bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Temperature Polycrystalline Silicon Thin-Film Transistors and Circuits on Flexible Substrates
Authors: van der Wilt P.C. , Kane M.G. , Limanov A.B. , Firester A.H. , Goodman L. , Lee J. , Abelson J.R. , Chitu A.M. , Im James S.
Published: February 2011

Low-defect-density polycrystalline Si on flexible substrates can be instrumental in realizing the full potential of macroelectronics. Direct deposition or solid-phase crystallization techniques are often incompatible with polymers and produce materials with high defect densities. Excimer-laser annealing is capable of producing films of reasonable quality directly on polymer and metallic substrates. Sequential lateral solidification (SLS) is an advanced pulsed-laser-crystallization technique capable of producing Si films on polymers with lower defect density than can be obtained via excimer-laser annealing. Circuits built directly on polymers using these SLS films show the highest performance reported to date.
Theory of Nanocomposite Network Transistors for Macroelectronics Applications
Authors: Alam M.A. , Pimparkar N. , Kumar S. , Murthy J.
Published: February 2011

A new class of nanocomposite network materials based on carbon nanotubes or silicon nanowires for thin-film transistors promises significant improvement in the performance of large-area electronics, or macroelectronics. Evaluation of this novel materials technology requires the development of device models. A multicomponent heterogeneous stick-percolation theory is used to show that the key features of this new transistor technology are the consequences of the percolating spatial geometry of the nanosticks (nanotubes, nanorods, or nanowires) that form the channel.
Biomaterials for Drug Delivery and Tissue Engineering
Authors: Langer Robert
Published: February 2011

The following article is an edited transcript based on the Von Hippel Award presentation by Robert Langer of the Massachusetts Institute of Technology on November 30, 2005, at the Materials Research Society Fall Meeting in Boston. Langer was honored with MRS's highest award for his “pioneering accomplishments in the science and application of biomaterials in drug delivery and tissue engineering, particularly in inventing the use of materials for protein and DNA delivery, and for his achievements in interdisciplinary research which have generated new medical products, created new fields of biomaterials science, and inspired research programs throughout the world.”
Polymer-Supported Membranes: Physical Models of Cell Surfaces
Authors: Tanaka Motomu
Published: February 2011

The functional modification of solid surfaces with plasma membrane models has been drawing increasing attention as a straightforward strategy to bridge soft biological materials and hard inorganic materials. Planar model membranes can be deposited either directly on solid substrates (solid-supported membranes), or on ultrathin polymer supports (polymer-supported membranes) that mimic the generic role of the extracellular matrix and the cell surface. The first part of this review provides an overview of advances in the fabrication of polymer-supported membranes. The middle section describes how such thin polymer interlayers can physically modulate the membrane–substrate contact. The last section introduces several methods to localize membranes and membrane proteins. Finally, some ideas are presented on combining supported membrane concepts with semiconductor technology toward applications in materials science.
Isotopically Controlled Semiconductors
Authors: Haller Eugene E.
Published: February 2011

The following article is an edited transcript based on the David Turnbull Lecture given by Eugene E. Haller (University of California, Berkeley) at the 2005 Materials Research Society Fall Meeting in Boston on November 29, 2005. The David Turnbull Lectureship is awarded to recognize the career of a scientist who has made outstanding contributions to understanding materials phenomena and properties through research, writing, and lecturing, as exemplified by the life work of David Turnbull. Haller was named the 2005 David Turnbull Lecturer for his “pioneering achievements and leadership in establishing the field of isotopically engineered semiconductors; for outstanding contributions to materials growth, doping and diffusion; and for excellence in lecturing, writing, and fostering international collaborations.”

The scientific interest, increased availability, and technological promise of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies of isotopically controlled semiconductor crystals. This article reviews results obtained with isotopically controlled semiconductor bulk and thin–film heterostructures. Isotopic composition affects several properties, such as phonon energies, band structure, and lattice constant, in subtle, yet—for their physical understanding–significant ways. Large isotope-related effects are observed for thermal conductivity in local vibrational modes of impurities and after neutron transmutation doping. Spectacularly sharp photo-luminescence lines have been observed in ultrapure, isotopically enriched silicon crystals. Isotope multilayer structures are especially well suited for studies of simultaneous self-and dopant-diffusion. The absence of any chemical, mechanical, or electrical driving forces makes possible the study of an ideal random-walk problem, in which moving atoms go in random directions at random intervals. Isotopically controlled semiconductors may find applications in quantum computing, nanoscience, and spintronics.
Ultrafast Dynamics of Laser-Excited Solids
Authors: Reis D.A. , Gaffney K.J. , Gilmer G.H. , Torralva B.
Published: February 2011

