bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of H2 Preconditioning on the Nucleation and Growth of Self-Assembled Germanium Islands on Silicon (001)
Authors: Dilliway Gabriela D.M. , Cowern Nicholas E.B. , Xu Lu , McNally Patrick J. , Jeynes Chris , Mendoza Ernest , Ashburn Peter , Bagnall Darren M. 
Published: April 2011

AbstractUnderstanding the effects of growth conditions on the process of self-organisation of Ge nanostructures on Si is a key requirement for their practical applications. In this study we investigate the effect of preconditioning with a high-temperature hydrogenation step on the nucleation and subsequent temporal evolution of Ge self-assembled islands on Si (001). Two sets of structures, with and without H2 preconditioning, were grown by low pressure chemical vapour deposition (LPCVD) at 650°C. Their structural and compositional evolution was characterised by Rutherford backscattering spectrometry (RBS), atomic force microscopy (AFM) and micro-Raman (νRaman) spectroscopy. In the absence of preconditioning, we observe the known evolution of self-assembled Ge nanostructures on Si (001), from small islands with a narrow size distribution, to a bimodal size distribution, through to large islands. Surface coverage and island size increase steadily as a function of deposition time. On the H2 preconditioned surface, however, both nucleation rates and surface coverage are greatly increased during the early stages of self-assembly. After the first five seconds, the density of the islands is twice that on the unconditioned surface, and the mean island size is also larger, but the subsequent evolution is much slower than in the case of the unconditioned surface. This retardation correlates with a relatively high measured stress within the islands. Our results demonstrate that standard processes used during growth, like H2 preconditioning, can yield dramatic changes in the uniformity and distribution of Ge nanostructures self-assembled on Si.
A New Synchrotron-based Technique for Measuring Stresses in Ultrathin Metallic Films
Authors: Böhm Jochen , Gruber Patric , Spolenak Ralph , Wanner Alexander , Arzt Eduard 
Published: April 2011

AbstractA novel synchrotron-based X-ray diffraction technique is presented by which it is possible to characterize the evolution of stresses in polycrystalline metallic films thinner than 100 nm. The film under investigation is deposited on a flexible polyimide substrate which is subjected to a uniaxial tensile test. The evolutions of longitudinal and transverse elastic strains in the film are monitored simultaneously by means of a high-resolution area detector. The strain resolution is better than 10−4. The samples are typically subjected to 6 % total strain and subsequently unloaded. First experiments carried out on Au films in the thickness range between 20 nm and 1000 nm show the usefulness and the power of this new technique.
Utilizing On-Chip Testing and Electron Microscopy to Study Fatigue and Wear in Polysilicon Structural Films
Authors: Alsem D.H. , Stach E.A. , Muhlstein C.L. , Dugger M.T. , Ritchie R.O. 
Published: April 2011

AbstractWear and fatigue are important factors in determining the reliability of microelectromechanical systems (MEMS). While the reliability of MEMS has received extensive attention, the physical mechanisms responsible for these failure modes have yet to be conclusively determined. In our work, we use a combination of on-chip testing methodologies and electron microscopy observations to investigate these mechanisms. Our previous studies have shown that fatigue in polysilicon structural thin films is a result of a ‘reaction-layer’ process, whereby high stresses induce a room-temperature mechanical thickening of the native oxide at the root of a notched cantilever beam, which subsequently undergoes moisture-assisted cracking. Devices from a more recent fabrication run are fatigued in ambient air to show that the post-release oxide layer thicknesses that were observed in our earlier experiments were not an artifact of that particular batch of polysilicon. New in vacuo data show that these silicon films do not display fatigue behavior when the post release oxide is prevented from growing, because of the absence of oxygen. Additionally, we are using polysilicon MEMS side-wall friction test specimens to study active mechanisms in sliding wear at the microscale. In particular, we have developed in vacuo and in situ experiments in the scanning electron microscope, with the objective of eventually determining the mechanisms causing both wear development and debris generation.
Size Effect on Crack Formation in Cu/Ta and Ta/Cu/Ta Thin Film Systems
Authors: Gruber P. , Böhm J. , Wanner A. , Sauter L. , Spolenak R. , Arzt E. 
Published: April 2011

