OPPORTUNITIES IN MATERIALS RESEARCH

Priority Analysis

In order to gather many viewpoints on opportunities in materials research, both basic and applied, COSMAT solicited the opinions of a broad cross section of the technical community both on specific materials topics that deserve attention and on relative priorities for research among various classes of materials, materials properties, and processes. These inquiries went to the presidents of materials and materials-related technical societies, to pertinent Gordon Research Conferences, and to individuals known for their work in the materials field. In all, information was received from nearly 1,000 persons, including the 555 usable responses to the COSMAT questionnaire on Priorities in the Field of Materials Science and Engineering. The information was handled by two task forces: one analyzed the quantitative responses to the priority questionnaire; the other developed brief descriptive summaries of some of the research opportunities that were identified most frequently. The main results of the quantitative analysis appear below, followed by the descriptive summaries.

The methodology used in analyzing the priority questionnaire is described in Appendix A.

To assess priorities in applied research, each respondent was asked to indicate on a scale of 1 (very high) to 5 (very low) the priority that should be given to applied research and engineering in a given materials specialty (out of a list of 46) to assure progress toward a national objective (nine Areas of Impact and 52 Subareas) in



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Materials and Man's Needs: Materials Science and Engineering OPPORTUNITIES IN MATERIALS RESEARCH Priority Analysis In order to gather many viewpoints on opportunities in materials research, both basic and applied, COSMAT solicited the opinions of a broad cross section of the technical community both on specific materials topics that deserve attention and on relative priorities for research among various classes of materials, materials properties, and processes. These inquiries went to the presidents of materials and materials-related technical societies, to pertinent Gordon Research Conferences, and to individuals known for their work in the materials field. In all, information was received from nearly 1,000 persons, including the 555 usable responses to the COSMAT questionnaire on Priorities in the Field of Materials Science and Engineering. The information was handled by two task forces: one analyzed the quantitative responses to the priority questionnaire; the other developed brief descriptive summaries of some of the research opportunities that were identified most frequently. The main results of the quantitative analysis appear below, followed by the descriptive summaries. The methodology used in analyzing the priority questionnaire is described in Appendix A. To assess priorities in applied research, each respondent was asked to indicate on a scale of 1 (very high) to 5 (very low) the priority that should be given to applied research and engineering in a given materials specialty (out of a list of 46) to assure progress toward a national objective (nine Areas of Impact and 52 Subareas) in

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Materials and Man's Needs: Materials Science and Engineering which he claimed to be knowledgeable. Other information from the respondent allowed the degree of his familiarity in each instance to be taken into account in the analysis. The results of this study, integrated for each of the nine areas of impact, are summarized in Table 15. (See Appendix A for more information on priorities for applied research in various areas of impact and lists of specific research topics identified as having high priority.) It is evident that some materials specialties are considered to be a high priority in certain areas of impact, but not in others. A few specialties, on the other hand, appear to have very broad relevance (Table 16). We would emphasize that the overall priority for a specialty cannot be established simply by totaling the stars across Table 15; this would presuppose that all areas of impact have equal levels of materials priority and correspond to sectors of comparable importance to the nation’s well-being. Rather, given the goal of advancing a selected area of impact, Table 15 indicates the relative priorities of the materials specialties in that context. Respondents were asked also, in connection with each materials specialty, to assign priorities to basic research problems not necessarily identified with any particular area of impact. The results differed somewhat in emphasis from those for applied research, but the two overlapped considerably; problems described under the basic research heading were often the same as those described by others under the applied research heading. The questionnaire results for priorities in basic research are summarized in Table 17. The various types of ratings designated in the right-hand columns are described in Appendix A. The materials specialties