We discuss recent experimental and theoretical results on ultrafast materials dynamics. Intense, femtosecond lasers can deposit energy in a time that is short compared with relaxation processes and can generate extremely large carrier densities that drive bond softening, nonthermal melting, and ablation. In particular, we present optical experiments on electronic softening of coherent phonons in bismuth and x-ray experiments on ultrafast disordering in indium antimonide that probe the bonding of the lattice under successively higher carrier concentrations. We review a number of molecular dynamics simulations and their assumptions, which address nonthermal melting. Large-scale molecular dynamics simulations elucidate the role of void formation in laser ablation.
Material Processing Using Femtosecond Lasers: Repairing Patterned Photomasks
Authors: Haight Richard , Longo Peter , Wagner Alfred
Published: February 2011

The use of ultrafast laser pulses is having an impact on materials processing in profound ways. “Machining” with femtosecond pulses affords considerable advantages over nanosecond pulses, such as subdiffraction-limited material ablation, where ablated spot dimensions are below that achievable when longer pulses are focused to the minimum spot size dictated by optical physics. These properties have been exploited to address what had become a critical problem in the semiconductor industry, the repair of patterned photomasks. We will describe how the fundamentals of femtosecond laser ablation have been implemented in a machine designed to repair photomasks. We will also describe experiments designed to deposit Cr metal onto fused-silica substrates using 100-fs, 400-nm light pulses at atmospheric pressure. Multiphoton dissociation of Cr(CO)6 adsorbed on fused-silica substrates initiates Cr deposition. The mechanisms for deposition on both transparent (fused silica) and absorbing (Cr metal) substrates are discussed. Finally, we describe experiments that were carried out to extend the photomask repair process to shorter wavelengths (below 200 nm) using light generated by frequency-mixing of ultrashort, 30-fs pulses in an Ar-filled capillary.
Dense Metal Membranes for the Production of High-Purity Hydrogen
Authors: Sholl David S. , Ma Y.H.
Published: February 2011

Dense metal membranes are a well-developed technology for the production of high-purity hydrogen. The physical mechanism of hydrogen transport across metal films—dissociation of molecular hydrogen, diffusion of interstitial atomic hydrogen, and subsequent recombinative desorption of molecular hydrogen—means that metal membranes can have extremely high selectivities for hydrogen transport relative to other gases. We describe current experimental and theoretical trends in the development of metal alloy membranes for hydrogen purification in practical, chemically robust processes.
The Application of Computational Modeling to Pharmaceutical Materials Science
Authors: Wassgren Carl , Curtis Jennifer Sinclair
Published: February 2011

Computational modeling is a ubiquitous technique in materials science, but until recently this approach has not been widely applied to the drug development process. The formation of particles, their kinematics, and their response to processing stresses are increasingly being studied using computational techniques (computational fluid dynamics and discrete element analysis). These computational techniques can be predictive tools to guide scientists who are designing pharmaceutical dosage forms with specific macroscopic properties. This article gives an overview of the types of computational methods that are used in pharmaceutical materials science and provides examples of their application to some problems from the literature and the authors' own work.
Silicon-Based Microchemical Systems: Characteristics and Applications
Authors: Jensen Klavs F.
Published: February 2011

Microfabrication techniques and scale-up by replication promise to transform classical batch-wise chemical laboratory procedures into integrated systems capable of providing new understanding and control of fundamental processes. Such integrated microchemical systems would enable rapid, continuous discovery and development of new products with the use of fewer resources and the generation of less waste. Additional opportunities exist for on-demand and on-site synthesis, with perhaps the first applications emerging in portable energy sources based on the conversion of hydrocarbons to hydrogen for miniaturized fuel cells.

Microchemical systems can be realized in a wide range of materials including stainless steel, glass, ceramics, silicon, and polymers. The high mechanical strength, excellent temperature characteristics, and good chemical compatibility of silicon combined with the existing fabrication infrastructure for microelectromechanical systems (MEMS) offer advantages in fabricating chemical microsystems that are compatible with strong solvents and operate at elevated temperatures and pressures. Furthermore, silicon-based microsensors for flow, pressure, and temperature can readily be integrated into the systems.

Microsystems for broad chemical applications should be discovery tools that can easily be applied by chemists and materials scientists while also having a convincing “scale-out” to at least small production levels. The interplay of both these capabilities is important in making microreaction technology successful. Perhaps the largest impact of microchemical systems will ultimately be the ability to explore reaction conditions and chemistry at conditions that are otherwise difficult to establish in the laboratory. Case studies are selected to illustrate microfluidic applications in which silicon adds advantages, specifically, integration of physical sensors and infrared spectroscopy, highthroughput experimentation in moisture-sensitive organic synthesis, controlled synthesis of nanoparticles (quantum dots), multiphase and heterogeneous catalytic reactions at elevated temperatures and pressures, and thermal management in the conversion of hydrocarbons to hydrogen.
Microfluidic Biomaterials
Authors: Stroock Abraham D. , Cabodi Mario
Published: February 2011

