bluuebunny/crossref_metadata_2025 huggingface dataset:
Auditory Cortex Encodes the Perceptual Interpretation of Ambiguous Sound
Authors: Kilian-Hütten Niclas , Valente Giancarlo , Vroomen Jean , Formisano Elia
Published: February 2011

The confounding of physical stimulus characteristics and perceptual interpretations of stimuli poses a problem for most neuroscientific studies of perception. In the auditory domain, this pertains to the entanglement of acoustics and percept. Traditionally, most study designs have relied on cognitive subtraction logic, which demands the use of one or more comparisons between stimulus types. This does not allow for a differentiation between effects due to acoustic differences (i.e., sensation) and those due to conscious perception. To overcome this problem, we used functional magnetic resonance imaging (fMRI) in humans and pattern-recognition analysis to identify activation patterns that encode the perceptual interpretation of physically identical, ambiguous sounds. We show that it is possible to retrieve the perceptual interpretation of ambiguous phonemes—information that is fully subjective to the listener—from fMRI measurements of brain activity in auditory areas in the superior temporal cortex, most prominently on the posterior bank of the left Heschl's gyrus and sulcus and in the adjoining left planum temporale. These findings suggest that, beyond the basic acoustic analysis of sounds, constructive perceptual processes take place in these relatively early cortical auditory networks. This disagrees with hierarchical models of auditory processing, which generally conceive of these areas as sets of feature detectors, whose task is restricted to the analysis of physical characteristics and the structure of sounds.
Cortical Connections of Area V6Av in the Macaque: A Visual-Input Node to the Eye/Hand Coordination System
Authors: Passarelli Lauretta , Rosa Marcello G. P. , Gamberini Michela , Bakola Sophia , Burman Kathleen J. , Fattori Patrizia , Galletti Claudio
Published: February 2011

The goal of the present study was to elucidate the corticocortical afferent connections of area V6Av, the ventral subregion of area V6A, using retrograde neuronal tracers combined with physiological and cytoarchitectonic analyses in the macaque monkey. The results revealed that V6Av receives many of its afferents from extrastriate area V6, and from regions of areas V2, V3, and V4 subserving peripheral vision. Additional extrastriate visual projections originate in dorsal stream areas MT and MST. Area V6Av does not receive projections directly from V1; such connections were only observed when the injection sites crossed into area V6. The strongest parietal lobe afferents originate in fields V6Ad, PGm, MIP (medial intraparaietal), and PG, with frontal lobe afferents originating from the frontal eye field, caudal area 46, and the rostral subdivision of the dorsal premotor area (F7). A comparison of their respective connections supports the view that V6Av is functionally distinct from adjacent areas (V6 and V6Ad). The strong afferents from V6 and other extrastriate areas are consistent with physiological data that suggest that V6Av is primarily a visual area, supporting the notion that V6Av is part of a dorsomedial cortical network performing fast form and motion analyses needed for the visual guidance of action.
Selective Toxicity by HDAC3 in Neurons: Regulation by Akt and GSK3β
Authors: Bardai Farah H. , D'Mello Santosh R.
Published: February 2011

Although it is well established that pharmacological inhibitors of classical histone deacetylases (HDACs) are protective in variousin vivomodels of neurodegenerative disease, the identity of the neurotoxic HDAC(s) that these inhibitors target to exert their protective effects has not been resolved. We find that HDAC3 is a protein with strong neurotoxic activity. Forced expression of HDAC3 induces death of otherwise healthy rat cerebellar granule neurons, whereas shRNA-mediated suppression of its expression protects against low-potassium-induced neuronal death. Forced expression of HDAC3 also promotes the death of rat cortical neurons and hippocampally derived HT22 cells, but has no effect on the viability of primary kidney fibroblasts or the HEK293 and HeLa cell lines. This suggests that the toxic effect of HDAC3 is cell selective and that neurons are sensitive to it. Neurotoxicity by HDAC3 is inhibited by treatment with IGF-1 as well as by the expression of a constitutively active form of Akt, an essential mediator of IGF-1 signaling. Protection against HDAC3-induced neurotoxicity is also achieved by the inhibition of GSK3β, a kinase inhibited by Akt that is widely implicated in the promotion of neurodegeneration in experimental models and in human pathologies. HDAC3 is directly phosphorylated by GSK3β, suggesting that the neuronal death-promoting action of GSK3β could be mediated through HDAC3 phosphorylation. In addition to demonstrating that HDAC3 has neurotoxic effects, our study identifies it as a downstream target of GSK3β.
Rescue of Progranulin Deficiency Associated with Frontotemporal Lobar Degeneration by Alkalizing Reagents and Inhibition of Vacuolar ATPase
Authors: Capell Anja , Liebscher Sabine , Fellerer Katrin , Brouwers Nathalie , Willem Michael , Lammich Sven , Gijselinck Ilse , Bittner Tobias , Carlson Aaron M. , Sasse Florenz , Kunze Brigitte , Steinmetz Heinrich , Jansen Rolf , Dormann Dorothee , Sleegers Kristel , Cruts Marc , Herms Jochen , Van Broeckhoven Christine , Haass Christian
Published: February 2011

