Materials Science Issues Research Articles

(Invited) Degradation of SiC Bipolar Devices: A Review of Likely Causes and Recent Advances in its Understanding

Degradation of 4H-SiC PiN diodes - a rapid increase in the forward voltage drop with operation time - has been a focus of research since it was observed a decade ago. A combination of electrical studies and microstructural characterization of the diodes revealed early on that associated with this degradation is a rapid increase in the number and extent of intrinsic stacking faults in the active region of the device. Because PiN diode is a bipolar device, and the degradation occurs under forward biasing, it was suspected that the expansion of stacking faults is driven by injection of electron-hole pairs (ehps). In many ways, this effect is similar to a phenomenon known as recombination-induced dislocation glide (REDG) that occurs in some other semiconductors, including in SiC. In this paper, after a review of the basic materials science issues regarding extended defects in SiC, recent explanations of degradation of PIN diodes are discussed.

Light Induced H2O Splitting: Device and Materials Science Issues

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Microwave Photochemistry. Applications in Organic Synthesis

This review article is the second of the comprehensive series on survey of the microwave photochemical and photocatalytic processes, and is focused specially on the microwave-assisted photochemical applications of the electrodeless discharge lamps (EDLs) in organic synthesis. The concept of microwave organic photochemistry is an important issue in synthetic chemistry and material science, and is presented in several schemes. Likewise, the various microwave photochemical reactor types (batch with external or internal light source, flow-through with external light source, annular flow-through with internal EDL, cylindrical flow-through surrounded with EDL, and mixed flow-through with internal EDL) with different arrangement of the lamps are described.

Polymorphic and mechanochromic luminescence modulation in the highly emissive dicyanodistyrylbenzene crystal: secondary bonding interaction in molecular stacking assembly

Understanding the role of self-assembly and electronic interactions of constituent molecules in determining optoelectronic properties of a molecular solid is a fundamental and essential issue in material science. Particularly, the correlation between the molecular stacking mode and modulated optical properties has barely been established in spite of its scientific and technological importance. Herein, we present dicyanodistyrylbenzene-based highly luminescent crystals which uniquely exhibit polymorphism and mechanochromism. In these materials, various secondary bonding interactions (local dipole interaction, C–H⋯π interaction, and C–H⋯N hydrogen bond) play key roles in molecular stacking assembly, as well as in polymorphic and mechanochromic behaviors. The two different polymorphic phases of dicyanodistyrylbenzene crystal were correlated to the different modes of local dipole coupling, which caused a substantial alternation of π–π overlap and excited state delocalization to give differently colored fluorescence emission. Most uniquely, the phase transformation between those crystalline phases was effected through thermal and mechanical processes. We have comprehensively carried out in-depth and systematic optical, structural, and photophysical investigations to establish unambiguous structure–property relationships.

Microwave Photochemistry and Photocatalysis. Part 1: Principles and Overview

The coupled activation of photochemical and photocatalytic reactions by using of two different types of radiation, microwave and UV/Vis, is covered by the new discipline called microwave photochemistry and photocatalysis. Such a connection might have a synergic effect on reaction efficiencies or, at least, enhance them by summing up the individual effects. The objective of this discipline is frequently, but not necessarily, connected to the electrodeless discharge lamp (EDL) as a novel light source which generates efficiently UV/Vis radiation when placed into a microwave field. This review article is focused on the general principles of microwave photochemistry and photocatalysis, i.e. generation of UV/Vis discharge in EDL (theory of the microwave discharges, construction of EDL, preparation of the thin titania films on EDL, spectral characteristics of EDL, and performance of EDL). Likewise, the various microwave photochemical and photocatalytic reactor types (batch with external or internal light source, flow-through with external light source, annular flow-through with internal EDL, and cylindrical flow-through surrounded with EDL) with different arrangement of the lamps are described. The concept of microwave photochemistry and photocatalysis as an important issue in synthetic chemistry and material science is presented in several tables.