Biomedical applications—prostheses, tissue engineering, drug delivery, and wound healing—demand increasingly sophisticated characteristics from the materials that come into contact with living systems in the laboratory and the clinic. With the development of microfluidics, there is an opportunity to create active biomaterials based on embedded microfluidic structures. These structures allow for control of the concentrations of soluble chemicals and hydrodynamic stresses within the material and at its interfaces, and thus allow one to tailor the environment experienced by the living tissue. In this article, we review initial efforts to develop these microfluidic biomaterials and present considerations regarding the required characteristics of the materials and of the microfluidic-mediated mass transfer. As specific examples, we present work toward microfluidic control of mass transfer in scaffolds for tissue engineering and in wound dressings.
Recent Developments in Bulk Thermoelectric Materials
Authors: Nolas George S. , Poon Joe , Kanatzidis Mercouri
Published: February 2011

Good thermoelectric materials possess low thermal conductivity while maximizing electric carrier transport. This article looks at various classes of materials to understand their behavior and determine methods to modify or “tune” them to optimize their thermoelectric properties. Whether it is the use of “rattlers” in cage structures such as skutterudites, or mixed-lattice atoms such as the complex half-Heusler alloys, the ability to manipulate the thermal conductivity of a material is essential in optimizing its properties for thermoelectric applications.
Materials for Multilayer Recording
Authors: Milster Tom D. , Zhang Yan
Published: February 2011

An attractive feature of optical discs is their capacity. Recent research has indicated that the capacity of optical discs can be increased by using multiple layers of bitwise data. Layers are spaced along the depth dimension of the discs. Individual layers are recorded and information is retrieved in a manner that is very similar to conventional optical disc systems using a single layer. The data capacity of each layer is nearly equal to the capacity of a single layer, thus increasing the capacity of a disc by a factor equal to the number of layers. In fact, dual-layer optical discs are already commercially available. With some storage materials, it is possible to record hundreds of data layers. However, system engineering trade-offs, like readout speed, are of concern. More conventional – materials can also be used for multilayer recording, but the number of layers is limited by the transmission properties of each layer. This article reviews the materials systems for multilayer recording, the interplay between materials properties and performance, and the optical systems used for multilayer recording.
Spin-Polarized Current in Spin Valves and Magnetic Tunnel Junctions
Authors: Parkin Stuart
Published: February 2011

Spin-polarized currents can be generated by spin-dependent diffusive scattering in magnetic thin-film structures or by spin-dependent tunneling across ultrathin dielectrics sandwiched between magnetic electrodes.By manipulating the magnetic moments of the magnetic components of these spintronic materials, their resistance can be significantly changed, allowing the development of highly sensitive magnetic-field detectors or advanced magnetic memory storage elements.Whereas the magneto-resistance of useful devices based on spin-dependent diffusive scattering has hardly changed since its discovery nearly two decades ago, in the past five years there has been a remarkably rapid development in both the basic understanding of spin-dependent tunneling and the magnitude of useful tunnel magnetoresistance values.In particular, it is now evident that the magnitude of the spin polarization of tunneling currents in magnetic tunnel junctions not only is related to the spin-dependent electronic structure of the ferromagnetic electrodes but also is considerably influenced by the properties of the tunnel barrier and its interfaces with the magnetic electrodes.Whereas the maximum tunnel magnetoresistance of devices using amorphous alumina tunnel barriers and 3d transition-metal alloy ferromagnetic electrodes is about 70% at room temperature, using crystalline MgO tunnel barriers in otherwise the same structures gives tunnel magnetoresistance values of more than 350% at room temperature.
Nanometer-Scale Laser Direct-Write Using Near-Field Optics
Authors: Grigoropoulos Costas P. , Hwang David J. , Chimmalgi Anant
Published: February 2011

This article summarizes research on laser-based processing and structuring of materials at the nanoscale using optical near-field schemes. Both apertureless and tapered fiber near-field scanning optical microscope probes can deliver highly confined irradiation at sufficiently high intensities to cause morphological and structural changes in materials at the nanometer level. The energy emitted by the probes and the absorption within the target material are predicted by carrying out calculations of the near-field electromagnetic distribution. The effects of shrinking laser beam dimensions compete with the energy diffusion into the target material. Experimental results have shown well-controlled subtractive material modification with minimum feature size in the neighborhood of 10 nm. Precise patterning can be achieved via laser-assisted chemical etching. Control of the nucleation of nanostructures via rapid melting and crystallization is demonstrated. The article concludes with an outlook to applications.
Molecules in the Solid State
Authors: Foxman Bruce M. , Ward Michael D.
Published: February 2011

