Ahmed H. Zewail

On a summer day of 2008, at one of my stays in Caltech, an enthusiastic Physics Master student from New York, whom Ahmed Zewail did not know before, wanted to meet the sole winner of the 1999 Nobel Prize for Chemistry. I was truly amazed to see Ahmed explain his research to the young man and show him his latest results with the excitement, fascination and joy of a PhD student getting his first results. This attitude embodies Ahmed’ personality, a man who, in spite of reaching the acmes of prestige and international recognition, kept a passion and rigour for Science and a great generosity and intelligence du coeur in his relation with others.

Ahmed Zewail was born in 1946 in Damanhur, in the delta of the Nile, Egypt. After obtaining his Master’s degree from the University of Alexandria in 1969, he choose the USA for his PhD, inspired by the style of his mentor, who had been trained in this country. He obtained the title of doctor in 1973 from the University of Pennsylvania, under the supervision of the late Robin Hochstrasser. He then moved to Berkeley where he spent two years as a postdoc in the group of Charles B. Harris. It was there that he started to work with the newly developed picosecond lasers, the springboard to the new research that he initiated at Caltech in 1976 as assistant professor. He developed his concepts about coherence and in a series of papers, which earned him tenure after two years, he pioneered studies of molecular coherence with lasers and was the first to introduce shaped pulses for the study of molecular processes. This work later lead to the birth of a new field of research, Femtochemistry. Indeed, as soon as the femtosecond laser appeared in the mid-1980s, he used it and achieved a breakthrough by demonstrating the visualization in “real-time”, of nuclear motion in molecular systems. Ahmed Zewail’s genius was his ability to convey the power and insight of the new discoveries by a judicious choice of the systems to study, going from simple ones to systems of ever greater complexity. The impact of his discoveries went quickly beyond chemistry as they dealt with the “atomic scale of time”, as he put it himself, opening new perspectives for research in Biology, Condensed Matter Physics and Materials Science. This, along with his enthusiasm and his sense of communication, brought about a real revolution in Science, which was recognised by the Nobel Committee barely 12 years after Ahmed’s first pioneering experiments.

During his Nobel lecture, Ahmed made a humoristic comment about the Prize citation not mentioning his work on ultrafast electron diffraction and microscopy. Indeed, already as he was starting the “Femtochemistry revolution” in the early 1990s, Ahmed Zewail was aware of the fact that optical-domain (ultraviolet, visible and infrared) spectroscopy does not deliver structure. Therefore, already then he started to combine the temporal resolution of femtosecond lasers, with the atomic-scale spatial resolution of electron-based structural methods (diffraction and microscopy), provided sufficiently short pulses of electrons could be generated. This was a daring and visionary choice, which now fully recovers its importance and depth. Indeed, while most of the community of ultrafast scientists (including the author of this piece) adopted ultrashort pulses of X-rays, he was the only scientist to go for ultrashort pulses of electrons. Just as with the discoveries leading to Femtochemistry, he adopted a systematic strategy starting with simple molecular systems and then increasing the complexity of the systems under study. By the early 2000s, he had achieved a great leap forward: the study by ultrafast electron diffraction and crystallography of dynamical processes in condensed phase systems, such as those of interfacial water on a hydrophilic surface, of adsorbates on surfaces, and important to biology, of phospholipids and fatty acid bilayers. In addition, he achieved yet another of his impressive turns with the development of real-time and real-space electron microscopy or 4D-EM, which in my opinion (and that of many others) represents a real revolution in structural dynamics. This technique is delivering an amazing degree of insight into the mechanisms behind a large class of phenomena in Condensed Matter Physics and Materials Science.

One impressive aspect of Ahmed Zewail’s achievements is the number of new avenues he has opened with each of his breakthroughs using electron-based techniques. New methods emerged from his labs, such as ultrafast EELS (electron energy loss spectroscopy), which combined with ultrafast microscopy, delivers the full dynamical and electronic information in real-time, real space and with energy resolution, or the so-called Photon-induced near-field electron microscopy (PINEM), which allows the visualization of the evanescent electric fields around excited species. PINEM has grown into a major tool for visualizing the time evolution of nano sized objects in Biology and Materials Science, and it is now making its way in the scientific community worldwide. Parallel, to this, he also demonstrated the impressive results of electron nano-diffraction, opening the way to the study of single nano-objects and of powders.

In the last few years, and despite his illness, which appeared in 2013, Ahmed Zewail went on widening the range and scope of systems one can study with 4D electron microscopy and diffraction and related methods in Biology, Nanoscience and Materials Science. It is the deep conviction of many (including the author) that he was bound to obtaining a second Nobel Prize for his outstanding achievements using electron-based techniques.

His innumerable scientific achievements (about 600 articles and over a dozen books) earned him an impressive number (over a 100) of prizes, awards and honorary degrees that it are impossible to list here. His former students and postdoctoral researchers (his “Science Family” as he liked to put it) can be found in leading positions in Science around the Globe.

Ahmed Zewail had another mission: his concerns for the “have-nots”, as he used to say, with special attention to the Arab World and more specifically, to his country of origin, Egypt. He considered the support for Science in the developing world of paramount importance for the betterment of its humanity (part of his Nobel Prize was donated to provide scholarships in Egypt). He became an ambassador of Science in the world even prior to being appointed United States First Science Envoy to the Middle East (2009-2011), President Obama’s Council of Advisors on Science and Technology (2009-2013) and UN Secretary General Ban Ki-moon’s Scientific Advisory Board (2013-). During the recent events in Egypt, he made it clear that he had no political ambitions. In fact, it was a leitmotiv of his that the best way to serve Egypt and the Arab world was to pursue excellence in Science. As a matter of fact, his long-term goal of building a world class Science and Technology University in Egypt, the Zewail City, was reached after years of hard work through the meanders of bureaucratic and political difficulties, especially in the last few years.

On one of the last occasions I met him, almost a year ago by the day, we spent an afternoon smoking cigars (that was a ritual every time we met) and chatting about Science, Politics and Life in general. Although, he was physically affected by his illness, I was profoundly impressed by his sparkling and uplifting spirit, his enthusiasm, his sense of humour, and his incisive thinking about Science problems. I left with a feeling of being with an immortal figure. In science and in the world at large, Ahmed’s influence is deep, broad and will last for generations. In this respect, he is immortal.