AbstractLayered structures of Cu and Ta thin films on silicon are well established for many technological applications in microelectronics. Electronic circuits used for flexible displays or wearable electronics are becoming increasingly popular. For such applications, the Cu/Ta system must be transferred to flexible substrates, incorporating a design rule for several percent of total strain. We have investigated the deformation behaviour of different Cu/Ta and Ta/Cu/Ta thin film systems on a flexible polyimide substrate subjected to total strains of more than 5%. A novel synchrotron X-ray diffraction technique allowed us to characterize the evolution of mechanical stress in very thin metallic films during isothermal tensile tests. We found that samples with a Cu film thickness below 300 nm showed a sudden stress decrease at a total strain of about 2.5%. This stress drop was attributed to fracture of the entire film system, initiated by cracks in the Ta layers.
Effect of Mold Dimensions on Temperature Distribution of Sintered Body during Plasma Activated Sintering
Authors: Lee Gil-Geun 
Published: April 2011

AbstractIn the present study, the focus is on the analysis of the effect of the mold dimensions on the temperature distribution of a sintered body during plasma activated sintering. The temperature distribution of a cylindrical mold with various dimensions was measured using K-type thermocouples. The temperature homogeneity of the mold was studied based on the direction and dimensions of the mold. A temperature gradient existed in the radial direction of the mold during the plasma activated sintering. Also, the magnitude of the temperature gradient was increased with increasing sintering temperature. In the longitudinal direction, however, there was no temperature gradient. The temperature gradient of the mold in the radial direction decreased with increasing inner diameter of the mold and its length.
Computer Simulated 3D Virtual Reality for Dynamical Modeling and Calculations of Carbon-Based Composite Materials
Authors: Kireitseu Maksim V. , Hui David , Bochkaryova Liya , Eremeev Sergey , Nedavniy Igor 
Published: April 2011

AbstractThe principal goal of the present paper is to demonstrate an application of modern software engineering tools for modeling virtual reality and molecular dynamics of novel nanocomposites. The main technical components of presented system are 1) software and nanoengineering tools for modeling of virtual reality, molecular dynamic and 3D video images of novel diamonds- containing nanocomposites and 2) Problem tracking system to be used during modeling of virtual reality. For a realistic simulation of the stability behavior of the reinforced material, the nonlinear intramolecular inter-actions between neighboring atoms have to be taken into account. A comparison shows the buckling sensitivity of different geometries. In order to reduce computational costs, it is necessary to develop suited homogenization techniques, so that shell elements can be applied.
Synthesis of Zeolite as Ordered Multi-Crystal Arrays using Uniformly Aligned Polyurethane as Templates
Authors: Lee Jin Seok , Lee Yun-Jo , Tae Eunju Lee , Park Yong Soo , Yoon Kyung Byung 
Published: April 2011

AbstractTwo types of glass plates coated with uniformly aligned polyurethane films were produced by repeating the cycles of the alternative exposures of the glass plates to 1,4-phenylene diisocyanate (PDI) and 2-butyne-1,4-diol (BDO) and to PDI and terephthalic acid bis-(2-hydroxy ethyl) ester (TBE) for 500 times at elevated temperatures. The glass plates coated with uniformly aligned poly-(PDI-BDO)500(500 represents the number of the cycle) produced monolayers of closely packed 2D arrays of silicalite-1 crystals with the average size of 370 × 200 × 500 nm on the glass plates upon immersion of the glass plates into a dense gel consisting of tetraethylorthosilicate (TEOS), tetrapropylammonium hydroxide (TPA+OH-), and water (mole ratio = 7:1.5:330) followed by the hydrothermal reaction at 180°C for 2 h. The silicalite-1 crystals were aligned with the c-axes perpendicular to the substrate plane. Upon switching the polymer from poly-(PDI-BDO)500to poly-(PDI-TBE)500the orientations of the silicalite-1 crystals in the 2D arrays changed from c to a axes perpendicular to the substrate. This report therefore demonstrates that the uniformly aligned polyurethane films serve as the templates for the growth of closely packed multi-crystal arrays of silicalite-1 in uniform orientations and the nature of the polyurethane film affects the resulting orientations of the crystals. We propose that the supramolecularly organized organic-inorganic composites consisting of the hydrolyzed organic products and the seed crystals responsible for the above phenomena.
Mechanism-based strain gradient crystal plasticity
Authors: Han Chung-Souk , Gao Huajian , Huang Yonggang , Nix William D. 
Published: April 2011

