THE CONDITIONS FOR DETECTING CONFINED MATERIAL IN THE CHANNELS CAVITIES OF ZEOLITES BY USING HREM

High resolution electron microscope images of zeolites recorded with the incident electron beam parallel to the main channels show an optical artifact. The contrast in the center of the channels is severely disturbed by dark spots caused by some Bragg reflections being insufficiently transferred by the objective lens. Since zeolites are being used as containers for other materials, the spots in electron micrographs will screen any materials located in the large zeolite channels. With experimental micrographs and image simulations it is shown that by changing the focus conditions the spot can be eliminated and hence, confined material can be imaged. Two representatives, mordenite and zeolite Y, are described in detail for the cases of one-dimensional and three-dimensional channel systems, respectively. © 1993 Academic Press, Inc.