## 2 Results
### Microstructure of the Annealed Ag[Gel/AIN NMLs  
#### 2.2.1 Structural Evolution by XRD  
Annealing in air at \(T\geq 400\)\({}^{\circ}\)C induces more pronounced structural changes of both the bias and non-bias NMLs. The first significant structural changes are observed at \(T\geq 400\)\({}^{\circ}\)C for either series. At temperatureThe XRD scans, as collected at room temperature before and after the annealing treatment, are shown in Figure 4. In the as-deposited state, the XRD scans confirm the preferential growth directions of Ag and AlN: i.e., only the Ag(111) and AlN(0002) peaks are visible in the \(\theta\)-2\(\theta\) scan (together with their corresponding second order reflections). Intense modulated reflections (commonly referred as satellite peaks) which originate from the periodicity of NML structure [22] arise for the non-bias sample after annealing in Ar (indicated by arrows in panel a). The appearance of intense satellite modulations upon annealing have been correlated with a decrease of the interface roughness [15]. The respective pole figures also show sharper Ag(111) and AlN(0002) rings after Ar annealing (Figure 3c), confirming a higher degree of crystallinity of the non-bias samples after annealing in Ar at \(T>200\)\({}^{\circ}\)C. The change in the NML microstructure of the bias samples after  
Figure 3: Pole figures of Ag \(\{111\}\) and AlN\(\{1013\}\) family of planes, as recorded from for the as deposited NMLs, produced (**a**) without substrate bias and (**b**) with substrate bias. The same pole figures as acquired after annealing of the NMLs in Ar at 700 \({}^{\circ}\)C are shown in (**c**,**d**).  
Figure 2: SEM micrographs in planar (**top**) and cross-sectional (**bottom**) view of the Ag[Ge]/AIN NMLs produced (**a**) without substrate bias and (**b**) with substrate bias.  
annealing in Ar is different: only very weak satellites appear at 400 \({}^{\circ}\)C, which again vanish at 700 \({}^{\circ}\)C, while, at the same time, new Ag reflections appear (Figure 4b). The appearance of the Ag(200) and Ag(220) reflections upon Ar-annealing is accompanied by a disappearance of the AlN reflections and a weakening of the Ag(111) ring in the respective pole figures (Figure 3c), which indicate a partial destruction of the original NML structure.s below 400 \({}^{\circ}\)C, no significant changes in the XRD patterns are observed for both samples. For the bias samples, the Ag(200) and (220) peaks become more pronounced at \(T\geq 400\)\({}^{\circ}\)C (Figure 4d), suggesting an increased Ag polycrystallinity. Annealing at 700 \({}^{\circ}\)C leads to a complete disappearance of the AlN peaks, while the Ag signal corresponds to that of polycrystalline Ag. This higher degree of polycrystallinity of Ag upon annealing in air can be attributed to the complete degradation of the multilayer structure of the bias sample, as accompanied by outflow of Ag to the outer surface (where it adopts a polycrystalline structure; see next session and Discussion). A similar response upon air-annealing is observed for the non-bias samples (Figure 4b), although the structural transition is shifted to somewhat higher temperatures (note: up to 400 \({}^{\circ}\)C, no additional Ag reflections are observed). At the same time, the AlN reflections have completely disappeared. The disappearance of the AlN reflections during air-annealing can be ascribed to oxygen penetration into the AlN layers, which subsequently reacts with the AlN nanolayers to form amorphous Al\({}_{2}\)O\({}_{3}\) (and N gas) [8]. The XRD analysis is blind to the formation of the amorphous Al oxide phase.