Science often advances through the introdction of new ideas which simplify the understanding of complex problems. Materials science is no exception to this rule. Concepts such as nucleation in crystal growth and spinodal decomposition, for example, have played essential roles in the modern understanding of the structure of materials. More recently, fractal geometry has emerged as an essential idea for understanding the kinetic growth of disordered materials. This review will introduce the concept of fractal geometry and demonstrate its application to the understanding of the structure of materials.

Fractal geometry is a natural concept used to describe random or disordered objects ranging from branched polymers to the earth's surface. Disordered materials seldom display translational or rotational symmetry so conventional crystallographic classification is of no value. These materials, however, often display “dilation symmetry,” which means they look geometrically self-similar under transformation of scale such as changing the magnification of a microscope. Surprisingly, most kinetic growth processes produce objects with self-similar fractal properties. It is now becoming clear that the origin of dilation symmetry is found in disorderly kinetic growth processes present in the formation of these materials.

The importance of interfaces for material science and electronic devices has stimulated great interest in the development of surface analytical tools. Among them, modern optical techniques using lasers have attracted the most attention in recent years. They have the advantage of being applicable to all interfaces accessible by light, and the high temporal, spatial, and spectral resolutions offer unique opportunities for studying ultrafast molecular dynamics and other transient phenomena at interfaces. Optical second harmonic generation (SHG) and sum-frequency generation (SFG) are particularly being noticed because of the many recent successful demonstrations of their versatility. This article briefly introduces these newly developed surface probes, first outlining the basic principles behind surface SHG and SFG, and then illustrating the power of the techniques with selected examples. A more complete treatment of the theory can be found in References 4–6. An overview of the earlier applications can be found in Reference 3.

SHG arises from the nonlinear polarization P(2)(2ω) induced in a medium by an incident laser field E(ω). In the electric dipole approximation, P is given by:

where is a second-order nonlinear susceptibility. For a medium with inversion symmetry, it follows directly from Eq. 1 that = 0. However, at an interface the surface nonlinear susceptibility is nonvanishing because there the inversion symmetry is necessarily broken.

I must support the judgment of the Materials Research Society in naming its principal award after von Hippel. His early work was on dielectrics, and that is the area in which my own introduction to materials science was made. In fact, I habitually claim that one of the inventors and fathers of the subject was E.B. Moullin, Reader in Electrical Engineering at Oxford and later Professor of Electrical Engineering at Cambridge. In 1933 he approached my chemistry tutor, Sidgwick, saying “I have this man Willis Jackson coming to do a D.Phil, with me. He knows how to measure dielectric loss. I think that if I can put a physical chemist to work alongside him we might make that cease to be just an engineering parameter to be measured and come to know what causes it—and then perhaps design new materials which are better.” Sidgwick nominated me as the physical chemist, and as far as I am concerned that is where the subject of materials science begins.

My subject is how you should display the statistics of orientations of polycrystals. For this subject I have several heroes from the past. They are Euler, of course, Rodrigues, Cayley and Klein. Of these the most unjustly neglected is Olinde Rodrigues, which is something I have only come to know in comparatively recent years. The whole subject is one to which I have returned on and off, learning a little more each time, since it was first put to me as a problem by C.G. Dunn just about 30 years ago.

Planar optical-guided-wave devices have been in existence for over 20 years. Two interesting, informative articles can be found in References 1 and 2. Much of the early work in guided-wave optics was on passive devices, but this was also when much of the theoretical understanding of optical-guided-wave (OGW) devices was developed. This theoretical understanding applies to active devices as well. It's interesting to note that the commercialization of passive, glass-based guided-wave devices has just occurred with product introductions by Corning & Nippon Sheet Glass. Active OGW devices (i.e., ones where the light properties can be altered with an applied voltage) have been reported since about 1975. In 1985, Crystal Technology, Inc. announced the first commercially available product—a high-speed, efficient, intensity modulator. Throughout the ten years in between, a huge amount of technical literature has been generated. Most of the work has centered on the Ti:LiNbO3 waveguide technology although several other material systems have been demonstrated as well.

Materials upon which optical-guided-wave modulators have been fabricated include: dielectrics such as lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and potassium titanyl phosphate (KTP); the III-V semiconductor compounds, gallium arsenide (GaAs) and indium phosphide (InP); and a variety of organic polymers. Of these materials, waveguides on LiNbO3 are clearly the most developed and are offered for sale commercially. For this reason I will concentrate on this material system while making comparisons to the other material systems when appropriate.

