Observations of solid–gas reactions by means of high-resolution transmission electron microscopy

Abstract

A controlled environment specimen chamber, or gas reaction cell, has been constructed for a 400 kV JEOL 4000EX transmission electron microscope. It allows high-resolution (better than 0.26 nm) observation of specimens while they are interacting at elevated temperatures (typically 600 °C) with low pressures of gas (typically 500 Pa). The application of the cell to the study of small metal particles, of interest in catalysis, is described. In particular, the behaviour of conventional supported particles is compared with that of particles produced within carbon nanotubes. Preliminary studies of the reduction of oxide particles to metal have indicated possible epitaxial relationships between the particles and the constraining carbon walls in certain cases, which suggest that it may be possible to tailor specific indexed surfaces to be preferentially available to reactant gases. Interactions between the electron beam and the gaseous environment, which may in turn affect the specimen, are then discussed. In particular, sputtering processes can both contaminate and damage the sample that is under investigation, although at higher temperatures, the damage is usually self-healing. In the special case of carbonaceous materials, the impact of inert gas atoms can promote fullerene nucleation.