Numerous loss-of-function mutations in the progranulin (GRN) gene cause frontotemporal lobar degeneration with ubiquitin and TAR–DNA binding protein 43-positive inclusions by reduced production and secretion of GRN. Consistent with the observation that GRN has neurotrophic properties, pharmacological stimulation of GRN production is a promising approach to rescueGRNhaploinsufficiency and prevent disease progression. We therefore searched for compounds capable of selectively increasing GRN levels. Here, we demonstrate that four independent and highly selective inhibitors of vacuolar ATPase (bafilomycin A1, concanamycin A, archazolid B, and apicularen A) significantly elevate intracellular and secreted GRN. Furthermore, clinically used alkalizing drugs, including chloroquine, bepridil, and amiodarone, similarly stimulate GRN production. Elevation of GRN levels occurs via a translational mechanism independent of lysosomal degradation, autophagy, or endocytosis. Importantly, alkalizing reagents rescue GRN deficiency in organotypic cortical slice cultures from a mouse model for GRN deficiency and in primary cells derived from human patients withGRNloss-of-function mutations. Thus, alkalizing reagents, specifically those already used in humans for other applications, and vacuolar ATPase inhibitors may be therapeutically used to prevent GRN-dependent neurodegeneration.
Superior Facial Expression, But Not Identity Recognition, in Mirror-Touch Synesthesia
Authors: Banissy Michael J. , Garrido Lúcia , Kusnir Flor , Duchaine Bradley , Walsh Vincent , Ward Jamie
Published: February 2011

Simulation models of expression recognition contend that to understand another's facial expressions, individuals map the perceived expression onto the same sensorimotor representations that are active during the experience of the perceived emotion. To investigate this view, the present study examines facial expression and identity recognition abilities in a rare group of participants who show facilitated sensorimotor simulation (mirror-touch synesthetes). Mirror-touch synesthetes experience touch on their own body when observing touch to another person. These experiences have been linked to heightened sensorimotor simulation in the shared-touch network (brain regions active during the passive observation and experience of touch). Mirror-touch synesthetes outperformed nonsynesthetic participants on measures of facial expression recognition, but not on control measures of face memory or facial identity perception. These findings imply a role for sensorimotor simulation processes in the recognition of facial affect, but not facial identity.
Lernen zum Anfassen: Ein Lernroboter in der Schule
Authors: Eimler Sabrina , von der Pütten Astrid , Krämer Nicole
Published: February 2011

Der vorliegende Beitrag stellt ein Vokabellernsystem vor, in dem die Körperlichkeit und die Attraktivität sowie die verbale und nonverbale Expressivität des Roboterhasen Nabaztag mit einer zusätzlichen Bildschirmapplikation kombiniert wurde, um Schüler zum Vokabeltraining zu motivieren. Ein integrierter Feedback-Mechanismus greift ergänzend die Idee des one-to-one Tutoring auf. Die Ergebnisse der in einer 5. Klasse durchgeführten Fallstudie zeigen, dass sowohl die pragmatische wie auch die hedonische Qualität der Anwendung von den Nutzern als sehr hoch bewertet wurden. Daneben sind auch die Nützlichkeit und Leichtigkeit im Umgang als sehr hoch eingeschätzt worden. Damit erfüllt die vorge-stellte Anwendung wichtige Grundvoraussetzungen für den erfolgreichen Einsatz eines Roboter-gestützten Lernsystems, das Kindern Spaß bereitet und sie zur erneuten Nutzung motiviert.
Elevated LH predicts ischaemic heart disease events in older men: the Health in Men Study
Authors: Hyde Zoë , Norman Paul E , Flicker Leon , Hankey Graeme J , McCaul Kieran A , Almeida Osvaldo P , Chubb S A Paul , Yeap Bu B
Published: February 2011

Context

Hypogonadism in men is associated with insulin resistance, elevations in pro-inflammatory cytokines and fibrinogen, and an atherogenic lipid profile. However, it is uncertain whether the age-related decline in testosterone is associated with ischaemic heart disease (IHD) events.

Objective

To determine whether testosterone and its associated hormones, sex hormone-binding globulin (SHBG) and LH, predict IHD events in older men.

Design

Prospective cohort study.

Methods

Between 2001 and 2004, 3637 community-dwelling men aged 70–88 years underwent a clinical assessment of cardiovascular risk factors and biochemical assessment of testosterone, SHBG and LH. Free testosterone was calculated using mass action equations. Participants were followed until December 2008 using electronic record linkage to capture IHD events (hospital admission or death).

Results

Mean follow-up was 5.1 years. During this period, 618 men (17.0%; 95% confidence interval (CI) 15.8, 18.3%) experienced an event, of which 160 were fatal. Men with higher baseline total or free testosterone levels experienced fewer IHD events (hazard ratio (HR)=0.89; 95% CI 0.82, 0.97 and HR=0.86; 95% CI 0.79, 0.94 for each one s.d. increase in total and free testosterone respectively). These associations were maintained after adjustment for age and waist:hip ratio but did not persist after adjustment for prevalent IHD or other cardiovascular risk factors. SHBG was not associated with IHD events. In contrast, higher LH levels were associated with reduced event-free survival in both univariate (HR=1.15; 95% CI 1.08, 1.22) and adjusted analyses (HR=1.08; 95% CI 1.01, 1.15).

