Clear as crystal
Three decades ago, Prof. Dan Shechtman looked into an electron microscope and couldn't believe what he saw. His discovery led to a new field of study and an ongoing candidacy for a Nobel Prize
By Asaf Shtull-Trauring Reproduced from Haaretz.
On a cool, clear Thursday morning in April 1982, Prof. Dan Shechtman was alone in the laboratory of the National Bureau of Standards in Gaithersburg, a handsome suburb of Washington D.C., where he was spending a sabbatical. At about 10 o'clock, he examined through an electron microscope a new crystal he had produced in his laboratory. The electron beam passed through the crystal and left a diffraction pattern of points of light on the screen of the microscope.
Shechtman counted the points: 10 points, arranged in a circle around a central point. He counted again and got the same result: 10 points. He had never before seen a pattern like this. Moreover, he realized immediately that the pattern he was looking at was impossible under the laws of crystallography, the science of crystals. He went out into the long corridor outside the lab, looking for someone with whom to share this strange finding. The corridor was empty. Returning to the lab, he looked again at the peculiar pattern of dots of light.
"I told myself that there is no such thing," he recalls. Since the birth of modern crystallography in 1912, when x-rays were diffracted from a crystal for the first time, until that moment 70 years later, this branch of science had relied on an unchallengeable basic tenet: the atoms in crystalline solids - such as metals, rocks or ceramic materials - are arranged in periodic order. The periodic pattern repeats itself throughout the crystal, as in a chessboard or a honeycomb hexagon. The regularity of the pattern dictates another important quality: crystals are composed of "tiles" possessing rotational symmetry. In other words, if the basic form that makes up the crystal is rotated, it will look exactly the same. A chessboard can be rotated four times, a quarter of a rotation each time, and it will look the same; the hexagon of a honeycomb can be rotated six times.
Crystallographers determined that there were only five possible rotational symmetries: single symmetry (there is only one way to rotate the tile so it will look the same ), double (two stages of rotation ), triangular, quadruple and hexagonal. The scientists concluded that there can be no pentagonal symmetry in crystals, since they cannot create periodic order - as anyone who has tried to cover a bathroom floor with five-sided tiles knows. In countless observations over many decades, crystallographers indeed saw only geometric crystals, all of them possessing rotational symmetry.
But on that April day in 1982, when Shechtman looked at the pattern of points created by the crystal of the alloy he had prepared in the lab from aluminum and manganese, he saw a structure that contradicted both rules: the 10 points that appeared through the microscope attested to the existence of pentagonal symmetry; and the immediate conclusion was that the crystal did not possess a periodic structure. Shechtman had discovered a new world, in which there are solid crystals, but the known order was gone.
"On that day the realization that this was something new trickled in, but I didn't yet know what it was," he relates.
From that very moment, when he hunched over an electron microscope and then went out to look for someone to join him in counting the 10 points, his conclusions sounded utterly baseless. Moreover, he had not come to the laboratory on the East Coast of the United States to produce far-reaching theoretical developments in the study of crystals, a field that in many ways had itself crystallized and solidified. Shechtman had been invited to the institute to do research on light alloys for the aircraft industry. Within days, his peculiar ideas generated suspicion and ridicule, to which he would be subjected for some time. Until he succeeded in convincing everyone.
Looking for a partner
"I told everyone who was ready to listen that I had material with pentagonal symmetry. People just laughed at me," Shechtman says in his office at the Technion, in Haifa. On one wall hang a row of certificates testifying that something major happened that day: the Rothschild Prize in Engineering, 1990; the Israel Prize in physics, 1998; the Wolf Prize in physics, 1999; the EMET Prize in chemistry, 2002. Amid the prize certificates Shechtman has hung Hieronymus Bosch's triptych "The Garden of Earthly Delights."