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Materials and Man's Needs: Materials Science and Engineering TABLE 15 Priorities for Applied Research in Materials by Area of Impact (x—indicates above-average priority; xxx—indicates highest priority.)   Communications, Computers, Control Consumer Goods Defense & Space Energy Environmental Quality Health Services Housing & Other Construction Production Equip. Transportation Equipment PROPERTIES   Atomic Structure (Crystallography and Defects) xx   x xx   x   Microstructure (Electron Microscope Level) xx x xx xx   xx   x xx Microstructure (Optical Microscope Level) x x x x   x   x Thermodynamic (Phase Equilibria; Change of State, etc.) x x x xx   x   Thermal (Thermal Cond., Phonons, Diffusion, etc.) x x x x   Mechanical and Acoustic (Strength, Creep, Fatigue, Damping, etc.)   x xxx xx   xx xx x xxx Optical (Emission, Absorption, Luminescence, Excitation, etc.) xx x   Electrical (Cond., Electron Trans., Ionic Cond., Thermoelec., Injection, Carrier Phen.) xxx x x x   x x x x Magnetic (Ferromagnetic, Resonance, Paramagnetic) x   Dielectric (Ferroelectric, Breakdown, Loss, Piezoelectric, etc.) xx x   Nuclear* (Radiation Damage. Absorption, Surface States, Catalysis, etc.) x   x   Chemical & Electrochemical* (Corrosion, Battery Phen., Oxidation, Flammability, etc.) x x x xxx xx xxx xx x xx Biological (Toxicity, Biodegradibility, etc.)   x   xx xxx x x x MATERIALS   Ceramics xx   x xx x x x x x Glasses and Amorphous Materials xx x x   x x x   Elemental and Compound Semiconductors xxx   x   Inorganic, Non-Metallic Elements and Compounds xx   x x x   Ferrous Metals and Alloys   x x x   x xx xx Non-Ferrous Structural Metals and Alloys   xx x x x x xx xx Non-Ferrous Conducting Metals and Alloys x   x   Plastics x xxx xx x xx xxx xx   xx Fibers and Textiles   x   x xx x   x Rubbers   x   xx   xx

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Materials and Man's Needs: Materials Science and Engineering   Communications, Computers, Control Consumer Goods Defense & Space Energy Environmental Quality Health Services Housing & Other Construction Production Equip. Transportation Equipment Composites   x xx x x xx xx   xx Organic and Organo-Metallic Compounds x x   x x xx x x x Thin Films xxx   Adhesives, Coatings, Finishes, Seals x xx xx   x xx x xxx Lubricants, Oils, Solvents, Cleansers   x   xx xxx Prosthetic and Medical Materials   xxx   Plain and Reinforced Concrete   x   Asphaltic and Bituminous Materials   x   x   Wood and Paper   xx   x xx x   PROCESSES   Extraction, Purification, Refining xx   x xx   Synthesis and Polymerization xx xx x x x xx x   x Solidification and Crystal Growth xx   x x   Metal Deformation and Processing   x x x   x xx Plastics Extrusion and Molding x xxx x x   xx xx x x Heat Treatment   x x   x xx Material Removal (Machining, Electrochemical, Grinding, etc.) x x x   xx Joining (Welding, Soldering, Brazing, Adhesive Bonding, etc.) x x xx x   x xx x xx Powder Processing   x x   x x Vapor and Electro-Deposition, Epitaxy xxx   Radiation Treatment (Ion Implantation, Electron Beam, UV, etc.) xx x x   x   Plating and Coating xx x x x   x x   x Chemical (Doping, Photoprocessing, Etching, etc.) xxx x x   x   Testing and Non-Destructive Testing x x xx xx x xx x xx x

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Materials and Man's Needs: Materials Science and Engineering   Communications, Computers, Control Consuner Goods Defense & Space Energy Environmental Quality Health Services Housing & Other Construction Production Equip. Transportation Equipment DISCIPLINES   Earth Sciences   x   x   Analytical Chemistry x x   x x   Physical Chemistry x x x x x x   Organic and Polymer Chemistry x xx x   x xxx xx   x Inorganic Chemistry x x   x x   Solid State Chemistry xxx x x xx   x x   Solid State Physics xxx x x xx   Ceramics and Glass xx x xx x x x xx x x Polymer Processing x xxx xx   x x   x Extractive Metallurgy   x   xx   Metals and Inorganic Materials Processing x   xx x x x   x x Physical Metallurgy x   xx xx x   x x Chemical Engineering x   x   xx   Mechanical Engineering   x xx x x x x x x Electronic Engineering xxx x xx x   x   x Aerospace Engineering   xx   Nuclear Engineering   x xx   Bioengineering   x   x xxx   Civil and Environmental Engineering   x   xxx   x   *Due to a typographical error in the original questionnaire, Nuclear and Surface Properties were entered as one item. However, respondents generally read it as Nuclear and included Surface Properties under Chemical and Electrochemical.

