An Atomic Force Microscopy Study of Surface Structures of Colloidal β-FeOOH Particles Forming Smectic Layers

Abstract

To obtain exact AFM surface images of colloidal particles with dimensions at most several to 10 times the diameters of the probe tip apexes, it is essential to closely pack the particles in order. We prepared monodisperse, square-prismic colloidal β-FeOOH particles from FeCl3 solutions and found that smectic ordering quickly occurs over a wide region from evaporating suspensions of the particles on substrates. Surface images of the ordered particles clearly showed various shapes of islands with a minimal step height of 1.09 nm, in good agreement with a cell constant by X-ray diffraction, but no spiral steps, suggesting 2D-nucleus formation and subsequent lateral growth of molecular layers on the colloid surfaces. Characteristic striped and one-stepped surfaces were also observed.