Analysis of strain in manganese nanoparticles using the optical moiré technique

Abstract

Manganese nanoparticles have been produced using the inert gas condensation technique. XRD has been used to analyse the particles, which contain a mixture of Mn-Mn oxide phases. Too few isolated reflections from any one phase have meant that broadening measurements are limited, and strain measurements are unreliable. Another way to measure strain in a sample is through analysis of lattice images taken using TEM. Observation of strains over long atomic distances can prove difficult, but a method of magnifying strain is by the optical moiré technique. A crystal lattice image with a grating superimposed over the top creates dark bands due to interference between the two. These dark bands are called moiré fringes and they can occur as an artefact in TEM images due to interference between two real crystal lattices. Here though they are implemented using a synthetic grating where the strain in crystalline solids can be studied. The manganese nanoparticle samples have been found to contain fully oxidised particles below 20nm diameter, and core shell particles above 20nm diameter. The technique has been used to study the core-shell particles, which consist of a β-Mn core and an oxide shell. The core is a single crystal and the moiré fringes show that there is no strain in that region. The oxide crystals in the shell are too fine for the technique to work, and so any strain in them must be measured using a different method. © 2008 IOP Publishing Ltd.