Crystallographic phase analysis of submicrometer particles by electron backscatter diffraction. (New Briefs).

The characterization and identification of small particles are critical to advanced manufacturing methods in semiconductor, pharmaceutical, metallurgy, and ceramics, as well as environmental monitoring and homeland security. The chemical compound identification of particles is essential to the understanding, improvement and control of electronic device yield, near-net-shape processes, drug effectiveness, environmental particulate health effects, and trace-explosive-particle forensic analysis.

In collaboration with Sandia National Laboratory, NIST is developing procedures for analyzing the crystallographic phase of individual sub-200 nm particles utilizing electron backscatter diffraction (EBSD) in the field emission scanning electron microscope. One of the difficulties in performing EBSD analysis of small particles is that the quality of EBSD patterns from particles less than about 200 nm in size, particularly particles with low average Z and or low density, is not sufficient to allow crystallographic phase identification.

Monte Carlo simulations of the electron trajectories from small particles indicate that most of the 20 keV beam electrons penetrate through these particles with minimum angular deflection. The vast majority of the transmitted electrons enter the mounting substrate where they are scattered diffusely, in the case of an amorphous substrate, and become a significant source of background noise in the EBSD patterns collected from these particles.

To improve the quality of EBSD images from sub-200 nm particles, NIST has designed an EBSD sample holder for mounting the particles onto a thin carbon film supported by a TEM grid. To significantly reduce the background signal from incoherently scattered electrons, the film is mounted over an electron trap so that the electrons penetrating through the particles also penetrate the film and are absorbed in the trap. Results show a significant improvement in the EBSD pattern quality from sub-200 nm [Al.sub.2.][O.sub.3] particles. This new approach dramatically improves our sensitivity in identifying the chemical compounds that make up crystalline particles.

CONTACT: John Small, [phone]; [e-mail].