Because of the importance of diatoms and the lack of information about their third dimension, a new method for the 3D reconstruction is explored, based on digital image correlation of several scanning electron microscope images. The accuracy of the method to reconstruct both centric and pennate (symmetrical and asymmetrical) diatoms was shown, independently of valve size and shape, and considering not only the general frustule morphology but also the intricate ornamentation. Several measurements were obtained, such as of the surface and projected areas and the valve volume. These results were validated by focused ion beam transverse cross section of one valve, and the quantitative results were compared with geometric models commonly applied. Furthermore, direct volume calculations based on 3D reconstructions have several advantages, such as it has higher taxonomic accuracy than the methods based on light microscopy; it solves the problems of the light halos; it allows the precise measurement of all linear dimensions, including the often neglected third dimension; natural samples can be measured directly; and it provides an exact estimate of cell volume, independently of its shape or alterations due to life cycle stage. This approach provides therefore a simple way to measure the morphological features of diatoms, even at a nanoscale, and can be applied to other microorganisms commonly illustrated by means of scanning electron microscopy.
This paper investigates the adhesive interface in a polymer/metal (polyethylene terephthalate/steel) laminate that is subjected to uniaxial strain. Cross-sections perpendicular to such interfaces were created with a focused ion beam and imaged with scanning electron microscopy during straining in the electron microscope. During in situ straining, glide steps formed by the steel caused traction at the interface and initiated crazes in the polyethylene terephthalate (PET). These crazes readily propagated along the free surface of the PET layer. Similar crazing has not been previously encountered in laminates that were pre-strained or in numerical calculations. The impact of focused ion beam treatments on mechanical properties of the polymer/metal laminate system was therefore investigated. It was found that mechanical properties such as toughness of PET are dramatically influenced by focused ion beam etching. It was also found that this change in mechanical properties has a different effect on the pre-strained and in situ strained samples.
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