Microscopy Method Achieves Nanoscale Diffraction

Caltech’s Ahmed H. Zewail and Aycan Yurtsever have achieved four-dimensional nanoscale diffraction by combining two existing techniques: convergent-beam electron diffraction and ultrafast electron microscopy (Science 2009, 326, 708). In convergent-beam ultrafast electron microscopy (CB-UEM), the researchers focus femtosecond electron pulses into a nanometer-sized beam that strikes the sample. They then initiate physical changes in the sample with femtosecond laser pulses and observe the changes with time-delayed electron pulses. The convergent electron beam allows them to observe diffraction from a tightly defined probe area of 10 to 300 nm, rather than over an averaged area of micrometers or larger. The time resolution is 10 orders of magnitude better than conventional transmission electron microscopy, they note. With CB-UEM, the researchers measured structural changes, temperatures, and amplitudes of atomic vibrations in a slab of crystalline silicon. “The achievement of nanoscale diffraction with CB-UEM opens the door to exploration of different structural, morphological, and electronic phenomena,” Zewail and Yurtsever write.