# XCT and DLW: Synergies of Two Techniques at Sub-Micrometer Resolution
## 2 Materials and Methods
### Sample Geometry and Slicing Software  
This work includes two basic sample geometries, a fractal pyramid (sample 1) and a four-sided pyramid (sample 2), see Table 1. Both pyramids had a side length of \(141\,\mathrm{\SIUnitSymbolMicro m}\) and a height of \(100\,\mathrm{\SIUnitSymbolMicro m}\). The used slicers were Femtika 3 DPoli Compiler (ver. 6.33) and Cura (ver. 6.9) for structures where the generated G-Code was then used in the 3 DPoli Compiler. The provided software Femtika 3 DPoli Compiler in the used fabrication setup is limited to fully polymerising one outer contour line and to completely filling the inner area of an object (with distinct programmed laser path vectors). This method can be a time-consuming fabrication approach. To overcome this limitation, it is possible to import G-code-files sliced in a slicer software such as PrusaSlicer ([[https://github.com/prusa3d/PrusaSlicer](https://github.com/prusa3d/PrusaSlicer)]([https://github.com/prusa3d/PrusaSlicer](https://github.com/prusa3d/PrusaSlicer)) (accessed on 16 October 2022)--License: AGPL 3.0) or Cura ([[https://github.com/Ultimaker/Cura](https://github.com/Ultimaker/Cura)]([https://github.com/Ultimaker/Cura](https://github.com/Ultimaker/Cura)) (accessed on 16 October 2022)--License: LGPL 3.0). Both are fully open-source and were initially used for FDM printers. These slicers offer a wide range of variables, which are not covered by the integrated device slicer 3 DPoli software. This includes the option of gradual infill, infill types, wall counts and an adaptive layer height. In general, infills geometrically trap non-polymerised polymer layer by layer, and thus can fabricate bigger volumes in less time compared to Femtika 3D Poli. Unpolymerised photoresist would have to be polymerised after DLW development.  
Sample 1 is a fractal pyramid, which is a split Octahedron Flake or Sierpinski Octahedron. It is a variant of fractal structures described by [PERSON] in two dimensions in 1915 [46] and three-dimensional structures by [PERSON] [47]. It was split in half to achieve the highest surface attachment by fabricating the structure on the resulting square surface plane. The structure had a recursion depth of 4 (cf. Figure 1).  
With a total height of \(100\,\mathrm{\SIUnitSymbolMicro m}\), the next smaller resulting triangle height was \(50\,\mathrm{\SIUnitSymbolMicro m}\), \(25\,\mathrm{\SIUnitSymbolMicro m}\), \(12.5\,\mathrm{\SIUnitSymbolMicro m}\) and \(6.25\,\mathrm{\SIUnitSymbolMicro m}\), respectively. Calculation of the surface area as well as volume of the octahedron fractal pyramid according to the recursion depth can be performed using formulas taken from [PERSON] [48]. For explanatory and illustration purposes, a 3D model with a cut in the X- and Y-plane is shown in Figure 2.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Type** & **Height: Side Length (\(\mathrm{\SIUnitSymbolMicro m}\))** & **Slicer** & **Slicer Options** \\ \hline
1 & Fractal Pyramid & 141; 100 & 3 DPoli & Hatching and Slicing distance = \(200\,\mathrm{nm}\) \\
2 & Full Pyramid & 141; 100 & Cura & 8 outer walls, single infill line every \(4\,\mathrm{\SIUnitSymbolMicro m}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of the two sample geometries.  
Figure 1: Illustration of a fractal triangle in 2D with increasing recursive depth of 0 to 3 (left to right).  
Sample 2 is a four-sided pyramid that was sliced by Cura with the following parameter set: 8 outer walls (8 contour lines set in by the hatching distance) and an infill structure of a single voxel line every 4 \(\mathrm{\SIUnitSymbolMicro m}\) in a rectangular pattern. Note that this sample is intended to be a bulk four-sided pyramid, but with an inner structure given by the infill parameters. The naming convention and an illustration of the used toolpath are shown in Figure 3.