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The Physical Sciences As the Basis for Modem Technology WILLIAM 0. BAKER In some fields of the highest innovation and sophisticated tech- nology, we are now seeing the elegant principles of twenizeth-ceraury physical science being combined into operational systems for dra- manc advances in economic and social functions. Since this tech- nology involves every aspect of the wide reaches of physical science gained during this century, we have a powerful answer to questions of the practical values of research. Indeed, I submit that the physical sciences have moved to a place where they will increasingly stim- ulate not just originate but sizmz~latelarge new fronners of tech- nology anal engineering. This discussion of the role of the physical sciences is enhanced by the context that die editors of this volume have created. Science is skillfully identified as to its human and institutional settings and its connections wad government, academia, and industry in the chapter on science and technology policy by Harvey Brooks. Likewise, Milton Katz's discussion of the legalides of innovation and He economy shows He kind of social system in which science is pursued. And He most challenging and pervasive scientific issues of all, those of bioscience and the genetic process, are treated by one of the primary explorers, James D. Watson. Thus, I have an exceptional and inviting opportunity to report briefly on how He physical sciences (nowadays almost qualifying as the "unnatural sciences") have developed as the intelligence base, perhaps even the m~nd-set, for invention, discovery, and innovation in world technology. 227
228 WILLIAM 0. BAKER CHRONOLOGY OF THE PHYSICAL SCIENCES It is usually assumed that the development of the physical sciences comes from atomic and molecular theory, postulated in Greek civilization and ex- tending into the times of Dalton and other pioneers in Western Europe. Concordantly, notions of waves and energy, of dynamics and mechanics, arose from Newton, Helmholtz, and Maxwell, attended in all cases by the indispensable Newtonian elements of calculus and other mathematics. These matters all have moved aloe=, in the last several centuries and form the conventional and highly productive basis for engineenn=, including modern and sophisticated aerospace designs and vehicles. But in this century particularly, new and compelling factors in the physical sciences have arisen These are vastly more subtle than the reasonable and even tactile phenomena of classical mechanics, fluid dynamics, and such phenomenological descriptions of how matter behaves. They were foreshad- owed by peculiarities of chemical reactions, whereby atomic and molecular conversions were increasingly shown tO be the basis for one category of transformation of matter. The periodic table of the elements and its rationalization of compound formation, electron exchange, the notion of ions in solution and of `'closed shells" all raised compelling questions. They were also implied, but not really foreshadowed, by the other domain, of thermodynamics, with Rum- ford's demonstration of the interconversion of mechanical work and heat. Especially central is the elegant elaboration of thermodynamics through the Third Law of Nernst, and admirable connections of chemical equilibria and free-energy-driven changes of state, analyzed by Gibbs and demonstrated beautifully at various schools, such as at Berkeley by Gilbert N. Lewis. What was being foreshadowed, of course, was quantum theory, quantum mechanics, and quantum statistics. Einstein's photoequivalents, Sommer- feld's operators, Heisenbera's uncertainty principle, and Bohr's structure of the atom launched the heroic era of the fine structure of matter. This was not much later than the time that J. J. Thomson, Rutherford, Roentgen, Moseley and the others laid out what was in the nucleus. The electron was the common interconnection (Figure 11. But it is important to remember that these masterworks of physical and chemical meaning, came along in pieces, not in unified understandings. Thus, although Rutherford and his school notably extended ideas of the nucleus and electron, when Einstein had thought of relativity and the interconversion of mass and energy (E = mc2), Ruth- erford was dubious. He is quoted as saying, to economist and humorist Stephen Leacock, "Oh, that stuff. We never bother with that in our work. '' ! Hahn and Strassmann then revealed what other particles could come out of the nucleus in fission, and others showed what could be converted in fusion, bringing us to a world where "unnatural science,'' and "unnatural technology" combine, even to threaten nature on the planet.
