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Analytical Transmission SEM for Nanomaterials

Summary:

This project develops low-energy transmission electron diffraction, imaging, and spectroscopy in the scanning electron microscope, to enable determinations of microscopic structure, defect types, and interface character in ultrathin films, nanoparticles, and nano-bio material systems, to overcome imaging and analytical challenges faced by conventional SEM and TEM methods.

Description:

Established imaging and diffraction techniques for measuring structure of nanomaterials and soft matter do not show both good contrast and high resolution, and they can cause significant material damage. This is particularly the case for isolated nanostructures such as individual nanoparticles and ultrathin films. For example, identifying the crystallographic phase of an unknown nanoparticle of diameter 5 nm to 10 nm is extremely difficult, even in the most powerful high-resolution TEMs commercially available today. The problem centers on the generation of electron scattering within small volumes. For structures in the size regime of 10 nm and smaller, electrons with energies of the order of 200 keV exhibit a mean free path for scattering that can easily approach an order of magnitude larger than the particle itself. Decreasing those energies to those typical of an SEM (~ 20 keV) decreases the mean free path to values commensurate with the particle size. As a result, more electrons will scatter, to provide the information-rich content needed to measure crystal phase, crystal orientation, defects, and internal order within nanostructures. 

A fully analytical transmission-SEM, alternatively considered a low-voltage STEM, would not only fuel more thorough characterization of nanoscale structures, enabling more precise process control and material reliability, but it would make available many powerful TEM-like capabilities to a large population of SEM users worldwide, in a diverse range of applications.

Major Accomplishments:

  • We demonstrated that the important Kikuchi scattering responsible for diffraction appears to occur within a few nanometers of the exit surface of the specimen. 
  • We have obtained t-EBSD patterns from several types of nanomaterials, including HfO2 films of thickness < 5 nm, Fe-Co particles of diameter ~ 10 nm, Pt particles of diameter ~ 2 nm, Fe3O4 particles of diameter ~ 8 nm, Ag particles of diameter ~ 10 nm, Al2O3 particles of diameter ~ 20 nm. 
  • We demonstrated that t-EBSD measurements can be made over a broad range of film thickness, ranging from < 5 nm to > 3 ?m. This can be explained by considering effects of mass-thickness on electron penetration.
R. R. Keller and R. H. Geiss, "Transmission EBSD from 10 nm domains in a scanning electron microscope," Journal of Microscopy vol. 245, pp. 245-251 (2012).

 

R. H. Geiss, K. P. Rice, and R. R. Keller, "Transmission EBSD in the Scanning Electron Microscope," Microscopy Today vol. 21, pp. 16-20 (2013).

 

National Research Council Post-Doctoral Research Opportunities: (you will be leaving NIST website when selecting these links)

Transmission Scanning Electron Microscopy for Nano- and Biotechnology

Applications of Transmission Scanning Electron Microscopy in Water Treatment and Sustainable Energy

Transmission EBSD set-up and example pattern.
Top: Experimental configuration for t-EBSD in SEM. Bottom: t-EBSD pattern from aluminum oxide nanoparticle.

Start Date:

October 3, 2011

End Date:

Ongoing

Lead Organizational Unit:

mml

Customers/Contributors/Collaborators:

Aimo Winkelmann, Max-Planck-Institut für Mikrostrukturphysik (you will be leaving NIST space when selecting this link)

 

 

Facilities/Tools Used:

LEO 1525 field emission SEM

JEOL 2000FX TEM

NIST Precision Imaging Facility

Staff:

Related Programs and Projects: