## 3 Results and Discussion  
Figure 2 demonstrates the plan view and cross-sectional scanning of Mo thin films using a combination of AFM and FESEM. The as-sputtered Mo thin film consisted of flake-like grains from, both 3D AFM and plan view FESEM images. These flake-like grains were transformed to stony-like ones upon annealing. Similar changes in morphology with annealing temperature were reported in Reference [10], where the authors attributed the stony-like grains to an association with Mo surface oxidation. From Figure 2c, the thickness of the thin films is around 1 \(\upmu\)m and remains unchanged regardless of heat treatments. Mo crystals in the as-sputtered sample had columnar grains along the cross-section of the film, which were packed perpendicular to the Si wafer substrate. With respect to annealing, new interfaces started to form within the grains, and the columnar feature of Mo crystals was lost when the sample was annealed in 900 \({}^{\circ}\)C, which was the recrystallization temperature of Mo [13]. As the annealing temperature increased above 900 \({}^{\circ}\)C, higher energy was obtained in the thin film to facilitate grain boundary migration. As a result, crystals were merged with adjacent grains, and subsequently the enlarged grains grew to a level where their volumes were comparable to the thickness of the film when the sample was annealed at the highest temperature of 1100 \({}^{\circ}\)C. The recrystallization process is usually accompanied by stress relaxation and crystalline texture evolution [14]. The latter effect will manifest as changes in X-ray diffraction (XRD) intensity in particular orientations, which will be discussed in the XRD analysis. Moreover, it is worth noting that no crack formation was identified in any of the samples, which indicated that the application of Si wafer as substrate had overcome the material degradation found in previously fused silica based samples [3; 4]. This improvement of material stability with respect to high temperature annealing process, has made Mo-Si promising as a whole for use as contact-substrate for Si QDs solar cells. Figure 2: _Cont._  
The surface roughness of all samples was determined from AFM measurements on a 1.0 \(\upmu\)m \(\times\) 1.0 \(\upmu\)m area, and the results are plotted in Figure 3 as a function of annealing temperature. It was noted that, post-sputtering heat treatments led to rough surfaces on thin films, which increased with annealing temperature following the linear relation indicated in Figure 3. The higher roughness could be explained by the results of larger grain size and formation of Mo oxide defects on the surface, as observed in plan-view FESEM scanning. Even though the maximum roughness obtained on the sample Mo-1100 reached around 30 nm, it is acceptable for fabrication of full Si QDs devices, which are typically 400-500 nm in thickness. Figure 2: (**a**) 3D Atomic force microscopy (AFM) images, (**b**) field emission scanning electron microscopy (FESEM) plan views, and (**c**) FESEM cross-sectional views of Mo thin films as a function of annealing temperature. The crystalline properties of Mo thin films, including preferred orientations and crystallite size, were studied via XRD over a 2\(\theta\) range from 30\({}^{\circ}\) to 90\({}^{\circ}\), with a step size of 0.01\({}^{\circ}\). The XRD spectra of each sample in Figure 4 was normalized to its corresponding maximum value. The main peaks identified at around 2\(\theta\) = 40.5\({}^{\circ}\) and 73.7\({}^{\circ}\) from all samples match the Mo Bragg reflections from (110) and (211) planes, respectively. Weak peaks originated from Mo (200) planes and were also detected on As-Mo, Mo-700, and Mo-800, whilst this peak was hardly noticeable on sample Mo-1000 and Mo-1100. For all annealed samples, XRD peaks related to Mo oxides were identified apart from the Bragg peaks of Mo, which explained the stony-like grains on the FESEM plan views, and the increased surface roughness from AFM.