bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid Thermal Transformation of A-15 Crystal Structure Metallic Thin Films
Authors: O'Keefe M. J. , Cerny C. L.
Published: April 2011

Physical vapor deposition of Group VI elements (Cr, Mo, W) can lead to the formation of a metastable A-15 crystal structure under certain processing conditions. Typically, a thermally induced transformation of the metastable A-15 structure into the equilibrium body centered cubic structure has been accomplished by conventional furnace annealing at T/Tm≈ 0.3 from tens of minutes to several hours. In this study we report on the use of rapid thermal annealing to transform sputter deposited A- 15 crystal structure tungsten and chromium thin films into body centered cubic films within the same temperature range but at times on the order of one minute. The minimum annealing times and temperatures required for complete transformation of the A-15 phase into the BCC phase varied from sample to sample, indicating that the transformation was dependent on the film characteristics. The electrical resistivity of A-15 Cr and W films was measured before and after rapid thermal annealing and was found to significantly decrease after transformation into the body center cubic phase.
RTP Based Tin Barrier Integrity for WF6 Processing During W-Plug Formation
Authors: Lee C. Y. , Yen H. , Hsia S. T. , Liu D. , Shah N. , Feldmeier K. , Wasserman Y.
Published: April 2011

The study evaluates the barrier integrity of Rapid Thermal Processed (RTP) titanium layer to form TiSi2/TiN and sputter deposited TiN layer annealed in RTP system. Various temperatures and ambient conditions were used during processing. Subsequent effects of the W-plug process on the TiN layer have been evaluated in terms of effects of WF6 on the underlying Ti/TiN layer.

Evaluation of the WF6 on the via side walls and the via corners will be the primary focus of this work. Results will be discussed in terms of effective TiN thickness the process of formation of TiN and its stability
An Analytic Approach to the Radiation Fields of Tubular Halogen Lamp Arrangements in RTP Reactor Blocks
Authors: Theiler Thomas
Published: April 2011

Starting with basic physical radiation principles and with Beers law formulas for the radiation characteristics of arrays of pointlike radiation sources and tubular halogen lamps are analytically derived. Different arrangements of tubular halogen lamps are considered and compared with each other. Homogeneity criteria are worked out and it is demonstrated that the minimum homogeneity distance between a plane in which all filaments are arranged parallel to each other, and an object depends only on the distance between two neighbouring filaments and thus can be given by a simple number. Interesting aspects for RTP equipment manufacturers as well as for users are demonstrated by comparing different lamp arrangements with each other: In crossed lamp fields latticelike inhomogeneity knots arise in the object plane at points where the lamp filaments of the upper and the lower lamp plane cross. If the filaments are arranged parallel to each other in two filament planes, very homogeneous results are obtained when the filaments of the two planes interlace.
Application of a Neural Manufacturing Concept to Process Modeling, Monitoring and Control
Authors: Fu Chi Yung , Petrich Loren , Law Benjamin
Published: April 2011

The cost of a fabrication line, such as one in a semiconductor house, has increased dramatically over the years, and it is possibly already past the point that some new start-up company can have sufficient capital to build a new fabrication line. Such capital-intensive manufacturing needs better utilization of resources and management of equipment to maximize its productivity. In order to maximize the return from such a capital-intensive manufacturing line, we need to work on the following: 1) increasing the yield, 2) enhancing the flexibility of the fabrication line, 3) improving quality, and finally 4) minimizing the down time of the processing equipment. Because of the significant advances now made in the fields of artificial neural networks, fuzzy logic, machine learning and genetic algorithms, we advocate the use of these new tools in manufacturing. We term the applications to manufacturing of these and other such tools that mimic human intelligence neural manufacturing. This paper describes the effort at the Lawrence Livermore National Laboratory (LLNL) [1] to use artificial neural networks to address certain semiconductor process modeling, monitoring and control questions.
Surface-Topography Simulations of Ionized Sputter Metal Deposition
Authors: Hamaguchi S. , Rossnagel S.M.
Published: April 2011

Numerical simulations are used to predict microscopic topography of deposited metal films in ionized magnetron sputter deposition experiments. The simulation takes into account ionized and neutral fluxes as deposition material sources and re–sputtering and re–deposition of the deposited material due to the ion bombardment. The shock-tracking algorithm is used to advance the moving surface boundary. Applications of this deposition technique include lining and filling of trenches, vias and dual damascene.
Simulation of Film Growth Contour in a Narrow Deep Trench and Film Crystallinity in LPCVD Process
Authors: Hwang Gyeong Soon , Shin Chee Burm , Moon Sang Heup
Published: April 2011

Deposition of a thin film in the LPCVD process has been simulated by a Monte–Carlo method based on a simple model taking into account the desorption, the surface reaction, and the surface migration of the film precursor. The model has been used for the simulation of the film profile obtained in a narrow and deep trench and of the film crystallinity on a flat surface. The simulation results describe successfully those obtained by experiments under various process conditions.
Simulation of the Nucleation and Growth of Si Grains Inside Au Thin Films
Authors: Pasa A. A. , Neugebauer M. , Losch W. , Bauer G. H.
Published: April 2011

