Quantitative Scanning Transmission Electron Microscopy for the Measurement of Thicknesses and Volumes of Individual Nano
- PDF / 476,081 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 82 Downloads / 189 Views
1184-HH01-06
Quantitative Scanning Transmission Electron Microscopy for the Measurement of Thicknesses and Volumes of Individual Nanoparticles Helge Heinrich1,2,3, Biao Yuan1,3, Haritha Nukala1,3, and Bo Yao1,3 1 Advanced Materials Processing and Analysis Center (AMPAC), University of Central Florida, Orlando, FL 32816, U.S.A. 2 Department of Physics, University of Central Florida, Orlando, FL 32816, U.S.A. 3 Department of Mechanical, Materials, & Aerospace Engineering, University of Central Florida, Orlando, FL 32816, U.S.A. ABSTRACT In Scanning Transmission Electron Microscopy (STEM) the High-Angle Annular DarkField (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.
INTRODUCTION Transmission electron microscopy (TEM) is a very powerful tool with a high lateral resolution of about 2 Å, which allows to image the individual atomic columns giving an insight into the atomic structure of materials. To get a comprehensive picture of a material it is often necessary to measure all three dimensions of a sample. The measurement of the sample thickness is very important to give a full three-dimensional description of each nanoparticle. Though TEM has a high lateral resolution, it is extremely difficult to determine the third dimension (sample thickness). The Atomic Force Microscope (AFM) provides a three-dimensional surface profile; it mainly uses the height of its probe tip to measure the surface topography. At high edges of a surface the AFM image yields incorrect height information as the AFM tip has a finite radius of curvature. Atomic Force Microscopy and TEM are complementary to each other: AFM has a better height reso
Data Loading...