The design and synthesis of solid-state materials constructed from molecules has emerged as an important frontier of materials research. Molecular materials promise an unparalleled opportunity for systematic manipulation of solid-state properties and functions by using molecular design principles and capitalizing on the versatility of organic synthesis. Furthermore, the use of molecular components may produce considerable economic benefits, whether by reducing fabrication cost or through increases in performance. The articles in this issue ofMRS Bulletincover recent discoveries and developments based on materials with properties and functions that hinge on the characteristics of their molecular constituents. These materials promise significant advances in several technologies of substantial commercial interest, including organic light-emitting diodes, nonlinear optics, gas separations, chiral separations, and molecular magnets.
Metal-Organic Frameworks for Asymmetric Catalysis and Chiral Separations
Authors: Lin Wenbin
Published: February 2011

Metal-organic frameworks (MOFs) are an interesting class of molecule-based hybrid materials built from metal-connecting points and bridging ligands. MOFs have received much attention, owing to their potential impact on many technological areas, including gas storage, separation, and heterogeneous catalysis. The modular nature of MOFs endows them with facile tunability, and as a result, properly designed MOFs can yield ideal heterogeneous catalysts with uniform active sites through judicious choice of the building blocks. Homochiral MOFs, which can be prepared by numerous approaches (construction from achiral components by seeding with a chiral single crystal, templating with coordinating chiral co-ligands, and building from metal-connecting nodes and chiral bridging ligands), represent a unique class of materials for the economical production of optically pure compounds, whether through asymmetric catalysis or enantioselective inclusion of chiral guest molecules in their porous frameworks. As such, homochiral MOFs promise new opportunities for developing chirotechnology. This contribution provides a brief overview of recent progress in the synthesis of homochiral porous MOFs and their applications in asymmetric catalysis and chiral separations.
The State of the Art and Future Prospects for Laser Direct-Write for Industrial and Commercial Applications
Authors: Sugioka Koji , Gu Bo , Holmes Andrew
Published: February 2011

Laser direct-write (LDW) is an established technology for manufacturing electronic and optoelectronic appliances such as cellular telephones, digital cameras, and notebook-type personal computers. One of the most successful applications is laser drilling of via holes on printed circuit boards for the manufacture of cellular telephones. Other practical applications include marking, dicing, trimming, repairing, patterning, bending, and rapid prototyping. In this article, the state of the art of LDW for industrial applications in Japan, the United States, and Europe is reviewed, and its future prospects are discussed.
The Evolution of Organometallic Complexes in Organic Light-Emitting Devices
Authors: Thompson Mark
Published: February 2011

This article is an edited transcript of the MRS Medal presentation given by Mark Thompson (University of Southern California) on November 28, 2006, at the Materials Research Society Fall Meeting in Boston. Thompson was awarded the Medal for the “development of highly efficient heavy-metal phosphor complexes.” The MRS Medal recognizes a specific outstanding recent discovery or advancement which is expected to have a major impact on the progress of any materials-related field.

Successful research efforts have led to improvements in the internal efficiencies of organic light-emitting devices (OLEDs) from 25% to 100%. The electroluminescence process in OLEDs involves the formation of both singlet and triplet excitons, formed in a ratio of 1:3. There is a drive to improve spin statistics by developing compounds in which triplet excitons, in addition to singlet excitons, can be used efficiently. Success with the incorporation of heavy-metal–based phosphors into OLEDs, in which the strong spin-orbit coupling of the metal atom allows for efficient molecular phosphorescence from triplet excitons, resulted in the identification and synthesis of an iridium complex, fac-tris-phenylpyridine iridium, with internal efficiencies of 100%. This, in turn, has led to the synthesis of more than 100 iridium- and platinum-based compounds, which have become the most efficient light-emitting compounds yet discovered. Intellectual property from Thompson's research in this field has led to more than 50 U.S. patents and substantial entrepreneurial investment toward commercial applications and devices.
The Materials Science of Cosmetics
Authors: Schnittger Steven , Sinha Moitreyee
Published: February 2011

The cosmetics industry is increasingly using sophisticated materials and technologies in their products and to measure their effectiveness. Understanding how these products interact with skin, adhere to skin, and deliver a benefit or create a visible effect leads to better and safer products. An understanding of the optics and mechanics of skin and the cosmetics–skin interface is important for achieving various visual and functional effects. This issue reviews the underlying science and the technical challenges behind the development of materials for the personal care and cosmetics industry.
Nanotechnology and Related Safety Issues for Delivery of Active Ingredients in Cosmetics
Authors: Somasundaran P. , Mehta Somil C. , Rhein Linda , Chakraborty Soma
Published: February 2011

