LabAdviser/314/Microscopy 314-307/SEM/Nova/Transmission Kikuchi diffraction: Difference between revisions

= Formation of Kikuchi lines =

Figures 8 and 9 show the IPFZ maps overlaid with pattern quality for temperatures varying from 20°C to 900°C. A preliminary investigation of the Au film at room temperature revealed a bimodal nanostructure, with the presence of small grains with size in the range of 30 nm and large grains with size in the 150 nm range. The latter ones showed a strong [111] out-of-plane texture. During heating, the [111] grains tended to grow faster than the [110] and [100] ones. It is also possible to observe that grain growth started at a temperature below 150°C, while holes are visible at 170°C (highlighted with a red circle). The holes were formed in the vicinity of non-preferentially oriented (non-PO) [110] and [100] grains, which were also the site where the hole growth was continuing.

The yellow rectangles follow instead the delayed hole growth due to the presence of preferentially oriented (PO) [111] grains: the hole is visible from 170°C and grows until it is completely surrounded by larger PO grains, subsequently its growth is retarded until 500°C, while other holes continue to grow. When a hole meets a grain having a low interface energy (in this case a [111] grain), edge retraction is inhibited due to the reduced driving force for dewetting, because these grains are energetically very stable. The low-interface energy grains, which inhibited the retraction, continue to grow at the expense of neighboring grains having higher interface energy, resulting in abnormal grain

The graph confirms the trend from the maps shown in Fig. 8, revealing that grain growth started already at 120°C. The PO grains were larger than the non-PO ones already from the starting nanostructure and grew considerably faster: by a temperature of 220°C, PO grains have almost triplicated their average size, while non-PO grains maintained their average size of 33 nm. Furthermore, up to 550°C practically only the PO grains grew. Fig. 10b shows the evolution of the number of indexed points for the two classes of grains, while Fig. 10c shows the number of grains of each class during annealing. The data shows that the fraction of indexed points and the number of non-PO grains started to decrease at the annealing temperature of 150°C. Considering that the holes were formed near non-PO grains as described above, the decrease of non-PO indexed points can be considered as a signal of hole formation in the film, even if holes are not visible in the image at that temperature. For PO grains, the fraction of indexed points kept increasing up to 350°C, while the number of grains already started to decrease at 180°C, indicating that such grains kept growing and coalescing before the dewetting process took place.

== Determination of the temperature of formation of the first hole ==

[[File:Picture66.png|500px|center|thumb|Fig. 11: a) IPFZ map of the growth direction of the 15 nm Au thin film at 210°C; b) signal from a dewetted area of the sample revealing no pattern and c) non-indexed pattern from a fine grain region.]]