bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Interactions of Actinide Ions with Geologic Materials Studied by XAFS
Authors: Sylwester E. R. , Hudson E. A. , Allen P. G. 
Published: April 2011

ABSTRACTWe have investigated the interaction of the actinyl ion, , with silica, alumina, and montmorillonite surfaces under ambient atmosphere and aqueous conditions using x-ray Absorption Fine Structure (XAFS) Spectroscopy. In acid solution (pH ∼ 3.5), the uranyl ion shows a strong interaction with the silica and alumina surfaces, and a relatively weak association with the montmorillonite surface. The extent of direct surface interaction is determined by comparing structural distortions in the equatorial bonding environment of the uranyl ion relative to the structure of a “free” uranyl aquo complex. Based on this formalism, surface complexation on silica and alumina occurs through an inner-sphere mechanism with surface oxygen atoms binding directly to the equatorial region of the uranyl ion. In contrast, sorption on montmorillonite occurs by an outer sphere mechanism in which the uranyl ion retains the simple aquo complex structure and binds to the surface via ion-exchange. In near-neutral solutions (pH ∼ 6), sorption on all of the materials is dominated by an inner-sphere mechanism. The formation of surface oligomeric species is also observed on silica and alumina.
Infrared Evaluation of Heat Generation During the Cyclic Deformation of a Cellular Al Alloy
Authors: Rabiei A. , Hutchinson J. W. , Evans A. G. 
Published: April 2011

ABSTRACTHeat generation from a notch during the compression-compression fatigue of a cellular Al alloy has been measured and compared with a model. The measurements indicate that heat is generated because of hysteresis occurring in narrow cyclic plastic zones outside the notch. This process continues until the notch closes. At closure, a brief period of heat generation arises because of friction along the notch faces. A plasticity model based on the Dugdale zone is shown to provide a reasonably accurate characterization of the heat generated, with the proviso that an “ineffective” zone be transposed onto the notch tip. It is found that the temperatures generated are too small to cause fatigue by thermal softening. A fatigue mechanism based on either geometric softening of the cells or crack growth in the cell walls is implied.
In Situ Observation of Oxidization Process at the Most Upper Surfaces by x-ray Surface Propagation Waves
Authors: Horiuchi Toshihisa , Ishida Kenji , Matsushige Kazumi 
Published: April 2011

ABSTRACTThe characteristics and applicable studies of the x rays scattered and propagating near the most upper surface of the substrate under the total reflection condition are described. Since the peak energy of the x rays gives direct information on the electron density of the surface materials, some experiments have been first conducted to confirm this. Then, an in-situ observation of oxidization processes for evaporated Cu films has been also conducted under a UV irradiation and an acid vapor exposure, revealing that there exist several oxidizing stages in time variations, namely a slight increase in the electron density at the initial stage, subsequently an abrupt decrease, and then steady value suggesting the sealing-off mechanism in the oxidization phenomena.
Dual Band Infrared Thermography as a NDT Tool for the Characterization of the Building Materials and Conservation Performance in Historic Structures
Authors: Moropoulou A. , Avdelidis N.P. , Koui M. , Kanellopoulos N.K. 
Published: April 2011

ABSTRACTInfrared thermography is a non-destructive investigation technique, which is largely used because of the outstanding advantages that it is capable to provide in a variety of applications and especially for conservation purposes of historic monuments, where destructive sectioning is prohibited. In the present work, dual band infrared thermography (3–5.4 μm and 8–12 μpm) is used, to evaluate the humidity distribution by capillary rise in reference samples of porous materials in lab, in order to validate the examination of real scale material systems in situ. The combined study of vapor/moisture transport in prototypes simulating porous materials under controlled environmental conditions (Relative Humidity 60–80% & Temperature 25–40°C), provides interpretation tools to the investigation by IR Thermography of transport phenomena occurring at the masonry. The cross-investigation of consolidated porous stones and of repair mortars, in lab and in situ on historic monuments in Greece, permits to evaluate the performance of conservation materials, regarding their compatibility to the porous building stones on historic masonries. It is deduced that Infrared Thermography by recording thermal maps of the real surfaces under study provides information on the differential behavior of the various materials on the masonry scale regarding the water impregnation and evaporation phenomena, which control the weathering effects in porous media. Hence, infrared thermography might be used as a nondestructive technique to evaluate on a micro and macro scale the performance of conservation interventions and materials, in compatibility to the original materials on the level of the structures.
Method and Instrumentation for Nondestructive Characterization of Surface Area and Pore Size Distribution of Thin Films in Their Deposited State
Authors: Boltz E. S. , Spooner Y. H. , Albanna S. G. , Taylor D. J. , Stallings A. R. , Abeyta J. P. 
Published: April 2011

