To date, bonding electron distributions have only been measured in homogeneous, single-phased, near ideal crystals, yet, most materials utilized in engineering applications have inhomogeneous structures. The properties of such materials are influenced by constituent phases which could be attributed to their chemical bonding.
This research seeks to employ a new approach to quantitative convergent-beam electron diffraction (QCBED) based on the multislice theory of electron scattering [ 1] to experimentally map and measure the bonding electron density of the embedded nanostructures (precipitates) in an aluminium-copper (Al-Cu) alloy [ 2]. This method eliminates the requirement for periodicity in the crystal structure along the direction of the incident beam and allows the bonding electron distributions in each slice of the scattering volume to be measured, including the region containing the buried precipitates. However, this entails that the precipitates and the surrounding matrix are coherent in the directions normal to the incident beam and parallel to the slices, a condition that is well met by the subject of the present work, θ′ precipitates in Al-Cu alloys [ 2].
At the present, the CBED patterns acquired through θ′ precipitates in the [001] Al direction are analysed in QCBED to experimentally measure structure factors which are the primary quantities used to derive electron distribution. Figure 1c shows the mean values and the uncertainties of the measurement results in QCBED for the low-order structure factors for each data set of the two CBED patterns collected from two different samples of Al-1.7 at% Cu alloy with the corresponding theoretical values for structure factors based on the independent atom model (IAM).