ChemInform Abstract: Development of High Density Magnetic Recording Media for Hard Disk Drives: Materials Science Issues and Challenges

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Catalytic Asymmetric Synthesis of Organofluorine Compounds Using Fluoral

Asymmetric synthesis of organofluorine compounds is an important issue in pharmaceutical chemistry and optoelectronic material science. In this respect, asymmetric catalysis of carboncarbon bond-forming reactions is the most attractive method. Asymmetric catalysis of ene, Mukaiyama-aldol and Friedel-Crafts reactions with fluoral is thus established using chiral binaphthol-derived titanium ((6-Br) -BINOL-Ti) catalysts to provide a practical synthetic route to the organofluorine compounds containing trifluoromethyl group.

Rheology of the Earth's mantle: A historical review

Historical development of our understanding of rheological properties of the Earth's mantle is reviewed. Rheological properties of the Earth's mantle control most of the important geological processes such as the style of mantle convection (e.g., stagnant lid versus plate tectonics) and the nature of thermal evolution. However, inferring the rheological properties of the Earth's mantle is challenging because of the presence of multiple mechanisms of deformation that have different dependence on time-scale (strain-rate), stress levels and other parameters. Through the integration of a broad range of observations including the elastic stiffness from tidal deformation and the viscosity from the concept of isostasy, a gross picture of rheological stratification of the Earth's mantle (a strong lithosphere, a weak asthenosphere and a strong layer below) was proposed in the mid-19th century. However, not only the physical basis for such a model was weak due to the lack of proper understanding of some materials science issues such as the interplay between elastic and viscous deformation but also the lack of understanding of temperature–depth relation associated with convection prevented our understanding of the rheological structure of the Earth's interior. Major progress occurred in the first half of the 20th century in our understanding of the atomistic mechanisms of plastic deformation in solids, and much of the theoretical framework on the plastic deformation of solids was established by late 1960s. Those developments provided a basis for scaling analyses that are critical to the applications of laboratory results to the Earth's interior. Major progress in laboratory studies on rheological properties occurred in the mid-1960s to the early 1970s in Griggs' lab using a new type of solid-medium high-pressure deformation apparatus to pressure ∼ 2 GPa and temperature ∼ 1600 K. The basic concepts such as the water weakening, non-linear rheology and deformation-induced lattice-preferred orientation were identified by their studies. However, large uncertainties in the stress measurements with this type of apparatus were recognized in the late 1970s and high-resolution experimental studies using synthetic samples were initiated in Paterson's lab in the mid-1980s using a high-resolution gas-medium deformation apparatus. However, experimental studies with such a gas-medium deformation apparatus can be conducted only at low pressures (< 0.5 GPa) and it is difficult to apply these low-pressure data to the Earth's interior deeper than ∼ 20 km. New experimental techniques to study rheological properties in Earth's deep interior have been developed during the last a few years. These techniques allow us to quantitatively study the rheological properties of Earth materials down to the lower mantle condition (∼ 24 GPa, ∼ 2000 K). Some geodynamic issues related to rheological properties are discussed including (i) the strength of the lithosphere and the origin of plate tectonics, (ii) the origin of the asthenosphere, and (iii) the deep mantle rheology and its influence on thermal history of Earth. Existing models on these topics are reviewed and new alternative models are discussed.