TTIE PHYSICAL SCIENCES AS THE BASIS FOR MODERN TECHNOLOGY ELECTRON CHARGE in, MASS MAGNETIC MOMENT 229 FIGURE 1 The electron (represented in this figure by its principal parameters) was recognized as the basic scientific unit for electrical engineering,. I have moved over this chronology of the physical sciences in order to account for what is presented in the remainder of this chapter. I submit that the physical sciences have moved since midcentury beyond their central position in intellectual understanding of the nature of the universe through physics and chemistry to a place where they will increasingly stimulate not just originate but stimulate large new frontiers of technology and en- gineering. This relatively recent situation is already having back-reactions of the kind identified by Harvey Brooks. But the complexity of such relations and the implications for research, education, and the acquisition of under- standing for its own sake are yet barely grasped. Let me speculate briefly on how this phase of He physical sciences emerged. It is said that the earlier preoccupation with individual atoms and molecules detached the fundamentals of the then new physics and chemistry from technical applications. The reason was that applications of new knowledge in technology and engineering, almost always involved massive assemblies of these new entities recognized as atoms and molecules. Even in the ;,as phase, which was a less common condition, but always in liquids and solids, there were numerous and complicated collisions and other interactions that were thought to obscure, perhaps hopelessly, the great appeal of being able to deal with individual particle behavior, or at least things beyond three- body interactions. The =,reat virtue (and indeed charm) of our century, especially of our last half century, has been the casting off of those shackles of thought. More importantly, it has been the inspired realization that the science of masses of matter, namely the therrnodynam~cs noted earlier, and the mechanics of individual molecules, atoms, ions, and particles could be wonderfully and elegantly merged. Thus, the quantum mechanics noted as the portal to the revolution, with its superb principle HE = Ed, is joined with the Second
230 WIGWAM 0. BAKER Law of Thennodynamics AF = AlI - TAS in concepts and quantitative formulations of matter and energy, of physics and chemistry. Hence, in marvelous ways our descnpt~on of nature, while incomplete, is now inclusive enough that we are seeing results as technology generated from the under- s~dina of how matter could be adapted to economic and social needs. One other element ought to be emphasized. It is Be work of the Braggs, following RoentgeIl's discovery of X rays. They found ways to lay out Be geometry, or the actual positions, of atoms and molecules In masses, by wave diffraction of X rays. This was reinforced and generalized by Davisson and Germer's discovery in Bell Laboratones of the dualism of waves and electrons and their demonstration of electron diffraction from the interaction of solid surfaces, as well as gases, with electron beams. Important industrial differences between two classes of nylons (a polymer discovered by Carothers at Du Pont) are revealed by X-ray diffraction showing how the molecules associate (Figure 2) SCHEMATIC Of SOLID STRUCTURE OF ~LYA~ 1~ C~AtNS hlADE FROM O=- NUMBERED ~)-AMINO ACIDS OR EVEN NUMBERED Dl(AMl~JES AND ACIDS) ~0=! SC hiE - AT IC Of SOLID STRUCTURE OF POLYAbtlDE CHAINS MADE FROM EVEN- NU~BERED CL-AMINO ACIDS OR ODD NUMBERED DI(AMINES AND ACIDS) ...o=< ~-~'0=< TO-DO-: ~N-~- 'N-1~ 0-< > > < - ''O=<N H < } ~ < > >=0--~-~' >=0-- 0= > < - ~~ >=0~ ~-N SO-SO=< > N -JO=< -~-' N-bl--O=< ~ ~ ~ I__. ~ --0=> ~ ~ ·-0=? ~-~0=< ~ ~ 0= ~ A- A- O=< ,N -~-- < - A- 0=; > ~ N-~- -°=~_~.~o=: ~ < NH--O= ~ N_~~ <=0--~- No -.HN :=O--~-N: :-0- FIGUR£ 2 Knowledge of detailed molecular structure and molecular packing in con- densed phasesas illus~ated in this figure by the varying molecular arrangements in the nylon families originated by Carothers now underlies the technology of synthetic fibers, plastics, rubbers, and other materials.
THE PHYSICAL SCIENCES AS THE BASIS FOR MODERN TECHNOLOGY 231 APPLIED SCONCE SUPPORT FOR INNOVATION AND TECHNOLOGY So now science is prepared to reinforce technology and engineering on the basis of the fundamental units of nature, of particles and energy. And new things are suggested and become technically attractive because of their scientific reality and qualities. This can be illustrated by a few case studies which in fact relate to major innovations and economic forces of these times and the years ahead. Crystals and Glasses The first case study is about the solid state and the role of crystals and glasses in modern manufacture and in high-performance systems, such as aerospace, electronics, computers, information handling, and communica- tions. We see that the scientific concepts described are now permitting statistical descriptions of real crystals. These crystals are regular arrangements of atomic units (ions, molecules) in cells. They aggregate in various geometrical forms, often randomly (Figure 31. But there are also vacancies or other imperfections inside the cells as well (Figure 41. We now find that the strength of matter, especially of metals and alloys, is often determined by the quantity and mobility of these dislocations. Science is showing how they can be pinned down, to inhibit the collapse of bridges and supertankers, for example Computer models of how crystals are formed have been created by Jackson and his contemporaries. The computer models illustrate how modern science is guiding technical improvements in the solidification of matter where hordes of atoms, not just two or three, are interacting (Figure 51. Yet the composition of the crystals may be pure within parts per billion or better, thanks to We zone refining discovered by W. G. Pfann as a foundation piece for semiconductor electronics and, ~us, the modem electronics industries. The scientific knowledge of what must and can be done in terms of Be perfection and purity of these systems has supported technical advance, so Hat electrical conductivity ranging over more than 10 orders of magnitude can be carefully regulated. Further, these solids, as glasses, are forming a new foundation for photonics, again with the requirements of purifier from light-absorbing and light-scattering elements of parts per billion (Figure 6). With silica glasses, the light transmission is as much improved in the last decade as it was in 3 ,000 years of earlier history of making glasses transparent (Figure 71. The latest figures on light beam losses of intensityless than 0.16 decibel (dB) per kilometer of pathway in the glassmean a "liquid" so clear that to lose as much light as through an ordinary high-quality win- dowpane would require that He new glass have a Pam a mile or so Hick! As might be expected, some of this glass is very strong, with filaments
232 WI! ~ lAM 0. BAKER ~N6LE CRYSTAL ~1~1111~1i111!'.- ~-lUTll,Tlll! At ~TItI:~T~TTI ~1 I T I ! I 1 I T I T T ': ', 11 | ~ ~1! T'11111~1 111 . If , 1: POLYCRYSTAL , RANDOM TEXTIJREB FIGURE 3 The orderly structure of solids creates c~ystallites. which in turn may them- selves be arranged in various orientations that govern useful properties of the solids. FIGUF{E 4 C~rstallites forming from regular packing of atoms, ions, or molecules are usually not quite perfect. Some missing units or vacancies occur, as shown in the schematic building up of a solid from identical (model) cubes.
