bluuebunny/crossref_metadata_2025 huggingface dataset:
In AquaManufacturing of a Three-Dimensional Nanostructure Using a Peptide Aptamer
Authors: Sano Ken-Ichi , Shiba Kiyotaka
Published: February 2011

TBP-1 is a 12-amino-acid peptide aptamer that has been isolated as a Ti binder using a peptide-phage system. Subsequent analyses have shown that TBP1 also binds Si and Ag, and has the ability to enhance the formation of titania and silica as well as nanoparticles of Ag. TBP-1 is thus a bifunctional peptide: a binder that also acts as a mediator of mineralization. These two functions can be grafted onto heterologous molecules. For instance, mutational analysis of the TBP-1 revealed that itsN-terminal hexapeptide, RKLPDA (minTBP-1), is sufficient for Ti binding. When the surface of ferritin, a nano-sized spherical cargo protein, was ornamented with minTBP-1 either genetically or chemically, the resultant modified ferritin acquired the ability to bind Ti and mediate mineralization. By alternately applying the binding and mineralization activities of the minTBP-1-modified nanocage, we were able to construct, in stepwise fashion, multilayer structures composed of titania (or silica) and nanocages. We named this process the biomimetic layer-by-layer (BioLBL) method. By coupling BioLBL with a conventional top-down lithographic method,in aquastructuralization of a three-dimensional (3D) configuration of nanomolecules was realized. As shown in this article, binding and mineralization activities of peptide aptamers, when they are combined with nanostructured materials, play active roles in manufacturing nanostrucutrein aqua.
Bioenabled Nanophotonics
Authors: Chen Yeechi , Munechika Keiko , Ginger David S.
Published: February 2011

Biological molecules such as oligonucleotides, proteins, or peptides can be used for the synthesis, recognition, and assembly of materials with nanoscale dimensions. Of particular interest are the fields of near-field optics and plasmonics. Many potential optical applications depend on the ability to control the relative positioning of organic dyes, plasmon-resonant metal nanoparticles, and semiconductor quantum dots with nanoscale precision. In this article, we describe some recent achievements in biological assembly and nanophotonics, and discuss potential uses of biological materials for assembling optically functional nanostructures. We emphasize the use of biological materials to build well-defined nanostructures for near-field plasmon-enhanced fluorescence.
In SituX-Ray Tomography Studies of Microstructural Evolution Combined with 3D Modeling
Authors: Buffière J.-Y. , Cloetens P. , Ludwig W. , Maire E. , Salvo L.
Published: February 2011

Synchrotron x-ray microtomography is a characterization technique increasingly used to obtain 3D images of the interior of optically opaque materials with a spatial resolution in the micrometer range. As a nondestructive technique, it enables the monitoring of microstructural evolution duringin situexperiments. In this article, examples from three different fields of metals research illustrate the contribution of x-ray tomography data to modeling: deformation of cellular materials, metal solidification, and fatigue crack growth in Al alloys. Conventionally, tomography probes the 3D distribution of the x-ray attenuation coefficient within a sample. However, this technique is also being extended to determine the local crystallographic orientation in the bulk of materials (diffraction contrast tomography), a key issue for the modeling of microstructure in metals.
Materials Challenges and Applications of Solution-Processed Organic Field-Effect Transistors
Authors: Sirringhaus Henning , Ando Masahiko
Published: February 2011

Organic field-effect transistors (FETs) are currently the focus of significant academic research and industrial development interest, as they potentially offer unique advantages over their inorganic counterparts in terms of cost reductions, compatibility with low-temperature and printing-based manufacturing, and potentially even performance. The first generation of products incorporating organic FETs is presently being introduced to the market. This article provides an overview of strategies for achieving high field-effect mobilities in solution-processed organic semiconductor films. We provide an assessment of materials challenges to meet performance and reliability requirements for a range of display and circuit applications and present an overview of state-of-the-art application demonstrations in active-matrix addressing of flexible eletrophoretic, organic light-emitting diode, and liquid-crystal displays, as well as radio-frequency identification tagging. We discuss how the unique functional properties of organic semiconductors, which allow comparatively easy integration of information processing, information storage, light emission, and light detection functions, might enable multifunctional applications that are not easy to create with other material systems.
The Materials Science of Bone: Lessons from Nature for Biomimetic Materials Synthesis
Authors: Oyen Michelle L.
Published: February 2011

There has been considerable recent interest in natural bone as a material, due in part to its interesting combination of mechanical properties: bone is stiff and tough but lightweight. This unusual combination of properties results from a nanocomposite structure of approximately equal volumes of mineral and hydrated organic matter. Much recent effort has been focused on the structure, properties, and performance at different length scales relative to the hierarchical organization of bone. Historically, such bone research has emphasized clinical and medical aspects, including engineering materials for bone augmentation or replacement, bone–biomaterial interactions and interfaces, and more recently, scaffolds for bone tissue engineering. However, within the fast-growing biomimetics field, the bone extracellular matrix is taken as a model for materials development. Efforts have been made both to mimic the bony material itself as well as to mimic the process by which bone forms.
Bioinspired Materials for Self-Cleaning and Self-Healing
Authors: Youngblood Jeffrey P. , Sottos Nancy R.
Published: February 2011

