The emergence of the field ion microscope, invented by E.W. Müller in 1951, allowed, for the first time, direct observation of metallic materials in real space on an atomic scale. Field ionization of rare gas atoms near the surface of the material allowed production of an atomic resolution image of the material; field evaporation of surface atoms allowed observation into the depth of the sample.

Field ion microscopy (FIM) has produced numerous impressive results, one of them being three-dimensional reconstruction of defect cascades produced by heavy ion irradiation in metals. FIM techniques have also contributed in a spectacular way to the knowledge of the crystallographic structure of grain boundaries. Surface diffusion as well as surface reconstruction phenomena are applications where, again, FIM gave surprisingly detailed information. This overview of applications of FIM in materials science emphasizes recent work. Detailed information and descriptions of earlier work can be found elsewhere.

During the development of FIM techniques, the basic shortcomings of the instrument for investigating metallic alloys were rapidly recognized. In Cu3Pd alloys, for instance, Cu atoms are darkly imaged and therefore appear as vacancies similar to Co atoms in PtCo and Pt3Co. It is thus impossible to distinguish vacancies from solute atoms. This clearly limited the quantitative use of FIM to study short-range

order in dilute alloys or to investigate long-range order (Figure 1). Similarly, in two-phase materials, precipitates often give rise to quite visible contrast. For instance, in nickel-based alloys, aluminum-enriched precipitates appear in bright contrast. It is therefore possible to find the size and also the number density of particles present in the material. However, FIM does not provide any composition data.

The atom probe field ion microscope is the most powerful and direct method for the analysis of materials at the atomic level. Since analyses are performed by collecting atoms one at a time from a small volume, it is possible to conduct fundamental characterization of materials at this level. The atom probe technique is applicable to a wide range of materials since its only restriction is that the material under analysis must possess at least some limited electrical conductance. Therefore, since its introduction in 1968, the atom probe field ion microscope has been used in many diverse applications in most branches of materials science. Many of the applications have exploited its high spatial resolution capabilities to perform microstructural characterizations of features such as grain boundaries and other interfaces and ultrafine scale precipitation that are not possible with other microanaly tical techniques. This article briefly outlines some of the capabilities and applications of the atom probe. The details of the atom probe technique are described elsewhere.

The power of the atom probe may be demonstrated by its ability to see and identify a single atom, which is particularly useful in characterizing solute segregation to grain boundaries or other interfaces. An example of a brightly-imaging solute atom at a grain boundary in a nickel aluminide is shown in Figure 1. In order to conclusively determine its identity, its image is aligned with the probe aperture in the center of the imaging screen and then the selected atom is carefully removed by field evaporation and analyzed in the time-of-flight mass spectrometer. This and many other bright spots in this material were shown to be boron atoms. This example also illustrates the light element analytical capability of the atom probe. In fact, the atom probe may to used to analyze all elements in the periodic table and has had applications ranging from characterizing the distribution of implanted hydrogen to phase transformations in uranium alloys.

An atomic-level understanding of surface phenomena is becoming increasingly important as materials scientists and engineers begin to fabricate new materials by controlling their growth at the nanometer or subnanometer scale. Recent advances in molecular beam epitaxy and chemical vapor deposition make it possible to assemble a crystalline solid or epitaxial overlayer literally one atomic layer at a time. The need to characterize the structure and composition of these complex materials in finer and finer detail has forced the traditional analytical tools (e.g., electron microscopy) to strive for better and better spatial resolution. It has also generated a virtual explosion in the proliferation of scanning probe microscopies inherently capable of viewing surface structure at the atomic level. This same need has recently rekindled an interest in the technique that first allowed scientists to view a solid surface in atomic detail: the field ion microscope (FIM). The unique attributes of this instrument and its successor, the atom probe mass spectrometer, make it possible to observe individual atoms on a solid surface, to remove atoms from the surface one atomic layer at a time, and to determine the chemical identity of the atoms as they are removed. The close match between these capabilities and the requirements of modern-day materials analysis have stimulated renewed efforts to use the FIM to gain fundamental insight into materials problems. This article discusses a few selected applications of the FIM, individually and combined with the atom probe, to phenomena occurring at the surface of solid materials.

The crystalline-to-amorphous (c-a) phase transformation can be induced by a variet of solid-state processes ranging from energetic particle irradiation, interface inter diffusion reactions, hydrogen charging and mechanical deformation to the application of high pressures. During the past decade, such transformations have become the focus of considerable research not only because of their potential technological applications, but also because of strong scientific interest in the relationship between the c-a transition and the melting process.