THE PHYSICAL SCIENCES AS THE BASIS FOR MODERN TECHNOLOGY 233 C_. FIGURE 5 Real crystals form by a series of cumulative atom placements. apparently aided by nuclei, or centers, such as in this computer-~enerated model conceived by Jackson. Oilman. and their co-workers. MAXIMUM TO LERAB LE CONCENTRATIONS FOR VARIOUS IMPURITY IONS Element Iron Co pper Chromium Cobalt IV anganese Nickel \/anadium Concentration, parts per billion 20 50 20 2 100 20 100 Concentration calculated from published values. Only one element is assumed to be present and In its worst valence state. Maximum tolerable loss is assumed to be 20 dB/km. FIGURE 6 Technical properties of engineering materials are often influenced by ex- ceedingly small quantities of impurities, through composition, packing, and forces in the solid state. Thus, the clarity of supertransparent light-guide glass is determined by the indicated (tiny) tolerable portions of common metallic elements.
234 WILLIAM o. BAKER . ,. it_ . .~.. ~ -H-ISTORI.C)AIE^FtEDUC.TION.- .O.F.. ~ . .., . . . .-. ;. - - ; i._- .. · an, An. ~ · . - =-~ ~ - QP.TI-CA-3~Li5SS- IN - GLASSES -;. it.. ... _~.. ~ . . .. . . ._ ... ... . ... . . Em, at_ ~~ = · ,~ Em,. ~ ~= as- I' ~ -em-- 107~- _. . .. .. ....... . lo~ :-. .. ....-.. ~ .. . . ---, y' . . 105 ~ ..... m- .. ... .. ,o4 . _ I ORGY ~ T I A N VENETIAN . BOHEMIAN '\\ \ O.1 ,. ~ 10 32 .... 63 3000 ~ 1000 1g00 i 1970 ~ 1! 379 - BAWD - - - 60 '78 ~ - - :- \ 1 _ . - Oh c, ' - 103 - -- .... ~ .. _.. a= . :_ 100 ~ . . Q. 0 : LITERATURE ~ _ 40 REFERENCES \ _ \ ~ `__ . . . . . . _ . _ . LOG; YEARS BACK FP`OA/l 1980 - -~ FIGURE 7 Illustration of the application of modern scientific pnoc~ples to Me punfication of glass, showing improvement in clarity (reduction in losses). In the past decade photon transmission has been increased almost as much again as the increase achieved through empirical improvements of the preceding 3,000 years. breaking only rawer uniformly in stresses of 800,000 to 1 million pounds per square inch, or much closer to the theoretical strength of SiO2 than was ever imagined to be possible. Phase Rule Applications Another fascinating example of how the bulk science of thermodynamics and the fine structural concepts of crystal structure and atomic interaction have combined is found in the modern applications of Me phase rule, enun- ciated by Gibbs. Namely, Plewes Figure 8) and his contemporaries have applied the complex distribution of phases in metal alloys, called spinodal
THE PHYSICAL SCIENCES AS THE BASIS FOR MODERN TECHNOLOGY 235 Decomposition (illustrated by classic gold-platinum liquid-solid curves; (see Figure 9), so precisely for Cu-Ni-Sn systems that defects and dislocations caused by the imperfect nature of crystals have been controlled in bronzes to give 300 percent of more improvement in yield strength (Figures 9 and 10) This has been applied dramatically to bronze springs and relays (Figure 11) and to a host of control systems for machines. But it represents, also, a historic reminder of what the physical sciences lead to. Recall that the destiny of kingdoms, of empires, and indeed of civilization was determined in the Bronze Age by the strength, the hardness, of the weaponry, shields, and spears made of bronze. Certainly much human ingenuity was devoted to the improvement of such metals, yet In the 1970s, the latter part of the twentieth ~ ~ :.f_<-'~ L~` ~, A' ~~ a, ~ _ ;_ 1~_;~ l P:'- art" " i'_ ~ .~'~ ~ .~ 1 1 me' ~ =~ - ~ ,_: 3 ~ ~ 'I iA , ~ '-I a,.. ~ __ FIGURE 8 Plewes measuring new mechanics of special spinodal bronzes.
236 1800 1600 1400 L) 1 200 o 1= 100 a -200 ~300 WI~AM 0. BAKER a(s) 1000 800 T1 600 1 1 1 1 t I +100 ; ! 1 ' j 1 `, 1 ~ 0 20 40 60 £~0 100 \1 1 L'qu i d \ L i quid ~ at\ '\N // \ I i ~ / / al(S)+a2ts) S / 1 1 \ am \ l L\: 1 1 ~ I t 1 1 ! At °/0 Au in Pt PHASE DIAGRAM FREE ENERGY CURV E AT T' a: INSI DE SPINODAL B: OUTSIDE S P I ~ O ~ A L FIGURE 9 Phase dials showing the fund~en~1 thermodynamic variations with temperature in the composition of varying amounts of gold in platinum, from which it is possible to select certain processing conditions yielding combinations of crystals of optimal physical properties in the alloy
THE PHYSICAL SCIENCES AS THE BASIS FOR MODEM TECHNOLOGY 237 TYPICAL MATERIAL YIELD STRENGTH (1 03pSi) ENHANCED YIELD STRENGTH (103psi) Cu-5Sn (PtlOSPttOR BRONZE) 70 110 TEXTURED Cu-12Ni 28Zn (NICKEL SILVER) 65 125 " Cu-9Nt2Sn (.IIOD. CUPRONICKEL) 45 105 " C~1.7Be (CI~PER BERYLLIUM) 145 170 " Cu-9tl-6Sn (.IOD. WPRO~CKEL) 50 150 SPINODAL FIGURE 10 Examples of structure enhancement compared to conventional yield strengths of classic bronzes and other copper alloys. Note the twofold improvement of nickel-silver alloy resulting from orientation of crystallites, and the threefold improvement of cupro- nickel by spinodal control in the processed solid. =; Or _, I : ,..' ' . . .. .. 1 11 _ ~ I At =, ~ l - . . :1 ~ l ~ _ I. ~1 it.; ~?~ ILL Al FIGURE 1 1 Application of scientifically processed alloys in the manufacture of essential commercial control equipment.
