In 1990, almost exactly five years after C60 Buckminsterfullerene (see Figure 1) was discovered serendipitously during a series of graphite laser vaporization experiments designed to simulate the chemistry in a red giant carbon star, the molecule was isolated in macroscopic amounts. This breakthrough has triggered an explosion of research, and the molecule has already exhibited a wide range of novel phenomena which promise exciting applications. In addition to generating intense experimental interest in its physicochemical properties, the molecule holds a particular fascination for theoreticians; indeed the existence of the molecule was predicted in 1970, some 15 years before its discovery in 1985. It is interesting to consider the intrinsic aesthetic aspects of this molecule which are responsible for the extraordinary charisma it has for scientists and nonscientists alike.

Although C60 and other such molecules had been predicted earlier on the basis of theoretical considerations, the identification of these molecules by mass spectrometry in the year 1985 is an important landmark. The discovery of a ready method of preparation by arc evaporation of graphite in 1990 gave a big boost to this area of research. Today, research on carbon has undergone a renaissance and the new carbon molecules and structures probably constitute the second greatest sensation in physical science since the 1986 discovery of high-temperature super-conductivity in cuprates.

These fascinating cage molecules of carbon, containing 6- and 5-membered rings, with considerable pi electron density, exhibit interesting chemical as well as materials properties. The phase transitionh of fullerenes and the electronic properties of the derivatives of C60 are indeed interesting. And, as if this were not enough, many other novel carbon structures have recently been discovered. Nanotubes are a major discovery. Closed on either end, nanotubes can be opened by mild oxidation at the reactive site at the closed end and can be filled with metals. Carbon onions made of concentric giant fullerenes constitute another interesting form of carbon. The onions have also been stuffed with metals and metal carbides. Clearly, carbon research has many surprises in store, with promising applications. It is only appropriate that the MRS Bulletin has dedicated a special issue to the new carbon structures and we are happy to serve as guest editors, presenting a wide variety of topics that convey the flavor of this fascinating field. We begin with a personal account of Buckminsterfullerene by co-guest editor Harry Kroto.

Disorder characterizes most of the materials that surround us in nature. Despite their great technological importance, materials with ordered crystalline structures are relatively rare. Examples of disordered materials, however, abound, and their forms can be as varied as their number. The paper on which these words are printed has a disordered structure composed of a highly interconnected network of fibers. It has also been coated with particulate materials to improve its properties and the visibility of the ink. The reading glasses you may require to focus on these words are composed of a glass or polymer material that is disordered on a molecular level. Even the structure of your hand holding this magazine is disordered. These and virtually all other disordered materials are typically parameterized by a characteristic length scale. Above this length scale, the material is homogeneous and the effects of the disorder are not directly manifest; below this characteristic length the disorder of the structure dominates, directly affecting the properties.

The range of characteristic length scales for the disordered materials around us is immense. For the glass or polymer of your reading glasses, it is microscopic; the disorder is apparent only at the molecular level, while above this level the material is homogeneous. For the paper on which this magazine is printed, the scale is larger; the paper is white partly because the disordered fiber network has within it structures that are comparable in size to the wavelength of light, resulting in strong scattering of the light.

The demand for manufacturing integrated circuit (IC) devices such as dynamic random access memory (DRAM), static random access memory (SRAM), electrically erasable and programmable read only memory (EEPROM) and logic devices with high circuit speed, high packing density and low power dissipation requires the downward scaling of feature sizes in ultralarge-scale integration (ULSI) structures. When chip size becomes smaller, the propagation delay time in a device is reduced. However, the importance of on-chip interconnect RC (resistance capacitance) delay to chip performance, reliability, and processing cost is increasing dramatically. When interconnect feature size decreases and clock frequencies increase, RC time delays become the major limitation in achieving high circuit speeds. The miniaturization of interconnect feature size also severely penalizes the overall performance of the interconnect, such as increasing interconnect resistance and interconnect current densities, which lead to reliability concerns due to electromigration. Lower resistance metal and lower dielectric materials are being considered to replace current Al and SiO2 interconnect materials. Innovative efforts in circuit design, process development, and the implementation of new materials can provide solutions. This issue of the MRS Bulletin focuses on the industrial viewpoint of copper interconnects. (A previous issue of the MRS Bulletin, June 1993, addressed university research approaches to copper metallization.) Articles in this issue, from six major semiconductor companies—IBM, Motorola, AT&T Bell Laboratories, SEMATECH/National Semiconductor, NTT, and Fujitsu—provide a real-world viewpoint of the challenges faced when replacing aluminum with copper. The articles published in both issues also contain a comprehensive list of references (more than 300) to articles, patents, and device applications related to copper metallization for ULSI applications.