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  • Dissemination of Knowledge
  • A. H. Zewail. Filming the Invisible in 4D, Sci. Am. 303, 74 (2010).

    Picture this: a movie revealing the inner workings of a cell or showing a nanomachine in action. A new microscopy is making such imaging possible. Four-dimensional electron microscopy produces "movies" of nanoscale processes occurring over time intervals as short as femtoseconds (10-15 second). The technique builds up each frame of the movie from thousands of individual shots taken at precisely defined times. It has applications in a wide range of fields, including materials science, nanotechnology and medicine...

    A. H. Zewail. Micrographia of the Twenty-First Century: From Camera Obscura to 4D Microscopy, Phil. Trans. R. Soc. A 368, 1191 (2010).

    In this paper, the evolutionary and revolutionary developments of microscopic imaging are overviewed with a perspective on origins. From Alhazen's camera obscura, to Hooke and van Leeuwenhoek's two-dimensional optical micrography, and on to three- and four-dimensional (4D) electron microscopy, these developments over a millennium have transformed humans' scope of visualization. The changes in the length and time scales involved are unimaginable, beginning with the visible shadows of candles at the centimetre and second scales, and ending with invisible atoms with space and time dimensions of sub-nanometre and femtosecond...

    G. K. Drayna and D. J. Flannigan; Mentor: A. H. Zewail. Ultrafast Electron Microscopy: Watching Atoms Move and Crystals Melt, Caltech Undergrad. Res. J. 8, 36 (2008).

    For decades, researchers have relied on static images provided by electron microscopy and static diffraction patterns provided by X-ray crystallography to infer how a system operates. The major drawback to these otherwise very powerful techniques is that no direct experimental evidence is gathered about the structure of the transition states of the system. That is, these techniques can only provide information about the three spatial dimensions; while information about how the system behaves in the fourth dimension—time—remains a mystery. Therefore, to overcome this fundamental problem, a methodology that can access all four dimensions simultaneously must be realized and demonstrated. The development of such a technology would mark a great day in the advancement of human knowledge. Fortunately, that day has arrived with the advent of Ultrafast Electron Microscopy (UEM)...

    J. S Baskin and A. H. Zewail. Freezing Atoms in Motion, J. Chem. Educ. 78, 737 (2001).

    The concept of the atom, proposed 24 centuries ago and rejected by Aristotle, was born on a purely philosophical basis, surely without anticipating some of the 20th century's most triumphant scientific discoveries. Atoms can now be seen, observed in motion, and manipulated...

    J. S. Baskin and A. H. Zewail. Freezing Time—In a Femtosecond, Sci. Spectra 14, 62 (1998).

    With ultrashort pulses of laser light, it has become possible to observe physical, chemical and biological changes with a resolution of femtoseconds, 15 orders of magnitude faster than the human heart beat, reaching the scale of atomic motion, spatial and temporal...

    A. H. Zewail. The Birth of Molecules, Sci. Am. 263, 76 (1990).

    In 1872 railroad magnate Leland Stanford wagered $25,000 that a galloping horse, at some point in stride, lifts all four hooves off the ground. To prove it, Stanford employed English photographer Eadweard Muybridge. After many attempts, Muybridge developed a camera shutter that opened and closed for only two thousandths of a second, enabling him to capture on film a horse flying through the air. During the past century, all scientific disciplines from astrophysics to zoology have exploited high-speed photography to revolutionize understanding of animal and mechanical motions that are quicker than the eye can follow...

    M. Gruebele and A. H. Zewail. Ultrafast Reaction Dynamics, Phys. Today 43, 24 (1990).

    With new laser techniques and with gas phase and molecular beam experiments, it is now possible to determine the ultrafast motion in isolated chemical reactions: chemistry on the 10-13-second time scale...

    A. H. Zewail. Laser Selective Chemistry: Is It Possible?, Phys. Today 33, 27 (1980).

    With sufficiently brief and intense radiation, properly tuned to specific resonances, we may be able to fulfill a chemist's dream, to break particular selected bonds in large molecules...

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