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

The holes in the film formed near non-preferentially oriented (non-PO) [110] and [100] grains and it was initially supposed that the decrease of non-PO indexed points from a temperature of 150°C could be considered as a signal of hole formation in the film, even if the holes were not yet visible in the map. However, the indexed point number criterion alone is not enough to evaluate the starting point of the dewetting, because the total number of indexed points is a convolution of

i) points that were initially indexed, but became not indexed with temperature due to the dewetting of the material

ii) points that were initially not indexed, due to the relatively large value of step sized used, but which started to get indexed with temperature when the growing grains became bigger than the step size.

Therefore it has been necessary to �nd another reliable evaluation criterion to con�rm the exact starting temperature of formation of the holes in the �lm. The new criterion used consisted in the evaluation of the quality of the Kikuchi patterns on the non-indexed areas of the map. Fig. 4.2a shows the IPFZ map acquired at 210°C: in this map there are several non-mapped (and therefore black) areas. Fig. 4.2b shows the Kikuchi pattern recorded from a dewetted area of the sample, while Fig. 4.2c shows the pattern from an area with very �ne grains (in the range of 10-20 nm). The di�erence between those two patterns is evident. In c) the Kikuchi pattern is visible, but indexing was di�cult due to the chosen step size and to the fact that the grain size was close to the physical resolution of the TKD technique; thus many patterns originated from grain boundaries were di�cult to be indexed. In b) no pattern is instead visible, indicating lack of crystalline material, i.e. only the Si3N4 substrate was present at that position.