bluuebunny/crossref_metadata_2025 huggingface dataset:
Three-Dimensional Coherent X-Ray Diffraction Microscopy
Authors: Robinson Ian K. , Miao Jianwei
Published: February 2011

X-rays have been widely used in the structural analysis of materials because of their significant penetration ability, at least on the length scale of the granularity of most materials. This allows, in principle, for fully three-dimensional characterization of the bulk properties of a material. One of the main advantages of x-ray diffraction over electron microscopy is that destructive sample preparation to create thin sections is often avoidable. A major disadvantage of x-ray diffraction with respect to electron microscopy is its inability to produce real-space images of the materials under investigation—there are simply no suitable lenses available. There has been significant progress in x-ray microscopy associated with the development of lenses, usually based on zone plates, Kirkpatrick–Baez mirrors, or compound refractive lenses. These technologies are far behind the development of electron optics, particularly for the large magnification ratios needed to attain high resolution. In this article, the authors report progress toward the development of an alternative general approach to imaging, the direct inversion of diffraction patterns by computation methods. By avoiding the use of an objective lens altogether, the technique is free from aberrations that limit the resolution, and it can be highly efficient with respect to radiation damage of the samples. It can take full advantage of the three-dimensional capability that comes from the x-ray penetration. The inversion step employs computational methods based on oversampling to obtain a general solution of the diffraction phase problem.
Carbon Nanotubes: Continued Innovations and Challenges
Authors: Dresselhaus M.S. , Dai H.
Published: February 2011

This article outlines the content of the April 2004 issue of MRS Bulletin on Advances in Carbon Nanotubes. Essentially, carbon nanotubes are self-assembling nanostructures constructed of sheets of hexagonal-shaped carbon atoms rolled up into cylinders. Carbon nanotubes have attracted a great deal of attention as model systems for nanoscience and for potential applications. The special interest in carbon nanotubes stems from their unique structure and properties: their very small size (down to ∼0.42 nm in diameter); the possibility for carbon nanotubes to be metallic or semiconducting, depending on their geometrical structure; their exceptional properties of ballistic transport; their extremely high thermal conductivity and high optical polarizability; and the possibilities of high structural perfection. Research in the carbon nanotube field has now advanced to the stage where a good understanding of the structure and many of the basic properties are in place, together with much appreciation of their interrelation. On the other hand, major gaps in basic knowledge remain, with the major obstacles confronting the carbon nanotube field being the lack of a detailed understanding of the nanotube growth mechanism and control of the synthesis process to produce nanotubes with a desired diameter and chirality. The brief review of the carbon nanotube field by leading experts in this issue comes at an opportune time. Many exciting results on the structural, electronic, optical, and transport properties of these tiny well-ordered structures have already been achieved, and the research is well enough developed to assess present progress and identify new research directions waiting to be explored.
Purification and Separation of Carbon Nanotubes
Authors: Haddon R.C. , Sippel J. , Rinzler A.G. , Papadimitrakopoulos F.
Published: February 2011

The problems posed by the synthesis and purification of single-walled carbon nanotubes (SWNTs) have inhibited progress in the field. In this article, we review the methods available for measuring the purity of SWNTs and the current status of processes designed to purify them.We emphasize the hierarchy of the purification steps that must be developed in order to obtain high-quality material suitable for the full range of advanced applications that are envisioned for the ultimate carbon nanofiber.We review two strategies for SWNT purification, the assessment of SWNT purity by use of near-IR spectroscopy and its application to the thermal oxidation of thin films of SWNTs, as well as recent advances in the separation of metallic and semiconducting SWNTs. While substantial progress has been made in the purification and separation of SWNTs, we note the need for quality control and quality assurance within the industry. Much work remains before pure SWNTs of specific lengths, diameters, and chirality can be made available for applications.
Electron Transport in Single-Walled Carbon Nanotubes
Authors: McEuen Paul L. , Park Ji-Yong
Published: February 2011

Single-walled carbon nanotubes (SWNTs) are emerging as an important new class of electronic materials. Both metallic and semiconducting SWNTs have electrical properties that rival or exceed the best metals or semiconductors known. In this article, we review recent transport and scanning probe experiments that investigate the electrical properties of SWNTs.We address the fundamental scattering mechanisms in SWNTs, both in linear response and at high bias.We also discuss the nature and properties of contacts to SWNTs. Finally, we discuss device performance issues and potential applications in electronics and sensing.
Carbon Nanotube Photophysics
Authors: Jorio A. , Saito R. , Hertel T. , Weisman R.B. , Dresselhaus G. , Dresselhaus M.S.
Published: February 2011

