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Keeney et al. Microstructures 2023;3:2023041 https://dx.doi.org/10.20517/microstructures.2023.41 Page 9 of 15

Figure 3. Representative topography and lateral (lat) DART-PFM phase and amplitude (amp) images of 7.9 nm (1.5 u.c.) B6TFMO on
NGO (001) as a function of AFM-based nano-machined depth. The scanning direction of the cantilever was parallel with the
[010] substrate axis.

Gradauskaite et al. [29,30] and Keeney et al. previously observed stripe domains for one u.c. thick (5 nm)
[27]
Aurivillius phase films that were terminated with complete Aurivillius layers and exhibited an atomically
flat surface. It was deemed that domain patterns are stabilized by the underlying NGO substrate, where the
lattice mismatch is progressively lost as film thickness increases. For films of two unit cells in thickness, an
isotropic random distribution of 180° domains was observed [29,30] . Therefore, the question arises as to
whether the onset of 45° striped domain observation in this work happens solely due to the ability to image
the B6TFMO film at decreased thickness, where the domain patterns are possibly stabilized by substrate
strain effects. Alternatively, the onset of striped domain observation from the nano-machining process may
be due to the removal of otherwise masking surface 2D islands, pits, and contaminants to reveal a smooth
B6TFMO surface terminated with a complete Aurivillius layer.