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Tantalum oxide thin films are of special interest as possible candidates for dielectric (high-k) layers to be applied in microelectronics [1]. Here we employ some procedures making use of extinction bend contours [2] that are often observed though scarcely applied in TEM studies of films/layers.
Amorphous Ta-O films prepared by anodization were crystallized upon heating or/and electron beam annealing. Bend contours were used to calculate the integral and local magnitudes of lattice bending (in fact gradients of crystal lattice orientation) accordingly. Besides there was examined the fine structure of extinction bend contours in dark field images), a period of oscillations being used to determine the depth of crystal intergrowth in the amorphous film.
The crystallized areas present small lath-shaped single crystals (length up to several micrometers, predominant phase was identified as trigonal Na2Ta4O11) with regularly alternating zone axis patterns outgoing from larger crystals with irregular broad bend contours (indicating much smaller crystal bending). Most of them are surrounded by fine grained material resembling porous polycrystalline structure (the grain boundaries are hardly distinguished indicating the crystallite sizes in the range of 50 – 200 nm). The main data for crystal lattice bending are consistent with our earlier data for other substances: the thinner the film, the larger is the crystal lattice bending. The maximal lattice bending is around 190°/μm in fine grained areas and 80°/μm in whiskers.
Earlier, different examples of individual crystals growing in amorphous films with strong lattice bending have been reported (e.g., in [2] where the term “transrotational” was also introduced for such crystals) with a set of observations establishing that it is an internal bending of the crystal lattice planes (in a flat crystal) rather than a case of a mere crystal bending. In this paper we presented much more complicated crystallized areas in which most probably there occurs some similar specific internal lattice bending.
[1] Min K.-H. and Sinclair R., J. Ceramic Proc. Res., 6 (2005) 17-19.
[2] Kolosov V. Yu. and Tholen A. R., Acta Mater., 48 (2000) 1829-1840.
*The work was partially supported by INTAS (project 00-100), pending support of RFBR. |