Conclusions

Dysregulation of the hypothalamic–pituitary–gonadal axis may be a risk factor for IHD. Further studies of men with either elevated LH or low testosterone are warranted.
Impaired glucose metabolism in Japanese patients with acromegaly is restored after successful pituitary surgery if pancreatic β-cell function is preserved
Authors: Kinoshita Yuka , Fujii Hiroko , Takeshita Akira , Taguchi Manabu , Miyakawa Megumi , Oyama Kenich , Yamada Shozo , Takeuchi Yasuhiro
Published: February 2011

Objective

Impaired glucose metabolism is common in acromegaly, but it is not clear how glucose metabolism is impaired or what predicts its restoration after cure of the disease. To identify factors involved in the impairment of glucose metabolism in acromegaly, we evaluated clinical parameters before and immediately after surgical cure of the disease.

Design and methods

We retrospectively analyzed clinical data of 92 consecutive Japanese patients with acromegaly who underwent successful pituitary surgery. Patients who had received medical therapy for acromegaly or insulin treatment for diabetes were excluded. We evaluated insulin resistance (IR) and pancreatic β-cell function in addition to GH and IGF1 levels before and after surgery.

Results

In this study of Japanese patients with acromegaly, average body mass index (BMI) was 23.4, and no patient had a BMI>30. IR was involved in the impairment of glucose metabolism, which was restored upon surgical cure of acromegaly if β-cell function was preserved. Insufficient β-cell function did not improve after normalization of GH/IGF1 and was associated with impaired glucose metabolism before and after surgery. Results of receiver operating characteristic analysis of preoperative clinical parameters suggest that insulinogenic index (IGI) >0.50 best predicts restoration of normal glucose metabolism upon cure of acromegaly in Japanese patients.

Conclusions

IR impairs glucose metabolism in acromegaly. Once β-cell function is impaired, abnormal glucose metabolism persists even after cure of acromegaly. IGI>0.50 indicates that β-cell function is preserved in non-obese Japanese patients with acromegaly.
Formation of SrBi2Ta2O9: Part II. Evidence of a bismuth-deficient pyrochlore phase
Authors: Rodriguez Mark A. , Boyle Timothy J. , Hernandez Bernadette A. , Buchheit Catherine D. , Eatough Michael O.
Published: February 2011

A bismuth-deficient pyrochlore phase has been observed in both powder and film samples fired at 775 °C. The estimated stoichiometry of this pyrochlore (based on calculated diffraction patterns) was Sr0.2(Sr0.5Bi0.7)Ta2O6.75. This bismuth-deficient pyrochlore phase may be considered deleterious to the formation of the SrBi2Ta2O9“SBT” ferroelectric compound since a significant presence of this pyrochlore compound implies a large deviation from the desired cation ratios. Additionally, films prepared on platinized silicon substrates indicate the SBT phase formation may be encouraged by the substrate; there appears to be some 00l preferential orientation for stoichiometric SBT thin films.
Thermal Spray: Current Status and Future Trends
Authors: Herman Herbert , Sampath Sanjay , McCune Robert
Published: February 2011

Thermal spray is a continuous, directed, melt-spray process in which particles (e.g., 1–50 μm in diameter) of virtually any material are melted and accelerated to high velocities, through either a combustion flame or a dc or rf nontransferred thermal-plasma arc. The molten or semimolten droplets impinge on a substrate and rapidly solidify to form a thin “splat.” The deposit is built up by successive impingement and interbonding among the splats. The splats accumulate into a wellbonded deposit, generally > 10 μm thick.
Advanced Diagnostics and Modeling of Spray Processes
Authors: Fincke James R. , Neiser Richard A.
Published: February 2011

The microstructure and properties of thermally sprayed deposits depend critically on the thermal- and kinetic-energy histories of the particles entrained in the hot-gas jet. At impact, the particle temperature, molten fraction, size, velocity, and chemistry, along with substrate temperature and surface characteristics, control the morphology of individual particle splats. These factors control the adhesion, strength, microstructure, and porosity of a coating and influence the residual-stress state. In order to produce higher-quality coatings and expand the use of this versatile family of technologies, the ability to model and measure particle behavior is essential.
Characterization of Transparent Conducting Oxides
Authors: Coutts Timothy J. , Young David L. , Li Xiaonan
Published: February 2011

As the areas of the major applications of transparent conducting oxides (TCOs) increase, demand will grow for materials having lower sheet resistance while retaining good optical properties. Simply increasing the film thickness is not acceptable because this would increase the optical absorptance. New materials must be developed with lower resistivities than previously achieved and with optical properties superior to those of the present generation of TCOs. This has now been recognized internationally, and novel materials are being investigated in Japan and the United States.
Polymer Electrolytes: Ionic Transport Mechanisms and Relaxation Coupling
Authors: Ratner Mark A. , Johansson Patrik , Shriver Duward F.
Published: February 2011

Polymer electrolytes have been a focus of the scientific community for a quarter century. They extend the realm of traditional solid-state ionics from hard materials to include soft materials and, in doing so, pose issues both fundamental (e.g., how are structure and transport defined in a concentrated electrolyte with an immobile solvent?) and technological (e.g., how can polymer ionics be used to construct electrochemical devices such as sensors, batteries, and fuel cells?)
Science and Applications of Mixed Conductors for Lithium Batteries
Authors: Thackeray Michael M. , Thomas John O. , Whittingham M. Stanley
Published: February 2011

