# Characterizations of Interfacial Solar Water Evaporation
## 2 Intrinsic Properties
### Transmission Electron Microscopy  
The fundamental idea behind transmission electron microscopy (TEM) is that solid-angle scattering occurs when an electron beam that has been accelerated, focused, and projected onto a very thin sample collides with a sample's atoms. Images can be created from the scattering angle because of its correlation to the sample density and thickness. High-resolution TEM (HRTEM) can be used to determine a material's crystallinity. Lattice planes (fringes) can be found in the HRTEM image of a crystalline material, and the interplanar distance (d) can be assessed by using a fast Fourier transform (FFT). The crystal phase and Miller indices of these planes may then be determined by contrasting the obtained d with that of a reference sample in the literature or PDFs. Selected-area electron  
Figure 5: SEM. (**a**) PPy-coated-SS photothermal membrane. Reproduced with permission from ref. [18], Copyright 2015, Wiley-VCH. (**b**) TiOx nanomaterials. Reproduced with permission from ref. [19], Copyright 2017, Wiley-VCH. (**c**) The bamboo charcoal. Reproduced with permission from ref. [20], Copyright 2019, Wiley-VCH.  
diffraction (SAED) patterns display the distribution of electrons dispersed by a material, and they are frequently examined in combination with HRTEM pictures. The SAED pattern of a crystalline sample should show spots or rings except an intense spot created by directly transmitted electrons in the middle. The crystalline composition of a particular region of a material is determined using the separation between a pair of diffraction spots and their angle with respect to the center spot. Compared to routine XRD patterns, which take minutes or even hours to record (although the time required may be greatly reduced with the use of synchrotron X-ray sources), SAED patterns can be produced in less than 1 s, which makes SAED a valuable additional technique.  
[PERSON] et al. [21] announced the first use of dual-phase MoN/Mo2N to facilitate interfacial solar evaporation under a single source. TEM images showed that the MoN particles had a rambutan-like shape and comprised nanograins with high crystallinity and that were somewhat curved with widths and lengths of 10-15 and 30-50 nm, respectively. HRTEM images were used to identify the dual phases in the MoN\({}_{\mathrm{x}}\) sample. Both cubic Mo2N and hexagonal MoN were found as indicated by the (111) plane of 2.40 and the (200) plane of 2.48. The FFT images of the diffraction pattern showed that both the hexagonal MoN and cubic Mo2N had monocrystalline structures (Figure 6a,b). [PERSON] et al. [22] presented molybdenum oxide quantum dots (MoO3-x QDs) with an absorption spectrum that matched that of solar radiation in both the visible and near-infrared ranges as a proof-of-concept for interfacial solar evaporation. Interestingly, adding more than 1 g of chitosan allowed for the production of uniform and monodispersed tiny quantum dots. Clear lattice fringes were seen in HRTEM pictures, and a lattice parameter of 0.229 nm was determined (Figure 6c).  
Figure 6: TEM pictures. (**a,b**) The dual-phase MoN/Mo2N. Reproduced with permission from ref. [21], Copyright 2018, Elsevier. (**c**) MoO3-x QDs. Reproduced with permission from ref. [22], Copyright 2017, The Royal Society of Chemistry.