ABSTRACTTPL has developed a method and instrumentation system for characterizing the surface area and pore size distribution of a thin-film or coating in its as-deposited state. Errors associated with destructive removal of the film are avoided and small sample sizes can be utilized with high-fidelity results.
X-ray Microtomography of Fatigue Crack Closure as a Function of Applied Load In Al-Li 2090 T8E41 Samples
Authors: Morano R. , Stock S.R. , Davis G.R. , Elliott J.C. 
Published: April 2011

ABSTRACTCrack closure is held to be responsible for very low fatigue crack growth rates in many alloys such as Al-Li 2090 T8E41, and early crack face contact during unloading or prolonged contact during loading seems to reduce the driving “force” for crack extension. High resolution x-ray computed tomography (i.e., microtomography) allows one to image the entire volumes of samples and to quantify opening as a function of applied load over the entire crack surface. Crack closure results are reported for a fatigue crack grown under load ratio R=0.1 in a compact tension sample of Al-Li 2090 T8E41; the crack was free to choose its path unconstrained by side-grooves which are normally used to suppress crack deflection. The inter-relationship between crack path, crack face contact and applied load level are discussed.
Nondestructive Evaluation of Fatigue in Titanium Alloys
Authors: Rösner H. , Meyendorf N. , Sathish S. , Matikas T.E. 
Published: April 2011

ABSTRACTDissipated heat has been measured by thermographic technique during fatigue experiments on Ti-6AI-4V. Surface temperature of the specimen was found sensitive to the amount of fatigue damage accumulated in the material. An increased heat dissipation due to fatigue can be related to continuous change in the microstructure (increased dislocation density, stacking faults etc.) of the material. A method based on passive thermography can be proposed to monitor damage accumulation in Ti-6Al-4V due to cyclic loading.
Real-Time Monitoring of Acoustic Linear and Nonlinear Behavior of Titanium Alloys During Cyclic Loading
Authors: Frouin J. , Maurer J. , Sathish S. , Eylon D. , Na J.K. , Matikas T.E. 
Published: April 2011

ABSTRACTVariation in acoustic nonlinearity has been monitored in real time during fatigue, on four dogbone specimens of Ti-6A1-4V, under low cycle fatigue conditions, from the virgin state all the way to fracture. The results of these experiments show that the acoustic nonlinearity undergoes large changes during the fatigue and follows a similar trend for the material under given fatigue test conditions. Transmission electron microscopic (TEM) examination of the samples with similar composition fatigued to different stages indicates a gradual change in the microstructure and dislocation density, which correlates with the changes in acoustic nonlinearity.
Evaluation of the Degradation Dynamics of Thin Silicon Dioxide Films Using Model-Independent Procedures
Authors: Rodríguez R. , Nafría M. , Miranda E. , Suñé J. , Aymerich X. 
Published: April 2011

ABSTRACTThe degradation and breakdown of thin silicon dioxide films has been analysed using a two-step stress method. This procedure allows the evaluation of the degradation induced by the electrical stress without any assumption about the microscopic nature of the degradation process. The method has been used to analyse and compare the degradation dynamics when constant-voltage (CVS) and constant-current stresses (CCS) are applied to the oxide. Moreover, it is shown that in the case of CVS, the fitting of the I-t characteristics can provide quantitative information about the degradation (degradation rate) and breakdown (mean-time-to-breakdown), without taking into account any degradation model.
Correlation Between Development of Leakage Current and Hydrogen Ionization in Ultrathin Silicon Dioxide Layers
Authors: Afanas'ev V. V. , Stesmans A. 
Published: April 2011

