This brief article describes the content of the January 2002 issue of MRS Bulletin focusing on Mechanical Properties in Small Dimensions. Articles discuss the current understanding ofstressevolution during thin-film growth, elastic and anelastic behavior, dislocation-mediated plasticity, creep deformation, and fracture. Emphasis is placed on explaining the mechanisms that underlie thewell-known fact that length scale can play a significant role in mechanical behavior.

This brief article describes the content of this issue of MRS Bulletin on Hydrogen Storage. Hydrogen is a powerful, clean, synthetic fuel with the inconvenient property of being an ideal gas under ambient conditions. In order to use hydrogen efficiently as a fuel, compacting it for mobile storage is a key issue. As an introduction to the following seven contributions on different storage techniques and their potential, we start with a description of the technical and socioeconomic aspects of the mobility and transport issues involved and present an overview of volumetric and gravimetric storage densities for hydrogen.

This brief article sets the context for the March 2002 issue of MRS Bulletin focusing on Alternative Gate Dielectrics for Microelectronics. Contributors are several experts from industry and academia engaged in the search for manufacturable solutions for a suitable alternative gate dielectric to SiO2 using high-dielectric-constant (high-ĸ) materials. Issues discussed in the articles include thermodynamics criteria for materials selection, materials interactions in the construction of the transistor gate stack, characterization of alternative materials, determination of suitable band offsets for candidate dielectrics, and integration of these alternative gate dielectrics in a manufacturable environment.

This issue of MRS Bulletin presents a review of the progress that vertical-cavity surface-emitting lasers (VCSELs) have made throughout the wavelength spectrum. A VCSEL is a semiconductor laser diode in which light propagates normal to the epitaxial layers. In its older cousin, the Fabry—Pérot laser, light propagates in the plane of the epitaxial layers and reflects from mirrors formed by cleaving a crystal facet across the active layers. No cleaving is required for VCSEL mirrors, which are formed from multiple layers of epitaxially grown or otherwise-deposited thin films. The simple twist in the direction of the laser beam with respect to the epitaxial layers is responsible for most of the unique attributes of VCSELs, which arise from their short cavity length, their completely lithographically defined cross section, and their reliance on only wafer-scale processes for device fabrication. The articles in this issue cover a range of topics, including blue devices, short-wavelength communications lasers, recent advances in 1.3-μm VCSELs, fundamental materials issues related to distributed Bragg reflectors, theoretical quantum-well gain calculations, and work on quantum-dot VCSELs.

The following is a Web Extra expanding upon the article “Understanding Precursor Phenomena for the R-Phase Transformation in Ti-Ni-Based Alloys” by Daisuke Shindo, Yasukazu Murakami, and Takuya Ohba, published in MRS Bulletin27 (2002) pp. 121–127. It provides a closer examination of the domain structure evolution over a temperature range extended beyond that shown in Figure 5 in the article, along with intensity profiles of the electron diffraction.

The following article is based on an edited transcript of the Turnbull Lecture presented by Jim Chelikowsky (University of Minnesota), recipient of the 2001 Materials Research Society David Turnbull Lectureship, at the 2001 MRS Fall Meeting on November 27 in Boston. Chelikowsky was cited for “contributions to the fundamental understanding of electronic, optical, mechanical, surface, and interface properties of bulk and nanostructured semiconductors, ceramics, and metals through ab initio calculations; and for excellence in teaching, lecturing, and writing.”

The primary aim of this issue of MRS Bulletin is to present an overview of the deployment of optical-fiber sensors in a selected range of applications. The topics covered include a general introduction to optical fibers; a review of the sensing mechanisms that are available to monitor strain, temperature, pressure, chemical species, damage, and acoustic emission; and the use of optical-fiber sensors in medical applications. This introductory article presents a brief discussion of the advantages and disadvantages of optical-fiber sensors.

