obituary IUCrJ John C. H. Spence (1946–2021) ISSN 2052-2525 Henry N. Chapman,a* S. Samar Hasnainb and Uwe Weierstallc PHYSICSjFELS aCFEL, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, Hamburg, 22607, Germany, bInstitute of Systems, Molecular and Integrative Biology, University of Liverpool, Life Sciences Building, Crown Street, Liverpool, Merseyside L69 7ZB, United Kingdom, and cArizona State University, PO Box 871504, Tempe, AZ 85287, USA. *Correspondence e-mail: [email protected]

Keywords: obituary; X-ray imaging; high-reso- lution electron microscopy; serial femtosecond ; X-ray free-electron lasers.

John C. H. Spence ForMemRS, Regent’s Professor and the Richard Snell Professor of at Arizona State University (ASU), who continuously blazed thrilling new trails in the science and methodology of electron and X-ray imaging, died on 28 June 2021. John’s career spanned developments in high-resolution electron microscopies to make the first observations of dislocation kinks at the atomic scale and the bonds in metal oxides and GaAs, to projection imaging using electrons emitted from a single-atom field- emission tip, to some of the first demonstrations of lensless X-ray imaging, and culmi- nating in the spectacular new field of serial femtosecond crystallography using X-ray free- electron lasers. He was fascinated by the phase problem in diffraction and crystal- lography, with a close intellectual connection to who made first attempts to utilize changes in unit-cell dimensions to map out the underlying molecular transform. The brightness inherent to undulator devices at synchrotron radiation facilities and, later, to X-ray free-electron lasers, provided coherent beams and fertile ground for fresh new ideas and methods in imaging and diffraction. John’s sweeping knowledge of Fourier optics and microscopy theory, coherent micro-diffraction, dynamical diffraction, solid- state and quantum physics, as well as an inventiveness for instrumentation harking back to the age of enlightenment (some of his heroes were Lord Rayleigh, Humphry Davy and James Clerk Maxwell) brought forth a stream of new instruments and methods. John was a prodigious writer of papers, books, emails, lists and post-it notes. He shared ideas freely and widely through such writings and through his enthusiastic talks and interactions with colleagues and strangers all around the world. John was born in Canberra, Australia. His father was a decorated Royal Australian Air Force (RAAF) pilot who was killed in action in the Korean War when John was four years old. His mother, a strong personality, imbued him with a keen sense of fairness, empathy, humanism and kindness that set him apart over the course of his entire academic career. He carried out his PhD at Melbourne University with Alan Spargo on electron energy loss spectroscopy (EELS). Together with CSIRO, Melbourne University