Introduction

Mixed conductors show significant mobility of both electronic and ionic species and were the subject of an earlier review in MRS Bulletin.1 The current review is restricted to those mixed conductors of interest for use in lithium batteries, with an emphasis on commercialization. The first lithium batteries were primary cells using pure lithium anodes and carbon monofluoride or manganese oxide as the cathode. Both were developed in Japan, the former for use in fishing floats and the latter for calculators and similar small devices. Such primary cells based mainly on MnO2 or FeS2 cathodes are still extensively used in watches, cameras, and so on. Lithium primary cells are also the main power source for many medical devices, such as pacemakers. In some of these applications, silver vanadate is the cathode.
Soft Chemical Routes to Heterostructured High-Tc Superconducting Materials
Authors: Choy Jin-Ho , Kwon Soon-Jae , Hwang Seong-Ju , Jang Eue-Soon
Published: February 2011

Recently, inorganic/inorganic and organic/inorganic heterostructured materials have attracted considerable research interest, due to their unusual physicochemical properties, which cannot be achieved by conventional solid-state reactions. In order to develop new hybrid materials, various synthetic approaches, such as vacuum deposition, Langmuir–Blodgett films, selfassembly, and intercalation techniques, have been explored. Among them, the intercalation reaction technique—that is, the reversible insertion of guest species into the two-dimensional host lattice—is expected to be one of the most effective tools for preparing new layered heterostructures because this process can provide a soft chemical way of hybridizing inorganic/inorganic, organic/inorganic, or biological/inorganic compounds. In fact, the intercalation/deintercalation process allows us to design high-performance materials in a solution at ambient temperature and pressure, just as “soft solution processing” provides a simple and economical route for advanced inorganic materials by means of an environmentally benign, lowenergy method. These unique advantages of the intercalation technique have led to its wide application to diverse fields of the solid-state sciences, namely, secondary (rechargeable) batteries, electrochromic systems, oxidation–reduction catalysts, separating agents, sorbents, and so on. Through these extensive studies, many kinds of low-dimensional compounds have been developed as host materials for the intercalation reaction, including graphite, transition-metal chalcogenides, transitionmetal oxides, aluminosilicates, metal phosphates, metal chalcogenohalides, and so on. Recently, the area of intercalation chemistry has been extended to high-Tc superconducting copper oxides, resulting in remarkable structural anisotropy.
Rectifying Self-Assembled Ultrathin Films
Authors: Cassagneau T. P. , Sweryda-Krawiec B. , Fendler J. H.
Published: February 2011

“Soft solution processing” is rapidly becoming a viable approach for the fabrication of advanced nanostructured materials. It involves the use of environmentally friendly chemicals and preparation methods with minimum energy input. Construction of ultrathin films by the room-temperature, layer-by-layer self-assembly of dilute aqueous solutions (or dispersions) of polyelectrolytes (or polymers), nanoparticles, and nanoplatelets is clearly soft solution processing (see the articles by Yoshimura et al. in this issue).
Electrochemical and Photoelectrochemical Processing for Oxide Films
Authors: Matsumoto Yasumichi
Published: February 2011

Metal oxides are important materials in industry. For example, there are many kinds of functional oxides: dielectric oxides such as BaTiO3 (perovskite), semiconductor oxides such as ZnO, ionic conductors such as Bi2O3, magnetic oxides such as Fe3−xMxO4 (spinel), and so on. These oxide materials must be prepared as films, nanodots, and layered films to increase their functionality for a wide variety of applications.
Visible Light-Emitting Diodes: Past, Present, and Very Bright Future
Authors: Craford M. George
Published: February 2011

Although research in and the development of visible light-emitting diodes (LEDs) began nearly 100 years ago, recent developments have made the field truly revolutionary. In this article, I will discuss the evolution of LEDs, provide a little history, describe some recent developments and emerging applications, and finally speculate as to where this technology might lead us in the future.
New Phenomena and Opportunities in Molecule-Based Magnets
Authors: Epstein Arthur J.
Published: February 2011

Molecule-based magnets display the full range of phenomena observed in conventional transition-metal and rareearth-based magnets, as well as unusual phenomena unique to themselves. These materials form in a wide range of one-, two-, and three-dimensional network structures, with disorder often playing a substantial role.
Organic Magnets
Authors: Veciana Jaume , Iwamura Hiizu
Published: February 2011

