Image-based nanocrystallography in future aberration-corrected transmission electron microscopes
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Image-based nanocrystallography in future aberration-corrected transmission electron microscopes P. Moeck 1, W. Qin 2, and P. B. Fraundorf 3 1
Department of Physics, Portland State University, P.O. Box 751, Portland, OR 97207-0751, [email protected] 2 Motorola Technology Solutions/SPS, MD CH305, Chandler, AZ 85284 3 Department of Physics and Astronomy and Center for Molecular Electronics, University of Missouri at St. Louis, MO 53121 ABSTRACT Since the crystallographic phase and morphology of many materials changes with the crystal size in the one to hundred nanometer range and the potential technological applications of nanoparticles are enormous, a need arises to determine the crystallography of nanoparticles individually. Direct space highresolution phase-contrast transmission electron microscopy (TEM) and atomic resolution Z-contrast scanning TEM when combined with goniometry of direct and/or reciprocal lattice vectors offer the possibility of developing dedicated nanocrystallography characterization methods for such small nanoparticles. Although experimentally feasible for cubic nanocrystals with lattice constants larger than 0.4 nm in contemporary high-resolution TEMs with modest tilt range, image-based nanocrystallography by means of transmission electron goniometry has so far only been employed by a few specialists worldwide. This is likely to change in the future with the availability of aberration-corrected TEMs. The reasons why this change is likely to happen are outlined in this paper. INTRODUCTION Since “nanotechnology as a whole is estimated to represent a market of $ 11 trillion by 2010 with nanomaterials growing from $ 490 million today to $ 900 million in 2005 and $ 11 billion in 2010” [1], there will prospectively be significant needs for the crystallographic characterization of individual nanoparticles. Imagine for example that you are developing industrial-grade diamonds and diamond coatings on the basis of SiC nanoparticles [2]. Optimizations of the processing routes would be speeded up by a means to determine the crystallographic phase of individual nanoparticles in direct space after different processing steps [3]. As the scientific community is well aware, phase diagrams and crystal morphologies (that are both crucial to all kinds of properties of nanoparticles) are frequently dependent on the size of the crystals in the one to hundred nanometer range [4-6]. Added to this size dependency of the lowest energy state of a structure, there is in the nanoparticle regime a strong tendency to metastability [7] and non-stoichiometry. In short, a whole new “crystallographic world” is waiting to be discovered in the nanoparticle realm. Textbook transmission electron microscopy (TEM) has traditionally provided structural and morphological information for nanocrystals larger than approximately 0.05 µm from a combination of (reciprocal space) convergent beam electron diffraction (CBED) patterns and (direct space) imaging. Due to the small size of many nanoparticles, these textbook methods are howev
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