Biological systems have the ability to sense, react, regulate, grow, regenerate, and heal. Recent advances in materials chemistry and micro- and nanoscale fabrication techniques have enabled biologically inspired materials systems that mimic many of these remarkable functions. This issue of MRS Bulletin highlights two promising classes of bioinspired materials systems: surfaces that can self-clean and polymers that can self-heal. Self-cleaning surfaces are based on the superhydrophobic effect, which causes water droplets to roll off with ease, carrying away dirt and debris. Design of these surfaces is inspired by the hydrophobic micro- and nanostructures of a lotus leaf. Self-healing materials are motivated by biological systems in which damage triggers a site-specific, autonomic healing response. Self-healing has been achieved using several different approaches for storing and triggering healing functionality in the polymer. In this issue, we examine the most successful strategies for self-cleaning and self-healing materials and discuss future research directions and opportunities for commercial applications.
Biological and Synthetic Self-Cleaning Surfaces
Authors: Genzer Jan , Marmur Abraham
Published: February 2011

In this contribution, we briefly discuss how various physicochemical properties of surfaces affect the wettability and self-cleaning character of both naturally occurring and synthetic surfaces. Using a few selected examples from nature, we discuss the superhydrophobic effect and antifouling character of such surfaces and how these properties are associated with variations in surface chemical composition and topography. We also review a few special case studies aimed at adopting these biomimetic schemes to design and fabricate functional self-cleaning surfaces.
Autonomic Healing of Polymers
Authors: White Scott R. , Caruso Mary M. , Moore Jeffrey S.
Published: February 2011

Self-healing polymers have experienced rapid technological advancement over the past seven years. They have moved from a conceptual demonstration to practical application in this time frame and have grown from a single design to a generic paradigm for modern materials development. Potential applications of self-healing polymers are quite broad, including microelectronic substrates and encapsulants, polymeric paints and coatings, structural composites, and biomedical devices. In this article, we focus on polymeric systems that heal in an autonomic fashion, that is, automatically and without human intervention. The types of systems under development and the future of this paradigm in advanced materials are discussed.
In Situ Heating Transmission Electron Microscopy
Authors: Saka Hiroyasu , Kamino Takeo , Ara Shigeo , Sasaki Katsuhiro
Published: February 2011

Temperature is one of the most important factors affecting the state and behavior of materials. In situ heating transmission electron microscopy (TEM) is a powerful tool for understanding such temperature effects, and recently in situ heating TEM has made significant progress in terms of temperature available and resolution attained. This article briefly describes newly developed specimen-heating holders, which are useful in carrying out in situ heating TEM experiments. It then focuses on three main applications of these specimen holders: solid–solid reactions, solid–liquid reactions (including highresolution observation of a solid–liquid interface, size dependence of the melting temperatures of one-, two- and three-dimensionally reduced systems, size dependence of the contact angle of fine metal liquid, and wetting of Si with liquid Au or Al) and solid–gas reactions. These results illustrate the benefit of in situ heating TEM for providing fundamental information on temperature effects on materials.
Electric and Magnetic Phenomena Studied byIn SituTransmission Electron Microscopy
Authors: Cumings John , Olsson Eva , Petford-Long Amanda K. , Zhu Yimei
Published: February 2011

There is a wide array of technologically significant materials whose response to electric and magnetic fields can make or break their utility for specific applications. Often, these electrical and magnetic properties are determined by nanoscale features that can be most effectively understood through electron microscopy studies. Here, we present an overview of the capabilities for transmission electron microscopy for uncovering information about electric and magnetic properties of materials in the context of operational devices. When devices are operated during microscope observations, a wealth of information is available about dynamics, including metastable and transitional states. Additionally, because the imaging beam is electrically charged, it can directly capture information about the electric and magnetic fields in and around devices of interest. This is perhaps most relevant to the growing areas of nanomaterials and nanodevice research. Several specific examples are presented of materials systems that have been explored with these techniques. We also provide a view of the future directions for research.
Whither Oxide Electronics?
Authors: Ramesh Ramamoorthy , Schlom Darrell G.
Published: February 2011

In this issue we have endeavored to answer the question, “Whither oxide electronics?” This issue provides a framework and perspective on the progress in the field of oxide electronics over the past several decades, as well as the challenges and opportunities in the years to come. Building on the foundations laid by the pioneers in the materials community and spurred by the discovery of high-temperature superconductivity, there has been both tremendous progress in understanding the complex science of oxide electronic materials and the discovery of other fascinating new phenomena, including colossal magnetoresistance, multiferrocity, and two-dimensional electron gases in correlated oxide systems. Thin-film heterostructures provide a pathway to create novel devices and combinations of physical phenomena. Indeed, the ability to synthesize and control oxide heterostructures using sophisticated deposition techniques has become a key enabler of the recent advances in this field. These oxides are beginning to enter mainstream products because of their higher performance, for example, ferroelectric memories and oxides with high dielectric constant for computers that run at higher speed and use less power.
Gate Oxides Beyond SiO2
Authors: Schlom Darrell G. , Guha Supratik , Datta Suman
Published: February 2011