The notion of organic molecular materials showing metallic properties, such as electric conductivity or ferromagnetism, started several decades ago as a mere dream of some members of the chemical community. The goal was to create an assembly of organic molecules or macromolecules containing only light elements (C, H, N, O, S, etc.) and yet possessing the electron/hole mobility or spin alignment that is inherent in typical metals or their oxides and different from the isolated molecular materials. Organic molecular conductors initially were developed during the 1960s, but the first examples of organic molecular magnets took several more decades to be discovered, owing to the more subtle and complex structural and electronic aspects of these materials. The flurry of activity in this field can be traced to the widely held belief that even the most sophisticated properties can be rationally designed by a systematic modification of organic molecular structures. This motivation was further fueled by increased synthetic capabilities, especially for obtaining large organic molecules with suitable structures and topologies, and also by the spectacular progress of supramolecular chemistry for materials development witnessed in recent years. Also noteworthy is the pioneering work performed in the 1960s by several physical organic chemists who unraveled different ways of aligning spins within open-shell molecules (i.e., triplet diradicals, carbenes, etc.), working against nature's tendency to align them in an antiparallel manner. Magnetic interactions between unpaired electrons, located on the singly occupied molecular orbitals (SOMOs) of di- and polyradicals, or between the adjacent open-shell molecules in crystals, are a crucial issue in this evolving field. Thus, depending upon the symmetry, degeneracy,and topological characteristics of SOMOs and also on the mode of arrangement of the molecules in a crystal, the resulting interaction can align the neighboring spins parallel or antiparallel (see the introductory article by Miller and Epstein in this issue of MRS Bulletin).
Hybrid Organic/Inorganic Magnets
Authors: Awaga Kunio , Coronado Eugenio , Drillon Marc
Published: February 2011

The construction of more and more complex systems starting from elemental molecular units used as building blocks is propelling several disciplines of burgeoning interest, such as supramolecular chemistry, molecular electronics, and molecular magnetism. In the particular context of magnetic molecular materials, an attractive possibility for adding complexity to the material is to use a hybrid approach in which an organic component is combined with an inorganic one. Both purely organic and purely inorganic approaches (see the articles in this issue by Veciana and Iwamura and by Miller, respectively) have been used extensively to obtain molecule-based magnets. The combination of these two kinds of magnetic molecular components has also been successfully explored to design polymeric magnets of different dimensionalities (the metal-radical approach). In this last case, both components play a magnetic role. A step forward in achieving multifunctionality is to design hybrid molecular materials formed by two independent molecular networks, such as anion/cation salts or host/guest solids, whereby each network furnishes distinct physical properties to the solid. This novel class of materials is interesting because it can give rise to the development of materials in which two properties in the same crystal lattice coexist, or materials that exhibit improved properties over those of the individual networks, or to new, unexpected properties due to the mutual interactions between them. One can imagine, for example, the combination of an extended inorganic magnetic layer opening the pathway to cooperative magnetism, with an organic or organometallic molecule that acts as a structural component controlling the interlayer separation. If the molecule inserted between the layers has unpaired electrons, a hybrid compound is produced that combines cooperative magnetism and paramagnetism. Other suitable combinations, such as electronic conductivity and magnetism, or nonlinear optics and magnetism, can also be achieved by wisely choosing the constituent molecules. In this article, we report some relevant examples that illustrate the potential of this hybrid approach in the context of molecule-based magnetic materials.
The Materials Science of Food
Authors: Donald Athene M.
Published: February 2011

Food is such a familiar “material” to all of us that it is easy to overlook the science input required at all stages in its manufacture, from production to consumption. Nevertheless, as the articles in this special issue of MRS Bulletin seek to prove, the materials-science approach is every bit as valid—and as useful—for food as it is for any more conventional system studied in our field. The familiar linkage of structure–property–processing serves equally well in the case of a chocolate bar as a steel bar.
The Materials Science of Chocolate
Authors: Fryer Peter , Pinschower Kerstin
Published: February 2011

Chocolate is a common confectionery material throughout the world that has seen generally increasing production trends over the last 10 years. Making chocolate requires an understanding of how the consumer perceives it. The preferred type of chocolate varies from country to country; for example, common U.S. and U.K. chocolate tastes are mutually incomprehensible, while the rest of Europe hates both of them! The different tastes and uses for chocolate reflect the histories of the industry in different places.
Bridging Size Scales with Self-Assembling Supramolecular Materials
Authors: Kazmaier Peter , Chopra Naveen
Published: February 2011

The notion of micromachines made up of miniature gears and motors may seem like a fairy tale. In 1959, Richard Feynman delivered a lecture entitled “There's Plenty of Room at the Bottom,” a bold prediction of what was to come in the future, where one could fit the entireEncyclopaedia Britannicaonto the head of a pin or use ions focused through a microscope lens in reverse to etch away silica to create patterns on a submicron scale. In retrospect, Feynman's hypotheses were amazingly accurate. He was describing the techniques of microlithography and the manipulation of atoms by scanning tunneling electron microscopy, methods that are commonplace today. Advances in biochemistry have revealed the enormous complexity of “simple” organisms, leading one to conclude that “micromachines” (of a complexity that a visionary giant such as Feynman had foreseen) have long been operating quite happily without any assistance from chemists!
Supramolecular Approaches to Nanoscale Dielectric Foams for Advanced Microelectronic Devices
Authors: Hawker Craig J. , Hedrick James L. , Miller Robert D. , Volksen Willi
Published: February 2011