AbstractTo model size dependent plastic deformation at micron and submicron length scales the theory of mechanism-based strain gradient plasticity (MSG) was developed. The MSG approach incorporates the concept of geometrically necessary dislocations into continuum plastic constitutive laws via Taylor hardening relation. This concept is extended here to develop a mechanism-based strain gradient theory for crystal plasticity (MSG-CP) based on the notions of dislocation density tensor and resolved density force corresponding to the Peach-Koehler force in dislocation theory. An effective density of geometrically necessary dislocations is defined on the basis of resolved density force for specific slip systems and is incorporated into the plastic constitutive laws via Taylor relation.
Texture and Microstructure Evolution in Silver Thin films with FACET
Authors: Rairkar Asit , Zhang Jie , Adams Jim 
Published: April 2011

AbstractMetallic polycrystalline thin films are used in a plethora of applications, including especially metallic interconnects for the microelectronics industry. Despite the numerous approaches at modeling and simulating processing of these films, there have not been any simulation tools, which can accurately predict texture and microstructure evolution in these films. We have developed a novel 2D model called FACET for the simulation of polycrystalline thin film growth at realistic spatial and time scales. The basic idea is to use the results of smaller-scale atomic simulations (density functional theory, molecular dynamics, and lattice Monte Carlo) to provide input and guidance on the evolution of grain structure and texture on a micron scale. The feature scale model is based on describing grains in terms of two-dimensional faceted surfaces and grain boundaries. The model includes the major phenomena involved in film growth, including deposition, nucleation, surface diffusion (on the substrate and on the growing film), inter-facet diffusion, and grain growth and coarsening. In addition, the texture of each grain is treated individually, so that the texture evolution of the system can be simulated. Predictions of the FACET code are compared with previous experimental studies of texture and microstructure in Silver films.
Deformation Mechanisms and Ductility of Nanostructured Al Alloys
Authors: Han Bing Q. , Mohamed Farghalli A. , Lavernia Enrique J. 
Published: April 2011

AbstractLow tensile ductility is one of the critical challenges facing the science and technology of nanostructured materials. As an example, despite the fact that high strength is frequently observed in bulk nanostructured Al alloys, ductility and work hardening are often observed to decrease with decreasing grain size. In the present study, the tensile ductility of bulk nanostructured aluminum alloys processed via severe plastic deformation and consolidation of mechanically milled powders is analyzed. Adding coarse grains to the nanostructured matrix is proposed as an approach to improve ductility.
On the Influence of the Misorientation of Grains, Grain Size and Boundary Volume on the Strength and Ductility of Ultrafine Grained Cu
Authors: Dalla Torre Florian H. , Lapovok Rimma , Thomson Peter F. , Sandlin James D. , Davies Chris H.J. , Pereloma Elena V. 
Published: April 2011

AbstractThe influence of the microstructure and the misorientation relationship of grains on mechanical properties is investigated in specimens of ultrafine-grained copper processed by equal channel angular extrusion (ECAE) route Bc for 1, 4 and 12 passes. XRD texture analyses have shown that the major texture component is developed during the first pass of ECAE, and remains approximately constant with greater number of passes. EBSD measurements indicate that the majority of grain boundaries are still of low angle (>15°), while after four and twelve passes more than 50 % of all boundaries are high angle ones. TEM analyses have shown that the microstructure evolves from microbands and elongated cells towards a more equiaxed homogenous microstructure. On the microscale observed by TEM the degree of misorientation among subgrains/cells increases and the width of boundaries decreases while the cell/subgrain size remains approximately constant as the number of passes increases. The mechanical properties show a saturation level with a maximum in the yield stress and UTS after 4 passes. The strength of the material decreases between the fourth and the twelfth passes and the uniform elongation increases. It is suggested that the increase in ductility (and decrease in strength) is associated with the decrease in width of boundaries leading to an increase in the mean free path of dislocations.
Experiment and FEM Analysis of Tensile Behavior of Bimodal Nanocrystalline Al-Mg Alloys
Authors: Lee Zonghoon , Lee Johnathan , Lavernia Enrique J. , Nutt Steven R. 
Published: April 2011