This year marks a major materials milestone in the makeup of silicon-based field-effect transistors: in the microprocessors produced by leading manufacturers, the SiO2gate dielectric is being replaced by a hafnium-based dielectric. The incredible electronic properties of the SiO2/silicon interface are the reason that silicon has dominated the semiconductor industry and helped it grow to over $250 billion in annual sales, as reported by the Semiconductor Industry Association (SIA), San Jose, CA. The shrinkage of transistor dimensions (Moore's law) has led to tremendous improvements in circuit speed and computer performance. At the same time, however, it has also led to exponential growth in the static power consumption of transistors due to quantum mechanical tunneling through an ever-thinner SiO2gate dielectric. This has spurred an intensive effort to find an alternative to SiO2with a higher dielectric constant (K) to temper this exploding power consumption. This article reviews the high-Kmaterials revolution that is enabling Moore's law to continue beyond SiO2.
Electric-Field Control of Magnetism in Complex Oxide Thin Films
Authors: Spaldin Nicola A. , Ramesh R.
Published: February 2011

In this article, we review current research efforts to control the magnetic behavior of complex oxide thin films using electric fields. After providing fundamental definitions of magnetoelectric response, we survey materials, architectures, and mechanisms that exhibit promise for such electric-field control of magnetism. Finally, we mention ideas for future research and discuss prospects for the field.
ZnO-Based Semiconductors as Building Blocks for Active Devices
Authors: Kamiya Toshio , Kawasaki Masashi
Published: February 2011

This article provides a review of materials and devices of wide-bandgap oxide semiconductors based on ZnO, highlighting the nature of the chemical bond. The electronic structures of these materials are very different from those of conventional covalently bonded semiconductors, owing to the ionic nature of the chemical bonds. Therefore, one needs to design and optimize fabrication processes and structures of active devices containing such materials, taking into account the peculiar defect formation mechanisms. A variety of active devices that have clear advantages over the conventional ones have been demonstrated, for example, ultraviolet light-emitting diodes, quantum Hall devices, and transparent and flexible thin-film transistors with high electron mobility, paving the way for future applications. The reasons behind the successes identify future challenges in research on oxide semiconductors.
In-Contact Molecular Spectroscopy of Liquid Lubricant Films
Authors: Cann P.M.
Published: February 2011

The primary role of a lubricant is to control the friction and wear of rubbing surfaces to optimize the operation of a component by forming an interfacial film separating the surfaces. Lubrication research seeks to develop new lubricant formulations and to optimize component life and performance. To do this, we must understand the mechanisms of film formation and film properties and the way these relate to operating conditions. In many engineering components, the lubricant film is subjected to severe mechanical and thermal stresses as it passes through the loaded zone. These severe conditions can result in molecular alignment or conformational change and the formation of new chemical species, which will impact the lubrication performance of the fluid. The lubricant response within the contact is often transient and thus has proved difficult to study by conventional surface analytical methods. One alternative is to replace one of the surfaces by a transparent window and use molecular microspectroscopy (infrared or Raman) to analyze the film within the contact zone formed during rubbing. This article reviews the development and application of in-contact molecular spectroscopy for the study of lubricant properties within the rubbing interface for both conventional and biolubrication systems. This technique has been used to study molecular conformation, chemical composition, and pressure distribution in the high-pressure region of the contact zone. However, challenges remain, including detecting very thin films, obtaining depth profile information, and applying these methods more generally to biotribology.
Cracklike Processes within Frictional Motion: Is Slow Frictional Sliding Really a Slow Process?
Authors: Rubinstein Shmuel M. , Cohen Gil , Fineberg Jay
Published: February 2011

The dynamics of frictional motion have been studied for hundreds of years, yet many aspects of these important processes are not understood. First described by Coulomb and Amontons as the transition from static to dynamic friction, the onset of frictional motion is central to fields as diverse as physics, tribology, mechanics of earthquakes, and fracture. We review recent studies in which fast (real-time) visualization of the true contact area along a rough spatially extended interface separating two blocks of like material has revealed the detailed dynamics of how this transition takes place. The onset of motion is preceded by a discrete sequence of rapid cracklike precursors, which are initiated at shear levels that are well below the threshold for static friction. These precursors systematically increase in spatial extent with the applied shear force and leave in their wake a significant redistribution of the true contact area. Their cumulative effect is such that, just prior to overall sliding of the blocks, a highly inhomogeneous contact profile is established along the interface. At the transition to overall motion, these precursor cracks trigger both slow propagation modes and modes that travel faster than the shear wave speed. Overall frictional motion takes place only when either the slow propagation modes or additional shear cracks excited by these slow modes traverse the entire interface. Surprisingly, in the resulting stick–slip motion, the surface contact profile retains the profile built up prior to the first slipping event. These results suggest a fracture-based mechanism for stick–slip motion that is qualitatively different from other descriptions.
Conjugated Polymer Actuators
Authors: Smela Elisabeth
Published: February 2011