. . : ~ - - ~ ~ - - . 238 Wll ~ l~ O. BIER century, greater strengths were generated for bronzes (in some cases by controlled texturing from knowing Me crystal structure, but in the best cases from the spinodal decomposition) than from the massive empirical efforts of earlier centunes. These relations of structure within solids to overall properties provide many new ways of improving materials. Purity and heat treatment can modify the content of dislocations, as shown by etch pits in the pioneering work by Pfann and Vogel (Figure 121. These demonstrate that atomic positions indeed affect the total energy balance in the solid. Similarly, the distance between atoms (and ions) is reflected in Me mechanical stiffness of the solid (Figure 131. In turn, that stiffness relates to the familiar '`hardness" of families of solids, in ways reflecting the valence, or quantum mechanical binding, of the various elements (Figure 141. Thus we can see Me reasons for varying, the tensile s~eng~s of substances that provide shelter, clothing, machines, and defense (Figure 15~. From gemlike single crystals, at one extreme (Figure 16), to combinations of ordered and amorphous molecules of polymers implied in electron- microscopic images of nylons for textiles (Figure 17), and polyethylene for plastics (Figure 18), scientific principles correlate with engineering uses. ...... i. At: `~ - .'w'~` - ' ,. ~ I` :^ ' . - , i. - FIGURE 12 Direct evidence of dislocation arrays in crystals, derived from the etching behavior of high-purity ger~llanium.
THE PHYSICAL SCIENCES AS THE BASIS FOR MODEM TECHNOLOGY _t C EN - E 104 103 ~ I I I I I I I I ~ \ \ C44- 225,OOOr~ C44- 528,000r~5 ·\ BAs \S i \ Gape age i Fit AlAs GaAs~ \ ~ Alsb \ InAs~\ \ ~InSb Nil FO\ as\ LiCI\ \ O \ LiEr ~NaCI KFO ~ I 1 1 1 NaBr \~?N~I KCI O\ . _ ~X 1.6 &0 2.4 2.S 3.2 3.6 INTERATOMIC DISTANCE ( 5) 239 FIGURE 13 Stiffness of a variety of simple solids as a function of the separation of atoms, or ions comprising them, showing that those which are bound tightly at very short distances are 10 to 100 tunes stiffer than those having longer separation between the units. Again, the fundamental atomic character is directly reflected in gross mechanical behavior. 1
240 WILLIAM 0. BAKER 104 K)3 cu oh co He to2 c 1o1 ~ ~ ~ "'1 ~ ~ i I ~ "'1 ~ l~L sic=/ COVALENT ~ / CRYSTALS /~< She \ GaPoi Edge ~GaAs /Gasb / Aunt / ~ THAI Sb IONIC ~ CRYSTALS ~ fir _iX ~ NaF- / / C~oPt / Au`~/Pdt ~ H/C44 0.013/ / Jo NaCI~/ /~Ag FCC RETAIN _ ~ / - K/KC~ - · KI pi ,,,, ,,,1 104 , . ,,, ., 105 103 SHEAR MODULUS (C44), K9/mm2 FIGURE 14 The familiar hardness of matter is directly reflected in the shear stiffness (modulus), characterized Trough the science of atomic composition and spacing. Material Silica Boron Filaments Deposited on Tungsten Patented Steel (0.9C) Tungsten Wire Graph ate F iber Keviar 49 ,B-Ti (1 3V-1 1 Cr-3Al) Nylon 66 Fiber Metal l ic G. lass ( Fe.72Cr.08P.1 3C.01) Mete I 1 tic G lass ( Pd.7 75Cu 06Si 1 65 ) Cu-12% Nib% Sn Tensile Strength (GN/m2) 10.5 7.0 4.2 3.9 3.2 2.8 2.3 1.05 3.8 3.S 1 .6 FIGURE 15 Examples of tensile strength in giganewtons per square meter (gn/m2) of various atomic and molecular compositions, showing, effects of atomic properties on gross mechanical behavior.
_ pe~4 Is AS ~~- 3~ ~ ~~ ~~:~;= Id Icy s - ~~ an, ~5: ~~ .~-~: ~ 0~0 ^~: Ems. sow =:~0 huge speck: o~ (ceded ~ dams ~ :~. `~ t7 E7s=~n Croak o; polvm~ w:~^ hIus~g 6 - Em. ~~m onenmnon of Is as ~ ~,~t of exs-.~ or ~~= :~e dim ~:s:~.im~ Steal s~herelu;~ Is.
