bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Characterization Of Morphological Evolution In Q = 2 Potts Model Aluminum Thin Films
Authors: Alsem D. H. , Stach E. A. , de Hosson J. Th. M.
Published: April 2011

In this research, we have focused on the morphological evolution of a model metal film / silicon substrate system. When aluminum (Al) is physical vapor deposited on (100) oriented single crystal silicon (Si) at 280 °C it grows heteroepitaxially. Crystallographically, the resulting films are a Potts model system with degeneracy two; their topology simulates a polycrystalline grain structure, with the two types of grains enveloping each other in a convoluted, maze-like arrangement. The morphological evolution of the films during annealing was determined via a combination of transmission electron microscopy (TEM) and atomic force microscopy (AFM). Films with thickness' of 100 to 500 nm were annealed in-situ in the TEM from 250 °C to 550 °C, and characterized using a (220) two-beam condition from one of the grain orientations. This yields predominantly white on black images, which are amenable to quantitative image processing techniques. As anticipated, the grain size increased linearly during the first annealing cycle. Also so-called sub-grain boundaries were observed. These low angle boundaries originate during film deposition when arrays of dislocations are introduced in the areas where coalescing islands of the same orientation meet. After cooling and reheating the sub-grain boundaries disappear. This happens because upon cooling, misfit dislocations were introduced into the films to relieve the thermal misfit strain, resulting in a dense array of dislocations at the film / substrate interface. These thermal misfit dislocations interact strongly with pre-existing sub-grain dislocations; this, in effect, heals the microstructure.
Room temperature grain growth in sputtered Cu films
Authors: Deduytsche D. , Detavernier C. , Debaerdemaeker J. , Van Meirhaeghe R.L. , Dauwe C. , Kuan T.S.
Published: April 2011

The results are presented of a study on grain growth in magnetron sputter deposited Cu films. Similarly to the well-known case of electroplated Cu, we observed significant changes in the microstructure of sputter deposited films during storage at room temperature, as evidenced by a decrease in sheet resistance (up to 40% decrease in less than 6 hours). Direct evidence for grain growth was observed by FIB and SEM and by a strong decrease in the XRD peak width. Moreover, a decrease in the total defect content of the film was observed as a function of storage time from positron annihilation experiments, probably reflecting the decreasing number of grain boundaries in the film. It is well known that the microstructure of an as-deposited film is strongly dependent on the deposition parameters. This relationship is summarized in the Thornton structure-growth zone diagram [7]. We have studied the kinetics of room temperature grain growth as a function of Ar pressure and substrate temperature for Cu films with a thickness between 50 nm and 1 micrometer. It is found that spontaneous grain growth during storage at room temperature occurs mainly for a zone T microstructure (at low Ar pressure and a substrate temperature below 40°C), while it does not occur for zone I (high Ar pressure, low substrate temperature) or zone II (substrate temperature > 100°C) microstructures.
Ge/Si(100) Island and Wetting Layer Composition
Authors: Zhang Yangting , Drucker Jeff
Published: April 2011

ABSTRATCT

Etching water soluble Ge-oxides was used to investigate Si interdiffusion into epitaxial Ge / Si(100) samples. The Ge coverage, θGe, was measured using Rutherford backscattering spectrometry (RBS) before and after water etching of samples grown at substrate temperatures between 400 °C and 650 °C. θGewas correlated with sample morphology determined using atomic force microscopy (AFM). The local Ge concentration was qualitatively assessed using energy dispersive x-ray (EDX) analysis. For samples grown at T=400 °C, water completely dissolves the islands and no Ge is detected by RBS. For samples grown at T=600 and 650 °C, AFM detects no change in the surface morphology and RBS indicates that θGedecreases by about 3 monolayers (ML). These results suggest that for growth at T=400 °C, both the islands and wetting layer are relatively pure Ge while for growth at T≥600 °C, the wetting layer is Ge rich compare to the SiGe alloy islands. EDX confirms this conclusion detecting no Ge signal between islands for etched samples grown at T≥600 °C. Our results suggest that for growth at T≥600 °C, Si interdiffusion into islands is through the region underneath the islands instead of from the wetting layer.
STM studies of island nucleation during hyperthermal atom deposition
Authors: Pomeroy Joshua M. , Brock Joel D.
Published: April 2011

We report fundamental changes in island nucleation dynamics as the kinetic energy of the constituent particles used for film grown is increased. A hyperthermal energy ion beam-line with precise control over ion kinetic energy was used to grow copper islands on a Cu(100) substrate. Dramatic increases in island densities were observed with increasing kinetic energy from thermal energies to 150 eV. We find that sputter erosion and the formation of adatom-vacancy pairs contribute to this increase. In addition, variations in flux and temperature suggest that the mean-field scaling exponent is sensitive to atomistic mechanisms activated by the ion beam.
Time-Dependent Capture Numbers with Repulsive Pair Interactions: Cu/Cu(111) and Ge/Si(001)
Authors: Venables J. A. , Brune H. , Drucker J.
Published: April 2011