The Si crystallization process induced by the presence of a gold thin film was computer simulated using a random resistor network and concepts of the percolation theory. The model considers initially a pure Au resistor network. The random appearance of Si nuclei corresponds to a high local variation of the resistance value. The crystallization process was simulated step-by-step and parameters as nucleation rate and growth rate were tested. Considering an interface limited reaction process, the simulated results are in good agreement with experimentally obtained in-situ electrical measurements and scanning electron microscopy micrographies.
Monte Carlo Simulation of Dislocation-Nucleated Etching of Silicon {111} Surfaces
Authors: Woodraska Donald L. , Lacosse Jason , Jaszczak John A.
Published: April 2011

We investigate equilibrium properties and thermal etching of the {111} surfaces of silicon, both with and without perpendicular intersecting dislocations, using Monte Carlo computer simulation. A modified solid-on-solid (SOS) approach is employed which realizes the correct diamond-cubic (DC) crystal structure. Nearest-neighbor interactions are incorporated to model the bonding, while the effects of a dislocation are incorporated by the addition of an energy field modeled as a core region and an elastic strained region. Dislocations are seen to nucleate the etching process and result in the formation of etch pits. Etch rates and etch-pit morphologies are investigated as a function of the chemical potential driving force for etching, the temperature, and the energy parameters used to model the dislocation.
Transient and Spatial Radiative Properties of Patterned Wafers during Rapid Thermal Processing
Authors: Wong Peter Y. , Miaoulis Ioannis N. , Madras Cynthia G.
Published: April 2011

Temperature measurements and processing uniformity continue to be major issues in Rapid Thermal Processing. Spatial and temporal variations in thermal radiative properties of the wafer surface are sources of non-uniformities and dynamic variations. These effects are due to changes in spectral distribution (wafer or heat source), oxidation, epitaxy, silicidation, and other microstructural transformations. Additionally, other variations are induced by the underlying (before processing) and developing (during processing) patterns on the wafer. Numerical simulations of Co silicidation that account for these factors are conducted to determine the radiative properties, heat transfer dynamics, and resultant processing uniformity.
Concurrent Design of an RTP Chamber and Advanced Control System
Authors: Spenc Paul , Schaper Charles , Kermant Ahmad
Published: April 2011

A concurrent-engineering approach is applied to the development of an axisymmetric rapidthermal-processing (RTP) reactor and its associated temperature controller. Using a detailed finiteelement thermal model as a surrogate for actual hardware, we have developed and tested a multi-input multi-output (MIMO) controller. Closed-loop simulations are performed by linking the control algorithm with the finite-element code. Simulations show that good temperature uniformity is maintained on the wafer during both steady and transient conditions. A numerical study shows the effect of ramp rate, feedback gain, sensor placement, and wafer-emissivity patterns on system performance.
Fundamental Mechanisms for Hg Vacancy and Interstitial Modeling in Mercury Cadmium Telluride
Authors: Holander S.L. , Robinson H.G. , Helms C.R.
Published: April 2011

Due to the large concentration of electrically active defects in Hg1-xCdxTe, it is important to properly account for them when designing fabrication processes for infrared focal plane arrays (IRFPAs). Stanford University's Mercury Cadmium Telluride Process Simulator, SUMerCad, is being developed to simulate the interaction of native defects and dopants in Hg0.8Cd0.2Te in order to accurately model various processing techniques. Non-linear coupled differential equations are used to model the physics of the diffusion mechanisms, rather than extrapolating the diffusion profiles from experimental data. The fundamental constants for the point defects were obtained by exercising the simulator over the various parameter spaces and comparing the results to experimental work and best principle calculations. The methodologies used, point defect mechanisms modeled, and parameters determined are discussed.
Experimental Results and Modeling of the Codiffusion of Donors and Acceptors in Si
Authors: Solmi S. , Valmorri S.
Published: April 2011

A model based on ion pairing for the simulation of donor and acceptor codiffusion in silicon is presented. The proposed model allows us to obtain a good agreement with the experimental profiles over a wide range of diffusion conditions, specially at high concentrations where the standard process simulator codes give results strongly inaccurate. Comparison of the simulations with new and literature codiffusion profiles is provided.
Measurement and Modeling of Intrinsic Stresses in CVD W Lines
Authors: Lee Jin , Ma Qing , Marieb Thomas , Mack Anne S. , Fujimoto Harry , Flinn Paul , Woolery Bruce , Keys Linda
Published: April 2011

We have studied stress states in chemical vapor deposited (CVD) tungsten (W) for both blanket films and lines, to understand better the mechanical implications of intrinsic stress for interconnection structures. Since W has a low mobility at its deposition temperature, a very large intrinsic stress develops during deposition. Intrinsic strains in blanket W films were measured with an X-ray technique. The measured strains correspond to a biaxial tensile stress of the order of 1 GPa. This result was used to provide an initial strain input in a finite element calculation to obtain intrinsic stress states in W lines. SEM observation of cross sections of the metal lines enabled us to determine the growth pattern of the W, and infer the boundary conditions during growth. Finite Element Method (FEM) calculations of the room temperature stress in the lines, including both intrinsic and thermal components, are in good agreement with X-ray determinations.
Time-Dependent Dielectric Breakdown in Thin Intrinsic SiO2 Films
Authors: Suehle J. S. , Chaparala P.
Published: April 2011

Time-Dependent Dielectric Breakdown studies were performed on 6.5-, 9-, 15-, 20-, and 22.5-nm thick SiO2 films over a wide range of stress temperatures and electric fields. Very high temperatures (400 °C) were used to accelerate breakdown so that stress tests could be performed at low electric fields close to those used for device operating conditions. The results indicate that the dependence of TDDB on electric field and temperature is different from that reported in earlier studies. Specifically, the electric-field-acceleration parameter is independent of temperature and the thermal activation energy was determined to be between 0.7 and 0.9 eV for stress fields below 7.0 MV/cm.