His colleagues, he says, attributed the discovery to the "twinning phenomenon," a convergence of crystals that can create a semblance of pentagonal symmetry. But Shechtman, who was familiar with the phenomenon from previous research, had already contemplated that possibility. Following a series of tests with the electron microscope on the day of the discovery, he ruled out the twinning phenomenon as a possible explanation.
In the months that followed, he tried to persuade his colleagues in the lab that what they were looking at was a previously unknown crystal. But in vain. "I knew my observations were in order. I couldn't explain the phenomenon, but I knew it was material that no one had seen before me, impossible material according to the laws of crystallography," he says. The incessant criticism sent him back to the microscope repeatedly in order to reexamine the alloy, but his initial insight remained intact.
One day, the administrative director of his research group approached him. "He gave a sheepish smile, placed a textbook on my desk and said, 'Please read what's written here.' I told him that I taught my students from the book, but that I also knew that we're dealing with something that exceeded the book's understanding," Shechtman says. The director returned 24 hours later and asked him to leave the research group, because he was "bringing disgrace" on the members.
"I felt rejected," Shechtman says. "As I see it, the head of the group expressed the view of many. He would not have reached that conclusion unless he heard from others that someone in his group was fiddling with nonsense."
Shechtman moved to another group and continued his research. However, the researchers at the institute were not able to check the discovery for themselves. Many of them did not know how to work with an electron microscope, which is the most appropriate tool for identifying rotational symmetries in small crystals. Moreover, he notes, "They were not really interested in dealing with it."
Shechtman also forwarded the findings to a friend, who was about to go on a scientific tour. When the friend returned, Shechtman relates, he brought an array of off-the-wall explanations for the 10 microscopic points, gleaned from colleagues. None of them took seriously the possibility that it was a case of pentagonal symmetry.
At the end of 1983, following the conclusion of his sabbatical, Shechtman returned to the Technion. He continued to share his discovery in Israel. But only one person was ready to listen in earnest: Prof. Ilan Blech, from the Technion's Faculty of Materials Science. He suggested that the two of them work together on the discovery. Within a short time he developed a model that derives the phenomenon from a pentagonal symmetry, which is one of the rotational symmetries of a three-dimensional body called an icosahedron - an entity composed of 20 identical equilateral triangular faces. Shechtman now felt sufficiently confident to publish an article on the subject.
Until then, he says, "I was afraid to publish alone, in case it turned out to be nonsense."
He returned to the National Bureau of Standards in Maryland in the summer of 1984, where he wrote the article together with Blech and send it to the Journal of Applied Physics. Within a short while a reply arrived from the editor, rejecting the article as not being of interest to physicists. "The editor later deeply regretted his decision," Shechtman says. Disappointed, Shechtman turned to the senior scientist John Cahn, who had invited him to work in the institute. Cahn initially had reservations, but afterward worked with Shechtman and proposed that they co-author an article. For the mathematical aspects he added a French crystallographer, Denis Gratias, and the three wrote an article that was a concise, refined version of the first article. They added Ilan Blech's name as a fourth author and sent the article to Physical Review Letters, which also deals with physics. The addition of Cahn's name turned out to be a winning move: the article appeared in November 1984, within a few weeks of its submission.
Fear and compliments
Publication of the article provoked a brouhaha in the scientific community. The discovery of a crystalline structure possessing pentagonal rotational symmetry and overall icosahedral symmetry - a concept that until then had been confined largely to the realm of mathematical amusements - demanded a fundamental change in all the textbooks on the subject. To get researchers to believe him, Shechtman described exactly how to prepare the alloy.
"There are people who keep the mode of preparation secret, but I wanted every researcher who had an appropriate laboratory to be able to prepare the material and examine it under an electron microscope within a few days," he says. "Telephone calls started coming in very soon from scientists around the world. 'I have it,' they told me."
