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Home , Clinton Davisson, Lester Germer, Mervin Kelly, Thomas Edison, Vacuum tube

THE INDUSTRIAL STRENGTH by MICHAEL RIORDAN

ORE THAN A DECADE before J. J. Thomson discovered the elec- tron, stumbled across a curious effect, patented Mit, and quickly forgot about it. Testing various carbon filaments for bulbs in 1883, he noticed a tiny current trickling in a single di- rection across a partially evacuated tube into which he had inserted a metal plate. Two decades later, British entrepreneur applied this effect to invent the “oscillation valve,” or —a two-termi- nal device that converts into direct. In the early such rectifiers served as critical elements in receivers, converting radio waves into the signals needed to drive earphones. In 1906 the American inventor happened to insert another elec- trode into one of these valves. To his delight, he discovered he could influ- ence the current flowing through this contraption by changing the on this third . The first vacuum-tube amplifier, it served initially as an improved . De Forest promptly dubbed his the and ap- plied for a patent. Much of the rest of his life would be spent in forming a se- ries of shaky companies to exploit this —and in an endless series of legal disputes over the rights to its use. These pioneers of understood only vaguely—if at all—that individual subatomic particles were streaming through their devices. For them, was still the fluid (or fluids) that the classical electrodynamicists of the nineteenth century thought to be related to stresses and disturbances in the luminiferous æther. Edison, Fleming and de Forest might have been dim- ly aware of Thomson’s discovery, especially after he won the 1906 Nobel

Copyright © 1996 by Michael Riordan. Adapted in part from Crystal Fire: The Birth of the , by Michel Riordan and Lillian Hoddeson, to be published in 1997 by W. W. Norton & Co.

30 SPRING 1997 PARTICLE

Prize in . But this knowledge development slowly be- had yet to percolate out of academ- came an organized practice per- ic research labs such as the Caven- formed by multidisciplinary teams dish and into industrial workshops. of salaried scientists and engineers Although he had earned a Ph.D. in working in well-equipped industrial physics from Yale, in his daily prac- labs. As the century waxed and quan- tice de Forest remained pretty much tum emerged to explain a systematic tinkerer in the Edison- the mysterious behavior of , ian vein, trying endless variations on atoms and molecules, these re- his gadgets in his halting attempts to searchers increasingly sported ad- improve their performance. vanced degrees in physics or chem- istry. A deeper understanding of the OLUMES COULD be writ- scientific principles governing the ten about the practical appli- behavior of matter gradually became Vcations that owe their exis- indispensable to the practice of in- tence to the understanding of dustrial research. As the noted his- electricity as a stream of subatomic torian of technology Thomas Hugh- particles rather than a continuous flu- es put it, “Independent inventors had id. While the clearly an- manipulated and ; tedated the discovery of the , industrial scientists would manip- for example, its modern manifesta- ulate electrons and molecules.” tions—cellular and touchtone phones, Few examples illustrate this evo- telefax machines, satellite communi- lutionary transformation better than cations—would be utterly impossible the case of the vacuum-tube ampli- without such knowledge. And the fier. For almost a decade after de For- ubiquitous set is of course est invented it, his audion found lit- just a highly refined version of the tle use beyond low-voltage appli- -ray tube that Thomson used cations in receivers—as a to determine the charge-to-mass ra- of weak radio signals. He tio of his beloved corpuscle. The field simply did not understand that the of electronics, a major subfield of gas remaining in his tube was im- electrical today, grew up peding the flow of electrons from fil- in the twentieth century around this ament to plate. At the higher volt- new conception of electricity, even- ages required for serious amplifica- tually taking its name in the 1920s tion, say in telephone communica- from the particle at its core. (We are tions, the device began, as one ob- perhaps fortunate that Thomson did server noted, “to fill with blue haze, not prevail in his choice of nomen- seem to , and then transmit no clature!) further speech until the incoming In parallel with the upsurge of current had been greatly reduced.” electronics, and in some part due to One corporation extremely inter- it, came a sweeping transformation ested in amplifying telephone signals of industrial research in America. was the American Telephone and Once the main province of highly Telegraph Company, then seeking to individualistic inventors search- develop a suitable “” for ing for a fruitful breakthrough, transcontinental phone service.