Conjugated polymer artificial muscles fill a unique niche in the electroactive polymer portfolio. They combine high strength, low voltage, and reasonable speed with versatile fabrication and design. This article reviews the actuation mechanism in these materials and presents some of the designs that have been developed for applications such as Braille displays, catheters, and bioMEMS devices.
Recent Developments in Artificial Molecular-Machine–Based Active Nanomaterials and Nanosystems
Authors: Huang Tony Jun
Published: February 2011

Artificial molecular machines capable of converting chemical, electrochemical, and photochemical energy into mechanical motion represent a high-impact, fast-growing field of interdisciplinary research. These molecular-scale systems utilize a “bottom-up” technology centered upon the design and manipulation of molecular assemblies and are potentially capable of delivering efficient actuation at length scales dramatically smaller than traditional microscale actuators. As actuation materials, molecular machines have many advantages, such as high strain (40%–60%), high force and energy densities, and the capability to maintain their actuation properties from the level of a single molecule to the macroscale. These advantages have inspired researchers to develop molecular-machine–based active nanomaterials and nanosystems, including electroactive and photoactive polymers. This article will discuss the structures and properties of artificial molecular machines, as well as review recent progress on efforts to move molecular machines from solution to surfaces to devices.
Carbon Dioxide Capture and Storage
Authors: Benson Sally M. , Orr Franklin M.
Published: February 2011

Reducing CO2 emissions from the use of fossil fuel is the primary purpose of carbon dioxide capture and storage (CCS). Two basic approaches to CCS are available.1,2 In one approach, CO2 is captured directly from the industrial source, concentrated into a nearly pure form, and then pumped deep underground for long-term storage (see Figure 1). As an alternative to storage in underground geological formations, it has also been suggested that CO2 could be stored in the ocean. This could be done either by dissolving it in the mid-depth ocean (1–3 km) or by forming pools of CO2 on the sea bottom where the ocean is deeper than 3 km and, consequently, CO2 is denser than seawater. The second approach to CCS captures CO2directly from the atmosphere by enhancing natural biological processes that sequester CO2 in plants, soils, and marine sediments. All of these options for CCS have been investigated over the past decade, their potential to mitigate CO2 emissions has been evaluated,1 and several summaries are available.1,3,4
Methane Hydrates: An Abundance of Clean Energy?
Authors: Rath B.B.
Published: February 2011

The discovery that gas hydrates (also called clathrate hydrates) can crystallize (Figure 1) as a solid by the combination of water and several types of gases exposed to low temperatures and elevated pressure goes back to the 1800s. French researchers were the frst to report the formation of methane, ethane, and propane hydrates.1 Results of these studies remained as scientifc novelties until the mid-1930s, when it was discovered in Germany that gas hydrates forming as solids above 0°C in gas pipelines blocked the fow of natural gas.2 This observation initiated a furry of activities both in Europe and in the United States to fnd various inhibitors to prevent hydrate formation in gas transmission lines. During the mid-1960s, it was recognized that nature, over millions of years, has deposited vast amounts of methane hydrates along most of the continental margins in the ocean sediments, as well as along the permafrost regions in Alaska, Canada, and Russia.3 Figure 2 shows the presence of methane hydrate deposits in the ocean sediments and in the permafrost regions of the world. These deposits are byproducts of microbial decomposition of organic matter or of Earth's geothermal heating distributed worldwide where temperature and pressure are suitable for hydrate formation. The distribution of organic carbon in Earth's crust as methane
Off-Grid Solar for Rural Development
Authors: Soboyejo Wole , Taylor Roger
Published: February 2011

The World Bank estimates that over two billion people on the planet live their daily lives without access to basic, reliable electric services. Rural populations in Africa, Latin America, Asia, and island nations need clean water, health services, communications, and light at night. Small, simple, solar electric systems are part of the solution—increasing the quality of life, often at a cost that is less than what is presently being spent for kerosene, dry-cell batteries, and the recharging of automotive batteries that must be lugged to the nearest town on a weekly basis (see Figure 1).
Electrical Energy Storage Using Flywheels
Authors: Whittingham M. Stanley
Published: February 2011

Flywheel energy storage systems use the kinetic energy stored in a rotor; they are often referred to as mechanical batteries. On charging, the fywheel is accelerated, and on power generation, it is slowed. Because the energy stored is proportional to the square of the speed, very high speeds are used, typically 20,000–100,000 revolutions per minute (rpm). To minimize energy loss due to friction, the rotors are spun in a vacuum and use magnetic bearings. The rotors today are typically made of high-strength carbon composites. One of the main limits to fywheels is the strength of the material used for the rotor: the stronger the rotor, the faster it can be spun, and the more energy it can store.
A Super-Green Factory: The Sharp Kameyama Plant
Authors: Kusakabe Tetsuo
Published: February 2011

Sharp Corporation is making a concerted effort to reduce environmental impacts to the greatest extent possible at its production facilities around the world, and it is applying its own original evaluation criteria to recognize those plants having an extremely high level of environmental performance as “SuperGreen Factories.”

