John Spence

John Spence, the Richard Snell Professor of Physics and a Regents Professor at Arizona State University (ASU), died peacefully on 28 June 2021 in Boston.

John was born in Canberra, Australia, on 24 April 1946. His father, Wing Cdr Louis T. Spence, led Australian Air Forces in the Korean War and was killed in action when John was only 4. John received his undergraduate degree and PhD from the University of Melbourne and then did a postdoc in Oxford. In 1976 he joined the famous ASU electron microscopy group founded by John Cowley, and he remained there for the remainder of his scientific career.

John was recognized as a pioneer in the development of advanced electron microscopy techniques. His book Experimental High Resolution Electron Microsopy, first published in 1980 shortly after he moved to ASU, was a well-known classic. His interests ranged far and wide over all aspects of electron and x-ray scattering, with applications in materials science and biology. In early work with his first postdoc, J. Tafto, he exploited electron channeling (ALCHEMI) to locate the sites of atoms selected by their spectroscopic signature. Later work with J.-M. Zuo and M. O’Keeffe used careful quantitative analysis of convergent beam diffraction patterns to map bonding charge densities. John always realized that limitations were ultimately due to sources and detectors, and he maintained a lifelong interest in improving these technologies.

As a way of using x rays for imaging, John pushed the development of various phase retrieval algorithms in coherent diffractive imaging. This marked the beginning of his involvement with synchrotrons, notably at Berkeley. He was the driving force behind the developments of femtosecond pulse diffractive imaging, where the aim was to acquire the data before the specimen had been destroyed by radiation damage. The first result was the determination of the structure of a large protein, Photosystem 2, from micron sized crystals using data acquired at the Stanford Linac Coherent Light Source. The specimen from P. Fromme consisted of protein microcrystals in liquid and was sprayed across the x-ray beam in a liquid microjet using an injector developed by B. Doak and U. Weierstall. The results showed that protein structures could be determined by injecting a slurry of micrometer sized crystals in random orientations at room temperature into the pulsed x-ray laser beam.

The fact that no large crystal was necessary and that radiation damage can be outrun by the short x-ray pulse duration generated widespread excitement. The method was termed Serial Femtosecond Crystallography, and what followed was a series of high profile publications on biomolecular structure and conformational changes. John was instrumental in the formation of the seven-university BioXFEL Science and Technology Center supported by NSF, and the project to build a compact x-ray free electron laser at ASU. More recently, together with J. Donatelli, John published a highly innovative solution on how to retrieve the crystal potential from electron diffraction intensities when there is multiple elastic scattering (dynamical diffraction), a problem that has puzzled many of us for half a century.

He expressed a desire to spend more time on the history of science. His fascinating book Lightspeed, on the history of the physics of light propagation and measurement of the speed of light, should have been the first of many.

John had an enthusiasm for physics that was contagious. He was outgoing and generous, never failing to give credit to others and advertising their work. He was always bouncing ideas around: The reaction of others was part of his process of refining and perfecting his thoughts.

There was much more to John than physics. He was an accomplished musician, with a love of both classical and contemporary music, founder of two rock groups in the department, a connoisseur of old British sports cars, and an avid sailor and glider pilot. An evening with John was never dull, full of stimulating conversation on a wide range of topics, not to mention the obligatory wine and the musical interlude! He will be sorely missed by the community of x-ray diffraction and electron microscopy researchers throughout the world.

For his many achievements, Spence received the Distinguished Physical Scientist Award of the Microscopy Society of America in 2006, the Buerger Award of the American Crystallographic Society in 2012, the J. M. Cowley Medal of the International Federation of Societies of Microscopy in 2014, and the Burton Medal of MSA. He shared the Gregori Aminoff prize of the Swedish Academy in 2021, and he was elected as a Foreign Member of the Royal Society.

He leaves behind his wife, Margaret, sister Penny, son Andrew, and grandchildren Maja and Louis.