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Materials and Man's Needs: Materials Science and Engineering TABLE 16 Applied Materials Research Problems of Broad Implication The combined opinions of a number of materials scientists and engineers suggest upon analysis that high priority be assigned to the generic problems in applied materials research, listed below. These problems are characterized by their broad implications and, for that reason, might well be considered by academic investigators. The problems were selected from among several thousand proposed, Properties Chemical: corrosion; stress corrosion; flammability; catalysis. Biological: biocompatibility; toxicity; allergenicity; biodegradability. Mechanical: fracture; fatigue; creep; friction; wear; lubrication. Defects and Microstructure: effects of impurities and crystallographic imperfections on properties. Electrical: superconductivity. Materials Composites: fracture toughness; interfacial phenomena; reliability. Thin Films: reliability; plating and coating. High Performance: superalloys; ceramics and glass. Plastics: property-structure relations; high performance. Processes Testing: nondestructive testing; characterization; analysis; interaction with optical, acoustical, and other forms of radiation. Joining: adhesives; welding. Polymer Processing: synthesis; extrusion; molding; recycling.

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Materials and Man's Needs: Materials Science and Engineering TABLE 17 Priorities for Basic Research in Materials (x—indicates above-average priority; xxx—indicates highest priority. Appendix A for explanation of analysis.) Rank, Allowing for Familiarity     Chemists Physicists Matallurgists Engineers   Uncorrected for Familiarity Corrected for Familiarity Experts Overall Rating OUT OF 13   PROPERTIES   6 7 7 1 Atomic Structure (Crystallography and Defects) xxx xx x xx 4 4 3 3 Microstructure (Electron Microscope Level) xxx xx x xx 13 13 13 12 Microstructure (Optical Microscope Level)   12 8 9 5 Thermodynamic (Phase Equilibria, Change of State, etc.) xx x   x 10 12 12 8 Thermal (Thermal Conductivity, Phonons, Diffusion, etc.) x   5 9 2 6 Mechanical & Acoustic (Strength, Creep, Fatigue, Damping, etc.) xxx xx xxx xxx 9 4 6 9 Optical (Emission, Absorption, Luminescence, Excitation, etc.) x x xx xx 3 3 8 7 Electrical (Conduction, Electron Trans., Ionic Cond., Thermoelectric, Injection, Carrier Phen.) xx xx xx xx 8 11 10 13 Magnetic (Ferromagnetic Resonance, Paramagnetic, etc.)   11 10 11 11 Dielectric (Ferroelectric, Breakdown, Loss, Piezoelectric, etc.)   7 6 5 10 Nuclear* (Radiation Damage. Absorption, Surface States, Catalysis) x x xx xx 2 2 1 2 Chemical & Electrochemical* (Corrosion, Battery Phen., Oxidation, Flammability, etc.) xxx xxx xxx xxx 1 1 3 4 Biological (Toxicity, Biodegradability, etc.) x xxx xxx xxx OUT OF 19   MATERIALS   3 5 1 5 Ceramics xxx xxx xxx xxx 6 1 6 4 Glasses and Amorphous xxx xxx xxx xxx 7 8 7 8 Elemental and Compound Semiconductors xx xx xxx xx 12 11 13 11 Inorganic, Non-Metallic Elements and Compounds x x xx x 10 16 18 16 Ferrous Metals and Alloys xx   x x 5 10 14 13 Non-Ferrous Structural Metals and Alloys xx x x x 13 12 19 15 Non-Ferrous Conducting Metals and Alloys x   4 7 3 3 Plastics xx xxx xxx xxx 11 14 11 14 Fibers and Textiles   14 15 12 12 Rubbers   1 2 2 1 Composites xxx xxx xxx xxx 16 6 10 9 Organic and Organo-Metallic Compounds   x x x 9 4 8 6 Thin Films x xx xx xx

