## 2 Materials and Methods
### Analysis Methods  
To investigate the microstructural features of the Al/Ni RMS on flat silicon and Al/Ni 3D-RMS, cross-section views in two directions--longitudinal and perpendicular to the multilayer planes--were prepared by focused ion beam (FIB) nanopilling (Auriga 60, Zeiss). Micrographs were obtained using the integrated scanning electron microscope (SEM) with an operating voltage of 5 kV, measurements made in tilted images were multiplied by a correction factor to obtain the correct dimensions. In addition, TEM micrographs and SAED patterns were obtained by using the TEM JEOL 2011 with an LaB\({}_{6}\) cathode and an operating voltage of 200 kV. TEM samples were prepared using the in situ lift out technique in a FIB/SEM (Helios Nanolab 600, FEI). SAED patterns were analyzed by using the software CrysTBox [21]. The analysis of the diameter of the surface structures was performed using MountainsMap\({}^{\otimes}\), version 7.4.9391 software with the operator motifs detection and analysis according to ISO 25178 detection algorithms (segmentation by watersheds) [22]. In order to quantify the curvature of the deposited layer due to the surface shape of the nanoneedles, the curvature of the layers was determined using the ImageJ software. Before and after RTA, both RMS and 3D-RMS, were examined using a Bruker D5000 Theta-Theta X-ray diffractometer equipped with a Cu K\(\alpha\) (\(\lambda\) = 0.15418 nm) radiation source used at 40 kV and 40 mA, working in Bragg-Brentano mode at speed of 1 s per step and using sampling steps of 0.02\({}^{\circ}\). The diffraction patterns were analyzed in the range of 20\({}^{\circ}\)-100\({}^{\circ}\) to identify crystalline phases by using a software package (Bruker DIFFEAC.EVA V5.1) [23]. Furthermore, calorimetric investigations of the as-deposited RMS were carried with a power-compensated Perkin Elmer Differential Scanning Calorimeter 8500 using Al pans under a constant high-purity Ar flow (99.99 mol.-%)  
Figure 1: Scanning electron microscopy images of the nanostructured Si substrate: (**a**) top view of the silicon needles with a tilt angle of 15\({}^{\circ}\); (**b**) cross section of the substrate providing a side view of the silicon needles.  
of 20 mL min\({}^{-1}\). The samples were continuously heated from 300 to 823 K with a constant rate of 0.333 K s\({}^{-1}\). A second run with the reacted material under identical conditions was used to determine baselines that could be subtracted from the first up-scan. The calorimeter was calibrated regarding its sensitivity and temperature by measuring the melting temperatures and melting enthalpies of In and Zn. Free-standing thin films of the RMS with planar morphology were obtained by mechanically peeling the thin film from the Si substrate. Several cuts of the film were stacked over each other in order to provide a sufficient mass (1.88 mg) for a good signal-to-noise ratio. However, for the 3D-RMS, the thin film could not be detached from the substrate. In this case, the multilayer thin films were measured with the Si substrate above and stacked on top of each other to attain the best possible signal-to-noise ratio. In this case, the total mass of the deposited multilayers was estimated by measuring the surface area of the used sample pieces by light microscopy and consequently calculating the total mass by using the mass densities of Ni and Al.