BEAM LINE 31 Among its leading scien- elements in excellent telephone re- tists was Frank Jewett, peaters. At the grand opening of the then working in the engi- Panama-Pacific Expositon held in neering department of its San Francisco on January 15, 1915, Division. inaugurated In 1902 he had earned a the nation’s first coast-to-coast Ph.D. in physics from the telephone service, talking to his for- , do- mer assistant Thomas Watson in ing his research under Al- . Recalling this event in his bert Michelson and be- autobiography, Millikan observed friending Robert Millikan. that “the electron—up to that time Harboring a hunch that the largely the plaything of the scien- electrical discharges in tist—had clearly entered the field evacuated tubes might as a patent agent in the supplying serve as the basis for a suit- of man’s commercial and industrial able repeater, Jewett ap- needs.” proached his old chum, Thus convinced of the value of sci- who in 1911 sent one of his entific research in an industrial set- brightest graduate stu- ting, Western Electric incorporated J. J. Thomson inspecting electron tubes dents, Harold Arnold, to Western its engineering department as a sep- in 1923 with Frank Jewett, the first Electric. Here was a young man arate entity—the Bell Telephone Lab- president of . (Courtesy AT&T steeped in the new thinking, who had oratories—in 1925, naming Jewett its Archives and AIP Library) just spent several years measuring first president. The very next year, the charges of individual electrons as an outgrowth of their research on on oil droplets. the performance of vacuum tubes When de Forest demonstrated his (also called electron tubes), Clinton audion to Western Electric scientists Davisson and estab- and engineers in October 1912, lished the wave of electrons, Arnold was present. He diagnosed which had been predicted a few years the blue haze as due to the recom- earlier by . For his bination of gas molecules that had pivotal work on electron , been ionized by energetic electrons. Davisson was to share the 1937 Then he solved its problems by use in physics with the of high vacuum, an -coated fil- British scientist George Thomson, ament, and other modifications dic- son of J. J. tated by a superior understanding soon ex- of the electronic discharge. (A similar plained the behavior not only of elec- development occurred simultaneu- trons in atoms but of the large osly at , but it lost ensembles of them that swarm about the ensuing patent fight to AT&T, freely within metals. Based on the which had wisely purchased the theoretical work of and appropriate rights to de Forest’s , Bell Labs even- patents.) tually figured out why an oxide- Within a year Western Electric coating worked so well on was making “high-vacuum thermi- filaments of vacuum tubes. It helped onic tubes” that served as active to lower the of the

32 SPRING 1997 Right: and Lester Germer with the apparatus they used to establish the wave nature of electrons. (Courtesy AT&T Archives)

Bottom: Graph from their 1927 Nature article showing diffraction peaks observed in from a nickel crystal. metal, thereby making it easier for electrons to escape from the sur- face—and substantially reducing the amount of power needed to heat a fil- ament. Such a fundamental under- standing of the physics of electrons proved crucial to further engineering advances in vacuum tubes that saved AT&T millions of dollars annually.

N THE LATE 1920S and early 1930s, , Rudolph IPeierls, Alan Wilson and other European physicists laid the foun- dations of modern solid-state physics in their theoretical studies of how above a few hundred megahertz, useful properties by finding physical waves of electrons slosh about with- where electron tubes had proved use- and chemical methods of controlling in the periodic potentials encoun- less. Crystal , with a deli- the arrangement of the atoms and tered inside crystalline materials. cate metal point pressed into a ger- electrons which compose solids.” Their work resulted in a theory of manium or surface, filled the The most important postwar solids in which there are specific al- gap nicely. By the end of the War, breakthrough to occur at Bell Labs lowed (or forbidden) energy levels— methods of purifying and doping was the invention of the called “bands”—that electrons can these substances to make easily con- in late 1947 and early 1948 by John (or cannot) occupy, analogous to the trolled, well-understood semicon- Bardeen, Walter Brattain, and Wil- Bohr orbitals of early quantum the- ductors had been perfected by sci- liam Shockley. And a key to their in- ory. Combined with practical meth- entists at such secret enclaves as the terpretation of transistor action was ods of calculating these band struc- Rad Lab at MIT and Britain’s Tele- a new physical phenomenon Shock- tures in actual substances, pioneered Research Estab- ley dubbed “minority carrier injec- by , band theory fos- lishment at Great Malvern. tion”—in which electrons and pos- tered a better understanding of why No laggard itself in these pursuits, itively charged quantum-mechanical certain materials act as electrical Bell Labs led the way during the post- entities called “holes” can flow by conductors and others as insulators. war years in applying wartime in the presence of one an- And, in a decade when electron insights and to the cre- other. Once again, a detailed scien- tubes reigned supreme as the active ation of practical new semiconduc- tific understanding of how individ- components of electronic circuits, tor components. “The quantum ual subatomic particles (and what, band theory began to elucidate the physics approach to structure of mat- in certain respects, act like their properties of intermediate materials ter has brought about greatly in- antiparticles) behave proved crucial called , whose myr- creased understanding of solid-state to a pivotal advance in electronics. iad spawn would eventually sup- phenomena,” wrote its vice president The transistor happened along at plant these tubes throughout elec- —another of Millikan’s a critical juncture in technological tronics. grad students—in 1945, authorizing history. For the electronic digital World War II spurred tremendous formation of a solid-state physics that also emerged from practical advances in the technolo- group. “The modern conception of wartime research could not have gy of semiconductors, largely due to the constitution of solids that has re- evolved much further without it. the fact that receivers sulted indicates that there are great The thousands of bulky, fragile needed rectifiers able to operate possibilities of producing new and electron tubes used in such early,

