# Fast One-Step Synthesis of Anisotropic Silver Nanoparticles
## 3 Results and Discussion  
Figure 2 shows the UV-Vis absorption spectra of a solution that was exposed to our process for 30 min at 69 \(\mu\)L/min H\({}_{2}\)O\({}_{2}\) flow, as well as a solution that was produced by laser ablation only. The latter showed a single sharp feature at 395 nm arising from the surface plasmon resonance of spherical Ag NPs. On the other hand, the spectrum from the solution exposed to irradiation and H\({}_{2}\)O\({}_{2}\) flow during the laser ablation process  
Figure 1: Schematic of the reaction setup, including a pulsed laser, a focusing lens, a reaction vessel containing a silver target, an illuminating LED, and a flow of H\({}_{2}\)O\({}_{2}\). appeared significantly different, as the main feature was red-shifted from that of spherical NPs, and additional features arose, including a low intensity one at 335 nm. Indeed, this is strong evidence that the Ag NPs in solution in this case were far from spherical and suggests that the nanoplates were formed during the process. The spectrum did not show significant variations by changing the H\({}_{2}\)O\({}_{2}\) flow rate between 23 \(\upmu\)L/min and 69 \(\upmu\)L/min, while increasing the flow rate above 100 \(\upmu\)L/min caused complete oxidation of the formed material, and the corresponding absorption spectrum would appear flat. Similarly, decreasing the TSC concentration to 0.1 mM did not change the absorption spectrum significantly, while increasing it up to 10 mM caused complete oxidation of the formed material (flat absorption spectrum). The main feature around 500 nm can be attributed to the in-plane dipole mode, while the peak at 335 nm can be attributed to the out-of-plane quadrupole mode, which is typical of Ag anisotropic structures [14; 32]. The other feature around 400 nm may be attributed to larger spherical NPs and/or to the in-plane quadrupole and out-of-plane dipole modes for NPTs or both. We also performed control experiments using either light irradiation or H\({}_{2}\)O\({}_{2}\) flow only. When only irradiation was used, without introducing any H\({}_{2}\)O\({}_{2}\), the process yielded only spherical NPs, with an absorption spectrum close to that shown in Figure 2. When only H\({}_{2}\)O\({}_{2}\) was introduced in the solution, without light irradiation, the transformation happened only to some extent (see Figure S2). We also performed a further control experiment, using no citrate in the solution. In this case, we observed an absorption spectrum with a single broad and asymmetrical feature (Figure S3), suggesting that only a broad distribution of spherical particles was formed. Such results indicate that citrate, light irradiation, and H\({}_{2}\)O\({}_{2}\) are all essential ingredients that cooperate in a successful process, as already shown for a similar two-step process [11]. Figure 3a,b shows representative SEM images of Ag NPTs produced by our process. We can observe Ag NPTs showing a mixture of shapes, including triangles, hexagons, circles, and other irregular ones. The size distribution shows that most NPTs were 70-90 nm in size (Figure 3c). Figure 4 shows an AFM image and the profiles obtained from the same samples analyzed by SEM. Figure 4a also shows NPTs with mixed shapes, and Figure 4b shows the thickness ranging between 10 nm and 25 nm. Figure 2: UV-Vis absorption spectra of Ag NPTs obtained by laser ablation under irradiation and H\({}_{2}\)O\({}_{2}\) flow (blue line) and Ag NPs obtained by laser ablation only (red line). The growth mechanism in this process can be elucidated within the framework of the reactions taking place among citrate, Ag, and H\({}_{2}\)O\({}_{2}\) in the presence of light.