AbstractThe tensile behavior of bimodal nanocrystalline Al-7.5Mg alloys was investigated using experiments and two-dimensional axisymmetric elastic-plastic finite element method (FEM). Cryomilled nanocrystalline powders blended with 15% and 30% unmilled coarse-grained powders were consolidated by hot isostatic pressing followed by extrusion to produce bulk bimodal nanocrystalline Al-7.5Mg alloys, which were comprised of nanocrystalline grains separated by coarse-grain regions. The calculated stress-strain curves have acceptable agreement with experimental curves of the bimodal structures. The bimodal Al-7.5Mg alloys show reasonable ductility while retaining enhanced strength compared to conventional alloys and nanocrystalline metals.
Biological Functionalization of Carbon Nanotubes
Authors: Sirdeshmukh Ranjani , Teker Kasif , Panchapakesan Balaji 
Published: April 2011

AbstractCarbon nanotubes are known for their exceptional mechanical and unique electronic properties. The size dependant properties of nanomaterials have made them attractive to develop highly sensitive sensors and detection systems. This is especially true in biological sciences, where the efficiency of detection systems reflect on the size of the detector and the sample required for detection. At approximately 1.5 to 10nm wide, and approximately 1.5 to 2μm long, the use of carbon nanotubes as sensors in biological systems would greatly increase the sensitivity of detection and diagnostics, for a reduced sample size consisting of few individual proteins and antibodies. Since all the atoms in carbon nanotubes are surface atoms, binding proteins or antibodies to the surfaces can greatly affect their surface states, and thus their electrical and optical properties. This effect can be exploited as a basis for detecting biological surface reactions in a single protein or antibody attached to carbon nanotube surfaces.In this paper, we show the binding of fluorescently tagged antibodies in phosphate buffered saline on the surfaces of carbon nanotubes. Investigations using a confocal microscope suggest a significant interaction of the antibodies with the surfaces of the nanotubes, the intensity depending on incubation time. Since the surface area to volume ratio of CNTs is high, the use of surfactant to separate the nanotubes creates a greater surface area for antibody attachment. The interaction between CNTs and antibodies is seen to be primarily due to adsorptive surface phenomenon, between the nanotube sidewalls and antibody molecule clusters.
Nanowiring Enzymes to Carbon Nanotube Probes
Authors: Collier C.P. , Esplandiu M.J. , Bittner V.G. , Shapiro I.R. 
Published: April 2011

AbstractThe observation of spectroscopic signals in response to mechanically induced changes in biological macromolecules can be enabled at an unprecedented level of resolution by coupling single-molecule manipulation/sensing using carbon nanotubes with single-molecule fluorescence imaging. Proteins, DNA and other biomolecules can be attached to nanotubes to give highly specific single-molecule probes for the investigation of intermolecular dynamics, the assembly of hybrid biological and nanoscale materials and the development of molecular electronics. Recent advances in nanotube fabrication and Atomic Force Microscope (AFM) imaging with nanotube tips have demonstrated the potential of these tools to achieve high-resolution images of single molecules. In addition, proof-of-principle demonstrations of nanotube functionalization and attachment of single molecules to these probes have been successfully made.Improved techniques for the growth and attachment of single wall carbon nanotubes as robust and well-characterized tools for AFM imaging are being developed. This work serves as a foundation toward development of single-molecule sensors and manipulators on nanotube AFM tips for a hybrid atomic force microscope that also has single-molecule fluorescence imaging capability. An individual single wall carbon nanotube (SWNT) attached to an AFM tip can function as a structural scaffold for nanoscale device fabrication on a scanning probe. Such a probe can have a novel role, to trigger specific biochemical reactions or conformational changes in a biological system with nanometer precision. The consequences of these perturbations can be read out in real time by single-molecule fluorescence and/or AFM sensing. For example, electrical wiring of single redox enzymes to carbon nanotube scanning probes will allow for observation and electrochemical control of single enzymatic reactions, by monitoring fluorescence from a redox-active cofactor or the formation of fluorescent products. Enzymes “nanowired” to carbon nanotube tips may enable extremely sensitive probing of biological stimulus-response with high spatial resolution, including product-induced signal transduction.
NanoLiterBioReactor: Monitoring of Long-Term Mammalian Cell Physiology at Nanofabricated Scale
Authors: Prokop Ales , Prokop Zdenka , Schaffer David , Kozlov Eugene , Wikswo John , Cliffel David , Baudenbacher Franz 
Published: April 2011

