## 3 Results and Discussion
### SEM Analysis--Effect of Processing Parameters on Morphology  
SEM was used to analyse the morphology of the nanoparticles as shown in Figure 8. Three samples (27C, 21C and 9C) that were fabricated at different processing parameters were analysed via SEM (refer to Table 1 and Figures 1-3 for details/processing parameters for these samples). Figure 8d-f are representative of three different samples at the same magnification; differences among these figures prove that laser processing parameters influence the nanoparticle size and yield. All samples show some agglomeration of the nanoparticles; they tend to form dendritic, tree-like structures as shown in Figure 8. This can be attributed to the drop-casting and evaporation method that was used for sample preparation. It is natural for a liquid to form colonies or divide into'mini reservoirs' during evaporation, hence when the liquid is gone, the nanoparticles that remain will resemble the shape of the evaporated liquid. Furthermore, during heating, the viscosity of the liquid decreases, causing the liquid to start moving, thereby splitting into sections as some of the liquid starts to evaporate. The nanoparticles can be deposited onto the substrate with higher accuracy using 3D printing techniques such as inkjet printing (moderate resolution/quality) and aerosol jetting (very high quality and resolution) for fabricating flexible nano/microelectronics. Most of the nanoparticles are spherical and tend to attach to each other due to weak van der Waal forces of attraction between them as shown in Figure 8a,f. It is worth noting that the nanoparticles attach well to the aluminium substrate through the simple drop-casting method without any surface modification or need for adhesive or laser sintering; this implies that drop casting is a viable manufacturing method for specific cases that do not require precise nanoparticle location placement.  
SEM images of samples 21C (Figure 8e) and 9C (Figure 8f) can be compared to observe the effect of laser fluence since the fluence is the only processing parameter differentiating these samples. Sample 21C and 9C were processed at a laser fluence of 1.83 J/cm\({}^{2}\) and 1.91 J/cm\({}^{2}\), respectively. At 200 nm magnification, it can be observed that both samples  
Figure 8: SEM images: (**a**) SEM image of sample 27C at 400 nm magnification and 30 kV acceleration voltage. (**b**) SEM image of sample 9C at 400 nm magnification and 20 kV acceleration voltage. (**c**) SEM image of sample 9C at 200 nm magnification and 30 kV acceleration voltage. (**d**) SEM image of sample 27C at 200 nm magnification and 30 kV acceleration voltage. (**e**) SEM image of sample 21C at 200 nm magnification and 20 kV acceleration voltage. (**f**) SEM image of sample 9C at 200 nm magnification and 9 kV acceleration voltage.  
have similar nanoparticle sizes which is in agreement with the DLS data that gave a mean nanoparticle diameter for sample 21C and 9C of 149.2 and 161.5 nm, respectively.  
Samples 27C (Figure 8d) and 21C (Figure 8e) can be compared to study the effect of scan speed. Sample 27C was processed at a scan speed of 3500 mm/s while 21C was processed at 3000 mm/s. Comparison of SEM images clearly show that sample 27C has a higher nanoparticle yield, meaning that a higher scan speed yields more nanoparticles. This is in agreement with the UV-Vis data of these samples. A higher scan speed means the laser is moving faster, hence it will interact with more powder particles per second. However, there is a limit to the scan speed as observed earlier (scan speeds >4000 mm/s is too fast and did not yield nanoparticles).