Our Kameyama plant, the frst such factory to be so recognized, is an integrated, start-to-fnish production facility for liquid-crystal display (LCD) televisions (TVs), from fabricating the LCD panel to assembling the fnished TV set (see Table I). Given that large amounts of energy are consumed to operate production equipment and to power air conditioning, we focused particular attention on environmental measures intended to reduce global warming and introduced an energy supply system that combines environmental friendliness and operational stability. As shown in Figure 1, this system is based on integrating different types of large-scale distributed power sources and consists of a gas-fred cogeneration system, a fuel cell system, and a photovoltaic power generating system. The power output of this system covers about one-third of the total electrical needs of the plant.
Nanoparticle Delivery: Targeting and Nonspecific Binding
Authors: Liu Rihe , Kay Brian K. , Jiang Shaoyi , Chen Shengfu
Published: February 2011

Targeted cancer therapies focus on molecular and cellular changes that are specific to cancer and hold the promise of harming fewer normal cells, reducing side effects, and improving the quality of life. One major challenge in cancer nanotechnology is how to selectively deliver nanoparticles to diseased tissues while simultaneously minimizing the accumulation onto the nanoparticle of unwanted materials (e.g., proteins in the blood) during the delivery process. Once therapeutic nanoparticles have been created, very often they are linked or coated to other molecules that assist in targeting the delivery of nanoparticles to different cell types of the body. These linkers or coatings have been termed targeting ligands or “smart molecules” because of their inherent ability to direct selective binding to cell types or states and, therefore, confer “smartness” to nanoparticles. Likewise, “smartness” can be imparted to the nanoparticles to selectively repel unwanted entities in the body. To date, such smart molecules can consist of peptides, antibodies, engineered proteins, nucleic acid aptamers, or small organic molecules. This review describes how such smart molecules are discovered, enhanced, and anchored to nanoparticles, with an emphasis on how to minimize nonspecific interactions of nanoparticles to unintended targets.
Atomic Layer Deposition of Dielectrics on Ge and III–V Materials for Ultrahigh Performance Transistors
Authors: Wallace Robert M. , McIntyre Paul C. , Kim Jiyoung , Nishi Yoshio
Published: February 2011

The prospect of utilizing alternative transistor channel materials for ultrahigh performance transistors will require suitable gate dielectrics for surface-channel field-effect devices. With the utilization of deposited gate dielectrics in large-scale production for Si-based integrated circuits by atomic layer deposition, extending this technology to channel materials that exhibit high bulk mobility behavior is of interest. A review of the current status for atomic layer deposited high-κ dielectrics on Ge and III–V channel materials is presented.
Nanoporous Metals by Alloy Corrosion: Formation and Mechanical Properties
Authors: Weissmüller Jörg , Newman Roger C. , Jin Hai-Jun , Hodge Andrea M. , Kysar Jeffrey W.
Published: February 2011

Nanoporous metals prepared by the corrosion of an alloy can take the form of monolithic, millimeter-sized bodies containing approximately 1015nanoscale ligaments per cubic millimeter. The ligament size can reach down to the very limits of stability of nanoscale objects. The processes by which nanoporous metals are formed have continued to be fascinating, even though their study in relation to surface treatment, metal refinement, and failure mechanisms can be traced back to ancient times. In fact, the prospect of using alloy corrosion as a means of making nanomaterials for fundamental studies and functional applications has led to a revived interest in the process. The quite distinct mechanical properties of nanoporous metals are one of the focus points of this interest, as relevant studies probe the deformation behavior of crystals at the lower end of the size scale. Furthermore, the coupling of bulk stress and strain to the forces acting along the surface of nanoporous metals provide unique opportunities for controlling the mechanical behavior through external variables such as the electrical or chemical potentials.
Novel Electromechanical Phenomena at the Nanoscale: Phenomenological Theory and Atomistic Modeling
Authors: Tagantsev Alexander K. , Meunier Vincent , Sharma Pradeep
Published: February 2011

