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Quantitative Scanning Transmission Electron Microscopy for the Measurement of Thicknesses and Volumes of Individual Nanoparticles

Published online by Cambridge University Press:  31 January 2011

Helge Heinrich ,
Biao Yuan ,
Haritha Nukala  and
Bo Yao
Helge Heinrich
Affiliation:
[email protected], University of Central Florida, AMPAC, Orlando, Florida, United States
Biao Yuan
Affiliation:
[email protected], University of Central Florida, AMPAC, Orlando, Florida, United States
Haritha Nukala
Affiliation:
[email protected], University of Central Florida, AMPAC, Orlando, Florida, United States
Bo Yao
Affiliation:
[email protected], University of Central Florida, AMPAC, Orlando, Florida, United States
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Abstract

In Scanning Transmission Electron Microscopy (STEM) the High-Angle Annular Dark-Field (HAADF) signal increases with atomic number and sample thickness, while dynamic scattering effects and sample orientation have little influence on the contrast. The sensitivity of the HAADF detector for a FEI F30 transmission electron microscope has been calibrated. Additionally, a nearly linear relationship of the HAADF signal with the incident electron current is confirmed. Cross sections of multilayered samples for contrast calibration were obtained by focused ion-beam (FIB) preparation. These cross sections contained several layers with known composition. A database with several pure elements and compounds has been compiled, containing experimental data on the fraction of electrons scattered onto the HAADF detector for each nanometer of sample thickness. Contrast simulations are based on the multi-slice formalism and confirm the differences in HAADF-scattering contrast for the elements and compounds. TEM offers high lateral resolution, but contains little or no information on the thickness of samples. Thickness maps in energy-filtered transmission electron microscopy, convergent-beam electron diffraction and tilt series are so far the only methods to determine thicknesses of particles in a transmission electron microscope. We show that the calibrated HAADF contrast can be used to determine the thicknesses of individual nanoparticles deposited on carbon films. With this information the volumes of nanoparticles with known composition were determined.

Keywords

transmission electron microscopy (TEM)nanoscalechemical composition
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1184: Symposium GG – Electron Crystallography for Materials Research and Quantitive Characterization of Nanostructured Materials , 2009 , 1184-HH01-06
Copyright
Copyright © Materials Research Society 2009

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References

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