Recent experiments and calculations have shown that weak repulsive interactions between adsorbate atoms may shift nucleation kinetics from the well-known diffusion limit towards the attachment-limited case. The distinctions between diffusion- and attachment-limited kinetics are clarified, and the increased importance of the transient nucleation regime in the latter case is shown to be due to a combination of delayed nucleation and reduced capture. A time-dependent interpolation scheme between attachment- and diffusion-limited capture numbers is proposed, and tested against KMC simulations. Using this scheme to interpret recent STM results on Cu/Cu(111), bounds on the maximum adatom-adatom potential repulsive energy of 12±2 meV are deduced. Time-dependent effects also occur in the growth and ripening of strained Ge islands on Si(001), and the similarities and differences between these two systems are discussed.
Structural properties of SiGe islands: Effect of capping
Authors: Stangl Julian , Hesse Anke , Holý Vaclav , Bauer Günther , Denker Ullrich , Schmidt Oliver G. , Kirfel O. , Gruützmacher D.
Published: April 2011

Self-organized nanostructures are increasingly important for novel optoelectronic devices, as high densities of quantum dots can be deposited directly during heteroepitaxial growth. Due to the elastic relaxation in 3D nanostructures, properties differing from 2D systems can be achieved, e.g., higher Ge contents in SiGe islands than in planar layers with the same total amount of Ge can be realized, enhancing the design freedom for, e.g., detectors or high frequency transistors. However, when such nanostructures are overgrown, which is inevitable for any application, they often undergo significant changes, partly eliminating their distinct advantages. We present an investigation of SiGe islands formed by deposition of pure Ge on Si (001). X-ray scattering and diffraction is employed to obtain the shape, strain and Ge distribution in uncapped as well as Si-capped islands. For the analysis, model calculations of the strain fields are required. The finite element method is used for uncapped islands, for buried nanostructures a novel analytical approach has been developed. For Tgrowth ∼ 650°C, optimized for island formation, the Ge content in the top part of uncapped islands reaches 100%, at an elastic relaxation of about 50%. During capping, the maximum Ge content considerably decreases to about 50%. At the same time, the islands become very flat, with a decrease in height from 13 to 6nm accompanied by an increase in base diameter from about 100 nm to 180 nm. The elastic relaxation decreases to about 2.5%, so that the buried islands have properties not very much different from 2D layers. Lowering the growth temperature for the Si cap, this effect can be avoided, for Tgrowth as low as 460°C, the structure of the uncapped islands can indeed be preserved.
Microstructural characterization of porous thin films
Authors: Djurfors B. , Brett M.J. , Ivey D.G.
Published: April 2011

A preliminary TEM investigation of porous films fabricated by glancing angle deposition has shown the importance of surface diffusion and crystal structure in determining the final microstructure of the film. Although the process variables are extremely important in defining the morphology of the film, their effects are limited in terms of final microstructure.
X-ray scattering studies of low-T Ag(001) and Cu(001) homoepitaxy: Vacancy trapping and surface morphology evolution
Authors: Botez Cristian E. , Li Kaile , Lu Erdong D. , Miceli Paul F. , Conrad Edward H. , Stephens Peter W.
Published: April 2011

We have used synchrotron x-ray diffraction to study the low-T homoepitaxial growth on Ag(001) and Cu(001) surfaces. For both systems, we found that a large, temperature-dependent vacancy concentration is incorporated in films grown below 160K. The vacancy trapping occurs concomitantly with substantial changes in the surface morphology, where a non-monotonic temperature dependence of the mean-square surface roughness has been previously observed. For Cu/Cu(001) we also found that the concentration of vacancies incorporated at 110K evolves, upon heating, according to the vacancy annealing behavior well-known from radiation damage studies of bulk copper and it is consistent with the activation energy for vacancy mobility.
Effects of the Amorphous Oxide Intergranular Layer Structure and Bonding on the Fracture Toughness of a High Purity Silicon Nitride
Authors: Ziegler A. , Kisielowski C. , Hoffmann M. J. , Ritchie R. O.
Published: April 2011

The microstructural evolution and structural characteristics and transitions in the thin grain-boundary oxide films in a silicon nitride ceramic, specifically between two adjacent grains and not the triple junctions, are investigated to find their effect on the macroscopic fracture properties. It is found that by heat treating a model Si3N4-2wt% Y2O3ceramic for ∼200 hr at 1400°C in air, the fracture toughness can be increased by ∼100%, coincident with a change in fracture mechanism from transgranular to intergranular. Structural phase transformations occur in the thin grain boundaries during oxidation that are revealed by XRD, EDX, Raman and EELS analyses. They affect the local bonding of atoms. It is concluded that only specific crystal “building blocks”, i.e., tetrahedra, are transformed along the grain boundary and the resulting difference in the atomic structure of the oxide interface is seen directly to alter the macroscopic fracture behavior.
Grain Boundary Segregation in Titanium Dioxide: Evaluation of Relative Driving Forces for Segregation
Authors: Wang Qinglei , Lian Guoda D. , Dickey Elizabeth C.
Published: April 2011

Solute segregation to grain boundaries is a fundamental phenomenon in polycrystalline metal-oxide electroceramics that has enormous implications for the macroscopic dielectric behavior of the materials. This paper presents a systematic study of solute segregation in a model dielectric, titanium dioxide. We investigate the relative role of the electrostatic versus strain energy driving forces for segregation by studying yttrium-doped specimens. Through analytical transmission electron microscopy studies, we quantitatively determine the segregation behavior of the material. The measured Gibbsian interfacial excesses are compared to thermodynamic predictions.
Phase Evolution During Crystallization of an Amorphous TiAl Film
Authors: Senkov O.N. , Uchic M.D.
Published: April 2011