ABSTRACTThe generation of leakage current across 3-6-nm thick thermal oxides on (100)Si under electrical stress or irradiation with 10-eV photons is compared with the radiation-induced defect generation in 35-66-nm thick SiO2 layers. The degradation of both ultrathin and conventional oxides appears correlated with the concentration of atomic hydrogen in the layer. Both the leakage currents and the irradiation-induced defects were found to have two components: one thermally unstable that correlates with the H-induced donor states, and another related to the permanent oxide network damage ascribed to H-assisted Si-O bond break. As both degradation processes involve a proton formed in the oxide, we suggest that H ionization either by electron emission or by trapping a hole triggers oxide degradation.
Initial Oxynitridation of a Si(001)-2×1 Surface by NO
Authors: Miyata Noriyuki , Watanabe Heiji , Ichikawa Masakazu 
Published: April 2011

AbstractWe have investigated the initial oxynitridation of an atomically flat Si(001)-2×l surface by NO. We found that appropriate oxynitridation conditions, in which oxide decomposition does not occur, are required to suppress the roughness of the NO-reacted Si surface. Under these conditions, we investigated the growth behavior and chemical structure. The first oxynitridation, in which NO reacts with the first Si layer on the Si(001)-2×l surface, takes place in a layer-bylayer manner caused by two-dimensional nucleation. However, further oxynitridation for the second Si layer proceeds in a three-dimensional manner in which the atomic-scale roughness at the oxynitride/Si interface increases. In addition, under our oxynitridation conditions, N is incorporated as N ≡ Si3, even though the oxynitride is ultrathin.
Paramagnetic Defects Related to Positive Charges in Silicon Oxynitride Films
Authors: Miura Y. , Fujieda S. , Hasegawa E. 
Published: April 2011

ABSTRACTElectron spin resonance (ESR) spectroscopy is used to explore the origin of positive charges in silicon oxynitride thin films formed in a N2O ambient. A new type of paramagnetic center in as-grown oxynitrides appeared as a single peak in the ESR spectrum with a zero crossing g value of 2.0006. This value suggests that the paramragnetic center is a kind of E' center. We investigated the quantitative behavior of the positive charge center and the paramagnetic center through the density changes induced by vacuum ultraviolet irradiation and hydrogen annealing. Based on the similar behavior of both types of center, we argue that the paramagnetic centers can account for a significant part of the positive charges specific to oxynitrides. Since the spin density increased with the oxynitridation temperature, the paramagnetic center is closely related to nitrogen incorporation processes.
Dynamics of Silicon Oxidation
Authors: Stoneham A. M. , Szymanski M. A. , Shluger A. L. 
Published: April 2011

ABSTRACTThe rate-determining process in dry oxidation of silicon for thicker oxides (say above 10 nm) is probably the interstitial diffusion of oxygen molecules. For thinner oxides (a few nm), this simple picture is inadequate. The Deal-Grove model of oxidation kinetics fails. Oxide usually grows by an essentially layer-by-layer process, with growth at terraces, not steps, and perhaps oscillatory roughening. Isotope experiments show that interstitial and network oxygens exchange close to the Si/oxide interface and close to the oxide/gas interface. These results imply limiting mechanisms other than diffusion, probably involving charged oxygen species. We have made Density Functional (DFT) Generalised Gradient Approximation (GGA) calculations for a range of neutral and charged oxygen species to assess relative stabilities, diffusion mechanisms, and propensity for isotope exchange. These results identify acceptable mechanisms. We have also used Monte-Carlo methods to examine the consequences of the image interaction bias, and also the effects of the charge transfer processes (like tunnelling) by which charged species form. We comment on implications for oxide quality, especially on the relationship between growth processes and the charge and energy localisation components of breakdown.
The Boundary Between Hard- and Soft-Breakdown in Ultrathin Silicon Dioxide Films
Authors: Toriumi A. , Satake H. 
Published: April 2011

ABSTRACTThe dielectric breakdown is an irreversible and transient process, and it is difficult to understand its dynamic characteristics. We notice that the post-breakdown electrical properties of silicon dioxide films may include much information on the dielectric breakdown mechanism. First, the resistance of silicon dioxide films after the dielectric breakdown is statistically investigated, and then this analysis is applied to differentiate the hard- from the soft-breakdown. In particular, we discuss the critical dependence of the boundary between the hard- and softbreakdown on the discharging time constant as well as the discharging energy at the breakdown, concerning the formation of the conductive filament in the insulator silicon dioxide films. It should be noted that the ratio of the soft- to the hard-breakdown changes in terms of the statistical distribution in the case that the growth parameters and the measurement conditions are changed. In partcular, the external inductance effect to modify the discharging time constant in the MOS circuit is discussed. The thickness limitation of the silicon dioxide film in the roadmap is in this transition region, and this fact will be of essential importance in the assessment of the reliability and the process control of silicon device fabrication in sub-5nm silicon dioxide regime.
A Study of Trap Profiles in Thin Silicon Dioxide Films at Dielectric Breakdown Using Percolation Model
Authors: Uno S. , Ishida A. , Okada K. , Sakura T. , Deguchi K. , Kamakura Y. , Taniguchi K. 
Published: April 2011