The growth of single crystals with precisely controlled properties is one of the most demanding goals of modern materials processing, and its realization depends on the application of fundamentals from solid-state physics, chemistry, thermodynamics, and transport phenomena. Bulk semiconductor substrates and many high-power solid-state laser host materials are typically produced by solidification from the melt. The quality of the crystals produced this way hinges on process conditions which are predominantly determined by the transport of heat, mass, and momentum in the melt and crystal. Accurate modeling of melt crystal growth promises to enhance our understanding of existing systems and improve the design and control of future processes, thereby accelerating the development of advanced materials and devices.

Theoretical modeling is often the only way to probe the complex interactions which characterize melt crystal growth, especially the effects of process changes on internal features of growth that cannot be directly measured on-line, such as the shape of the melt/crystal interface or temperature gradients within the growing crystal. In this way, computer simulation can serve as a design tool for developing control strategies and process innovations. Further, modeling serves as a test-bed for theoretical experiments which extend our knowledge of how fundamental physical phenomena govern the process.

This report attempts to provide a glimpse of how analysis and modeling have impacted the understanding of Czochralski (CZ) crystal growth. The reader is referred to several excellent reviews for more in-depth information regarding melt crystal growth modeling.

Modern compound semiconductor devices are usually fabricated in one or more layers of single-crystal material, which are epitaxially grown on a crystalline substrate. Since most of these semiconductors decompose into their constituent components at high temperature, epitaxial growth in its simplest form can be accomplished by transporting individual components to a heated substrate, where they react to form the compound semiconductor. This is the basis of molecular beam epitaxy (MBE), where the process is carried out in an ultrahigh vacuum environment.

Growth of these materials in an atmospheric (or reduced pressure) environment is highly advantageous from a commercial point of view. However, this presents a problem, since one of the components usually has a very low vapor pressure. For III-V compounds such as GaAs, AlAs, InAs, and InP, this is the column III component. Consequently, a technique must be provided to transport these elements by means of volatile compounds. This process is known as chemical vapor epitaxy, with halogenic compounds often used as transport agents. One example of this approach is the growth of GaAs from GaCl and AsCl3. During growth, the AsCl3 is made to prereact with gallium to form volatile GaCl, which is stable at elevated temperatures and can be transported to the substrate. High quality GaAs can be made by this process, and it is widely used for making a number of GaAs devices.

Chaired by J. Murray Gibson (AT&T Bell Laboratories), S. Thomas Picraux (Sandia National Laboratories), and Barry E. Scheetz (Pennsylvania State University), the 1987 MRS Fall Meeting in Boston shattered several attendance records as it offered an unprecedented collection of leading-edge technical symposia and short courses. Activities began before the start of the technical symposia with a one-day short course on Conventional and High Temperature Superconductors on Sunday, November 29. The 20 technical symposia ran from Monday through Friday, November 30-December 4, and short courses continued through Saturday, December 5.

Rounding out the schedule were several additional events: the popular lunchtime Symposium X on Frontiers of Materials Research, a forum on Education in Materials Science and Engineering with an address by National Science Foundation director Erich Bloch, a workshop on Specimen Preparation for Transmission Electron Microscopy of Materials, the Plenary Address by William C. DeVries on “Medical and Materials Issues of the Total Artificial Heart” (to be published in an upcoming issue of the BULLETIN), and the Von Hippel Award lecture on “Orientation Mapping” given by the award's 1987 recipient, Sir Charles Frank (see p. 24 in this issue).

Total meeting attendance passed 3,500, making 1987 another year of record growth for MRS. Similarly, the number of short courses and shortcourse students rose over previous years, and the increasingly popular equipment exhibit overflowed to additional booths outside the main exhibit hall. One exhibit featured its own speaker, Yorick, a talking skeleton, from the Division of Mechanics and Materials Science, U.S. Food and Drug Administration Center for Devices and Radiological Health.

The National Nanofabrication Facility began in 1977 out of the scientific community's recognition of a national need for an openly accessible resource in microfabrication. The NNF was then known as the National Research and Resource Facility for Submicron Structures (NRRFSS). In establishing the NRRFSS, Cornell University and the National Science Foundation launched an ambitious experiment both in an advanced technology and in a new research methodology. The current charter of the facility, which differs little from NRRFSS' original charter, is to:

∎ Develop state-of-the-art instrumentation and processes for fabrication and characterization of structures at dimensions below 100 nm.

∎ Provide for both nanofabrication and microfabrication a national facility that is available to any qualified researcher from U.S. universities, industry, and federal laboratories.

∎ Aggressively pursue applications of nanofabrication techniques in a broad spectrum of engineering and scientific disciplines.