Materials Science: State of the Art 2010

Each week, Advanced Materials brings you a Review of a cutting-edge topic in materials science, accompanied by a number of short Communications. This issue, however, is different. For the first time, we have selected eight review articles written by leaders in their respective fields to survey what we believe to be the state of the art in materials science in early 2010. From molecular electronics to biomaterials, solar cells to inorganic structures, we hope these reviews will provide an overview of some of the most exciting advances being made in materials science as we enter the second decade of the 20th century. As featured on the cover of this issue, Wenping Hu and Daoben Zhu (Insitute of Chemistry, Chinese Academy of Sciences) review ten years of progress in the development of nanogap electrodes. Electrodes with a nanometer gap can be used for the study of nanometer- and molecular-scale phenomena. Single-molecule transistors, carbon nanotube electrodes, DNA nanowires, and more have all been studied using this technique, and the authors predict a bright future for the field as challenges in reliable electrode manufacture and determining the number of molecules between a nanogap are met and overcome. A major theme in molecular electronics has been the study of single-molecule junctions. While this facilitates theoretical modeling, researchers have faced issues with reproducibility. Ayelet Vilan and David Cahen of the Weizmann Institute of Science and Antoine Kahn of Princeton review ensemble molecular junctions. The study of large, two-dimensional molecular monolayers on silicon has resulted in high-quality, reproducible systems for the study of charge transport mechanisms and energy levels in such hybrid systems. High-efficiency intermediate band solar cells are reviewed by Antonio Luque and Antonio Martí (Universidad Politécnica de Madrid). Since the first report of the concept more than a decade ago, their maximum theoretical efficiency of 63% has proven a tempting target, and work on systems based on quantum dots and on IB alloys have been pursued. Significant progress has been made, and further work on improving the efficiency might lead to low-cost, high-efficiency thin photovoltaics. David Kaplan (Tufts) examines the state of the art in bio-microfluidics: the application of biomaterials and bioinspired design to microfluidics. Biopolymers such as silk or fibroin can replace polydimethylsiloxane and be functionalized with bioactive or stimuli-responsive components. In the future, a bio-microfluidic system might be designed to interface with existing vasculature, disintegrating over time to be replaced with native tissue, resulting in engineered tissue with enhanced transport properties during its development. The incorporation of stem cells into strategies for tissue engineering requires better understanding of the interactions of stem cells with their synthetic environment. To this end, Jason Burdick (University of Pennsylvania) reviews how materials influence stem cell differentiation. The material structure, the chemistry, and the presentation and delivery of differentiation factors influence the differentiation of mensenchymal stem cells, as can control of the cell morphology and the mechanical properties and interactions of the surrounding matrix. Stem cells are sensitive to their microenviroments, and rationally controlling many different variables in a tissue engineering scaffold will be critical for complex regenerative medicine challenges. Rainer Haag and co-workers comprehensively discuss recent progress in developing dendritic polyglycols for biomedical applications. The well-defined structure, monodispersity, and tunable surface functionality of dendrimers, coupled with the non-recognition of polyols by the immune system, make these structures interesting targets for development of nanomedical applications. Metal oxides present a stunningly broad range of structural, electronic, optical, and magnetic properties, making them critical for technological applications as well as presenting fundamental materials science issues. In his review, Scott Chambers (Pacific Northwest National Laboratory) discusses crystalline oxide film growth and, in particular, examines doped transition metal oxides and complex oxides, giving examples where fundamental understanding of the properties has elucidated structure-function relationships. Finally, while applications of ionic liquids for solvent extraction and organic catalysis are well know, the use of ionic liquids for inorganic material synthesis is less than a decade old. As featured on the inside cover of this issue, Sheng Dai (Oak Ridge National Laboratory) and co-workers review progress in ionic liquid mediated synthesis of metal and non-metal nanoparticles, porous silica, metal oxides, metal chalcogenides, porous frameworks, and materials functionalized with ionic liquids.

Tutorial on x-ray microLaue diffraction

MicroLaue diffraction combines the oldest x-ray diffraction method–Laue diffraction–with the most modern x-ray sources, optics and detectors. The combination can resolve complex materials into single-crystal-like submicron volumes. This unique ability to nondestructively map crystal structure at and below a sample surface, with high spatial and strain resolution can address long-standing fundamental issues in materials science. For example, the three-dimensional evolution of mesoscale structure and the self organization of defects can be observed nondestructively to understand the origins of inhomogeneous grain growth, deformation and fracture.

Structure Sensitive Properties of Liquid Al–Si Alloys

Development and application of new expedient aluminum-based light alloys are a key issue in current material science. In this study measurements are presented for the thermophysical properties of liquid Al–7Si, AlSi7Mg, and AlSi8Cu3 (mass%) alloys, which are the most utilized casting alloys in the aluminum industry. Experimental data with respect to the density, viscosity, and the electrical and thermal conductivities have been determined in a wide temperature range, and corresponding fit relations have been derived. Comparisons with already published data and scaling relations available in the literature are given.

