## 3 Results
### Crystalline Structure  
For a better understanding of the observed nanostructure, TEM and diffraction image simulations have been carried out for the martensitic and austenitic phase of NiCoMnAl and combinations of both. As a basis for the multislice simulation a B2 structure for  
Figure 3: Selected area diffraction pattern (upper row) and corresponding dark field images (lower row) of the same checkerboard area. The diffraction spots used for the respective DF images are marked by the orange circles. austenite and a tetragonal distorted B2 structure for martensite with a 14 M modulation has been assumed. In Figure 4 the results are shown, simulated at 200 kV acceleration voltage, at a temperature of 300 K and a defocus of \(-\)60 nm. The number of layers and their thickness had to be decreased due to computational effort. It can be seen that the diffraction image of the austenite resembles its cubic structure where the martensite only allows a different class of reflexes to be excited, resulting in an unordered superposition in the center with lines of diffraction spots. Placing these two configurations of the material on top of each other leads to a pattern of austenite acting as a base with added reflexes from martensite around the excited austenite reflexes. More reflexes are visible on the austenite reflexes in the preferred scattering direction of the martensite, less in the perpendicular direction. Of course, not all of the reflexes shown in the simulation are strong enough to be visible in the TEM, depending on the specimen thickness and all contained crystal structures the electron wave has to cross. By employing FFT on the simulated diffraction pattern, possible HRTEM images can be generated (Figure 4b), which give insights in the structure. Especially, the 14M modulation of the martensite is visible in the image (Figure 4b, center). Processing the simulated diffraction pattern of martensite on top of austenite (Figure 4b, right) reveals the origin of the observed Moire patterns in the dark checkerboard fields. The direction of the Moire patterns gives information about the orientation of the martensite cell and the periodicity is measured to be 2.01 nm. A first step to identify the microstructural properties of the checkerboard has been carried out by XRD analysis. A 0/20-scan for the (002)\({}_{\text{M}}\) peak as well as the (004)\({}_{\text{A}}\) and (400)\({}_{\text{M}}\) peaks are shown in Figure 5a,b), respectively. A linear function has been used for background subtraction and the peaks have been fitted by Pseudo-Voigt-functions. The fit of the (004)\({}_{\text{A}}\) peak yields a 20-angle of (64.721 \(\pm\) 0.009)\({}^{\circ}\), from which, according to [PERSON]'s equation, a lattice constant of (5.761 \(\pm\) 0.008) A for the austenite unit cell has been calculated. For the martensite (002)\({}_{\text{M}}\) peak a position of (26.803 \(\pm\) 0.023)\({}^{\circ}\) and for the (400)\({}_{\text{M}}\) peak a position of (67.720 \(\pm\) 0.010)\({}^{\circ}\) have been determined. Therefore, the unit cell parameters of the tetragonal cell have been calculated to be \(a\) = (5.534 \(\pm\) 0.010) A and \(c\) = (6.652 \(\pm\) 0.018) A. These values are in close agreement with lattice constants found in  
Figure 4: (**a**) Multislice simulation of diffraction images for the pure austenitic (left) and martensitic (centre) phase of NiCoMnAl and 3 nm martensite on top of 3 nm austenite (right). (**b**) Corresponding TEM images created via FFT of the diffraction pattern. The images are still depending on parameters such as defocus and camera length. other studies for this alloy [30]. Here, a tetragonality factor \(c_{\rm T}\) = (1.202 \(\pm\) 0.003) for the martensite has been determined. In order to adapt the fit for the (004)\({}_{\rm A}\) and (400)\({}_{\rm M}\) peak, the (002) peak from the V seed layer located at (60.781 \(\pm\) 0.013)\({}^{\circ}\) has to be considered as well.