∎ Train students, scientists, and engineers in nanofabrication and microfabrication and their applications.

∎ Transfer nanofabrication technology and information to the research and development communities.

To meet these goals, faculty involved with the NRRFSS committed themselves to establishing a world-class research center. They hired staff, purchased equipment, built a new building, attracted new students and faculty, and began innovative research that either utilized microfabrication techniques or advanced those techniques.

The Institut Max von Laue-Paul Langevin (ILL) at Grenoble, France was formally founded in January 1967, with the signature of an intergovernmental convention between France and the Federal Republic of Germany. The aim was to provide the scientific community of the affiliated countries with a unique neutron beam facility applicable in fields such as the physics of condensed matter, chemistry, biology, nuclear physics, and materials science. The construction of the Institut and its high flux reactor was undertaken as a joint French-German project, with a total capital investment of 335 million French francs.

The reactor first went critical in August 1971 and reached its full power of 57 MW for the first time in December 1971. The year 1972 saw the startup of the cold and hot sources, the first instruments, and the beginning of the experimental program.

On January 1, 1973, the United Kingdom joined the Institut as a third equal partner, contributing its share to the total capital investment. In December 1986, an agreement on “Scientific Membership” for Spain was signed for a period of five years starting January 1, 1987. The ILL is a nontrading company under French civil law. The three countries are represented by the following associates: Kernforschungszentrum Karlsruhe GmbH (W. Germany), Centre National de la Recherche Scientifique (France), Commissariat à l'Energie Atomique (France), and Science and Engineering Research Council (United Kingdom). These associates are represented on a Steering Committee which establishes the general rules of the management of the ILL.

Thermal wave physics is playing an ever increasing role in the on-line characterization of semiconductor materials and devices. This is especially true for thermal wave methods that employ laser beams for both the generation and detection of thermal waves. For the modulated reflectance method discussed here, the pump and probe beams are focused on the same spot. They therefore achieve the noncontact advantage of optical methods in addition to the optimum condition for high spatial resolution, a necessary condition for thermal wave measurements on product wafers.

When a material is excited with an intensity-modulated laser beam or pump, a thermal wave is generated in the material and in the air above the sample. The material within this heated region will undergo a thermal expansion which can be detected with a probe beam interferometer or by deflecting the probe beam from the thermoelastic deformation of the surface. Since the complex refractive index of most materials depends on temperature, a modulated temperature will also induce a corresponding modulation in the refractive index and consequently a modulation on a probe beam passing anywhere near the thermal wave. A probe beam directed along the heated surface of the sample, for example, will be deflected as it passes through the heated region above the surface. This mirage effect can also be observed within the sample by directing a transmitting probe through the heated region beneath the surface. Likewise, using a probe beam directed onto the sample surface one can observe a modulation in reflection, transmission, or scattering. A related noncontact method is the photothermal measurement of infrared radiation emitted from the material's heated region. Note that with all these detection methods, thermal wave measurements can be, and most often are, done in air and at room temperature.

In 1907 Weiss postulated that a ferro-magnet has many small regions or domains that are spontaneously magnetized below the Curie temperature. In an unmagnetized ferromagnetic specimen the domains form so as to minimize the free energy, which includes contributions from the exchange energy, crystal and shape anisotropy energy, magnetostrictive energy, and so on. The actual size and shape of domains can only be calculated for the simplest geometries and for idealized materials. To investigate magnetic microstructure and how it determines macroscopic magnetic properties, we want to be able to see domain configurations and understand how the magnetic microstructure is changed by external influences and varying material properties. The observation of microscopic domain configurations can aid in engineering magnetic materials with desired magnetic properties.

Domains were first observed using the Bitter method in which fine magnetic particles collect on the surface of a specimen in the field gradients at domain walls. Domains can also be observed by electron microscopy, with scanning electron microscopy, or at higher resolution with transmission electron microscopy. Specimens must be thinned to about 100 nm for use in the TEM. This, in turn, changes their magnetic properties. The magneto-optic Kerr effect has the advantage that the signal is directly related to the magnetization of the specimen and not just to the leakage fields or internal magnetic fields as in the methods mentioned above. This technique has the disadvantage of being limited to an optical resolution of typically 1μm.

The beginning of June saw the cities of Tokyo, Kyoto, and Shanghai host to several weeks of interdisciplinary exchanges on a broad spectrum of materials topics. The meetings began with the MRS International Meeting on Advanced Materials (May 30 - June 3) and continued with the Shanghai Workshop on Characterization of Ion Implantation in Silicon (June 2-3) held as part of the 7th International Conference on Ion Implantation Technology in Kyoto (June 7-10), the 6th International Conference on Ion Beam Modification of Materials (June 12-17), and the JSAP-MRS International Conference on Electronic Materials (June 13-15).

