , Nowak B.
Published: April 2011

Thin polymer layers gain importance as interlevel dielectrics in microelectronic devices. One major drawback of this class of material is instability of mechanical properties under changing climatic condition. The paper deals with evaluation of the bulge test as complementary method for investigation of humidity induced alterations of mechanical properties. It describes measurement of intrinsic as well as humidity induced stress in polymer layers. The given results agree very well with those obtained by substrate bending. Furthermore, bulge testing proved the assumption of earlier work, that change of mechanical stress is due to a humidity induced swelling process that can be described phenomenologically by expansion coefficient and a biaxial Young's modulus independent from relative humidity. Results are given and discussed for two types of polyimide.