The increasing demands of miniaturization in the microelectronics industry has forced continual improvement in the materials that are used in the fabrication of semiconductor devices. Advances in photoresists for microlithographic applications have reduced the feature size to 0.25 µm and below, and this drive to eversmaller features, coupled with the introduction of copper, has placed increasing demands on the dielectric material. Materials with lower dielectric constants (depicted in dark gray in Figure 1) are therefore required to more efficiently insulate these submicron features, such as the copper interconnect lines used to connect the transistors and memory cells in these advanced multilevel devices (Figure 1). This allows the minimization of crosstalk, signal delays, and power consumption. While vapor-deposited silicon dioxide and other derivatives are currently being employed, they suffer from unacceptably high dielectric constants (ε > 3.6) and are unacceptable for future generations of microelectronic devices.
Atomistic Aspects of Brittle Fracture
Authors: Gumbsch Peter , Cannon Rowland M.
Published: February 2011

The mechanical properties of materials are ultimately determined by events occurring on the atomic scale. In the case of brittle fracture, this connection is obvious, since the crack in a perfectly brittle material must be atomically sharp at its tip. The crack moves by breaking individual bonds between atoms and can therefore be regarded as a macroscopic probe for the atomic bonding. Nevertheless, traditional analysis of brittle-fracture processes resorts to the treatment of Griffith,1 which implies thermodynamic equilibrium. The Griffith criterion for the mechanical stability of a crack can be formulated as a balance of the crack driving force, the energyrelease rate G, and the surface energy ɣs of the two freshly exposed fracture surfaces: G = 2ɣs. The crack driving force can be obtained from elasticity theory. Within linear elasticity, the crack is characterized by a singularity in the stress field that decays as the inverse square root of the distance R from the crack. The strength of the singularity is characterized by the stressintensity factor K, the square of which directly gives access to the energy-release rate (G = K2/E′, where E′ is an appropriate elastic modulus). While this linear elastic description of the material is not disputed for brittle materials, except for a few atomic bonds around the crack, the assumption that the resistance of the material to crack propagation will only be characterized by the surface energy of the fracture surfaces is certainly worth some further consideration. Such considerations should range from examining atomic details at the tip of a single brittle crack to the relevance of more complex fracture events involving additional irreversible processes and complex crack geometries.
Dynamic Fracture in Disordered Media
Authors: Selinger Robin L. B. , Corbett John M.
Published: February 2011

While it is possible to carry out fracture experiments in single crystals, in everyday experience fracture occurs in heterogeneous and often disordered materials. Tear a piece of paper, and the resulting ragged edge shows evidence of the local variation in the paper's mechanical properties. One might expect the same behavior in fracture of other disordered materials such as polycrystalline solids, fiber composites, and concrete.
Diffusion Mechanisms and Intrinsic Point-Defect Properties in Silicon
Authors: Bracht Hartmut
Published: February 2011

High-purity silicon used for the growth of single crystals is a material with a high resistivity. Small traces of foreign atoms, which are mainly substitutionally dissolved on lattice sites, make the material highly conductive and therefore suitable for electronic applications. The controlled incorporation of extrinsic point defects in silicon is the main task for the production of electronic devices. Homogeneous doping is generally achieved by adding a controlled amount of the dopant element to the silicon melt. However, the fabrication of electronic devices like diodes, transistors, and complex integrated circuits requires spatially inhomogeneous dopant distributions. Control of the inhomogeneous doping profiles demanded by the considerations outlined in the article by Packan in this issue requires a detailed knowledge of the atomic mechanisms of dopant diffusion in silicon, the properties of intrinsic point defects like vacancies (V) and self-interstitials (I), and the interactions among different point defects.
Enhanced Diffusion in Silicon Processing
Authors: Cowern Nicholas , Rafferty Conor
Published: February 2011

Semiconductor-grade silicon is one of the most perfect crystalline materials that can be fabricated. It contains less than 1 ppb of unintended impurities and negligible twins or dislocations. Dopants can diffuse in this near-ideal crystal only by interacting with atomic-scale point defects: interstitial atoms or vacancies. These defects migrate through the silicon lattice, occasionally binding with a dopant atom and displacing it by one or more lattice positions.
Simulation of Defects and Diffusion Phenomena in Silicon
Authors: Law Mark E. , Gilmer George H. , Jaraíz Martin
Published: February 2011

Simulation of front-end processing is a critical component of integrated-circuit (IC) technology development. Today's electronics are so small that characterization of their material parameters is very difficult and expensive. Simulation is often the only effective tool for exploring the lateral and vertical doping profiles of a modern device at the level of detail required for optimization. Additionally, the cost of fabrication and test lots increases with each technology generation; for this reason, simulation becomes especially costeffective, if it can be made accurate. Increasingly, process simulation is being performed by harnessing a hierarchy of tools. Ab initio and molecular-dynamics (MD) codes are used to generate insight into the physics of individual particle reactions in the silicon lattice. This information can be fed to kinetic Monte Carlo (MC) codes to establish the dominant, critical mechanisms. Finally, traditional continuum codes can make use of this information and couple with the other process steps to simulate the entire process flow. Both MC and continuum codes can be compared with experiment in order to validate the calculations.
Theory of Thermal Conduction in Nonmetals
Authors: Srivastava G.P.
Published: February 2011

One of the fundamental physical properties of a material is its ability to conduct heat. Understanding and controlling the thermal conductivity of nonmetallic materials has been of much interest, mainly because this transport parameter is an important factor in determining the performance and reliability of various device applications.
Fabrication of Porous Metal Bonded Diamond Grinding Wheels for Flat-Surface Nanomachining
Authors: Matsumaru Koji , Takata Atsushi
Published: February 2011