Failure distributions of high-quality current-generation oxide films are shown to be of single mode and have dispersions that are not sensitive to stress electric field or temperature, unlike distributions observed for oxides examined in earlier studies. These results have implications on the choice of the correct physical model to describe TDDB in thin films. The data also demonstrate for the first time the reliability of silicon dioxide films at very high temperatures.
Effect of Electric ARC Plasma Jet Treatment on Mos Structure Reliability
Authors: Maslovsky V. M. , Pavlov G. Ya.
Published: April 2011

The effect of electric arc plasma jet treatment (APJT) on MOS structure reliability has been investigated. Si/SiO2/Si*/Al structures have been studied using the technique of constant current charge to breakdown before and after APJT. The study showed that APJT can improve MOS structure reliability: constant current charge to breakdown Qbd increased to more than 5 C·cm-2 and breakdown field Ebd increased to more than 20 MV/cm. This result was attributed to a structural modification of SiO2 and its interfaces as a result of APJT. Evidence for these structural changes is the appearance of additional SiO2 IR absorption peak which was observed by us.
Modeling of the Structure and Reliability of Near-Bamboo Interconnects
Authors: Thompson C.V. , Joo Y.-C. , Knowlton B.D.
Published: April 2011

When interconnect feature sizes (e.g., widths) and grain sizes are comparable, their average electromigration-lifetime increases. However, reliability increase occurs for a population of lines only if microstructural weak links, such as polygranular clusters, become unlikely throughout the population. Lifetime statistics and grain structure statistics are linked in a way which must be understood in order to take advantage of lifetime improvements through line-width-dependent and line-length-dependent current density limits. An analytic model has been developed which allows calculation of the polygranular cluster length distribution as a function of line width, line length and current density, given continuous-film median grain sizes and grain size deviations. A simple analytic model for the effect of post-patterning anneals on polygranular cluster length distributions is also presented. These models are shown to be consistent with detailed computer simulations of grain structures and grain structure evolution in interconnects. Improved grain structure models will enable less-conservative integrated circuit design practice, allowing design of higher performance circuits.
A Comparative Study on the Titanium Nitride (TiN) as a Diffusion Barrier Between Al/Si and Cu/Si: Failure Mechanism and Effect of “Stuffing”
Authors: Park Ki-Chul , Kim Ki-Bum
Published: April 2011

The diffusion barrier properties of 100-nm-thick TiN films, both as-deposited and "stuffed", were investigated in both Al/TiN/Si and Cu/TiN/Si metallization systems. In Al/TiN/Si systems, the TiN barrier fails by the formation of both Al spikes and Si pits in the Si substrate. However, in Cu/TiN/Si systems, the failure of TiN diffusion barriers occurs by the predominant diffusion of Cu into the Si substrate, which forms dislocations along the projection of Si {111} plane and precipitates (presumably Cu-silicides) around the dislocation. In Al/TiN/Si systems, it is shown that the diffusion barrier property of TiN is significantly enhanced by "stuffing" in N2 ambient prior to Al deposition. However, in Cu/TiN/Si systems, it is found that the "stuffing" of TiN does not improve the diffusion barrier property as it does in Al/TiN/Si systems.
The Effects of Processing on the Microstructure of Copper Thin Films on Tantalum Barrier Layers
Authors: Zielinski E.M. , Vinci R.P. , Bravman J.C.
Published: April 2011

abstract

Preferred crystallographic orientation and grain size distribution were characterized as a function of processing for sputtered Cu films on Ta underlayers. The Ta barrier layer was deposited at two temperatures, 30 and 100 °C. Cu was deposited at 30, 150 and 250 °C on the 30 °C Ta, and at 100, 150, 200 and 250 °C on the 100 °C Ta. In the first set of samples, with increasing deposition temperature, the Cu (111) fiber texture grew weaker and the volume fraction of randomly oriented grains increased from 0.23 to 0.74. In contrast, for the films deposited on the 100 °C Ta, with increasing deposition temperature, Cu (111) fiber texture strengthened and the fractions of randomly oriented and twinned grains decreased. Grain size was lognormally distributed in all samples and varied approximately parabolically with deposition temperature. At a given deposition temperature, median grain size in the Cu was larger in the films deposited on the 100 °C Ta. These results will be related to the microstructure of the Ta underlayers. Cu microstructure on the 100 °C Ta is shown to be influenced by textural inheritance from the Ta underlayer. Microstructure of the Cu on 30 °C Ta is discussed in terms of trace contaminants.
Surface Passivation of Cu by Annealing Cu/Al Multilayer Films
Authors: Wang W. , Lanford W.A. , Murarka S.P.
Published: April 2011

