Condensed-Matter Physics (1986) / Chapter Skim
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C New Materials
C New Materials
Pages 248-257
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From page 248... ...
In many cases these departures represent the limiting behavior that also makes the phenomenon of technological value, for example, the highest stored energy density or lowest hysteresis loss in magnetic materials, the highest mobility in semiconductors, or the highest critical temperatures, magnetic fields, and currents in superconductors. In this appendix we first identify the materials that have had a major impact on condensed-matter physics in the past decade, second understand how they were discovered, and third recommend how the chances of such discoveries can be maximized in the future.
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From page 249... ...
either basic knowledge or technical applications, must be closed by feedback of these results to the individuals carrying out novel and creative synthesis. The motivation for completing this synthesis loop can be scientific or technological.
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From page 250... ...
Chevrel phases were shown to exhibit superconductivity, which was then destroyed by ferromagnetism at a lower temperature. There followed exceptionally productive examples of the synthesis loop, where an extremely close coupling between basic scientific evaluation, theoretical input, and synthesis led to rapid progress and understanding of how superconductivity, ferromagnetism, and antiferromagnetism can coexist.
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From page 251... ...
The synthesis methods used in the creation of glasses include not only rapid quenching of bulk materials but also the quenching of films onto low-temperature substrates, first used to produce an amorphous material in 1954. Artificially Structured Materials The most remarkable advance in the past decade was the creation of what are known as artificially structured materials (see Chapter 1~.
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From page 252... ...
Popular materials for these studies include the two-dimensional electron gas in MOSFETs, in which the carrier density is tuned by the gate voltage, and codeposited mixtures of metals and insulators, where the carrier density is varied by changing the insulator content. Such studies have given new insight into the nature of electronic transport, elastic- and inelastic-scattering processes, the localization of electrons in disordered metals and the interactions between them, and even the phase coherence of the electron wave function in nonsuperconducting metals.
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From page 253... ...
The deposition of metals on insulators has begun to benefit from advances in vacuum and surface-science techniques, and the growth of such layers is now taking place in ultrahigh vacuum, with in situ analysis of the growing film. The ability to control substrate temperature and to deposit simultaneously or sequentially from multiple sources has led to the development of extremely versatile materials synthesis systems and may, to some extent, replace the traditional synthesis of bulk samples.
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From page 254... ...
For example, ion beam/solid interactions are being used to dope and amorphize semiconductors and to produce new metallic alloys by implantation and ion mixing, while the interaction of ion beams with organic films produces conducting layers and has applications to lithography. Laser processing of semiconductors can result in single-crystal growth and in anomalously high levels of incorporation of dopants.
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From page 255... ...
For example, drawing a Cu ingot containing a dispersion of Nb particles results in a multifilamentary wire that can be reacted to form superconducting Nb3Sn filaments. The interest to date in these multifilamentary materials has centered largely on their mechanical properties, but it has also been shown that by etching away the Cu matrix, fine single filaments can be produced that have unusual physical properties: high electrical resistivity and high strength, for example.
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From page 256... ...
MAJOR CONCERNS From the discussion above, it is clear that materials that have received the greatest attention in the last decade can be divided roughly equally into bulk materials and artificially structured materials. The major concerns of the 1980s that can be identified from what has been said in this appendix are different with respect to these two classes of materials.
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From page 257... ...
Second, in studies of bulk materials, physicists will continue to extend their interest away from perfect single crystals of simple materials to materials with complex structures and large unit cells, especially structures with internal clusters or internal channels where properties can be modified by intercalation or ion insertion. Third, the U.S.
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