The information content of lattice resolved high angle tilt series of nanoparticles
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1026-C08-04
The information content of lattice resolved high angle tilt series of nanoparticles Xiaojing Xu, Zineb Saghi, Beverley Inkson, and Günter Möbus Engineering Materials, University of Sheffield, Mappin Street, Sheffield, United Kingdom ABSTRACT Gold nanoparticles are observed by high-resolution electron microscopy over a high tilt range equivalent to tomographic data acquisition. It is demonstrated how the lattice resolved contrast can be used to identify the internal multiply-twinned microstructure, as the large number of viewing direction allows to image each of the grain-to-grain displacement vectors in at least one image. Furthermore application of tomographic reconstruction is shown after binarisation of the original images to estimate the external shape from the support of the particle in the case of convex objects. INTRODUCTION Metallic nanoparticles exhibit a rich variety of microstructures differing in external shapes and symmetries, depending on size and/or manufacturing route. Also a greater choice of (meta-)stable crystal structures compared to the bulk is observed, and the preferred structure often includes grain boundaries and stacking faults, especially low-energy twins, which allow the particle surfaces to adjust to preferred crystallographic configurations without too much of cost in energy for the volume [1-5]. Gold nanoparticles have been one of the preferred objects of study in the nanoparticle field [6-7], due to the easy production, the clean surfaces and the interesting range of morphologies, linked to the relatively low stacking fault energy. High resolution electron microscopy is currently perhaps the most widely chosen characterization technique for nanoparticles [2, 6], while aberration corrected HAADF-STEM [8] and electron nanodiffraction [9] are very promising alternatives to achieve atomic resolution. For three-dimensional characterization of nanoparticles, electron tomography [10] has been shown applicable if incoherent imaging is used to suppress lattice contrast and diffraction contrast [11-13]. This can be achieved by dark field TEM or STEM, chemical mapping by EFTEM or EDX, or single window EFTEM modes. If bright field imaging is the chosen technique, then a reliable 3D result can also be achieved, however under restrictions of a constant particle density, and a convexity constraint for the particle cross-sections perpendicular to the tomographic rotation axis [14-15]. In either of these novel tomography modes, any crystallography information is suppressed. In the present study, it is attempted to explore how the technical development of ultra-high tilt specimen holders driven by tomography research can be turned useful for lattice resolved image series across a similar tilt range.
EXPERIMENT (i) Commercially available Au nanoparticles in aqueous solution were diluted in distilled water and de-agglomerated by ultrasonic vibration for several minutes. The suspension was then dropped onto a copper grid with a continuous carbon film. The grid was used in conjunction with a
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