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Materials and Man's Needs: Materials Science and Engineering Rank, Allowing for Familiarity     Chemists Physicists Metallurgists Engineers   Uncorrected for Familiarity Corrected for Familiarity Experts Overall Rating 8 9 4 2 Adhesives, Coatings, Finishes, Seals xx xx x xx 15 13 9 10 Lubricants, Oils, Solvents, Cleansers   x   2 3 5 7 Prosthetic and Medical Materials x xxx xxx xxx 17 17 15 17 Plain and Reinforced Concrete   19 18 17 19 Asphaltic and Bituminous Materials   18 19 16 18 Wood and Paper   OUT OF 14   PROCESSES   2 4 5 8 Extraction, Purification, Refining x xx xxx xx 4 1 3 2 Synthesis and Polymerization xx xxx xx xx 8 5 9 3 Solidification and Crystal Growth xxx x xx xx 6 11 12 12 Metal Deformation and Processing x   13 12 7 10 Plastics Extrusion and Molding   11 14 14 14 Heat Treatment   10 13 13 13 Material Removal (Machining, Electrochemical, Grinding, etc.)   5 9 2 5 Joining (Welding, Soldering, Brazing, Adhesive Bonding, etc.) xx xx xxx xx 3 10 4 7 Powder Processing x x xx x 9 3 10 4 Vapor and Electro-Deposition, Epitaxy x x xx x 7 2 8 9 Radiation Treatment (Ion Implantation, Electron Beam, UV, etc,)   x xxx x 12 8 6 11 Plating and Coating x   14 6 11 6 Chemical (Doping, Photo-Processing, Etching, etc.)   xx   1 7 1 1 Testing and Non-Destructive Testing xxx xxx xxx xxx *Due to a typographical error in the original questionnaire, Nuclear and Surface Properties were entered as one item. However, respondees generally read it as Nuclear and included Surface Properties under Chemical and Electrochemical.

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Materials and Man's Needs: Materials Science and Engineering given highest priority (three stars in Overall Rating) for basic research are: Properties: biological; chemical, particularly surfaces; mechanical. Materials: ceramics; composites; glass and amorphous; plastics; prosthetic. Processes: testing and nondestructive testing. As with applied research, lists of basic research topics in the various specialties appear in Appendix A. Information from the priorities questionnaire also allowed comparisons to be made among respondents grouped according to their fields of highest degree. The left side of Table 17 shows the rankings arrived at in this way by four groups—chemists, physicists, metallurgists (including ceramists), and engineers—taking into account average familiarity within each group for each specialty. The rankings display both good correspondence and intriguing differences. It appears, for example, that those who would be expected to know most about a given specialty sometimes rate it lower than do materials professionals in the other disciplinary groups. Thus metallurgists rate the priority of basic research on ferrous metals lower than do any of the other disciplinary groups; physicists, who have much to contribute to nondestructive-testing methods and instrumentation, rate it seventh among processes, while the other three groups rate it first. A possible interpretation of the rank orderings on the left side of Table 17 is that they are arranged roughly in accordance with the degree of opportunity as perceived by the four groups of professionals. That is, the highest-ranked items are those of greatest scope and need for generating new knowledge.