In the past two decades, the fact that “small is different” has been established for a wide variety of phenomena, including electrical, optical, magnetic, and mechanical behavior of materials. However, one largely untapped but potentially very important area of nanoscience involves the interplay of electricity and mechanics at the nanoscale. In this article, predicated on both phenomenological approaches and atomistic calculations, we summarize the state-of-the-art in understanding electromechanical coupling at the nanoscale. First, we address flexoelectricity—the coupling of strain gradient to polarization. Flexoelectricity exists in both piezoelectric and nonpiezoelectric dielectrics. As a high-order spatial-dispersion effect, the flexoelectricity becomes more and more important with the reduction of the spatial scale of the problem. Exploitation of this phenomenon and the associated nanoscale size effects can lead to tantalizing applications, such as “piezoelectric nanocomposites without using piezoelectric materials.” The second issue concerns electromechanical effects at the dielectric/metal interface. An interface in solids typically exhibits a lower symmetry compared to that of the associated adhering materials. This symmetry reduction can drastically affect the electromechanical and dielectric behavior of the material at the nanoscale.
Probing Diffusion Kinetics with Secondary Ion Mass Spectrometry
Authors: De Souza Roger A. , Martin Manfred
Published: February 2011

Secondary ion mass spectrometry (SIMS) is a powerful analytical technique for determining elemental and isotopic distributions in solids. One of its main attractions to researchers in the field of solid-state ionics is its ability to distinguish between isotopes of the same chemical element as a function of position in a solid. With enriched stable isotopes as diffusion sources, this allows self-diffusion kinetics in solids to be studied. In this article, taking oxygen isotope diffusion in oxides as our main example, we present the standard experimental method, and, subsequently, we discuss several promising developments, in particular the opportunities offered by thin-film geometries, and the investigation of inhomogeneous systems, including possible fast diffusion along grain boundaries and making space-charge layers at interfaces “visible.” These examples demonstrate that SIMS is capable of probing mass transport processes over various length scales, ranging from some nanometers to hundreds of micrometers.
Current Status of GaN-Based Solid-State Lighting
Authors: Nakamura Shuji
Published: February 2011

The continuous improvement in luminous efficacy of “white” light-emitting-diode (LED) sources offers the potential of considerable energy savings in general lighting applications. Recent experiments at UCSB have demonstrated 117 lumens per watt (lm/W) in white LEDs, with further improvements expected in the near future. Considerable progress has also been achieved using nonpolar GaN, such as a-plane {1120} and m-plane {1100} GaN, or semipolar GaN substrates. Such devices avoid the deleterious effects of charge separation due to spontaneous and piezoelectric polarization inherent in most c-axis-oriented devices.
Detached Bridgman Growth—A Standard Crystal Growth Method with a New Twist
Authors: Cröll Arne , Volz Martin P.
Published: February 2011

Bridgman or vertical gradient freeze (VGF) crystal growth processes have several advantages compared to other melt growth methods, especially the possibility to achieve a low level of thermal stress and low dislocation densities in the grown crystals. However, crystals grown in contact with a crucible usually suffer from mechanical stress during cooling, reducing the structural quality. The “detached” or “dewetted” Bridgman growth avoids this problem and has recently been investigated in more detail as a promising tool to improve crystal quality. Detached growth, where the crystal is separated from the crucible wall by a gap of 10–100 μm, was found originally in some microgravity experiments going back to 1975. Considerable improvements of crystal quality were reported for those cases; however, the reasons for the detachment were not fully understood. In the last 10–15 years, theoretical investigations as well as new experiments have shown beyond a doubt that detached growth can, in principle, be achieved in Earth's gravity with the same advantages that were demonstrated in the crystals grown under microgravity. It could be shown that the ability to achieve detachment depends on a complex interplay of the wetting of the melt with the crucible and the crystal as well as the pressure balance in the system, including the hydrostatic pressure, the gas pressure above the melt, and the pressure below the melt. It turns out that for stable detachment, only, specific combinations of meniscus shape, gap size, wetting angle, growth angle, and pressures work. The conditions that lead to detachment are thus highly specific for a given system.
Double Tungstate and Molybdate Crystals for Laser and Nonlinear Optical Applications
Authors: Zharikov E.V. , Zaldo C. , Díaz F.
Published: February 2011

The renaissance of double tungstate (DW) and double molybdate (DMo) crystals is due to the vigorous recent progress in growth and characterization of these materials in the form of both bulk crystals with centimeter dimensions and epitaxial layers. “Double” refers to compounds having two ions with the generic composition MT(XO4)2 (where M = Li+, Na+, or K+; T = Ln3+, Y3+, or Bi3+; and X = W6+ or Mo6+). These compounds crystallize primarily in two phases belonging to the monoclinic (C2/c) and tetragonal (l4) structures. The specific properties of both types of crystals and the major technological challenges associated with the Czochralski and top-seeded solution growth of rare-earth doped crystals are presented. The performance of specific crystals is discussed in terms of their applications as tunable, thin-disk, and ultrashort (<100 fs) pulsed lasers or as nonlinear elements for laser Raman shifting.
High-Performance Piezoelectric Single Crystals of Complex Perovskite Solid Solutions
Authors: Ye Zuo-Guang
Published: February 2011