During the week preceding the meetings, the International Trade Center grounds at Harumi were the site of an Advanced Materials and Engineering Exhibition. Machine tools, CAD/CAM, and advanced materials exhibits filled three pavilions. The Materials Research Society was represented in the advanced materials area where, through a brochure translated into Japanese, the Society and its programs were introduced to the exhibit's visitors.

The concept for the MRS International Meeting on Advanced Materials held May 30 to June 3 took root several years ago and represents the first “MRS-style” event to be organized in Japan. Based on the enthusiastic participation by Japanese scientists and by a healthy complement of foreign scientists, it should repeat. MRS First Vice President R.P.H. Chang has been responsible for the interaction between the Materials Research Society and the meeting Organizers.

General chairmen for the event were S. Somiya of the Nishi Tokyo University (currently a Principal Editor for Journal of Materials Research) and M. Doyama of Nagoya University. They assembled some 20 topical symposia which were held in two buildings of the Sunshine City complex in the Ikebukuro district of Tokyo. All the sessions were very well attended, with total meeting registrant numbers reaching over 1,500.

Realistic simulation of the atomic-scale properties of complex systems has long been a goal of scientists interested in the behavior of condensed matter. Until recently, the role of atomistic simulation techniques has been to address rather idealized problems in statistical mechanics. Treatment of more realistic materials has been uncommon not because suitable approaches toward simulating such materials were unknown, but rather because the computer power available was inadequate. Recently, major advances have occurred in the complexity of systems subject to atomistic simulation, primarily due to a dramatic increase in availability of computer power. These new capabilities have driven the development of atomic-scale descriptions of real materials accurate enough for atomistic simulation of a wide range of specific materials science problems.

In this section, we will outline several of the techniques used to simulate the microscopic behavior of an atomistic system. The first method introduced for atomistic simulation was the molecular dynamics technique, in which Newton's equations of motion for the individual atoms are integrated numerically for given interatomic and external forces. One of the first uses of this technique was the study, by Fermi, Pasta, and Ulam, of randomization of vibrational energy in a one-dimensional chain of atoms. Although the results of this initial application were to some extent unsatisfactory, the molecular dynamics technique has since been applied to a wide range of problems in the statistical mechanics of condensed media.

The high-temperature structural properties of ceramics make them unique candidates for application in such systems as advanced gas turbines and other heat engines. Of concern, however, is the variability in fast fracture strength of structural ceramics which is due, in part, to the sensitivity of ceramics to very small (e.g., 20–50 μm) critical flaws and the difficulty in detecting and characterizing this type of flaw by nondestructive examination (NDE) techniques.

The flaw sensitivity of ceramics and the typically wide variation in flaw sizes result in the situation illustrated in Figure 1, which is a frequency distribution of fast fracture strengths for a hypothetical structural ceramic with characteristic strength of 350 MPa and Weibull modulus of 5. The strength requirement, 250 MPa, for a particular application is shown. In this illustration, a significant fraction of the population of ceramic parts, 17%, has a strength below the 250 MPa requirement.

The situation illustrated in Figure 1 is typical of structural ceramics today: although in many cases the average properties of a specific ceramic may be suitable for the intended use, a significant fraction of the parts made of that material will be unsuitable. The unacceptable parts are, of course, very difficult to distinguish from the rest of the population.

Journal of Materials Research was conceived and launched in less than two years from initial conception and is now in its third year of publication. The Journal's immediate success is a result of its unique purpose and of the meticulous attention given it by a few dozen committed seientists. With little or no Publishing management experience, they were guided by their need for scientific information as they developed a Journal that would fill a void in the literature on advanced materials. The following is a description of the Journal's evolution from inception to the valuable scientific medium it is today.

Journal of Materials Research will soon begin its fourth volume, a very satisfying milestone for those of us who helped launch it. The Journal was designed to fill a unique role for researchers and the libraries which serve them. It's worth recounting how the myriad of qualitative and quantitative aspects of the Journal's creation quickly fell into place, for it's a story of dedicated volunteers, lofty goals, and an Organization which itself, at the time, was almost too young to tackle so formidable a task.

The Materials Research Society (MRS) was founded in 1973 expressly to provide a forum for reporting scientific research on new materials in an interdisciplinary format, encompassing physical, chemical and engineering developments that all affect the advancement of materials. The opportunities to do this under the auspices of the existing societies at that time were few or nonexistent.