ABSTRACTA Monte Carlo simulation of wear-out process in thin silicon dioxide films is performed to investigate the correlation between the electron trap distribution and the dielectric breakdown. Non-uniformity of the trap generation and its dependence on the stress conditions are monitored by the measurements of the charge centroid. In order to include these experimental observations into Degraeve's percolation model [IEDM Tech. Dig., pp.863-866 (1995)], we introduce exponential trap profiles decaying from the Si/SiO2interface. Our new model successfully reproduces critical threshold voltage shifts from the information about critical charge centroids for various stress conditions. Finally, as a reasonable explanation of the stress dependent breakdown properties, we suggest that the bond strain caused by lattice mismatch at the interface is accelerated by the electric field.
Precise characterization of ultrathin nitride/oxide gate dielectrics by grazing x-ray reflectance and spectroscopic ellipsometry
Authors: Boher Pierre , Piel Jean Philippe , Stehle Jean Louis 
Published: April 2011

ABSTRACTPrecise characterization of nitride/oxide gate structures becomes a challenging task due to the very thin thickness (<3-4nm), which will be needed in the next generation integrated circuits. Conventional techniques such as spectroscopic ellipsometry in the visible range becomes difficult to apply because of the great correlation between thickness and optical indices. To overcome this problem the following strategy is applied. First, grazing x-ray reflectance is used on all the samples to extract the different layer thicknesses using a simple model. Second, spectroscopi ellipsometry from deep UV 190nm to 850nm is applied and the results fitted with the structural models deduced from the x-ray results. In this conditions the nitrogen content of the films can be precisely determined. This kind of analysis has been made on a series of nitride/oxide gate structures with variable thicknesses and degree of nitridation. Regression results are discussed and compared to x-ray photoemission results obtained on the same samples.
Deposition and Characterization of Ultrathin Ta2O5 Layers Deposited on Silicon From a Ta(OC2H5)5 Precursor
Authors: Chaneliere C. , Autran J.L. , Reynard J.P. , Michailos J. , Barla K. , Ushikawa H. , Hiroe A. , Shimomura K. , Kakimoto A. 
Published: April 2011

ABSTRACTUltra-thin tantalum pentoxide (Ta2O5) layers of thicknesses ranging from 6 to 10 nm were deposited by low pressure chemical vapor deposition from Ta(OC2 H5)5 on rapid thermal nitrided silicon substrates. Films were annealed in UV-O3 at 450°C, in dry O2 at 750°C or by using a combination of these two treatments. The physico-chemical properties were studied by TEM and SIMS. Results showed an oxidation of the interfacial region during annealing. The C and H contaminants are reduced during the O2 post-deposition treatment, and this step may also lead to a modification of the chemical state of C in Ta2O5. Both capacitance-voltage and current-voltage measurements were performed on Al/Ta2O5/Si structures. Excellent electrical properties were recorded: high dielectric constant (between 14.8 and 19 in the case of the double step annealing, which corresponds to an equivalent SiO2 thickness ranging from 2.0 to 2.3 nm), low leakage current densities (close to 5×10−9 A.cm−2 @ 1MV.cm−1) and promising long-term reliability.
Band Alignments of High-K Dielectrics on Si and Pt
Authors: Robertson J , Riassi E , Maria J-P , Kingon A I 
Published: April 2011