However, despite the success in repeating the experiment in several labs, only a few scientists accepted the thesis of pentagonal symmetry. Leading scientists rejected Shechtman's conclusions, and towering above all of them was Linus Pauling, the only person ever to have been awarded the Nobel Prize twice on his own, once for chemistry and once for peace, and considered one of the most important chemists of the 20th century. The issue of quasiperiodic crystals continued to exercise him from the moment the article was published in 1984 until his death a decade later.
"There are tens of thousands of chemists in the United States, and Pauling was their star," Shechtman notes. "He would open the conferences of the American Chemical Society, and quasiperiodic crystals were always his topic. I attended one of the conferences, at Stanford. Thousands of people were there, and he attacked me. He would stand on those platforms and declare, 'Danny Shechtman is talking nonsense. There is no such thing as quasicrystals, only quasi-scientists.'
"At first, being the target of this crusade was scary at an existential level," Shechtman admits. One day, he relates, his daughter came back from school and told him she had learned about Linus Pauling. "She asked me if this was the same Linus Pauling who was against me; because if so, she said, he must be right."
Shechtman was concerned that his promotion would be impeded. "I knew that if it turned out to be a flop, it would be a major flop." Nevertheless, he says, he was very confident about the findings. Not long after the article's publication, Shechtman received a copy of "The Structure of Scientific Revolutions," by the philosopher of science Thomas Kuhn. That iconic book deals with the process by which scientific paradigms are produced and replaced. "I went through stage after stage, just as Kuhn describes. I told myself I have gone through chapter one, I have gone through chapter two, and I know what lies ahead."
In the first years following the discovery, Shechtman's support came primarily from physicists and mathematicians. But crystallographers had a serious problem with the findings: Shechtman had used an electron microscope, whereas their main tool was the x-ray. "It's as though a mechanical engineer were to explain to a heart surgeon how to perform an operation," Shechtman says. "From their point of view, I was not a crystallographer, because I had used a tool they considered imprecise and illegitimate."
It was not easy to repeat the successful experiment with the use of x-rays, which produce more accurate results than a microscope but demand larger single quasi-periodic crystals. However, in 1987, friends of Shechtman's from France and Japan succeeded in growing quasi-periodic crystals large enough for x-rays to repeat and verify what he had discovered with the electron microscope: the existence of pentagonal symmetry.
"In the forefront of science there is not much difference between religion and science People harbor beliefs. The argument with Linus Pauling was almost theological."
That summer of 1987, Shechtman presented the photographs at a large conference of crystallographers in Perth, Australia. This brought about the turning point he had been anticipating for the past five years. "Suddenly people told me, 'Now you're talking,'" he recalls. After the Perth conference, recognition of Shechtman's achievement began to trickle down into the ranks of the scientists. Linus Pauling, however, persisted in his opposition until his final day.
"In the forefront of science there is not much difference between religion and science," Shechtman says. "People harbor beliefs. That's what happens when people believe something religiously. The argument with Linus Pauling was almost theological." Still, their disagreements never deteriorated to the personal level. "At conferences people would wait for fights to break out between us over dinner. But Pauling was always cordial. He was a New Yorker with southern manners. We would sit and talk for hours about things we agreed on. For example, he was a big advocate of vitamin C, and so am I. We agreed about everything, but not about quasicrystals."
|Nobel Laureate and top Materials Scientist Linus Pauling.|
As his fear of not finding employment faded, Pauling's assaults became a compliment for Shechtman. "I realized that if it's Pauling against Shechtman, then at some level we are equals. From a situation in which I was on the floor and he was on the ceiling, I saw that very slowly, over a period of 10 years, the balance was shifting," he says. At the beginning of the 1990s, with Pauling also in his nineties, he made a gesture to Shechtman, inviting him to write a joint article, "Shechtman-Pauling," on quasiperiodic crystals. Shechtman replied that he would be delighted to co-author the article with him, but that Pauling first had to agree that quasi-periodic crystals in fact exist. Pauling's rejoinder was that it was apparently still too soon for a joint article. A year later, he died. With his death, the opposition to Shechtman in the scientific community vanished.