Surface passivation of Cu by annealing Cu/Al multilayer films (Cu/Al/Cu/Al/Cu) on SiO2 has been demonstrated. Cu/Al multilayer films were annealed from 300°C to 500°C. The buried Al is transported to the Cu surface during annealing, forming A12O3 at the exposed surface. The Cu in annealed Cu/Al multilayer films shows no oxidation when heated in air at 300°C for 24 hrs. The electrical resistivity of these films is 2.3 μΩ cm.
A Highly Reliable Al Line with Controlled Texture and Grain Boundaries
Authors: Hasunuma M. , Toyoda H. , Kawanoue T. , Ito S. , Kaneko H. , Miyauchi M.
Published: April 2011

In order to clarify the relationship between Al line reliability and film microstructure, especially grain boundary structure and crystal texture, we have tested three kinds of highly textured Al lines, namely, single-crystal Al line, quasi-single-crystal Al line and hypertextured Al line, and two kinds of conventional Al lines deposited on TiN/Ti and on SiO2. Consequently, the empirical relation between the electromigration (EM) lifetime of Al line † and the (111) full width at half maximum (FWHM) value ω is described by † ∝ ω-2 [1]. This improvement of Al line reliability results from as following reasons; firstly, homogeneous microstructure and high activation energy of 1.28eV for the single-crystal Al line (ω=0.18°); secondly, sub-grain boundaries which consisted of dislocation arrays found in the quasi-single-crystal Al line (ω=0.26°) has turned out to be no more effective mass transport paths because dislocation lines are perpendicular to the direction of electron wind. Although there exist plural grain boundary diffusion paths in the newly developed hypertextured Al line (ω=0.5°) formed by using an amorphous Ta-Al underlayer {1], the vacancy flux along the line has been suppressed to the same order of magnitude of single crystal line. It has been clarified that the decrease of FWHM value has promoted the formation of sub-grain boundaries and low-angle boundaries with detailed orientation analysis of individual grains in the hypertextured film. The longer EM lifetime for the hypertextured Al line is considered to be due to the small grain boundary diffusivities for these stable grain boundaries, and this diffusivity reduction resulted in the suppression of void/hillock pair in the Al lines. These results have confirmed that controlling texture and/or grain boundary itself is a promising approach to develop reliable Al lines which withstand higher current densities required in future ULSIs.
Microtexture Measurements of Aluminum VLSI Metallization
Authors: Barr D.L. , Brown W.L. , Marcus M.A. , Ohring M.
Published: April 2011

The microtexture of thin film aluminum has been studied using Electron Backscatter Diffraction (EBSD). The results indicate that, while the overwhelming majority of polycrystallite grains have a <111> fiber texture with the < 111 > axis within -5° of the surface normal, 1-2 % of the grains deposited on SiO2 show large deviations off of this axis. The off-texture grains are typically much smaller than those that are <111> textured. These observations have been made for Al(Cu) films with several different Cu concentrations and for different substrate materials. The statistical distributions of the orientations in the different cases are presented. Electrical stressing of 0.8 um Al(0.5%Cu) lines resulted in elimination of the small number of grains with off- orientation.
The Role of Process Choices in Reliability Fail Modes
Authors: Geffken Robert M.
Published: April 2011

Projections on density, performance and cost attributes of a new technology generation are relatively easy to accomplish. However, defining the reliability attributes is
more problematic, particularly if the technology contains many new process elements or tools. The choices made by a development team for processes, tools, process
sequences and product-layout rules often determine the process defect reliability fail modes of a technology. These process defects define the reliability level of products
rather than classic reliability fail mechanisms such as electromigration, stress migration and corrosion. As such, development teams and their reliability counterparts
need to focus on potential sources of process-defect reliability fail modes and their control.
Quantitative Three-Dimensional Characterization of the Morphology of Stressed and Electromigrated Aluminum Lines
Authors: Ramseyer George O. , Beasock Joseph V. , Helbig Herbert F. , Walsh Lois H.
Published: April 2011

The volumes of slit, edge, erosion and erosion/slit voids in stressed and electromigrated aluminum conductor lines were quantitatively determined with low resolution standard and high resolution enhanced tips by atomic force microscopy. These three-dimensional results were compared to semiquantitative determinations of void volumes extrapolated from two-dimensional backscattered scanning electron microscopy area determinations of the passivated aluminum conductor. After the passivation was removed by plasma etching, void volumes were also determined from two-dimensional scanning electron microscopy micrographs. The volumes of the nearest hillocks on the anodic side of the voids were quantitatively determined by atomic force microscopy, and these hillock volumes were determined to be independent of the respective void volumes.
The Influence of Grain Structure on the Reliability of Narrow Al-Based Interconnects
Authors: Kang S.H. , Kim C. , Génin F.Y. , Morris J.W.
Published: April 2011

The work reported here concerns the effect of grain structure on electromigration failure in pure Al and Al-2wt.%Cu-lwt.%Si lines. The grain structures of fine lines were controlled by annealing after patterning to promote the formation of "bamboo" structures. Significant improvements in the median time to failure (MTF) and the deviation of the time to failure (DTF) were observed with the development of near-bamboo structures with polygranular-segment lengths shorter than ~ 5 μm. The most common failure sites are voids or slits across bamboo grains at the upstream ends of polygranular segments. The time-to-failure decreases with the polygranular segment length, and can be significantly enhanced by controlling the grain structure.
Electromigration Damage and Failure Distributions in Al-4wt.%Cu Interconnects
Authors: Shih W. C. , Greer A. L.
Published: April 2011

