bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Genesis of Nuclei and Phase Separation on an Atomic Scale
Authors: Seidman David N. 
Published: February 2011

AbstractTurnbull performed much experimental and theoretical research on nucleation and on fundamental aspects of phase transformations in condensed matter. Nucleation of precipitates followed in parallel or sequentially by their growth and coarsening is a complex scientific subject and technologically highly relevant because of the many critical roles played by structural metallic alloys and their relevance to the energy problem. The focus herein is on nucleation, growth, and coarsening of precipitates employing atom-probe tomography, lattice kinetic Monte Carlo simulations, and diffusion theory, which constitute a unique approach for studying phase separation in concentrated multicomponent alloys.
Hard Materials with Tunable Porosity
Authors: Erlebacher Jonah , Seshadri Ram 
Published: February 2011

AbstractPorous metals and ceramic materials are of critical importance in catalysis, sensing, and adsorption technologies and exhibit unusual mechanical, magnetic, electrical, and optical properties compared to nonporous bulk materials. Materials with nanoscale porosity often are formed through molecular self-assembly processes that lock in a particular length scale; consider, for instance, the assembly of crystalline mesoporous zeolites with a pore size of 2–50 nm or the evolution of structural domains in block copolymers. Of recent interest has been the identification of general kinetic pattern-forming principles that underlie the formation of mesoporous materials without a locked- in length scale. When materials are kinetically locked out of thermodynamic equilibrium, temperature or chemistry can be used as a “knob” to tune their microstructure and properties. In this issue of the MRS Bulletin, we explore new porous metal and ceramic materials, which we collectively refer to as “hard” materials, formed by pattern-forming instabilities, either in the bulk or at interfaces, and discuss how such nonequilibrium processing can be used to tune porosity and properties. The focus on hard materials here involves thermal, chemical, and electrochemical processing usually not compatible with soft (for example, polymeric) porous materials and generally adds to the rich variety of routes to fabricate porous materials.
Materials at 200 mph: Making NASCAR Faster and Safer
Authors: Leslie-Pelecky Diandra 
Published: February 2011

AbstractSpeed is the ultimate goal of racing, and materials are an increasingly important area of research for making race cars faster. The splitter, which produces front downforce, is made from Tegris, a polypropylene composite offering comparable stiffness and improved impact properties at significantly lower cost than alternative materials. Engine blocks must be cast iron, but careful control of microstructure using precision manufacturing methods produces a lighter engine block that generates more horsepower.Speed and excitement must be balanced with safety, and materials are key players here, as well. Energy-dissipating foams in the car and the barriers surrounding the tracks allow drivers to walk away uninjured from accidents. Fire-resistant polymers protect drivers from high-temperature fuel fires, and technology transfer from the National Aeronautics and Space Administration (NASA) to the National Association for Stock Car Auto Racing (NASCAR) in the form of a low-temperature carbon monoxide catalyst filters the drivers' air.Sports are an outstanding way of showing the public how materials science and engineering are relevant to their lives and interests. Materials science and engineering is just that much more exciting when it's traveling at two hundred miles an hour.
Piezoelectric Thin Films for Sensors, Actuators, and Energy Harvesting
Authors: Muralt P. , Polcawich R. G. , Trolier-McKinstry S. 
Published: February 2011