Development of high density magnetic recording media for hard disk drives: materials science issues and challenges

<title/>The tremendous increase in areal density of hard disk drives is mainly ascribed to harmonic development between magnetic recording media and heads in their scaling, especially allowing a commercial transition from the longitudinal to perpendicular recording system. This paper reviews the main features, recent breakthroughs and future potentials of both the longitudinal and the perpendicular media from a viewpoint of materials science. Special attention is firstly paid to the ‘trilemma’ problem for the media, i.e. the compromise among writability, thermal stability and signal to noise ratio (SNR). The evolution of media materials these years are then addressed with emphasis on the thermodynamic origin of magnetically induced phase separation of Co-Cr based alloys, which governs media noise and coercivity, and its applications to the current longitudinal media. The materials challenges for media to achieve 500 Gb in.−2 and above are further predicted from the viewpoints of thermal stability improvement and microstructure control of media materials, and their engineering issues have been discussed for the current Co-Cr based alloys, potential FePt and CoPt ordered, phase separated Co-W based alloys and magnetic rare earth compounds. Finally, the future media approaching 1 Tb in.−2 and beyond are addressed with respect to the principles, progress, engineering challenges and future directions.

Density, Viscosity, and Electrical Conductivity of Hypoeutectic Al-Cu Liquid Alloys

New workable aluminum-based light alloys are a key issue in current materials science. In this work, thermophysical properties (density, viscosity, and electrical conductivity) of liquid Al-4 wt pct Cu, Al-20 wt pct Cu, Al-30 wt pct Cu, and AlCu4TiMg alloys have been measured in a wide temperature range. The anomalies with respect to the concentration dependence of the electrical conductivity are explained in terms of the s-d hybridization model. A comparison with data and scaling relations available in the literature is given.

A DFT study on the hydrolysis stabilities of silica molecular chains and rings based on the two-membered rings

The reactivity of silica toward to water is an important issue in environmental science and materials science for many years. In this paper, we study the hydrolysis stabilities of silica molecular chains and molecular rings based on two-membered silica ring by performing density functional theory calculations. It is found that the hydrolysis for the linear molecular chains firstly takes place in the middle parts and carries on gradually to the ends. In contrast with the early conjecture that the molecular rings might have higher hydrolysis stability than the corresponding linear chains, we find that these fully coordinated molecular rings are less stable than the corresponding molecular chains with the presence of water molecule.

Dynamical properties of the relaxor ferroelectric 0.71Pb(Ni/sub 1/3/Nb/sub 2/3/)O/sub 3/-O.29PbTiO/sub 3/ probed by brillouin and raman scattering

Abstract-Structural phase transitions in relaxor ferroelectric materials remain to be one of the most puzzling issues in materials science. In the present work, we have investigated relaxational and vibrational properties of a relaxor ferroelectric 0.71Pb(Ni(1/3)Nb(2/3))O(3)-O.29PbTiO(3) single crystal by means of inelastic light scattering measurements. Analysis based on the spectra has shown anomalous behaviors at Burns' temperature T(d), freezing temperature T(f) , those are related to a development of polar nanoregions (PNRs). The PNR must play a key role in the relaxor nature, and obtained results provide new insights into the relaxational dynamics in the PNRs and into how they develop below T(f).

Coherent Control of Optically Generated and Detected Picosecond Surface Acoustic Phonons

Coherent control of elementary optical excitations is a key issue in ultrafast materials science. Manipulation of electronic and vibronic excitations in solids as well as chemical and biological systems on ultrafast time scales has attracted a great deal of attention recently. In semiconductors, coherent control of vibronic excitations has been demonstrated for bulk acoustic and optical phonons generated in superlattice structures. The bandwidth of these approaches is typically fully utilized by employing a 1-D geometry where the laser spot size is much larger than the superlattice repeat length. In this presentation we demonstrate coherent control of optically generated picosecond surface acoustic waves using sub-optical wavelength absorption gratings. The generation and detection characteristics of two material systems are investigated (aluminum absorption gratings on Si and GaAs substrates).