242 WIGWAM 0 BAKER FIGURE 18 Electron ~crosco~ picture of complex s~ct~e of ~ imp commercial plastic, polyethylene, indicating how long chain molecules form Reboils which then extend between sphen~lite and senucrystalline aggregates. Hydrocarbons The combination of the macroscience of energy and entropy and the mi- croscience of structure and quantum mechanical binding and interactions appears in other domains Hat are already decisive in twentieth-century civ- ilizat~on and economy, and it is also likely to have continuing profound effects in the developing world for centuries to come. An example is hy- drocarbon, among other carbon derivatives. In the case of hydrocarbons, the most prominent application is their use as the energy source for heating and internal-combustion engines, as in automobiles. However, they also play increasingly important roles as hydrocarbon polymers, like polyethylene and polypropylene. Their use as packaging, insulating, and preserving material, even as plumbing and water-distnbution ducts, as well as dielectrics for
THE PHYSICAL SCIENCES AS THE BASIS FOR MODERN TECHNOLOGY 243 electrical energy and telecommunications systems, may eventually have as profound an impact as in fuels. They constitute, therefore, a rather suitable example of how the vast technologies represented in these uses are directly and effectively supported by physical science. We need to know, for instance, how hydrocarbons oxidize, which is the basis for their use as an energy source. But, on the other hand, for their use for packaging, plastics, ducts, diele~cs, and so on, prevention of oxidation is paramount. It has been admirably established, and is being continually refined, Mat this is a chain reaction involving radicals whose influence can also be modified (or inhib- ited) and relatively well controlled (Figures 19 and 20~. We see further that in such crucial uses as cable, piping,, plumbing, roofing, and other structures, hydrocarbons like polyethylene and polypropylene can be decisively protected against oxidation by small amounts of carbon black or other chemically and physically elegant reagents (Figure 211.These cir- cumstances are all the result of applying atomic and molecular theory and scientific analysis to these synthetic materials or their natural petroleum precursors. KINETIC SCHEME FOR HYDROCARBON OXIDATION (1) RH (2) R' + O2 (3) ROO- + RH (4) ROOH (5) RO-+RH (6) HO-+RH R ROO ROOH+R RO- + HO- ROH + R ~ HOH ~ R' (7) ROO'(RO' etc.) ~ Inert Products (it ROO' + AH (9) RO'+ AH (10) HO' + AH RH= POLYMER initiation Propagation Chain Branching T. , . ermlnatlon ROOH + A ROH ~A' Inhibition HOH ~ A' AH = /NH/B/TOR FIGURE 19 Chemical steps in the major process of burning hydrocarbons, as in auto mobile engines, and in stabilizing hydrocarbon polymers, as in plastics, against degra- daiion by similar oxidation in the atmosphere.
244 WIGWAM 0. BAKER A ~ _ z X _ O _ INDUCTION PERIOD Tl ME TO REACT WITH A SPECI F I C VOLUME OF OXYGEN / J / / / / TI ME ~ FIGURE 20 Typical example of behavior of an unstabilized hydrocarbon exposed to air, showing gradual early reaction followed by rapid oxidation. ¢ 50 40 on o 'A 30 z al 20 Z 10 w x o . _ L~ HIT :~ ~ ~2S~ _ _ o E 4~¢ ~~ 0 100 200 300 400 500 600 700 800 900 1000 TIME IN HOURS (AT 140° C ) FIGURE 21 Example of important commercial stabilization of plastic against air oxi- dation, as a function of weight percent of carbon added. Surface Technology Beyond Be pervasive domains of bulk matter and of media for light guides, cables, and the like lie many other examples of how extensive innovations and engineering are emerging increasingly from applied science. The wide realm of surface technology is a compelling example.
THE PHYSICAL SCIENCES AS THE BASIS FOR MODERN TECHNOLOGY 245 Take first the films on which much of modern society depends, for instance, paper. The control and fabncat~on of paper depend heavily on gauges and machine responses generated by radioactive isotopes. Indeed, the modern chronicle of surfaces and films, which define so much of our economy and the substance of the information age, now illustrates a fine coalition of atomistic science. In this, quantum mechanical knowledge of particles, fields, charges, and bulk matter behavior developed from work in modern solid- state theory and experiment, reveals the detailed configuration at surfaces. For instance, semiconductors, transistors, and other junction devices are activated electronically by certain additional atoms, called donors or accep- tors, which shift the charge populations and field conditions in germanium, silicon, indium phosphide, and so on. These effects are themselves deriva- tives of the classically recognized electron-holding or electronegativity effects in the elements. For decades, such behavior in ions and homopolar systems, metals, and insulators has been a major topic in physics and chemistry. Classes of matter can be categorized as to electrical conductivity by these electronegativity effects (Figure 221. 105 103 E 10 ~ ~3 10-5 ~o7 . ' I ~ G,~~9 ' METALS InSb .UAu ( ·Li3Bi KAu \~Pb=) Tl(I) ~93 ~2~In=) /:R"U Gates ~=:~0 t · . Li WOK - - sb(m In(m) \ ~ GoI3 MOLEC1JLAR MELTS M-X (HALIDES) t OF LOCI oBr PI AS M-Y (CHALCOGENIDEI;) ·Se aTe M-M' (METAL-METAL1 - ELECTRONEGATIVITY DIRE FIGURE 22 Diagram of electrical conducting properties of diverse classes of materials, as determined by the electronegativity differences in their atoms, showing intimate con- nection of atomic structure with technical electromagnetic behavior.
