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- Volume 36, 2006
Annual Review of Materials Research - Volume 36, 2006
Volume 36, 2006
- Preface
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STRUCTURAL ORDER IN LIQUIDS INDUCED BY INTERFACES WITH CRYSTALS
Vol. 36 (2006), pp. 1–48More Less▪ AbstractInterfaces between solids and liquids are important for a range of materials processes, including soldering and brazing, liquid-phase sintering, crystal growth, and lubrication. There is a wealth of fundamental studies on solid-liquid interfaces in materials, primarily focused on thermodynamics (relative interface energies and segregation effects) from high-temperature wetting experiments, which is often applied to processing design. Less is known about the atomistic structure at solid-liquid interfaces, mainly because of the difficulty involved in obtaining such information experimentally. This work reviews both theoretical and experimental studies of atomistic configurations at solid-liquid interfaces, focusing on the issue of ordering in the liquid adjacent to crystalline solids.
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POSITRON ANNIHILATION AS A METHOD TO CHARACTERIZE POROUS MATERIALS
Vol. 36 (2006), pp. 49–79More Less▪ AbstractBeam-based positron annihilation spectroscopy (PAS) is a powerful porosimetry technique with broad applicability in the characterization of nanoporous thin films, especially insulators. Pore sizes and distributions in the 0.3–30 nm range are nondestructively determined with only the implantation of low-energy positrons from a table-top beam. Depth-profiling with PAS has proven to be an ideal way to measure the interconnection length of pores, search for depth-dependent inhomogeneities or damage in the pore structure, and explore porosity hidden beneath dense layers or diffusion barriers. The capability of PAS is rapidly maturing as new intense positron beams around the globe spawn more accessible PAS facilities. After a short primer on the physics of positrons in insulators, the various probe techniques of PAS are briefly summarized, followed by a more detailed discussion of the wide range of nanoporous film parameters that PAS can characterize.
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FERROELASTIC DOMAIN STRUCTURE AND SWITCHING IN EPITAXIAL FERROELECTRIC THIN FILMS
Kilho Lee, and Sunggi BaikVol. 36 (2006), pp. 81–116More Less▪ AbstractUnique ferroelastic polytwin domains are formed in epitaxial ferroelectric thin films prepared on single-crystal substrates and critically influence various ferroelectric properties. This chapter reviews theoretical as well as experimental studies on various thermomechanical strain factors and their relaxation involved in domain formation and switching during film processing and device fabrication and application. Two major strain relaxation mechanisms, misfit strain relaxation by dislocations and the formation of polytwin structures, are reviewed. The critical factors controlling the final domain structures, such as substrate selection, film composition, film thickness, introduction of an interlayer, and the lateral size of film patterning, are described in detail. This chapter also includes recent experimental evidence of ferroelastic domain switching in such highly confined epitaxial thin films as well as in small islands.
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MICROGELS: Old Materials with New Applications
Vol. 36 (2006), pp. 117–142More Less▪ AbstractThis review describes the most recent progress in the use of polymer multiresponsive microgels as central components of advanced, functional colloidal materials. Significant areas of development include the use of microgels as microreactors for templated synthesis of inorganic nanoparticles with predetermined properties, as optically active materials including lenses and photonic crystals, and as primary units in site-specific and controlled drug delivery systems. In the last category, both synthetic and biopolymeric microgels are discussed.
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MECHANICAL BEHAVIOR AND CHARACTERIZATION OF MICROCAPSULES
Vol. 36 (2006), pp. 143–178More Less▪ AbstractIn recent years microcapsule systems have found applications in many areas of science and technology. Their use to a large extent depends on how mechanical properties are understood and controlled. Here we review different experimental techniques recently developed to probe microcapsule mechanics and to characterize other physical properties of the shell material and capsule interior. We illustrate the potential of these experimental techniques and theoretical models by using data obtained for polyelectrolyte multilayer microcapsules, one of the most promising systems that shows extremely rich behavior. Applications and/or extensions of methods to study other capsule systems, including bioengineered composites and even living cells, would be straightforward.
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HYDROGEN IN SEMICONDUCTORS
Vol. 36 (2006), pp. 179–198More Less▪ AbstractHydrogen strongly affects the properties of electronic materials. Interstitial monatomic hydrogen is always electrically active and usually counteracts the prevailing conductivity of the semiconductor. In some materials, however, hydrogen acts as a source of doping. We describe the mechanisms that govern interactions between hydrogen and semiconductors, including monatomic hydrogen, hydrogen molecules, and hydrogen-related complexes. We also discuss the behavior of hydrogen on the surface and its role in the growth process. The fundamental principles are illustrated with practical examples, many of them for the technologically relevant case of gallium nitride.
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PROGRESS IN PLASTIC ELECTRONICS DEVICES
Vol. 36 (2006), pp. 199–230More Less▪ AbstractOrganic field-effect transistors (OFETs) based on solution-processible polymeric as well as small molecular semiconductors have shown impressive improvements in their performance during recent years. These devices have been developed to realize low-cost, large-area electronic products. This review gives an overview of the materials’ aspect, charge-transport, and device physics of OFETs, focusing mainly on the organic semiconductor and organic dielectric materials and their mutual interface. Recent developments in the understanding of the relationship between microstructure and charge transport, the influence of processing techniques, and gate dielectric are reviewed. Comparative data of charge-carrier mobility of most organic semiconductors have been compiled. Ambipolar charge transport in OFETs and its applications to integrated circuits as well as ambipolar light-emitting transistors are also reviewed. Many interesting questions regarding how the molecular and electronic structures at the interface of the organic semiconductor and organic insulator influence device performance and stability remain to be explored.
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SYNTHESIS OF COLLOIDAL PARTICLES IN MINIEMULSIONS
Vol. 36 (2006), pp. 231–279More Less▪ AbstractMiniemulsions are specially formulated heterophase systems in which stable nanodroplets of one phase are dispersed in a second, continuous phase. Because each of the nanodroplets can be regarded as a nanoscopic, individual batch reactor, a whole variety of reactions and processes resulting in both organic and inorganic nanoparticles can be performed. This chapter reviews the wide range of possibilities of reactions in miniemulsions for the formation of structured nanoparticles. Different kinds of polymerizations, such as radical, anionic, and enzymatic polymerization, as well as polyaddition and polycondensation can be carried out in the nanodroplets, which permits the formulation of a variety of polymers, copolymers, or hybrid particles that previously have not been synthesized in other heterophase processes. Additionally, this review shows that miniemulsions are also highly suited for the encapsulation of various organic and inorganic, solid or liquid materials and for the functionalization of the particle surface.
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AMORPHOUS POROUS MIXED OXIDES: Sol-Gel Ways to a Highly Versatile Class of Materials and Catalysts
Vol. 36 (2006), pp. 281–331More Less▪ AbstractThis review discusses the preparation, characterization, and application of amorphous porous mixed oxides, a rapidly growing class of materials with wide applications and a huge potential for the tailoring of chemical composition, microstructure, porosity, and surface properties. In contrast to crystalline materials, these amorphous mixed oxides are prepared under mild reaction conditions in ambient atmosphere. An ever-increasing variety of precursors, additives, modifiers, solvents, catalysts, and posttreatment conditions provide ample fine-tuning options. These materials often display properties commonly associated with well-defined crystalline phases. The functional properties of such solids are largely unexplored and provide a tremendous opportunity for the development of new or alternative materials (solids with a function). Here, emphasis is paid to micro- and mesoporous mixed oxides and their catalytic properties. Easy access to these materials is offset by their much more problematic characterization. Microstructure, chemical structure, morphology, and pore sizes often show broad distributions, and materials description cannot compare with the precise data associated with crystalline phases. The facile preparation and accessibility of these materials make them ideally suited for the application of high-throughput technologies (HTT), which dramatically accelerate searches for new materials as well as fine tuning and optimization. HTT also allow investigators for the first time to access and optimize multinary mixed oxides on a realistic timescale.
