FEI has released the Tecnai™ Femto ultrafast electron microscope (UEM), enabling scientists to explore ultrafast events and processes that occur at the atomic and molecular spatial scale over time spans measured in femtoseconds (10-15 seconds).
These include such fundamental processes as the absorption of light energy and its transformation into heat or mechanical changes (photoactuation) and the crystallization or recrystallization of materials-including large biological molecules for structural analysis.
The Tecnai Femto is the first system to commercialize the patented ultrafast electron microscopy technology pioneered by Nobel laureate Prof. Ahmed Zewail at the California Institute of Technology. The first Tecnai Femto UEM will be installed at the University of Minnesota in November 2013.
David Flannigan, Ray D. and Mary T. Johnson/Mayon Plastics assistant professor in the Department of Chemical Engineering and Materials Science at the University of Minnesota, and previously a member of Professor Zewail’s research team at Cal Tech, explained, “Over the last decade microscope manufacturers like FEI have developed instruments that have made observations of objects as small as individual atoms relatively routine. Ultrafast electron microscopy now gives us a powerful tool to look at the movements and changes that occur at this scale. Because the distances are so small, the time scale is also condensed--it doesn’t take very long to travel a nanometer or two. Using single-electron pulses, we have measured changes over time periods as short as tens of femtoseconds--those are millionths of a billionth of a second.”
“This is a truly revolutionary technology,” stated Trisha Rice, FEI’s vice president and general manager of the Materials Science Business Unit. “Until now, the only commercially-released instruments that could look at processes at this time scale were limited to observations of bulk materials. The Tecnai Femto UEM is the first to combine femtosecond time resolution with nanometer spatial resolution, allowing researchers to see the structural changes that occur at the atomic scale in response to the energetic stimuli.”
Flannigan added, “The literature already contains a wide variety of UEM applications described over two generations of instrument development in Zewail’s lab at Cal Tech since he began this work in 2004. For instance, we looked at the mechanical properties and photoactuation of silicon nitride cantilevers and at the photo-induced heating and expansion of carbon nanotubes. Looking forward, we plan to focus our attention on the development of new applications with important practical value. For example, we want to look at the crystallization of biological macro molecules preparatory to structural analysis, which could lead to important advances in understanding the structure-function relationships of complex living systems.”
The Tecnai Femto is a member of FEI’s Tecnai family of transmission electron microscopes (TEM). It has been modified to accommodate ultra short laser pulses that stimulate a brief “flash” of photoelectrons from the electron source, and a precisely-timed pulse of laser energy directed at the sample as a stimulus.
To achieve the highest temporal resolution when observing reversible processes, the Tecnai Femto UEM operates in stroboscopic mode where a large number of precisely-timed flashes, each containing as few as a single electron, build up a representative image of the sample at a given delay between stimulus and flash.
The delay is then adjusted incrementally and another image acquired, resulting ultimately in a sequence of images much like the frames of a motion picture. For irreversible processes, such as fractures, the instrument can be operated in the single pulse mode with many electrons in the pulse, but unlike the femtosecond single-electron mode, the time resolution reaches picoseconds to nanoseconds because of Coulomb repulsion. Importantly, the instrument can also be operated in conventional continuous-beam TEM mode.