Unpassivated 2.1μm and 1.1μm wide lines of Al-4wt.%Cu have been electromigration-stressed to failure under accelerated testing conditions (up to 300 °C and 2 x 1010 A m-2). The line resistance and microstructure and the development of electromigration damage are discontinuously recorded. Distributions of damage sites (hillocks and voids) along the line lengths are measured, and the evolution of the distributions with stressing time is followed. The distances between damage sites show a clear correlation with the grain structure. Damage and failure sites are concentrated near the end of the lines at which electrons enter.
Grain Structure and Electromigration Testing of Deep Sub- Micrometer Cu Interconnects
Authors: Frankovic Richard , Bernstein Gary H.
Published: April 2011

Copper interconnect test stripes were fabricated by electron-beam lithography, evaporation and lift-off to linewidths as small as 140 nm. Grain structure in the as-deposited films exhibited smaller standard deviation than long-term annealed films. Grain growth during the anneal step increased maximum grain size by 2.5 times. Electromigration lifetime testing indicated these interconnects have 2-4 orders-of-magnitude greater normal-use lifetimes than large cross-sectional area, large-grain Al-alloy interconnects.
Effect of Annealing and Passivation on the Electromigration and Linewidth Dependence
Authors: Carnes R.O. , Lee C.H. , Keating P.T. , Barrall II E.M. , York B.R. , Grivna G.M. , Bauguess S.W. , Dreyer M.L. , Edwards S.R.
Published: April 2011

Continued miniaturization of conductor geometry below 0.5μm has by a concomitant decrease in Al deposition temperature, typically below 300°C. The degree of reliability exhibited by these films is strongly dependent on the grain size distribution and metallurgical configuration. This investigation focuses on the impact of post-deposition processing on changes in conductor microstructure and electromigration for films deposited at low temperature. AlCu(l%)Si(l%) was deposited at 300°C on PECVD phosphosilicate glass. The impact of post-deposition thermal budget on the as deposited grain size and distribution, preferred orientation and stress/strain states were analyzed using scanning electron microscopy, X-Ray diffraction and bending beam technique, respectively. These characteristics were also measured on unpassivated films subjected to the same thermal budget as SiO2 passivated films so that the geometric confinement and Al-SiO2 surface interaction could be quantified. Electromigration characteristics were measured for linewidths in the range W=1.0μm to W=10μm, for passivated and unpassivated films. A direct correlation between passivation and grain size was observed for both failure modes. This paper will also discuss the relationship between film stress and preferred orientation, the observed failure modes and their linewidth dependence.
Fast Thermal Cycling - Enhanced Electromigratton Failures in Si/TiSi2W-Ti/Al-Si-Cu Multilayer Contacts
Authors: Ivkin Victor V. , Baranov Valentin V.
Published: April 2011

Failure mechanisms of TiSi2/W-Ti(15%)/Al-Si(l%)-Cu(2%) multilayer thin film contact to silicon shallow junction (0,25 μm) have been investigated. Both a fast temperature cycling (with 300 ms thermal cycle period) and a high constant temperature were used as means for the degradation processes acceleration. We have shown that stress time could be reduced by the factor of 10 or more if the temperature of adjacent contact region was cycled by a pulsed electrical current passed through the semiconductor region lying under the investigated contacts. Our data have also indicated that W-Ti barrier layer serves to reduce drastically the electromigration degradation of thin film contacts for failures caused by an increase in junction leakage on the one hand and on the other hand it serves to intensify the electromigration degradation caused by an increase in contact resistance. These distinctions have been explained through structural-morphological investigations of the contact layers surface morphology. They showed a reduction in size of crystallines of the sputter deposited Al-Si-Cu top layer with W-Ti barrier layer present.
Correlation of The Mechanical Properties of Silicon Oxynitride Films to Processing Parameters, Film Stoichiometry, and Hydride Bond Concentration
Authors: Moinpour Mansour , Moghadam Farhad , Williams Byron
Published: April 2011

A selective range of hydrated silicon oxynitride thin films (SixOyNz:H) have been characterized in terms of their stress, hardness, and modulus in order to mechanically qualify them for use as an encapsulation layer for memory devices (e.g., Flash and EPROM memories). These films are analyzed by RBS and HFS for stoichiometry. The films exhibited stress values between 1.86 x 109 to -3.54 x 109 dyne/cm2 and showed a linear correlation with the hydride ratio (N-H/Si-H). An Ultra Micro-Indentation System (UMIS) measured hardness values between 10.5 GPa to 16.2 GPa while the elastic modulus varied between 119.1 to 141.2 GPa. The monatomic increase of modulus with hardness is attributed to increased amounts of nitrogen and nitrogen hydride bonding in the silicon oxynitride samples.
Dual-Mode Ion Switching Conducting Polymer Films as High Energy Supercapacitor Materials
Authors: Naoi Katsuhiko , Oura Yasushi
Published: April 2011