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Materials and Man's Needs: Materials Science and Engineering These rankings, however, clearly must be interpreted with care. In particular, they should not be taken necessarily to indicate relative increments of needed research support; rather they might be taken to suggest the relative sizes of programs within overall materials research budgets. Nor do the rank orderings show the existing importance of various specialties to the related applied research and engineering. Ferrous metals and alloys, for example, are essential to the economy, but evidently the respondents (even the metallurgical group) felt that basic research in this field might be expected to yield diminishing returns today, perhaps because of extensive research in the past. Materials like concrete, asphalt, and wood, in contrast, have not been subjected to comparable basic research, so that the corresponding fundamental understanding may not yet be advanced to the point where research opportunities are recognizable, even by experts in the field. Yet, in view of the enormous role of the latter materials in the nation’s economy and way of life, a modest investment in research could ultimately yield a relatively large return compared with that from many other research areas. Selected Priority Problems in Materials Research Based on Questionnaire Responses Corrosion. Although much progress has been made in understanding the thermodynamics and kinetics of the corrosion process, the mechanisms of localized corrosion are not well understood, nor are those for imparting resistance or protection against aqueous or gaseous corrosion.

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Materials and Man's Needs: Materials Science and Engineering For localized corrosion like pitting and stress corrosion, initiation is distinct from propagation. Initiation may involve the breakdown of a surface film; important factors to be studied are variations in film composition and microstructure down to the atomic level and their interaction with the environment. Corrosion can be initiated also at surface inhomogeneities, but the types have not been characterized clearly. The propagation of stress-corrosion, hydrogen-embrittlement, and corrosion-fatigue cracks demands further investigation. As the use of high-strength materials increases, these problems become more important. Susceptibility to hydrogen embrittlement, for example, increases with the strength of the steel. The mechanism of stress corrosion probably differs in detail from system to system. Problems pertinent to many systems include the role of mechanical fracture; the effect of stress on the rate of anodic dissolution; continuous versus discontinuous cracking; the relevancy of continuum mechanics as opposed to atomistic analyses of crack propagation; the effect of defect structure and of chemical composition and distribution at the macro and micro levels in the metal; and the role of hydrogen generated at the crack tip. High-technology industries often must cope with unexplored conditions. Thus, research is required for corrosion in aqueous media at high temperature, high pressure, or both; in the ocean, near the surface and at great depth; in highly corrosive body fluids for prostheses; and in gaseous media for thin metal films, whose properties may differ radically from those of the bulk material.

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Materials and Man's Needs: Materials Science and Engineering Surfaces offer an extra degree of freedom for the arrangement of atoms statistically on the lattice sites. The statistical mechanics of this situation, extending in three dimensions over several atomic layers, needs considerable development. The roughness of a surface on the atomic scale has a major impact on adsorption, surface diffusion, and crystal growth, but very little is yet known about the detailed role of surface roughness in these processes. The electronic properties of surfaces in simple systems warrant considerable attention. There is some controversy about the extent to which surfaces can be treated as an extension of the bulk—that is, whether the discontinuity in properties at the surface is great enough to require new concepts and analytical procedures. Our theoretical models for surface electronic properties, surface relaxation, and surface structure are rudimentary. The extent to which surface states on semiconductors are intrinsic to the surface or associated with surface impurities is under debate. Surface states occur both at free surfaces and at interfaces, such as the silicon-silicon oxide interface. It has been shown recently that various surface states on semiconductors correlate with various surface structures as revealed by low-energy electron diffraction. Surface nucleation, vapor deposition, adsorption, and surface contamination, topics with clear practical significance are currently being investigated in detail for a variety of systems, with emphasis on the simpler systems. The kinetic and thermodynamic properties of vapor deposits can be obtained by mass spectrometric methods, and the distribution of clusters on the surface can be determined by diffraction methods. Classical surface nucleation theory is inadequate to

