Femtometre resolution using electron diffraction

GENERAL SEMINAR: Dr. Richard Beanland, Department of Physics, University of Warwick Coventry CV4 7AL, UK

Electron diffraction has several advantages for the study of materials, in particular its ability to access nm-sized volumes and its greater sensitivity to lighter elements in comparison with X-rays and neutrons. Nevertheless, it is incapable of producing reliable intensities in simple scattering experiments due to multiple scattering effects and is thus rarely used. This problem can be overcome by collecting large amounts of data with the use of computer control. The approach can be applied on any modern TEM.  The resulting diffraction patterns have a wealth of detail and as an example Fig. 1 shows digital large-angle electron diffraction data from BaTiO₃, taken with a 2100 LaB₆ microscope at 200 keV

I show in this presentation that these data, as well as being visually appealing, can yield information about atom coordinates to a precision of a few tens of femtometres, as well as being sensitive to thermal vibrations and bonding. Thus, highly accurate measurement of crystal structure and bonding may be readily achievable using any modern TEM.

Figure 1. Montage of digital large-angle convergent beam electron diffraction (D-LACBED) patterns taken at the [001] zone axis of tetragonal barium titanate at room temperature.