The electropolymerized polypyrrole films formed from micellar solution of anionic surfactants, viz., Dodecylbenzene sulfonate(DBS), showed potential-dependent anion and cation ion switching behavior and the peculiar columnar structure. The formation process and the redox of the polypyrrole was studied with the in situ atomic force microscopy (AFM) and electrochemical quartz crystal microbalance(EQCM) methods. In-situ AFM observation clearly indicated that such a columnar structure started to form around critical charge densities of 60-100 mC cm−2. The cyclic voltammogram for the PPy doped with DBS− film showed two redox couples, each of which corresponds to a cation and an anion exchange process. Thus, the film behaves as a dual-mode ion doping/undoping exchanger. As the PPy film was prepared in higher concentration of the surfactant dopant, where the micelles are formed in solution, the resulting film showed a considerably higher(ca. three orders of magnitude) diffusion coefficient compared to ordinary PPy films so far reported. Such an enhanced diffusivity of ions could be attributed to a peculiar structure of the polymer formed. The feasibility of such polypyrrole in use of supercapacitor material was discussed.
Dual Intercalating Molten Electrolyte Batteries
Authors: Carlin R. T. , De Long H. C. , Fuller J. , Lauderdale W. J. , Naughton T. , Trulove P. C. , Bahn C. S.
Published: April 2011

Dual Intercalating Molten Electrolyte (DIME) electrodes and cells have been examined using a number of low-melting and room-temperature molten salts. A cell with a chloroaluminate melt achieved a cycling efficiency of 85% with a discharge voltage of 2.92 V. Coke-elastomer composite electrodes underwent cation reductive intercalation without experiencing the exfoliation and degradation seen for graphite rods. Theoretical studies for an imidazolium-graphite intercalate predict the graphite layer spacing expands between 5.18 and 8.01 Å upon insertion of the imidazolium molecule into the graphite lattice.
High Surface Area Electrode Materials by Derect Metallization of Porous Substrates
Authors: Chyan Oliver , Chen Jin-Jian , Liu Min , Richmond Michael G. , Yang Kaiyuan
Published: April 2011

Recent advances in high surface area (HSA) electrode materials have played an important role in the development of high-performance batteries and fuel cells. HSA electrodes can significantly increase the power-density of batteries and fuel cells by enhancing the heterogeneous electrochemical reaction rate and concurrently reducing battery and fuel cell size and weight. The compactness of HSA electrodes can also reduce the ohmic potential drop, which has the clear advantage of reducing power losses. This paper reports results on utilizing direct metallization of porous substrates to prepare new HSA electrode materials. Specifically, Nickel HSA electrode materials, relevant to the Ni-Cd and metal-hydride rechargeable batteries, were prepared on porous carbon substrates by direct thermolysis of organometallic precursors and/or electroless Ni plating. SEM and XPS characterization results indicate a Ni metallic film was conformally coated over the porous carbon skeleton. The real electroactive areas were determined electrochemically in NaOH solution and results will be discussed in correlation with the metallization conditions.
Long Endurance Materials for Aluminum Fuel Cell Systems
Authors: Hall Susan E. , Carter Dennis L. , Weber Carl L.
Published: April 2011

Appropriate selection of long endurance materials is critical to the cost effective use of fuel cell technology for near-term commercial and defense applications. To effectively transition this technology from laboratory prototype to fielded system, the durability of all fuel cell subsystems must be addressed. Material selection based upon a thorough understanding of system performance requirements, operational environments, and user interfaces not only provides high reliability and enhanced safety, but also lowers life cycle costs.

This paper discusses the development of an Aluminum Fuel Cell Power System (FCPS) for the Advanced Research Projects Agency (ARPA) Unmanned Underwater Vehicle (UUV) program, focusing on the operational endurance testing that was conducted to evaluate candidate materials for cell stack, electrolyte, and coolant subsystems.

The FCPS is a 15 kW closed aluminum-oxygen fuel cell system that provides up to 1.1 MWh energy. Loral has completed small-scale bench tests and is currently fabricating a full-scale system to be demonstrated in 1995. Requirements that strongly influenced material selection included: chemical compatibility - 4M KOH electrolyte pumped at 50°C, with dissolved aluminum and hydrargillite; system operational objectives - time between refueling and maintenance ranging from daily startup / shutdown to three weeks continuous; ARPA program objectives - commercial components, rapid prototyping, low life cycle costs.

A materials / component endurance test program was established and conducted early in the design phase of the FCPS program. To date, Loral has completed over 3000 operational test hours, with nearly 8000 hours of accumulated exposure to KOH. Results of these tests have been incorporated into the FCPS detailed design, and are expected to significantly enhance the performance of the fielded system. This program is sponsored by ARPA Maritime Systems Technology Office under NASA contract NAS3-26715.
Lithium Storage Mechanism in Nongraphitizable Carbon
Authors: Nagap Aisaku , Ishikawa Minoru , Masuko Jiro , Sonobe Naohiro , Chuman Hiroshi , Iwasaki Takao
Published: April 2011

A nongraphitizable carbon prepared from the cross-linked petroleum pitch and carbonized at 1473 K was found to have a unique structure and a charge capacity of more than 600 Ah/kg. A main peak of the 7Li Nuclear Magnetic Resonance spectra of the charged carbon shifted downfield with an increase of charge capacity. A Knight shift of lithium in the carbon charged to 600 Ah/kg reached 110 ppm when LiCl was used as the reference of 0 ppm. This shift was clearly distinguished from that of the lithium state in the first stage of the graphite intercalation compound, because the latter was observed at 45 ppm. A modified extended Hükel molecular orbital calculation showed that the average net electron density on lithium atoms drastically increased with increasing concentration of lithium atoms if the aromatic molecular planes are more than 0.5 nm apart. Both the experimental and theoretical results suggest that lithium atoms form clusters in this nongraphitizable carbon.
Thermal Stability of the Oxygen Ion Conductor Bicuvox.10 In Different Gaseous Atmospheres
Authors: W.Breiter Manfred , Reiselhuber Karl , Dorner Gertrude
Published: April 2011

