Characterization of the Morphology of Faceted Particles by Transmission Electron Microscopy
- PDF / 679,246 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 21 Downloads / 154 Views
Characterization of the Morphology of Faceted Particles by Transmission Electron Microscopy Shirley Turner, David S. Bright Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899-8371 ABSTRACT Faceting in a polyhedral rutile particle was modeled from transmission electron microscopy images. A double-tilt, rotate transmission electron microscope (TEM) sample holder was used to manipulate the particle. Using this holder, it was possible to align the c axis of the particle along one of the axes of the sample holder. This alignment allowed images to be obtained of the particle in several orientations around its c axis. Comparison of dimensions and angles obtained to those obtained for hypothetical models of the particle gives information about its likely prismatic and pyramidal faceting. This approach to facet modeling is useful for more complete determination of the faceting in individual euhedral particles using transmission electron microscopy.
INTRODUCTION Identification of the faceting in polyhedral particles is important in many applications. For example, different facets in catalysts have different efficiencies for promoting reactions. In pigment particles, certain morphologies are more desirable for durability of paint. Characterizing the morphology of particles with transmission electron microscopy is challenging because a TEM image is a two-dimensional (2D) projection of the material. In the biological field, 3D reconstruction techniques have long been used to derive 3D models of cellular and other biological structures from 2D TEM images. Recently, there have been several efforts to apply similar reconstruction techniques in the material science field [1-4]. The techniques have been applied to deriving the distribution of metal particles on silicates [1,2], channels in zeolites [1], and particles in nanocomposites [4]. The 3D reconstruction techniques have not yet been used to derive information about the faceting of particles. At present, such faceting information is typically derived by examining oriented crystallites and measuring angles between linear features in the outline of the 2D projections. If several crystallites are found in different orientations, a 3D model for the typical particle can be derived. Such a 3D model is an average of information from different particles and is not particle specific. In this work, a double-tilt, rotate (2TR) holder is used to orient and tilt a particle to derive information for comparison with morphological models. The 2TR holder has three degrees of freedom theoretically allowing the TEM operator to align a crystallographic direction of interest along one of the tilt axes. This alignment is not possible with conventional double-tilt or rotate-tilt holders unless serendipity leads to a suitably oriented particle. When a crystallographic direction of interest is suitably oriented, tilting of the particle around that direction can allow for measurement of dimensions and comparison to models of crystallite fa
Data Loading...