AbstractThere is a need for microminiaturized cell-culture environments, i.e., NanoLiter BioReactors (NBRs), for growing and maintaining populations of up to several hundred cultured mammalian cells in volumes three orders of magnitude smaller than those contained in standard multi-well screening plates. Reduced NBR volumes would not only shorten the time required for diffusive mixing, for achieving thermal equilibrium, and for cells to grow to confluence, but also simplify accurate cell counting, minimize required volumes of expensive analytical pharmaceuticals or toxins, and allow for thousands of culture chambers on a single instrumented chip. These devices would enable the development of a new class of miniature, automated cell- based bioanalysis arrays for monitoring the immediate environment of multiple cell lines and assessing the effects of drug or toxin exposure. The challenge, beyond that of optimizing the NBR physically, is to detect cellular response, provide appropriate control signals, and, eventually, facilitate closed-loop adjustments of the environment–e.g., to control temperature, pH, ionic concentration, etc., to maintain homeostasis, or to apply drugs or toxins followed by the adaptive administration of a selective toxin antidote. To characterize in a nonspecific manner the metabolic activity of cells, the biosensor elements of the NBR might include planar pH, dissolved oxygen, and redox potential sensors, or even an isothermal picocalorimeter (pC) to monitor thermodynamic response. Equipped with such sensors, the NBR could be used to perform short- and long-term cultivation of several mammalian cell lines in a perfused system, and to monitor their response to analytes in a massively parallel format. This approach will enable automated, parallel, and multiphasic monitoring of multiple cell lines for drug and toxicology screening. An added bonus is the possibility of studying cell populations with low cell counts whose constituents are completely detached from typical tissue environment, or populations in controlled physical and chemical gradients.
A Probabilistic Model for Degradation of the Engineered Barriers System in the Yucca Mountain Repository
Authors: Qin Z. , Shoesmith D.W. 
Published: April 2011

AbstractA probabilistic model to predict the lifetimes of the engineered barrier system proposed for the Yucca Mountain repository is described. The model assumes that the titanium Grade-7 drip shield will fail by hydrogen-induced cracking and the Alloy-22 waste package by a combination of passive and crevice corrosion. The model predicts that crevice corrosion of the waste package can be completely avoided ifthe drip shield deflects seepage drips for between 2000 (realistic behaviour) and 6000 years (conservative behaviour). Sensitivity calculations on the crevice corrosion model suggest that early waste package failure is extremely unlikely providing the drip shield performs its function for a minimum of ~ 300 years.
Radionuclides Release Model for Performance Assessment Studies of Spent Nuclear Fuel in Geological Disposal
Authors: Poinssot Christophe , Lovera Patrick , Ferry Cécile 
Published: April 2011

AbstractIn the framework of the research conducted on the long term evolution of spent nuclear fuel in geological disposal conditions, a source term model has been developed to evaluate the instantaneous release of RN (Instant Release Fraction IRF) and the delayed release of the RN which are embedded within the matrix. This model takes into account all the scientific results currently available in the literature except the hydrogen effect. IRF was assessed by considering the evolution with time of the RN inventories located within the fuel microstructure to which no confinement properties can be allocated on the long term (rim, gap, grain boundaries). It allows to propose some reference bounding values for the IRF as a function of time of canister breaching and burnup. The matrix radiolytic dissolution was modeled by a simple kinetic model neglecting the radiolytic species recombination and the influence of aqueous ligands and radiolytic oxidants were supposed to completely react with the fuel surface. Spent fuel performance was therefore demonstrated to deeply depend on the reactive surface area.