Electron tomography about

For many years efforts have been made to collect more detailed information about the 3rd dimension in TEM. For thin samples (< 50 nm) through-focus series [6] and electron holography [7,8] have been applied successfully. In this paper we mainly restrict the discussion to electron tomography (ET) that can be applied to thicker samples (50-500 nm). For an overview of the several modes of 3D-TEM that elaborates on the microscopy aspects we refer to an earlier review [4], Here we will summarize the principle and practical aspects of ET for the study of molecular sieves. 

First-of-its kind results [14,15] with electron tomography for the study of zeolites have been obtained with Ag/Na-Y. The location of the Ag particles of about 10 nm could be unequivocally established with respect to the surface and the interior of the crystals. The moderate resolution of 5 nm of the reconstructed images in this study related to the rather large zeolite crystals (500 nm) involved. Hereafter, we first discuss in more detail the use of electron tomography to study mesopores in zeolite crystals and, secondly, case studies involving metal particles and pore architecture of ordered mesoporous materials. 

Transmission electron microscopy (TEM) and high-resolution TEM gives invaluable information about the fine structure of the nanopores of the zeolites, crystal orientation, their lattice fringes and lattice composition, and crystallinity (by using electron diffraction). Even 3D morphology with nanometer resolution is achievable using electron tomography. 

The radioisotope nitrogen-13 has a relatively short half-life of about 10 minutes that produces a positron as it decays. This makes N-13 useful in PET (Positron Emission Tomography) scan technology, in which it is injected into the patient. The positive electrons (positrons) interact with the patient s negative electrons to produce an image similar to an X-ray. 

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