## 3 Results and Discussion
### Material Characterization  
The Raman spectroscopy measurements were performed for the qualitative analysis of the samples to check if the prepared samples were MoS\({}_{2}\). The spectra presented in Figure 9 were taken at 5% of laser power for the CA sample and 1% of laser power for the FA sample. Both spectra of MoS\({}_{2}\) samples show similar vibrational modes. The main peaks can be seen at \(\sim\)383 and \(\sim\)408 cm\({}^{-1}\) corresponding to the E\({}^{1}\)\({}_{2g}\) and A\({}_{1g}\) vibrational modes of bulk MoS\({}_{2}\), respectively. Other peaks located at \(\sim\)188, \(\sim\)230, \(\sim\)456, and \(\sim\)629 cm\({}^{-1}\) are attributed to the typical stretching vibrations of MoS\({}_{2}\)[33].  
At the beginning of the measurement for both samples, the same conditions were applied (i.e., laser power, illumination time, and number of counts). Measurements for particles synthesized using FA and CA were performed under the same conditions (same laser power (5%), same number of counts, same measurement area, and same length of exposure) and spectra are shown in Figure 10. It was observed that for the sample prepared with formic acid, peaks mainly from molybdenum oxides were visible, while for the citric acid sample, mainly MoS\({}_{2}\) was present.  
Based on these results, it was decided to decrease the laser power used to check if the oxides formed on the formic acid sample were due to the measurement conditions or were formed during precipitation. For both samples, again the same measurement conditions were applied (spectra shown in Figure 11).  
It can be observed that for the formic acid sample, when a lower laser power was used the signal from molybdenum oxides disappeared, and mainly peaks from MoS\({}_{2}\) were visible. The sample prepared with citric acid in both measurement conditions mainly showed peaks from MoS\({}_{2}\). From this experiment, it was assumed that MoS\({}_{2}\) prepared with formic acid is less stable because with the same measurement conditions, the particles are more easily oxidized (which might also be connected to their smaller size). The sample prepared with CA showed much lower susceptibility to laser oxidation; however, the sample was not homogeneous, and Mo-oxides were visible at most of the points where the measurements were taken (a spectrum of the sample obtained with CA in a different spot is presented in Figure 12).  
The SEM images are presented in Figure 13. Comparing the SEM pictures of both samples, it can be seen that the particles obtained with the use of formic acid are smaller, and their structure has more wrinkles which have higher electron beam transmittance compared to particles obtained with citric acid. This might suggest that the thickness of the particles obtained with formic acid is lower, and the material looks more fragile. The sample obtained with citric acid looks denser and thicker.  
Figure 8: PSD (**a**) by number, (**c**) surface area, (**e**) volume of particles synthesized using citric acid; PSD (**b**) by number, (**d**) surface area, (**f**) volume of particles synthesized using formic acid.  
Figure 11: Raman spectra of MoS\({}_{2}\) prepared with (**a**) CA and (**b**) FA at 1% laser power.  
Figure 10: Raman spectra of MoS\({}_{2}\) prepared with (**a**) CA and (**b**) FA at 5% laser power.  
Figure 9: Raman spectra of MoS\({}_{2}\) prepared with citric (CA) and formic acid (FA).