The articles thus far in this MRS Bulletin issue on Emerging Methods for Micro- and Nanofabrication have addressed the creation of structures or devices on a small scale. What is implicit in some of these articles is that a substrate of sufficient flatness is available upon which to build these structures in a controlled way. A related area, therefore, is the formation of these flat surfaces, as well as the development of the tools to make them.
Peruvian Black Pottery Production and Metalworking: A Middle Sicán CraftWorkshop at Huaca Sialupe
Authors: Shimada Izumi , Wagner Ursel
Published: February 2011

The technical sophistication and virtuosity of prehispanic Andean ceramics are so often praised in the literature that it may appear that there is a large body of supportive, empirical findings. To the contrary, in-depth technical and more comprehensive technological studies have been rare. To achieve a comprehensive understanding of the many facets and stages of the technology and organization of craft production requires a correspondingly comprehensive, sustained effort—one built on interdisciplinary collaboration and longterm regional study of environmental, historical, social, and technological factors.
Materials Science Aspects of Photonic Crystals
Authors: Polman Albert , Wiltzius Pierre
Published: February 2011

The electronics revolution of the past 50 years has its roots in two scientific and technological areas. On the one hand, there have been tremendous advancements in our understanding of the physics of metals, dielectrics, and semiconductors, leading to the development of devices such as the transistor. On the other hand, a variety of processing techniques such as thin-film growth and deposition, ion implantation, and photolithography have allowed the massive integration of electronic functionality within a very small area, leading to microprocessors and high-density memory, among other innovations.
Microstructured Silica as an Optical-Fiber Material
Authors: Knight J.C. , Birks T.A. , Mangan B.J. , Russell P.St.J.
Published: February 2011

Conventional optical fibers are fabricated by creating a preform from two different glasses and drawing the preform down at an elevated temperature to form a fiber. A waveguide core is created in the preform by embedding a glass with a higher refractive index within a lower-index “cladding” material. Over the last few years, researchers at several laboratories have demonstrated very different forms of optical-fiber waveguides by using a drawing process to produce two-dimensionally microstructured materials in the form of fine “photoniccrystal fibers” (PCFs). One such waveguide is represented schematically in Figure 1. It consists of a silica fiber with a regular pattern of tiny airholes that run down the entire length. The optical properties of the microstructured silica cladding material enable the formation of guided waves in the pure silica core.
Electrochemically Prepared Pore Arrays for Photonic-Crystal Applications
Authors: Wehrspohn R.B. , Schilling J.
Published: February 2011

In the last few years, photonic crystals have gained considerable interest due to their ability to “mold the flow of light.” Photonic crystals are physically based on Bragg reflections of electromagnetic waves. In simple terms, a one-dimensional (1D) photonic crystal is a periodic stack of thin dielectric films with two different refractive indices, n1 and n2. The two important geometrical parameters determining the wavelength of the photonic bandgap are the lattice constant, a = d1(n1) + d2(n2), and the ratio of d1 to a (where d1 is the thickness of the layer with refractive index n1, and d2 is the thickness of layer n2). For a simple quarter-wavelength stack, the center wavelength λ of the 1D photonic crystal would be simply λ = 2n1d1 + 2n2d2. In the case of 2D photonic crystals, the concept is extended to either airholes in a dielectric medium or dielectric rods in air. Therefore, ordered porous dielectric materials like porous silicon or porous alumina are intrinsically 2D photonic crystals.
Technical Studies and Replication of Guan Ware, an Ancient Chinese Ceramic
Authors: Jiazhi Li , Zequn Deng , Jiming Xu
Published: February 2011

When North China was invaded in 1127, the emperor of the Song dynasty moved the capital to Lin'an (now called Hangzhou) in Zhejiang Province southeast of Shanghai. He established the Southern Song dynasty (1127–1279 a.d.), known as a period of cultural flowering and stability in Chinese history. Several years later, official kilns were built by court officials to meet the need for the porcelains required for use at the Southern Song palace.
Challenges in Plutonium and Actinide Materials Science
Authors: Terminello Louis J.
Published: February 2011

There are perhaps no more controversial materials in our society than the actinides—the elements above actinium in the periodic table that include uranium, plutonium, and many other radioactive elements. They are at the same time vilified by some for their potentially catastrophic impact on the environment and global health and praised by others for their role in ending the Cold War. And yet, at the heart of both these issues is a tremendous amount of fundamental research and technology that is essential for the actinides' rational use, safe disposition, reliable long-term storage, and the remediation of their impact on the environment.
Plutonium Oxide Systems and Related Corrosion Products
Authors: Haire R.G. , Haschke J.M.
Published: February 2011

Elemental plutonium is considered to be one of the most complex elements in the periodic table and, by some, one of the more toxic, given its moderate radioactivity and that it is a heavy metal. Essentially a manuf actured element (only traces are found in nature), it was first discovered and produced some six decades ago. Amazingly, hundreds of tons of plutonium are pre sently in existence. Crystalline solids formed by plutonium and nonmetallic elements (e.g., hydrogen, oxygen, halides, etc.) were some of the first compounds investigated, and oxides and oxide-related materials have always been important compounds.
Materials Science Research for the Conservation of Sculpture and Monuments
Authors: Scherer George W. , Flatt Robert , Wheeler George
Published: February 2011

