Observing Dynamic Processes in Real Time

Directly observing the transient structures as they occur during reactions is vital to understanding many of the fundamental phenomena at the heart of chemistry, biology and materials science. While electron microscopy provides the ability to see the atoms that are present at interfaces or defects in nanostructures, and ultrafast optical, X-ray and electron methods allow the dynamics that occur on a molecular level to be analyzed, combining the two capabilities to study the evolution of systems from the atomic and molecular all the way up to the mesoscale requires the development of a new imaging capability.  Replacing the standard field-emission source and using lasers to create a large pulse of electrons by photoemission, the dynamic transmission electron microscope (DTEM) forms direct images with the spatial resolution of a TEM and a temporal resolution that is essentially defined by the laser that is used to create the pulse (typically this in the range of 1microsecond to 1nanosecond).  Combining this temporal resolution with in situ stages allows the dynamical behavior of nanostructures in gases (up to atmospheric pressure), liquids and solids to be studied with unparalleled spatio-temporal resolution. These high-resolution images permit scientists to determine the interactions of atoms and molecules to form larger scale structures to be observed directly, rather than inverting to an unknown structure from diffraction patterns or spectra as is typical for other methods. Furthermore, as this temporal resolution can essentially “freeze” the effects of Brownian motion in place, biological samples can be studied in their natural hydrated state.  The ability to generate many consecutive pulses means that the potential exists to obtain movies that show the structural changes that occur during a biochemical process.  Creating, controlling and manipulating the large pulse of electrons represents the major challenge in developing and applying DTEM, but the technologies to potentially extend the temporal resolution even further into the sub-nanosecond regime already exist.  In this presentation, the basics behind the operation of the DTEM, its potential for future enhancements, and its application to a wide range of scientific challenges, including materials for energy technologies and biological systems, will be discussed.