Offline methods of analysis such as TEM, SEM, and scanning probe microscopy (SPM). In addition to obtaining distributions of lengths and diameters, microscopy can directly investigate the detailed structure and composition of individual fibers. Although each of these types of microscopy is useful for providing size-distribution analysis in selected applications [75-79], only TEM permits diffraction analysis, compositional analysis of zeptoliter-sized (10-21) volumes, plus atomic lattice and internal defect-structure imaging. With fibers for which confirmation of atomic structure and/or composition is relevant (e.g., in analysis of asbestos  and carbon nanotubes), TEM may therefore provide the most definitive results even when it does not offer the best counting statistics. Thus, this review focuses on TEM analysis of nanotubes and nanofibers.
Modern electron and scanning probe microscopes are becoming more like nanolaboratories, capable of fielding a wide range of experiments on specimens whose field of view has been magnified by factors of 1010 to 1016. The main issues facing the microscopist, therefore, are (1) getting the specimen into the microscope without size bias, and (2) defining a limited set of experiments that will provide adequate statistics in a reasonable amount of time. These are therefore the topics of the next two sections.
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