Structural Fingerprinting of Nanocrystals: Advantages of Precession Electron Diffraction, Automated Crystallite Orientat
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Structural Fingerprinting of Nanocrystals: Advantages of Precession Electron Diffraction, Automated Crystallite Orientation and Phase Maps Peter Moeck1, Sergei Rouvimov1, Edgar F. Rauch2, and Stavros Nicolopoulos3 1
Nano-Crystallography Group, Department of Physics, Portland State University, Portland, OR 97207-0751 & Oregon Nanoscience and Microtechnologies Institute 2 SIMAP/GPM2 Laboratoire, CNRS-Grenoble INP, BP 46 101 rue de la Physique, 38402 Saint Martin d'Hères, France 3 NanoMEGAS SPRL, Boulevard Edmond Machterns No 79, Saint Jean Molenbeek, Brussels, B1080, Belgium
ABSTRACT Strategies for the structurally identification of nanocrystals from Precession Electron Diffraction (PED) patterns in a Transmission Electron Microscope (TEM) are outlined. A single-crystal PED pattern may be utilized for the structural identification of an individual nanocrystal. Ensembles of nanocrystals may be fingerprinted structurally from “powder PED patterns”. Highly reliable “crystal orientation & structure” maps may be obtained from automatically recorded and processed scanningPED patterns at spatial resolutions that are superior to those of the competing electron backscattering diffraction technique of scanning electron microscopy. The analysis procedure of that automated technique has recently been extended to Fourier transforms of high resolution TEM images, resulting in similarly effective mappings. Open-access crystallographic databases are mentioned as they may be utilized in support of our structural fingerprinting strategies.
INTRODUCTION This paper outlines structural fingerprinting strategies of nanocrystals in a TEM on the basis of PED patterns [1-7]. To appreciate the advantages of this diffraction mode for structural fingerprinting, its basics will be discussed in the main part of this paper. There is also structural fingerprinting on the basis of high resolution (HR or lattice-fringe) TEM images [8-10]. That method and its unique advantage for structural fingerprinting, i.e., the possibility to extract structure factor phase angles will, however, not be discussed here since a comprehensive description is published in open access [8]. We will accordingly deal only in passing with the possibility that one can obtain highly reliable crystal orientation & structure maps from HRTEM images [11] by an extension of the automated processing of single-crystal PED patterns [4,7]. Searching for structural information that is extracted by our structural fingerprinting strategies in crystallographic databases and matching it with high figures of merit to that of candidate structures allows for highly discriminatory identifications of nanocrystals, even without additional chemical information as obtainable in analytical TEMs. As an alternative to commercial databases, one may use open-access databases, which provide together some 100,000 crystal structure data sets (that include atomic coordinates, unit cell parameters, and the space group). The major open-access crystallography databases that can be utilized for
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