Nature exhibits a variety of remarkable phenomena that are useful but difficult to imitate in real life. Examples are the “touch me not” plant (Mimosa pudica), which folds up upon being attacked, or microbes that deposit on ocean vessels even under hostile conditions. Understanding the mechanisms governing these phenomena can prove powerful for developing new classes of cosmetic products. This article examines the development of novel materials with functional properties such as controlled delivery and the deposition of sensory attributes (fragrances, flavors, etc.) desirable in cosmetic products. Particularly, systems based on polymer/surfactant chemistry are explored for achieving transport and release of cosmetic and pharmaceutical molecules at desired rates. The hybrid polymers and nanogel particle systems discussed here represent new classes of materials with nanodomains that can be tuned to extract and deliver cosmetic attributes by means of changes in natural parameters such as temperature and pH. While the safety of existing nanomaterials marketed for decades has not been an issue, methods are urgently needed to validate the toxicological safety of future nanomaterials.
Challenges in Cosmetic Formulations: Appearance, Long Wear, and Comfort
Authors: Maitra Prithwiraj , Brahms John
Published: February 2011

Cosmetics are products that are designed to maintain or improve visual appearance when applied to skin. Skin is a mechanically flexible substrate that changes in chemical and surface properties during the course of the day. Sebum (an oily substance secreted by the sebaceous glands) and perspiration (a secretion of mostly salt water by the eccrine glands) as well as environmental insults work counter to the desired benefits of cosmetics on physical appearance. Recent advances in the ability to control morphology and chemical properties have led to novel materials that in turn have enabled the development of cosmetics that provide, on the one hand, a more natural look, and on the other, unique and unprecedented visual effects. Progress in understanding skin biomechanics and surface properties lead to product formulations with unprecedented wear and performance characteristics. This article reviews recent advances in the ability to control the optical, bulk, and surface properties of materials, and their application to improved cosmetic formulations.
The Need for Microstructural Measurement Techniques in the Study of Cosmetic Product Properties
Authors: Cummins P. G. , Fthenakis C.
Published: February 2011

A cosmetic product is often a complex non-homogeneous mixture of physicochemical units including polymers, small molecules, surface-active species, and particles. In use, it is applied to an equally heterogeneous substrate, skin. Consequently, materials structure as well as composition and the nature of the surfaces are relevant to a clear understanding of any technologically important product property or process. No longer is it sufficient to answer the classical questions of analysis—what and how much?—for many applications; we must now ask the additional questions of where, how organized, and how is it manifest to the customer? Although analytical sciences have, for many years, been applied to the problem of characterizing what is in chemical systems, the need to understand spatial and interfacial interactions has received much less attention. The explosive growth, however, in electronics, computing, biology, mathematical methodologies, microscopy, and optics now present the cosmetic industry with a new set of tools that can be utilized to address this issue. It is the objective of this article to highlight some of these measurement advances and how they might have relevance in the cosmetics industry in the coming years.
Coupled Quantum–Atomistic and Quantum–Continuum Mechanics Methods in Materials Research
Authors: Ramasubramaniam Ashwin , Carter Emily A.
Published: February 2011

The interface of quantum mechanics methods with classical atomistic simulation techniques, such as molecular dynamics and Monte Carlo, continues to be an area of considerable promise and interest. Such coupled quantum–atomistic approaches have been developed and employed, for example, to gain a comprehensive understanding of the energetics, kinetics, and dynamics of chemical processes involving surfaces and interfaces of hard materials. More recently, it has become possible to directly couple first-principles electronic structure techniques to continuum solid mechanics, either on the fly with feedback between length scales or by information passing between length scales. We discuss, with tutorial examples, the merging of quantum mechanics with molecular dynamics and Monte Carlo simulations, as well as quantum–continuum coupled techniques. We illustrate the opportunities offered by incorporation of information from quantum mechanics (reducing assumptions in higher length-scale models) and outline the challenges associated with achieving full predictive capability for the behavior of materials.
Hybrid Continuum Mechanics and Atomistic Methods for Simulating Materials Deformation and Failure
Authors: Miller Ronald E. , Tadmor Ellad B.
Published: February 2011

Many aspects of materials deformation and failure are controlled by atomic-scale phenomena that can be explored using molecular statics and molecular dynamics simulations. However, many of these phenomena involve processes on multiple length scales with the result that full molecular statics/molecular dynamics simulations of the entire system are too large to be tractable. In this review, we discuss hybrid models that perform molecular statics/molecular dynamics simulations “without all the atoms,” aimed at retaining atomistic detail at a fraction of the computational cost. These methods couple a fully atomistic model in critical regions to regions described by less-expensive continuum methods where they can provide an adequate representation of the important physics. We give an overview of the challenges such models present, with a focus on recent work to address issues of dynamics and finite (non-zero) temperature.
Atomic-Resolution Environmental Transmission Electron Microscopy for Probing Gas–Solid Reactions in Heterogeneous Catalysis
Authors: Gai Pratibha L. , Boyes Edward D. , Helveg Stig , Hansen Poul L. , Giorgio Suzanne , Henry Claude R.
Published: February 2011