Phase evolution during crystallization of an amorphous TiAl film produced by physical vapor deposition (PVD) was studied using differential thermal analysis (DTA), x-ray diffraction (XRD), and transmission electron microscopy (TEM). The following sequence of phase transformations was observed during continuous heating from room temperature: amorphous → body centered cubic (β) → hexagonal close-packed (α) → tetragonal (γ) → ordered α2. The β phase was formed as near-spherical particles that were evenly distributed in the amorphous phase, and the size of these particles was approximately 90 nm. Formation of the α phase by decomposition of β and the remaining amorphous phases led to a very fine feathery-like microstructure arranged in colonies of approximately 100 nm in size. The transformation of the metastable α phase into a mixture of the γ and α2 phases led to formation of an equiaxed γ-grain structure with a grain size of about 150 nm after heating to 850°C.
Diffusion and Relaxation in Glasses and their Melts
Authors: Caprion D. , Kluge M. , Schober H. R.
Published: April 2011

Results of computer simulations of diffusion and relaxation in the liquid and the glassy state are presented for model systems and Cu33Zr67 and Se. The diffusion constant and the intermediate self scattering function show the typical behavior upon quenching from the liquid to the glass. The diffusion constant in the undercooled liquid can be fitted both with a Vogel-Fulcher or a mode coupling law. However, its pressure derivative, the activation volume, clearly follows the prediction of the mode coupling theory. From the diffusional isotope effect in the liquid we conclude that collectivity increases upon quenching to the glass transition. Checking the relaxations in the glass we find collective hopping of chains of atoms as elementary process. Both in the glassy state and in the undercooled liquid we observe an increase oc ∝√ι ofthe non-Gaussianity of the self correlation function, which measures the dynamic heterogeneity. This can be understood from the collective jump mechanism.
Relaxation Dynamics of Glass-Forming Liquids Studied by Ultrasonic Spectroscopy: Stretched Response of Supercooled Ethylbenzene
Authors: Cutroni M. , Mandanici A.
Published: April 2011

Glass forming liquids exhibit their strong or fragile behaviour as a function of temperature, featuring a smaller or greater deviation from a simple Arrhenius law. The size of such deviation on a typical time scale of 10-6 s characterizes the ‘kinetic fragility’ F1/2 of a given material. Ultrasonic experiments in the MHz region are then suitable to show how the relaxational properties are influenced by the ‘fragile’ character of the liquid investigated. On this basis, measurements of acoustic attenuation at fixed frequency (15 MHz) have been performed on glass forming liquid ethylbenzene in the temperature range 100 K-300 K and compared with previous results on simple supercooled liquids derived from benzene. To prevent crystallization each temperature point below 190 K was reached by cooling the sample directly from 300 K and using also different cooling rates. Measurements have given evidence of a mechanical relaxation process: below the melting temperature the acoustic attenuation exhibits a peak and correspondingly the sound velocity increases from liquid-like to solid-like values. A stretched response function is required to reproduce the observed behaviour. The values of the Kohlrausch-Williams-Watts stretching parameter βkww which describe the experimental data are very low, if compared to those obtained for other glass-forming liquids.
Calculated Effect of Alloy Additions on the Saturation Magnetization of Fe0.80B0.20
Authors: Nicholson D. M. C. , Wang Yang , Widom Mike
Published: April 2011

The great number of different local environments in amorphous alloys leads to the evolution of complicated non collinear magnetic structures. Alloy additions can affect the magnetic structure in surprising ways. For example, replacement of a small amount of Fe with Co increases the saturation magnetization even though Co has a much smaller moment than Fe. The calculated behavior of the magnetic structure of (Fe(1-x)Mx) 0.8B0.2 with M=Co, Cr, Zr, and Mn2Zr are presented.
Structure of Shear Bands in Zirconium-Based Metallic Glasses Observed by Transmission Electron Microscopy
Authors: Gu Xiaofeng , Livi Kenneth J. T. , Hufnagel Todd C.
Published: April 2011

We have used transmission electron microscopy (TEM) to investigate the structure of shear bands produced by bending electron-transparent Zr52.5Cu17.9Ni14.6Al10Ti5metallic glass specimens. Shear bands were located by comparing the structure of the specimens before and after deformation. The shear band spacing is influenced by the structure of the specimen; portions of the specimen with a significant population of nanocrystals show a smaller separation between shear bands. Quantitative high resolution TEM analysis based on ratio technique has been used to explore the defect structure in shear bands. High density and void-like defects with size of about 1 nm were found in shear bands formed in both amorphous and nanocrystalline areas. A simple model was proposed to explain the formation of these defects.
Elevated Temperature Fatigue Crack Propagation of a Zr-Ti-Cu-Ni-Be Bulk Metallic Glass
Authors: Hess Peter A. , Dauskardt Reinhold H.
Published: April 2011