A study of the thermal stability of the oxygen ion conductor BICUVOX.10 was carried out on small pieces of the polycrystalline material by combined TGA and DTA measurements in air, nitrogen, oxygen and helium. The TGA measurements demonstrated that the weight change was less than 0.1% in the different gases. The DTA curves were practically the same. There is evidence for the occurence of a phase change. TGA curves were also taken on BICUVOX.10, the parent compound Bi4V2O11, and the oxides CuO, B2o2, V2O5. under hydrogen. The comparison of the reduction curves shows that BICUVOX.10 is stable up to about 550C with respect to a direct reduction by molecular hydrogen.
Material Characteristics and the Performance of Electrochemical Capacitors for Electric/Hybrid Vehicle Applications
Authors: Burke A.F. , Murphy T.C.
Published: April 2011

Electrochemical capacitors (ultracapacitors) are one approach to meeting the high power requirements for the energy storage system in an electric vehicle. Energy is stored in an electrochemical capacitor by charge separation in the double layer formed in the micropores of a very high surface area electrode material, which does not undergo chemical change as in a battery. Consequently, the material requirements for capacitors are very different from those of batteries. In the last several years, a number of promising material technologies have been identified for use in electrochemical capacitors. These include activated carbon fibers, foams, and composites, doped conducting polymers, and mixed metal oxides. The most important material property is its specific capacitance (F/gm or F/cm3). Carbon materials with specific capacitances of 100 to 300 F/gm have been developed. Doped polymer materials having specific capacitances of 300 to 400 F/gm are also being studied. In addition to high specific capacitance, the electrode material must also have a low electronic resistivity ( < 0.1 Ω-cm) in order that charge can be distributed with minimum voltage drop in the electrode. Electrochemical capacitor cells have been fabricated using the various material technologies with both aqueous and organic electrolytes. Tests of the cells have shown near ideal charge/discharge characteristics — that is, the voltage versus time curves are nearly linear for constant current tests. The energy densities of 1 V cells, using aqueous electrolytes, are 1 to 1.5 W-h/kg and those of 3 V cells, using organic electrolytes are 7 to 10 W-h/kg. Most of the cells have high power densities of 1 to 3 kW/kg. Numerous new materials for electrochemical capacitors have been identified, processed, and tested in electrodes and cells in recent years and progress is rapid in this relatively new field of research.
Order-Disorder Transitions in Gadolinium Zirconate: A Potential Electrolyte Material in Solid Oxide Fuel Cells
Authors: Meilicke Scott , Haile Sossina
Published: April 2011

Rare-earth, yttrium, and calcium doped zirconates are the materials of choice for electrolytes in solid oxide fuel cells. The dopant in these materials serves not only to stabilized the cubic phase of zirconia, but also to introduce anion defects that presumably increase the ionic conductivity. In order to understand the relationships between anion defect distribution, thermal history and ionic conductivity, the structural properties of gadolinium zirconate, Gd2Zr207, have been examined via high-temperature x-ray powder diffraction. Gadolinium zirconate is an ideal material for such a structure-property-processing study: it shows ordering of defects at low temperatures, taking on a pyrochlore structure, and disordering at elevated temperature, taking on a defect fluorite structure. Diffraction experiments, performed as functions of time and temperature, confirmed the transition temperature to lie between 1500 and 1550 °C. They also revealed that the transformation takes place most rapidly just below the transition temperature, indicating that the ordering process is kinetically constrained at low temperatures. Moreover, x-ray data collected at room temperature from quenched samples were found to be as useful, if not more so, than those collected in situ at high temperature. The latter are affected by thermal scattering, severely compromising data quality.
Irradiation Mixing of Al into U3Si
Authors: Birtcher R. C. , Ding F.-R. , Kestel B. J. , Baldo P. M. , Zaluzec N. J.
Published: April 2011

Thermal and irradiation induced intermixing of uranium suicide reactor fuels with the aluminum cladding is an important consideration in understanding their fission gas and fuel swelling behavior. We have used Rutherford backscattering to follow the behavior of an Al thin film on U3Si and U3Si2 during 1.5 MeV Kr ion irradiation at temperatures of 30 and 350°C. After an initial dose during which no intermixing occurs, the Al mixes quickly into U3Si. The threshold dose is believed to be associated with an oxide layer between the Al and the uranium suicide. At 300°C and doses greater than threshold, rates of mixing and aluminide phase growth are extracted.
Lateral Sputtering by Gas Cluster Ion Beams and its Applications to Atomic Level Surface Modification
Authors: Yamada Isao , Matsuo Jiro
Published: April 2011

Gas cluster ion beam equipment (max. voltage 30kV) for sputtering has been developed. Cluster ion beams from gaseous materials such as Ar, O2, N2 and compound materials such as SF6, N2O, CO2 can be generated by expanding them through a Laval nozzle into a high-vacuum region. With this equipment sputtering process fundamentals have been studied. One of the unique characteristics of gas cluster ion bombardment is lateral sputtering. This is shown experimentally by measuring the angular distribution of sputtered atoms and is predicted by molecular dynamics simulation. Dependencies of sputtering yield (10-1000 times higher than for the monomer ion case) on cluster ion size and on ion beam energy for different substrate surfaces have been obtained. Examples of surface smoothing (typically less than 1 nm average roughness) on metals, semiconductors and insulators and of surface cleaning are presented.
Enhanced Diffusion of High-Temperature Implanted Aluminum in Silicon Carbide
Authors: Suvorov A V. , Usov I.O. , Sokolov V.V. , Suvorova A.A.
Published: April 2011

