John A. Small

Objective: To develop methods to improve the quality of electron backscatter diffraction patterns from particles less than 300 nm in size.

Problem: In our initial work on the phase identification analysis of individual particles by EBSD, we observed that the quality of the EBSD patterns from particles less than about 300 nm in size was poor, especially for low density materials, when the particles were mounted on bulk carbon substrates. This poor quality limits the utility of the technique.

Approach: As part of the division's program for materials characterization we are investigating methods for particle identification in the scanning electron microscope/electron microprobe based on electron backscatter diffraction from particles in the 100 nm and above size range. We suspect that the poor pattern quality from submicrometer particles is the result of electron scattering from areas other than the particle of interest. In the case of the very small particles many of the incident electrons exit the particle volume without diffracting and enter the substrate. This not only decreases the intensity of the diffraction signal but also increases the average noise in the EBSD pattern, reducing the signal-to-noise ratio in the pattern to an unacceptably low level.

To improve the EBSD pattern quality for submicrometer particles a sample holder was constructed that enables particle mounting on a thin, electron transparent, substrate. The thin substrate should dramatically reduce the noise contribution from electrons that scatter into the substrate and thus improve pattern quality from very small particles.

Results and Future Plans: Figure 1c is the EBSD pattern from a 160 nm Al2O3 particle mounted on a bulk carbon substrate (Figure 1a). Figure 1d is the EBSD pattern from a 150 nm Al2O3 particle mounted on a 20 nm carbon thin-film (Figure 1b). The quality of the EBSD pattern from the particle mounted on the thin substrate is clearly superior to the pattern from the particle mounted on the bulk substrate and has a high enough signal-to-noise ratio to conduct a phase identification analysis of the particle and identify it as hexagonal Al2O3. Future plans include investigating other thin-film compositions and low accelerating voltages to extend the application of EBSD phase identification to particles less than 100 nm in size. Publications: JA Small, JR Michael, and DE Newbury, Microbeam Analysis 2000, Institute of Physics Conference Series #165, 305-306, 2000. JA Small, JR Michael, "Phase identification of individual crystalline particles by electron backscatter diffraction (EBSD)", Submitted to JOM (in press).

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