The sub-Tg elevated temperature fatigue propagation behavior of a Zr-based bulk metallic glass was examined. Fatigue crack-growth rates as a function of the applied stress intensity range, ΔK, are reported. Increased testing temperature was found to increase ΔKTH. Examination of crack surfaces at near-threshold growth rates revealed the presence of elongated ridges perpendicular to the crack front at higher temperatures; these ridges were absent in specimens tested at lower temperatures. The size of the features was found to increase with temperature and applied ΔK, finally breaking up at higher growth rates. Mechanisms responsible for the ridge formation are described, and modeled in terms of fluid meniscus instabilities that occur at the fatigue crack tip.
Microstructures and properties of the tungsten wire/particle reinforced Zr57Nb5Al10Cu15.4Ni12.6 metallic glass composites
Authors: Choi-Yim Haein , Schroers Jan , Johnson William L.
Published: April 2011

Tungsten wire or particle reinforced metallic glass matrix composites are produced by infiltrating liquid Zr57Nb5Al10Cu15.4Ni12.6 (Vit106) into tungsten reinforcements at 1150 K and at 1425 K. X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy are carried out to characterize the composite. The matrix of the composite processed at 1150 K is mostly amorphous, with some embedded crystals. During processing, tungsten dissolves in the glass-forming melt and upon quenching precipitates over a relatively narrow zone near the interface between the tungsten and matrix. In the composites processed at 1425 K, tungsten dissolves in the melt and diffuses through the liquid medium, and then reprecipitates upon quenching. The faster kinetics at this high temperature results uniform distribution of the crystals throughout the matrix. Mechanical properties of the differently processed composites containing wires and particles are compared and discussed. The composites exhibit a plasticity of up to 16 % without sacrificing the high strength to failure that is comparable to monolithic Vit 106.
Sorption of Pu(III-IV) Onto Tio2: A Preliminary Study
Authors: Olsson M. , Nilsson H. , Jakobsson A. M. , Albinsson Y.
Published: April 2011

A preliminary study of the sorption of reduced plutonium (III-IV) onto TiO2 has been done under anoxic conditions at varying pH and ionic strength. The first approach was to study tetravalent Pu, but the sorption decreases with time in this case. This is probably due to disproportionation of Pu(IV) at the TiO2 surface, which then acts as a catalyst. A further observation that supports this explanation is that the sorption of Pu(IV) onto the walls of the experimental equipment is in some cases higher than the sorption of (disproportioned) Pu onto the oxide.

Pu(III) sorption onto the oxide was also investigated and showed similarities with the previously investigated sorption of Pm(III) in a similar system.
The Conservation of Ancient Glass
Authors: Paterakis Alice Boccia
Published: April 2011

Glass undergoes various corrosion mechanisms during burial. The state of deterioration and corrosion phenomena are deciding factors in the choice of conservation materials and techniques. Among the conservation treatments reviewed for ancient, archaeological glass are pre-treatment storage, cleaning, consolidation of weakened and de-vitrified glass, adhesives for reconstruction, and fill materials for restoration. The most recent materials and techniques used by conservators are presented. The concepts of permanence and reversibility with regard to conservation methods and materials are examined.
Cell Density Dependent Reduction Kinetics of Hexavalent Uranium byShewanella oneidensis
Authors: Mullen Lisa , Klepac Vanja , Pharino Chanathip , Czerwinski Ken , Polz Martin
Published: April 2011

Shewanella oneidensisis a widely distributed species of bacteria and is known to utilize several elements such as iron, manganese and sulfur as electron acceptors. In an anoxic environment lacking more electrochemically favourable electron acceptorsS. oneidensisis shown to reduce uranium, changing its oxidation state from hexavalent to tetravalent, by the following reaction: H2+ UO22+→ 2H++ UO2. The uranyl solution concentration (U(VI)) was measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), and the reduction data were fit to first order. Several cell concentrations were examined and both the rate of uranyl reduction and the total amount of uranyl reduced are found to be dependent upon cell density. The largest rate constant was 0.7 hr-1corresponding to a cell density of 2.4*109cells/mL and an initial reduction rate of 1414 μM/hr. A cell concentration of 6.6*108cells/mL gave rise to an initial reduction rate of 400μM U(VI) per hour, and had, within a period of 72 hours approximately 98% of the original 2 mM uranyl acetate reduced, as opposed to only 87% for 2.4*109cells/mL.
Sand/Bentonite Barriers and Gas Migration: The GMT Large-Scale In-Situ Test in the Grimsel Test Site
Authors: Vomvoris S. , Lanyon B. , Marschall P. , Ando K. , Adachi T. , Fujiwara A. , Yamamoto S.
Published: April 2011

The Gas Migration Test in the engineered barrier system (GMT) investigates the migration of waste-generated gas from low and intermediate level waste in a silo-type disposal concept. The EBS has now been emplaced and saturation was initiated in August 2001. The saturation patterns show heterogeneity within and between different layers of the EBS. Plans for the remaining test sequence are also presented.
Corrosion Behavior of Carbon Steel and Stainless Steel Materials under Salt Deposits in Simulated Dry Repository Environments
Authors: Yang Lietai , Pabalan Roberto T. , Browning Lauren , Dunn Darrell S.
Published: April 2011