In single-walled carbon nanotubes (SWNTs), their electronic and vibrational structure as well as their charge-carrier dynamics are crucial for potential ultrasmall optical device applications. SWNT properties have now been obtained from optical absorption and time-resolved photoemission and, at the single-nanotube level, by resonance Raman scattering and photoluminescence studies. This article presents an overview of SWNT photophysics, discussing important findings for the characterization of carbon nanotube properties and directions for future research and potential applications. The unique optical properties observed in SWNTs are due to the one-dimensional confinement of electronic states, resulting in van Hove singularities in the nanotube density of states. Optical measurements of phonons, charge-carrier dynamics, and the electronic transition energy van Hove singularities are discussed.
Why Does Concrete Set?: The Nature of Cohesion Forces in Hardened Cement-Based Materials
Authors: Pellenq Roland J.-M. , Van Damme Henri
Published: February 2011

Unlike other porous materials such as sandstone, brick, or porous glass, the interatomic bonding continuity of cement-based materials like concrete is far from obvious. When scrutinized at the micro- or nanoscopic level, the continuity of the ionic–covalent bonding in the solid phase is interrupted almost everywhere by water molecules or liquid water films. The same situation is found in set plaster.Yet, plaster and cementitious materials are able to withstand stresses of the same order of magnitude as rocks. Molecular simulation studies and direct-force measurements by atomic force microscopy provide strong arguments for predicting that short- and medium-range surface forces mediated by partially or totally hydrated calcium ions are the essential components of cement strength, with additional contributions from van der Waals and capillary forces. This provides a clue for understanding the nano- and mesostructure of cement-based materials and new levers for improving their properties.
Ultra-Durable Concretes: Structure at the Micro- and Nanoscale
Authors: Vernet Christian P.
Published: February 2011

Ultrahigh-performance concretes (UHPCs) are obtained by optimizing several technologies: minimizing the amount of water added, using superplasticizers and a wide particle size distribution, and packing the particles to improve fluidity with minimized water additions and to optimize load-carrying capacity. Fibers can be incorporated to increase ductility, leading to ultrahigh-performance fiber-reinforced concretes (UHPFRCs). Such enhanced concretes can approach the compressive strength of steel, with a remarkable improvement in durability. UHPCs offer new solutions for innovative construction, especially in aggressive environments.
Plasmonic Materials for Surface-Enhanced Sensing and Spectroscopy
Authors: Haes Amanda J. , Haynes Christy L. , McFarland Adam D. , Schatz George C. , Van Duyne Richard P. , Zou Shengli
Published: February 2011

Localized surface plasmon resonance (LSPR) excitation in silver and gold nanoparticles produces strong extinction and scattering spectra that in recent years have been used for important sensing and spectroscopy applications. This article describes the fabrication, characterization, and computational electrodynamics of plasmonic materials that take advantage of this concept.Two applications of these plasmonic materials are presented: (1) the development of an ultrasensitive nanoscale optical biosensor based on LSPR wavelength-shift spectroscopy and (2) the use of plasmon-sampled and wavelength-scanned surface-enhanced Raman excitation spectroscopy (SERES) to provide new insight into the electromagnetic-field enhancement mechanism.
Complex Adaptive Matter: Emergent Phenomena in Materials
Authors: Cox Daniel L. , Pines David
Published: February 2011

In the study of matter, both living and inanimate, the breakthrough discoveries and most scientists' intellectual obsessions often flow from what we call emergent behavior: phenomena not readily predictable from a detailed knowledge of the material subunits alone. We call systems that display emergent behavior complex adaptive matter, and their relevant organizing principles are unique to their scales of length and time. This issue of MRS Bulletin provides an overview of the aggregate of research on complex adaptive matter through a survey of five examples, ranging from intrinsically disordered electron matter in high-temperature superconductors to protein aggregates in amyloid diseases like Alzheimer's. We explain the philosophy and motivation for this research, noting that the study of emergent phenomena complements a globally reductionist scientific approach by seeking to identify, with intellectual precision, the relevant organizing principles governing the behavior. Our authors focus on the character of emergence for their particular systems, the role of materials research approaches to the problems, and the efforts to identify the organizing principles at work.
Geometrically Frustrated Matter—Magnets to Molecules
Authors: Ramirez A. P.
Published: February 2011

Geometric frustration occurs when a set of degrees of freedom is incompatible with the space it occupies. A purely geometric example is the impossibility of close-packing pentagons in two dimensions. Another simple example is atomic magnetic moments with antiferromagnetic interactions. These moments lower their interaction energy by pointing antiparallel to their neighbors, an arrangement incompatible with the occupation of a crystal lattice of triangular symmetry. Other manifestations of frustration occur in ice, glass, liquid crystals, and correlated metals. Because frustration governs the rules of packing, examples are also found in biological materials, as in the self-assembly of liposomes that form nanotubules. Geometric frustration is essentially “many-body” in nature: the basic concept is trivial on the scale of three particles, but complex and anharmonic for an Avogadro's number of particles. In fact, geometrically frustrated systems are so anharmonic that no general theoretical framework exists to explain their collective behavior. This article will explore the basic concepts of geometric frustration and illustrate these concepts with examples from magnetism, crystal structures, and molecular systems.
The Semiconductor p–n Junction “Ultimate Lamp”
Authors: Holonyak Nick
Published: February 2011

