Crystal orientation analyses of biominerals using Kikuchi patterns in TEM

Abstract

This paper shows that Kikuchi pattern analysis in a transmission electron microscope (TEM) using recent techniques is superior to conventional electron diffraction analysis for determining crystal orientation in an assemblage of small crystals such as those of biogenic origin. A CCD camera with a wide view and large dynamic range was used together with a dedicated program to analyze the patterns and enable real-time and unique determination of crystal orientation. Convergent illumination of the incident beam was effective in enhancing the Kikuchi patterns and in improving spatial resolution. Two example biominerals are characterized by Kikuchi pattern analysis; one is spinel-law twins in several tens of nanometers width magnetite crystals from magnetotactic bacteria. The other is crystal orientation and the alignment of calcite fragments in coccolith.