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NANOFIBROUS MATERIALS AND THEIR APPLICATIONS
Vol. 36 (2006), pp. 333–368More Less▪ AbstractNanostructured fibrous materials have been made more readily available in large part owing to recent advances in electrospinning and related technologies, including the use of electrostatic or gas-blowing forces as well as a combination of both forces. The nonwoven structure has unique features, including interconnected pores and a very large surface-to-volume ratio, which enable such nanofibrous scaffolds to have many biomedical and industrial applications. The chemical composition of electrospun membranes can be adjusted through the use of different polymers, polymer blends, or nanocomposites made of organic or inorganic materials. In addition to the control of material composition, the processing flexibility in maneuvering physical parameters and structures, such as fiber diameter, mesh size, porosity, texture, and pattern formation, offers the capability to design electrospun scaffolds that can meet the demands of numerous practical applications. This review provides a selective description of the fabrication of nanofibrous membranes and applications with specific examples in anti-adhesion in surgery and ultrafiltration in water treatment.
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THE USE OF POLYMER DESIGN IN RESORBABLE COLLOIDS
Vol. 36 (2006), pp. 369–395More Less▪ AbstractDuring the past decade, researchers in the field of polymer chemistry have developed a wide range of very powerful procedures for constructing ever-more-sophisticated polymers. These methods subsequently have been used in suitable systems to solve specific medical problems. This is complicated, and many key factors such as mechanical properties, biocompatibility, biodegradation, stability, and degradation profile must be considered. Colloid particle systems can be used to solve many biomedical- and pharmaceutical-related problems, and it is expected that nanotechnology can be used to develop these materials, devices, and systems even further. For example, an injectible scaffold system with a defined release and degradation profile has huge potential for the repair and regeneration of damaged tissues. This short, nonexhaustive review presents examples of polymer architecture in resorbable particles that have been compared and tested in biomedical applications. We also discuss the design of polymers for core-shell structures.
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PROGRESS IN CERAMIC LASERS
Vol. 36 (2006), pp. 397–429More Less▪ AbstractYttrium aluminum garnet (YAG) (Y3Al5O12) single crystals doped with active species such as Nd and Yb have been used as laser media in solid-state lasers requiring high energy and excellent beam quality. This is because single crystals have extremely high thermal mechanical properties and optical qualities and because they enable high-efficiency laser oscillation. In 1995 the authors, using polycrystalline Nd:YAG, demonstrated a high-efficiency laser that was comparable to a single-crystal laser. Subsequently, single-longitudinal-mode oscillation, green and blue laser oscillation, and ultrashort-pulse laser oscillation were reported. Using the ceramic powder approach, the authors developed a composite laser element with a complicated structure that could not be produced by crystal growth techniques. This review discusses problems of conventional single-crystal growth, the fabrication and characteristics of ceramic lasers, laser oscillation properties (continuous-wave and pulse operation), light-scattering sources in ceramics, and typical applications of ceramic lasers.
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IN SITU SYNCHROTRON X-RAY STUDIES OF FERROELECTRIC THIN FILMS
Vol. 36 (2006), pp. 431–465More Less▪ AbstractThis paper reviews recent in situ studies of ferroelectric thin films using synchrotron X-ray scattering, with an emphasis on single-crystal perovskite films. We describe observations of thin film growth, the ferroelectric phase transition, and structural evolution during ferroelectric switching. The importance of quantitatively characterizing the internal structure of ferroelectric films under controlled electrical and mechanical boundary conditions is discussed.
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PROGRESS IN MICROSTRUCTURED OPTICAL FIBERS
Vol. 36 (2006), pp. 467–495More Less▪ AbstractThe development of microstructured optical fibers has led to the realization of many optical properties in fiber form that were not previously attainable. This chapter reviews the background to this work and overviews both the fundamentals of and progress in fabricating and modeling these structures. Until relatively recently, most of the work in this field was based on silica glass; this chapter provides an update on progress in developing microstructured fibers from other materials such as soft glasses. Some of the key applications of microstructured fibers, including nonlinear fiber–based devices and fibers for high power light delivery, are also reviewed.