AbstractPiezoelectric microelectromechanical systems (MEMS) offer the opportunity for high-sensitivity sensors and large displacement, low-voltage actuators. In particular, recent advances in the deposition of perovskite thin films point to a generation of MEMS devices capable of large displacements at complementary metal oxide semiconductor-compatible voltage levels. Moreover, if the devices are mounted in mechanically noisy environments, they also can be used for energy harvesting. Key to all of these applications is the ability to obtain high piezoelectric coefficients and retain these coefficients throughout the microfabrication process. This article will review the impact of composition, orientation, and microstructure on the piezoelectric properties of perovskite thin films such as PbZr1−xTixO3(PZT). Superior piezoelectric coefficients (e31, fof −18 C/m2) are achieved in {001}-oriented PbZr0.52Ti0.48O3films with improved compositional homogeneity on Si substrates. The advent of such high piezoelectric responses in films opens up a wide variety of possible applications. A few examples of these, including low-voltage radio frequency MEMS switches and resonators, actuators for millimeter-scale robotics, droplet ejectors, energy scavengers for unattended sensors, and medical imaging transducers, will be discussed.
Molecular, Supramolecular, and Macromolecular Motors and Artificial Muscles
Authors: Li Dongbo , Paxton Walter F. , Baughman Ray H. , Huang Tony Jun , Stoddart J. Fraser , Weiss Paul S. 
Published: February 2011

AbstractRecent developments in chemical synthesis, nanoscale assembly, and molecular-scale measurements enable the extension of the concept of macroscopic machines to the molecular and supramolecular levels. Molecular machines are capable of performing mechanical movements in response to external stimuli. They offer the potential to couple electrical or other forms of energy to mechanical action at the nano- and molecular scales. Working hierarchically and in concert, they can form actuators referred to as artificial muscles, in analogy to biological systems. We describe the principles behind driven motion and assembly at the molecular scale and recent advances in the field of molecular-level electromechanical machines, molecular motors, and artificial muscles. We discuss the challenges and successes in making these assemblies work cooperatively to function at larger scales.
Reticular Chemistry and Metal-Organic Frameworks for Clean Energy
Authors: Yaghi Omar M. , Li Qiaowei 
Published: February 2011

AbstractReticular chemistry concerns the linking of molecular building blocks into predetermined structures using strong bonds. We have been working on creating and developing the conceptual and practical basis of this new area of research. As a result, new classes of crystalline porous materials have been designed and synthesized: metal-organic frameworks, zeolitic imidazolate frameworks, and covalent organic frameworks. Crystals of this type have exceptional surface areas (2,000−6,000 m2/g) and take up voluminous amounts of hydrogen (7.5 wt% at 77 K and 3−4 × 106 Pa), methane (50 wt% at 298 K and 2.5 × 106 Pa), and carbon dioxide (140 wt% at 298 K and 3 × 106 Pa). We have driven the basic science all the way to applications without losing sight of our quest for understanding the underlying molecular aspects of this chemistry. The presentation was focused on the design concepts, synthesis, and structure of these materials, with emphasis on their applications to onboard energy storage.
An Atom-Probe Tomography Primer
Authors: Seidman David N. , Stiller Krystyna 
Published: February 2011

AbstractAtom-probe tomography (APT) is in the midst of a dynamic renaissance as a result of the development of well-engineered commercial instruments that are both robust and ergonomic and capable of collecting large data sets, hundreds of millions of atoms, in short time periods compared to their predecessor instruments. An APT setup involves a field-ion microscope coupled directly to a special time-of-flight (TOF) mass spectrometer that permits one to determine the mass-to-charge states of individual field-evaporated ions plus theirx-,y-, andz-coordinates in a specimen in direct space with subnanoscale resolution. The three-dimensional (3D) data sets acquired are analyzed using increasingly sophisticated software programs that utilize high-end workstations, which permit one to handle continuously increasing large data sets. APT has the unique ability to dissect a lattice, with subnanometer-scale spatial resolution, using either voltage or laser pulses, on an atom-by-atom and atomic plane-by-plane basis and to reconstruct it in 3D with the chemical identity of each detected atom identified by TOF mass spectrometry. Employing pico- or femtosecond laser pulses using visible (green or blue light) to ultraviolet light makes the analysis of metallic, semiconducting, ceramic, and organic materials practical to different degrees of success. The utilization of dual-beam focused ion-beam microscopy for the preparation of microtip specimens from multilayer and surface films, semiconductor devices, and for producing site-specific specimens greatly extends the capabilities of APT to a wider range of scientific and engineering problems than could previously be studied for a wide range of materials: metals, semiconductors, ceramics, biominerals, and organic materials.
Solid-State Ionics in the 21st Century: Current Status and Future Prospects
Authors: Kim Sangtae , Yamaguchi Shu , Elliott James A. 
Published: February 2011

