# Characterizations of Interfacial Solar Water Evaporation
## 2 Intrinsic Properties
### Raman Spectroscopy  
Raman spectroscopy is a nondestructive and highly sensitive technique for micro-area analysis that can be used to identify the structural, optical, and electronic properties of materials. Once the wavelength of incoming light is less than the absorption edge, a semiconductor absorbs optically. The Raman spectrum is a graph that can be used to quantify and visualize the quantity and frequency of photons. Typically, visible or near-infrared (NIR) wavelengths are used to detect Raman waves. Thus, Raman spectroscopy is more advantageous than infrared (IR) spectroscopy. Similar to FTIR, Raman spectroscopy may be used to examine the chemical composition of a material.  
[PERSON] et al. [13] described for the first time black titania with a distinct nanocage structure for solar desalination. They used Raman spectroscopy to clarify the nature of the structural alterations following reduction. Previous research had ascribed the four Raman active modes of anatase to Raman peaks at 136, 390, 509, and 633 cm\({}^{-1}\). A comparison between the black TiO\({}_{2}\) nanocages and pure anatase nanoparticles revealed a clear widening and blue shift for the peak centered at 136 cm\({}^{-1}\). Raman scattering is known to be sensitive to crystallinity and structure, so the shift indicated that the reduction disrupted the original symmetry of the titania lattice (Figure 3a). [PERSON] et al. [14] created a bi-layered photothermal membrane with polystyrene foam on the bottom and a porous film of reduced graphene oxide (rGO) on top. The Raman spectra indicated that GO was successfully reduced to rGO during HI treatment. Two distinct peaks were detected at 1359 and 1609 cm\({}^{-1}\) for GO, which matched the well-known G and D bands. The G and D bands remained after reduction, but their intensity ratio (I\({}_{\text{D}}\)/I\({}_{\text{G}}\)) increased noticeably from 0.88 in GO to 1.03 in rGO owing to the more isolated sp2 domains that are present in the latter (Figure 3b). [PERSON] et al. [15] presented MoO\({}_{3-\chi}\), which is a multifunctional material that may be used for both wastewater purification and solar-driven saltwater desalination. Compared to M550 Air, the intensity ratios of the two wagging modes of the terminal Mo=O1 group at 283 cm\({}^{-1}\) (B\({}_{\text{2g}}\)) and 290 cm\({}^{-1}\) (B\({}_{\text{3g}}\)) for M160 were significantly reduced and practically vanished. This drop in the intensity ratio supports earlier research and indicates a break in symmetry caused by OVS (Oxygen Vacancies), which implies a larger concentration of OVs in M160 than in M550 Air (Figure 3c). [PERSON] et al. [16] presented tightly packed silver nanoparticles that self-assemble into porous templates, which they used to establish an asymmetric plasmonic structure with the dual purposes of water purification and pollution monitoring. They assessed the effectiveness of chemical detection using the glossy side of APS by using Rhodamine 6 G (R6G), which is the most widely used molecule in Raman spectroscopy. In comparison to a rough Ag film, the glossy side of the asymmetric plasmonic structure detected RG6 at a Raman intensity more than two orders of magnitude greater (Figure 3d).