Materials Problems and Approaches for TEM and TEM/STEM Analyses - Sample Preparation Topic for Transmission Electron Microscopy - page 69

Fig. 4.9 Illustration of atomic planes in ( a ) a bulk perfect silicon single crystal ( J. Ayache,
CSNSM-IN2P3-CNRS, Orsay ), ( b )aYBa 2 Cu 3 O 7 -SrTiO 3 multilayer material ( J. Ayache, CSNSM-
IN2P3-CNRS, Orsay ), and ( c ) lattice fringes in a carbon nanotube ( Qiang F. Fritz Haber Max
Planck Institute, Berlin )

c

a b

Fig. 4.10 Pictures of a SrTiO 3 bicrystal grain boundary produced by three high-resolution tech-
niques: ( a ) HRTEM, ( b ) phase image after reconstructing a focal series of HRTEM images, and
( c ) HAADF chemical contrast image ( J. Ayache, Lawrence Berkeley Laboratory, NCEM, Berkeley,
CA, USA )

the complex wave function of the electrons exiting the sample. This is obtained by
reconstructing a focal series of HRTEM images (Fig. 10b ). It must be noted that the
contrasts obtained are similar, but correspond to different atoms. In Fig. 4.10a , the
atomic columns of Sr and TiO are visible; in Fig. 4.10b , the visible columns belong
to oxygen and Sr or TiO. The last two columns in Fig. 4.10b are not discernable
in this system or under these conditions. The first method serves to unambiguously
highlight the arrangement of heavy atoms (which provide a high intensity). The sec-
ond method allows for better discrimination between light atoms and heavy atoms.
The reconstruction of the images leads to the specimen phase and amplitude, i.e.,
allows it to go back to its crystal potential. The statistical error on the measurements
of the crystal lattice parameter is not more than 0.001%. This type of analysis pro-
vides quantitative measurements of the crystalline parameters to determine atomic
plane relaxation variations at the level of a crystal defect or an interface and gives
access to stoichiometry.
HRTEM may be performed with a 200 keV accelerating voltage on samples with
a thickness less than 50 nm, with a resolution of 0.23 nm. The resolution can be