X-ray powder diffraction is one of the most widely used techniques by scientists engaged in the synthesis, analysis, and characterization of solids. It is estimated that there are now about 25,000 users throughout the world, of which about one third are in the United States. Any single-phase polycrystalline material gives an x-ray pattern which can be regarded as a unique “fingerprint,” and modern automated search-and-match techniques used in conjunction with the Powder Diffraction File (maintained by the International Center for Diffraction Data, Swarthmore, PA) allow routine analysis of samples in minutes. From an x-ray pattern of good quality it is possible to determine unit cell parameters with high accuracy and impurity concentrations of 1-5%, so that powder techniques are extremely valuable in phase equilibrium studies and residual stress measurements, for example. In addition, a detailed analysis of line shapes gives information about physical properties such as the size and shape of the individual crystallites, microscopic strain, and stacking disorder.

In the early days of crystallography many simple (and some not-so-simple) structures were solved from x-ray powder diffraction patterns, but the obvious limitations to the number of individual reflection intensities which can be estimated and the increasing sophistication of single-crystal techniques resulted in a decline in the importance of this application in the 1950s and 1960s.

Spectroscopic ellipsometry (SE) is the newest nondestructive and nonperturbing technique for characterizing surfaces, interfaces, and multilayer structures. The technique was originally developed and perfected by Aspnes of Bell Laboratories and a commercial instrument is currently available. After a brief description of the basic principles involved in this technique, one of its many applications — the depth profiling of multilayer structures — is described. Further details about SE and its other applications can be found elsewhere.

The automated spectroscopic ellipsometer that has been built in our laboratory is based on the design of Aspnes and Studna. A schematic diagram of the instrument is shown in Figure 1. It is basically a rotating analyzer ellipsometer operated by an on-line Apple computer, and it has spectroscopic scanning capability. Plane polarized monochromatic light is allowed to be incident on the sample at a chosen angle of incidence. The characteristics of the elliptically polarized reflected light is analyzed by a rotating analyzer. As Budde has shown, Fourier analysis of the detector output in a rotating analyzer ellipsometer yields the desired ellipsometric parameters Δ and ψ characterizing the material under study. Aspnes has pointed out that with proper design, alignment and operation, the precision attained is very high, and accuracy of the data is also as high as that attainable with null ellipsometers. The results of our own studies confirm these conclusions. Such measurements are carried out at a number of discrete wavelengths (˜100) distributed uniformly in the UV-visible-near IR spectral range.

We have been interested in fabricating structures which can have dimensions on the scale of molecules (˜10 Å). By producing lithographic structures on the molecular-scale length, we obtain a new class of materials with unusual chemical properties. The materials contain pores which have been shown to restrict the mobility and adsorption of molecules. This restriction is the basis of size- and shape-selective chemistry which is used in many modern separation and catalytic processes.

Features in our materials are significantly smaller than the smallest nano-structures produced with electron beam lithography. To date 20–50 Å features have been produced with electron beam lithography which uses ionization from beam-solid interactions to drive radiation chemistry in a resist layer. These dimensions are near fundamental limits which come from beam-solid interactions and the response of the resist system. Further limitations occur when the nanostructural pattern must be transferred from the resist layer into a useful metal or semiconductor structure. Methods have not been devised to fully exploit the accuracy with which resist patterns can be defined, and the smallest useful transferred structures have dimensions of ˜80–100 Å.

To produce the smallest of all lithographic structures, we use a new method for pattern generation. Instead of using radiation chemistry to define a pattern, we use the organization of layers in deposited superlattices.

Materials research is a long-standing tradition at Carnegie Mellon. Since its inception as Carnegie Technical Schools in 1906, the metallurgy program has flourished on the campus. Evolving from a single department involved in metals research formed in 1906, leading-edge, interdisciplinary materials research has grown considerably, with materials-related research now carried out in many departments. These include Chemical Engineering, Chemistry, Civil Engineering, Electrical and Computer Engineering (ECE), Mathematics, Mechanical Engineering, Physics, and Mellon Institute (an affiliate of the University), and, of course, Metallurgical Engineering and Materials Science (MEMS). It is beyond the scope of this article to cover every aspect of materials-related research at Carnegie Mellon. Consequently, we have decided to concentrate on materials and topics of particular interest to MRS members.

The current research pertaining to materials at Carnegie Mellon can be broadly classified by material type into three categories: metals and alloys, polymers, and electronic and magnetic materials.

The major thrust on research in metals and alloys is in MEMS. In addition, there are a number of complementary efforts in Chemical Engineering and Mechanical Engineering. For example, Prof. Sides of Chemical Engineering is evaluating electrolytic extraction of aluminum from its ores, while Professors Prinz, Sinclair, Steif, Swedlow, and Wright of Mechanical Engineering are examining the macroscopic flow behavior of metals and alloys and its relevance in manufacturing engineering. Prof. Prinz is also interested in vibratory compaction of metal powders, both from experimental and modeling points of view.

I would like to express my gratitude to the Awards Committee and its chairman for bringing me here today. One of the effects, and not the least, of this award is to call on my earliest recollections from the United States. In the Fall of 1956, I arrived in Boston at the Massachusetts Institute of Technology (MIT) as a postdoctoral fellow in the laboratory of Prof. von Hippel. My stay in the Materials Research Laboratory of MIT was a determining influence in my future work.

The many-body problem is the study of the effects of interaction between bodies on the behavior of a many-body system. The importance of the many-body problem derives from the fact that almost any real physical system is composed of a set of interacting particles. Another essential aspect is that the many-body problem is not a branch of solid-state or atomic or nuclear physics but deals with general methods applicable to all many-body systems.

Because of the complexity of the many-body problem, one of the preferred solutions is simply to ignore it. One can always say, “Let us admit that the particles forming the system do not interact or that their interaction is so weak that the effect can be considered negligible.” In many cases, this method produced good results, and one of the great mysteries is why.