Relaxor-based single crystals of complex perovskite solid solutions, Pb(Mg1/3Nb2/3)O3–PbTiO3[PMN–PT] and Pb(Zn1/3Nb2/3)O3–PbTiO3[PZN–PT], exhibit extraordinary piezoelectric performance, with extremely high piezoelectric coefficients, very large electromechanical coupling factors, and exceptionally high strain levels. These materials outperform the currently used Pb(Zr1–xTix)O3[PZT] ceramics, making them the materials of choice for the next generation of electromechanical transducers for a broad range of advanced applications. In this article, recent major advances in the development of piezocrystals are reviewed in terms of crystal growth, piezoelectric properties, crystal chemistry, domain structure, and device applications.
Nonpolar and Semipolar Group III Nitride-Based Materials
Authors: Speck J. S. , Chichibu S. F.
Published: February 2011

GaN and its alloys with InN and AlN are materials systems that have enabled the revolution in solid-state lighting and high-power/high-frequency electronics. GaN-based materials naturally form in a hexagonal wurtzite structure and are naturally grown in a (0001) c-axis orientation. Because the wurtzite structure is polar, GaN-based heterostructures have large internal electric fields due to discontinuities in spontaneous and piezoelectric polarization. For optoelectronic devices, such as light-emitting diodes and laser diodes, the internal electric field is generally deleterious as it causes a spatial separation of electron and hole wave functions in the quantum wells, which, in turn, likely decreases efficiency. Growth of GaN-based heterostructures in alternative orientations, which have reduced (semipolar orientations) or no polarization (nonpolar) in the growth direction, has been a major area of research in recent years. This issue highlights many of the key developments in nonpolar and semipolar nitride materials and devices.
Development of Nonpolar and Semipolar InGaN/GaN Visible Light-Emitting Diodes
Authors: Feezell Daniel F. , Schmidt Mathew C. , DenBaars Steven P. , Nakamura Shuji
Published: February 2011

This article reviews the development of nonpolar and semipolar InGaN/GaN light-emitting diodes (LEDs), emphasizing structures on freestanding bulk GaN. A brief history of LED development on each orientation is provided, followed by a discussion of the most relevant and recent results. The context is related to several current LED issues, such as the realization of high-efficiency white solid-state lighting, potential solutions to the “green gap,” and applications for polarized emitters. The section on nonpolar LEDs highlights high-power violet and blue emitters and considers the effects of indium incorporation and substrate miscut. The section on semipolar GaN reviews the development of LEDs in the violet, blue, green, and yellow regions and highlights the potential of InGaN/GaN LEDs as an alternative technology to AlInGaP for yellow emitters. A brief review of polarization anisotropy also is included for each orientation. Finally, a two source white light system utilizing a nonpolar blue LED and a semipolar yellow LED is presented.
Semipolar III Nitride Semiconductors: Crystal Growth, Device Fabrication, and Optical Anisotropy
Authors: Funato Mitsuru , Kawakami Yoichi
Published: February 2011

Semipolar InGaN/GaN quantum wells (QWs) are quite attractive as visible light emitters. One of the reasons is that a better optical transition probability is expected because of weaker internal electric fields, compared to conventional polar QWs. In addition, in-plane optical polarization anisotropy, which is absent in conventional QWs, is another relevant property because it affects device design and also may provide a means for novel applications. We revealed that the in-plane optical anisotropy in semipolar QWs switched from one direction perpendicular to the [0001] crystal axis to the perpendicular direction as the In composition increases. This is a property unique to semipolar QWs and enables, for example, to make cavity mirrors of laser diodes by cleavage. In this article, we describe the concept of semipolar planes and fabrication of high-quality epitaxial films for semipolar QWs. Furthermore, we discuss device fabrication and optical polarization anisotropy.
Nonpolar-Oriented GaN Films for Polarization-Sensitive and Narrow-Band Photodetectors
Authors: Grahn Holger T.
Published: February 2011

This article reviews the optical polarization properties of unstrained and strained GaN films with a nonpolar orientation. In unstrained a -plane GaN films, the A exciton becomes completely linearly polarized perpendicular to the c-axis, whereas the B and C excitons are only partially polarized. In m -plane or a -plane GaN films under anisotropic in-plane compressive strain, all three interband transitions between the three uppermost valence bands and the conduction band can become linearly polarized for sufficiently large strain values. The complete linear polarization can be directly observed in reflection, transmission, or photoreflectance by a polarization-dependent energy gap. This complete linear polarization can be used to realize polarization-sensitive photodetectors in the ultraviolet spectral range, which do not need a polarization filter in front of the photodetector. By combining a polarization filter and photodetector or two photodetectors from the same material with their c-axes oriented perpendicular to each other, a narrowband photodetection configuration can be achieved in the ultraviolet spectral range with a band width below 8 nm. Since both realizations are also polarization sensitive, a configuration with four photodetectors is necessary to achieve narrow-band sensitivity regardless of the polarization state of the incident light. At the same time, the configuration with four photodetectors allows for the determination of the absolute angle of polarization.
Engineering Materials for Regenerative Medicine
Authors: Prasad Shastri V. , Lendlein Andreas
Published: February 2011

