SIR CHARLES W. OATLEY (1904-1996)

BY LORD ALEC N. BROERS

SIR CHARLES WILLIAM OATLEY¹ was a senior member of the team of scientists and engineers who developed radar in Britain during World War II. After the war, he moved to the University of Cambridge, where he modernized the teaching of electrical engineering and led a research team that developed the modern scanning electron microscope (SEM). Initially, the adoption of the SEM was slow, but it grew rapidly after about 10 years. Today, an estimated 500,000 surface SEMs are in use in scientific, technological, and medical laboratories around the world. It became one of the most significant scientific instruments developed in the second half of the 20th century.

Charles was born in Frome, Somerset, England, on Feb. 14, 1904, and died in Cambridge on March 11, 1996, at age 92. His father, William Oatley, owned a successful bakery business. Though he had no formal education in the sciences, he was intensely interested in technological advances and was among the first to power his bakery with electricity. He gave Charles an electric motor for his sixth birthday, surely a unique present for a six-year-old in 1910 and taught him how to use a treasured Watson Royal microscope. As a child, Charles became familiar with electricity and microscopy. His mother, née Ada Mary Dorrington, was a schoolteacher.

Charles attended a local council school until age 12, then became a boarder at Bedford Modern School, where he excelled in science and demonstrated natural leadership and athleticism. He served as head boy and captained the swimming and Rugby Fives teams. Rugby Fives is a handball game played in an enclosed court, similar to squash. It would prove pivotal to his future, as a Rugby Fives match first brought him to Cambridge University. He was immediately captivated by its magnificent college buildings and storied scientific legacy, and he became determined to study there.

He subsequently earned an exhibition (scholarship) to St John’s College, Cambridge, where he began studying for a degree in natural sciences in 1922. His first year went well – he earned first-class honors and played water polo for the university. He also captained the swimming team in his final year. His supervisor was Sir Edward Victor Appleton, a physicist and pioneer in radiophysics who would go on to win the Nobel Prize in Physics in 1947. Among his fellow freshmen was John Cockcroft, seven years his senior, who studied mathematics rather than natural sciences. The two became good friends, and Cockcroft later shared the Nobel Prize in Physics in 1951 with Ernest Walton for splitting the atomic nucleus. Their friendship would become an important influence in Charles’s career.

During his third and final year, he was interviewed by Ernest Rutherford, who agreed to take him on to do research in nuclear physics. However, Charles was unable to secure the necessary funding to become a research student, and the opportunity became impossible. Instead, Appleton, who had moved to King’s College London, encouraged him to go into industry and helped him get a job at a small company called Radio Accessories that made electronic valves (vacuum tubes). This work introduced him to manufacturing techniques and the practical world of electronics, which would later prove valuable in his radar research.

By the end of 1926, new valves from GEC and Mullard caused a severe drop in sales for Radio Accessories. To compensate, the company entered a partnership with Raytheon in the United States to make gas-filled rectifiers. Charles was tasked with producing the first of these valves and traveled to Boston to learn the process. However, the project was never completed. The company’s financial situation deteriorated further, and it went bankrupt at the end of 1927. Aware of the company’s troubles, Appleton offered him a lectureship at King’s College that summer, which he accepted.

Charles spent the next 12 years at King’s College teaching and examining – “learning the elements of his trade,” as he put it. He traveled throughout Britain as an external examiner for the Oxford and Cambridge Schools Examination Board and served as a consultant for six years with Lissen Ltd., a small company that made radios and batteries. Though he had little time for research, he produced several influential papers in physics and electronics. Among them was a Methuen monograph on wireless receivers,² widely read by professionals and one that helped establish his reputation as an expert on radio receivers.

In 1928, at an old boys’ reunion at Bedford Modern School, he met Dorothy Enid West, the headmaster’s daughter. They married in 1930. Their sons, John and Michael, were born in 1932 and 1935. Enid was born in May 1905 and died in Cambridge in 2001.

In 1939, he was surprised to get a letter from Cockcroft inviting him to join a small group of physicists tasked with learning about scientific developments critical to the war effort. These included the secret work of R.A. Watson-Watt on radar and the Chain Home stations under construction along Britain’s eastern and southern coasts. Recognizing the importance of this work, he immediately arranged to take unpaid leave from King’s College for the duration of the war. By Sept. 3, 1939, the day war was declared, he was back in Cambridge at the Cavendish Laboratory, working with other members of Cockcroft’s group to convert Pye television receivers into radar sets capable of detecting submarines. These radar sets were built using essential test equipment, based on 200 MHz wavemeters designed by Charles.