Advances in atomic-resolution environmental transmission electron microscopy (ETEM) and related techniques for probing gas–solid reactionsin situare described. The capabilities of ETEM allow the dynamic nanostructure of heterogeneous catalysts in their functioning states to be directly monitored in real time. Applications of ETEM in catalysis are outlined, and they illustrate significant new insights into the dynamic nanostructure of the catalyst materials and their modes of operation.
Challenges and Opportunities in Multifunctional Nanocomposite Structures for Aerospace Applications
Authors: Baur Jeff , Silverman Edward
Published: February 2011

One important application of nanocomposites is their use in engineered structural composites. Among the wide variety of structural applications, fiber-reinforced composites for aerospace structures have some of the most demanding physical, chemical, electrical, thermal, and mechanical property requirements. Nanocomposites offer tremendous po tential to improve the properties of advanced engineered composites with modest additional weight and easy integration into current proc essing schemes. Sig nificant progress has been made in fulfilling this vision. In particular, nanocomposites have been applied at numerous locations within hierarchical composites to improve specific properties and optimize the multifunctional properties of the overall structure. Within this ar ticle, we review the status of nanocomposite incorporation into aerospace composite structures and the need for continued development.
Polymer Nanocomposites for Biomedical Applications
Authors: Hule Rohan A. , Pochan Darrin J.
Published: February 2011

Bionanocomposites have established themselves as a promising class of hybrid materials derived from natural and synthetic biodegradable polymers and organic/inorganic fillers. Different chemistries and compositions can lead to applications from tissue engineering to load-bearing composites for bone reconstruction. A critical factor underlying biomedical nanocomposite properties is interaction between the chosen matrix and the filler. This ar ticle discusses current efforts and key research challenges in the development of these ma te rials for use in potential biomedical applications.
Advanced Inorganic Materials for Photovoltaics
Authors: Slaoui Abdelilah , Collins Reuben T.
Published: February 2011

By 2050, world annual energy consumption is predicted to grow from the present 13 terawatt - years (TWyr) to nearly 30 TWyr. Although all energy sources must be considered in meeting this challenge, solar energy may arguably be the only carbon-free source capable of supplying a significant fraction of energy at these levels. This issue of MRS Bulletin reviews the status and future development of solar photovoltaic technologies based on inorganic materials. The discussion begins with materials and cell designs for second-generation photovoltaics based on thin films [a-Si:H, Si, Cu(In, Ga)(Se, S)2, CdTe]. Recent advances in tandem cells and concentrators are alsoreported, along with photovoltaic approaches involving nanoscale materials such as quantum dot arrays. Finally, work on transparent conducting oxides that are critical to nearly all cell designs are discussed.
Amorphous Silicon, Microcrystalline Silicon, and Thin-Film Polycrystalline Silicon Solar Cells
Authors: Schropp Ruud E.I. , Carius Reinhard , Beaucarne Guy
Published: February 2011

Thin-film solar cell technologies based on Si with a thickness of less than a few micrometers combine the low-cost potential of thin-film technologies with the advantages of Si as an abundantly available element in the earth's crust and a readily manufacturable material for photovoltaics (PVs). In recent years, several technologies have been developed that promise to take the performance of thin-film silicon PVs well beyond that of the currently established amorphous Si PV technology. Thin-film silicon, like no other thin-film material, is very effective in tandem and triple-junction solar cells. The research and development on thin crystalline silicon on foreign substrates can be divided into two different routes: a low-temperature route compatible with standard float glass or even plastic substrates, and a high-temperature route (>600°C). This article reviews the material properties and technological challenges of the different thin-film silicon PV materials.
Materials Challenges for CdTe and CuInSe2Photovoltaics
Authors: Beach Joseph D. , McCandless Brian E.
Published: February 2011

The record laboratory cell (∼1 cm2area) efficiency for thin-film cadmium telluride (CdTe) is 16.5%, and that for a copper indium diselenide (CuInSe2) thin-film alloy is 19.5%. Commercially produced CdTe and CuInSe2modules (0.5–1 m2area) have efficiencies in the 7–11% range. Research is needed both to increase laboratory cell efficiencies and to bring those small - area efficiencies to large-area production. Increases in laboratory CdTe cell efficiency will require increasing open-circuit voltage, which will allow cells to harvest more energy from each absorbed photon. This will require extending the minority carrier lifetime from its present τ ≤ 2 ns to τ ≥ 10 ns and increasing hole concentration in the CdTe beyond 1015cm2, which appears to be limited by compensating defects. Increasing laboratory CuInSe2-based cell efficiency significantly beyond 19.5% will also require increasing the open-circuit voltage, either by increasing the bandgap, the doping level, or the minority carrier lifetime. The photovoltaic cells in commercial modules occupy tens of square centimeters, and both models and experiments have shown that low-performing regions in small fractions of a cell can significantly reduce the overall cell per formance. Increases in commercial module efficiency will require control of materials properties across large deposition areas in a high-throughput environment to minimize such non-uniformities. This article discusses approaches used and research needed to increase the ultimate efficiencies of CdTe- and CuInSe2-based devices and translate these gains to commercial photovoltaic modules.
High-Efficiency Multijunction Solar Cells
Authors: Dimroth Frank , Kurtz Sarah
Published: February 2011

