Microsc. Microanal. Microstruct. 3, 71-81 (1992)
DOI: 10.1051/mmm:019920030107100

Theoretical image processing of simulated supported particles (1-3 nm)

Geneviève Nihoul

G.M.E.T, Groupe Matériaux, University of Toulon, B.P. 132,83957 La Grade Cedex, France

Abstract
The images of supported nanoparticules obtained by High Resolution Transmission Electron Microscopy are often difficult to interpret. The small size of the particles, the existence of Fresnel fringes and the presence of a stabilizing carbon film all contribute to blur the images. Quantitative results on the size and the morphology of the particles or information about the interface substrate-particle have to be extracted from the images as a direct interpretation is difficult (and hazardous). Simulation of images, starting from a model and computing all the changes in the electron wave introduced by the specimen and the microscope, is a great help to understand the experimental images. Image processing is also used to improve the visibility of the particles and of their interface with their substrate. However, it is well known that image processing can also introduce artefacts in numerous ways. In this paper, we have studied three different Fourier filters: a band pass filter, a Bragg filter and a new filtering by subtraction of the amorphous background. Their possibilities and their limitations, together with their reliability, are tested on computed images in order to use them, safely, on experimental HRTEM images of nanoparticles.

Résumé
Les images de nanoparticules obtenues par HRTEM sont souvent difficiles à interpréter. La petite taille des particules, l'existence de franges de Fresnel et la présence de films stabilisateurs de carbone contribuent à déformer les images. Les résultats quantitatifs sur la taille et la morphologie des particules doivent être dégagés des images dont l'interprétation directe est difficile (et risquée). Le traitement d'images est utilisé pour améliorer la visibilité des particules et de leur interface avec le substrat. Néanmoins, il est bien connu que le traitement d'images peut aussi introduire des nombreux artefacts. Nous présentons ici l'étude de 3 filtres de Fourier différents dont les possibilités et limites ont été testées sur des images simulées de façon à pouvoir les utiliser, sûrement, sur des images expérimentales de nanoparticules.

PACS
6118 - Other methods of structure determination.
8110A - Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation.
6146 - Nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals.
4230V - Image forming and processing.

Key words
Image processing -- Nanoparticles -- TEM -- High-resolution methods -- Fourier transformation -- Band-pass filters -- Fourier filters -- Bragg filters -- MgO substrate


© EDP Sciences 1992