Simple diagrams are used to show the transformation of a thin sample of intrinsic, direct-gap semiconductor from an ideal “flat-band” photopumped recombination-radiation light source into a current-driven, p–n junction “ultimate lamp,” a light-emitting diode.
Network Phases in Block Copolymer Melts
Authors: Bates Frank S.
Published: February 2011

The following article is an edited transcript based on the David Turnbull Lecture given by Frank S. Bates of the University of Minnesota on December 1, 2004, at the Materials Research Society Fall Meeting in Boston. Bates received the award for “pioneering contributions to the fundamental understanding of structure and properties of complex polymeric materials, particularly block copolymers and polymeric vesicles, coupled with outstanding lecturing, writing, teaching, and educational leadership.” This article outlines the research accomplishments of a group of Bates' students that provide fresh insights into the molecular factors governing complex self-assembly in block copolymers. Three triply periodic and multicontinuous network phases were discovered in poly(isoprene-bstyrene-b-ethylene oxide) (ISO) triblock copolymers.Two cubic phases (Q230 and Q214) and an orthorhombic phase (O70) were identified using small-angle x-ray scattering (SAXS), transmission electron microscopy (TEM), birefringence measurements, and dynamic mechanical spectroscopy, along with level-set modeling. These findings establish a concrete strategy for locating potentially valuable network morphologies in ABC triblock copolymer melts.
Importance of Pico-Scale Topography of Surfaces for Adhesion, Friction, and Failure
Authors: Israelachvili Jacob N.
Published: February 2011

This article is an edited transcript based on the MRS Medal Award presentation given by Jacob N. Israelachvili on December 1, 2004, at the Materials Research Society Fall Meeting in Boston. An expanded article on this topic will be published in the August 2005 issue of the Journal of Materials Research. Recent experimental results have shown how surface texture, surface energy, and the bulk properties of materials can affect their adhesion and friction and, in turn, determine some of the fundamental differences between modes of failure of materials. Theoretical modeling and computer simulations, among other methods, provide examples and comparisons of surfaces that are rough or smooth, hard or soft (for example, viscoelastic), adhesive or non-adhesive, and dry (unlubricated) or lubricated. Such studies clarify the molecular and atomic basis of many well-established adhesion and tribological laws and empirical observations, revealing insights and relationships between nanoscale (molecular) and macroscale processes. Also of critical importance are the effects that occur at the sub-nanoscale, that is, in the sub-angstrom or picoscale regime. It is demonstrated and argued that the ultrafine picoscale details of a surface lattice, or its roughness, can be the most important factor in determining its friction (and mode II fracture), whereas such effects are quantitatively less important for adhesion and mode I fracture processes.
Innovations in Biomaterials: Achievements and Opportunities
Authors: Bergman Rebecca M.
Published: February 2011

This article is an edited transcript based on a presentation given by Rebecca M. Bergman (Medtronic Inc.) as part of Symposium X—Frontiers of Materials Research on November 30, 2004, at the Materials Research Society Fall Meeting in Boston. Materials innovations have been at the heart of many important advances in implantable medical devices. Miniaturization, improved durability and longevity, enhanced biocompatibility, and controlled delivery are several areas where materials innovations have been important in advancing medical products and therapies. The demands on materials used in the physiological environment are stringent and include requirements related to materials properties as well as safety, quality, and reliability. Looking ahead, materials will undoubtedly continue to be an enabling technology for future innovations in medicine, including novel therapies such as tissue engineering, cell therapy, and gene therapy.
Electrolytes for Solid-Oxide Fuel Cells
Authors: Yokokawa Harumi , Sakai Natsuko , Horita Teruhisa , Yamaji Katsuhiko , Brito M. E.
Published: February 2011

Three solid-oxide fuel cell (SOFC) electrolytes, yttria-stabilized zirconia (YSZ), rare-earth–doped ceria (REDC), and lanthanum strontium gallium magnesium oxide (LSGM), are reviewed on their electrical properties, materials compatibility, and mass transport properties in relation to their use in SOFCs. For the fluorite-type oxides (zirconia and ceria), electrical properties and thermodynamic stability are discussed in relation to their valence stability and the size of the host and dopant ions. Materials compatibility with electrodes is examined in terms of physicochemical features and their relationship to the electrochemical reactions. The application of secondary ion mass spectrometry (SIMS) to detect interface reactivity is demonstrated. The usefulness of doped ceria is discussed as an interlayer to prevent chemical reactions at the electrode–electrolyte interfaces and also as an oxide component in Ni–cermet anodes to avoid carbon deposition on nickel surfaces. Finally, the importance of cation diffusivity in LSGM is discussed, with an emphasis on the grain-boundary effects.
Designer Materials for Nucleic Acid Delivery
Authors: Reineke Theresa M. , Grinstaff Mark W.
Published: February 2011

