Koji Kimoto Director of the Surface Physics and Structure Unit, Advanced Key Technologies Division, Special interview NIMS History of the advancement of the electron microscope as viewed from Japan Today, the resolution of electron microscopes has reached the sub-atomic level of The Next 50 pm*. How was this accomplished? The key terms are “high voltage” and “aberration correction.” Here, the two scientists in a teacher-student relationship—Nobuo Tanaka, Presi- Nobuo Tanaka dent of The Japanese Society of Microscopy, and Koji Kimoto, a NIMS unit director, Ambition of President of The Japanese Society of Microscopy, who has been working on materials research using a cutting-edge electron micro- Professor Emeritus of Nagoya University scope—will discuss the history of the development of the electron microscope. Microscopists * 1 pm (picometer) is one-trillionth of 1 m. Humankind’s ambition to see more However, there was a problem in realizing an II broke out, the subcommittee no longer had corrected, resolution can be improved by minute details electron microscope; the image of a specimen access to information from Germany. However, shortening the wavelengths of the electrons. With long lineage and formed by electrons couldn’t be magnified the subcommittee continued its own develop- To achieve this, an ultra-high voltage elec- Kimoto: I would like to begin our talk on the using glass lenses. Amid this situation, the Ger- ment activities, and succeeded in the manu- tron microscope was developed in which the subject of the invention of the electron micro- man physicist Hans Busch suggested in 1926 facture of Japan’s first commercial product in wavelengths of electrons were shortened by continued challenges scope. I have noticed that people who see an that magnetic fields generated by running elec- 1941. I was once told by my mentor, late Pro- accelerating the electrons by applying high electron microscope for the first time often look tric current through a donut-shaped coil could fessor Ryoji Uyeda, that when the war ended voltage to them. Atomic resolution was nearly surprised due to the huge differences in size be used to direct electron beams in a way anal- in 1945, he didn’t feel that Japan was behind in achieved as early as around 1990 when I was a and shape between an electron microscope and ogous to the way that glass convex lenses direct the electron microscope science & engineering university student. Only Japanese manufactur- the optical microscopes which they are familiar light in an optical microscope. Then, in 1931, at all, based on the information that started to ers were producing ultra-high voltage electron Wanting to see things in fine detail is with from science classes at school. the German physicist Ernst Ruska successfully come in from abroad again. Japan Electron Op- microscopes at that time, and they were also Tanaka: The optical microscopes commonly created the world’s first electron microscope. tics Laboratory Co. Ltd., a precursor of JEOL exporting the microscopes overseas. one of intellectual desires of human nature. seen in school science classes magnify small Ltd., which is one of the major electron micro- Tanaka: Ultra-high voltage electron micro- samples using glass convex lenses through Early development in Japan scope manufacturers today, was established scopes once dominated around the world, but Out of such desire, humans invented a microscope which the light illuminating the sample travels in 1946. And in 1949, the Japanese Society a limitation was reached in terms of further magnifying things with light. to form enlarged images. The first optical Kimoto: I believe that the development of of Electron Microscopy was launched. I am shortening the wavelengths of electrons by microscope was invented in the 17th-century electron microscopes in Japan began when the currently serving as a president of the society, increasing the acceleration voltage. According But scientists’ ambition was not satisfied there. in the Netherlands. On the other hand, looking subcommittee of the Japan Society for the Pro- and it is one of the older scientific societies in to Einstein’s special theory of relativity, as the into the history of electron microscopes, we motion of Science (JSPS) was founded in 1939. Japan. speed of electrons nears the speed of light, the They stepped into an even more Lilliputian world. ultimately arrive at the 1923 account by the Is that correct? mass of the electrons increases. So, eventually In the course of this pursuit, French physicist Louis de Broglie, who said Tanaka: The news that the first electron mi- Strategy involving high voltage the effort to increase the speed of electrons that electrons are also waves. Before that, croscope was invented in Germany quickly reached a plateau. Due to this situation, the they suceeded in looking at atoms electrons had been considered as particles. reached Japan. Then, based on the idea that Kimoto: Electron microscopes are capable of resolution of ultra-high voltage electron mi- Electron microscope originated from the idea croscopes remained unimproved for a certain using