In-situ coupled multielectrode array sensors were used to measure the non-uniform corrosion of carbon steel and stainless steel materials under KCl salt deposit in simulated dry repository environments. It was found that the initiation of non-uniform corrosion occurs at a relative humidity that is 14% lower than the deliquescence relative humidity of the chloride salt. It was found also that once significant corrosion had occurred, the non-uniform corrosion process for the carbon steel material under the salt deposit continues at relative humidities as low as 27%.
Characterization of a Cerium-Rich Pyrochlore-Based Ceramic Nuclear Waste Form
Authors: Gieré R. , Segvich S. , BUCK E. C.
Published: April 2011

Titanate ceramics have been proposed as candidate materials for immobilizing excess weapons plutonium. This study focuses on the characterization of a titanate-based ceramic through X-ray diffraction (XRD), electron probe microanalysis, and electron energy-loss spectroscopy (EELS). Three distinct phases have been identified, and their volume fraction was determined from element distribution maps using Scionimage-NIH Analysis software. This analysis revealed that the pyrochlore-group phase betafite (A2Ti2O7) forms the matrix of the ceramic and occupies 90.4% of the volume. Uniformly distributed in this matrix are perovskite (A2Ti2O6) and Hf-enriched rutile (TiO2), which account for 6.4 vol% and 3.1 vol%, respectively. The studied ceramic exhibits a very low porosity (0.3 vol%), which is characterized by small (<6 μm), rounded and isolated voids. In the studied ceramic, A-site cations are represented by Ca, rare earth elements, and Hf. The powder XRD pattern of the ceramic allowed refining the unit cell parameters for the cubic betafite, which is characterized by a cell edge of 10.132±0.003Å. The EELS data indicate that Ce is present as both Ce3+ and Ce4+ in betafite, whereas in perovskite, all Ce is trivalent.
Hydration of Magnesium Oxide in the Waste Isolation Pilot Plant
Authors: Snider Anna C.
Published: April 2011

Magnesium oxide (MgO) is the only engineered barrier being emplaced in the Waste Isolation Pilot Plant (WIPP), a U.S. Department of Energy repository for transuranic waste. MgO will lower dissolved concentrations of actinides by consuming CO2 from possible microbial activity, by buffering the pH between 8.5 and 9.5, and by reducing the amount of free water in the repository. This paper discusses results from experiments measuring the hydration of MgO. Results suggest that periclase (MgO) hydrates rapidly to brucite (Mg(OH)2) in de-ionized water and 4 M NaCl solution at 90°C; the hydration rate decreases as temperature decreases. In ERDA-6, a NaCl-rich WIPP brine, MgO hydrates directly to brucite; in GWB, a high-Mg brine, periclase hydrates to magnesium chloride hydroxide hydrate(s) until the dissolved Mg2+ concentration decreases, and brucite becomes the stable phase. Under humid conditions MgO fully hydrates at higher humidities(> 50%). All data are consistent with diffusion-limited hydration reactions.
Radiolytic Modelling: Application To Spent Fuel Dissolution Experiments
Authors: Merino Juan , Cera Esther , Bruno Jordi
Published: April 2011

In this work we describe our first efforts to simulate the chemical evolution of the spent fuel/water system in dissolution experiments using a radiolytic model. These experiments were carried out with spent fuel fragments in deionized water [1]. In order to build the radiolytic model, a set of reactions were selected, together with their kinetic constants, including the catalytic decomposition of H2O2 in the UO2 surface and a reaction mechanism for UO2 oxidation and dissolution. Averaged alpha and beta G-values were used, neglecting gamma radiation. Diffusion to the gas phase was treated thermodynamically assuming Henry's law. The computer code used in the simulations was CHEMSIMUL [9]. First attempts to simulate the experimental results were not successful and a sensitivity analysis was carried out. As a result of this, the kinetic constant of the reaction OH• + H2 → H• + H2O, the only reaction that consumes hydrogen in the system, was identified as a key parameter, together with the kinetic constants of the UO2 oxidation and dissolution reactions. Varying these parameters we were able to reproduce the experimental data. Although more simulations are needed, these results are encouraging because they give us more confidence in the use of radiolytic models as useful tools to predict the long-term alteration rate of the spent fuel under repository conditions, which is our ultimate goal.
Characterization and Modeling of Wafer and Die Level Uniformity in Deep Reactive Ion Etching (DRIE)
Authors: Sun Hongwei , Hill Tyrone , Schmidt Martin , Boning Duane
Published: April 2011

Wafer and die level uniformity effects in Deep Reactive Ion Etching (DRIE) are quantitatively modeled and characterized. A two-level etching model has been developed to predict non-uniformities in high-speed rotating microstructures. The separation of wafer level and die level effects is achieved by sequentially etching wafers with uniformly distributed holes. The wafer level loadings range from 0.06% to 17.6%. Resulting wafer maps reflect the transition from an ion-limited region to a neutral-transport limited region. Additionally, long-range die-level interactions are also evaluated. Resulting die-level etching non-uniformities have a comparable magnitude to wafer-level effects. A model taking into account both the diffusion and reaction rate of neutrals is applied to predict the etching of up to 21 dies. Agreement between measurement and prediction support the hypothesis that the depletion of radicals is the main cause of die-level etch variation. The characterization and prediction methods are applied to etching a micro-scale turbine engine.
Electromechanical Behavior in Micromachined Piezoelectric Membranes
Authors: Robinson M. C. , Raupp J. C. , Demir I. , Richards C. D. , Richards R. F. , Bahr D. F.
Published: April 2011