In February 1940, he followed Cockcroft to a new facility in Christchurch, soon to be known as the Air Defense Research and Development Establishment (ADRDE), which oversaw all of the army’s radar development. Cockcroft was appointed superintendent in April 1941. Charles’s initial task was to improve the receivers used in the coastal defense system, where noise performance of the input valves proved crucial. At the time, receiver performance was tested by pointing them toward The Needles, off the Isle of Wight, and listening for echo noise – an imprecise and subjective method. Charles developed a new signal generator that enabled quantitative measurement of the valves’ noise characteristics. The tests revealed that special valves developed by GEC for this purpose were virtually useless, as they had been tested using large signals that failed to account for noise. To address this, he formed what became known as the “Oatley Basic Group,” which systematically conducted quantitative testing on all components and equipment used at the establishment.

As the work at ADRDE expanded, improved coordination with other radar establishments became increasingly important, and his responsibilities broadened. He was appointed deputy superintendent to Cockcroft in 1943 and became acting director in 1944, when Cockcroft moved to Canada to lead the Montreal Laboratory. There, Cockcroft oversaw the development of the ZEEP and NRX reactors and the establishment of the Chalk River Laboratories. By then, ADRDE had relocated to Malvern and had been renamed the Radar Research and Development Establishment (RRDE). Its staff had grown to 1,000 people.

By the end of the war, Charles had come to know most of the individuals who had contributed to Britain’s radar defense systems and had developed unrivaled expertise in radar and electronics. Although offered the position of superintendent, he chose instead to return to university teaching and research. King’s College London offered him a readership in physics – a position just below professor – but he believed his experience had better prepared him to focus on electronics rather than physics. Ultimately, John Baker (later Lord Baker), then head of the Engineering Department in Cambridge, arranged for him to be appointed to a lectureship in engineering and a fellowship at Trinity College.

By 1945, when he returned to Cambridge, Baker had introduced a new two-part Mechanical Science Tripos (the undergraduate engineering degree). Previously, the degree had been general, covering all aspects of engineering. The new structure allowed students to specialize in their third year. Charles developed the electrical engineering lectures and laboratory courses for the new program. His electron physics course was entirely new for engineering students and drew heavily on his experience at King’s College. Topics included quantum theory, kinetic theory of gases and vacuum techniques, thermionic and field emission, gas discharges, lens systems, photometry, and radiation pyrometry. Later, he introduced electron optics, and when the transistor was invented, semiconductor theory and statistical mechanics replaced some of the earlier material.

Before leaving RRDE, he set up a large-scale distribution scheme to deliver surplus equipment to Cambridge. This included truckloads of power supplies, oscillators, oscilloscopes, and individual electronic components. He managed the initiative on behalf of the entire university, and it made an invaluable contribution to postwar research in Cambridge. At the Engineering Department, he introduced research projects in mass spectrometry, microwave amplifiers, an electron trajectory analogue plotter, noise in valve amplifiers, flicker noise, electron-induced conductivity in diamond, and most importantly, the SEM.

He received no encouragement from the electron microscope community in pursuing the SEM. M. Knoll and M. von Ardenne in Germany had built an SEM before the war, and V.K. Zworykin (NAE 1965), J. Hillier (NAE 1967), and R.L. Snyder had built one at RCA in the United States in the 1940s. However, those early instruments produced disappointing results when examining the surfaces of bulk samples directly. At the time, researchers believed better results could be achieved by examining thin-film replicas of surfaces using a transmission electron microscope. In short, the community viewed the SEM as a dead end. Charles, however, believed the SEM was well suited for university research – speculative and exploratory. The project also leveraged his unrivaled knowledge in electronic scanning systems developed during the war.

The first SEM, known as SEM1, was built by his student Dennis McMullan, who began work in 1948. Unlike earlier instruments, SEM1 used an electron multiplier with beryllium-copper dynodes to collect electrons scattered from the specimen surface. The specimen was positioned at a relatively steep angle – 25 degrees to the beam – and a higher beam voltage of 10 to 25 kilovolts was used to minimize contamination effects on secondary electron emission. While the images were not as noise-free or high-resolution as those from modern instruments, they were strikingly three-dimensional due to the narrow electron beam’s large depth of focus, which had a half angle of only 5 x 10-3 radians. These results convinced Charles of SEM’s scientific and technological value. He launched a broad research program and encouraged students to explore every aspect of SEM performance and application.