AbstractThe phenomenon of ion migration in solids forms the basis for a wide variety of electrochemical applications, ranging from power generators and chemical sensors to ionic switches. Solid-state ionics (SSI) is the field of research concerning ionic motions in solids and the materials properties associated with them. Owing to the ever-growing technological importance of electrochemical devices, together with the discoveries of various solids displaying superior ionic conductivity at relatively low temperatures, research activities in this field have grown rapidly since the 1960s, culminating in “nanoionics”: the area of SSI concerned with nanometer-scale systems. This theme issue introduces key research issues that we believe are, and will remain, the main research topics in nanoionics and SSI during the 21st century. These include the application of cutting-edge experimental techniques, such as secondary ion mass spectroscopy and nuclear magnetic resonance, to investigate ionic diffusion in both bulk solids and at interfaces, as well as the use of atomic-scale modeling as a virtual probe of ionic conduction mechanisms and defect interactions. We highlight the effects of protonic conduction at the nanometer scale and how better control of interfaces can be employed to make secondary lithium batteries based on nanoionics principles. Finally, in addition to power generation and storage, the emergence of atomic switches based on cation diffusion shows great promise in developing next-generation transistors using SSI.
Ion Dynamics at Interfaces: Nuclear Magnetic Resonance Studies
Authors: Heitjans Paul , Wilkening Martin 
Published: February 2011

AbstractInterface engineering and the study of diffusion and transport processes through and along interfacial regions play important roles in materials science and energy research. For the latter, nanostructured materials are increasingly considered to act as powerful electrodes and solid electrolytes in sustainable energy systems, such as Li ion batteries. This is due to reduced diffusion lengths achieved when going to the nanometer scale and the fact that nanocrystalline materials with an average particle size of less than about 50 nm often show an enhanced diffusivity of their charge carriers. In this article, we show examples of how solid-state nuclear magnetic resonance (NMR) spectroscopy can be used to study the diffusion parameters of Li cations located in the interfacial regions separately from those in the interior of the grains. This article will demonstrate the future challenges and perspectives of Li NMR as a powerful tool of probing dynamic properties in functional materials.
Li Ion Migration at the Interfaces
Authors: Jamnik Janko , Gaberscek Miran 
Published: February 2011

AbstractDuring the past decade, the electrochemical properties (energy density, power capability, and cycling stability) of practical lithium (Li) batteries have been enormously improved. Surprisingly, although the knowledge exists of how to prepare excellent batteries, a detailed understanding of how they actually work is still lacking. In particular, the impact of interfaces in electrode composites is poorly understood. Here, we collect the most advanced mechanistic studies performed in our laboratory or published in recent literature and try to embed this knowledge into the well-established concepts used in solid-state ionics for many decades. In particular, we focus on the so-called perpendicular and parallel interfacial effects. We show that much of the old wisdom can be applied to batteries, although there are several important differences. We discuss, in some detail, the effects of charge incorporation, electronic interphase contacting, electrode porosity, and heterogeneous doping in selected advanced electrode materials and emphasize the future perspectives.
The Chemistry of Single-Walled Nanotubes
Authors: Strano Michael S. , Boghossian Ardemis A. , Kim Woo-Jae , Barone Paul W. , Jeng Esther S. , Heller Daniel A. , Nair Nitish , Jin Hong , Sharma Richa , Lee Chang Young 
Published: February 2011