ABSTRACTMaterials with a high dielectric constant (K) such as tantalum pentoxide (Ta2O5) and barium strontium titanate (BST) are needed for insulators in dynamic random access memory capacitors and as gate dielectrics in future silicon devices. The band offsets of these oxides must be over 1 eV for both electrons and holes, to minimise leakage currents due to Schottky emission. We have calculated the band alignments of many high K materials on Si and metals using the method of charge neutrality levels. Ta2O5 and BST have rather small conduction band offsets on Si, because the band alignments are quite asymmetric. Other wide gap materials Al2O3, Y2O3, ZrO2 and ZrSiO4 are found to have offsets of over 1.5 eV for both electrons and holes, suggesting that these are preferable dielectrics. Zirconates such as BaZrO3 have wider gaps than the titanates, but they still have rather low conduction band offsets on Si. The implications of the results for future generations of MOSFETs and DRAMS are discussed.
Influence of the Deposition Parameters on the Electrical and Mechanical Properties of Physically Vapor-Deposited Iridium and Rhodium Thin Films
Authors: Golecki Ilan , Eagan Margaret 
Published: April 2011

AbstractIridium and rhodium thin films have been formed by e-gun physical vapor deposition on thin-chromium-coated, thermally-oxidized, silicon substrates. Cr, Ir and Rh deposition rates and substrate temperature during deposition were measured and controlled. The effects of the latter deposition parameters on the sheet resistance and stress of the Ir and Rh films are presented and it is demonstrated that both stress and sheet resistance can be desirably minimized by proper choice of the process conditions. The resistivity of these Rh and Ir thin films has been measured at room temperature. Rh can be formed in a wider process window than Ir. Rh films with Rsh = 0.1 Ω/square have been obtained at a thickness of 0.6 ¼m.
The Influence of Thermal History and Alloying Elements on Temporary Strengthening of Thin Al-Cu Films
Authors: Lokker J. P. , Janssen G. C. A. M. , Radelaar S. 
Published: April 2011

AbstractThe influence of Cu on the response of Al-Cu thin films to thermally induced stress is studied. The copper concentration is varied between 0 and 1.15 at. %. It is proposed that copper atoms which have not formed precipitates, largely affect the mechanical behaviour. This idea is supported by the following observations. An isothermal hold results in temporary strengthening of the films. The extent of this strengthening increases with copper concentration, increases with decreasing isothermal hold temperature and saturates with increasing isothermal hold period. Based on these observations the large tensile stress increase below 200 °C is ascribed to the formation of Cottrell atmospheres.
In Situ Study of Dislocation Behavior in Columnar Al Thin Film on Si Substrate During Thermal Cycling
Authors: Allen Charles W. , Schroeder Herbert , Hiller Jon M. 
Published: April 2011

AbstractIn situ transmission electron microscopy (150 kV) has been employed to study the evolution of dislocation microstructures during relatively rapid thermal cycling of a 200 nm Al thin film on Si substrate. After a few thermal cycles between 150 and 500°C, nearly stable Al columnar grain structure is established with average grain less than a μm. On rapid cooling (3–30+ °C/s) from 500°C, dislocations first appear at a nominal temperature of 360–380°C, quickly multiplying and forming planar glide plane arrays on further cooling. From a large number of such experiments we have attempted to deduce the dislocation evolution during thermal cycling in these polycrystalline Al films and to account qualitatively for the results on a simple dislocation model.
Silicide Induced Mechanical Stress in Si: What are the Consequences for MOS Technology
Authors: Maex Karen , Steegen An 
Published: April 2011

AbstractIn this paper, a detailed analysis of silicide induced stress is presented. Micro-Raman spectroscopy measurements of the silicide induced stress in the silicon substrate are combined with simulations by Finite Element Modeling down to 0.1 μm MOS technologies. It is shown that the scaling possibilities of TiSi2 and of CoSi2 are both hampered by the increasing silicide stress, which can even result in the generation of dislocations in the silicon substrate. Because of the difference in material properties between TiSi2 and CoSi2, TiSi2 induces a higher stress in the silicon substrate than CoSi2. It is also proven that the silicide induced stress affects the performance of transistors and diodes. Therefore, the mechanical characteristics related to the silicide formation become a critical parameter in the optimization of the silicide for sub-0.25μm MOS technologies.
Influence of Nanometer-Scale Multilayered Thin Films on Fatigue Crack Initiation
Authors: Stoudt M. R. , Cammarata R. C. , Ricker R. E. 
Published: April 2011

AbstractThe hypothesis that a thin nanometer-scale multilayered surface film could delay crack initiation and extend fatigue lives was evaluated by electrodepositing a Cu-Ni multilayer on Cu fatigue samples. A significant improvement in fatigue lives resulted and this improvement is attributed to properties of the multilayer coating.