The Human Genome Project continues to reveal the genetic basis for numerous acquired and inherited diseases ranging from cancer, HIV, and heart disease to muscular dystrophy and hemophilia. With this wealth of information, the ability to design patient-specific drugs that alter the cellular machinery at the genetic level in a way that controls or treats a specific disease will increasingly become a reality. Designing nucleic acid drugs as well as engineering novel delivery vehicles that encapsulate and effectively transport genetic materials into cells provides an opportunity to enhance the understanding of disease mechanisms and may help treat or cure these diseases. This issue of MRS Bulletin on “Designer Materials for Nucleic Acid Delivery” explores the diverse materials—polymers, lipids, nanoparticles, biocompatible scaffolds, and engineered peptides—that are being evaluated for the intracellular delivery of nucleic acids. These synthetic delivery systems are actively being investigated for many research purposes that range from gene-based therapy, genetic vaccine, and RNA interference to gene function and cellular signaling studies. This area is currently being pursued by a broad group of academic, clinical, and industrial researchers at both the fundamental and applied level, motivated by the widespread implications for human health. In this introductory article, we provide a general tutorial to gene-based therapies and a brief overview of the many areas of materials research that are currently making a tremendous impact on this interdisciplinary field.We conclude with a discussion of the future challenges that materials researchers face in developing viable nucleic acid delivery vehicles.
Polymeric Controlled Nucleic Acid Delivery
Authors: Leong Kam W.
Published: February 2011

Gene therapy harbors great promise for the treatment of a variety of inherited and acquired diseases, but its potential can be realized only with safe and effective carriers. Although viruses can efficiently transfer foreign genes to cells, their long-term safety remains a concern. Polymers can serve as a carrier to facilitate gene transfer, either by condensing DNA to the size of nanoparticles that can be internalized by cells, or by entrapping DNA in matrices or micro/nanoparticles for sustained release. However, polymeric controlled gene delivery remains highly inefficient. This review covers the major barriers for nonviral gene transfer and briefly describes the different types of polymers developed to overcome these barriers. With the tremendous promise of genetic medicine, nonviral gene delivery is a worthy goal for biomaterials and nanotechnology research.
Functional Amphiphiles for Gene Delivery
Authors: Barthélémy Philippe , Camplo Michel
Published: February 2011

The design of safe and efficient gene transfer vectors remains one of the key challenges in gene therapy. Despite their remarkable transfection efficiency, viral vectors suffer from known safety issues. Consequently, significant research activity has been undertaken to develop nonviral approaches to gene transfer during the last decade. Numerous academic and industrial research groups are investigating synthetic cationic vectors, such as cationic amphiphiles, with the objective of increasing the gene transfection activity. Within this area, the development of functional synthetic vectors that respond to local environmental effects have met with success. These synthetic vectors are based on mechanistic principles and represent a significant departure from earlier systems. Many of these systems for gene deliveryin vitroandin vivoare discussed in this article.
Directing the Assembly of Molecular Crystals
Authors: Ward Michael D.
Published: February 2011

Crystalline materials made from molecular components can possess useful properties that can be tailored through judicious selection of their molecular building blocks.The utility of these materials, however, depends on molecular packing in the crystal lattice as well as the properties of the individual molecules themselves. Consequently, further advances hinge on our ability to manipulate solid-state structure in a rational and systematic manner. Although computational prediction of crystal structure remains elusive, empirical guidelines for assembling molecules into preordained crystal architectures are emerging rapidly. This article briefly describes the current state of the field, emphasizing the design of crystalline materials with structures reinforced by a twodimensional hydrogen-bonded network, which serves as a platform for the synthesis of a diverse collection of compounds. These include host frameworks with cavities supported by organic “pillars” that can be interchanged to manipulate the size, shape, and character of the inclusion cavities as well as the overall lattice architecture and metrics. This research has revealed some principles for crystal design that may prove useful in general while enabling exploration of the utility of these compounds.
Arthur R. von Hippel, In Memoriam (1898–2003): A Tribute to the Interdisciplinary Materials Research He Spawned
Authors: Dresselhaus M.S. , Chaudhari P.
Published: February 2011

This article introduces the November 2005 issue of MRS Bulletin on the life and works of Arthur Robert von Hippel, who pioneered the interdisciplinary approach to materials research. This issue of MRS Bulletin celebrates his long life, his large volume of work, and the overall impact he had on materials research as practiced today. This introductory article summarizes the start and progression of the various fields presented in this issue, and how many were inspired directly by von Hippel's work and ways, and how new fields continue to emerge based on the same foundations of interdisciplinarity. The articles in this issue cover research areas in which von Hippel was involved, namely, ferroelectrics and magnetism; fields that thrived on an interdisciplinary approach that von Hippel represented, such as semiconductors; and areas that reflect his own vision about materials research and interests later in life, including molecular design and biomaterials. Before the scientific work is presented, the issue begins with a personal sketch of von Hippel, contributed by his son Frank N. von Hippel.
Fabrication of Sub-45-nm Structures for the Next Generation of Devices: A Lot of Effort for a Little Device
Authors: Watkins James J. , Bishop David J.
Published: February 2011

