# On the Properties of WC/SiC Multilayers
## 3 Results and Discussion
Figure 8: SAXRD experimental data and fits of the same WC/SiC multilayer before and after anneal at 700 \({}^{\circ}\)C for 24 h.  
The analogous HAXRD spectra of WC/SiC samples in as-deposited state are featureless (Figure 10) apart from two already mentioned peaks associated with the Si substrate. This implies that both SiC and WC are amorphous in multilayers with periods between 3.85 nm and 28.5 nm with nominal \(\Gamma=0.5\). Heating to 700 \({}^{\circ}\)C for 1 h increases peak intensities of W (110) and W (211) in 21 nm period W/SiC multilayer as seen in Figure 11 indicating an increase in crystal size of W crystals with increasing \begin{table}
\begin{tabular}{c c c c c} \hline  & & \multicolumn{2}{c}{**W/SiC**} \\ \hline
**T** (\({}^{\circ}\)**C) & **Time (h)** & **Period (nm)** & **Stress (MPa)** & **Roughness (nm)** \\ \hline As-deposited & - & 3.86 & \(-\)361 & 0.12 \\
700 & 1 & 3.76 & 1130 & \\
700 & 6 & 3.75 & 1113 & \\
700 & 24 & 3.74 & 1130 & 0.16 \\ \hline As-deposited & - & 3.8 & \(-\)300 & 0.13 \\
850 & 1 & delaminated & - & - \\ \hline \end{tabular}
\end{table} 
Table 4: W/SiC short multilayer period, stress and surface roughness as a function of annealing temperature. Data following as-deposited sample originate from the same sample. Figure 10: HAXRD scans of as-deposited WC/SiC multilayers of different multilayer period thicknesses. Figure 9: HAXRD scans of as-deposited W/SiC multilayers of different multilayer period thicknesses. temperature. However, annealing WC/SiC multilayer of a similar period (28.5 nm) under the same conditions causes almost no change (Figure 11). In short period multilayers (3.8 nm), hence below W amorphous-to crystalline transition, both W/SiC and WC/SiC show no crystalline phase either before or after anneal to 700 \({}^{\circ}\)C (Figure 12). In this case, all layers remained amorphous even after being annealed for 24 h at this temperature. Cross-section TEM images of WC/SiC multilayer also show no changes in the microstructure of this multilayer annealed to 700 \({}^{\circ}\)C for 24 h (Figure 13). In particular, there is no indication of crystals in any of the two materials, consistent with the results obtained with different methods presented above. The electron diffraction pattern (insert) shows Bragg spots but these are due to the single crystal Si substrate. This is because the used beam was large and illuminated both the multilayer and the substrate, simultaneously. The slightly stronger diffuse ring observed in the annealed sample (Figure 13a) can be explained with a longer exposure time. Based on electron diffraction, high resolution  
Figure 11: HAXRD spectra of as-deposited and annealed W/SiC (21.3 nm) and WC/SiC (28.5 nm) multilayers. The samples were annealed to 700 \({}^{\circ}\)C for 1 h.  
Figure 12: HAXRD spectra of as-deposited and annealed W/SiC (3.8 nm) and WC/SiC (3.8 nm) multilayers. The samples were annealed to 700 \({}^{\circ}\)C for 24 h.  
TEM and dark field imaging (not shown here) we conclude that the layers are amorphous not only in as deposited multilayer but also after annealing to 700 \({}^{\circ}\)C for 24 h.  
Since both materials in WC/SiC multilayers are alloys we are also interested in the elemental composition of the sputtered layers and any changes induced by high temperature annealing. RBS spectra of two identical samples, as-deposited and annealed to 700 \({}^{\circ}\)C for 24 h were measured (for details see Experimental Section). They show identical composition to within experimental error. The analysis was repeated several times to confirm these results. Figure 14 shows a full RBS spectrum of as-deposited WC/SiC sample and a zoomed region corresponding to W in WC layer. The densities of WC and SiC (atoms/cm\({}^{2}\)) were calculated empirically from the bulk elemental densities, and used to calculate the RBS thicknesses (Tables 5 and 6). Using equation:  
\[\mathrm{D_{real}}=(\mathrm{D_{RBS}}\times\mathrm{T_{RBS}})/\mathrm{T_{real}}, \tag{2}\]  
one can calculate the density (atoms/cm\({}^{3}\)) if the thickness is known.