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Materials and Man's Needs: Materials Science and Engineering account for the results of such measurements, and major modifications of the theory appear to be necessary. Adsorbed atoms can be identified by Auger spectroscopy, even at a small fraction of a monolayer coverage. Auger spectroscopy coupled with ion bombardment can be used for profiling, to get at bulk composition profiles below the surface. Low-energy electron diffraction is just entering the stage at which the position of surface atoms can be determined quantitatively with some accuracy. These methods are also being used extensively to monitor the cleanliness and structure of surfaces and to investigate production problems involving contamination at surfaces. The electronic and chemical properties of surfaces and adsorbed species are being investigated by a variety of methods. Photoelectron spectroscopy and ultraviolet photoemission spectroscopy are used to obtain band-structure data. Knowledge of electronic and chemical bonding can be derived from ion neutralization spectroscopy. Infrared reflection spectroscopy gives information about chemical bonding, and insights concerning deep electronic levels can be obtained from the analysis of Auger spectra. The techniques developed for surface research, such as ion mass analysis and Auger spectroscopy, are providing the best, and often the only, methods for investigating materials problems associated with thin films, grain boundary segregation, interdiffusion phenomena, and trace analysis. The trend toward miniaturization in electronics, resulting from economic, reliability, and high-frequency considerations, points toward growing importance of surfaces. The concepts of miniaturization are best embodied in the technology of large-scale integrated

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Materials and Man's Needs: Materials Science and Engineering circuits, where surface and grain-boundary diffusion often dominate bulk diffusion processes. This trend is expected to continue, particularly as optical microcircuitry is developed. The elucidation of catalytic processes is not detailed in most cases. Considerable qualitative insight is available, but the roles of surface structure, surface defects, surface geometry, surface electronic properties, and even the bulk properties of catalysts have not been clarified in detail. Notable advances have been made in the area of adhesion, where knowledge of the role of adlayers and their interaction has contributed significantly. Friction is understood in some detail, especially the role and interaction of the asperities in sliding contact, but the process is difficult to treat from a fundamental standpoint, let alone circumvent in practice. From a practical point of view, the lubrication of sliding contacts is fairly well understood, but cold welding can be a serious problem in electrical contacts. Erosion, corrosion, and contamination of electrical contacts as a result of arcing remain serious problems. Deeper knowledge of the behavior of surfaces can also be expected to improve our control over the important practical problem of corrosion—the interaction of a metal with its environment. The presence of water or an electrolyte solution changes the physics and chemistry of metal surfaces significantly. The surface energy is altered and becomes a strong function of the charge in the electrical double layer at the metal/solution interface. The equilibrium surface structure may be different from that in the presence of the metal’s

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Materials and Man's Needs: Materials Science and Engineering own vapor or in a vacuum, and it presents extra problems because the interface is not readily examined in situ. Some metals, such as silver, undergo surface rearrangement in aqueous solution at room temperature. Alloys generally undergo a change in their equilibrium or steady-state surface composition. The atomistics of these phenomena are poorly defined. There is much ignorance regarding the effects of surface stress, defect structure, and nonequilibrium conditions on the reactivity of metal surfaces, and these effects are of major importance in the performance of materials. One- and Two-Dimensional Systems. Until recently, calculations of physical phenomena in one- or two-dimensional systems were considered to be mainly of academic interest. Onsager’s famous exact solution for a simple two-dimensional lattice inspired solid-state physicists and engendered hope for eventual similar success in three-dimensional systems. Within the past four or five years, however, a variety of magnetic, superconducting, and resistive materials have been prepared that exhibit exceedingly large anisotropies in their thermodynamic, transport, and collective properties. (See subsequent section on collective behavior.) The anisotropies are so pronounced that microscopic interactions along a line or within a plane may be several orders of magnitude greater than in the transverse directions. Tetragonal crystals of the K2NiF4 family, for example, exhibit inplane magnetic exchange forces several thousand times larger than the out-of-plane exchanges, with the result that below about –170ºC truly two-dimensional long-range magnetic order occurs. Neutron diffraction and optical experiments have confirmed the two-dimensional