For the last four decades, the feature sizes of electronic devices for computers have been reduced by a factor of two roughly every 18 months. The result has been a tremendous increase in computational power and reduction in the cost of computing, as measured by cost per function, of nearly 30% annually, so that computations can be done for a billionth of the cost of using the technology of the 1950s. However, devices will soon be so small that the current technology used to produce them will have reached its limits, and the graininess of individual atoms will affect their behavior. This issue focuses on techniques to make tiny devices with dimensions under 45 nm (45 billionths of a meter) for the next generation of devices.Techniques start with coupling currently used 193-nm and 157-nm optical lithography with liquid immersion to reduce the effective wavelength. Other techniques include microprinting, self-assembly, templating, and using supercritical fluids to avoid the effects of surface tension while enabling solution-based processing at such small dimensions. The development of three-dimensional structures that are approaching this scale is also discussed.The methods presented will have an effect on many areas of technology, including, in addition to electronics, advanced sensor technology, energy conversion, catalysis, and nanoelectromechanical systems.
Imprint Materials for Nanoscale Devices
Authors: Stewart Michael D. , Willson C. Grant
Published: February 2011

Nanoimprint lithography is a potentially low-cost, high-resolution patterning technique, but most of the surrounding development work has been directed toward tool designs and processing techniques. There remains a tremendous opportunity and need to develop new materials for specific nanoimprint applications. This article provides an overview of relevant materials-related development work for nanoimprint lithographic applications. Material requirements for nanoimprint patterning for the sub-45-nm integrated-circuit regime are discussed, along with proposed nanoimprint applications such as imprintable dielectrics, conducting polymers, biocompatible materials, and materials for microfluidic devices. Polymers available for thermal nanoimprint processing and photocurable precursors for ultraviolet-assisted nanoimprint lithography are discussed.
Fabrication of Device Nanostructures Using Supercritical Fluids
Authors: O'Neil Adam , Watkins James J.
Published: February 2011

Supercritical fluids including carbon dioxide offer a combination of properties that are uniquely suited for device fabrication at the nanoscale. Liquid-like densities, favorable transport properties, and the absence of surface tension enable solution-based processing in an environment that behaves much like a gas. These characteristics provide a means for extending “top-down” processing methods including metal deposition, cleaning, etching, and surface modification chemistries to the smallest device features. The interaction of carbon dioxide with polymeric materials also enables complete structural specification of nanostructured metal oxide films using a “bottom-up” approach in which deposition reactions are conducted within sacrificial, pre-organized templates dilated by the fluid. The result is high-fidelity replication of the template structure in a new material. In particular, block copolymer templates yield well-ordered porous silica and titania films containing spherical or vertically aligned pores that can serve as device substrates for applications in microelectronics, detection arrays, and energy conversion. Finally, the synthesis of nanoparticles and nanowires in supercritical fluids is developing rapidly and offers promise for the efficient production of well-defined materials. In this review, we summarize these developments and discuss their potential for nextgeneration device fabrication.
Three-Dimensional Microfabrication by Two-Photon Lithography
Authors: Yang Da , Jhaveri Shalin J. , Ober Christopher K.
Published: February 2011

The controlled formation of submicrometer-scale structures in three dimensions is of increasing interest in many applications. Not intended to produce the smallest structures, but instead aimed at complex topographies, two-photon lithography is an intrinsic 3D lithography technique that enables the fabrication of structures difficult to access by conventional single-photon processes with far greater spatial resolution than other 3D microfabrication techniques. By tightly focusing a femtosecond laser beam into a resin, subsequent photo-induced reactions such as polymerization occur only in the close vicinity of the focal point, allowing the fabrication of a 3D structure by directly writing 3D patterns. The current research effort in two-photon lithography is largely devoted to the design and synthesis of high-efficiency photoinitiators and sensitizers, as well as the development of new materials and systems. This article provides an overview of the progress in two-photon processes for the formation of complex images and the development of patterned structures.
The Chemistry and Physics of Semiconductor Nanowires
Authors: Yang Peidong
Published: February 2011