The mammalian physiology represents a level of sophistication in materials design, assembly, and function that has yet to be replicated by the modern tools of materials science. Although, the building blocks of our body (pluripotent stem and progenitor cells) are still available within our tissues, the absence of the biological and structural cues that drove the development process early on, in an adult, limits our ability to regenerate after an injury. The goal of regenerative medicine is therefore to recapitulate embryonic events within an artificially defined materials space (i.e., the niche) so that the repair processes can be triggered using our reservoir of stem cells. This engineering of the regenerative niche will require an interdisciplinary exercise involving materials scientists, biologists, and clinicians. The success of this exercise will hinge on our ability to develop materials that incorporate principles of wound healing, lessons from immunology and developmental biology, and knowledge of cellular mechanics and molecular biology such that they can mimic the cellular environment, instruct cells to make fate decisions, and direct the hierarchical organization of tissues. This article presents the current state of this challenge in the implementation of regenerative therapies.
Designing and Engineering Stem Cell Niches
Authors: Teixeira Ana I. , Hermanson Ola , Werner Carsten
Published: February 2011

Stem cells have received a lot of attention due to great promises in medical treatment, for example, by replacing lost and sick cells and re-constituting cell populations. There are several classes of stem cells, including embryonic, fetal, and adult tissue specific. More recently, the generation of so-called induced pluripotent stem (iPS) cells from differentiated cells has been established. Common criteria for all types of stem cells include their ability to self-renew and to retain their ability to differentiate in response to specific cues. These characteristics, as well as the instructive steering of the cells into differentiation, are largely dependent on the microenvironment surrounding the cells. Such “stem cell friendly” microenvironments, provided by structural and biochemical components, are often referred to as niches. Biomaterials offer attractive solutions to engineer functional stem cell niches and to steer stem cell state and fatein vitroas well asin vivo. Among materials used so far, promising results have been achieved with low-toxicity and biodegradable polymers, such as polyglycolic acid and related materials, as well as other polymers used as structural “scaffolds” for engineering of extracellular matrix components. To improve the efficiency of stem cell control and the design of the biomaterials, interfaces among stem cell research, developmental biology, regenerative medicine, chemical engineering, and materials research are rapidly developing. Here we provide an introduction to stem cell biology and principles of niche engineering and give an overview of recent advancements in stem cell niche engineering from two stem cell systems—blood and brain.
Wound Healing Versus Regeneration: Role of the Tissue Environment in Regenerative Medicine
Authors: Atala Anthony , Irvine Darrell J. , Moses Marsha , Shaunak Sunil
Published: February 2011

One of the major challenges in the field of regenerative medicine is how to optimize tissue regeneration in the body by therapeutically manipulating its natural ability to form scar at the time of injury or disease. It is often the balance between tissue regeneration, a process that is activated at the onset of disease, and scar formation, which develops as a result of the disease process that determines the ability of the tissue or organ to be functional. Using biomaterials as scaffolds often can provide a “bridge” for normal tissue edges to regenerate over small distances, usually up to 1 cm. Larger tissue defect gaps typically require both scaffolds and cells for normal tissue regeneration to occur without scar formation. Various strategies can help to modulate the scar response and can potentially enhance tissue regeneration. Understanding the mechanistic basis of such multivariate interactions as the scar microenvironment, the immune system, extracellular matrix, and inflammatory cytokines may enable the design of tissue engineering and wound healing strategies that directly modulate the healing response in a manner favorable to regeneration.
Progress in Carbon Nanotube Electronics and Photonics
Authors: Avouris Phaedon , Martel Richard
Published: February 2011

In electronics and photonics, intrinsic properties of semiconducting materials play a dominant role in achieving high-performance devices and circuits. In this respect, carbon nanotubes are prime candidates because of their exceptionally high carrier mobility, low capacitance, and strong optical response (direct bandgap). Although these properties compare very favorably with those of crystalline silicon, several issues related to their synthesis, processing, and assembly have challenged efforts for making electronic and photonic devices. Tremendous progress, nevertheless, has been achieved over the years, and much has been learned from novel photonic devices and electronic circuits. We review some of the developments in nanotube transistor performance optimization, ac operation, nanotube circuits, self-assembly, thin-film devices, and nanotube optical devices such as light emitters and detectors. We also examine the issues and opportunities that still exist.
New Nanofabrication Strategies: Inspired by Biomineralization
Authors: Aizenberg Joanna
Published: February 2011

Nature produces a wide variety of exquisite mineralized tissues, fulfilling diverse functions. Organisms exercise a level of molecular control over the detailed nano- and microstructure of the biomaterials that is unparalleled in today's technology. Our understanding of the underlying design principles of biomaterials provides ample opportunities for developing new approaches to materials fabrication at the nanometer and micrometer scale. It is clear that valuable materials lessons can be taught by any organism. I will exemplify this point by describing new nano- and microfabrication strategies and devices that have been inspired by the studies of biomineralization in echinoderms. The topics will include self-assembly, control of crystallization, synthesis of adaptive optical structures, hybrid materials, and novel actuation systems at the nanoscale level.