IUCrJ (2021). 8, 705–708 https://doi.org/10.1107/S2052252521007879 705 obituary was an early bastion of electron microscopy. In a postdoctoral mode TEM images. He then combined, together with Uwe fellowship at Oxford University with Sir Peter Hirsch, David Weierstall, an STM with a time-of-flight spectrometer for Cockayne and Mike Whelan, John advanced dynamical identifying atomic species on surfaces. He often quoted diffraction theory and the pursuit of imaging atoms in the Humphry Davy, ‘Nothing tends so much to the advancement TEM, using channelling and lensing effects caused by columns of knowledge as the application of a new instrument’ and of atoms in a crystal. He arrived in the USA in 1976 to join the loved the ingenuity of our scientific forebears (his joy jumps group of John Cowley, a former Melbourne professor and off the pages of his recent book ‘Lightspeed’ on the history of founder of the Center for High Resolution Electron Micro- the measurement of the speed of light). scopy at Arizona State University. There, he worked on the In addition to his developments of electron microscopy for theory of the scanning transmission electron microscope materials, John was the driving force to obtain an NSF grant to (STEM), continued EELS in this microscope configuration, acquire a cryo-EM at ASU, which is now installed in the and further developed ideas to use the electron wavefield Southwestern Center for Aberration Corrected Electron propagating through a crystal as a form of lens or as a way to Microscopy. For his achievements in Electron Microscopy, locate dopant atoms by measuring X-ray fluorescence as a John received the Distinguished Scientist Award of the function of the phase of standing wave. He used high-resolu- Microscopy Society of America in 2006, the Buerger Medal of tion TEM to image defects in semiconductors, solving the the American Crystallographic Society in 2012, the J. M. famous question of the ‘shuffle or glide’ mechanism of dislo- Cowley Medal of the International Federation of Societies of cation cores in silicon. In 1995, together with Harry Kolar he Microscopy in 2014, the Burton Medal of Microscopy Society was able to image moving dislocation kinks along partial of America (1980) and a Humboldt Senior Scientist Award in dislocations by taking advantage of forbidden f.c.c. reflections. 1991. John became a Fellow of the Royal Society (Foreign He also made the first observations of Pendello¨sung radiation Member) in 2015, and a Corresponding (Foreign) Member of and coherent Bremsstrahlung due to electrons passing through the Australian Academy of Science in 2016. He was also a the periodic potentials of crystals, a forerunner of his latest Fellow of the American Association for the Advancement of work at the BioDesign Institute, together with Bill Graves, on Science, of the National Academy of Inventors, the American developing a compact XFEL. Physical Society, the Microscopy Society of America, of the In the 1980s, as an assistant professor and together with Royal Microscopy Society, of the Institute of Physics (UK), Mike O’Keefe and Jian-Min Zuo, John continued developing and an Overseas fellow of Churchill College Cambridge, UK. convergent-beam electron diffraction in the STEM to quan- A sabbatical at Lawrence Berkeley Laboratory in 1997– titatively and accurately map out charge density distributions. 1998 and a decade of summers spent there in research and on This culminated in the direct observation of atomic d-orbitals scientific advisory committees brought about a new chapter in of copper oxide. With Mike O’Keefe in 2005, he also was the John’s interests. The demonstration of direct phasing of a first to apply the charge flipping algorithm to experimental coherent X-ray diffraction pattern of a non-periodic object by data and solve a real structure. At this time, John also started John Miao, David Sayre and others in 1999, sparked John’s to investigate various mathematical approaches to directly interest. He initiated a long-running series of international solve the many-beam dynamical diffraction inversion problem workshops on coherence and phase retrieval where he for determining unknown crystal structures. He kept returning brought together the communities of convergent-beam elec- to this quest for the rest of his life and was finally able to tron diffraction, electron holography, electron ptychography, publish an elegant and complete solution based upon an the budding X-ray diffractive imaging, and leading experts in iterative method of projections together with Jeffrey Dona- non-convex optimization problems. John began investigating telli. In a talk he gave on the topic in May 2021, John remarked the opportunities and limits of the approach with Malcolm on how satisfied he was to have completed this work, saying it Howells (Henry Chapman later joining). They carried out the was what he was most proud of. But in addition to these first demonstration of lensless imaging in three dimensions, theoretical underpinnings, John was quite the tinkerer and had using soft X rays, and explored limitations due to radiation a love of instrumentation (and vintage cars). One major damage. A question was whether the approach could realize achievement coming out of John’s lab was the first CCD atomic imaging of macromolecules without needing to crys- camera for electron microscopy in 1986, later fully developed tallize them. While the idea of out-running radiation damage by Gatan. In the early 1990s, he was able to obtain low energy using would-be free-electron laser pulses had just been electron projection and reflection holograms using a single published by Janos Hajdu’s group, John had many other ideas atom electron field emission source, with Weida Qian and later which he pursued with characteristic vigour, such as diffracting Uwe Weierstall. Around that time John became interested in with a continuous X-ray or electron source from a stream of and investigated the possibility of imaging biological speci- molecules aligned in a polarized laser field, and resurrecting mens at electron energies below the carbon K-shell to reduce an old idea, due to Kam, of calculating intensity correlations radiation damage. With Theo Vecchione, he worked on from snapshot coherent diffraction patterns of an ensemble of designing a coherent photofield electron source for fast identical but randomly oriented molecules. Correlations of imaging. Enthralled by the invention of the scanning tunnel- photons scattered from the same molecule would accumulate ling microscope, he placed one inside a TEM holder, together whereas those from different molecules would wash out. The with William Lo, to make simultaneous STM and reflection short exposure times would freeze out any blurring due to

