Our group has developed a dark-field imaging mode for DTEM that enables the highest combined spatial and temporal resolution imaging of nanoparticles achieved thus far.

By enabling the scientific community direct experimental insight into the behavior of nanometer-scale systems at nanosecond time intervals, ADF-DTEM promises to give engineers and scientists a powerful method for exploring systems that are at the core of some of the most crucial energy technologies of both today and tomorrow.

—Daniel Masiel of the University of California (Davis), lead author

15 ns pulsed ADF image of tiny gold particles dispersed on a holey carbon film. The line scans show the improved signal-to-background ratio obtained by using an ADF aperture for pulsed imaging. Source: masiel et al. Click to enlarge.

A DTEM is a transmission electron microscope that has been modified to include a laser-driven photocathode that can produce a single intense pulse of electrons with a duration of only 15 ns. While the instrument has the potential to provide insight into nanoparticle catalyst dynamics by enabling direct imaging with high spatial and temporal resolution, the limited signal-to-background ratios attainable for dispersed nanoparticle samples have made such studies difficult to perform at optimal resolutions.

To overcome these limitations, Masiel and co-workers fabricated an annular objective lens aperture that permits images to be obtained with a threefold increase in the signal-to-background ratio. This annular dark-field imaging mode improves the contrast attainable in 15 ns-pulsed electron images and allows particles as small as 30 nm in diameter to be observed.

Other techniques such as coherent diffractive imaging (using coherent X-rays) or in situ TEM offer direct imaging data but at the cost of either spatial or temporal resolution. This is not the case for ADF-DTEM, the researchers say.

Resources

• Daniel J. Masiel, Bryan W. Reed, Thomas B. LaGrange, Geoffrey H. Campbell, Ting Guo, Nigel D. Browning (2010) Time-Resolved Annular Dark Field Imaging of Catalyst Nanoparticles. ChemPhysChem, doi: 10.1002/cphc.201000274