Piezoelectric materials can convert mechanical and electrical energy, a particularly useful tool in developing micro and nanoscale systems. Characterizing the electromechanical behavior is essential to the design and optimization of the material's and device's performance. This paper examines the influence of boundary (clamping) conditions, relative thickness variations between the active one to two micron thick piezoelectric membrane and underlying passive support structure, and the electrode coverage on the electromechanical behavior. Membranes were fabricated with silicon and lead zirconate titanate (PZT) with a ratio of Zr to Ti of 40:60 that provide thickness ratios between 1:2 and 2:1 by depositing the PZT using sequential solution deposition. PZT films contain a tensile stress that accumulates during processing, therefore a compressive stressed layer of tungsten was sputtered on bulk micromachined membranes to produce a near zero net residual stress. A nonlinear finite element numerical simulation technique is utilized for the analysis of the composite thin film. A comparison between the behavioral trends determined by simulation and experimental methods will be discussed.
Thermophysical Properties of Ni Films for LIGA Microsystems
Authors: Borca-Tasciuc Diana-Andra , Nimbalkar Rajesh , Chen Gang , Graham Samuel , Borca-Tasciuc Theodorian
Published: April 2011

This work reports temperature dependent thermophysical properties characterization of electrodeposited Ni and NiMn alloys intended for LIGA Microsystems applications. A steady-state method is used to determine the in-plane thermal conductivity. Anisotropic thermal diffusivity characterization is performed using a photothermoelectric technique. The measured thermal properties are dependent on the deposition method and also on subsequent temperature annealing steps. The thermal transport measurement results are correlated with scanning electron microscopy studies of the grain structure and measurements of the electrical transport properties.
Control of Stress in a Metal–Nitride–Metal Sandwich for CMOS-Compatible Surface Micromachining
Authors: Davies Rhodri R. , Combes David J. , McNie Mark E. , Brunson Kevin M
Published: April 2011

Further to previous work, which demonstrated the ability to engineer the in- and out-of-plane stress components in PECVD silicon nitride, this paper reports on the control of stress in a metal-nitride-metal sandwich. The addition of a symmetric metallisation to the core nitride layer provides additional functionality by enabling electrical connectivity and electrostatic transduction. This represents a widely applicable structural layer for CMOS-compatible surface micromachining.

The use of advanced test structures coupled with wafer curvature measurements has allowed for detailed analysis of the stress components within the metal-nitride-metal sandwich and enables predictive engineering of the mechanical properties of the structural layer. Relationships between the in- and out-of-plane stress components of the metal-nitride-metal sandwich as a function of the nitride RF deposition power are reported and discussed. In comparison to values measured for nitride-only, a -30MPa/μm stress gradient offset is observed. A mechanism for the decrease in the stress gradient with the addition of the metallisation is proposed and compares well to modelling.

The optimised metal-nitride-metal sandwich can be repeatably engineered to realise low tensile in-plane stress (100MPa) and low out-of-plane stress gradient (0 ± 10MPa/μm). The effective Young's Modulus of the metal-nitride-metal sandwich was determined to be 150GPa; and a value of 195GPa was calculated for the nitride layer using analytical modelling. Work to further reduce the in-plane stress whilst maintaining low stress gradient is in progress by independently tuning the strain of the metal layers.
Assembly of nano-domain buildings blocks of copper oxalate with a cubic morphology
Authors: Soare L. C. , Bowen P. , Lemaître J. , Hofmann H. , Pijolat M. , Valdivieso F.
Published: April 2011

Metallic copper nanostructured particles were synthesised by thermal decomposition of a CuC2O4 precursor obtained via the precipitation reaction between Cu(NO3)2·6H2O and Na2C2O4 in the present of hydroxyl propyl methyl cellulose (HPMC). X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM) and thermogravimetric analysis (TG) were used to characterise the particles and their evolution during the transformation to metallic copper. We highlight the nanostructured nature of the oxalate precursor, which is made up of anisotropic nanosized buildings blocks (25nm by 40nm). These produce an anisotropy in the oxalate particle and influence the decomposition pathway. The results show the evolution of the nanostructure as a function of degree of reaction and a possible kinetic model is discussed.
Nanocomposite Material for Sensing of Halogenated Methanes: A Model Based on Charge Transfer Interaction for Selectivity
Authors: Sangoi Rajiv , Fuller L. , Santhanam K. S. V.
Published: April 2011

A unique nanocomposite of poly (3-methylthiophene) with functionalized multiwalled carbon nanotubes (MWNT) has been synthesized that shows selective sensing for halogenated methanes. The sensor has been found to give the highest response for chloroform and none for methane. A tentative model has been proposed for this selective sensing of halogenated methanes.
Theoretical studies of Electronic Structures and Optical Absorptions of Encapsulated Guest Alkali Metal Atoms in ITQ-4 Zeolite
Authors: Li Hong , Mahanti S. D.
Published: April 2011