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TIN-BASED GROUP IV SEMICONDUCTORS: New Platforms for Opto- and Microelectronics on Silicon
Vol. 36 (2006), pp. 497–554More Less▪ AbstractNew classes of Sn-containing group IV semiconductors are described. Novel CVD routes lead to growth of a broad range of Ge1−ySny alloys and compounds directly on Si substrates. The direct bandgap (E0) and optical transitions E0+Δ0, E1, E1+Δ1, E0′, and E2 of Ge1−ySny exhibit strong nonlinearities in the compositional dependence, and their bowing parameters correlate with those in Ge1 −xSix, suggesting a scaling behavior for the electronic properties. The Ge1−ySny films can be used as “virtual substrates” for the subsequent growth of Ge1−x−ySixSny ternaries. These are created for the first time and exhibit unprecedented thermal stability, superior crystallinity and unique optical and strain properties such as adjustable bandgaps, and controllable strain states (compressive, relaxed, and tensile). The synthesis of Ge1−x−ySixSny makes it possible to decouple strain and bandgap and adds new levels of flexibility to the design of group IV devices. The Ge-Si-Sn system also represents a new class of “designer” templates for the monolithic integration of III-V and II-VI semiconductors with Si electronics.
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HYDROGEN IN METALS: Microstructural Aspects
A. Pundt, and R. KirchheimVol. 36 (2006), pp. 555–608More Less▪ AbstractMetal-hydrogen (M-H) systems are interesting from both a theoretical and a practical point of view. M-H systems are utilized for energy-storage systems, in sensor applications, and in catalysis. These systems are often exploited as models for studying basic material properties, especially when the size of these systems is small and nonbulk-like contributions become dominant. Surfaces, nanocrystals, vacancy- and dislocation-rich materials, thin films, multilayers, and clusters as systems of major interest are addressed in this review. We show that the hydrogen solubility of M-H systems is strongly affected by the morphology and microstructure of and the stress between regions of different hydrogen concentration. For small-sized systems, surface- or interface-related sites become important and change the overall solubility as well as the phase boundaries of M-H systems. In thin films deposited on stiff substrates, compressive stresses evolve during hydrogen loading because the films are effectively clamped to substrates. These stresses are in the GPa range and strongly depend on microstructure. Nanoparticles even change their crystallographic structure, which results in completely new phases.
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Previous Volumes
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Volume 54 (2024)
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Volume 53 (2023)
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Volume 52 (2022)
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Volume 51 (2021)
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Volume 50 (2020)
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Volume 49 (2019)
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Volume 48 (2018)
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Volume 47 (2017)
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Volume 46 (2016)
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Volume 45 (2015)
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Volume 44 (2014)
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Volume 43 (2013)
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Volume 42 (2012)
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Volume 41 (2011)
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Volume 40 (2010)
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Volume 39 (2009)
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Volume 38 (2008)
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Volume 37 (2007)
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Volume 36 (2006)
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Volume 35 (2005)
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Volume 34 (2004)
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Volume 33 (2003)
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Volume 32 (2002)
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Volume 31 (2001)
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Volume 30 (2000)
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Volume 29 (1999)
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Volume 28 (1998)
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Volume 27 (1997)
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Volume 26 (1996)
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Volume 25 (1995)
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Volume 24 (1994)
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Volume 23 (1993)
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Volume 22 (1992)
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Volume 21 (1991)
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Volume 20 (1990)
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Volume 19 (1989)
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Volume 18 (1988)
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Volume 17 (1987)
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Volume 16 (1986)
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Volume 15 (1985)
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Volume 14 (1984)
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Volume 13 (1983)
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Volume 12 (1982)
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Volume 11 (1981)
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Volume 10 (1980)
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Volume 9 (1979)
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Volume 8 (1978)
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Volume 7 (1977)
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Volume 6 (1976)
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Volume 5 (1975)
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Volume 4 (1974)
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Volume 3 (1973)
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Volume 2 (1972)
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Volume 1 (1971)
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Volume 0 (1932)