The primary aim of this issue of MRS Bulletin is to present an overview of the materials issues in chemical–mechanical planarization (CMP), also known as chemical–mechanial polishing, a process that is used in the semiconductor industry to isolate and connect individual transistors on a chip. The CMP process has been the fastest-growing semiconductor operation in the last decade, and its future growth is being fueled by the introduction of copper-based interconnects in advanced microprocessors and other devices. Articles in this issue range from providing a fundamental understanding of the CMP process to the latest advancements in the field. Topics covered in these articles include an overview of CMP, fundamental principles of slurry design, understanding wafer–pad–slurry interactions, process integration issues, the formulation of abrasive-free slurries for copper polishing, understanding surface topography issues in shallow trench isolation, and emerging applications.

This introductory article reviews the topics covered in this issue of MRS Bulletin on advanced flat-panel displays and materials. The common requirements of flat-panel displays are compact dimensions, low power consumption, light weight, and high performance. Flat-panel displays are incorporated in many consumer products as well as in a large range of industrial, medical, military, transportation-related, and scientific instruments. In recent years, there have been dramatic improvements in flat-panel display technology due to an enhanced understanding of various new or existing materials as well as fabrication processes. “Flat-panel display” is a general term that includes many different types of technologies. It includes panels that are in mass production, such as passive or active addressed liquid-crystal displays or plasma displays, and those in the early production or development stages, such as organic light-emitting devices or electrophoretic displays. It also includes novel products that are based on the principle of flat-panel display technology, such as solid-state x-ray imagers. The articles in this issue cover a range of these topics.

The full potential of wireless devices remains unattainable due to limitations in battery performance. It is the thesis of the guest editors and contributing authors of this issue of MRS Bulletin that there is much room for improvement, that we are still far from the practical limits of the technology, and that materials research has the capability to pave the way for a new generation of rechargeable batteries that will offer a dramatic improvement in power delivery over anything available today. The basics of battery operation, including the relevant electrochemistry, are reviewed, unsolved problems are enumerated, and prospective solutions are indicated.

This brief article describes the content of the June 2002 issue of MRS Bulletin focusing on Electroactive Organic Materials. These materials are now being considered as the active components in displays, electronic circuits, solar cells, chemical and biological sensors, actuators, lasers, memory elements, and fuel cells. The flexibility of their molecular design and synthesis makes it possible to fine-tune the physical properties and material structure of organic solids to meet the requirements of technologically significant applications. In contrast to inorganic materials, active organic thin films can be deposited at much lower substrate temperatures (less than 120°C) in low-vacuum or atmospheric-pressure environments. It has been demonstrated that low-cost deposition techniques such as solution spin-coating, casting, and even printing can be used for the deposition of solution-soluble organic materials. These processing advantages, together with the natural abundance of organic solids, make electroactive organic materials attractive for large-area and low-cost applications.

Combinatorial methods are high-efficiency methods to create large composition “libraries” of materials, for example, continuous composition variations, and test those compositions systematically in parallel for specific properties of interest, in contrast to the time-consuming one-composition-at-a-time approach. These methods have captured the attention of the materials industry with the promise of providing new discoveries “faster, better, and cheaper.” However, in the academic community, combinatorial methods often meet with less enthusiasm, perhaps due to the perception of combinatorial methodology as an Edisonian approach to science. The facts are quite to the contrary. In addition to impressive successes arising from the application of combinatorial methods to materials discovery, results coming out of systematic high-throughput investigations of complex materials phenomena (which would be too time-consuming or expensive to undertake) provide data leading to improvement in theories and models of materials chemistry and physics. Indeed, combinatorial methods provide a new paradigm for advancing a central scientific goal—the fundamental understanding of structure–property relationships of materials behavior.

As-deposited thin films grown by vapor deposition often exhibit large intrinsic stresses that can lead to film failure. While this is an “old” materials problem, our understanding has only recently begun to evolve in a more sophisticated fashion. Sensitive real-time measurements of stress evolution during thin-film deposition reveal a generic compressive–tensile–compressive behavior that correlates with island nucleation and growth, island coalescence, and postcoalescence film growth. In this article, we review the fundamental mechanisms that can generate stresses during the growth of Volmer–Weber thin films. Compressive stresses in both discontinuous and continuous films are generated by surface-stress effects. Tensile stresses are created during island coalescence and grain growth. Compressive stresses can also result from the flux-driven incorporation of excess atoms within grain boundaries. While significant progress has been made in this field recently, further modeling and experimentation are needed to quantitatively sort out the importance of the different mechanisms to the overall behavior.

