Scanning ultrafast electron microscopy (S-UEM) as a time-resolved method with resolutions in both space and time has been successfully developed by researchers at Caltech. The approach is demonstrated in the investigation of the dynamics of semiconducting and metallic materials visualized using secondary-electron images and backscattering electron diffraction patterns. |
Scientists
who pioneered a revolutionary 3-D microscope technique are now
describing an extension of that technology into a new dimension that
promises sweeping applications in medicine, biological research, and
development of new electronic devices. Their reports on so-called 4-D
scanning ultrafast electron microscopy, and a related technique, appear
in two papers in the Journal of the American Chemical Society.
Chemistry
Nobel Laureate Ahmed H. Zewail and colleagues moved high-resolution
images of vanishingly small nanoscale objects from three dimensions to
four dimensions when they discovered a way to integrate time into
traditional electron microscopy observations. Their laser-driven
technology allowed researchers to visualize 3-D structures such as a
ring-shaped carbon nanotube while it wiggled in response to heating,
over a time scale of femtoseconds. A femtosecond is one millionth of one
billionth of a second. But the 3-D information obtained with that
approach was limited because it showed objects as stationary, rather
than while undergoing their natural movements.
The
scientists describe how 4-D scanning ultrafast electron microscopy and
scanning transmission ultrafast electron microscopy overcome that
limitation, and allow deeper insights into the innermost structure of
materials. The reports show how the technique can be used to investigate
atomic-scale dynamics on metal surfaces, and watch the vibrations of a
single silver nanowire and a gold nanoparticle. The new techniques
“promise to have wide ranging applications in materials science and in
single-particle biological imaging,” they write.
Zewail
and colleagues acknowledge funding from the National Science
Foundation, the Air Force Office of Scientific Research, the Gordon
& Betty Moore Physical Biology Center at Caltech, and the Arab Fund
for Economic and Social Development.
Image dynamical change of single-crystal CdSe at selected frame times. The dashed ellipses indicate the locations for 1/e of the maximum laser fluence used. No observable change at very negative time signifies the recovery of the system to an equilibriated state after each pump-probe event (upper left panel). |
4D Scanning Ultrafast Electron Microscopy: Visualization of Materials Surface Dynamics