246 WI] ~ l~ 0. BAKER Inventions for getting these atoms (e.g., arsenic, phosphorus, and others) into the junction devices by diffusion and other clever methods dominated the early periods of integrated circuitry (Frosch and Denck). However, ad- ditional ways have especially been applied to Win films and surfaces. One of the.best has been to accelerate ions, as Cockcroft and Walton have done in the fundamental study of nuclei and of elementary particles. These ions can then be implanted into the surfaces of the semiconductors and produce, at appropriate depths and concentrations, the desired electronic responses. The whole system of ion implantation is also interesting, for its potential for improving wear on the surface of bearings, for generating new catalysts, and especially for inhibiting corrosion. Every phase of its application in technology, however, is based on the experiences of the original scientists interested in colliding particles and elementary interactions. A particularly fascinating modern instance of the continuing, versatility of this science is how beams of ions can be directed down certain channels or pathways in crystals or films to produce not only importantly modified struc- tures, but also information from scattering and interactions about the nature of their host solid (Figure 231. Electron beams are among the simplest but most highly useful embodi- ments of these particles. Here, in the work of J. West and collaborators, the old technology of makin, electrets has been recast (by charging surfaces of insulators). Now, all advanced telephones depend for their voice transducers not on the century-old (and invaluable) performance of carbon microphones, but on charged films of special polymers like polytetrafluroethylene. These have been treated so that when bombarded with an electron beam (Figure 24) the electrons are trapped quite permanently. The result compares with what we have learned about the trapping of charges in silicon and germanium. This realm of organic-polymer capture of electrons produces the most ef- fective voice transducers so far achieved, and it is opening much more widely the fields of teleconferencing and other special microphonic uses. It is also suggesting new realms of scientific research related to energy processes in living tissue, such as ion transport across membranes. Particle bombardment can, of course, be extendedin the sense noted earlier about the dualism of waves and particles (Bohr's complementarily principle) to beams of photons, which are still smaller particles than elec- ~ons. In this case laser-pulsed beams on the surfaces of crystals produce valuable and increasingly used effects A burst of photons lasting a hundred- millionth of a second from a laser of 532-nanometer wavelength causes heating at a depth of a micrometer in a silicon surface. This heating, is immediately quenched, at about a billion degrees Kelvin per second transient, by the solid below the surface. Vanous important metastable conditions can thus be obtained, as the current work of W. Brown and his associates dem-
THE PHYSICAL SCIENCES AS THE BASIS FOR MODE~ TECHNOLOGY -- ~ CHANNELING ION BEAM 1~ ~ O O O O O~ O O O O O O O O O O O O O O O O O O O O ~ O O O O O O - __ o ~S - J ~ lo_C_ J W _ lo-2 100 - p RANDOM B CHANNELED I I 77 _ _: _~< B RANDONI \p CHANNELED SILICON IMPLANTAT10N WITH 400KoV BORON OR PHOS. 10ls IONS /CM2 . . 1 . . J o 247 200 °~00 600 800 ANNEALIN(; TE~PERAT\IRE (°C1 FIGURE 23 Examples of distribution of ions implanted by nuclear accelerators into single c~ystals of silicon, as determined by the directions in the crystal and subsequent heating to redistribute the acceptor (boron) or donor (phosphoms) units.
248 WIGWAM 0. BAKER . . , ~ c~ ~ · ~ -. ~ ~ ; ~~ ~ ~ '' ' ~ Ailll.^ ~ ~ ~ ~ ~ ~ ~ 4~ _ ~3 FIGURE 24 Schematic of implantation of electrons in polymer films to form long-lived elec~ets, which then can act as efficient microphones and other electromechanical ~ans- ducers. onstrates, aloe, with that of others working in this field. Indeed, this process can be regulated so that the entire heating effect is due to electron-photon collisions, rather than a conventional phonon excitation by movement of the bulk atoms in the solid. Nuclear Science and Radioisotopes Recall, also, the already vast and growing role of the science of chart,ed particles in the characterization of matter and its reactions, far beyond the surface and film phenomena. Namely, the group of more than 1,600 new isotopes created by nuclear reactions (particularly of neutrons), along with 300 naturally occulting stable isotopes, form Me corpus of technology for Facing chemical reactions. These methods are especially dominant in research on organic and living matter. Analysis using, these schemes commonly in- volves radioactive counting instruments and mass spectroscopy, in which the isotopic atom becomes a charged particle. Likewise, in reference to We use of unstable nuclei with their useful radiation output, the synthetic technetium- 99 derived from neuron bombardment of molybdenum is the most widely