Novel phases of functional inorganic chemical systems can be efficiently explored using high-throughput thin-film fabrication techniques coupled with rapid characterization schemes. High-throughput investigation of thin-film materials has already led to the discovery of new dielectric and magnetic materials. In this article, we review various high-throughput thin-film synthesis/evaluation techniques and discuss examples of exciting discoveries and new applications of combinatorial techniques.

As a first step in the identification of suitable alternative gate dielectrics for metal oxide semiconductor field-effect transistors (MOSFETs), we have used tabulated thermodynamic data to comprehensively assess the thermodynamic stability of binary oxides and nitrides in contact with silicon at temperatures from 300 K to 1600 K. Sufficient data exist to conclude that the vast majority of binary oxides and nitrides are thermodynamically unstable in contact with silicon. The dielectrics that remain are candidate materials for alternative gate dielectrics. Of these remaining candidates, the oxides have a significantly higher dielectric constant (ĸ) than the nitrides. We then extend this thermodynamic approach to multicomponent oxides comprising the candidate binary oxides. The result is a relatively small number of silicon-compatible gate dielectric materials with ĸ values substantially greater than that of SiO2 and optical bandgaps ≥ eV.

The following article is based on the MRS Medal talk by Norm Bartelt (Sandia National Laboratories, California), presented at the 2001 Materials Research Society Fall Meeting on November 29 in Boston. Bartelt received the Medal for his “contributions to the statistical mechanics of materials surfaces.” A long-standing goal of materials science research has been to predict the long-term evolution of the microstructure of materials from a knowledge of atomic processes. This is usually extremely difficult to do in any detail because of the large number of atomic processes to consider, many of which are poorly understood. On solid surfaces, however, progress in the prediction of microstructural evolution can now be made because of advances in real-time microscopy that allow the characterization of the time evolution of microstructure in unprecedented detail. These observations directly reveal the complex relationships between collective thermal fluctuations on atomic scales and deterministic behavior on macroscopic scales. In this presentation, attempts to construct models of these observations are discussed.

The following is a Web Extra expanding upon the introductory article, “Science and Technology of Shape-Memory Alloys: New Developments,” by Kazuhiro Otsuka and Tomoyuki Kakeshita, Guest Editors, published in MRS Bulletin27 (2002) pp. 91–100.

The ability of excited states (excitons) to migrate rapidly and efficiently through conjugated polymers makes these materials ideal for use in sensors based on fluorescence quenching or amplification of fluorescence signals. The structural features we are able to introduce into these polymers have allowed us both to design highly sensitive fluorescent sensors for specific analytes, such as the explosive trinitrotoluene (TNT), and to create assemblies that control energy transfer along a predetermined path. The principles involved have broad utility in the design of sensory materials as well as of electronic devices and display components based on electronic polymers.

The formulation of slurries for chemical–mechanical planarization (CMP) is currently considered more of an art than a science, due to the lack of understanding of the wafer, slurry, and pad interactions involved. Several factors, including the large number of input variables for slurries and the synergistic interplay among input variables and output parameters, further complicate our ability to understand CMP phenomena. This article provides a fundamental basis for the choice of chemical additives and particles needed for present-day and next-generation slurry design. The effect of these components on nanoscale and microscale interaction phenomena is investigated. Methodologies are suggested for the development of next-generation slurries required to overcome CMP challenges related to defectivity and the surface topography of soft materials such as Low-κ dielectrics and copper.

Vertical-cavity surface-emitting lasers (VCSELs) based on gallium nitride semiconductor heterostructures represent a contemporary focus of research, the aim of which is to develop a new class of planar microdevices in the blue, violet, and near-ultraviolet ranges. We review recent progress in this exploratory area, to highlight the challenges and scientific excitement associated with the efforts that are under way to create flexible, short-wavelength sources for applications expected to range from biomedical diagnostics to solid-state displays and lighting.