Electron Diffraction-Based Metrology of Nanocrystalline Materials

In this work, an electron diffraction based orientation mapping system installed on a transmission electron microscope (TEM) is used to examine nanocrystalline Cu, W and Al thin films as well as Cu/Nb nanolamellar composites with feature sizes in the range of 1-100 nm. Nanosized beams are used to scan areas of interest while spot diffraction patterns are recorded. Spot diffraction patterns are cross correlated with pre-calculated templates for orientation determination. Precession is used to reduce the dynamical effect, increasing orientation mapping reliability. With calibration of reference frames and careful choice of experimental parameters, e.g., step size, spot size and precession angle, orientation maps with high quality are collected. This TEM electron diffraction based orientation mapping technique is used to measure mean grain size, grain size distribution, twin boundary length fraction, orientation texture, misorientation texture, the grain boundary character distribution (GBCD) as well as the heterophase interface character and plane distribution for statistically significant populations with feature sizes in the 1-100 nm region. The GBCD of nanocrystalline Cu films is found to be comparable with microcrystalline Cu. The twin boundary length fraction of nanocrystalline Cu films also compares favorably with predictions of models developed for micron-scale materials. For the nanocrystalline W film, the GBCD is correlated with that for a micrometer-sized ferritic steel sample, which also has a body-centered cubic crystal structure. For the nanocrystalline Al film, the grain size is measured using both the orientation mapping-based and image-based methods. The two methods give the same grain size value but different grain size distributions. The GBCD of the Al film is different from bulk Al with micrometer sized grains in that it has high peak intensity at the coherent O3 boundary position. The orientation and misorientation texture of three nanolamellar Cu/Nb composites fabricated by the accumulative roll bonding (ARB) technique are measured. The interfacial texture of the Cu/Nb composites is similar to their ARB-fabricated counterparts with thicknesses in the range of 200-600 nm, but is different from Cu/Nb films fabricated by sputter deposition.