An ab-initio study of the electronic structures and optical absorption spectrum of the guest Cs and Na atoms absorbed in the pure silica ITQ-4 zeolite channels was carried out using density functional theory (DFT) and plane wave basis. Completely different geometries were found for doped Cs and Na in the channels. For Cs doping, a zig-zag chain was formed along the channel and a metallic band structure was obtained. However, a dimer structure around the channel center was found for Na doping and a narrow band gap semiconductor was observed for this system. Correspondingly, the calculated optical absorption spectrum also showed distinctive characters for Cs and Na dopings. Our theoretical results for Cs doping are compared with experimental measurements and previous DFT calculation with local orbital basis; better agreement with experiments has been reached than the previous calculation. For the Na doping, our theoretical predictions need to be confirmed by future experiments.
Pulsed Laser Deposition Parameter Optimization for Growth of Alumina (Al2O3) Thin Film on Silicon (100)
Authors: Wang Xinyu , Yarmolenko Sergey , Kumar Dhananjay , Xu Zhigang , Sankar Jagannathan
Published: April 2011

Pulsed laser deposition (PLD) technique was used to grow alumina (Al2O3) thin films on (100) silicon substrate under different deposition conditions. The relationship between Al2O3thin film thickness, hardness, elastic modulus, surface morphology and PLD parameters such as laser energy and substrate temperature was investigated. The Film thickness was found to increase with an increase in laser energy and to decrease with an increase in substrate temperature. The film hardness and elastic modulus increases as substrate temperature increases. We have also shown that films are amorphous at lower substrate temperatures and transform to mixture of amorphous and crystalline phases. The ratio of amorphous to crystalline phases decreases with increase in temperature. The surfaces of Al2O3film grown using PLD was found very smooth with least root square roughness less than 2 nm.
Oxygen Diffusivity and Defect Transport in Pure and Yb Doped Nano-crystalline Ceria
Authors: Saraf Laxmikant , Shutthanandan V. , Thevuthasan S. , Wang C. M. , Koch K. T. , Andreasen J. A. , Marina O. , Zhang Y.
Published: April 2011

Oxygen (18O) diffusivity in sol-gel synthesized nano-crystalline ceria films of average grain size of 3 nm and 7 nm, annealed at 300 °C and 450 °C for one hour respectively is examined by nuclear reaction analysis (NRA). Diffusivity and electrical transport properties measured by a. c. impedance spectroscopy were compared with microcrystalline ceria film of average grain size 38 nm annealed at 900 °C for one hour. Effect of enhanced oxygen diffusion along with reduced ionic transport in nano-crystalline ceria and reduced oxygen diffusion along with enhanced ionic transport in microcrystalline ceria are correlated to long range ordering, grain boundary scattering and defect density. Enhancement in the conductivity with reduction in activation energy from 1 eV to 0.5 eV in the case 4 atom% ytterbium (Yb) doped ceria compared to pure ceria is a result of increased oxygen vacancies taking part in the defect transport.
Mean Inner Potential of Nanostructured Noble Metal Catalysts - Pt/TiO2 Catalyst -
Authors: Ichikawa S. , Akita T. , Okazaki K. , Okumura M. , Tanaka K. , Kohyama M.
Published: April 2011

Catalytic properties of noble metal catalysts are often caused by their nanostructures. Gold catalysts are typical cases. It is especially interesting that the catalytic property of gold suddenly changes to resemble that of platinum when the mean size of gold dispersed on certain oxides is <2nm. This phenomenon should be owing to the change of the local electronic structure of the gold particle or the interface between the gold and the oxides, however its detail has not been cleared yet. We measured the mean inner potential of gold particles supported on TiO2 using electron holography and HREM, and found that the mean inner potential of gold depend largely on the size of the gold particles. When the size is >5nm, the mean inner potential is the same as the reported values of bulk gold (experimental: 21–23V, calculated: 25–30V). When the size is <5nm, it begins to increase >30V, and it begins to increase suddenly >40V at the size <2nm. It indicates that the electronic structure of the gold particle varies from that of the bulk state as the size of the gold reduces due to the nano-size effect or the interaction at the interface, since the mean inner potential is sensitive to the electronic state of the outer valence electron. On the other hand, the behavior of the platinum catalysts is different from that of gold catalysts. When the size of the platinum particle on the TiO2 support is >1.5nm, the mean inner potential of platinum is the same as that of the bulk (∼25V). In case of the particle with the size <1.5nm, it begins to increase and the increase rate is lower than that of the gold particles with the size <2nm. It is suggested to be due to the difference of the interaction with TiO2.
Hierarchically Ordered Multi-Component Block Copolymer/Particle Nanocomposite Materials
Authors: Bockstaller M. R. , Thomas E. L.
Published: April 2011

This contribution reviews the structure formation processes that are observed in binary diblock copolymer/particle and ternary diblock copolymer/particle1/particle2 mixtures. The particle core size, the polymer domain spacing as well as the particle surface chemistry are shown to determine three distinct morphological types in particle/block copolymer composites, which is the preferential layer homogeneous distribution, the interfacial segregation and center alignment of the nanocrystals within one polymer domain. The different microstructural environments of the sequestered component that are implied by the respective particle distribution result in distinctively different optical properties of the composite and have important consequences for the prospects of metal nanocrystal/block copolymer composites as a platform for photonic crystal engineering. A detailed comparison between morphological studies and theoretical predictions will be presented that aims to better understand and control morphologies of structured cluster matter and its relation to the respective optical and mechanical properties of new microstructured composite materials.
Low Frequency Dynamics of Confined Proteins
Authors: Korb Jean-Pierre , Bryant Robert G.
Published: April 2011