A common feature underlies all solid state amorphization processes: The atomic disorder created in the crystalline lattice in the form of static atomic displacement can induce volume change and elastic softening of the lattice. A particularly striking example of the softening effect is shown in Figure 1 for the case of radiation-induced amorphization of the intermetallic compound Zr3Al. The compound, which has the Ll2 (Cu3Au)-type superlattice structure, was irradiated with energetic ion at room temperature in a high-voltage electron microscope interfaced to a tandem ion accelerator. The rapid decrease in the intensities of both fundamental and superlattice reflections show that irradiation introduces antisite defects (chemical disorder) as well as static atomic displacements. The disordering of the long-range ordered structure, which occurs prior to the onset of amorphization, is accompanied by a volume expansion of about 2.5% and a ~25% decrease in the average velocity of sound. This decrease in sound velocity corresponds to a ~50% decrease in the average shear modulus, which is comparable to that observed for many metals during heating to melting. The volume dependence of this disorder-induced elastic softening is also similar to that associated with heating. In both cases, the shear modulus is a linearly decreasing function of volume expansion. However, for a given amount of expansion, the softening associated with static atomic displacements is nearly twice as large as that associated with increasing anharmonic lattice vibrations.

Cheese is a popular food among people of all ages and its popularity stems from its nutritional value and convenience. Cheese comes in many varieties, shapes, and sizes. It makes an ideal snack food. The recent expansion of ethnic foods that include cheese as an ingredient is somewhat responsible for the increased use of cheese. Per capita consumption of cheese has roughly doubled over the past 20 years. The annual U.S. per capita consumption increased from 12.4 to 24.7 lbs. Rapidly expanding restaurant pizza sales and changes in lifestyles that emphasize convenience food are also major factors affecting cheese trends. The increasing popularity of pizza has caused consumption of mozzarella cheese to more than double in the past decade alone. Cheese sales in 1993 reached about $17.2 billion. Concerns over fat intake and its affect on health has resulted in a growing production of the “light” varieties, which represent about 38% of all new cheese products introduced in the past two years.

The origin of cheese as a staple in the human diet is lost in history. By some accounts, cheese has been around for 6,000 to 7,000 years. It was standard fare for the Egyptians of about 2000 B.C. and many types were made by the Romans. Cheese making skills were brought by settlers who migrated due to famine, conflicts, and invasions. The Roman invasion of Britain brought a new art of cheesemaking to that country, although cheese may have been made there previously.

Ice cream and frozen desserts are popular throughout the world, but the United States is the largest consumer of ice cream. In the United States it is estimated that 46.8 pints per capita of ice cream and frozen desserts were consumed in 1992.

Physically, ice cream is a foam in which the continuous phase is a partially frozen emulsion. Foams are also important for foods such as whipped toppings, souffle, mousse, meringue, and angel food cake. The structure of the foam affects the appearance, texture, consistency, lightness, and mouthfeel of these foods. A foam is mostly air and is characterized by high viscosity, low density, high surface area, and high surface energy. Food foams such as ice cream have an air content of 40-50% by volume. The continuous phase is a concentrated, unfrozen aqueous solution containing soluble milk salts, lactose, and added sugars. The dispersed solids (i.e., proteins, salts, stabilizer, and fat) are in the colloidal state and in the form of an emulsion. The ice crystals exist in the coarsely dispersed phase, occupying a major portion of the space between air cells.

Until the 18th century, the word “art” meant the product of the artisan (not the artist) and, by extension, also meant the product itself. Objects manufactured by craftsmen had, first of all, a useful function, although they might also have had a symbolic or aesthetic meaning. The concept of aesthetics is actually much older, considering the antiquity of Rome and Greece. And in Egypt, 3,500 years ago, at Saqqara, the first stone pyramid was engraved by scribes expressing their admiration for it.

These artisans were famous for the quality of their work, for their genius in mastering their knowledge. One is reminded of Phidias in Athens, Michelangelo and Julius II, or Leonardo da Vinci and Francois the 1st.

However, the social status of such artists was probably not very different from the status of other exceptional artisans in fields such as jewelry, metallurgy, clothing, music, etc. “Ĺart pour l'art,” a tenet which ignored the function of the object, arose only during the last century. In other words, almost all objects or artifacts in museums were originally devised and built to achieve a very specific and useful function.