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Materials and Man's Needs: Materials Science and Engineering nature of the electron-spin dynamics (magnons) and the critical behavior as well. Similar striking behavior in one-dimensional antiferromagnetism has been observed. Layered-structure transition-metal dichalcogenides (MoS2, etc.) have long been recognized as effective lubricants. They have now been found to be essentially two-dimensional superconductors, whose properties can be altered markedly by chemically changing the spacing between layers. Certain organometallic complexes have exhibited one-dimensional manifestations of antiferromagnetism and the metal-insulator transition. The recent evidence of unusually high electrical conductivity in some crystals made up of organic molecules (abbreviated to TTF/TCNQ) has excited considerable interest in the possibility of high-temperature superconductivity in such materials. Whether the high conductivity in fact is related to superconducting phenomena has yet to be demonstrated. But whatever the origin of the effect, if it is real it is a major breakthrough in the properties of organic materials. These discoveries have kindled lively theoretical and experimental interest in the physics of less than three dimensions. The consequences of extreme anisotropy of microscopic interactions must be explored more fully. The effects of lower dimensionality on collective modes, e.g., electron and heat transport, must be clarified. Particularly intriguing is the effect of a microscopic upper limit to the interaction distance in certain directions on the critical properties near phase transitions in lower dimensional systems. While some magnetic transitions have been studied in this context, virtually nothing has been done on structural, order-disorder, or

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Materials and Man's Needs: Materials Science and Engineering ferroelectric transitions in less than three dimensions. Further advance in the physics and chemistry of two-dimensional systems is also essential to the eventual understanding of catalysis. Because of the extreme anisotropy in bonding strength in the layered-structure materials, study of their mechanical behavior could lead to superior lubricants or high-strength components, as demonstrated already in graphite. In the usual powder form, graphite is a widely used lubricant. Precursor polymer filaments can be processed to yield dense, highly oriented graphite fibers that exhibit axial strengths that are a significant fraction of the theoretical strength. Because in some ways they are fundamentally different from bulk materials, thin films and filaments are of renewed interest to solid-state physicists. The fabrication of structures that extend only a few tens of angstroms in one or two directions has made clear the opportunity for more careful experiments and sophisticated interpretations in the physics of such structures. Two indicative examples are the observation of a nearly fivefold increase in the superconducting transition temperature in thin films of aluminum and the increased sound-attenuation coefficient of small-diameter glass fibers. Physical Properties of Polymeric Materials. Polymeric substances, whether natural (such as cotton, wool, and silk) or synthetic (including rubber, rayon, and celluloid), owe their remarkable physical and chemical properties to the long-chain molecules of which they are composed and which set them apart from a host of other materials. Recognition of the key role of long-chain molecules was one of the singular discoveries of this century. It led to intense research to

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Materials and Man's Needs: Materials Science and Engineering find how variations in the structure of these giant molecules, through new approaches in chemical synthesis, could be invoked to cause valuable changes in the physical properties of plastics. Yet, to put the structure/ property relationship of polymeric materials on a firm, fundamental, and quantitative basis remains a prime challenge to materials research, even greater in complexity than the parallel challenge posed by amorphous inorganic materials. In polymeric materials the molecules may be arranged in an orderly chain-folded fashion; in this form plastics bear some correspondence to the familiar inorganic crystalline materials. But more often the molecules are arranged in a haphazard fashion, resembling perhaps a bowl of spaghetti; this is the counterpart of the disordered, glassy state of inorganic matter. And as with inorganic glasses there can be partial devitrification in plastics. In view of the primitive state of theoretical concepts and analytical procedures for dealing with ordinary glasses, it is not surprising that we are a very long way from being able to go the whole distance of determining from first principles the fundamental properties of the polymeric molecules themselves and then the physical properties of the macroscopic plastic materials. Collective Behavior. One of the most useful concepts in solid-state physics is that of the collective mode, that is, a simple excitation of a system of interacting electrons and/or atoms. This concept has permitted the handling of complicated many-body (1023) systems in terms of a very few degrees of freedom. The basic idea is to regard the structure and composition of the system as given and to seek its

