In today's highly demanding technological environment, one of the main challenges in new material design is combining seemingly irreconcilable thermomechanical properties in the same component (e.g., high heat and corrosion resistance, high strength in elevated-temperature applications and high resistance to wear, and high toughness in load-bearing elements). In many cases, the problem may be solved by using coatings or by layering dissimilar materials. From a structural viewpoint, a major disadvantage of these techniques, particularly in ceramic coating of metals, has been the resulting high thermal and residual stresses and relatively poor bonding strength. Thus, in thin films, coatings, and layered materials, surface cracking and debonding or delamination have been common forms of mechanical failure. One effective way of reducing residual and thermal stresses and enhancing bonding strength has been to eliminate material-property discontinuities by grading the material composition near the interfaces or through the coating. These new materials, with continuously varying compositions or volume fractions, are known as functionally graded materials (FGMs).

In developing FGMs, research on the mechanics, and particularly on the fracture mechanics of these inhomogeneous materials, is needed to provide technical support to materials scientists and to manufacturing and design engineers. In the past, fracture mechanics has been useful both as a screening tool during material processing and as a design and maintenance tool for service-life assessment. Broadly speaking, fracture mechanics involves studying the effect of the applied loads, the component/flaw geometry, and the environmental conditions on the fracture of engineering materials.

Synthesized magnetic structures are of interest due to their unique and unusual properties, which are governed by their micromagnetic structure. For example, giant-magnetoresistance (GMR) multilayer structures composed of magnetic layers separated by nonmagnetic spacers, and granular GMR films composed of magnetic and nonmagnetic metals exhibit phenomena whose interpretation requires knowledge of both the physical and micromagnetic structure at nanometer-length scales. Techniques for magnetic-microstructure imaging are based on the interaction between a probe and either the magnetic microstructure itself (magnetization) or a physical quantity related to the magnetization distribution (e.g., magnetostriction, magnetic induction). Transmission methods are sensitive to bulk magnetic microstructure averaged along the direction of the incident probe; surface structure is lost. Reflection techniques interact with the near-surface region and no information is obtained about the bulk structure aside from those properties that can be inferred from appropriate boundary conditions.

Electron-optical methods represent the widest class of high-spatial-resolution, magnetic-domain imaging techniques. The most advanced techniques provide the highest contrast, sensitivity, and point resolution (1 nm). Electron holography offers quantitative micromagnetic information at high spatial resolution, a feature missing in most magnetic-imaging techniques. Quantitative information can be extracted from the absolutely calibrated electron wavelength and a knowledge of electron phase shifts in electromagnetic fields. High sensitivity, nanometer spatial resolution, and absolute calibration make electron holography a powerful tool for examining magnetic microstructure. In electron holography, both the amplitude and phase of the transmitted electron waves can be recovered in contrast to conventional electron microscopy where only the intensity is available. The phase, containing information about the local distribution of electromagnetic fields, can be retrieved from an electron hologram.

Micromagnetic theory concerns detailed magnetization configurations and the magnetization-reversal processes in a ferromagnetic system. By combining the original micromagnetic theory with a dynamic description of magnetization orientations, one can simulate complete magnetization processes and calculate important properties such as magnetic hysteresis and magnetic switching dynamics. Not only can micromagnetic simulation predict complex magnetic-domain configurations in a ferromagnetic system, it also can generate transient pictures showing how a complex domain configuration forms. Very important among these systems are ferromagnetic thin films, particularly those used in sensors and recording devices. Micromagnetic modeling not only has enriched our understanding of existing magnetic films but has also been used to successfully predict the magnetic properties of new film microstructures created for particular applications.

In this article, a brief introduction of micromagnetic-modeling theory will be given. Modeling of soft and hard magnetic films will be discussed separately through two examples illustrating the essence of micromagnetic-magnetization processes in these films.

A crucial step in the manufacture of very large-scale integration (VLSI) integrated circuits is the fabrication of reliable, low-resistance metal interconnects between semiconductor devices. The fabrication of these interconnects is generally performed by depositing a blanket metal film and then patterning it by lithographic and etching techniques. The primary means of depositing thin metal films for VLSI interconnects are sputtering and chemical vapor deposition (CVD).

The creation of reliable interconnects is, however, complicated by a number of issues. In order to obtain low contact resistance, to inhibit reactions with the silicon, and to provide good adhesion to both Si and SiO2, contact, barrier, and adhesion layers are generally deposited prior to the deposition of the low-resistance metal film that forms the bulk of the interconnect. If these layers are to provide an effective barrier to diffusion of the interconnection metal to the silicon, they must be deposited in a uniform, homogeneous form. It is also necessary that the primary interconnect material have as high step coverage as is possible in order to reduce current crowding, local heating effects, and electromigration. Unfortunately, as VLSI circuit densities have increased, the fabrication of interconnects requires high aspect-ratio contact cuts, and relatively severe local topographies can result. These factors make it difficult to deposit films with good step and bottom coverage.

In addition to these concerns with the film surface profile, another factor is becoming increasingly significant. Both sputtering and CVD produce thin films with characteristic microstructures. This microstructure consists of columns or grains separated by grain boundaries and voids.

Various methods are used in functionally gradient materials technology to control the composition and structure of a composite.

The chemical vapor deposition (CVD) method yields a deposit with source gases by applying variou s forms of energy (heat, light, plasma, etc.) to the gases after they are introduced into a CVD reactor. Hydride, bromide, and chloride are generally used for source materials. By continually changing the mixture ratio of source gases or by controlling the CVD conditions such as deposition temperatures, gas pressure, and gas-flow rate, CVD permits relatively easy syntheses of various FGMs (to a maximum thickness on the order of a centimeter).