AbstractThe unique structural, electronic, and mechanical properties of single-walled carbon nanotubes (SWNTs) have opened the doors to developments that push the limits of science. These advancements not only further scientific discovery, but also result in the development of everyday practical applications. These applications vary from singlemolecule sensors to nano-scaled transistors to multi-modal biosensors. This article focuses on three distinct developments made as a result of recent advances in spectroscopy of SWNTs. The first system examines the use of SWNTs for molecular detection using near-infrared light to produce tunable fluorescent sensors that are highly photostable. The second system examines the use of a 4-hydroxybenzene diazonium reagent to sort SWNTs based on electronic structure to create on-chip modifications of nano-electronic devices. The third system characterizes nanotube networks for such applications as flexible electronics, exploring the irreversible binding of adsorbates onto nanotube networks using electrical transport and Raman spectroscopy.
Atomistic Simulations of Mechanics of Nanostructures
Authors: Huang Hanchen , Van Swygenhoven Helena 
Published: February 2011

AbstractNanostructures can be in the form of nanoparticles or nanograins, nanowires or nanotubes, and nanoplates or multilayers. These nanostructures may be used individually or embedded in a bulk material. In both cases, they share two common features. First, the small dimensions minimize or even eliminate the presence of defects. Second, nanostructures entail large surface or interface areas. The absence of defects makes nanostructure materials stronger than their bulk counterparts, leading to the eventual realization of ideal strength. The presence of surfaces and interfaces may either reduce or increase the strength. Atomistic simulations can provide insight into the deformation mechanism at the atomic and electronic level, something that is very difficult to obtain from experiments. This article describes generic features of nanostructures and summarizes the five areas presented in the articles in this issue.
Mechanics of Ultra-Strength Materials
Authors: Zhu Ting , Li Ju , Ogata Shigenobu , Yip Sidney 
Published: February 2011

AbstractRecent experiments on nanoscale materials, including nanowires, nanopillars, nanoparticles, nanolayers, and nanocrystals, have revealed a host of “ultra-strength” phenomena, defined by stresses in the material generally rising up to a significant fraction of the ideal strength—the highest achievable strength of a defect-free crystal. This article presents an overview of the strength-controlling deformation mechanisms and related mechanics models in ultra-strength nanoscale materials. The critical role of the activation volume is highlighted in understanding the deformation mechanisms, as well as the size, temperature, and strain rate dependence of ultra strength.
What is the Limit of Nanoparticle Strengthening?
Authors: Chrzan D.C. , Morris J.W. , Osetsky Y.N. , Stoller R.E. , Zinkle S.J. 
Published: February 2011

AbstractThe stress required to deform a perfect crystal to its elastic limit while maintaining perfect periodicity, the so-called ideal strength, sets the gold standard for the strength of a given material. Materials this strong would be of obvious engineering importance, potentially enabling more efficient turbines for energy production, lighter materials for transportation applications, and more reliable materials for nuclear reactor applications. In practice, the strength of engineering materials is often more than two orders of magnitude less than the ideal strength due to easily activated deformation processes involving dislocations. For many materials, precipitate strengthening is a promising approach to impede dislocation motion and thereby improves strength and creep resistance. This observation begs the question: What are the limits of nanoparticle strengthening? Can the ideal strength of a matrix material be reached? To answer these questions, we need a detailed, atomic scale understanding of the interactions between dislocations and obstacles. Fortunately, simulations are beginning to explore this interaction.
Mechanics of Crystalline Nanowires
Authors: Park Harold S. , Cai Wei , Espinosa Horacio D. , Huang Hanchen 
Published: February 2011

AbstractNanowires are among the most exciting one-dimensional nanomaterials because of their unique properties, which result primarily from their chemical composition and large surface area to volume ratio. These properties make them ideal building blocks for the development of next generation electronics, opto-electronics, and sensor systems. In this article, we focus on the unique mechanical properties of nanowires, which emerge from surface atoms having different electron densities and fewer bonding neighbors than atoms lying within the nanowire bulk. In this respect, atomistic simulations have revealed a plethora of novel surface-driven mechanical behavior and properties, including both increases and decreases in elastic stiffness, phase transformations, shape memory, and pseudoelastic effects. This article reviews such atomistic simulations, as well as experimental data of these phenomena, while assessing future challenges and directions.
Nanomechanical Architectures—Mechanics-Driven Fabrication Based on Crystalline Membranes
Authors: Liu Feng , Lagally Max G. , Zang Ji 
Published: February 2011