THE PHYSICS SCIENCES AS THE BASIS FOR MODEM TECHNOLOGY 249 used Isotope in nuclear medicine nowadays. However, these cases are but symbolic of the immense scope of elementary- and radioactive-particle sci- ence in support of a multitude of industrial, governmental, and social initia- tives. I-his delicacy of identifying atomically the behavior of virtually all tech- nical and en;,ineenng systems has, of course, brought along many more conventional analytic and control schemes, themselves derived earlier from the principles of physics and chemistry. Optical spectroscopy is a distin- guished example; now with Rarnan surface-enhanced spectra, the ordinary gas-phase sensitivity may be increased about a million times, to the detection of 109 molecules or less. Moreover, using laser activation, studies at Oak Ridge National Laboratory have observed single atoms of cesium in a cloud of 10~9 other atoms. Similarly, David Joy's Nonimpact spectroscopy can determine light elements quantitatively in a sample whose total mass may be only 10- ~8 a millionth of a millionth of a millionth of a gram. Opt~cal- emission spectroscopy can respond to as few as a million molecules per cubic centimeter, and fluorescence following laser exposure to liquid jets from high-pressure liquid chromatography has permitted the detection of a billion or less aflatoxin molecules per cubic centimeter. SCIENCE SUPPORTING MEASUREMENT AND SYSTEMS Physical science thus has not only provided a conceptual and intellectual base for modern technology, but repeatedly has injected quantification. In this way the entire character of technical engineering and economic operation has been enhanced beyond the empincal, often purely descriptive, stages on which manufacture and mining depended for a thousand years. In some fields of the highest innovation and sophisticated technology, we are now seeing the elegant principles of twentieth-century physical science, along with the experiments and techniques achieved, being combined into operational systems for dramatic advances in economic and social functions. These are seen especially in Me new arenas of communications and com- puters; of inflation handling; of sensing, command, and control; of in- dustnal automation and national security; and indeed (in the wide range of electonics, photonics, and circuitry) in the new systems of personal action, education, and entertainment. These resources universally involve semicon- ductor junction devices, which, in turn, have to be assembled with metallic conductors and strong organic or inorganic insulators and with various heat and mechanical qualities. In this systems realm, atoms, molecules, charges, and waves must be made to perform with great precision. This need is being, met by synthesizing, preferably in Din film- and surface-controlled forms, new states of matter (Figure 251. This has been done especially by R. Dingle, A. C. Gossard, and W. Wiegmann, based on the liquid-phase epitaxy work
250 WIl4AM 0. BAKER of M. Panish, the film studies of J. M. Poate, members of AT&T Bell Laboratories, and now the contributions of a variety of workers in other laboratories around the world. These schemes of generating beams of atoms or molecules that then form condensed matter of predetermined, and often unprecedented, properties si=,- nify a heroic combination of physics and chemistry, of Gibbs's phase prin- ciples and Heisenberg, Sommerfeld, and Einstein's quantum mechanics, of the Braggs' and Davisson's structural diffraction waves in crystals, of He Bardeen-Brattain-Shockley discovery of the transistor effect, and, win the solid-state injection laser embodying Schalow and Towne's revelation of new forms of light itself, the laser In examining a little further this making in the laboratory, and now in He factory, of unique and productive forms of matter, it should be emphasized that this is only the beginning. For in the times ahead, the exposed surfaces of the manufactures of most industries may involve these same synthetic processes. It is already fair to say, however, that the digital systems (com- puters, communications, and controls) on which modern industry and gov- ernment increasingly depend will shortly be using these schemes throughout. Thus, since as noted, this technology does involve nearly every aspect of He wide reaches of physical science gained during this century, we have a powerful answer to questions of the practical values of research. When the press and politicians question its relevance or economic return, it can be EFFUSION OVENS MASS S'=-TROME:ER _ _ _ _ SCREEN I_ \G~ \ / As / ULTRA \ H IGH VACUUM J "% HEATED GoAs S U BStR ATE SHUTTER M OLECULAR BEAMS - ELECTRON ~ BEAM FIGURE 25 Arrangement of molecular beam and atomic beam generators for gallium and arsenic to create new semiconductor films of unique quality for digital circuitry, such as in high-performance computers.
THE PHYSICAL SCIENCES AS THE BASIS FOR MODEM TECHNOLOGY HIGH blOBILIlY MODULATION-DOPED SEMICONDUCTORS 251 WAS _ · - ~~.- e AIS3AS 2504 ====____ \\~.PW~6a~s 4lGa~s (3 110BILE ELECTRON ~ SILICON ATOM FIGURE 26 Electron micrograph showing the molecularly layered structures deposited by the molecular beam and yielding charge mob~liiies and other technological advantages previously unknown. stated Mat there is simply no evidence Mat this synthesis of new states of matter by molecular-beam deposition and epitaxy could have happened em- pirically and without Me vast scientific base summarized here. Indeed, the behavior of the domains produced, for instance, win gallium arsenide and alternating additions of aluminum gallium arsenide in Me pres- ence of a silicon substrate, exhibits charge mobilities never before achieved (Figure 261. The resulting transistors are already He essence of supercom- puters and superspeed circuitry. However, the ~eoreuca1 significance of these new structures is also profound. For instance, it happens Hat quantum mechanics is generally taught, and was early conceived, in terms of the quantized behavior of a particle in a box. The Hamiltonian operator dominant in Schrodinger's equation is illustrated as describing the behavior of such a model. The charges in He layered structures produced by molecular-beam epitaxy (Figure 26) are the best, and in some ways He only, case in which an experimental quantum particle in a box has been achieved. Thus, we are seeing In this, as in so many other cases of the development of solid-state science, and now in photonics, the interaction of technology in stimulating further scienuf~c insight. Remarkable scientific combinations win technological outputs are also proceeding rapidly in the molecular-beam epitaxy processes themselves (Figure 271. For instance, M. Panish, referred to above with regard to his earlier work in liquid-phase epitaxy, has now introduced gas-phase sources
