# XCT and DLW: Synergies of Two Techniques at Sub-Micrometer Resolution
## 3 Results  
### Fabrication Method--Practical Difficulties and Workflow Modifications  
In previous works by [PERSON] et al. [30], XRM structures were fabricated on a 750 \(\upmu\)m pillar with the dip-in technology by Nanoscribe. With the SZ2080 photoresist, the dip-in method is not applicable. As SZ2080 must be baked [6] before the fabrication step, a preparation where a drop is casted on a small pillar, only very low structure heights would have been manufacturable as the drop height would be limited by the contact angle between pillar and photoresist. Thus, a conventional preparation technique on a flat substrate was preferred. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Voltage (kV)** & **Power (W)** & **Filter** & **SOD (mm)** & **ODD (mm)** & **Mgeo** & **Mopt** & **texp (s)** & **PSeff (\(\upmu\)m)** & **Nproj** \\ \hline
40 & 3 & None & 10 & 10 & 2x & 40x & 14 & 0.33 & 801 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of XCT imaging parameters, including source–object distance (SOD), object–detector distance (ODD), geometrical magnification (M\({}_{\text{gro}}\)), optical magnification (M\({}_{\text{opt}}\)), exposure time (texp), effective pixel size (PSeff) and number of projections (Nproj). Figure 4: (a) X-ray spectrum of the used setup calculated with aRTist (parameters see Section 2.4). Note that most photons are created in the low-energy range around 10 kV (characteristic lines of tungsten) and at the mean energy of the bremsstrahlung at around 15 kV. (b) Total linear attenuation coefficients of glass (SiO\({}_{2}\), \(\rho_{Si}=2.2\) g \(\cdot\) cm\({}^{-3}\)), SZ2080 (C\({}_{36}\)H\({}_{68}\)O\({}_{20}\)Si\({}_{4}\)Zr, \(\rho_{SZ2080}=1.2\) g \(\cdot\) cm\({}^{-3}\)) and PET (C\({}_{10}\)H\({}_{8}\)O\({}_{4}\), \(\rho_{PET}=1.38\) g \(\cdot\) cm\({}^{-3}\)). Commonly, a glass substrate is used for DLW fabrication. However, glass and the deposited photoresist SZ2080 both intrinsically hold a very similar mass attenuation coefficient over the used X-ray energy spectrum, cf. Figure 4. In addition, the substrate and deposited polymer have very different sizes and material shadowing may occur here. To be precise, there are practical difficulties to image and align a big and flat (6 \(\times\) 6 \(\times\) 0.17 mm\({}^{3}\)) substrate with a small (0.141 \(\times\) 0.141 \(\times\) 0.1 mm\({}^{3}\)) sample on top in-plane along the X-ray beam path without any tilt. Consequently, precession of the substrate that shadows the deposited structure over a wide range of the angular views may occur, cf. Figure 5. In general, for high-aspect-ratio samples, an out-of-plane alignment is preferred, as the substrate's long side/thick edge passes the angular views only two times quickly. In an out-of-plane alignment, the pyramid's top/bottom is imaged frontally and image information is maximised over a wide range of angular views. Note that the length of the X-ray beam path through the long side/thick edge is very large (up to 60 times larger) compared to the short side/thin edge and/or the pyramid's size. Glass is difficult to cut or break when considering the small size of the pyramid. It was not possible to prepare glass substrates with a side length smaller than 6 mm. To overcome these practical difficulties, the 170 um glass substrate was substituted by a 0.17 mm PET foil with a much lower mass attenuation coefficient and density \(\rho\), cf. Figure 4b. Moreover, samples are scanned out-of-plane, for which the substrate size was reduced to about 3 \(\times\) 6 mm\({}^{2}\). Thus, a longer X-ray travelling path through the substrate with a high aspect ratio was compensated by choosing a substrate with low attenuation coefficient and optimised sample alignment. In the PET-SZ2080 sample system, SZ2080 is a high absorbing material. When exchanging the standard glass substrate by a PET-polymer substrate, a modification of the DLW fabrication process is needed, as illustrated in Figure 6. The mechanical properties of glass and polymer are very different.