## 3 Results
### Influence of the Layer Thicknesses on the Checkerboard Formation  
In order to check if the observed pattern is an exception or caused by a general formation mechanism in these type of thin film systems, the sample has been reproduced and different intercalation and active layer thicknesses have been investigated. In Figure 8 TEM images of four different samples have been summarized. The details of the investigated sample systems and an explanation of the sample nomenclature are given in Table 1. In the survey image in Figure 8a of a sample with 7 martensitic intercalations (MI7-30/100) no checkerboard structure can be identified easily, but on closer inspection, rectangular regions containing Moire-patterns can be identified (see inset). Similar to the sample with 13 MIs those regions are tilted by 45\({}^{\circ}\) to the sample surface. Another shared feature for both  
Figure 6: (**a**) HRTEM image of a section of the checkerboard. The red boxes mark the fields from that FFTs have been obtained. The FFT of box 1 is given in (**b**) of box 2 is shown in (**c**) and (**d**) corresponds to box 3. (**e**) Overlay of the FFTs b) and (**c**) illustrating the perpendicular orientation of adjacent martensite nuclei. (**f**) Enlarged image of box 1 indicating the region where a line profile across the Moiré pattern has been obtained and (**g**) the resulting line profile with a measured distance of 2.07 nm between the Moiré fringes.  
samples is the perpendicular arrangement of the Moire-patterns of two adjacent regions. Thus, the sample might be on the verge of forming the regular arrangement of martensite nuclei. In the MI6-30/30 and MI6-30/50 samples the checkerboard arrangement is present, as can be seen in Figure 8b,c. The contrast between the rectangular regions is not as large as before, caused by the smaller thickness of both cross sections. Nevertheless, the field sizes have been determined to be about (25.3 \(\pm\) 8.2) nm for the small squares, (46.8 \(\pm\) 7.6) nm for the large squares and (25.3 \(\pm\) 8.2) nm \(\times\) (46.8 \(\pm\) 7.6) nm for rectangle areas of sample MI6-30/30. For the MI6-30/50 sample, slightly larger field sizes have been measured: (38.3 \(\pm\) 5.2) nm for the small squares, (53.7 \(\pm\) 6.6) nm for the large squares and (38.3 \(\pm\) 5.2) nm \(\times\) (53.7 \(\pm\) 6.6) nm for the rectangle regions. The measured values are similar to that one's measured from the MI13-sample, pictured in Figure 2. Therefore, the sizes of the checkerboard fields seem to be almost independent from the thicknesses of the intercalation and active layers.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample Name** & **MI Number** & **MI Thickness [nm]** & **AL Number** & **AL Thickness [nm]** \\ \hline MI7-30/100 & 7 & 30 & 6 & 100 \\ MI6-30/30 & 6 & 30 & 5 & 30 \\ MI6-30/50 & 6 & 30 & 5 & 50 \\ MI6-10/30 & 6 & 10 & 5 & 30 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Overview about the details of the investigated sample systems. The sample names contain the number of the martensitic intercalation (MI) and the nominal thicknesses of the layers in nm for MIs and active layers (AL).  
Figure 7: Temperature evolution of the checkerboard sample: (**a**) TEM images acquired between 323 K to 403K and their corresponding FFT diffraction pattern (**b**). All FFTs have been contrast adjusted. (**c**) TEM image of the specimen recorded at 103 K (enhanced in contrast to make the Moiré pattern more visible) and corresponding SAED pattern.  
Whereas, in the MI6-10/30 sample no notable features of a checkerboard formation can be identified (Figure 8d), representing together with the MI7-30/100 sample the limits for the thicknesses of the MIs and the ALs for the checkerboard formation.