252 WIt r l~ O. BAKER ~3 It,j .A . ~ '_ '.2 -~;N ~~ ', ' . ,. i:.,, :~ . :, ;~ ~ - - FIGURE 27 Example of the precise and sophisticated high-vacuum apparatus developed by Hags~om to control and analyze molecular beam epitaxy and the synthesis of new thin crystal forms of matter. Of elements to form the beams. This replaces having to depend on sometimes poorly defined solid reservoirs for atom and molecule emission. This flex- ibility has moved forward with W. Tsang into ''chemical-beam epitaxy," in which all of the component elements come in gas form, such as metallo- organic compounds of gallium and indium. This exceedingly attractive sys- tem, which seems certain to have a strong impact on heterogeneous-catalysis creation in the chemical industry, on surface stabilization, and in various other applications mentioned, is termed MOCVD metallo-organic chemical vapor deposition. It is being controlled by highly sophisticated flow tech- niques regulated by microprocessors and yielding kinetics of particle synthesis in the high vacuum, which are themselves of deep interest to the chemical and materials industries. It should be emphasized again at this point that the universe of innovation supported by atomic and molecular surface and film synthesis is a striking derivative of the long-tenn studies of high vacuum and surface purification, epitomized by the research of Homer Hagstrom. On the one hand, recall that energy states and surface physics were essential in the discovery of the transistor; they were, in fact, the crucial features in Bardeen's pioneering theory. Beyond that, however, the superb experimental extensions of surface physics by Ha:,strom and his associates are dependent on the achievement
THE PHYSICS SCIENCES AS THE BASIS FOR MODERN TECHNOLOGY 253 of unprecedented cleanliness and surface characterization involving, among other things, consistent and controllable vacuua of 10- ~: torr or better. This is an emptiness beyond that of outer space, and yet it has become a factory- controlled process (Figure 271. The intense importance and decisive role of these researchers in the electronic-photonic-matenals regime is well sym- bolized by the diagram of Hagstrom's latest research apparatus (Figure 28), which includes working units of ultraviolet, photoemission, energy-loss, and Auger-electron spectroscopies. These are all notable examples of modern quantum physics, including electron-diffraction and ion-neutralization spec- troscopy, which have had their own historic roles in the physical sciences of the twentieth century. In this context it is also appropriate to denote the rapidly moving frontier use of this science and technology in electronic and photonic systems in- novation. Thus, the selectively built heterostructure transistor obtained from molecular-beam epitaxy, including a multilayered sandwich of ultrapure gal- lium arsenide with aluminum gallium arsenide layers that are heavily doped, O ,0 I ...... ~ . ~ ~ .... . ~ SF - TER1NG cad AND SAMPLE PR OCESSING ION-NEUTRALIZATIO.I IPORT 2) SPECTROSCOPY (PORT 1 ) E - PORATOR 1 aIt- ~ - -' at 2 ! ~ =- -ENERGY a£CTR~ \ ~ DIP FRACTION AND _ _. ' _ ; ~ SAMPLE PROCESSING SPj' /~_. (PORT ~ ) ;~ 11~1~ E~aroR 2 11 __ N. \ . ~ ~ ~ ILL' ~~ O j ~ 4 ~ as' ; j ~ INLET ~ SEPTUM PUMP 20R ~ , \ 2 et J____! I ~ ~ __ - - - ' ~ l ~ ELECTRON ~ 11~ 11 E & - -/////////// &2 ~ ~ B2 ~ U 1 ..... , _ COt cl - brag - AGUE T C] AWL PUMP ~ ~ _ 1 ~ PU - I FIGURE 28 Schematic of apparatus for precise surface charactenzation. ~ ~2 R£~ACTABLE GAS ,~E, U LT - VIOLET PHOTOE ~ ISSUE. ENERGY LOSS, AND AUGER ELECTRON SPECTROSCOPIES (PORT 4)
254 wI] r BAD 0. BAKER has been shown by J. DiLorenzo to provide a new rin:,-oscillator circuit. It is effectively operating as a switch at 90 billion operations per second, far beyond anything ever before reached in integrated circuitry. Over embod- iments provide such records as frequency dividers working at 10 gigacycles, at low temperatures. The work of R. Dangle, [I. Stunner, and A. Gossard has indeed already shown the doubling of electron mobility in the gallium arsenide-alum~nunn gallium arsenide case referred to earlier. Electron monon is 20 tunes as fast at low temperatures. This will undoubtedly be developed into important structures for photonics, eventually including integrated optoelectronic circuits. In this regard ge:Tnanium, silicon, and Weir combinations, which yield stained su- perlat~ces, have already been achieved by John Dean of Bell Laboratones. Also, Julia Phillips has grown calcium fluoride on silicon, so Mat staking new insulator-semiconductor systems are in progress. Likewise, these advanced em itaxial techniques are being used in Be production of new magnetic rare eats systems and in superconductors. Accordingly, our expectations of extensive innovation from this new basic science are appropnate. Finally, it is appropriate to accent In every connection that physical science, to which I attribute so much of the base for the technology and economy of this age, is, in turn, heavily dependent on mathematics and the conceptions of logic and encoding that are Be base for computers, analysis, and Be treatment of atomic and molecular events. Newton and Maxwell were referred to at the beginning of this chapter; we should also remember the host of mathematicians who mastered statistical mechanics, group theory, symbolic logic, and an array of other elegant representations of Be mind. While our progress in physical science is an adornment of civilization, its modern excellence and extent derive especially from bow the content and Be modes of Bought Mat mathematics has engendered. Overall, it is gratifying that the science of Aristotle and Plato, of Newton and Einstein, is now so well joined win He technology of humankind, which I have described elsewhere* as "~e ways of making Dings and doing things." *[Random House Encyclopedia (New York: Random House, 1977), p. 1578.
