Starting in the 1950s, AT&T has been involved in the design, installation, and operation of undersea coaxial cable systems to provide international and inter-island telecommunication services. These systems are analog transmission systems, utilizing frequency division multiplexing to simultaneously transmit multiple channels over a single cable. With the passage of time, and in response to an ever growing demand for services, the frequency bandwidths of successive systems have been increased to accommodate the need for increased traffic density. The increases in bandwidth have been accompanied by increases in copper ohmic losses, brought about by the skin effect phenomenon, mandating ever shorter spacing between repeaters, and consequently larger numbers of repeaters for a given system length. The reliability outlook for extending coaxial cable technology beyond its present capacity, with a decrease in repeater spacing below the current value of about 9 km, is not favorable.

Fortunately, we now have available optical fibers for transmission media. Unlike coaxial cable, the fiber medium is not limited by the skin effect phenomenon. Using fiber technology, we can transmit large amounts of traffic through a very small cross-sectional areas, using repeaters at infrequent intervals. Moreover, undersea fiber optical systems utilize digital (as opposed to analog) transmission, a format extremely advantageous in terms of transmission quality and the types of services that can be offered.

In principle, all materials science problems are easy to solve. One describes the system using quantum mechanical wave functions, solves the Schrödinger equation using the appropriate boundary conditions, and converts the result into the microscopic and/or macroscopic observables of interest. Unfortunately, carrying out this program is usually many orders of magnitude too difficult. As a result, various approximations and simplifications are introduced to obtain descriptions having the minimum complexity to describe a given class of phenomena. (A simple example is the treatment of lattice vibrations in solids using a ball-and-spring description.) Such a simplified description is called a model.

Due to the complexity of virtually all problems concerning materials, it is fair to say that the use of models is ubiquitous in materials science. In many situations, however, models sufficiently complex to describe the phenomena of interest are too difficult to be solved analytically. The computer has played an essential role in obtaining descriptions of material behavior based on such complex models. Traditionally, the amount of computer power available has restricted such models to idealized problems, which are then used as prototypes for the actual problems. Recently, however, the role of modeling has expanded to include treatment of specific and realistic materials problems. Development of these new classes of applications has been driven by the tremendous increase in computer power which has become available to the average researcher. The increase in computer capacity has catalyzed implementation of more realistic descriptions of material response.

Thin film materials pervade our everyday life as transparent conductors in LCD watches and computer displays and in defrosters for automobiles... antireflection coatings for camera lenses… optical fibers for communication … architectural glass coatings for both color and energy efficiency… solar cells… decorative coatings on plastics such as for toys and automobiles parts… a whole host of electronic and optoelectronic devices… hard coatings for cutting tools, drill bits, and bearings … even metallic coatings inside potato chip bags to keep the chips crisp!

Without thin films our lifestyles would be drastically different. And this trend toward increased use of thin film technology will only continue.

The varied reasons for using thin films and the specific deposition processes for preparing them are often complex; but usually relate to function, cost, beauty, materials and energy efficiency, and performance. In addition to technological applications, scientists are finding thin films to be an invaluable tool for investigating new physical phenomena, even at the quantum level. For instance, two of the most important new materials—high temperature ceramic superconductors and diamond coatings — are currently being made by several thin film deposition processes in order to explore both their scientific and technological potential.

Just 25 years ago the variety of deposition processes for preparing thin films was quite limited. Thin film scientists and technologists had at their disposal electrodeposition, elementary chemical vapor deposition, evaporation, and dc sputtering. Commercial equipment for electron-beam evaporation, a mainstay in the optical coatings industry, was just being developed. Most of the deposition processes reviewed in this and next month's MRS BULLETIN were either not commercially available or were not even conceived of then.