AbstractBending of thin sheets or ribbons is a ubiquitous phenomenon that impacts our daily lives, from the household thermostat to sensors in airbags. At nanometer-scale thicknesses, the mechanics responsible for bending and other distortions in sheets can be employed to create a nanofabrication approach leading to novel nanostructures. The process and resulting structures have been aptly referred to as “nanomechanical architecture.” In this article, we review recent progress in atomistic simulations that not only have helped to reveal the physical mechanisms underlying this nanofabrication approach, but also have made predictions of new nanostructures that can be created. The simulations demonstrate the importance of the atomic structure of the crystalline membrane and of the intrinsic surface stress in governing membrane bending behavior at the nanoscale and making the behavior fundamentally distinct from that at the macroscale. Molecular dynamics simulations of the bending of patterned graphene (a single-atomic layer film) suggest a new method for synthesizing carbon nanotubes with unprecedented control over their size and chirality.
Crystal Growth from the Melt under External Force Fields
Authors: Rudolph P. , Kakimoto K. 
Published: February 2011

AbstractThe present and future demands of industrial bulk crystal growth from the melt are concentrated on improved crystal quality, increased yield, and reduced costs. To meet these challenges, the size of the melt volume must be markedly increased. As a result, violent convective perturbations appear within the melts due to turbulent heat and mass flows. They disturb the single crystal growth and give rise to compositional inhomogeneities. The application of external force fields is an effective method to dampen and control these flows. After introducing different stabilizing variants, such as constant and accelerated melt rotation, mechanical vibrations, and electric current, this article focuses on the use of magnetic fields. Nonsteady fields became very popular because, in this case, the needed strength of the magnetic induction is much lower than for steady fields. A new low-energy low-cost technology that combines heat and magnetic field generation in one module placed close to the melt crucible is introduced.
Advances in Bulk Crystal Growth of AlN and GaN
Authors: Ehrentraut Dirk , Sitar Zlatko 
Published: February 2011

AbstractAluminum nitride (AlN) and gallium nitride (GaN) play an essential role in modern electronics, particularly in optoelectronics. Highly efficient light-emitting devices covering the ultraviolet to green spectral region are fabricated from these materials. Despite all efforts, the growth of large-size and high-quality AlN and GaN crystals for substrates, which are thermally and lattice-matched to the AlGaN-based device structures, is still in its infancy. This is due to the high equilibrium vapor pressure of nitrogen above these compounds, which requires growth techniques employing either the vapor phase or liquid solutions. The best commercially available GaN substrates show a high dislocation density of >105 per cm2 and strong bowing with a radius of curvature smaller than 10 m. This article reviews current growth techniques that look promising and may become commercially viable.
Growth of Optical Crystals by the Micro-Pulling-Down Method
Authors: Yoshikawa Akira , Chani Valery 
Published: February 2011

AbstractThe micro-pulling-down technique is a crystal growth method that has been mostly developed since 1992. The general scheme of the growth system is relatively simple: the melt (oxide, fluoride, metal) residing in a crucible is transported in downward through microcapillary channel(s) made in the bottom of the crucible. Two driving forces (capillary action and gravity) support the delivery of the melt to the liquid/solid growth interface formed under the crucible due to a properly established temperature gradient. Appropriate configuration of the crucible bottom allows for controlling of the crystal shape (fibers, rods, tubes, plates) and the dimensions of the crystals' cross sections that range approximately from 0.1 to 10 mm. A great number of scientifically and industrially important optical crystal fibers have been successfully produced using this method.