electrons instead of light. Japan should manufacture its own electron mi- achieving atomic-level resolution in theory, but that if electrons are waves, then it must be croscopes, the 37th subcommittee for research their initial resolutions were lower than their period. While looking back on the past endeavors toward feasible to observe magnified images of small on electron microscopes was organized in the potential. samples using electrons in a similar way to how JSPS with Shoji Seto, professor of The Univer- Tanaka: The electrons that pass through the Lineages surrounding electron micro- accomplishing atomic-level vision, an optical microscope works. sity of Tokyo, appointed as a chairman. periphery of a lens contribute to a blurred scopes: Germany and Japan Wavelengths determine resolution. When visible let’s take a glance at what is coming next Kimoto: I also heard that in addition to re- image, as they deviate from the focal point. light, with wavelengths ranging between 380 searchers from universities and research insti- This effect is called a spherical aberration, Kimoto: In the meanwhile, Germany was try- in the world of electron microscopy. and 800 nm (1 nm [nanometer] is one-billionth tutes, engineers from manufacturers joined the which reduces a microscope’s resolution. ing to correct spherical aberrations. This effort of 1 m), is used, the maximum possible resolu- subcommittee. Since the time when the electron microscope was led by Harald Rose, Maximilian Haider tion attained is about 100 nm. In comparison, Tanaka: Some manufacturers such as Hitachi, was invented, this aberration has been a cause and Knut Wolf Urban who won the 2015 when electrons with wavelengths much shorter Ltd., Shimadzu Corp., Tokyo Shibaura Denki of problems. In addition, achieving electrical NIMS Award. You know them very well and than those of visible lights are used, observation (currently Toshiba Corp.) and Yokogawa Elec- stability had been a challenge for many years. you were closely following their research in of atomic-level objects is possible in theory. tric Corp. indeed took part. When World War Kimoto: Even if aberrations are not fully progress. How did they develop the aberration 02 NIMS NOW 2015 No.6 NIMS NOW 2015 No.6 03 Special interview History of the advancement of the electron microscope as viewed from Japan correction technology? Miyake, Kikuchi and Uyeda respectively pur- was difficult to correct aberrations using film. as a committed engineer. When he tested the advancements. In addition, this correction resolution of 50 pm or less. Furthermore, sample I brought, the device wasn’t good technology also reduced the measurement Japan developed its own aberration correc- Tanaka: To start with, you might be wonder- sued study on X-ray diffraction, atomic nuclei Tanaka: It was the early 1990s when various ing why the aberration correction technology and electron microscopy, respectively. There technologies, such as CCD digital cameras enough for my applied research purposes time, for instance, from one hour to one min- tion device, and succeeded in correcting was developed in Germany, not Japan. That is are some other lineages of researchers through capable of in-situ aberration measurements and at that time. After I explained to him the ute. This reduction is important especially fifth-order aberrations. Japan is also working because Germany had a sound academic foun- which many outstanding discoveries were software capable of high-precision control, problems, he brilliantly fixed them in three from the perspective of industrial use such as on the correction of chromatic aberration. At dation that developed with the creation of elec- made. Nevertheless, in the aspect of aberration became fully available. Also, the aberration months. He was an outstanding engineer, a semiconductor production management. present, only two or three countries are able tron microscopes, and was supported by a long correction, the German lineage was superior to measurement method proposed by Friedrich wonderful person and very reliable. In to manufacture transmission electron micro- lineage of researchers. In regard to aberrations, its Japanese counterpart. Zemlin in the late-1970s was helpful. And addition to the performance of the device, our Moving forward from the stage of scopes (TEMs) equipped with aberration cor- German physicist Otto Scherzer began basic finally, applying aberration correction, relationship of trust was also vital. “merely capturing images” rection devices. I believe that Japan definitely research from the 1930s. In 1970s, Rose was Challenge the impossible enhanced resolution of an electron microscope Kimoto: Since Haider gave his all to the de- has caught up with leading countries in this field. an associate professor working at Scherzer’s was achieved for the first time in the world in velopment of the device, he probably would Kimoto: Aberration correction devices have Kimoto: In the future, what kind of electron only have sold the device to people who been becoming popular these days, but the cur- microscope technologies do you think need to laboratory.