OBSERVATIONS OF SOLID-GAS REACTIONS BY MEANS OF HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY

A controlled environment specimen chamber, or gas reaction cell, has b een constructed for a 400 kV JEOL 4000EX transmission electron microsc ope. It allows high-resolution (better than 0.26 nm) observation of sp ecimens while they are interacting at elevated temperatures (typically 600 degrees C) with low pressures of gas (typically 500 Pa). The appl ication of the cell to the study of small metal particles, of interest in catalysis, is described. In particular, the behaviour of conventio nal supported particles is compared with that of particles produced wi thin carbon manitobas. Preliminary studies of the reduction of oxide p articles to metal have indicated possible epitaxial relationships betw een the particles and the constraining carbon walls in certain cases, which suggest that it may be possible to tailor specific indexed surfa ces to be preferentially available to reactant gases. Interactions bet ween the electron beam and the gaseous environment, which may in turn affect the specimen, are then discussed. In particular, sputtering pro cesses can both contaminate and damage the sample that is under invest igation, although at higher temperatures, the damage is usually self-h ealing. In the special case of carbonaceous materials, the impact of i nert gas atoms can promote fullerene nucleation.