Three-dimensional characterization of Guinier-Preston zones in an Al-Cu alloy using depth-sectioning technique

Guinier-Preston (GP) zones formed as nanometer-sized Cu-rich monolayers in α-Al matrix phase during aging process have been investigated using depth-sectioning technique, where through-focal high-angle annular dark-field (HAADF) images were recorded along a <001> zone axis of the α-Al phase using aberration-corrected scanning transmission electron microscopy (STEM). HAADF intensities of the GP zones in the through-focal series vary with defocus settings, depending on the depths of the GP zones in the sample. Determination of the depth of a GP zone is not straightforward because the electron wave function of the STEM probe in the aligned crystalline material is affected by electron channeling. The depths of GP zones were then estimated via comparison with multislice simulations where GP zones were arranged at various depths in a supercell, and HAADF intensities were simulated with various defocus values. We show that the depth-sectioning technique can be used to investigate three-dimensional configurations of GP zones in the sample.