Abstract
Scanning electron microscopy (SEM) is an indispensable characterization technique for materials science. More recently, scanning electron microscopes can be equipped with scanning transmission electron microscopy (STEM) detectors, which considerably extend their capabilities. It is demonstrated in this work that the correlative application of SEM and STEM imaging techniques provides comprehensive sample information on nanomaterials. This is highlighted by the use of a modern scanning electron microscope, which is equipped with in-lens and in-column detectors, a double-tilt holder for electron transparent specimens and a CCD camera for the acquisition of on-axis diffraction patterns. Using multi-walled carbon nanotubes and Pt/Al2O3 powder samples we will show that a complete characterization can be achieved by combining STEM (mass-thickness and diffraction) contrast and SEM (topography and materials) contrast. This is not possible in a standard transmission electron microscope where topography information cannot be routinely obtained. We also exploit the large tilt angle range of the specimen holder to perform 180 degrees STEM tomography on multi-walled carbon nanotubes, which avoids the missing wedge artifacts.
Highlights
Scanning electron microscopy (SEM) has become an indispensable tool in material research ever since its invention
In combination with a double-tilt sample holder, specimens can be oriented into specific diffraction conditions yielding the capability for defect analysis, e.g. Burgers vector determination, which could be previously performed only in transmission electron microscopes [13]. Despite these developments, there are still only few studies, which emphasize the opportunities of scanning transmission electron microscopy (STEM)-in-SEM and correlative SEM/low-keV STEM. This was the motivation for this work where we demonstrate the versatility of imaging in modern scanning electron microscopes and the opportunities of correlative SEM/low-keV STEM
A corresponding 30 keV BFSTEM image is shown in Fig. 3b where the dark features within the carbon nanotubes (CNTs) are the result of changes of the diffraction conditions
Summary
Scanning electron microscopy (SEM) has become an indispensable tool in material research ever since its invention. Due to the possibility of high-resolution surface topography imaging of bulk samples and comparable low cost of scanning electron microscopes, SEM is one of the most important microscopy techniques and is available in many laboratories. Recent advances in resolution and the implementation of scanning (S) TEM detectors in scanning electron microscopes extend the capability of these instruments by allowing the study of electron-transparent specimens [1,2,3]. Considering that STEM in scanning electron microscopes is performed at electron energies B 30 keV, it is often referred to as lowkeV STEM, STEM-in-SEM or transmission (T) SEM [4]. The transmission mode in SEM was shown to be promising for the investigation of nanoparticles [10]
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