BEAM LINE 33 room-filling com- laboratory, Fermi replied, “They puters as the ENI- really are very fine gadgets, and I AC and UNIVAC hope very much that they might be burned out with useful in our work.” all-too-frustrating frequency. Only HOMSON’S DISCOVERY large corporations, triggered a spectacular cen- the armed services Ttury of in both and government science and technology. Paced by in- Lee de Forest, inventor of the vacuum- agencies could afford these massive, creasingly detailed knowledge of the tube amplifier, and Bell Labs President power-hungry monstrosities and the electron’s properties and behavior, Mervin Kelly. (Courtesy AT&T Archives) vigilant staff to keep them operating. scientists and engineers developed “It seems to me,” Shockley con- many other advanced devices— jectured in December 1949, “that lasers, light-emitting , mi- in these brains the transistor is crowave tubes, solar cells and high- the ideal nerve cell.” speed microprocessors, to name But the transistor has proved to be several—that are essential to mod- much more than merely a replace- ern computing and global commu- ment for electron tubes and electro- nications. Today we know the mass mechanical . Shrunk to less and charge of the electron to better than a ten-thousandth of its original than seven significant figures. Aided size and swarming by the millions by quantum mechanics, we can ac- across the surfaces of microchips, curately calculate its energy levels it has opened up entirely unexpect- in all kinds of atoms, molecules and ed realms of electronic possibility, solid-state substances. Largely tak- which even the most farsighted could en for granted, such information is not have anticipated during those crucial for the precision control of booming postwar years. The transis- electrons at the submicron scales tor was, as historians Ernest Braun that characterize many leading-edge and Stuart MacDonald observed, “the technologies. harbinger of an entirely new sort of Of critical importance in attain- electronics with the capacity not just ing this deep understanding was the to influence an industry or a scientific ease with which electrons can be discipline, but to change a culture.” detached from other forms of matter Characteristically, particle physi- and manipulated using electromag- cists were among the first to glimpse netic fields. Such features were read- the potential ramifications of this ily apparent in Thomson’s landmark revolutionary new solid-state am- experiments, for example, and plifier. “I would be very anxious to Millikan exploited them in his re- do some experimenting to learn search. In certain key instances the about the techniques of your new energy required corresponds to that Germanium triods,” wrote Fermi to of in visible light. This Shockley in early January 1949 unique partnership between the elec- (misspelling the final word). After re- tron and (whose centennial ceiving a few samples and testing we will also celebrate in the not-too- them at his University of Chicago distant future) is central to much of

34 SPRING 1997 Left: , , and Walter Brattain, who shared the 1956 for the invention of the transistor. (Courtesy AT&T Archives)

Bottom: Page from Brattain’s lab notebook that records the 23 December 1947 demonstration of the first transistor. (Courtesy AT&T Archives)

advanced technology. Perhaps this composed this arti- complementary relationship is one cle while staring at a reason why, during the past decade luminous screen— or so, we have witnessed the emer- behind which a blaz- gence of a “photonics” industry that ing stream of elec- threatens to supplant electronics in trons traces out my some commercial sectors. fumbling thoughts No comparable partnership exists, as my fingertips tap for example, between quarks and glu- keys that activate ons. Quarks are not detachable, at transistor-laden mi- least not yet, and gluon fields do not croprocessors deep extend to infinity like the electro- within my comput- magnetic. It makes all the difference er. And some of you in the world. We still have only rough now read my words values for the quark masses, espe- on luminous screens cially the up and down quarks that of your own, con- make up the bulk of ordinary mat- veyed to your desks ter. Only a few wild-eyed speculators by surging rivers of electrons and dare to mention the possibility of photons pulsating as ones and zeroes “quarkonics” or “gluonics” indus- through an intricate network that tries. Maybe one day soon we will stretches into almost every corner of manipulate quarks for practical ben- the globe. The only paper involved efit, say by using high-energy elec- in the exchange is the pages marked tron beams. Perhaps, but I seriously with red ink that now lie crumpled doubt it will ever amount to much in my wastebasket. of an industry. For now, quarks and We all owe a debt to J. J. gluons remain the playthings of pure Thomson—and the scientists and physics. engineers who followed the path that Just a hundred years after its dis- he pioneered—for taming the first covery, the electron sits at the core subatomic particle and adapting its of modern life. Where previous gen- unique properties for the practical erations of writers, for example, used applications that are relentlessly re- chemical inks and mechanical defining what it means to be human. devices to cast their ideas onto paper (and deliver them to readers), I have

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