W.C. Nixon joined the group in 1961 and later oversaw the work of R.F.W. Pease (NAE 1997) and A.N. Broers (NAE 1994). K.C.A. Smith optimized the electron optical performance of the SEM and concluded that secondary electrons, rather than high-energy scattered electrons, should be used to form images. He also built the first SEM for commercial applications. O.C. Wells studied atomic number contrast and stereo-microscopy. T.E. Everhart (NAE 1978) demonstrated voltage contrast in semiconductor devices and developed a more efficient secondary electron detector that significantly improved the signal-to-noise ratios. R.F.M. Thornley characterized and optimized this new detector and explored the use of low voltages to examine nonconducting specimens at very low temperatures. P.J. Spreadbury explored how the SEM could be simplified. A.D.G. Stewart studied in situ surface etching by ion bombardment and later directed the technical development of the Stereoscan at the Cambridge Scientific Instrument Company (CIC). H. Ahmed observed specimens, mainly dispenser cathodes, at high temperatures. Pease built a high-resolution SEM that reached the theoretical beam diameter limit of 5 nanometers using a tungsten filament cathode. Broers continued Stewart’s work on ion-bombarded surfaces and pioneered the use of the SEM in fabricating nanostructures, including 50-nanometer metal wires. Following Nixon’s advice, he also used photoresists, originally developed for integrated circuits, to produce 100-nanometer wires.

The most significant improvement to SEM resolution and image quality came from the Everhart-Thornley detector. Designed to amplify the picoamp-level secondary electron signal without introducing noise, it eliminated the need to float the head amplifier at a high voltage or expose electron multiplier dynodes to the atmosphere when changing samples. Everhart built the detector at Charles’s suggestion, using a plastic organic scintillator coupled to a photomultiplier via a light pipe. Secondary electrons are attracted to a few hundred volts and accelerated through a copper mesh onto an aluminum-coated scintillator held at about 10 kilovolts. The resulting light signal passes through the light pipe to the photomultiplier, located outside the vacuum system. A grounded outer case shields the microscope beam from the high voltage of the scintillator.

The first successful commercial application of the SEM was in the examination of paper. D. Atack of the Pulp and Paper Research Institute of Canada (PPRIC) used SEM1 built by K.C.A. Smith, during a sabbatical in Cambridge in the mid-1950s. His work demonstrated the SEM’s potential, prompting PPRIC to acquire an instrument for its Montreal laboratories. With no commercial SEMS available at the time, Charles arranged to have one (SEM3) constructed in the Engineering Department and delivered via the Scientific Apparatus Department of AEI (formerly Metropolitan Vickers). The idea was that if successful, SEM3 could serve as a prototype for a commercial system AEI was considering developing. Ken Smith supervised SEM3’s construction, which was shipped to Montreal in 1958 and was fully operational by 1960. Its location made it accessible to North American companies, and the first to use it was Dupont, which rented time on the microscope and subsequently ordered on of the first Stereoscans built by CIC.

While Charles had been encouraging both AEI and CIC to pursue commercial production, AEI attempted to adapt a preexisting microanalyzer rather than build on their SEM3 knowledge. That instrument failed commercially. CIC, on the other hand, successfully developed the Stereoscan alongside its Microscan x-ray microanalyzer, using shared components and drawing directly from Charles’s research group’s experience. Oatley credited CIC’s success to the leadership of managing director Pritchard, chief engineer Bergen, and Stewart’s technical expertise. As Charles recalled: “The first four production models were delivered respectively to the University of Wales, the University of Leeds, the University of Munster, and the Central Electricity Research Laboratories. By this time, the company had launched a publicity campaign, and orders began to roll in. An additional batch of 12 microscopes was put in hand, and then a further 40... The SEM had come of age.” By the end of 1971, according to Stewart, CIC had delivered 520 Stereoscans.

JEOL soon followed CIC in manufacturing SEMs, and as of 2025, more than 10 companies worldwide are producing surface imaging SEMs.

Over the course of his distinguished career, Oatley received numerous honors, awards, and honorary degrees. He was appointed an Officer of the Order of the British Empire (O.B.E.) in 1956 and received the Achievement Award from the Worshipful Company of Instrument Makers in 1966. In 1969, he was awarded the Duddell Medal by the Institute of Physics, elected a Fellow of The Royal Society, and received the Royal Society’s Royal Medal. The following year, he was honored with the Faraday Medal from the Institution of Electrical Engineers and named an Honorary Fellow of the Royal Microscopical Society. In 1973, he received the Royal Society’s Mullard Award. He was awarded honorary doctorates from Heriot-Watt University (D.Sc., 1974), the University of Bath (D.Sc., 1977), and the University of Cambridge (Sc.D., 1990). In 1974, he was knighted as a Knight Bachelor, and in 1976 he was named a Founding Fellow of the Royal Academy of Engineering and a Fellow of King’s College London. He became a Foreign Associate of the National Academy of Engineering in 1979, received the James Alfred Ewing Medal from the Institution of Civil Engineers in 1981, the Distinguished Scientist Award from the Microscopy Society of America in 1984, and the Howard N. Potts Medal from the Franklin Institute in 1989.

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¹In writing this memorial, I have drawn extensively from material published in Volume 133 of Advances in Imaging and Electron Physics, edited by P.W. Hawkes, titled “Sir Charles Oatley and the Scanning Electron Microscope” (Elsevier).
²Oatley CW. 1932. Wireless Receivers. The Principles of their Design. London: Methuen.