The following article is based on the Outstanding Young Investigator Award presentation given by Peidong Yang of the University of California, Berkeley, on April 14, 2004, at the Materials Research Society Spring Meeting in San Francisco.Yang was cited for “innovative synthesis of a broad range of nanowires and nanowireheterostructure materials, and the discovery of optically induced lasing in individual nanowire devices.” One-dimensional nanostructures are of both fundamental and technological interest.They not only exhibit interesting electronic and optical properties associated with their low dimensionality and the quantum confinement effect, but they also represent critical components in potential nanoscale devices. In this article, the vapor–liquid–solid crystal growth mechanism will be briefly introduced for the general synthesis of nanowires of different compositions, sizes, and orientation. Unique properties, including light-emission and thermoelectricity, will be discussed. In addition to the recent extensive studies on “single-component” nanowires, of increasing importance is incorporating different interfaces and controlling doping profiles within individual single-crystalline nanowires. Epitaxial growth plays a significant role in fabricating such nanowire heterostructures. Recent research on superlattice nanowires and other nanostructures with horizontal junctions will be presented. The implication of these heterojunction nanowires in light-emission and energy conversion will be discussed. Ways to assemble these one-dimensional nanostructures will also be presented.
Toward the Rational Design of Open-Framework Materials
Authors: Cheetham Anthony K. , Rao C. N. R.
Published: February 2011

In spite of the enormous level of interest in open-framework materials (materials with porous channel structures, such as zeolites), the mechanisms by which they are formed are in many cases poorly understood. As a consequence, our ability to design reaction conditions that might lead to the formation of particular crystal architectures is quite limited. This article discusses the state of the art in this area, with particular emphasis on our joint work that was recently recognized by the 2004 S miya Award from the International Union of Materials Research Societies (IUMRS) and presented at the 2004 Materials Research Society Spring Meeting/IUMRS 9th International Conference on Electronic Materials.
Can We Build a Large-Scale Quantum Computer Using Semiconductor Materials?
Authors: Kane B. E.
Published: February 2011

The following article is based on the Symposium X presentation given by Bruce E. Kane (University of Maryland) at the 2004 Materials Research Society Spring Meeting in San Francisco. Quantum computing has the potential to revolutionize our ability to solve certain classes of difficult problems. A quantum computer is able to manipulate individual two-level quantum states (“qubits”) in the same way that a conventional computer processes binary ones and zeroes. Here, Kane discusses some of the most promising proposals for quantum computing, in which the qubit is associated with single-electron spins in semiconductors. While current research is focused on devices at the one- and two-qubit level, there is hope that cross-fertilization with advancing conventional computer technology will enable the eventual development of a large-scale (thousands of qubits) semiconductor quantum computer.The author focuses on materials issues that will need to be surmounted if large-scale quantum computing is to be realizable. He argues in particular that inherent fluctuations in doped semiconductors will severely limit scaling and that scalable quantum computing in semiconductors may only be possible at the end of the road of Moore's law scaling, when devices are engineered and fabricated at the atomic level.
Dye-Sensitized Solid-State Heterojunction Solar Cells
Authors: Grätzel Michael
Published: February 2011

The dye-sensitized solar cell (DSSC) provides a technically and economically viable alternative concept to present-day p–n junction photovoltaic devices. In contrast to conventional silicon systems, where the semiconductor assumes both the task of light absorption and charge carrier transport, these two functions are separated in DSSCs. The use of sensitizers having a broad absorption band in conjunction with wide-bandgap semiconductor films of mesoporous or nanocrystalline morphology permits harvesting a large fraction of sunlight. There are good prospects that these devices can attain the conversion efficiency of liquid-electrolyte-based dye-sensitized solar cells, which currently stands at 11%. In this article, we present the current state of the field, the realm of our review being restricted to the discussion of organic molecular hole conductors, which have demonstrated the best performance to date.
Smart Materials with Dynamically Controllable Surfaces
Authors: Lahann Joerg , Langer Robert
Published: February 2011

Recent progress in various biotechnology fields, such as microfluidics, tissue engineering, and cellular biology, has created a great demand for substrates that can undergo defined remodeling with time. As a result, the latest research on materials with dynamically controllable surface properties has led to a variety of novel smart surface designs.
Cell-Sheet Engineering Using Intelligent Surfaces
Authors: Yang Joseph , Yamato Masayuki , Okano Teruo
Published: February 2011

The possibility of recreating various tissues and organs for the purpose of regenerative medicine has received much interest. However, the field of tissue engineering has been restricted by the limitations of conventional approaches. A method to circumvent the need for traditional scaffold-based technologies is cell-sheet engineering, which uses temperature-responsive culture dishes. These surfaces, which are created by grafting the temperature-responsive polymer poly(N-isopropylacrylamide) onto ordinary culture dishes, enable the non-invasive harvesting of cells as intact sheets by simple temperature reduction. This article reviews current research on the applications of cell-sheet engineering for the reconstruction of various tissues, as well as the intelligent surfaces used by this novel technology.
Bioactive Patterns at the 100-nm Scale Produced Using Multifunctional Physisorbed Monolayers
Authors: Vörös Janos , Blättler Thomas , Textor Marcus
Published: February 2011