We present the frequency dependence of the proton spin-lattice relaxation rate 1/T1 in variously hydrated proteins. We present also the case of proteins confined in heavily hydrated gels where the rotation has been immobilized. The relaxation efficiency increases according to a power law at low frequencies. The temperature dependence of the protein protons T1 demonstrates that relaxation results from a direct spin-phonon process instead of a Raman process at temperatures above 273K. We propose a theory that accounts for experiments and depends on the dynamical distribution of states, the localization of the disturbances along and transverse to the peptide chains, and the spatial distribution of hydrogen in the structure. In hydrated and confined proteins, the motions of the backbone that dominate the relaxation process are transverse rather than along the peptide chain. We show that the protein structure adjusts to hydration from the lyophilized state to the fully hydrated state in small increment steps.
Interplay between slow interfacial water diffusion and colloid dynamics: A way to probe colloidal transitions.
Authors: Levitz P.E.
Published: April 2011

Particle fluctuations in colloidal suspensions are generally considered to be much slower than the embedded fluid dynamics. It was recently proposed that the fluid self-diffusion nearby an interface follows Lévy statistics, extending the time domain of the fluid dynamics towards the low frequency range. It is then possible to probe colloidal particle motion and especially its evolution during a phase transition looking at the slow dynamics of the fluid molecule close to an particle surface. Using field cycling NMR relaxometry, we show how the slow and confined water dynamics at proximity of a colloidal surface provide an original way to follow the glass transition of a colloidal system made of plate-like Laponite particles, a synthetic clay. The interplay between fluid Levy dynamics and particle jamming is discussed. An analytical model involving correlated elementary water time steps on the colloidal interface is proposed and critically compared to our experimental data. The method permits probing of colloidal motions and especially their evolution during a phase transition in a new way. This method can be extended to other systems including mineral lyotropic liquid crystals and biological molecular structures.
Slow Dynamics and the Glass Transition in Confining Systems
Authors: Wang Li-Min , He Fang , Richert Ranko
Published: April 2011

The slow dynamics associated with the structural relaxation of glass forming materials near the glass transition is very sensitive to the effects of small confining geometries. Based upon the experimental results of triplet state solvation dynamics, we explore the extent to which confinement effects can be rationalized solely in terms of interfacial dynamics which are modified relative to the bulk situation. The importance of the interfacial conditions is emphasized by observing the changes due to the surface chemistry, by comparing relaxation times at and further away from the surface, and by studying the effects of ‘soft’ versus ‘hard’ confining materials. While ‘hard’ confinement by porous solids is observed to result in slower dynamics and an increased glass transition temperature Tg for propylene glycol, our 4.6 nm nanodroplets suspended in a more fluid environment display faster structural relaxation, equivalent to a reduction of Tg as observed in free standing polymer films.
Metal – polymer interfaces and their effect on the glass transition of thin polystyrene films
Authors: Sharp J.S. , Forrest J.A.
Published: April 2011

We present a study of polystyrene-metal interfaces and discuss the relationship between the interfacial structure and anomalies in the measured glass transition temperature (Tg) of thin metal capped polystyrene (PS) films. The PS films used in these studies were coated with an evaporated metal layer of either Aluminum (Al) or gold (Au) and the Tg values were measured with ellipsometry. Uncoated PS films were also measured and these samples showed Tg values that were reduced relative to the bulk value for film thicknesses (h) less than 40 nm. Films coated with Au were shown to have measured Tg values that were the same as the bulk value (Tgbulk=370 K) for all the film thicknesses studied (h ≥ 8nm). The Al coated PS films had measured Tg values that were the same as the uncoated PS films. The observed differences are discussed in terms of the differences in the structure of the metal-polymer interfaces produced during thermal evaporation of the metal layers. A novel sample preparation procedure was developed to enable us to use Atomic Force Microscopy (AFM) to directly measure the structure of the buried polymer-metal interfaces. The measurements performed on these systems support the suggestion that the interfacial structure is different for the two metal-polymer interfaces studied and that these differences may be the cause of the anomalies in the measured Tgs of these samples.
Fatigue Crack Growth and Fracture Toughness in Bimodal Al 5083
Authors: Pao P. S. , Jones H. N. , Feng C. R.
Published: April 2011

The fatigue crack growth rates and fracture toughness of bulk nanocrystalline Al 5083 having a bimodal grain size distribution were investigated. The nanocrystalline powders were prepared by mechanically ball milling spray atomized Al 5083 powders in liquid nitrogen. This nanocrystalline powder was blended with 50 wt% spray atomized large grained Al 5083 powders. The blended powder was then cold pressed, degassed, and extruded into rods. The bimodal Al 5083 thus produced consists of nanocrystalline grain bands and coarse grain bands. While the yield strength of the bimodal Al 5083 is about 25% lower than that of the all nanocrystalline Al 5083, its tensile ductility is almost 50% greater. In addition, the fracture toughness of the bimodal material is about 85% higher than that of the all nanocrystalline counterpart. Fatigue crack growth rates of bimodal Al 5083 are about 30% lower than those of all nanocrystalline Al 5083. The lower fatigue crack growth rates are accompanied by more tortuous crack paths when the crack propagated through the coarse grain regions in the bimodal Al 5083.