Skin friction blistering: computer model

Friction blisters, a common injury in sports and military operations, can adversely effect or even halt performance. Given its frequency and hazardous nature, recent research efforts appear limited. Blistering can be treated as a delamination phenomenon; similar issues in materials science have been extensively investigated in theory and experiment. An obstacle in studying blistering is the difficulty of conducting experiment on humans and animals. Computer modeling thus becomes a preferred tool. This paper used a dynamic non-linear finite-element model with a blister-characterized structure and contact algorithm for outer materials and blister roof to investigate the effects on deformation and stress of an existing blister by changing the friction coefficient and elastic modulus of the material in contact with the blister. Through the dynamics mode and harmonic frequency approach, we demonstrated that the loading frequency leads to dramatic changes of displacement and stress in spite of otherwise similar loading. Our simulations show that an increased friction coefficient does not necessarily result in an increase in either the stress on the hot spot or blister deformation; local maximum friction stress and Von Mises stress exist for some friction coefficients over the wide range examined here. In addition, the stiffness of contact material on blistering is also investigated, and no significant effects on deformation and Von Mises stress are found, again at the range used. The model and method provided here may be useful for evaluating loading environments and contact materials in reducing blistering incidents. The coupling finite-element model can predict the effects of friction coefficient and contacting materials&apos stiffness on blister deformation and hot spot stress.

Pattern information extraction from crystal structures

Determining the crystal structure parameters of a material is an important issue in crystallography and material science. Knowing the crystal structure parameters helps in understanding the physical behavior of material. It can be difficult to obtain crystal parameters for complex structures, particularly those materials that show local symmetry as well as global symmetry. This work provides a tool that extracts crystal parameters such as primitive vectors, basis vectors and space groups from the atomic coordinates of crystal structures. A visualization tool for examining crystals is also provided. Accordingly, this work could help crystallographers, chemists and material scientists to analyze crystal structures efficiently. Program summary Title of program: BilKristal Catalogue identifier: ADYU_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADYU_v1_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: None Programming language used: C, C++, Microsoft .NET Framework 1.1 and OpenGL Libraries Computer: Personal Computers with Windows operating system Operating system: Windows XP Professional RAM: 20–60 MB No. of lines in distributed program, including test data, etc.:899 779 No. of bytes in distributed program, including test date, etc.:9 271 521 Distribution format:tar.gz External routines/libraries: Microsoft .NET Framework 1.1. For visualization tool, graphics card driver should also support OpenGL Nature of problem: Determining crystal structure parameters of a material is a quite important issue in crystallography. Knowing the crystal structure parameters helps to understand physical behavior of material. For complex structures, particularly, for materials which also contain local symmetry as well as global symmetry, obtaining crystal parameters can be quite hard. Solution method: The tool extracts crystal parameters such as primitive vectors, basis vectors and identify the space group from atomic coordinates of crystal structures. Restrictions: Assumptions are explained in the paper. However, none of them can be considered as a restriction onto the complexity of the problem. Running time: All the examples presented in the paper take less than 30 seconds on a 2.4 GHz Pentium 4 computer.

Materials Science Issues for the Fabrication of Nanocrystal Memory Devices by Ultra Low Energy Ion Implantation

Nanocrystal memories are attractive candidate for the development of non volatile memory devices for deep submicron technologies. In a nanocrystal memory device, a 2D network of isolated nanocrystals is buried in the gate dielectric of a MOS and replaces the classical polysilicon layer used in floating gate (flash) memories. Recently, we have demonstrated a route to fabricate these devices at low cost by using ultra low energy ion implantation. Obviously, all the electrical characteristics of the device depend on the characteristics of the nanocrystal population (sizes and densities) but also on their exact location with respect to the gate and channel of the MOS transistor. It is the goal of this paper to report on the main materials science aspects of the fabrication of 2D arrays of Si nanocrystals in thin SiO2 layers and at tunable distances from their SiO2/interfaces.

Biological issues in materials science and engineering: Interdisciplinarity and the bio-materials paradigm

Biological systems and processes have had, and continue to have, important implications and applications in materials extraction, processing, and performance. This paper illustrates some interdisciplinary, biological issues in materials science and engineering. These include metal extraction involving bacterial catalysis, galvanic couples, bacterial-assisted corrosion and degradation of materials, biosorption and bioremediation of toxic and other heavy metals, metal and material implants and prostheses and related dental and medical biomaterials developments and applications, nanomaterials health benefits and toxicity issue, and biomimetics and biologically inspired materials developments. These and other examples provide compelling evidence and arguments for emphasizing biological sicences in materials science and engineering curricula and the implementation of a bio-materials paradigm to facilitate the emergence of innovative interdisciplinarity involving the biological sciences and materials sciences and engineering.