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Materials and Man's Needs: Materials Science and Engineering responses to various types of disturbance. The complete set of these responses forms the so-called “normal modes” or “elementary excitations” of the system, which provide the basis for many of its static and dynamic properties. Since a single elementary excitation involves the participation of all the atoms in the system, the concept is quite powerful in elucidating the cooperative behavior among large numbers of particles that results in a particular phenomenon or property. As was indicated briefly in the discussion of phase transitions, the collective-mode concept has been fruitful in describing even anomalous material properties. Although the elementary excitation concept has become very familiar to physicists (the words phonon, plasmon, magnon, etc., are well incorporated into the solid-state vocabulary), it still has great potential for significant growth. Extensions of the concept should prove valuable in at least two directions: (a) nonlinearities and interactions among elementary excitations; and (b) elementary excitations in systems lacking long-range order. Recent experimental advances have permitted fairly direct and precise study of the more familiar excitations on the one hand, and the generation, detection, and study of some new excitations on the other. In the former category are inelastic scattering (both light and neutron) and acoustic, magneto-optic, and certain solid-state plasma experiments. The latter include super high-frequency phonon and second-sound generation by electron-pair deexcitation in superconductors; the launching of stable-amplitude pulses of both mechanical (e.g., solitons) and electromagnetic (e.g., self-induced transparency) nature; and propagating electroacoustic domains in semiconductors. For the future, better understanding can be expected

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Materials and Man's Needs: Materials Science and Engineering of the interactions among these excitations, leading to optimized manipulation of such interactions for energy or information transfer. Less straightforward, perhaps, but certainly no less important is the second direction: studies of elementary excitations in systems lacking long-range order. In amorphous solids and liquids, effort of this kind has been under way for some time. Already, for example, some microscopic understanding of electronic, optical, and acoustical properties of such materials has emerged. Recent generalizations of the hydrodynamic equations to shorter-length and higher-frequency domains have revealed the smooth transition from collective, phonon-like behavior to diffusive and even single-particle behavior in liquids. Some of these trends should also be evident in viscoelastic solids, but the picture is not yet clear. Similar mathematical techniques have been employed to describe elementary excitations in the paramagnetic (disordered) phase of a spin system. The collective modes of the liquid-crystal state are under investigation and should illuminate that important intermediate regime between well-developed long-range order (crystal) and the more transient short-range order (liquid). Another attractive possibility lies in extending the collective-mode concept to large but finite structures, particularly to macro-molecules. From the point of view that a large molecule approximates a small solid, the existence of collective motions within the molecule is clear. However, the detailed nature of such excitations and their role in transport of charge, strain, spin, etc. within the molecule remain as unusual challenges to both theorist and experimentalist in

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Materials and Man's Needs: Materials Science and Engineering solid-state physics. A true science base for “molecular engineering” rests largely on progress in this direction. Nonequilibrium Systems. Basic understanding of the physics of materials under equilibrium conditions is far ahead of that for nonequilibrium systems. While the reasons are not hard to find (such as the limitations of thermodynamics and statistical mechanics), the increasing importance of nonequilibrium phenomena requires that substantial effort be directed to alleviating these deficiencies. Lasers and negative-resistance semiconductor devices are familiar examples of nonequilibrium physics in action. Recent progress in clarifying the transient and threshold behavior has illuminated analogies with equilibrium higher-order phase transitions. It is intriguing to consider more general instabilities such as hydrodynamic, magnetohydrodynamic, and plasma phenomena from this point of view. The problem of turbulence may be the most challenging and important of these. Autocatalytic chemical reaction systems give rise to large spatial and temporal variations in composition. The familiar convective instability can cause extreme problems in crystal growth from the melt. Indeed, the behavior of the atmosphere, the oceans, and even of the earth’s crust is strongly influenced by such hydrodynamic instabilities. With new laser techniques, materials under extreme transient conditions (shock waves and high electric, magnetic, or optical fields) can be studied in real time with a resolution of ~10–12 second. Scattering, absorption, and fluorescence experiments, which have proved so valuable in guiding theories of materials at equilibrium, should begin soon to do the same for nonequilibrium systems. A

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Materials and Man's Needs: Materials Science and Engineering foretaste of what might be in store is the use of these fast laser pulses to study short-lived excited states of radicals and molecules, with consequent insights into the detailed sequence of atomic or molecular events taking place in chemical reactions.