The efficiency of a solar cell can be increased by stacking multiple solar cells with a range of bandgap energies, resulting in a multijunction solar cell with a maximum the oretical efficiency limit of 86.8% III–V compound semiconductors are good candidates for fabricating such multijunction solar cells for two reasons: they can be grown with excellent material quality; and their bandgaps span a wide spectral range, mostly with direct bandgaps, implying a high absorption coefficient. These factors are the reason for the success of this technology, which has achieved 39% efficiency, the highest solar-to-electric conversion efficiency of any photovoltaic device to date. This article explores the materials science of today's high-efficiency multijunction cells and describes challenges associated with new materials developments and how they may lead to next-generation, multijunction solar cell concepts.
Solar Cells Based on Quantum Dots: Multiple Exciton Generation and Intermediate Bands
Authors: Luque Antonio , Martí Antonio , Nozik Arthur J.
Published: February 2011

Semiconductor quantum dots may be used in so-called third-generation solar cells that have the potential to greatly increase the photon conversion efficiency via two effects: (1) the production of multiple excitons from a single photon of sufficient energy and (2) the formation of intermediate bands in the bandgap that use sub-bandgap photons to form separable electron–hole pairs. This is possible because quantization of energy levels in quantum dots produces the following effects: enhanced Auger processes and Coulomb coupling between charge carriers; elimination of the requirement to conserve crystal momentum; slowed hot electron–hole pair (exciton) cooling; multiple exciton generation; and formation of minibands (delocalized electronic states) in quantum dot arrays. For exciton multiplication, very high quantum yields of 300–700% for exciton formation in PbSe, PbS, PbTe, and CdSe quantum dots have been reported at photon energies about 4–8 times the HOMO–LUMO transition energy (quantum dot bandgap), respectively, indicating the formation of 3–7 excitons/photon, depending upon the photon energy. For intermediate-band solar cells, quantum dots are used to create the intermediate bands from the con fined electron states in the conduction band. By means of the intermediate band, it is possible to absorb below-bandgap energy photons. This is predicted to produce solar cells with enhanced photocurrent without voltage degradation.
Piezoelectric Nanostructures: From Growth Phenomena to Electric Nanogenerators
Authors: Wang Zhong Lin
Published: February 2011

Zinc oxide is a unique material that exhibits semiconducting, piezoelectric, and pyroelectric multifunctionalities. By controlling the size and orientation of the polar surfaces of ZnO nanobelts, single - crystal nanocombs, nanorings, nanohelices, nanosprings, and nanobows of ZnO have been synthesized. This article centers on the fundamental growth mechanism and fabrication of electromechanical devices based on piezoelectric ZnO nanostructures, including a nanogenerator using aligned ZnO nanowires for converting nanoscale mechanical energy into electric energy. The mechanism of the electric nanogenerator relies on the unique coupling of the piezoelectric and semiconducting properties of ZnO, which is the fundamental principle of nano - piezotronics, a new field using the piezoelectric effect for fabricating electronic devices and components. The approach has the potential of converting biological mechanical energy, acoustic/ultrasonic vibration energy, and biofluid hydraulic energy into electricity, demonstrating a new pathway for self - powering of wireless nanodevices and nanosystems.
Directed Growth of Branched Nanowire Structures
Authors: Dick Kimberly A. , Deppert Knut , Karlsson Lisa S. , Larsson Magnus W. , Seifert Werner , Wallenberg L. Reine , Samuelson Lars
Published: February 2011

We describe the production of hierarchical branched nanowire structures by the sequential seeding of multiple wire generations with metal nanoparticles. Such complex structures represent the next step in the study of functional nanowires, as they increase the potential functionality of nanostructures produced in a self-assembled way. It is possible, for example, to fabricate a variety of active heterostructure segments with different compositions and diameters within a single connected structure. The focus of this work is on epitaxial III-V semiconductor branched nanowire structures, with the two materials GaP and In As used as typical examples of branched structures with cubic (zinc blende) and hexagonal (wurtzite) crystal structures. The general morphology of these structures will be described, as well as the relationship between morphology and crystal structure.
Fundamentals of Focused Ion Beam Nanostructural Processing: Below, At, and Above the Surface
Authors: MoberlyChan Warren J. , Adams David P. , Aziz Michael J. , Hobler Gerhard , Schenkel Thomas
Published: February 2011