Recently, a variety of patterning techniques have reached feature sizes of 100 nm or less, a size range very relevant to biology. Proteins, vesicles, and macromolecular assemblies can now be handled and specifically placed onto predefined artificial patterns, triggering defined functions in cells and revealing the details of cell–surface interactions. Simultaneously, novel surface chemistries have been developed that are able to induce specific bioresponses (e.g., mimicking the features of the extracellular matrix) and at the same time suppress the nonspecific effects of complex biological solutions. This article reviews the basic principles and properties of multifunctional physisorbed monolayers that can be used in combination with nanopatterning techniques to create biologically relevant surface features. Furthermore, selected examples of nanopatterns created by novel combinations of different top-down and bottom-up approaches are presented, including systems with specific bioligands, proteins, vesicles, and cells.
Advances in Silicon Carbide Electronics
Authors: Zolper J. C. , Skowronski M.
Published: February 2011

After substantial investment in research and development over the last decade, silicon carbide materials and devices are coming of age. The concerted efforts that made this possible have resulted in breakthroughs in our understanding of materials issues such as compensation mechanisms in high-purity crystals, dislocation properties, and the formation of SiC/SiO2 interfaces, as well as device design and processing. The progress accomplished over the last eight years in SiC-based electronic materials is summarized in this issue of MRS Bulletin.
Bulk Crystal Growth, Epitaxy, and Defect Reduction in Silicon Carbide Materials for Microwave and Power Devices
Authors: Sumakeris J. J. , Jenny J. R. , Powell A. R.
Published: February 2011

We discuss continuing materials technology improvements that have transformed silicon carbide from an intriguing laboratory material into a premier manufacturable semiconductor technology. This advancement is demonstrated by reduced micropipe densities as low as 0.22 cm−2 on 3-in.-diameter conductive wafers and 16 cm−2 on 100-mm-diameter conductive wafers. For high-purity semi-insulating materials, we confirm that the carbon vacancy is the dominant deep-level trapping state, and we report very consistent cross-wafer activation energies derived from temperature-dependent resistivity.Warm-wall and hot-wall SiC epitaxy platforms are discussed in terms of capability and applications. Specific procedures that essentially eliminate forward-voltage drift in bipolar SiC devices are presented in detail.
Interface Passivation for Silicon Dioxide Layers on Silicon Carbide
Authors: Dhar Sarit , Wang Shurui , Williams John R. , Pantelides Sokrates T. , Feldman Leonard C.
Published: February 2011

Silicon carbide is a promising semiconductor for advanced power devices that can outperform Si devices in extreme environments (high power, high temperature, and high frequency). In this article, we discuss recent progress in the development of passivation techniques for the SiO2/4H-SiC interface critical to the development of SiC metal oxide semiconductor field-effect transistor (MOSFET) technology. Significant reductions in the interface trap density have been achieved, with corresponding increases in the effective carrier (electron) mobility for inversion-mode 4H-SiC MOSFETs. Advances in interface passivation have revived interest in SiC MOSFETs for a potentially lucrative commercial market for devices that operate at 5 kV and below.
Silicon Carbide Power Field-Effect Transistors
Authors: Zhao Jian H.
Published: February 2011

Silicon carbide power field-effect transistors, including power vertical-junction FETs (VJFETs) and metal oxide semiconductor FETs (MOSFETs), are unipolar power switches that have been investigated for high-temperature and high-power-density applications. Recent progress and results will be reviewed for different device designs such as normally-OFF and normally-ON VJFETs, double-implanted MOSFETs, and U-shaped-channel MOSFETs. The advantages and disadvantages of SiC VJFETs and MOSFETs will be discussed. Remaining challenges will be identified.
SiC MESFETs for High-Frequency Applications
Authors: Sriram S. , Ward A. , Henning J. , Allen S. T.
Published: February 2011

Significant progress has been made in the development of SiC metal semiconductor field-effect transistors (MESFETs) and monolithic microwave integrated-circuit (MMIC) power amplifiers for high-frequency power applications. Three-inch-diameter high-purity semi-insulating 4H-SiC substrates have been used in this development, enabling high-volume fabrication with improved performance by minimizing surface- and substrate-related trapping issues previously observed in MESFETs. These devices exhibit excellent reliability characteristics, with mean time to failure in excess of 500 h at a junction temperature of 410°C. A sampling of these devices has also been running for over 5000 h in an rf high-temperature operating-life test, with negligible changes in performance. High-power SiC MMIC amplifiers have also been demonstrated with excellent yield and repeatability. These MMIC amplifiers show power performance characteristics not previously available with conventional GaAs technology. These developments have led to the commercial availability of SiC rf power MESFETs and to the release of a foundry process for MMIC fabrication.
Hybrid Organic–Nanocrystal Solar Cells
Authors: Milliron Delia J. , Gur Ilan , Alivisatos A. Paul
Published: February 2011