Mountains give the illusion of durability because their grand scale hides the continual weathering of their surfaces. When the same stone is used to create a sculpture, the loss of a few millimeters suffices to spoil, or even eliminate, the features of a face; the rate of loss may be surprising, but it is not necessarily unnatural.
Traditional Oil Paints: The Effects of Long-Term Chemical and Mechanical Properties on Restoration Efforts
Authors: Mecklenburg Marion F. , Tumosa Charles S.
Published: February 2011

Some of the most important cultural icons in the world are oil paintings. Preserving them for future generations requires a fundamental understanding of the long-term chemical, mechanical, and physical behavior of their components. If the properties are understood, modeling and even predicting the effects of exposure to changes in temperature, relative humidity, shock, and vibration are possible.
The Challenge of Preserving Modern Art: A Technical Investigation of Paints Used in Selected Works by Willem de Kooning and Jackson Pollock
Authors: Lake Susan
Published: February 2011

Willem de Kooning (1904–1997) and Jackson Pollock (1912–1956) are perhaps the best-known members of the abstract expressionist movement, a group of diverse artists from disparate backgrounds who radically transformed American art during the 1940s and into the 1950s. While the development and legacy of abstract expressionism remains a subject of considerable debate, what this diverse group of artists had in common was the belief that the materials, and the ways the artists applied them, are crucial to the expression of their art.
Dynamic Studies of Semiconductor Growth Processes Using In Situ Electron Microscopy
Authors: Ross Frances M.
Published: February 2011

We have heard a lot about the exciting new materials being used in microelectronics, and I would like to describe some experiments making use of in situ electron microscopy to try to understand the mechanisms of the reactions that these materials undergo during deposition and processing. I will discuss experiments in which we carry out one of these reactions within an electron microscope and record the effect on the specimen in real time. We then use measurements from the recordings to analyze the reaction mechanism in a quantitative way. In this article, I will cover two types of experiments. First, I will describe experiments in which we examine the motion of surface and interface steps during reactions, and I will discuss how that information allows us to determine reaction mechanisms. In this context, I will consider silicon oxidation and silicide formation. In the second type of experiment, we look at how surface morphology changes during reactions. In particular, we will try to understand the growth mechanism of “quantum dots,” which are becoming important for some novel microelectronic applications. After discussing these results, I will describe our attempts to extend the technique of in situ electron microscopy to look at systems other than the solid—solid or gas—solid interface.
Progress in the Atomic-Scale Analysis of Materials with the Three-Dimensional Atom Probe
Authors: Cerezo A. , Larson D. J. , Smith G. D. W.
Published: February 2011

Exactly 50 years ago, E.W. Müller became the first person to observe single atoms, with the aid of the field-ion microscope (FIM). In 1967, with John Panitz and S. Brooks McLane, Müller's invention of the atom probe meant that, in his words, “We can now really deal much more intimately with the individual atoms which we encounter, since we know their names.” By combining position-sensitive detection with the time-of-flight mass spectrometry of single atoms in the atom probe, Cerezo and co-workers in the late 1980s built an instrument capable of reconstructing the three-dimensional (3D) atomic distribution of elements present in a material. The instruments that are capable of microanalysis at this level, called generically 3D atom probes (3DAPs), were the subject of two articles published inMRS Bulletinin 1994. In this article, we review some of the progress in the field since that time, in particular, the expansion of the range of materials problems that can be addressed by this powerful technique.
Materials Research by Means of Multiscale Computer Simulation
Authors: de la Rubia Tomás Díaz , Bulatov Vasily V.
Published: February 2011

Predicting the properties and performance of materials is central to the success of major industries producing a vast range of consumer goods and to research programs at laboratories and universities around the world. For many years, scientists have longed to have computer simulations that predict the behavior of materials and track the evolution of their microstructures from the atomic to the engineering scales. Until recently, such simulations had been little more than an elusive goal.
Micromechanics of Fracture: Connecting Physics to Engineering
Authors: Needleman A. , Van der Giessen E.
Published: February 2011

This nursery rhyme is one of the oldest, most familiar, and shortest treatises on fracture mechanics in the literature. Nevertheless, it makes several important points: (1) fracture occurs in response to some driving force (for Humpty, a “great fall”), (2) fracture involves material separation, and (3) fracture is irreversible.
Microelectro-mechanical Systems: Technology and Applications
Authors: Bishop David , Heuer Arthur , Williams David
Published: February 2011

Microelectromechanical systems, or MEMS, constitute a group of microdevices that are just beginning to affect many areas of science and technology. In diverse fields including the automotive industry, aeronautics, cellular communications, chemistry, acoustics, and display technologies and other photonic systems, these highly functional devices are making a big name for themselves, despite their diminutive size.
Surface Micromachining: A Brief Introduction
Authors: Mehregany Mehran , Zorman Christian A.
Published: February 2011

The rapid expansion of microelectromechanical systems (MEMS) into new application areas is due in large part to the development of surface-micromachining techniques that allow the fabrication of a wide variety of MEMS devices with structural components that can execute motion in at least one direction.