This article considers the fundamentals of what happens in a solid when it is impacted by a medium-energy gallium ion. The study of the ion/sample interaction at the nanometer scale is applicable to most focused ion beam (FIB)–based work even if the FIB/sample interaction is only a step in the process, for example, micromachining or microelectronics device processing. Whereas the objective in other articles in this issue is to use the FIB tool to characterize a material or to machine a device or transmission electron microscopy sample, the goal of the FIB in this article is to have the FIB/sample interaction itself become the product. To that end, the FIB/sample interaction is considered in three categories according to geometry: below, at, and above the surface. First, the FIB ions can penetrate the top atom layer(s) and interact below the surface. Ion implantation and ion damage on flat surfaces have been comprehensively examined; however, FIB applications require the further investigation of high doses in three-dimensional profiles. Second, the ions can interact at the surface, where a morphological instability can lead to ripples and surface self-organization, which can depend on boundary conditions for site-specific and compound FIB processing. Third, the FIB may interact above the surface (and/or produce secondary particles that interact above the surface). Such ion beam–assisted deposition, FIB–CVD (chemical vapor deposition), offers an elaborate complexity in three dimensions with an FIB using a gas injection system. At the nanometer scale, these three regimes—below, at, and above the surface—can require an interdependent understanding to be judiciously controlled by the FIB.
Smart Nanotextiles: A Review of Materials and Applications
Authors: Coyle Shirley , Wu Yanzhe , Lau King-Tong , De Rossi Danilo , Wallace Gordon , Diamond Dermot
Published: February 2011

The development of smart nanotextiles has the potential to revolutionize the functionality of our clothing and the fabrics in our surroundings. Nanoscale manipulation results in new functionalities for intelligent textiles, including self-cleaning, sensing, actuating, and communicating. This is made possible by such developments as new materials, fibers, and finishings; inherently conducting polymers; carbon nanotubes; and antimicrobial nanocoatings. These additional functionalities have numerous applications, encompassing healthcare, sports, military applications, and fashion. The wearer and the surrounding environment may be monitored in an innocuous manner, giving continuous updates of individual health status or environmental hazards. More generally, smart textiles become a critical part of the emerging area of body sensor networks incorporating sensing, actuation, control, and wireless data transmission. This article reviews current research in nanotechnology application to textiles, from fiber manipulation and development to end uses of smart nanotextiles.
Laser Direct-Write Processing
Authors: Arnold Craig B. , Piqué Alberto
Published: February 2011

Direct-write techniques enable computer-controlled two- and three-dimensional pattern formation in a serial fashion. Among these techniques, the versatility offered by laser-based direct-write methods is unique, given their ability to add, remove, and modify different types of materials without physical contact between a tool or nozzle and the material of interest. Laser pulses used to generate the patterns can be manipulated to control the composition, structure, and even properties of individual three-dimensional volumes of materials across length scales spanning six orders of magnitude, from nanometers to millimeters. Such resolution, combined with the ability to process complex or delicate material systems, enables laser direct-write tools to fabricate structures that are not possible to generate using other serial or parallel fabrication techniques. The goal of the articles in this issue ofMRS Bulletinis to illustrate the range of materials processing capabilities, fundamental research opportunities, and commercially viable applications that can be achieved using recently developed laser direct-write techniques. We hope that the articles provide the reader with a fresh perspective on the challenges and opportunities that these powerful techniques offer for the fabrication of novel devices and structures.
Molecular Biomimetics: Genetic Synthesis, Assembly, and Formation of Materials Using Peptides
Authors: Tamerler Candan , Sarikaya Mehmet
Published: February 2011

In nature, the molecular-recognition ability of peptides and, consequently, their functions are evolved through successive cycles of mutation and selection. Using biology as a guide, it is now possible to select, tailor, and control peptide–solid interactions and exploit them in novel ways. Combinatorial mutagenesis provides a protocol to genetically select short peptides with specific affinity to the surfaces of a variety of materials including metals, ceramics, and semiconductors. In the articles of this issue, we describe molecular characterization of inorganic-binding peptides; explain their further tailoring using post-selection genetic engineering and bioinformatics; and finally demonstrate their utility as molecular synthesizers, erectors, and assemblers. The peptides become fundamental building blocks of functional materials, each uniquely designed for an application in areas ranging from practical engineering to medicine.
Biofunctionalized Nanoparticles and Their Uses
Authors: Tomczak Melanie M. , Slocik Joseph M. , Stone Morley O. , Naik Rajesh R.
Published: February 2011

Nanotechnology is revolutionizing the way that sensing, electronic, optical, and medical devices are designed because the properties of nanostructures are distinct from their bulk-material counterparts. The incorporation of nanomaterials into devices and sensors to exploit their unique properties has been a challenge because they must be functionalized in a manner that does not destroy their properties. Biological macromolecules can non-covalently or covalently bind to nanomaterials, resulting in the formation of biofunctionalized nanoparticles. These biofunctionalized nanoparticles are exemplified by the peptide-mediated suspension of carbon nanotubes in solution and the templating of bimetallic nanoparticles using multifunctional peptides.