The diffusion of aluminum in silicon carbide during high-temperature A1+ ion implantation was studied using secondary ion mass spectrometry (SIMS). Transmission electron microscopy (TEM) has been used to determine the microstructure of the implanted sample. A 6H-SiC wafer was implanted at a temperature of 1800 °C with 40 keV Al ions to a dose of 2 x 1016 cm-2. It was established that an Al step-like profile starts at the interface between the crystal region and the damaged layer. The radiation enhanced diffusion coefficient of Al at the interface was determined to be Di = 2.8 x 10-12 cm2/s, about two orders of magnitude higher than the thermally activated diffusion coefficient. The Si vacancy-rich near-surface layer formed by this implantation condition is believed to play a significant role in enhanced Al diffusion.
Carbon Nitride (Cnx) Films Formed by Ion Implantation into Thin Carbon Films
Authors: Husein Imad F. , Zhou Yuanzhong , Chan Chung , Kleiman Jacob I. , Gudimenko Yu , Leung Ka-Ngo
Published: April 2011

Carbon nitride (CNX) films were prepared by nitrogen ion implantation into carbon films (a-C) deposited on Si substrates by the anodic vacuum arc. Plasma Immersion Ion Implantation (PIII) and Ion Beam (IB) implantation methods were used. X-ray Photoelectron Spectroscopy (XPS) C Is and N Is spectra of all CNX films indicate the formation of carbon-nitrogen bonds. The bonds are associated with the C 1s peaks at 286.6 eV and 285.6 eV , and the N 1s peaks at 399.1 eV and 400.6 eV. Raman spectra show that the structure of the implanted films (CNX) becomes more amorphous as the two broad peaks at 1577 cm-1 (G line) and 1350 cm-1 (D line) observed in the a-C films disappear and a broad asymmetric peak around 1500 cm-1 is formed. The interfacial tension between the a-C films and the substrate , obtained from the contact angle measurements, decreased by more than half after nitrogen implantation.
The Improvement of Mechanical Properties of Aluminum Nitride and Alumina by 1 Kev Ar+ Ion Irradiation in Reactive Gas Environment
Authors: Koh S.K. , Son Y.-B. , Gam J.-S. , Kim C.-J. , Choi W.K. , Jung H.-J.
Published: April 2011

Ar ions with 1 keV energy was irradiated on aluminum nitride in an O2 environment to increase the bonding strength with Cu and also on alumina in an N2 environment to increase the bending strength. Cu(1000 Å) films were deposited by ion-beam sputter on Ar+ irradiated/unirradiated A1N surfaces and the change of the bond strength was investigated by a scratch test. For the study of chemical structural change on the Ar+ irradiated A1N surface, Cu(50Å) were deposited on an A1N substrate and XPS depth profile analysis was performed. Cu films deposited on Ar+ irradiated A1N under an O2 environment showed the bond strength of 30 Newton by a scratch test. On the basis of Cu3p, A12p near core levels and OI s, N1 s core level spectra, it was found that the improvement of bond strength of Cu films on the AlN surface resulted from the formation of intermediate layers such as copper oxide and aluminum oxynitride. The bending strength of polycrystalline alumina irradiated by Ar ions in an N2 environment was also increased.
Modification of the Wettability of Plexiglas and Carbon by Means of Ion Beam Implantation: Application to Fluid Management and Materials Processing in Microgravity.
Authors: Pageau J.F. , Ross G.G. , Couture É. , Poirier A. , Quirion F.
Published: April 2011

In the absence of gravity, the behaviour of a liquid within a container will depend on its ability to wet the container. For instance, we evidenced that wetting property is involved in the propagation of perturbation, at the liquid-air interface. Because of perturbation in space, there is a strong interest in the modification of wetting properties for fluid management and materials processing in microgravity. The use of low energy (-500 eV) ion beams is attractive. Combining their low mean range (a few nm) and erosion rate, they are well suited for the modification at will of surface composition. Nitrogen, oxygen and neon ions of low energy were used to bombard the surface of plexiglas (polymethylmethacrylate or PMMA) and carbon samples at different fluences. Advancing and receding contact angles were measured before and after the implantation. A decrease of the contact angle as a function of the fluence of implanted ions was measured. A partial recovery of the contact angles as a function of time after the implantation was also observed. There was evidence that the long term value of the contact angles was influenced by the composition of the gas surrounding the samples. These results are discussed in terms of the development of a new technology for the modification at will of wetting properties of materials.
Tight-Binding Molecular Dynamics Simulations on Point Defects Diffusion and Interactions in Crystalline Silicon
Authors: tang M. , colombo L. , Diaz De La Rubia T.
Published: April 2011

Tight-binding molecular dynamics (TBMD) simulations are performed (i) to evaluate the formation and binding energies of point defects and defect clusters, (ii) to compute the diffusivity of self-interstitial and vacancy in crystalline silicon, and (iii) to characterize the diffusion path and mechanism at the atomistic level. In addition, the interaction between individual defects and their clustering is investigated.