Precession electron diffraction and its utility for structural fingerprinting in the transmission electron microscope

Abstract

Abstract. Precession electron diffraction (PED) in a transmission electron microscope (TEM) is discussed in order to illustrate its utility for structural fingerprinting of nanocrystals. While individual nanocrystals may be fingerprinted structurally from PED spot patterns, ensembles of nanocrystals may be fingerprinted from powder PED ring patterns.

Precession electron diffraction and its advantages for structural fingerprinting in the transmission electron microscope

“…Nanometer crystal sizes have, on the other hand, exactly the opposite effect on the feasibility of our strategy of structural fingerprinting from PED patterns [5][6][7]. This is because as the crystal becomes smaller, its shape amplitude extends in reciprocal space.…”

“…More diffraction spots will, therefore, appear in a PED pattern as intersections of diffracted electron beams (on a precessing Ewald sphere) with the plane recording medium of a TEM. The combined weak phase object/kinematic diffraction or phase object/quasi-kinematic diffraction approximations [7] of transmission electron microscopy (TEM) will also be reasonably well adhered to during the recording of the experimental data from nanometer sized crystallites.…”

“…4a, with its PED pattern counterparts, Fig. 4b-d, demonstrates that a nanocrystal does not need to be oriented with a low indexed zone-axis exactly parallel to the optical axis of the TEM in order to allow for advanced structural fingerprinting in the TEM on the basis of the diffracted intensities [6,7].…”

“…5b and c, illustrates, however, that structural fingerprinting from PED patterns will not be affected unduly by such primary electron beam tilt mis-alignments. These tolerances to crystal mis-orientations and primary electron beam tilt mis-alignments lessen the experimental efforts for effective structural fingerprinting on the basis of PED patterns [6,7].…”

“…By contrast, the novelty of the strategy that will be illustrated here briefly is due to the combination of information on the projected reciprocal lattice geometry with information on the projected point symmetry, and approximate structure factor moduli [6][7][8]. This strategy is, however, only applicable to nanocrystals, since it relies on kinematic or quasi-kinematic scattering approximations.…”