Extinction contrast from coherent distortion-free particles

Abstract

The contrast for electron transmission of thin foils containing coherent undistorted particles with a different scattering factor from the matrix has been calculated. From these results visibility criteria and contrast effects of small particles are discussed. A method of forming images of extremely small particles (nearly 10 Å) is derived. Small Ni₃Al particles have been made visible by this method. In addition a method for determination of size statistics is proposed. The calculated contrast has been confirmed with Ni–Cr-Al alloys containing Ni₃Al particles.