706 Henry N. Chapman et al. John C. H. Spence (1946–2021) IUCrJ (2021). 8, 705–708 obituary rigid-body rotations. John coined the phrase ‘diffraction against high odds. Will it lase? Will it be useful? The past five before destruction’ for outrunning the Coulomb explosion years have seen their vision vindicated with breakthrough with intense femtosecond-duration pulses and joined the large applications in many fields, from materials science and atomic collaboration, along with Janos Hajdu, Ilme Schlichting, Petra and molecular physics to condensed matter physics and Fromme and Henry Chapman and many others, to carry out biology.’ first experiments at the Linac Coherent Light Source, the first He had a high sense of community service which was X-ray FEL. The success of the method which was later termed reflected in many arenas including his service to the Interna- serial femtosecond crystallography (in homage to John’s tional Union of Crystallography. In addition to his position as earlier idea of creating orientational order with a laser) relied the Main Editor (Physics and FEL Science and Technology) of on many factors – one of the most important being liquid IUCrJ since the journal’s launch, John was Co-editor of Acta microjets for crystal delivery, that John perfected with Bruce Cryst. A from 1989 to 1999 and served on the IUCr Doak, Dan Deponte and Uwe Weierstall. The method became Commissions on Electron Diffraction (now Electron Crystal- the most widely used technique at XFELs, providing radia- lography) (1996–2002; Chair 2002–2005) and Charge, Spin and tion-damage-free structures of macromolecules at room Momentum Densities (now Quantum Crystallography) (1999– temperature and with temporal resolution. This was in no 2008). When in 2012, after one of us (SSH), as Editor-in-chief small part due to the effort of many collaborators in the NSF of the IUCr journals, approached John to lead one of the Science and Technology Center ‘BioXFEL’ which John sections (Physics, and FEL Science and Technology) at the founded and of which he was Director of Science, and which ASCA meeting at Adelaide outlining the vision and ambition now consists of 13 partner institutions. He was always open to for IUCrJ, he immediately saw its importance. Despite enor- new ideas and generous with his time, encouraging new mous demands on his time he agreed and started coming up projects and researchers wishing to make use of the new with ideas how to make IUCrJ a natural home for FEL XFEL technology. Thus he paved the way of utilizing serial Science and Technology. The launch of the IUCrJ was crystallographic approaches to obtain structures free from announced on 5 December 2012 with five main editors (E. N. radiation-induced chemistry (and associated structural Baker, C. R. A. Catlow, G. R. Desiraju, S. Larsen, J. C. H. changes), and structural enzymology via developments such as Spence). In addition to assembling a fantastic team of Co- mix-and-inject systems. Together with Janos Hajdu and Henry editors for his section and encouraging key authors to submit Chapman, John was awarded the 2021 Gregori Aminoff Prize high quality papers, John led from the front as is reflected in an of the Royal Swedish Academy of Sciences for their contri- important contribution, entitled ‘Ab-initio phasing using butions to FEL-based structural biology. Sadly, John did not nanocrystal shape transforms with incomplete unit cells’ that live to attend the ceremony which was postponed due to the appeared in the Inaugural issue. current pandemic. John had many other interests included sailing, vintage cars John was a prolific writer and his monographs High Reso- and music. He was passionate about playing the piano, guitar lution Electron Microscopy and Electron Microdiffraction and flute, and performed with other ASU faculty and postdocs (with Jian-Min Zuo) are indispensable classics for electron in several bands over the years. His most recent ensemble microscopists. His emails, like his conversations, were full of ‘Who Knew’ wowed attendees of many conferences – they irreverent wit, blinding insights, advice and encouragements, were a special feature of the BioXFEL conferences. and often hard to keep up with. His writings showed in-depth John will be remembered for his wit, generosity, openness, understanding of the topic but clear understanding of the sense of duties to the wider community and above all for his factors that contributed to the success of the latest advance- tremendous scientific contributions across the sciences, ment. One such example is his first editorial, entitled ‘X-ray reflected in some of the books and papers given below. lasers and crystallography’, as the Main Editor (Physics and John is survived by his wife, Margaret, sister, Penny, son, FEL Science and Technology) of IUCrJ where he wrote ‘As so Andrew with his wife Rebecka and two grandchildren, and by often happens in the history of science, the breakthrough three stepsons, James, Daniel and Peter Stanzler and their eventually occurred at the interface of several fields – families. synchrotron science (and especially their insertion devices), laser physics, and work on microwave tubes for radar, emer- Acknowledgements ging from the second world war.’ ‘All of this culminated recently in the construction of the first hard-X-ray laser, the We thank Margaret Spence for clarifications and input. US Department of Energy’s Linac Coherent Light Source (LCLS), at their SLAC laboratory near Stanford. The first References X-ray lasing occurred in that two-mile long tunnel on 21 April Chapman, H. N., Fromme, P., Barty, A., White, T. A., Kirian, R. A., 21 2009 at about 2 kV, in an all-or-nothing moment of intense Aquila, A., Hunter, M. S., Schulz, J., DePonte, D. P., Weierstall, U., excitement, as theoretical predictions proved spot-on.’ He Doak, R. B., Maia, F. R. N. C., Martin, A. V., Schlichting, I., Lomb, went on to acknowledge foresight of DOE ‘The gamble taken L., Coppola, N., Shoeman, R. L., Epp, S. W., Hartmann, R., Rolles, 6 D., Rudenko, A., Foucar, L., Kimmel, N., Weidenspointner, G., by the DOE in committing to the $600 10 construction of Holl, P., Liang, M., Barthelmess, M., Caleman, C., Boutet, S., the LCLS around 2004 was laudable, in these days when low- Bogan, M. J., Krzywinski, J., Bostedt, C., Bajt, S., Gumprecht, L., risk incremental science seems the only way to attract funding Rudek, B., Erk, B., Schmidt, C., Ho¨mke, A., Reich, C., Pietschner,

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