TEM and FESEM: The Right Combination for Enhanced Particle Characterization

K. L. Bunker, D. McAllister, K. A. Allison, K. Wagner, K. Rickabaugh, A. M. Levine, B. R. Strohmeier, and R. J. Lee RJ Lee Group, Inc., 350 Hochberg Road, Monroeville, PA, 15146, USA Transmission electron microscopy (TEM) has been a valuable technique for many years for characterizing the morphology, structure, and chemistry of microscopic particles and nanostructures because of its capacity to combine high magnification and high resolution imaging along with selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS). However, TEM can only provide a projection image of the general overall shape of the particle. Therefore, the true shape, morphology, and dimensions of a specific particle may be significantly different from what is observed in the TEM image. Field emission scanning electron microscopy (FESEM) can provide high resolution secondary elect ron (SE) imaging capabilities at magnifications similar to those used during TEM analyses. Augmenting TEM analyses with high resolution FESEM provides the opportunity to more fully and accurately characterize the overall shape, surface roughness, structure, and chemistry of particulate materials. The combined use of TEM and FESEM for characterizing and distinguishing between asbestos and non-asbestos amphibole mineral particles has previously been reported by this laboratory [1-3]. In this study, the combined TEM/FESEM method has been extended to other types of particles, including carbon black, carbon nanotubes, soot, and various types of minerals. The method involves the preparation of samples on standard TEM sample grids, which can be analyzed in the TEM and in the FESEM through the use of a modified grid holder. Particles located and analyzed in the TEM can be relocated in the FESEM on a particle-by-particle basis with the aid of low magnification TEM field images and TEM analyst sketches of the particles located in the individual grid openings. TEM is the primary technique recommended by the American Society for Testing and Materials (ASTM) for the characterization of carbon black particulate [4]. Figure 1 (a) shows a TEM image and (b) FESEM SE image obtained for an aggregate of carbon black particles. In the TEM image, it is difficult to distinguish and size the individual carbon black particles. However, the FESEM image clearly shows the individual particles as well as more detailed morphological information. Similarly, TEM is commonly used for the characterization of carbon nanotubes. Figure 2 (a) compares a TEM image and (b) FESEM SE image obtained for a cluster of carbon nanotubes. The FESEM image more clearly shows the 3-dimensional nature of the nanotubes. This study has demonstrated that FESEM is a valuable complementary tool to TEM for fully characterizing particulate materials. References 1. K. E. Harris et al., Modern Research and Educational Topics in Microscopy, Formatex Research Center, Badajoz, Spain, 2007. 2. B. R. Strohmeier et al., Microscopy Today 15 (2007) 44. 3. B. R. Strohmeier et al., The Microscope, 55 (2007) 173. 4. ASTM Method D6602-03b, West Conshohocken, PA, 2003.