Recent results have demonstrated that hybrid photovoltaic cells based on a blend of inorganic nanocrystals and polymers possess significant potential for low-cost, scalable solar power conversion. Colloidal semiconductor nanocrystals, like polymers, are solution processable and chemically synthesized, but possess the advantageous properties of inorganic semiconductors such as a broad spectral absorption range and high carrier mobilities. Significant advances in hybrid solar cells have followed the development of elongated nanocrystal rods and branched nanocrystals, which enable more effective charge transport. The incorporation of these larger nanostructures into polymers has required optimization of blend morphology using solvent mixtures. Future advances will rely on new nanocrystals, such as cadmium telluride tetrapods, that have the potential to enhance light absorption and further improve charge transport. Gains can also be made by incorporating application-specific organic components, including electroactive surfactants which control the physical and electronic interactions between nanocrystals and polymer.
Shape-Controlled Synthesis and Surface Plasmonic Properties of Metallic Nanostructures
Authors: Xia Younan , Halas Naomi J.
Published: February 2011

The interaction of light with free electrons in a gold or silver nanostructure can give rise to collective excitations commonly known as surface plasmons. Plasmons provide a powerful means of confining light to metal/dielectric interfaces, which in turn can generate intense local electromagnetic fields and significantly amplify the signal derived from analytical techniques that rely on light, such as Raman scattering. With plasmons, photonic signals can be manipulated on the nanoscale, enabling integration with electronics (which is now moving into the nano regime). However, to benefit from their interesting plasmonic properties, metal structures of controlled shape (and size) must be fabricated on the nanoscale. This issue of MRS Bulletin examines how gold and silver nanostructures can be prepared with controllable shapes to tailor their surface plasmon resonances and highlights some of the unique applications that result, including enhancement of electromagnetic fields, optical imaging, light transmission, colorimetric sensing, and nanoscale waveguiding.
Shape-Controlled Synthesis of Silver and Gold Nanostructures
Authors: Wiley Benjamin , Sun Yugang , Chen Jingyi , Cang Hu , Li Zhi-Yuan , Li Xingde , Xia Younan
Published: February 2011

This article provides a brief account of solution-phase methods that generate silver and gold nanostructures with well-controlled shapes. It is organized into five sections: The first section discusses the nucleation and formation of seeds from which nanostructures grow. The next two sections explain how seeds with fairly isotropic shapes can grow anisotropically into distinct morphologies. Polyol synthesis is selected as an example to illustrate this concept. Specifically, we discuss the growth of silver nanocubes (with and without truncated corners), nanowires, and triangular nanoplates. In the fourth section, we show that silver nanostructures can be transformed into hollow gold nanostructures through a galvanic replacement reaction. Examples include nanoboxes, nanocages, nanotubes (both single- and multi-walled), and nanorattles. The fifth section briefly outlines a potential medical application for gold nanocages.We conclude with some perspectives on areas for future work.
Playing with Plasmons: Tuning the Optical Resonant Properties of Metallic Nanoshells
Authors: Halas Naomi
Published: February 2011

Nanoshells, concentric nanoparticles consisting of a dielectric core and a metallic shell, are simple spherical nanostructures with unique, geometrically tunable optical resonances. As with all metallic nanostructures, their optical properties are controlled by the collective electronic resonance, or plasmon resonance, of the constituent metal, typically silver or gold. In striking contrast to the resonant properties of solid metallic nanostructures, which exhibit only a weak tunability with size or aspect ratio, the optical resonance of a nanoshell is extraordinarily sensitive to the inner and outer dimensions of the metallic shell layer. The underlying reason for this lies beyond classical electromagnetic theory, where plasmon-resonant nanoparticles follow a mesoscale analogue of molecular orbital theory, hybridizing in precisely the same manner as the individual atomic wave functions in simple molecules. This plasmon hybridization picture provides an essential “design rule” for metallic nanostructures that can allow us to effectively predict their optical resonant properties. Such a systematic control of the far-field optical resonances of metallic nanostructures is accomplished simultaneously with control of the field at the surface of the nanostructure. The nanoshell geometry is ideal for tuning and optimizing the near-field response as a stand-alone surface-enhanced Raman spectroscopy (SERS) nanosensor substrate and as a surface-plasmon-resonant nanosensor.Tuning the plasmon resonance of nanoshells into the near-infrared region of the spectrum has enabled a variety of biomedical applications that exploit the strong optical contrast available with nanoshells in a spectral region where blood and tissue are optimally transparent.
Spintronics: The Future of Data Storage?
Authors: Wolf S.A. , Treger Daryl , Chtchelkanova Almadena
Published: February 2011

Reasearch and technology developments in the field of spintronics have grown tremendously in the past 10-15 years and already have had a major impact on the data storage industry.The future looks even brighter, as many new spintronic discoveries have been recently made that promise an even bigger impact in the future.This article summarizes the past accomplishments, describes some of the major discoveries that will have a lasting impact on the field, and discusses some of the technologies that may revolutionize data storage in the next decade.