Towards 3D image-based nanocrystallography by means of transmission electron goniometry
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Towards 3D image-based nanocrystallography by means of transmission electron goniometry Peter Moeck 1*, Wentao Qin 2, and Philip B. Fraundorf 3 1
Department of Physics, Portland State University, P.O. Box 751, Portland, OR 97207-0751, *[email protected] Technology Solutions, Freescale Semiconductor, Inc., MD CH305, Chandler, AZ 85224 3 Department of Physics and Astronomy and Center for Molecular Electronics, University of Missouri at St. Louis, MO 53121 2
ABSTRACT It is well known that the crystallographic phase and morphology of many materials changes with the crystal size in the tens of nanometer range and that many nanocrystals possess structural defects in excess of their equilibrium levels. A need to determine the ideal and real structure of individual nanoparticles, therefore, arises. High-resolution phase-contrast transmission electron microscopy (TEM) and atomic resolution Z-contrast scanning TEM (STEM) when combined with transmission electron goniometry offer the opportunity of develop dedicated methods for the crystallographic characterization of nanoparticles in three dimensions. This paper describes tilt strategies for taking data from individual nanocrystals “as found”, so as to provide information on their lattice structure and orientation, as well as on the structure and orientation of their surfaces and structural defects. Internet based java applets that facilitate the application of this technique for cubic crystals with calibrated tilt-rotation and double-tilt holders are mentioned briefly. The enhanced viability of image-based nanocrystallography in future aberration-corrected TEMs and STEMs is illustrated on a nanocrystal model system. INTRODUCTION 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 tens of nanometer range. Added to this size dependency of the lowest thermodynamical potential of a structure, there is in the nanoparticle regime a strong tendency to metastability and non-stoichiometry. Moreover, many nanocrystals possess structural defects in three (3D), two (2D) and one (1D) dimension as well as point defects in excess of their thermodynamical equilibrium levels. It goes without saying that these structural defects affect the properties of the nanoparticles and are strongly dependent on the particulars of the nanoparticle synthesis and processing procedures. In short, a whole new “crystallographic world” is waiting to be discovered in the nanoparticle realm. The first aim of this paper is to discuss aspects of transmission electron goniometry. Secondly, we mention internet bases java applets that can be employed for the transmission electron goniometry of cubic crystals with calibrated tilt-rotation and double-tilt TEM specimen holders/goniometers. Finally, we discuss the so called “cubicminimalistic tilt procedure” for sub-stoichiometric WC1-x nanocrystals with halite (rock salt) structure. The enhanced viability of image-based nanocrystallography in future
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