Visualization of nanostructured porous silicon by a combination of transmission electron microscopy and atomic force microscopy

Abstract

The observation of red-, near-infrared, and nonphotoluminescent porous silicon structures both by transmission electron microscopy as well as by atomic force microscopy provides a consistent structural picture of the species responsible for the visible luminescence observed in these samples. The topography of the tops are seen in detail by atomic force microscopy, while the valleys are better observed by transmission electron microscopy; the observation techniques are therefore complementary. By measuring the apex radius of curvature of the atomic force microscope tip, it is possible to determine the porous silicon particle size by simple geometrical arguments. For red-photoluminescent porous silicon, the measured particle diameter using atomic force microscopy was 55 Å and the particle height 4 Å. The corrected particle diameter of 17 Å is in close agreement with the 15 Å value measured by transmission electron microscopy.