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
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
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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