# On the Properties of WC/SiC Multilayers
## 2 Experimental Section  
All samples used in this study were prepared in our lab using a magnetron sputtering system with four 7.6 cm diameter magnetrons. W/SiC and WC/SiC multilayers were deposited on super-polished Si wafers using ultra-high purity Kr (99.999%) gas at 0.2 Pa. Depositions were performed at constant powers of 100 W (W target), 100 W (WC target) and 220 W (SiC target). Substrates, which were mounted on a platter, spun at 100 rpm during the deposition. Layer thickness and uniformity was achieved by controlling the platter velocity. Several multilayers of both material pairs (W/SiC and WC/SiC) with different periods ranging from 3.8 nm to 28 nm were prepared and then stored in a dry N\({}_{2}\) environment (Table 1). Thermal annealing was performed in a cold wall, high-temperature vacuum (10\({}^{-7}\) Pa) furnace with programmed heating and cooling cycles (HSD Engineering Inc., Oakland, CA, USA). Samples were annealed at temperatures from 100 \({}^{\circ}\)C to 900 \({}^{\circ}\)C. A heating rate of 6.7 \({}^{\circ}\)C/min was used to reach the targeted temperature which was controlled within \(\pm\)2 \({}^{\circ}\)C. The listed annealing times refer to the time at the final temperature and do not include the heating and cooling cycle. However, the measurements with different experimental techniques listed below were preformed after each listed annealing temperature cycle, at room temperature. The system was cooled down without any active cooling system until it reached 50 \({}^{\circ}\)C at which point the furnace was vented with dry N\({}_{2}\). Small Angle X-Ray Diffraction (SAXRD) and High Angle X-Ray Diffraction (HAXRD) measurements were performed with X'Pert PRO MRD (Panalytical, The Netherlands) equipped with a PIXcel detector, a high-resolution goniometer and a Ge (220) asymmetric four-crystal incidence beam monochromator tuned to Cu K\(\alpha\) radiation (0.15418 nm). SAXRD scans between 0.1\({}^{\circ}\)-7\({}^{\circ}\) were collected with 0.002\({}^{\circ}\) steps. We used the IMD [16] software package to fit the data. HAXRD scans between 30\({}^{\circ}\)-80\({}^{\circ}\) (90\({}^{\circ}\)) were collected to monitor changes in the microstructure of the multilayers. A Multiple Beam Optical Sensor Ultra-Scan stress system (k-Space Associates, Inc., Dexter, MI, USA) was used to monitor changes in the curvature of the samples before and after each annealing cycle. A two-dimensional (2D) curvature of the sample was mapped with a laser array and subtracted from the sample's initial curvature. Changes in the beam spacing are related to the stress-induced curvature via Stoney's equation [17] in which stress is normalized to the multilayer's total thickness. Atomic Force Microscopy (AFM) images were obtained on bare Si substrates, and multilayer-coated W/SiC and WC/SiC samples (before and after annealing) with a Dimension Icon (Bruker, Karlsruhe, Germany) microscope. This AFM is equipped with an acoustic hood and vibration isolation table with noise floor of less than 0.03 nm RMS. The probe tips (Si doped with Sb) had a tip radius of 8 nm and a resonance frequency of 75 kHz. Atomic force micrographs across 1 \(\upmu\)m \(\times\) 1 \(\upmu\)m areas (512 \(\times\) 512 pixels) were collected in a tapping mode at a 1 Hz scan rate and processed using the Bruker NanoScope Analysis software. These measurements give multilayers' surface high spatial frequency roughness, which is referred as \"Roughness\" in the tables below. Rutherford Backscattering (RBS) analysis (Evans Analytical Group, San Diego, CA, USA) was used to obtain quantitative depth profiles of Si, C and W, and the stoichiometry of SiC and WC layers. Due to the limited depth resolution of the RBS method, samples had to consist of much thicker SiC and WC layers than used in multilayers listed in Table 1. Consequently, samples for RBS analysis consisted